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IC 
 
 9045 
 
 Bureau of Mines Information Circular/1985 
 
 Water-Jet-Assisted Cutting 
 
 Proceedings: Bureau of Mines Open Industry 
 Meeting, Pittsburgh, PA, June 21, 1984 
 
 Compiled by Charles D. Taylor and Robert J. Evans 
 
 <^- 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 tflNES 75TH A^ 
 
Information Circular 9045 
 
 // 
 
 Water-Jet-Assisted Cutting 
 
 Proceedings: Bureau of Mines Open Industry 
 Meeting, Pittsburgh, PA, June 21, 1984 
 
 Compiled by Charles D. Taylor and Robert J. Evans 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
w 
 
 
 XP- 
 
 <\v 
 
 Library of Congress Cataloging in Publication Data: 
 
 Water-jet-assisted cutting 
 
 
 
 
 (Information circular ; 
 
 9045) 
 
 
 
 Bibliography. 
 
 
 
 
 Supt. of Docs, no.: I 2 
 
 3.27:9045. 
 
 
 
 1. Hydraulic mining- 
 
 -Congresses. 
 
 2. Water-jet— Congresses. 3. 
 
 Jet cutting— Congresses. 
 
 I. Taylor, 
 
 Charles D. (Charles 
 
 Darrell), 
 
 1946- . [I. Evans, Robert J. III. United States. Bureau 
 
 of Mines. 
 
 IV. Scries: Information 
 
 circular (United States. Bureau of 
 
 Mines) ; 
 
 9045. 
 
 
 
 
 TN295.U4 [TN2781 
 
 622s [622' 
 
 .321 85-600095 
 
 
Go 
 
 S CONTENTS 
 
 Page 
 O 
 
 Abstract 1 
 
 ^_q Introduction, by John N. Murphy and Bradley V. Johnson 2 
 
 "^\Water-jet-assisted rock cutting — the present state of the art, by Michael Hood. 3 
 — Analysis of mechanical tool force reductions when using water-jet-assisted cut- 
 
 ' ting, by R. J. Evans, H. J. Handewith, and C. D. Taylor 21 
 
 Experience with boom-type roadheaders equipped with high-pressure water-jet 
 systems for roadway drivage in British coal mines, by A. H. Morris and 
 
 M. G. Tomlin 29 
 
 Development work for coal winning technology, by Dr. E. H. Henkel 40 
 
 The water-jet plow, by David A. Summers 49 
 
 Design review of Jarvis Clark jetbolter, by William C. Griffiths 58 
 
 Water-jet-assisted tunnel boring, by Dr. Levent Ozdemir 63 
 
 Investigation of optimizing traverse speed of water-jet-assisted drag picks, 
 
 by R. J. Evans, H. J. Handewith, and C. D. Taylor 69 
 
 Optimization of water-jet systems for mining applications, by 
 
 Dr. James M. Reichman 77 
 
 do 
 
 o 
 
 a) 
 

 UNIT OF MEASURE ABBREVIATIONS USED IN THIS 
 
 REPORT 
 
 cm 
 
 centimeter 
 
 L/min 
 
 liter per minute 
 
 ft 
 
 foot 
 
 lb 
 
 pound 
 
 ft/h 
 
 foot per hour 
 
 lb/ft 3 
 
 pound per cubic foot 
 
 ft-lb 
 
 foot pound 
 
 Ibf 
 
 pound force 
 
 \ ft/lbf 
 
 foot pound force 
 
 lbf/in 2 
 
 pound force per 
 square inch 
 
 ft/mi n 
 
 foot per minute 
 
 
 
 
 
 m 
 
 meter 
 
 g/m 3 
 
 gram per cubic meter 
 
 
 
 
 
 m 3 /(kW-h) 
 
 cubic meter per 
 
 gal 
 
 gallon 
 
 
 kilowatt hour 
 
 gal/min 
 
 gallon per minute 
 
 m/min 
 
 meter per minute 
 
 h 
 
 hour 
 
 m/s 
 
 meter per second 
 
 hp 
 
 horsepower 
 
 mg/m 3 
 
 milligram per 
 cubic meter 
 
 Hz 
 
 Hertz 
 
 
 
 
 
 min 
 
 minute 
 
 in 
 
 inch 
 
 
 
 
 
 MJ/m 3 
 
 megajoule per 
 
 (in-lbf)/in 3 
 
 energy/ volume (relative 
 measure of cutting 
 
 
 cubic meter 
 
 
 efficiency) 
 
 mm 
 
 millimeter 
 
 in/r 
 
 inch per revolution 
 
 mm/s 
 
 millimeter per second 
 
 in/s 
 
 inch per second 
 
 ym 
 
 micrometer ! 
 
 kg 
 
 kilogram 
 
 MN/m 
 
 meganewton per meter 
 
 kj 
 
 kilo joule 
 
 MPa 
 
 megapascal 
 
 kJ/m 
 
 kilojoule per meter 
 
 pet 
 
 percent 
 
 kJ/m 3 
 
 kilojoule per cubic 
 meter 
 
 psi 
 
 pound per square inch 
 
 
 
 psig 
 
 pound per square inch, 
 
 km 
 
 kilometer 
 
 
 gauge 
 
 kN 
 
 kilonewton 
 
 r/min 
 
 revolution per minute 
 
 ksi 
 
 thousand pounds per 
 square inch 
 
 s 
 
 second 
 
 
 
 ton/h 
 
 ton (short) per hour 
 
 kW 
 
 kilowatt 
 
 
 
 
 
 ton/min 
 
 ton (short) per minute 
 
 kW-h 
 
 kilowatt hour 
 
 
 
 
 
 wt pet 
 
 weight percent 
 
 kW/m 2 
 
 kilowatt per square 
 meter 
 
 
 
WATER-JET-ASSISTED CUTTING 
 
 Proceedings: Bureau of Mines Open Industry Meeting, 
 Pittsburgh, PA, June 21, 1984 
 
 Compiled by Charles D. Taylor and Robert J. Evans 
 
 ABSTRACT 
 
 Greater mining productivity requires a more efficient cutting process. 
 The cutting force available from today's mining machines has been opti- 
 mized with respect to machine size and weight. Researchers have shown 
 that when employing water-jet-assisted cutting, bit forces and drum 
 torques can be reduced significantly, which may allow mining machines to 
 become lighter and more efficient. 
 
 The Bureau of Mines has initiated a program to develop a water- 
 jet-assisted rotary cutting system using the conventional bit assisted 
 by a directed water jet operating at moderate pressures (3,000 to 
 10,000 psi). This water-jet-assisted cutting system has the potential 
 to improve cutting efficiency without increasing machine horsepower or 
 water usage (beyond what is presently used for dust control) or requir- 
 ing fundamental changes in mining practice. In- addition to improvements 
 in productivity, other anticipated benefits of water-jet cutting include 
 reduced generation of respirable dust, elimination of frictional igni- 
 tions, increased bit life, reduced fines, and fewer machine vibrations. 
 
 The papers presented at this open industry meeting discuss the devel- 
 opment of water-jet-assisted cutting technology and future application 
 of this technology to a variety of mining techniques including roof 
 drilling and longwall mining. 
 
 1 1ndustrial hygienist. 
 ^Civil engineer. 
 Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
 
INTRODUCTION 
 By John N. Murphy 1 and Bradley V. Johnson 2 
 
 There have been numerous investigations 
 relative to the use of high-pressure wa- 
 ter jets to cut various materials; mate- 
 rials considered for this type of cutting 
 process have ranged from relatively soft 
 materials, such as coal, to harder sub- 
 stances, including granite and quartzitic 
 materials. While there has been signifi- 
 cant progress in this area and some nota- 
 ble successes for specific applications, 
 many problems remain, including general 
 system performance, erosion of jets at 
 high pressure, jet stability, and the 
 availability and reliability of rotating 
 high-pressure seals. 
 
 Research conducted by the Bureau and 
 by Bureau of Mines contractors has 
 shown that the application of relatively 
 low-pressure water jets, i.e., 5,000 to 
 20,000 psi, in conjunction with the 
 classical mechanical cutting pick, gives 
 significant increases in performance. 
 Performance has been measured in a vari- 
 ety of ways, including reductions in the 
 cutting forces required, the wear life 
 of the mechanical cutter bit, reduced 
 machine vibration, and reductions in gen- 
 erated dust and noise. While these en- 
 hancements are of direct benefit in terms 
 of today's mining machinery, they offer 
 the potential for the application of ex- 
 isting machines to more difficult min- 
 ing conditions, e.g., hard roof, or al- 
 ternatively higher production rates in 
 less difficult strata, as well as the 
 health and safety benefits of reduced 
 
 — i 
 
 'Research director, Pittsburgh Research 
 
 Center, Bureau of Mines, Pittsburgh, PA. 
 
 2 Staff engineer, Division of Conserva- 
 tion and Development, Mining Research, 
 Bureau of Mines, Washington, DC. 
 
 dust and noise. Perhaps equally important 
 are the future considerations in terms of 
 machine design realizing the benefits of 
 water-jet-assisted cutting; specifically, 
 smaller, lighter, more mobile machines 
 can be realized. The significant reduc- 
 tions in vibrations that have been ob- 
 served to date also offer the opportunity 
 for significant changes in the structural 
 design of machines. 
 
 It has also been demonstrated, in a 
 preliminary fashion, that the application 
 of the low-pressure water jets can sig- 
 nificantly reduce, or perhaps eliminate, 
 concerns about frictional ignition from 
 cutting picks impacting hard roof or py- 
 ritic inclusions. 
 
 As the proceedings of this Bureau of 
 Mines-sponsored water-jet-cutting seminar 
 will demonstrate, significant progress 
 has been made in the understanding of the 
 water-jet-assisted cutting process, the 
 optimization of machine design parame- 
 ters, and the field trials of various 
 prototype machines utilizing water-jet- 
 assisted cutting. The results to date 
 have been extremely promising, which in 
 part was the basis for this seminar, so 
 that the industry could be aware of and 
 utilize the progress made to date. How- 
 ever, more work is required before design 
 engineers can successfully apply this 
 promising technology to the machine of 
 their choice. Ongoing Bureau work will 
 certainly contribute toward the reali- 
 zation of this goal. These proceedings 
 provide a realistic assessment of the 
 current state of the art, and the bib- 
 liographic references with each article 
 can provide additional information if 
 required. 
 
WATER-JET-ASSISTED ROCK CUTTING — THE PRESENT STATE OF THE ART 
 
 By Michael Hood 1 
 
 ABSTRACT 
 
 The benefits of using moderate-pressure 
 water jets to assist mechanical tools, 
 notably drag bits, are reviewed. These 
 benefits include reduced bit forces, es- 
 pecially the bit normal force; reduced 
 bit wear; reduced dust make; and reduced 
 incidence of frictional sparking. The 
 research work that has been conducted to 
 date to investigate this phenomenon has 
 been largely empirical. Experiments are 
 described that extend the data bank of 
 this empirical knowledge. In addition, 
 experiments aimed at gaining a better un- 
 derstanding of the fundamentals of the 
 rock fragmentation process with this hy- 
 brid cutting method are outlined. 
 
 Results from the first of these experi- 
 mental series are used to make recommen- 
 dations as to the position of the jet 
 with respect to the bit, the standoff 
 distance between the nozzle exit and the 
 bit-rock interface, and the jet energy. 
 In addition, preliminary findings are 
 
 reported regarding the increased jet en- 
 ergy necessary to maintain substantial 
 reductions in the bit forces when the bit 
 velocity is increased. Results from the 
 second test series are discussed in the 
 context of rock fracture behavior induced 
 by mechanical tools acting alone. The 
 likely influence of water jets on these 
 fracture processes is analyzed. It is 
 concluded that , in terms of the bit force 
 reductions, a dominant effect of the jets 
 when used in conjunction with sharp drag 
 bits is continuous removal of the rock 
 debris that forms ahead of the advancing 
 bit. The observed reductions of bit wear 
 and incidence of frictional sparking are 
 attributed to reduced heat loading of the 
 bit during the cutting operation. Reduc- 
 tions in the dust make are attributed to 
 effective wetting of the fine rock parti- 
 cles before they become entrained in the 
 airstream. 
 
 INTRODUCTION 
 
 Breaking rock from an in situ rock mass 
 is carried out today using either a com- 
 bination of mechanical tools (to drill 
 holes) and explosives, or mechanical 
 tools alone to cut the material from the 
 face. It is evident that mechanical 
 tools play a crucial role in what could 
 be termed primary rock breaking, and it 
 is instructive to review the princi- 
 ples by which these tools induce rock 
 fracture. 
 
 First, the importance of rock breaking 
 in modern western mining should be high- 
 lighted. About 8.5 million tons of ore 
 and waste are mined each year in the 
 United States alone ( 1_) . 2 Tunnel drivage 
 
 ' Associate professor, Mining Engi- 
 neering, University of California, at 
 Berkeley, CA. 
 
 ^Underlined numbers in parentheses re- 
 fer to items in the list of references at 
 the end of this paper. 
 
 each year by the countries of the Organi- 
 zation of Economic Cooperation and Devel- 
 opment (OECD) is about 50,000 km. In the 
 
 10,000 km of 
 year just in 
 
 of the total 
 in the United 
 kW'h annually, 
 
 United States alone about 
 roadways are driven each 
 coal mines. Almost 2 pet 
 electric power generated 
 States, about 34 billion 
 is used in rock breakage processes. Ad- 
 mittedly, most of this energy is spent in 
 secondary rock breaking, i.e., crushing 
 and comminution, rather than in primary 
 breaking from an in situ rock mass. 
 However, these secondary processes also 
 employ mechanical means to induce frac- 
 ture. It should be noted the rock break- 
 ing processes are extremely inefficient. 
 In primary processes, less than 10 pet of 
 the energy supplied at the cutting bit 
 generates new surface area, and in sec- 
 ondary processes, less than 1 pet of the 
 applied energy is used to generate new 
 surfaces (1). Thus, a conclusion may be 
 
drawn that vast quantities of material 
 are extracted from the earth's crust each 
 
 year and that this activity 
 large quantities of energy. 
 
 utilizes 
 
 ACKNOWLEDGMENT 
 
 This work was funded by the U.S. De- 
 partment of Energy under the Fossil Fuel, 
 
 Coal Mining Program. Later this program 
 was transferred to the Bureau of Mines. 
 
 MECHANICALLY INDUCED ROCK FRACTURE PROCESSES 
 
 A mechanical tool induces fracture in 
 rock by the application of load through 
 the tool to the rock. This load can be 
 resolved into components acting normal 
 and parallel to the rock surface. With 
 some tools, for example, rolling cutters 
 such as disc cutters and tricone bits, 
 the normal force is the dominant compo- 
 nent (fig. L4). With other tools, for 
 example, sharp drag bits, the parallel or 
 cutting force is the dominant component 
 (fig. IS). The former may be described 
 as an indentation process, and the latter 
 
 A 
 
 \7 
 
 / 
 
 /K 
 
 \ 
 
 y/w/^/WA&y/< 
 
 \ 
 
 / 
 
 M 
 
 MW/AMWAM* 
 
 B 
 
 c 
 
 FIGURE 1. - Normal {A) and shearer (S) 
 forces applied to induce rock fracture. 
 
 as a cleavage process. Both of these 
 techniques were used by stone age man. 
 
 Figure 2A shows the stress distribution 
 in an elastic halfspace beneath a circu- 
 lar punch: the indentation case. Figure 
 2B shows the stress distribution in an 
 elastic quarterplane with a line load 
 normal to one of the surfaces: the 
 cleavage case. Despite the differences 
 in the way these loads are applied, the 
 final result in terms of the mechanisms 
 of crack propagation appears to be the 
 same for both indentation and cleavage 
 loading systems. In both cases chip for- 
 mation occurs as a result of tensile 
 crack growth. Tensile cracking ahead of 
 
 %i Edge of punch 
 
 B 
 
 Edge of punch 
 
 FIGURE 2. - Stress distributions for in- 
 dentation (.4) and cleavage (£>) cases. 
 
sharp drag bits was recognized by Evans 
 and Murrell (2^) . More recent work (3_-4) 
 has shown that, although the stress field 
 induced in the rock by an indenter is 
 predominantly compressive, a tensile 
 crack is initiated adjacent to the cor- 
 ners of the tool. This crack propagates 
 initially in a Hertzian manner at some 
 angle to the rock surface. Propagation 
 of this crack then ceases, and the appli- 
 cation of additional load results in 
 failure by triaxial crushing beneath the 
 tool. Subsequently a tensile crack, ini- 
 tiated towards the base of the Hertzian 
 crack, propagates up to the surface to 
 
 form a rock chip. The rock chips formed 
 by both indentation and cleavage process- 
 es show a marked similarity, substantiat- 
 ing the claim that the final mechanisms 
 of failure, i.e., crack growth, are iden- 
 tical. The relative inefficiency of the 
 indentation process can be explained us- 
 ing this model in terms of the additional 
 energy required to crush the rock beneath 
 the tool in order to propagate the crack 
 that forms the rock chip. Early man rec- 
 ognized that cleavage was the more effi- 
 cient of the two breaking processes and 
 used this method for forming arrowheads . 
 
 CURRENT ROCK BREAKING PRACTICE 
 
 The current state of the art is that 
 most primary rock breaking is accom- 
 plished by drilling and blasting. In 
 hard and medium-strength rocks, drill 
 bits apply indentation loads to the rock 
 to induce fracture. Only in weak rocks 
 are rotary drills that induce fracture 
 by cleavage employed. The reason that 
 cleavage is selected as a breaking method 
 only in a few rock cutting situations is 
 the limited strength of the bit materi- 
 als. Cemented tungsten carbide, which is 
 used ubiquitously as a cutting edge for 
 rock bits, is a brittle material. It has 
 extremely high strength in compression 
 but is relatively weak in tension. It is 
 difficult to design bits to induce di- 
 rectly tensile (cleavage) fractures in 
 rock without inducing tensile stresses in 
 the tool material. Consequently, the 
 loading arrangement usually configured is 
 such that only compressive forces are 
 applied to the bits and, by implication, 
 compression forces (indentation loads) 
 are applied to the rock. 
 
 The weakest rock types are mined today 
 not by drilling and blasting but in a 
 cutting operation, machining the seam or 
 ore directly from the face. Coal mining 
 serves as an example. The advantage of 
 this approach is that it permits the cy- 
 clic drill-and-blast process to be re- 
 placed by a continuous operation. The 
 cutting machine becomes one unit in a 
 system that cuts and loads the ore at the 
 face and transports it from the mine. 
 These cutting machines usually employ 
 
 bits that break the rock in a cleavage 
 process. Present technology also permits 
 continuous excavation for tunnel drivage 
 of medium and even strong rocks. The ma- 
 chines in this case employ rolling cut- 
 ters that break the rock by indentation. 
 Excavation of these stronger rocks is 
 feasible only where limited quantities of 
 the rock are to be removed. Thus, at 
 present , technology is not available for 
 continuous excavation of these rock types 
 for mining ore bodies , although there is 
 considerable incentive in terms of in- 
 creased productivity to achieve this 
 goal. 
 
 The strength of the bit material, the 
 tungsten carbide inserts, controls the 
 upper limit on the power that is trans- 
 mitted to the bits. This is true whether 
 the loading method is cleavage or inden- 
 tation. It will be shown theoretically 
 and demonstrated in practice (fig. 3) 
 that when the power at the bit exceeds a 
 critical level, this results in rapid 
 thermal deterioration of the bit insert, 
 which quickly leads to bit failure. The 
 specific power, i.e., the power required 
 to excavate unit area of the rockface, is 
 given by 
 
 P c = E c x r 
 
 where P s = specific power, kW/m 2 , 
 
 E s = specific energy, kJ/m 3 , 
 
 and r = rate of excavation (face 
 advance), m/s. 
 
Bit damaged by thermal overload 
 
 FIGURE 3. - Bit failure due to thermal deterioration. 
 
 Specific energy is defined as the ener- 
 gy required to remove a unit volume of 
 rock from the face. Thus, this term is a 
 measure of the efficiency of the rock 
 breaking process. The specific energy of 
 a given breaking process depends only on 
 that process and the rock type. Further- 
 more, it has been noted that specific 
 energy is related in an inverse power 
 manner to the mean size of the rock frag- 
 ments produced (fig. 4). 
 
 The following statements can now be 
 made. First, from the expression above, 
 it is apparent that since specific energy 
 is a constant for a given breaking pro- 
 cess, the rate of rock excavation is 
 
 directly proportional to the power trans- 
 mitted to the rock. If this power is to 
 be transmitted only through cutting bits, 
 then the fundamental limitation on the 
 rate of rock excavation is the strength 
 of the bit materials. Two approaches to 
 overcome this limitation seem feasible. 
 Either the strength of the bit material 
 could be increased, or some of the power 
 required to break the rock could be sup- 
 plied by means other than through a 
 cutting bit. The former approach is a 
 problem for the materials scientist. An 
 example of the latter approach is the use 
 of explosives, placed in drilled holes, 
 to cause rock fracture. 
 
Second, from figure 4 it can be seen 
 that explosives are an efficient means 
 of rock excavation. Mechanical breaking 
 methods — percussive and drilling, roller 
 bit boring, and drag bit cutting — are 
 moderately efficient processes. The in- 
 efficient techniques are the more exot- 
 ic breaking methods: electron beam guns, 
 lasers, flame jet piercing, and water jet 
 erosion. These inefficient processes re- 
 quire several orders of magnitude more 
 energy than explosives to break the rock. 
 This result was, probably, the main find- 
 ing to come from the flurry of research 
 activity, conducted in the late 1960's 
 and 1970' s, into rock breaking processes 
 (5-7). This work was conducted to deter- 
 mine the feasibility of applying these 
 so-called exotic techniques for the pur- 
 pose of rock excavation. In most cases 
 it was found that, while technically 
 feasible, the processes did not warrant 
 further development because of the very 
 large additional energy expenditures 
 required. 
 
 Third, although the logarithmic rela- 
 tionship between particle size and energy 
 has been known since the last century and 
 various workers have ascribed empirical 
 
 a. 
 
 CO 
 
 I0 5 
 
 I0 4 
 
 f 103 
 
 102 
 
 10' 
 
 Diamond 
 cutting 
 
 Percussive- 
 drilling 
 
 -Jet piercing 
 ^Erosion drilling 
 
 -Drag-bit cutting 
 "Roller bit boring 
 
 Impact- 
 driven 
 ^wedge 
 
 Explosives" 
 
 I0 l 
 0.01 
 
 _L 
 
 0.1 
 
 100 
 
 1,000 
 
 I 10 
 SIZE, mm 
 
 FIGURE 4. - Specific energy as a function of 
 particle size for variousrock-breaking processes. 
 
 relationships to describe this behavior 
 (8), a fundamental understanding of the 
 rock fracture mechanisms that caused this 
 phenomenon has yet to be derived. An im- 
 proved understanding of these processes 
 may well enable the development of more 
 efficient rock breaking techniques. 
 
 THE DEVELOPMENT OF WATER- JET-ASSIST TECHNOLOGY 
 
 The development of a hybrid cutting 
 system, using moderate-pressure water 
 jets in combination with a mechanical 
 tool, was inspired originally by a need 
 to overcome a limitation alluded to 
 above, i.e. , thermal deterioration of the 
 tool when power needed to achieve reason- 
 able penetration rates was applied ( 9_) . 
 In this application, drag bits were being 
 used to cut in strong, abrasive rocks. 
 It was discovered that suitably directed 
 jets, at pressures less than 10,000 psi, 
 would reduce the forces acting on the bit 
 
 substantially. In the laboratory, cut- 
 ting in norite, the bit cutting force 
 was reduced by a factor of about three 
 times (fig. 5^4). Underground, cutting 
 in quartzite, this force component was 
 reduced about five times. Other results 
 of equal significance from this test 
 suite were the findings that the bit 
 normal force was reduced even more dra- 
 matically than the bit cutting force 
 (fig. 5B). Also, the bit temperatures 
 were reduced substantially when the jets 
 were employed. 
 
200 
 160 
 
 LU 
 O 
 
 o 
 
 -i — i — i — i — i — i — i — i i r 
 
 Approx line of max available force 
 
 KEY 
 
 • With water jets 
 
 .4, Peak cutting force 
 j I i I i_ 
 
 * No water jet — 
 
 I L 
 
 200 
 
 1 
 
 II 1* ' 
 
 1 ' 1 
 
 i 
 
 1 ' 
 
 _ 
 
 160 
 120 
 
 
 • 
 
 • 
 
 • 
 • 
 
 • 
 • 
 
 - 
 
 80 
 
 
 
 
 
 
 - 
 
 40 
 
 1 
 
 Peak penetrating 
 1 i 1 i 
 
 force 
 1 i 1 
 
 i 
 
 I 
 
 — 
 
 2 4 6 8 10 12 
 
 DEPTH OF CUT, mm 
 
 FIGURE 5. - Bit cutting {A) and normal {B) 
 forces while cutting in norite with and without 
 water-jet assist. 
 
 Other workers (10-12) also using drag 
 bits assisted by moderate-pressure water 
 jets have cut a variety of medium and 
 strong rocks. These researchers have 
 found similar substantial bit force re- 
 ductions when the jets are employed. 
 Figure 6 gives the results of cutting in 
 Dakota sandstone with and without water 
 jets. It appears that in all cases at 
 least a 40- to 50-pct reduction in the 
 bit cutting force was realized. Also, 
 the bit normal force was reduced more 
 than the bit cutting force. A further 
 substantial benefit from the use of these 
 jets was revealed by Tomlin (12) , who 
 conducted his experiments on a roadheader 
 mining machine at an underground test 
 
 O 
 
 LlI 
 O 
 
 a: 
 o 
 
 
 
 i i r 
 
 KEY 
 
 * Without water jet 
 
 • With water jet, 
 10,000 psi pressure A 
 
 Drag 
 
 _] 
 
 ..u 
 .5 
 
 A 
 
 1 
 
 A 
 
 1 
 
 A 
 
 1 
 
 A _ 
 
 .0 
 
 
 
 
 • 
 
 .5 
 
 
 
 
 — 
 
 
 
 • 
 1 
 
 • 
 1 
 
 Normal 
 
 1 
 
 0.2 0.4 0.6 0.8 
 
 BIT PENETRATION, in 
 
 FIGURE 6. - Bit forces with and without jet 
 assistance, cutting in Dakota sandstone. 
 
 site. Using this machine it was discov- 
 ered that the water jets have a substan- 
 tial health and safety benefit in that 
 they cause the dust make at the cutter- 
 head to be reduced significantly. The 
 water jets also decrease, and perhaps 
 even eliminate, the incidence of fric- 
 tional sparking. 
 
 IMPLICATIONS OF THE RESEARCH FINDINGS 
 
 The ability to reduce bit forces sub- 
 stantially overcomes the fundamental re- 
 quirement of limiting power to the bit to 
 prevent its deterioration. Thus drag 
 bits now find application in rock types 
 where previously the rock was considered 
 too strong. 
 
 Many machines that employ drag bits as 
 cutting tools are limited in terms of the 
 maximum torque that they can exert at 
 
 the cutterhead. Furthermore, it is found 
 that the stresses imposed on the gear- 
 trains to the head are proportional to 
 the torque to the fifth power, that is, 
 
 a = T5 
 
 where 
 
 and 
 
 a = stress, 
 T = torque. 
 
Thus, if the cutterhead torque is dou- 
 bled, the stresses in the geartrain are 
 increased by a factor of about 32 times. 
 Conversely, of course, if the torque is 
 halved, the stresses are reduced in like 
 manner. The ability to reduce the bit 
 cutting forces consistently by a factor 
 of at least 2 implies that drum torques 
 could be halved while the rate of mining 
 is maintained. In some applications this 
 has an obvious potential for improving 
 machine reliability. 
 
 Bit failure often is induced by 
 high normal forces acting on the car- 
 bide insert. The ability to reduce this 
 force component even more dramatically 
 than the bit cutting force component 
 implies that the bit failure rate might 
 be decreased substantially by the use of 
 moderate-pressure water jets. This would 
 have two consequences: (1) The direct 
 cost of bits would be decreased, and (2) 
 the time lost changing bits, which can 
 be a significant portion of the overall 
 downtime (13) , would be reduced. 
 
 The ability to reduce bit temperatures 
 while cutting also would substantially 
 reduce the rate of bit wear and thus the 
 bit failure rate. Significant reductions 
 in bit temperatures have been reported 
 when water jets are used despite the fact 
 that the depth of cut has been increased 
 to a value where the bit cutting force is 
 the same with jets as without. Other 
 evidence for substantial reductions in 
 bit temperatures comes from field trials 
 with a roadheader where workers report 
 that the bits are cool enough to touch 
 when they exit the cut. Why the bits are 
 cooled to the extent reported is not 
 clear. Calculations predict that the 
 convective cooling effect of a jet would 
 not significantly increase the heat 
 transfer from the bit-rock interface. 
 The model used in these calculations as- 
 sumes that heat is generated by friction 
 beneath the bit wearflat. It is assumed 
 that the water contacts the leading face 
 of the bit but does not penetrate beneath 
 
 the bit wearflat. This second assumption 
 is based on simple calculations that show 
 that the pressure beneath the wearflat 
 generally is greater, by an order of mag- 
 nitude or more, than the pressure of 
 these moderate-pressure jets. If the 
 second assumption is in error and water 
 does penetrate beneath the wearflat, then 
 this could result in significant bit tem- 
 perature reductions. Recent work by 
 Friedman ( 14 ) on the fracture pattern 
 left in a rock groove cut by a drag bit 
 indicates a possible mechanism for trap- 
 ping water in preexisting flaws ahead of 
 the bit. This water then would be con- 
 strained beneath the wearflat with the 
 forward passage of the bit. 
 
 The potential for a dramatic reduction 
 in the incidence of frictional sparking, 
 a major concern in gassy mines, is almost 
 certainly a consequence of the reduced 
 heat loads on the bit. The predominant 
 cause of frictional ignitions and explo- 
 sions in coal mines is sparking between 
 the bits and the rock (15) . Furthermore, 
 the incidence of frictional ignitions 
 continues to increase, reflecting the in- 
 crease in mechanization (15). Ignitions 
 occur in appropriate methane-air mixture 
 when the energy level of a heat source 
 is above a critical minimum level. The 
 apparent substantial reduction in the 
 heat levels generated within the bits 
 when moderate-pressure water jets are 
 used to assist the cutting operation 
 would explain the observed reduction in 
 ignitions. 
 
 Another safety and health hazard, which 
 apparently is reduced substantially by 
 the use of a water-jet-assist system, is 
 mine dust. It is generally accepted that 
 the primary source of dust in an under- 
 ground mine where excavation is carried 
 out using a cutting machine is the bit- 
 rock interface. Past attention to con- 
 trolling this hazard has concentrated on 
 directing the airflow to move the dust 
 particles away from the workers and in- 
 stalling scrubbers on machines to remove 
 
10 
 
 dust particles from the airstream. 
 Despite considerable advances in these 
 areas , directed mainly by the Bureau 
 of Mines over the last 15 years, there 
 probably is not one longwall coal face 
 in the United States today that is in 
 regular compliance with the very strict 
 dust standards. This water-jet-assist 
 approach appears to offer the potential 
 
 for preventing small particles from be- 
 coming entrained in the airstream; that 
 is , it may inhibit the generation of dust 
 particles. This may herald a major ad- 
 vance in dust control since it is evi- 
 dent that inhibition of dust formation is 
 a superior control strategy to dust 
 suppression. 
 
 REMAINING TECHNOLOGICAL PROBLEMS 
 
 Despite the considerable promise of 
 water-jet-assist technology, its applica- 
 tion to mining machines has been slow. 
 Two reasons for this can be found. 
 First, current understanding of the mech- 
 anism by which the jets assist the break- 
 ing process is poor. It might be argued 
 that such understanding is of academic 
 interest only; after all, stone age man 
 fashioned arrowheads without a grasp of 
 the theories of fracture mechanics. How- 
 ever, an examination of the results of 
 various workers (figs. 5-6) reveals that 
 bit force reductions of factors of less 
 than 2 to as much as 5 have been report- 
 ed. Parameters that affect these force 
 reductions include jet pressure, jet flow 
 rate, jet position (with respect to the 
 bit-rock interface) , the standoff dis- 
 tance between the water jet nozzle and 
 the rock, bit geometry, bit velocity, and 
 rock type. Until recently the relative 
 importance of these parameters in influ- 
 encing bit force reductions has been un- 
 clear. Evidently, a machine designer 
 needs guidance in this area in order to 
 incorporate a water jet system onto a 
 mining machine. 
 
 Second, although the jet pressures at 
 which these systems operate are not high, 
 some development of hardware to enable 
 the jets to be channeled to the bits is 
 required. This hardware includes a reli- 
 able swivel and a phasing system to en- 
 sure that only those bits actually in 
 contact with the rock are assisted. 
 
 The following section addresses the 
 first of these problem areas. The devel- 
 opment of an hypothesis to describe a 
 physical process follows one of two ap- 
 proaches . In the one approach a mathe- 
 matical model of the process is proposed 
 and experiments are conducted subsequent- 
 ly to verify the model. The alternate 
 method is to conduct experiments first 
 and to use the empirical data that are 
 generated to derive the mathematical mod- 
 el. The latter approach has been adopted 
 in this investigation. The work is not 
 yet complete. The present study de- 
 scribes some key experiments which add to 
 the data bank of empirical knowledge in 
 this work area and which suggest physical 
 processes by which the jets act to assist 
 rock breakage. 
 
 EXPERIMENTAL PROCEDURES AND RESULTS 
 
 Experiments were conducted in the la- 
 boratory cutting the rock in a linear 
 planing machine. These tests were car- 
 ried out to determine the relative impor- 
 tance of the parameters listed above on 
 
 the reduction of bit forces using water 
 jets. To limit the experimental program 
 to a manageable size, the parameters in- 
 vestigated were limited. Parameters not 
 studied in this test series were bit 
 
11 
 
 geometry, rock type, depth of cut, and 
 nozzle geometry. A V-faced chisel, or 
 radial, pick was employed. All cutting 
 experiments were conducted in Indiana 
 Limestone. The properties of this rock 
 are described by Krech (16). The depth 
 of cut taken was 15 mm. The nozzle em- 
 ployed for the water jet used a 13° 
 included angle convergent section and a 
 parallel section at the exit. This de- 
 sign performed well in tests conducted 
 by Leach and Walker ( 17 ) . The parameters 
 studied follow: 
 
 1. Jet position. Three jet configura- 
 tions were examined (fig. 7): 
 
 A. Two jets parallel to the lead- 
 ing face of the pick, about 1 mm ahead 
 of this face. 
 
 B. A single jet parallel to the 
 leading face of the pick, aligned in 
 the center of the tungsten carbide in- 
 sert, again about 1 mm ahead of the 
 face. 
 
 C. A single jet directed behind 
 the pick in the path of the pick. 
 
 2. Standoff distance. Using the opti- 
 mum jet position (above), three standoff 
 distances were examined: 25, 50, and 
 75 mm. 
 
 3. Jet pressure . A range of jet pres- 
 sures up to a maximum of 10,000 psi was 
 tested. 
 
 4. Jet flow rate . Three different 
 nozzle diameters were tested in this test 
 suite at jet pressures of 0.6, 0.8, and 
 1.0 mm. The flow rates corresponding to 
 these nozzles at various pressures are 
 given below. 
 
 5. Pick velocity . Two pick velocities 
 were examined: 0.06 and 0.25 m/s. 
 
 Nozzle 
 
 Side view 
 
 •Nozzle 
 
 Front view 
 
 Nozzle 
 .holder 
 
 Water inlet 
 
 Adjustable standoff 1 
 25 mm, 50 mm, 75 mm 
 
 Side view 
 
 Nozzle 
 
 Front view 
 
 Tungsten 
 carbide tip 
 
 tmsm 
 
 Nozzle 
 
 mm> 
 
 50 mm 
 
 FIGURE 7. - Positioning of the jets with re- 
 spect to the bit. A, Two jets ahead of the bit; 
 B, single jet ahead of the bit; C, single jet be- 
 hind bit. 
 
 JET POSITION 
 
 It was found that the optimal jet ar- 
 rangement for this bit cutting in this 
 rock type was a single jet directed 1 mm 
 ahead of the leading face of the bit. 
 The finding that the optimal jet position 
 is ahead of the bit contradicts results 
 reported by Ropchan (10) in which it is 
 claimed that the greatest force reduc- 
 tions were achieved when a single jet was 
 directed behind the bit. The major dif- 
 ference between the present investigation 
 and the program conducted by Ropchan is 
 
 the bit geometry. In the earlier study a 
 point attack bit was used for the cutting 
 experiments that employed water-jet as- 
 sist. Only modest bit force reductions 
 were reported when the water jet was di- 
 rected ahead of the bit. It may be that 
 the geometry of the point attack bit is 
 not capable of exploiting fully the ad- 
 vantages of assistance with water jets. 
 
 It should be pointed out that previous 
 work has shown that close proximity of 
 the jet to the leading face of the bit is 
 
12 
 
 crucial to obtaining significant bit 
 force reductions. If, during the cut, 
 the jet strikes the rock 10 mm or even 5 
 mm ahead of the bit, its effectiveness in 
 reducing the bit forces is decreased dra- 
 matically. On the other hand, it is im- 
 portant to insure that the jets do not 
 
 strike the tungsten carbide insert be- 
 cause they cause rapid erosion of this 
 insert. Accurate positioning of the jet 
 with respect to the bit is a crucial fac- 
 tor in obtaining maximum benefit from the 
 water jets. 
 
 STANDOFF DISTANCE 
 
 The standoff distance was found not to 
 affect the bit force reductions provided 
 that this distance was less than 100 
 times the jet nozzle diameter. However, 
 at distances greater than this, the re- 
 duction in these forces fell rapidly. 
 This finding should be qualified since, 
 almost certainly, the result depends on 
 
 the nozzle geometry and on the inlet con- 
 ditions of the nozzle. The usefulness of 
 this result probably is that it provides 
 a rule of thumb for calculating an ac- 
 ceptable standoff distance. One justifi- 
 cation for using this result is that it 
 accords with other, more precise, labora- 
 tory measurements (17). 
 
 JET ENERGY 
 
 During the cutting operation the reduc- 
 tions in the bit forces were found to be 
 affected both by the pressure at which 
 the jet was operating and by the flow 
 rate of the jet. However, careful analy- 
 sis of the experimental data revealed 
 that it was the combination of these two 
 parameters, the jet power, that con- 
 trolled these reductions. The results 
 indicated that the magnitude of the re- 
 ductions in bit forces is some function 
 of the jet power normalized with respect 
 to the bit velocity. This parameter has 
 units of kilojoules per meter, or jet en- 
 ergy per unit length of cut. A typical 
 curve for a slow cutting speed is given 
 
 in figure 8. This result, in general, 
 accords with intuition. It would be ex- 
 pected that, over a certain length of the 
 cut, the bit force reductions would in- 
 crease as the energy of the jet in- 
 creased. In addition, it may be antici- 
 pated that these force reductions would 
 reach a limit beyond which an increase in 
 the jet energy would produce little or no 
 effect. The results obtained indicate 
 that these force reductions attain a max- 
 imum. When the normalized jet power is 
 increased beyond this maximum, the bit 
 force reductions again start to decrease. 
 This behavior is not well understood. 
 
 BIT VELOCITY 
 
 The tests described above all were con- 
 ducted at a pick velocity of 0.06 m/s. 
 The maximum possible bit velocity in this 
 test suite was constrained by the experi- 
 mental apparatus to 0.25 m/s. Although 
 this represents an increase in speed of a 
 factor of 4, it still is about four times 
 less than typical bit speeds on mining 
 machines. Nevertheless, a comparison of 
 tests conducted at these high and low 
 laboratory bit velocities is of interest 
 since it reveals the trend in the influ- 
 ence of jet parameters on bit force 
 reductions. 
 
 1 r~ 
 
 KEY 
 
 - Slow speed 
 
 — Fast speed 
 
 _L 
 
 50 100 150 200 250 300 
 
 JET ENERGY PER UNIT LENGTH, kJ/m 
 
 FIGURE 8. - Measured bit force as a function 
 of the normalized jet power. 
 
13 
 
 Results from experiments carried out at 
 the higher bit speed of 0.25 m/s are also 
 plotted as a function of normalized jet 
 power in figure 8. Inspection of this 
 curve shows that the trend observed pre- 
 viously for the lower speed tests, i.e., 
 a rapid decrease in the bit forces with 
 increasing jet energy up to some maximum 
 jet energy, is reproduced at the higher 
 bit speed. Moreover, visual inspection 
 of these curves shows that their sta- 
 tionary points correspond to bit force 
 reductions of about 50 pet at the low 
 bit speed and about 45 pet at the high 
 bit speed. The corresponding jet ener- 
 gies per unit length of cut are about 30 
 and 120 kj/m, respectively. It might be 
 concluded that provided that an appropri- 
 ate energy is supplied to the jet, the 
 bit force reductions are not affected 
 significantly by changes in bit velocity. 
 Furthermore, the jet energy appears to 
 increase linearly with bit velocity. 
 
 However, closer inspection of these 
 curves reveals that the maximum force 
 
 reductions are not necessarily the opti- 
 mum operating points. Because, in most 
 cases, the rate of change of increase in 
 force reductions slows at some fairly 
 well defined point in the curve and the 
 difference in force reductions between 
 this point and the maximum is small, this 
 point of change may be the most energy 
 efficient point at which to operate the 
 system. At present the analysis has 
 progressed only to the point of identi- 
 fying these optimum points by visual 
 inspection. These are marked in fig- 
 ure 8. It can be observed that in this 
 figure the normalized jet power changes 
 by a factor of 2 while the bit velocity, 
 as noted, changes by a factor of 4. 
 This result was repeated using two other 
 nozzle sizes. 
 
 Extrapolation of these admittedly lim- 
 ited data to calculate the probable jet 
 power requirement for bits cutting at 
 velocities of 1 m/s indicates that the 
 jet power to an individual bit may be 
 about 15 kW. 
 
 INVESTIGATION OF BREAKAGE MECHANISMS 
 
 An additional suite of experiments was 
 performed. These experiments were de- 
 signed specifically to throw light on the 
 mechanisms of rock breakage when water 
 jets at moderate pressures are employed 
 to assist rock cutting with drag bits. 
 
 Three mechanisms by which the jets 
 might act to reduce the bit forces were 
 proposed: 
 
 1. Chemical attack of the rock by the 
 water, i.e., stress corrosion cracking. 
 
 2. Initiation of a crack by the bit at 
 low bit-force levels, and subsequent 
 propagation of the crack by the water jet 
 to form a chip ahead of the bit. 
 
 3. Effective clearance of the rock 
 particles from the region adjacent to the 
 bit. 
 
 STRESS CORROSION CRACKING 
 
 It is known that stress corrosion 
 cracking (SCC) can produce significant 
 reduction in the fracture strength of 
 rock (18-20) . However, the effectiveness 
 of this approach in reducing fracture 
 toughness decreases as the velocity of 
 the crack front increases. This study 
 was conducted to determine whether this 
 mechanism could be effective when frac- 
 tures are produced in a dynamic manner. 
 
 A series of high-speed films of the 
 cutting operation was made using a film 
 speed of 1,000 frames per second. Films 
 were made both with and without the 
 use of water jets to assist the cutting 
 
 process. The approximate speed of crack 
 propagation for the large rock chip that 
 forms ahead of the bit was determined 
 from careful viewing of these films. 
 These chips typically were 80 mm in 
 length and they were formed within one 
 or, at most, two frames on the film. 
 This implies a crack propagation velocity 
 of about 80 m/s. Stress corrosion crack- 
 ing is known to be a rate-dependent phe- 
 nomenon, i.e. , a unique relationship ex- 
 ists between the rate of change of crack 
 length with respect to time and the 
 stress intensity factor at the crack 
 tip (21). Furthermore, there exists a 
 
14 
 
 limiting crack velocity beyond which 
 stress corrosion plays no part in the 
 fracture process. For most brittle mate- 
 rials, including rock, this limiting ve- 
 locity appears to be of the order of 10~ 4 
 m/s to 10" 1 m/s (21). Thus, the fracture 
 velocity observed in these cutting tests 
 
 is at least two orders of magnitude high- 
 er than the maximum velocity at which SCC 
 could be invoked as a mechanism for re- 
 ducing the fracture strength and thereby 
 reducing the bit forces. Therefore, this 
 hypothesis was rejected. 
 
 DRIVAGE OF CRACKS BY WATER PRESSURE 
 
 In addition to the large chip that is 
 formed ahead of the bit in its forward 
 passage through the rock, a large number 
 of small rock chips also are created. A 
 two-dimensional representation of this 
 breakage process is shown in figure 9. 
 Immediately after the formation of a 
 large chip the depth of the cut seen by 
 the bit is zero. As the bit continues 
 its forward passage, the depth of cut in- 
 creases and small rock fragments are 
 broken ahead of the bit; these fragments 
 are pushed ahead of the bit. Although 
 details of the fracture process that pro- 
 duces these fragments still are not well 
 understood, almost certainly a tensile 
 crack is initiated in the rock adjacent 
 to the corner of the bit between the 
 leading bit face and the bottom surface 
 of the bit for the case when the drag bit 
 is sharp. In other words, it is a 
 cleavage-type crack. On the other hand, 
 when the drag bit is blunt, i.e., a wear- 
 flat exists because of a zero clearance 
 
 Rock surface left 
 by previous chip - 
 
 ^$SSS35^SSSS5^ 
 
 Rock crushed ahead of bit, 
 applying indentation load to the rock 
 
 Compacted crushed 
 Scale, mm material beneath 
 
 FIGURE 9. - Chipping process ahead of 
 sharp drag bit. 
 
 angle between the bottom surface of the 
 bit and the rock, then this tensile crack 
 is initiated by indentation. In these 
 processes it is known that crack initia- 
 tion occurs with relatively low forces 
 applied to the bit. A considerable in- 
 crease in the bit force is required to 
 cause this fledgling crack to propagate 
 to form a rock chip. 
 
 Thus, a plausible explanation for the 
 influence of water jets in reducing bit 
 forces is that the jet enters the crack 
 initiated by and ahead of the bit, and 
 the jet energy causes this crack to prop- 
 agate to form a rock chip. Evidence sup- 
 porting the mechanism of rock breakage 
 was provided in a series of indentation 
 experiments reported by Hood (22). In 
 these tests rock specimens were loaded in 
 a quasi-static manner in a series of 
 punch tests with a blunt drag bit serving 
 as the punch. It was found that when wa- 
 ter jets were directed, at moderate pres- 
 sure, onto the rock surface immediately 
 adjacent to the bit, the force required 
 to cause the rock to fail and a chip to 
 form was reduced significantly. The ex- 
 planation given for this reduced bit 
 force was that full development of the 
 fracture that produces the large rock 
 chip ahead of the bit occurs only after 
 the rock beneath the bit is crushed in an 
 energy-consuming and inefficient process. 
 By driving the crack with the water jet 
 less crushing of the rock by the bit took 
 place , and thus mechanical energy that 
 normally would have been supplied by the 
 bit was saved. 
 
 In the present test series the drag bit 
 used was sharp and the purpose of this 
 investigation was to determine whether a 
 similar mechanism for crack drivage by 
 water pressure was employed. It was ar- 
 gued that smaller quantities of finely 
 crushed rock particles would be formed if 
 
15 
 
 jet pressure was responsible for driv- 
 ing the cracks that formed the major 
 rock chips. Experiments were conducted 
 in which all of the fragments produced 
 during the cutting operation were col- 
 lected. Size analyses of these particles 
 revealed no discernible difference in 
 the distribution of particle size with 
 and without water jet assistance of the 
 cutting process. A preliminary conclu- 
 sion was drawn that the efficiency of 
 the cutting process is not increased by 
 crack drivage with water pressure when 
 
 moderate-pressure jets are used to assist 
 sharp drag bits. This conclusion must be 
 regarded as tentative since the experi- 
 mental technique used, analysis of the 
 particle size, is not definitive. For 
 example, although the quantity of fines 
 was found to be the same in cuts made 
 both with and without the use of water 
 jets, the fines in the water-jet-assisted 
 cuts may have been formed by erosion of 
 the chip edges by the jets, while the 
 fines in the dry cuts were produced by 
 crushing. 
 
 CHIP CLEARANCE BY JETS 
 
 When water jets are not used during the 
 cutting operation, the rock chips formed 
 prior to the formation of a large chip 
 are pushed ahead of the leading bit face. 
 Therefore, stresses applied to the intact 
 rock by the bit are transmitted through a 
 region of crushed material. This materi- 
 al acts as a cushion, and the applied 
 stresses are distributed more evenly and 
 over a larger area than would be the case 
 if no crushed material was present. This 
 results in higher bit forces causing rock 
 breakage. 
 
 Also, it is known that the strength of 
 rock is increased dramatically by the ap- 
 plication of confining pressure even when 
 the confining pressure is small '(23) . 
 The weight of the rock fragments that are 
 pushed ahead of the bit in its forward 
 progress through the cut is so small as 
 to be negligible in terms of the confine- 
 ment that it could provide. However, 
 it is possible or even likely that this 
 crushed material could be wedged between 
 the front face of the bit and the in- 
 clined surface of the intact rock face 
 (fig. 9). In this case appreciable con- 
 fining pressure might be applied to the 
 underlying rock, and thus the energy re- 
 quired to propagate a crack to form a 
 rock chip would be increased. The like- 
 lihood of wedged rock fragments confining 
 the rock in this manner would seem to be 
 higher for bits with either zero or nega- 
 tive rake angles. Cutting experiments 
 (24) have shown that bit forces indeed 
 are increased as the bit rake angle 
 changes from positive through zero to 
 negative. Since the fracture process is 
 
 tensile in all cases, this mechanism 
 of confinement of rock particles may pro- 
 vide the explanation for these force 
 differences. 
 
 Therefore, the hypothesis developed to 
 explain the action of the jets in reduc- 
 ing bit forces was that they removed 
 rock debris as it was formed ahead of the 
 advancing bit . This would permit higher 
 stresses to be applied to the rock by re- 
 moving the cushion of crushed material. 
 Also, any enhancement in rock strength as 
 a result of confining stress applied 
 through this debris would be removed. 
 
 Experiments were conducted to investi- 
 gate the effect of confinement of rock 
 particles ahead of an advancing drag bit. 
 A plate fixture was mounted in front of 
 the bit 25 mm above the rock surface 
 (fig. 10). This plate prevented upward 
 movement by the rock chips once the 
 height of the debris in front of the bit 
 exceeded 25 mm. In other words , this 
 fixture caused the effect of confinement 
 of the rock chips to be exaggerated. 
 Tests were conducted both with and with- 
 out the use of water jets assisting the 
 cutting process. 
 
 Representative samples of the cutting 
 force-time traces that were recorded both 
 with and without the fixture and with and 
 without the use of water jets are given 
 in figures 11 and 12. Figure 11 A shows 
 the typical sawtooth trace obtained for a 
 dry cut without the fixture. The cutting 
 force increases from zero, or some low 
 value, in an oscillatory but linear man- 
 ner, up to a maximum. Beyond this maxi- 
 mum value the force decreases rapidly to 
 
16 
 
 25-mm-wide 
 metal fixture 
 
 15-mm 
 cut depth 
 
 ^^^^^^m^^^^^ 
 
 Crushed zone 
 
 FIGURE 10. - Plate fixture ahead of drag bit. 
 
 12 3 4 
 
 TIME, s 
 
 FIGURE 11. - Dry cuts without (.4) and with 
 (B) plate fixture. 
 
 a value close to zero, and the cycle is 
 repeated. This characteristic signature 
 is explained in terms of the observed 
 chip formation process in front of the 
 advancing bit (fig. 9). Immediately af- 
 ter a large chip is formed, the instan- 
 taneous depth of the cut is low or zero, 
 and thus the bit cutting force is low or 
 zero. As the bit advances it encounters 
 a ramp formed by the bottom surface of 
 the previous chip. Thus, the depth of 
 cut that the bit sees increases, in an 
 approximately linear fashion, from a val- 
 ue close to zero to the depth of cut pre- 
 determined in the experiment. The forma- 
 tion of small rock chips as this ramp is 
 excavated together with crushing of those 
 
 UJ 
 
 o 
 rr 
 o 
 
 TIME, s 
 FIGURE 12. - Water-jet-assisted cuts without 
 {A) and with (B) plate fixture. 
 
 chips as they are pushed ahead of the bit 
 accounts for the oscillatory nature of 
 the trace. The force continues to in- 
 crease because the depth of cut relative 
 to the bit is increasing. At some point 
 the pressure beneath the crushed material 
 is sufficient to initiate and propagate 
 another major chip. The instantaneous 
 depth of cut ahead of the bit returns to 
 a low value, and the cycle is repeated. 
 
 When the metal fixture was used for dry 
 cuts, this same signature was repeated 
 but it became much more exaggerated (fig. 
 116). The area beneath each sawtooth 
 oscillation, representing the mechanical 
 energy required to form one large rock 
 chip, is much increased. 
 
17 
 
 The equivalent traces without and with 
 the metal fixture mounted ahead of the 
 bit but with water-jet assistance are 
 given in figures 12A and 125, respective- 
 ly. A notable feature of these plots is 
 that although saw-tooth oscillations 
 still can be distinguished, in general, 
 they are of short duration so that the 
 area under the curves , and thus the ex- 
 penditure of mechanical energy, is small. 
 Little difference can be observed by 
 visual inspection of these plots. This 
 small difference is reflected in the rel- 
 atively small difference in the measured 
 cutting forces when jets were used. 
 These forces for this set of experiments 
 are given in table 1. The mechanical 
 energy supplied to the bit in these ex- 
 periments is given in table 2. 
 
 TABLE 1. - Bit forces with and without 
 metal plate, kilonewtons 
 
 TABLE 2. - Mechanical energy supplied 
 to the bit, kilo joules 
 
 With water jets: 
 
 Mean 
 
 Mean peak 
 
 Without water jets: 
 
 Mean 
 
 Mean peak 
 
 With 
 
 Without 
 
 plate 
 
 plate 
 
 2.95 
 
 2.24 
 
 7.99 
 
 6.82 
 
 6.63 
 
 3.94 
 
 12.40 
 
 8.45 
 
 With water jets..., 
 Without water jets, 
 
 With 
 plate 
 
 3.47 
 7.76 
 
 Without 
 plate 
 
 2.62 
 4.62 
 
 High-speed films made of the cutting 
 operation when water-jet assistance was 
 employed showed that rock particles 
 were removed from the region ahead of 
 the bit immediately after they were 
 formed. This contrasts with evidence 
 from similar films made of the cutting 
 operation when water jets were not used, 
 which indicated that rock chips were 
 carried ahead of the bit for the com- 
 plete length of the cut. Further evi- 
 dence as to the effectiveness of this 
 flushing operation using jets was pro- 
 vided by examination of the groove after 
 the bit had passed. With dry cuts this 
 groove bottom was packed with finely 
 crushed material which obviously had been 
 forced and/or trapped beneath the bit 
 wear-flat. With water-jet-assisted cuts 
 this groove bottom contained no crushed 
 material. 
 
 DISCUSSIONS OF FINDINGS AND CONCLUSIONS 
 
 The experimental evidence supports the 
 hypothesis that the dominant mechanism by 
 which moderate-pressure water jets act 
 to assist the rock cutting process using 
 sharp drag bits is by effective chip 
 clearance from the region ahead of the 
 bit. Removal of these rock particles 
 causes a reduction in the measured bit 
 forces because the stresses transmitted 
 to the rock by the bit are increased 
 for a given bit load. In addition, the 
 confining stress that may be applied by 
 these rock particles to the intact rock 
 when cutting dry is removed. This also 
 would cause a reduction in the bit forces 
 necessary to excavate the rock. 
 
 It was noted above that in order to 
 reduce bit forces substantially it is 
 important that the jet be positioned 
 within 1 or 2 mm of the leading face of 
 the bit. The necessity for this accurate 
 
 positioning of the jet was provided by 
 the high-speed films of the cutting oper- 
 ation. When jets are not used, platelike 
 particles form and are pushed ahead of 
 the bit. If the jet is directed too far 
 ahead of the leading bit face, it strikes 
 the center of one of these particles and 
 the jet energy, which is insufficient 
 to damage the rock, is dissipated harm- 
 lessly. On the other hand, when the jet 
 is directed immediately adjacent to the 
 leading bit face, it penetrates beneath 
 the edge of these particles and the ener- 
 gy dissipated as it strikes the intact 
 rock ahead of the bit lifts and removes 
 all debris in this region. 
 
 The experimental finding that jet ener- 
 gy does not have to increase linearly 
 with bit velocity is consistent with this 
 hypothesis for jet assistance, i.e., that 
 the dominant influence of the jets is 
 
18 
 
 removal of broken material from ahead of 
 the bit. 
 
 Another possible mechanism by which the 
 jets may assist the cutting process is 
 crack drivage by jet pressure. Apparent- 
 ly this does occur with blunt bits and 
 may or may not take place with sharp 
 bits; the experimental results are un- 
 clear. The third possibility for reduc- 
 ing bit force as examined in this study 
 was stress corrosion cracking. Apparent- 
 ly this does not influence the breakage 
 process . 
 
 A substantial reduction in bit tempera- 
 tures by the use of water jets is not 
 predicted by theory if the assumption is 
 made that the dominant mode of heat 
 transfer is convective and that cooling 
 takes place from the leading bit face. 
 However, laboratory and field tests have 
 shown that bit temperatures are reduced 
 substantially when jets are used. What- 
 ever the flaw in the mathematical model, 
 the fact that heat loads to the bit dur- 
 ing the cutting operation are signifi- 
 cantly decreased when jets are used al- 
 most certainly accounts for the observed 
 dramatic reduction in frictional spark- 
 ing. Furthermore, this finding, taken 
 together with reduced bit normal force 
 that is observed even when the depth of 
 cut is increased so that the bit cutting 
 force is not decreased, probably accounts 
 for the reported reductions in bit wear 
 and breakage. 
 
 Dust might be defined as those fine 
 particles that become entrained in the 
 air. On a coal face it is known that 
 dust accounts for only a very small frac- 
 tion of the fine particles that are gen- 
 erated during the cutting operation. Re- 
 sults from these experiments indicate 
 that the quantity of fines produced is 
 not different when water jets are used. 
 However, measurements show that dust 
 quantities at the face are reduced sub- 
 stantially when jets are used to assist 
 the cutting process (12) . Thus, it must 
 be assumed that the effect of the jets is 
 to wet the fine particles as they are 
 produced at the face before they become 
 entrained in the ventilation airstream. 
 This assumption is consistent with the 
 model proposed in this paper to describe 
 the dominant effect of the jets on the 
 
 rock fracture process, i.e., that the 
 jets act to flush chips and rock debris 
 from the region ahead of the bit . For 
 this flushing operation to be most effec- 
 tive, the jet is aimed directly at the 
 small region where the rock particles, 
 both small and large, are initiated. 
 Thus, before these particles are removed 
 from the face they have been wetted by 
 the jet. These wetted particles are much 
 less likely to become entrained in the 
 airstream. 
 
 Another factor with a high potential 
 for achieving even further reductions in 
 the dust make is the possibility of re- 
 designing the cutting machine to take 
 deeper cuts at lower bit velocities. It 
 has been known for decades that fewer 
 fines are produced by deep, widely spaced 
 cuts (25). It is known also that the en- 
 trainment process has much to do with 
 bit, or drum, velocity. The problem with 
 putting this knowledge into practice 
 on mining machinery has been that this 
 cutting method places high unbalanced 
 loads on the drum and that high drum 
 torque is needed. Water-jet assistance 
 offers the potential for overcoming these 
 difficulties. 
 
 The other research results are summa- 
 rized as follows. Parameters influencing 
 the effectiveness of water jets in reduc- 
 ing bit forces were examined. It was 
 found that the optimal jet position for 
 assisting a sharp chisel bit was immedi- 
 ately ahead of the leading face of the 
 bit. The jet should strike the rock no 
 more than 1 or 2 mm ahead of this face. 
 The standoff distance will depend on the 
 nozzle geometry and the nozzle inlet con- 
 ditions. It was found in these tests 
 that the nozzle exit should be within 100 
 nozzle diameters to be most effective. 
 Although jet pressure and jet flow rate 
 both affect the reduction in the bit 
 forces, the jet power per unit length of 
 cut was found to be the parameter that 
 controlled the magnitude of these force 
 reductions. The optimal value of this 
 normalized jet power parameter was found 
 to depend on bit velocity. An extrapola- 
 tion from limited experimental data 
 yielded an estimate for the jet power of 
 15 kW per bit for bit velocities of about 
 1 m/s. 
 
19 
 
 REFERENCES 
 
 1. National Research Council, Nation- 
 al Materials Advisory Board. Comminution 
 and Energy Consumption. Natl. Acad. 
 Press, Publ. NMAB-36, 1981, 283 pp. 
 
 2. Evans, I., and S. A. F. Murrell. 
 Wedge Penetration Into Coal. Colliery 
 Guardian, v. 39, No. 455, Jan. 1962, pp. 
 11-16. 
 
 3. Hood, M. Phenomena Related to the 
 Failure of Strong Rock Adjacent to an 
 Indenter. J. S. Afr. Inst. Min. and 
 Metall., v. 78, No. 5, Dec. 1977, p. 113. 
 
 4. Cook, N. G. W. , M. Hood, and F. 
 Tsai. Observations of Crack Growth in 
 Hard Rock Loaded by an Indenter. Int. J. 
 Rock Mech. and Min. Sci., v. 21, No. 2, 
 1984, pp. 97-107. 
 
 5. Liessmann, Y. Das Mikrowellenver- 
 fahren zur Zerkleinerung von Gestein- 
 verschusanlage und Erzielten Ergebrisse 
 (The Microwaves for Rock Breaking — 
 Experimental Techniques and Results). 
 Bergbautechnik, v. 16, No. 10, 1966, p. 
 537. 
 
 6. Carstens, J. P. Thermal Fracture 
 of Rock — A Review of Experimental Re- 
 sults. Paper in North American Rapid Ex- 
 cavation and Tunneling Conference, ed. by 
 K. S. Lane and L. A. Garfield (Proc. 
 Conf., Chicago, IL, June 5-7, 1972). 
 AIME, 1972, pp. 1363-1392. 
 
 7. Summers, D. A., and D. J. Bush- 
 nell. Preliminary Experimentation of the 
 Design of the Water Jet Drilling Device. 
 Paper E2 in Third International Symposium 
 on Jet Cutting Technology (IIT Res. 
 Inst., Chicago, IL, May 11-13, 1976). 
 BHRA Fluid Engineering, Cranfield, Bed- 
 ford, England, 1976, pp. E2-E21. 
 
 8. Bond, F. C. Third Theory of Com- 
 minution. Trans. AIME, v. 193, 1952, pp. 
 484-494. 
 
 9. Hood, M. Cutting Strong Rock With 
 a Drag Bit Assisted by High Pressure Wa- 
 ter Jets. J. S. Afr. Inst. Min. and 
 Metall., v. 77, No. 4, Nov. 1976, pp. 79- 
 90. 
 
 10. Ropchan, D. , F. D. Wang, and J. 
 Wolgamott. Application of Water Jet As- 
 sisted Drag Bit and Pick Cutter for the 
 Cutting of Coal Measure Rocks (U.S. Dep. 
 Energy contract ET-77-A-01-9082, CO Sch. 
 
 Mines). Apr. 1980, NTIS DOE/ET/ 1 2463-1 , 
 120 pp. 
 
 11. Dubugnon, 0. An Experimental 
 Study of Water Assisted Drag Bit Cutting 
 of Rocks. Paper in First U.S. Water Jet 
 Symposium (Golden, CO, Apr. 7-9, 1981). 
 CO Sch. Mines Press, Golden, CO, 1981, 
 pp. II-4.1 to II-4.11. 
 
 12. Tomlin, M. G. Field Trials With 
 10,000 psi Prototype System. Paper in 
 Seminar on Water Jet Assisted Roadheaders 
 for Rock Excavation (Pittsburgh, PA, May 
 26-27, 1982). U.S. Dep. Energy and U.K. 
 National Coal Board, 1982, pp. Cl-Cll. 
 
 13. Pimental, I. R. A., J. T. Urie, 
 and W. J. Douglas. Evaluation of Long- 
 wall Industrial Engineering Data (U.S. 
 Dep. Energy contract ET-77-C-01-8915, 
 Ketron Inc., Wayne, PA). 1981, 11 pp.; 
 NTIS DOE/ET/ 12532-T2. 
 
 14. Friedman, M. Analysis of Rock De- 
 formation and Fracture Induced by Rock 
 Cutting Tools Used in Coal Mining (U.S. 
 Dep. Energy contract AC04-76DP00789, Tex- 
 as A & M Univ., College Station, TX) . 
 Sandia National Laboratory, Albuquerque, 
 NM, Contractor Rep. SAND 83-7007, Mar. 
 1983, 36 pp. 
 
 15. Richmond, J. K. , G. C. Price, 
 M. J. Sapko, and E. M. Kawenski. Histor- 
 ical Summary of Coal Mine Explosions in 
 the United States, 1959-81. BuMines 
 IC 8909, 1983, 53 pp. 
 
 16. Krech, W. W. , R. A. Henderson, and 
 K. E. Hjelmstad. A Standard Rock Suite 
 for Rapid Excavation Research. BuMines 
 RI 7865, 1974, 29 pp. 
 
 17. Leach, S. J., and G. I. Walker. 
 The Application of High Speed Liquid Jets 
 to Cutting; Some Aspects of Rock Cutting 
 by High Speed Water Jets. Proc. R. Soc. 
 London, Ser. A, v. 260, 1966, pp. 295- 
 308. 
 
 18. Hoagland, R. G. , G. T. Hahn, and 
 A. R. Rosenfield. Influence of Micro- 
 structure on Fracture Propagation in 
 Rock. Rock Mech., v. 5, 1973, pp. 77- 
 106. 
 
 19. Westwood, A. R. C. Control and 
 Application of Environment Sensitive 
 Fracture Processes. J. Mater. Sci., v. 
 9, 1974, pp. 1871-1895. 
 
20 
 
 20. Schmidt, R. A. Fracture Mechanics 
 of Oil Shale; Unconfined Fracture Tough- 
 ness, Stress Corrosion Crackling, and 
 Tension Test Results. Paper in Energy 
 Resources and Excavation Technology 
 (Proc. 18th Symp. on Rock Mechanics, Key- 
 stone, CO, June 22-24, 1977). CO Sch. 
 Mines Press, Golden, CO, 1977, pp. 2A2-1 
 to 2A2-6. 
 
 21. Barton, C. C. Variables in Frac- 
 ture Energy and Toughness Testing of 
 Rock. Paper in Issues in Rock Mechanics 
 (Proc. 23d U.S. Symp. on Rock Mechanics, 
 Univ. CA— Berkeley, Aug. 25-27, 1982). 
 Society of Mining Engineers, AIME, 1982, 
 pp. 449-462. 
 
 22. Hood, M. A Study of Methods To 
 Improve the Performance of Drag Bits Used 
 To Cut Hard Rock. Ph.D. Thesis, Dep. 
 Min. Eng. , Univ. Witwatersrand, Republic 
 of South Africa, 1978, 150 pp.; available 
 from M. Hood, Univ. CA, Berkeley, CA. 
 
 23. Jaeger, J. C. , and N. G. W. Cook. 
 Fundamentals of Rock Mechanics. Chapman 
 and Hall, London, 3d ed. , 1979, 593 pp. 
 
 24. Roxborough, F. F. Cutting Rocks 
 With Picks. Min. Eng. (London), v. 132, 
 No. 153, June 1973, pp. 445-455. 
 
 25. Barker, J. S., C. D. Pomeroy, and 
 D. Whittaker. The M.R.E. Large Pick 
 Shearer Drum. Min. Eng. (London), v. 
 125, No. 65, Feb. 1966, pp. 323-333. 
 
21 
 
 ANALYSIS OF MECHANICAL TOOL FORCE REDUCTIONS 
 WHEN USING WATER-JET-ASSISTED CUTTING 
 
 By R. J. Evans, 1 H. J. Handewith, 2 and C. D. Taylor 3 
 
 ABSTRACT 
 
 Water-jet-assisted cutting is the syn- 
 ergistic combination of a mechanical pick 
 and a directed moderate-pressure water 
 jet which greatly facilitates the cutting 
 process. The water jet assists the me- 
 chanical pick by lubricating the cutting 
 process, by cleaning the crushed zone 
 directly in front of the bit to reduce 
 friction, by cooling the mechanical tool 
 to improve bit life, and by exploiting 
 cracks close to the bit to promote chip 
 fragmentation. 
 
 An In-Seam Tester, which is a 
 hydraulically activated single pick 
 
 instrumented to measure and record cut- 
 ting forces, was designed and fabricated 
 by the Bureau of Mines to obtain design 
 data for a rotary drum cutting system 
 using moderate-pressure jets (3,000 to 
 10,000 psi) . Data are presented for 
 cutting trials in a simulated coal block, 
 underground in the Pittsburgh coal seam, 
 and on test blocks of sandstone and 
 limestone for water-jet-assisted and dry 
 cutting. Data are presented which indi- 
 cate that pick forces are significantly 
 reduced when using water-jet-assisted 
 cutting. 
 
 BACKGROUND 
 
 The last major breakthrough in coal 
 mining cutting tool technology was in the 
 1940's, when the introduction of tungsten 
 carbide significantly increased the life 
 and cutting ability of mechanical tools. 
 Recent studies with water-jet-assisted 
 cutting indicate that significant im- 
 provements can be made to the cutting 
 process by using this new technology. 
 
 Using conventional cutting technology, 
 today's coal mining machines, such as 
 the continuous miner and longwall shear- 
 er, have generally been optimized with 
 respect to their cutting ability in re- 
 lation to their size and weight. When 
 cutting, these machines must accept high 
 reactive torque and thrust forces. The 
 ability to react to these forces is a 
 function of the machine's weight and 
 
 'Supervisory civil engineer, Pittsburgh 
 Research Center, Bureau of Mines, Pitts- 
 burgh, PA. 
 
 ^Project research supervisor, Boeing 
 Services International Inc., Pittsburgh, 
 PA. 
 
 tractive effort. Attempts to increase 
 thrust and torque have resulted in in- 
 creased machine weight and size, thereby 
 decreasing machine maneuverability and 
 productivity. 
 
 The potential for a major advance in 
 cutting technology has been indicated by 
 researchers using water-jet-assisted cut- 
 ting systems. Experiments have been con- 
 ducted in a wide variety of rock types 
 (both in the laboratory and underground) 
 that demonstrate substantial improvements 
 in cutting performance along with sig- 
 nificant improvements in health and safe- 
 ty. These improvements include signifi- 
 cant reductions in pick cutting and 
 normal forces; improvements in bit life, 
 with substantial reduction in failures of 
 the tungsten carbide inserts; reduction 
 in fines; significant reductions in dust; 
 and reduction of frictional ignitions. 
 
 3 Industrial hygienist, Pittsburgh Re- 
 search Center, Bureau of Mines, Pitts- 
 burgh, PA. 
 
22 
 
 APPROACH 
 
 The Bureau of Mines is currently pur- 
 suing a program to develop a water- 
 jet-assisted rotary cutting system that 
 can be used for a longwall shearer or a 
 continuous miner. This system will use 
 water-jet pressure ranging from 3,000 to 
 9,000 psi, without increasing current 
 water usage or significantly increasing 
 total power consumption. Research has 
 shown that water-jet-assisted cutting has 
 the potential to reduce machine thrust 
 and torque when compared to conventional 
 cutting. The limits of this study are 
 shown in figure 1 bounded by the shaded 
 area. Previous researchers explored this 
 new technology through laboratory testing 
 of coal and coal measure rock for frac- 
 ture properties but fall short of the 
 desired goal to predict mining machine 
 performance, component wear, and costs. 
 The approach adopted here was to use 
 an In-Seam Tester to find the relation- 
 ships between dry and water-jet-assisted 
 
 UJ 
 
 o 
 
 fl 
 
 2.5 3 4 5 6 7 8 9 10 
 PRESSURE, I0 3 psi 
 FIGURE 1. - Water-jet study range of force and 
 ow rate parameters. 
 
 FIGURE 2. - Heavy-duty In-Seam Tester. 
 
23 
 
 cutting in coal and coal measure rocks. 
 The In-Seam Tester (fig. 2) is a hydrau- 
 lically powered single pick that cuts up- 
 ward in a linear plane at 25 ft/min. The 
 pick is instrumented with a four-pillar 
 dynamometer to measure and record the 
 orthogonal cutting forces as illustrated 
 in figure 3. 
 
 The rationale for using an In-Seam 
 Tester is that one of the major diffi- 
 culties facing investigators conducting 
 laboratory coal cutting tests is to en- 
 sure that the relatively small samples 
 being cut are representative with re- 
 spect to the confined ground-induced 
 stresses. This is more of a problem with 
 coal than other rock types because of 
 cleat and joint presence in the coal mass 
 and dehydration and temperature changes 
 that occur when blocks of coal are 
 removed from the mine. The In-Seam Test- 
 er will allow use of full-scale tools to 
 avoid potential errors in force scalar 
 relationships . 
 
 Cutting tests were made on coalcrete, 
 underground in the Pittsburgh coal seam, 
 and on blocks of limestone and sandstone. 
 Properties of these materials are shown 
 in table 1. Coalcrete (cement, flyash, 
 and coal) is a synthetic coal block that 
 is cast in place to simulate coal 
 properties. 
 
 Two cutting tools were tested: the 
 longwall flat pick and the conical bit 
 
 FIGURE 3. - Force reactions on a cutting bit. 
 
 (fig. 4). Each cutting tool was tested 
 with and without water-jet assist using a 
 front-mounted water jet that impinges 
 directly in front of the cutting tool us- 
 ing three pressure ranges: 3,000, 6,000, 
 and 9,000 psi. 
 
 The orthogonal bit forces were measured 
 with a four-pillar dynamometer that was 
 designed and fabricated at the Pittsburgh 
 Research Center. One inherent feature of 
 the dynamometer is that it is more sensi- 
 tive to side and cutting forces than it 
 is to normal force. 
 
 The water-jet nozzles were made from 
 stainless steel, 3/8-in-diam hexagonal 
 socket head screws, which were machined 
 down to an internal Leech and Walker con- 
 figuration. Three nozzle exit diameter 
 sizes (0.6, 0.8, and 1.0 mm) were used 
 (fig. 1). 
 
 TABLE 1. - Material properties and test results 
 
 Item 
 
 Density lb/ft. 
 
 Porosity pet. 
 
 Unconfined strength, psi: 
 
 Compressive 
 
 Shearer 
 
 Hardgrove grindability index 
 
 Cutting force with flat bit, lbf: 
 
 Dry 
 
 Wet ] 
 
 Cutting force reduction pet. 
 
 Depth of cut in. 
 
 Bit spacing in. 
 
 Berea 
 sandstone 
 
 Indiana 
 limestone 
 
 Coalcrete 
 block 
 
 Pittsburgh 
 seam coal 
 
 130 
 1.98 
 
 8,300 
 
 NA 
 NA 
 
 3,620 
 
 1,695 
 
 53 
 
 1 
 
 2 
 
 145 
 14.1 
 
 4,700 
 
 NA 
 NA 
 
 NA 
 
 NA 
 
 NA 
 
 1 
 
 2 
 
 106 
 
 NA 
 
 898 
 
 132 
 
 62 
 
 350 
 
 380 
 
 Neg 
 
 1.5 
 
 3 
 
 85 
 
 NA 
 
 NA 
 NA 
 58 
 
 450 
 390 
 Neg 
 1.5 
 3 
 
 NA Not available. Neg Negligible. 
 
 ^sing 3,000-psi water jets with 0.015-in-diam jet nozzle. 
 
24 
 
 FIGURE 4. - Flat and conical cutting bits. 
 
 Each cutting test with the In-Seam 
 Tester consisted of data from 140 in of 
 rock-coal cutting. The cutting stroke on 
 the Tester is 14 in. Each cut had 10 in 
 of steady-state cutting data recorded. 
 The typical cutting sequence progresses 
 from left to right with 3-in spacing 
 between each cut. The depth of cut 
 ranged from 1 to 2 in, depending on the 
 spacing and cutting material, as shown in 
 figure 5. After each test, a cleanup cut 
 was made, progressing from right to left, 
 using half spacing that cut between each 
 groove of the previous cut. 
 
 Dust measurements for dry and wet cuts 
 were made during operation of the In-Seam 
 Tester. Dust levels were measured during 
 cutting by drawing air near the cutting 
 tool through a duct connected to a dust 
 box. A vacuum pump was used to draw dust 
 from the cutting surface into the duct 
 and through the dust box. Two cyclones 
 were placed inside and near the middle of 
 the box, connected to tubing that carried 
 dust from the cyclones to sampling in- 
 struments located outside the sampling 
 box. 
 
 1.5- in depth 
 of cut typical 
 
 FIGURE 5. - Cutting sequence of coal face. 
 
25 
 
 RESULTS 
 
 Water-jet-assisted cutting is the syn- 
 ergistic combination of a mechanical tool 
 and a directed high-pressure water jet. 
 The high-pressure jet exploits any cracks 
 in the vicinity, lubricates the cutting 
 process, increases bit life, and reduces 
 dust and incidence of frictional igni- 
 tion. Water jets are especially effec- 
 tive when cutting a granular texture like 
 sandstone. 
 
 Tests conducted on Berea sandstone, 
 with properties as shown in table 1, dem- 
 onstrated a 53-pct reduction in net cut- 
 ting force and a peak force reduction of 
 39 pet when using a conical bit and a 
 0.015-in-diam jet nozzle with 3,000-psi 
 pressure. These tests were conducted at 
 a 1-in depth of cut and 2-in spacing and 
 compare very favorably with reported 
 results. 4 
 
 When cutting softer materials such as 
 coalcrete and Pittsburgh seam coal, the 
 spacing was increased to 3 in and the 
 depth to 1-1/2 in to provide higher force 
 levels. The flat pick assisted by a 
 3,000-psi jet indicated negligible force 
 reductions. When cutting with the coni- 
 cal bit, force reductions of 15 pet were 
 observed. The conical bit was far more 
 susceptible to the influence of 3,000-psi 
 water jet than the flat longwall pick. 
 As shown in table 2 , the conical bit re- 
 quired twice as much cutting force as the 
 flat pick. Tests in the coalcrete block 
 and Pittsburgh seam coal clearly demon- 
 strated that both materials exhibited 
 negligible cutting force reductions with 
 the 3,000-psi jet assist. 
 
 The cutting of limestone with the coni- 
 cal bit and 3,000-psi water indicated a 
 30-pct reduction in normal force and 17- 
 pct reduction in cutting force for a net 
 resultant reduction of 24 pet. This 
 agreed favorably with Ropchan's work. 5 
 Rock chip distribution studies were 
 
 ^Ropchan, D., F. D. Wang, and J. Wolga- 
 mott. Application of Water-Jet-Assisted 
 Drag Bit and Pick Cutter for the Cutting 
 of Coal Measure Rocks (U.S. Dep. Energy 
 contract ET-77-a-01-9082, CO Sch. Mines). 
 Apr. 1980, 120 pp.; NTIS DOE/ET/ 12463-1. 
 
 5 Work cited in footnote 4. 
 
 TABLE 2. - Bit cutting force reactions 
 in coalcrete (l-l/2-in penetration 
 and 3-in spacing) 
 
 Cutting force, lbf: 
 Dry 
 
 With water-jet 
 assist 
 
 Force reduction. .pet, 
 
 Flat long- 
 wall bit 
 
 360 
 
 370 
 Neg 
 
 Neg Negligible. 
 
 conducted on the limestone tests to eval- 
 uate cutting efficiency of the conical 
 bit and flat pick. As shown in figure 6, 
 the flat pick produced more larger chips 
 at greater depths of cut than the conical 
 pick and is therefore more efficient. At 
 more shallow depths of cut the conical 
 bit is more efficient. 
 
 To verify this observation, cutting 
 forces were compared for dry and water- 
 jet cutting on all of the test materials. 
 It was found that the flat longwall pick 
 used only 40 pet of the cutting force re- 
 quired by the conical bit at the same 
 depth of cut and bit spacing. 
 
 Testing with 6,000-psi water-jet assist 
 resulted in substantial force reductions 
 when using the flat and conical picks, 
 
 Standard 
 sieve size 
 
 Extrapolation 
 
 o Flat bit, f/ 2 -in DOC 
 
 ''8 1 
 
 • Flat bit, l-in DOC 
 
 a conical bit, l/g-in DOC 
 
 ^Conicalbit, 1-inDOC ^ N O.^O.I8 9 5in) 
 
 I in 
 
 3/b 
 
 No.16 (0.0469 in) 
 20 40 60 80 100 
 
 CUMULATIVE PERCENT PASSING 
 FIGURE 6. - Rock distribution study. (Numbers 
 at right represent standard sieve sizes; DOC = depth 
 of cut.) 
 
26 
 
 indicating a strong susceptibility to 
 higher jet pressures. In addition, a re- 
 markable decrease in the magnitude and 
 number of peak cutting forces was evident 
 as shown in figures 7 and 8. These fig- 
 ures show typical cuts taken with the In- 
 Seam Tester when cutting the synthetic 
 coal block with the flat and conical pick 
 both dry and with 1,000 and 2,000 psi 
 water-jet assist. The number and magni- 
 tude of peak forces were reduced dramat- 
 ically when using water-jet assist, which 
 makes for a much smoother cutting process 
 that will increase machine reliabil- 
 ity and life. These advantages compare 
 
 Normal, with 1,000 psi water 
 
 Cutting, with 1,000 psi water 
 
 Normal, dry 
 
 ^Ayl^A/VvV^^^A^_ 
 
 Cutting, dry 
 FIGURE 7. • Flat-bit peak cutting forces. 
 
 favorably with results reported by 
 Ropchan. 6 
 
 Cutting forces were reduced approxi- 
 mately 35 pet when cutting coalcrete us- 
 ing 6,000-psi water-jet assist with a 
 flat bit (fig. 9). The interesting fea- 
 ture of this curve is that the cutting- 
 force reduction decreases as jet pres- 
 sure is increased beyond 6,000 psi. The 
 plausible reason for this is that at 
 higher jet pressures the jet cuts a slot 
 beyond the depth of the mechanical tool, 
 which decreases the assistance to the 
 chip fragmentation process. More data 
 will be required to adequately explain 
 this phenomenon. 
 
 This same phenomenon is also true for 
 the gross force reduction, which is the 
 cumulative effect of the orthogonal cut- 
 ting forces. As shown in figure 10, the 
 force reduction decreases as jet pressure 
 is increased beyond 6,000 psi. The same 
 reason given above for reductions noted 
 in cutting forces may also be applied 
 here for gross force reductions. Again, 
 more data will be required to explain 
 this phenomenon. 
 
 Before a water-jet-assisted rotary 
 cutting system can be employed, a number 
 of problems associated with the use of 
 water jets at 3,000 to 10,000 psi need to 
 be resolved for the equipment to func- 
 tion. These problems include provision 
 for delivering high-pressure water to the 
 rotating drum (cutting head), protection 
 
 ^Work cited in footnote 4. 
 
 Normal, with 2,000 psi water 
 
 /AjWL 
 
 Cutting, with 2,000 psi water 
 
 Normal, dry 
 
 Cutting, dry 
 FIGURE 8. - Conical-bit peak cutting forces. 
 
 Ld 
 
 <r 
 o 
 
 04 
 
 10 
 5 20 
 y 30 
 
 Q 
 Ld 
 
 * 40 
 
 50 
 
 0123456789 10 
 
 WATER JET PRESSURE, I0 3 psig 
 
 FIGURE 9. - Flat-bit cutting force reduction 
 while cutting coalcrete using 0.6-mm nozzle 
 (correlation coefficient = 0.66). 
 
 1a _ 
 
 \ A 
 
 ^^^^ A ^ 
 
 A "1" 
 
 A 
 
 4 i ♦ I T • 1 I I I 
 
27 
 
 o 
 
 3 
 Q 
 UJ 
 
 cc 
 
 LU 
 O 
 OC 
 O 
 
 UJ 
 
 I- 
 to 
 > 
 en 
 
 CO 
 
 to 
 o 
 
 ce 
 o 
 
 -iu 
 0' 
 
 i 
 
 1 
 
 i 
 
 i 
 
 i 
 
 i 
 
 i 
 
 
 I 
 
 10 
 
 
 
 
 
 
 
 
 
 - 
 
 20 
 
 
 
 
 
 
 
 
 
 - 
 
 30 
 
 
 
 
 A 
 
 
 
 
 A 
 
 A 
 
 40 
 
 
 
 ▲ 
 
 
 
 
 
 
 
 
 ▲ 
 
 ▲ 
 
 ▲ 
 
 50 
 60 ( 
 
 - A 
 1 
 
 1 
 
 I 
 
 I 
 
 I 
 
 I 
 
 I 
 
 I 
 
 1 
 
 ) 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 K 
 
 _ 2.0 
 
 WATER JET PRESSURE, I0 3 psig 
 
 FIGURE 10. - Flat-bit gross system force re- 
 duction while cutting coalcrete using 0.6-mm 
 nozzle (correlation coefficient = 0.76). 
 
 of the nozzles from rock debris and other 
 possibilities of mechanical damage, a 
 method for quickly and easily replacing 
 nozzles that become worn by erosion, and 
 a system for phasing water-jet activation 
 only when the bit is in contact with the 
 cutting surface. This last provision may 
 be necessary to prevent excessive water 
 usage and to minimize the energy required 
 to operate the jets. 
 
 One major aspect of this study was to 
 ensure that the total amount of water 
 added to the cut coal did not exceed what 
 is presently used on continuous miners 
 and coal shearers. As shown in figure 
 1 1 , the weight of water added to coal is 
 inversely proportional to the machine 
 mining rate. The current upper limit 
 accepted by industry is approximately 1.3 
 pet water for each ton of mined coal. 
 The water-jet-assisted mining rate re- 
 flects the water- jet-induced lower bit 
 forces. However, the water-jet-assisted 
 system does not include a phasing system, 
 
 E 
 
 4— 
 
 o 
 
 c 
 o 
 
 4— 
 
 o 
 
 Q. 
 
 3 
 
 of 
 
 UJ 
 
 5 
 
 .5 - 
 
 1.0 
 
 Water-jet 
 assisted 
 
 30gal/min 
 
 60 gal /mirf 
 
 25 gal/min 
 gal/min 
 15 gal/min 
 
 j_ 
 
 j_ 
 
 _L 
 
 5 10 15 20 25 
 
 MINING RATE,ton/min 
 FIGURE 11. - Percent water in cut coal using 
 various mining methods. 
 
 100 
 90 
 
 1 
 
 1 1 1 
 ^ — o 
 
 i i i ■ ■■ i - — 
 
 
 
 / 
 
 
 - 
 
 - f*~ 
 
 — Extrapolation 
 
 - 
 
 -1 
 
 Reduction (pet) = 
 
 Dust dry- dust wet 
 
 7T— ; ( ioo) - 
 
 Dust dry 
 
 1 
 
 
 - 
 
 1 
 
 1 1 
 
 1 1 1 
 
 i i i i 
 
 80 
 
 * 70 
 
 o 60 
 B 50 
 
 UJ 
 
 or 
 
 t- 40 
 
 30 
 
 20 - 
 
 10 
 
 123456789 
 
 WATER-JET PRESSURE, I0 3 psi 
 
 FIGURE 12. - Water-jet-assisted dust reduc- 
 tion potential. 
 
 which could cut total water usage by a 
 factor of two-thirds. With such a phas- 
 ing system, the water could be reduced to 
 approximately 0.50 pet per ton of mined 
 coal. This observation was made using 
 the 0.015-in-diam jet nozzle with 6,000 
 psig and a flow rate of 1.2 gal/min per 
 nozzle. 
 
28 
 
 Water-jet-assisted cutting significant- 
 ly reduces coal dust when cutting the 
 Pittsburgh coal seam underground at 
 the Pittsburgh Research Center (fig. 12). 
 
 At 4,000 psi, dust reduction was 90 pet 
 when compared to dry cutting. Beyond 
 4,000 psi no further dust reduction was 
 evident . 
 
 CONCLUSION 
 
 Four test materials have been evaluated 
 with 3,000-psi water-jet assist. Al- 
 though effective in coal measure rock, 
 this jet pressure was ineffective in coal 
 and coalcrete. Testing to date indicates 
 that the flat pick is the more efficient 
 cutting tool. Work has commenced using 
 higher pressures. Results indicate that 
 
 the 6,000-psi water jets will be effec- 
 tive in coal and coalcrete. Though in 
 the early research stage, the water- 
 jet-assisted cutting program, which is 
 being conducted at the Pittsburgh Re- 
 search Center, has proved encouraging. 
 It does warrant further study. 
 
29 
 
 EXPERIENCE WITH BOOM-TYPE ROADHEADERS EQUIPPED WITH HIGH-PRESSURE 
 WATER- JET SYSTEMS FOR ROADWAY DRIVAGE IN BRITISH COAL MINES 
 
 By A. H. Morris 1 and M. G. Tomlin 2 
 
 ABSTRACT 
 
 In 1978, collaboration was established 
 between the Bureau of Mines and the 
 National Coal Board (United Kingdom) 
 (NCB) on a project to develop and test a 
 high-pressure water-jet system fitted to 
 a boom-type roadheader. Earlier labora- 
 tory trials had indicated that such a 
 system could significantly improve the 
 cutting performance of a roadheader and 
 that other benefits in terms of extended 
 pick life, better dust suppression and 
 reduced frictional sparking would also be 
 achieved. 
 
 Surface trials with a prototype sys- 
 tem showed that the expected benefits 
 could be realized, and further equipment 
 
 development was then carried out so that 
 the potential of the technique could be 
 assessed when applied in production 
 situations. 
 
 Four production-type water-jet systems, 
 each incorporating different features as 
 regards pump units, seals, nozzles, etc., 
 have been produced and fitted to road- 
 headers. The first of these has success- 
 fully completed an underground trial, and 
 trials with the others are proceeding. 
 The experience gained with these ma- 
 chines, the performance of the water-jet 
 systems, and their effect on operation 
 are discussed. 
 
 INTRODUCTION 
 
 Operating trials with a boom-type road- 
 header equipped with the National Coal 
 Board prototype high-pressure water-jet 
 system were carried out at Middleton 
 Limestone Mine in 1981. 3 Figure 1 shows 
 the system in operation. During these 
 trials , the technique showed good poten- 
 tial for improving the roadheader cut- 
 ting performance. It was agreed that 
 the development of preproduction versions 
 
 should proceed, so that full-scale un- 
 derground trials could take place. Two 
 machines would be produced by Anderson 
 Strathclyde and Dosco, respectively, us- 
 ing technical information and trial re- 
 sults provided by NCB's Mines Research 
 and Development Establishment (MRDE); two 
 others would be Dosco Mk.IIA machines 
 modified by MRDE. 
 
 ACKNOWLEDGMENT 
 
 The authors thank the Director of Min- 
 ing Research and Development, National 
 Coal Board, for permission to publish 
 this paper. The views expressed are 
 
 1 Chief project manager. 
 
 2 Project engineer. 
 Mines Research and Development Estab- 
 lishment, Tunneling and Transport Branch, 
 National Coal Board, Bretby, United 
 Kingdom. 
 
 their own 
 the NCB. 
 
 and not necessarily those of 
 
 3piumpton, N. A., and M. G. Tomlin. 
 The Development of a Water Jet System To 
 Improve the Performance of a Boom Type 
 Roadheader. Paper in 6th International 
 Symposium on Jet Cutting Technology 
 (Univ. Surrey, United Kingdom, Apr. 6-8, 
 1982). BHRA Fluid Engineering, Crans- 
 field, Bedford, United Kingdom, 1982, 
 pp. 267-282. 
 
30 
 
 FIGURE 1. - NCB prototype high-pressure water-jet system. 
 
 DEVELOPMENT OF PREPRODUCTION VERSION 
 
 GENERAL 
 
 The high-pressure water-jet system op- 
 erates at a maximum water pressure of 
 10,000 psi. It comprises a high-pressure 
 water pump and a rotary seal unit to in- 
 troduce the water into the roadheader 
 drive shaft and cutting head, the cutting 
 head being equipped with nozzles to di- 
 rect high-pressure jets into the area of 
 the cutting picks. Operational experi- 
 ence with the prototype system indicated 
 that considerable further development 
 of the rotary seal was necessary if an 
 acceptable life expectancy were to be 
 achieved in a production environment and 
 that there was scope for improvement 
 
 in nozzle design to produce more ef- 
 ficient jets. The original roadheader 
 equipped with the prototype system was 
 retained at the limestone mine to gain 
 further operational experience and for 
 use as a test bed for new seal and nozzle 
 developments. 
 
 ROTARY SEAL DEVELOPMENT 
 
 Development of the high-pressure water 
 seal for the prototype system had been 
 concentrated on the requirement to fit 
 such a seal around the cutting head shaft 
 as shown in figure 2. Further develop- 
 ment based on this configuration resulted 
 in an increase in seal life from 50 to 
 
31 
 
 -Pressure cylinder 
 SeaK \ ^Seal 
 
 -Cutting head shaft 
 FIGURE 2. - Rotary seal assembly. 
 
 Cutting head shaft 
 -Cutting head 
 
 Layshaft gearbox 
 
 Epicyclic gearbox 
 
 Water passage-^ 1 — Small-diameter rotary seal 
 
 FIGURE 3. - Section through layshaft gearbox. 
 
 140 h, though this was unpredictable and 
 still far short of the minimum accepta- 
 ble life of about 500 h. A seal change 
 was also a major operation, and machine 
 downtime was excessive. Because of these 
 factors, development was switched to 
 two alternative approaches. Both incor- 
 porate a small-diameter seal built into a 
 cartridge assembly, which is readily ac- 
 cessible and can be easily and quickly 
 changed, thus reducing the importance of 
 seal life as a limiting factor; also it 
 was expected that seal life would dramat- 
 ically improve as the diameter decreased. 
 
 The first approach was to introduce a 
 layshaft gearbox into the roadheader boom 
 prior to the cutting head shaft (fig. 3). 
 A gearbox was designed and manufactured 
 (fig. 4) and extensively tested on the 
 roadheader. It proved completely relia- 
 ble in operation, and the seal unit could 
 be changed in a few minutes. The small- 
 diameter seal unit developed concurrently 
 for this application also proved success- 
 ful, and seal lives in excess of 200 h 
 were achieved. 
 
 The second alternative is shown in fig- 
 ure 5. The roadheader boom has been mod- 
 ified to accommodate an axial water pas- 
 sage along its full length, with the 
 
 FIGURE 4. - Layshaft gearbox. 
 
32 
 
 Epicyclic gearbox- 
 
 Boom trunk 
 
 Cutting 
 head 
 
 Small -diameter 
 Motor-, / rotary seal 
 
 Water passage through motor, 
 epicyclic gearbox,and boom trunk 
 
 FIGURE 5. - Boom with axial water passage. 
 
 3 xZ? 
 
 Diam D 
 
 FIGURE 6. - Tungsten carbide nozzle. 
 
 Delrin 
 
 Sapphire insert 
 FIGURE 7. - Synthetic sapphire nozzle. 
 
 small-diameter seal unit mounted at the 
 end remote from the cutting head. While 
 time restrictions prevented this method 
 being tested in situ, it was felt that it 
 had every chance of success. 
 
 Both methods have been adopted in the 
 preproduction systems described later. 
 
 NOZZLE DEVELOPMENT 
 
 A test program was initiated to assess 
 the comparative performance of various 
 nozzle types against that of the simple, 
 synthetic sapphire orifices used on 
 the prototype system. Nozzle performance 
 was recorded on a test rig by measur- 
 ing the pressure profile across the jet 
 stream at various distances from the 
 nozzle. 
 
 The type of nozzle which gave best re- 
 sults is shown in figure 6. Manufactured 
 from tungsten carbide, this type has a 
 highly polished inner face with a surface 
 finish of 0.15 ym. Nozzles of similar 
 shape, but made from stainless steel and 
 with an inset synthetic sapphire orifice, 
 as shown in figure 7, also gave good re- 
 sults, although slightly inferior to the 
 tungsten carbide type. 
 
 Nozzle life and efficiency ratings 
 could not be established during the test- 
 ing period, and it was decided that both 
 types should be incorporated in the pre- 
 production versions. This would allow 
 assessment of the useful life of each 
 type by regularly checking the perform- 
 ance of sample nozzles on the test rig 
 and recording any fall off in efficency 
 over long periods. 
 
 DESCRIPTION OF PREPRODUCTION SYSTEMS 
 
 NCB PREPRODUCTION VERSION TYPE 1 
 
 The type 1 system closely resembles the 
 prototype system used at Middleton Lime- 
 stone Mine, with some refinements based 
 on test results and further development 
 work. 
 
 The base machine is a Dosco Mk.IIA 
 roadheader as shown in figure 8. High- 
 pressure water is generated by an oil- 
 water intensifier mounted on the road- 
 header boom. Maximum output from the 
 intensifier is 45 L/min at 10,000 psi 
 
 pressure, and it is powered by a hydrau- 
 lic swashplate pump unit at the rear of 
 the machine. This pump unit is fitted 
 with a remote control system to allow the 
 machine operator to select either high- 
 pressure water output from the inten- 
 sifier or low-pressure output for dust 
 suppression purposes if high-pressure jet 
 assistance is not required. 
 
 A layshaft gearbox with small-diameter 
 seal unit is fitted into the boom to ac- 
 cept the water output from the intensi- 
 fier. The cutting head is equipped with 
 
33 
 
 FIGURE 8. - NCB preproduction version, type 1. 
 
 FIGURE 9. - Cutting head. 
 
34 
 
 tungsten carbide nozzles. These stand 
 clear of the cutting head body to mini- 
 mize the standoff distance from nozzle to 
 pick tip and are protected from external 
 damage by steel shrouds, as shown in fig- 
 ure 9. 
 
 The water-jet system is interlocked 
 with the roadheader electrical and hy- 
 draulic circuits for "operator" protec- 
 tion. Prestart warning is given by low- 
 pressure drenching sprays directed at the 
 cutting head, while the high-pressure 
 jets cannot be switched on unless the 
 cutting head is running. 
 
 NCB PREPRODUCTION VERSION TYPE 2 
 
 The type 2 preproduction version is 
 shown in figure 10. The only difference 
 between the type 2 and type 1 systems is 
 that, for the type 2, the single intensi- 
 fier mounted on the roadheader boom has 
 been replaced by two smaller intensifiers 
 of equivalent capacity. These are mount- 
 ed on each side of the boom, as shown in 
 figure 11, to improve the machine opera- 
 tor's view of the cutting head. 
 
 DOSCO PREPRODUCTION SYSTEM 
 
 The Dosco system is again based on 
 a Dosco MK.IIA roadheader, which has 
 been modified to accommodate the high- 
 pressure water pump on the machine base 
 (fig. 12). Some machine components have 
 been interchanged, to enable a 150-kW 
 
 through-shaft motor to be mounted at the 
 side of the machine. This motor is then 
 used to drive both the roadheader hydrau- 
 lic pump and the high-pressure water 
 pump. The pump used is a diaphragm-type, 
 fixed-displacement unit with a maximum 
 output of 45 L/min at 10,000-psi pres- 
 sure. A water header tank is mounted 
 above the pump , and the hydraulic circuit 
 is arranged so that surplus output can 
 be dumped back to this tank when high- 
 pressure water is not required. 
 
 A layshaft gearbox with small-diameter 
 seal is fitted into the boom, as on the 
 NCB systems, and high-pressure water is 
 fed to this via a rigid steel pipe sys- 
 tem; horizontal and vertical articulated 
 joints accommodate movement of the road- 
 header boom. The cutting head is similar 
 in design to those used on the NCB sys- 
 tems , except that it is equipped with 
 synthetic sapphire nozzles. 
 
 ANDERSON STRATHCLYDE 
 PREPRODUCTION SYSTEM 
 
 This system has been installed on an 
 Anderson Strathclyde RH22 roadheader and 
 is shown in figure 13. A triplex-piston 
 type high-pressure water pump and water 
 header tank are mounted on the rear of 
 the machine behind the driver's position. 
 This pump has a higher capacity — 68 L/min 
 at 10,000-psi pressure — than the three 
 systems previously described. 
 
 FIGURE 10. - NCB preproduction version, type 2. 
 
35 
 
 FIGURE 11. - Twin intensifiers mounted on boom. 
 
 The roadheader is equipped with a boom 
 incorporating an axial water passage 
 and has a small-diameter rotary seal 
 mounted at the motor end. The boom has 
 a telescopic facility, and a sliding 
 seal arrangement is incorporated in the 
 water passage at the cutting head end. 
 High-pressure water is fed to the boom 
 by means of a flexible hose which, for 
 
 reasons of safety, is shrouded by another 
 heavy-duty hydraulic hose. The cutting 
 head is based on the normal design used 
 on the RH22 roadheader and has provision 
 for high-pressure nozzles to be fitted in 
 front of all 24 picks. As on the two NCB 
 systems , the nozzles used are tungsten 
 carbide. 
 
36 
 
 FIGURE 12. - Dosco preproduction system. 
 UNDERGROUND TRIALS 
 
 GENERAL 
 
 At the time of writing, the two NCB 
 systems and the Dosco system had been 
 commissioned and deployed to collieries, 
 but trials had not yet commenced. Com- 
 ments, therefore, are restricted to the 
 performance of the Anderson Strathclyde 
 roadheader, which has been in operation 
 at Sutton Manor Colliery since August 
 1983. 
 
 Before taking the roadheader under- 
 ground, operator training was carried out 
 on the surface by MRDE and Anderson 
 Strathclyde. Colliery staff were made 
 familiar with the high-pressure equipment 
 and its operation and were made aware of 
 the hazards involved if the equipment was 
 misused or if the rules established for 
 safe operation were broken. 
 
 The roadheader is being used to drive a 
 main access roadway to coal reserves in 
 the High Florida Seam. The roadway pass- 
 es through a wide variety of strata, 
 ranging from soft mudstones to hard silt- 
 stones and sandstones with some ironstone 
 bands and inclusions. So far, approxi- 
 mately 150 m of drivage has been com- 
 pleted with good results; the water-jet 
 system is in continuous use and has been 
 readily accepted by the heading teams. 
 Colliery staff are satisfied that it is 
 contributing significantly to the overall 
 performance of the roadheader. 
 
 CUTTING PERFORMANCE 
 
 The comparative cutting performance 
 of the roadheader with and without 
 high-pressure jet assistance is being 
 
37 
 
 FIGURE 13. - Anderson Strathclyde preproduction system. 
 
 monitored in different strata as the 
 roadway advances. The results of the 
 tests completed to date are summarized in 
 table 1. Increases in cutting rate and 
 reductions in specific energy require- 
 ments have been recorded in all cases, 
 although there is considerable variation 
 for each rock type. Examination of the 
 
 recorder traces of the cutting head power 
 consumption during tests also indicates a 
 marked reduction in vibration when jet 
 assistance is used. This was also vis- 
 ually evident. Again, the effect has 
 varied in the different rock types, but 
 was extremely significant in some cases, 
 as illustrated in figure 14. 
 
 TABLE 1. - Comparative cutting performance with and without high-pressure 
 jet assistance 
 
 Test 
 
 Rock type 
 
 Strength, psi 
 
 Cutting rate, 
 ton/h 
 
 Specific energy 
 requirement , 
 
 
 Compressive 
 
 Tensile 
 
 With 
 
 Without 
 
 m 3 /(kW«h) 
 
 
 With 
 
 Without 
 
 1 
 
 
 8,400 
 6,300 
 11,800 
 10,200 
 5,900 
 5,900 
 6,500 
 
 2,200 
 2,100 
 3,000 
 2,700 
 1,700 
 1,900 
 1,700 
 
 16.8 
 17.1 
 2.8 
 7.8 
 10.1 
 37.4 
 16.2 
 
 15.2 
 
 11.1 
 
 2.5 
 
 2.8 
 
 8.1 
 
 18.4 
 
 13.0 
 
 2.20 
 2.23 
 9.00 
 2.87 
 3.32 
 1.21 
 1.65 
 
 3.58 
 
 2 
 3 
 
 
 3.32 
 10.27 
 
 4 
 5 
 
 Siltstone and/or sandstone 
 
 8.90 
 4.09 
 
 6 
 
 
 2.46 
 
 7 
 
 
 2.30 
 
38 
 
 With jets NL 
 
 Without jets 
 
 J ^ 
 
 
 TIME 
 
 DUST SUPPRESSION 
 
 From the onset of the trial it was ob- 
 vious that dust suppression with high- 
 pressure jets was far superior to that 
 achieved with conventional low-pressure 
 (300-psi) sprays. This, in fact, has 
 caused problems when monitoring the ma- 
 chine cutting performance, since the op- 
 erators are extremely reluctant to oper- 
 ate without jet assistance even for short 
 test periods. Continuous monitoring of 
 respirable dust levels in the roadway 
 over full working shift periods has shown 
 that levels below 2 mg/m 3 have been con- 
 sistently maintained, even though forcing 
 ventilation is used. This is well below 
 the maximum acceptable level of 5 mg/m 3 . 
 
 The results of an individual series of 
 tests carried out to establish the res- 
 pirable dust make during the cutting cy- 
 cle are given in figure 15. These tests 
 were carried out consecutively in the 
 same band of strata, and, by fitting 
 suitably sized nozzles for each test the 
 water flow of 68 L/min was kept constant 
 over a range of pressures from 300 to 
 10,000 psi. The benefits, in terms of 
 dust reduction, of increasing the water 
 pressure are apparent. 
 
 PICK LIFE 
 
 Pick consumption on the length of 
 drivage already completed has averaged 
 0.7 per meter of advance. Since jet 
 assistance has been used continuously, no 
 comparison can be made with pick consump- 
 tion when jet assistance is not used. 
 However, one short test has been carried 
 out, and this indicates that considerable 
 increase in pick life is being achieved. 
 
 CT 
 
 c/) 
 Q 
 
 Ld 
 
 _J 
 CD 
 < 
 
 or 
 
 FIGURE 14. - Cutting head power versus time trace. — 
 
 to 
 
 e 
 
 100 
 
 WATER PRESSURE, 10* psi 
 
 FIGURE 15. - Results of dust suppression tests. 
 
 For the purposes of this test, two noz- 
 zles were blanked off, one adjacent to a 
 pick near the front of the cutting head 
 and the other adjacent to a pick at the 
 rear of the cutting head. During 1 m of 
 advance , the front pick needed to be 
 changed three times and the rear pick 
 twice. Only 1 of the other 22 picks on 
 the head failed during the same period. 
 It was hoped that this test could be re- 
 peated over a longer period so that accu- 
 rate comparisons could be established; 
 however, occasional sparking was noted 
 during the test from the two picks with- 
 out jets, and, in view of the gaseous 
 conditions prevailing in the roadway, the 
 test was not repeated. 
 
 EQUIPMENT PERFORMANCE 
 
 The high-pressure water system has op- 
 erated well, and the only problems en- 
 countered have been with the sliding seal 
 in the telescopic boom. This has failed 
 on three occasions but has since been re- 
 designed and is now proving reliable in 
 operation. 
 
 Expected problems due to nozzle block- 
 ages and water accumulation on the road- 
 way floor (based on operational experi- 
 ence with the prototype system) have not 
 been as severe as expected. 
 
39 
 
 The water feed to the high-pressure 
 pump is filtered at 10 um through a bank 
 of filters of diminishing size; normally, 
 only one or two nozzles become blocked 
 during a working week. Blockages can 
 easily be cleared using a twist drill of 
 the same diameter as the nozzle orifice. 
 
 The floor of the roadway has remained 
 generally dry, although some pools of 
 
 water have accumulated in the working 
 area. These do not affect maneuverabil- 
 ity of the roadheader, though some prob- 
 lems have occurred with the loading-out 
 conveyors due to slurry causing block- 
 ages. A pump has been installed in the 
 roadway to clear the water if it becomes 
 excessive. 
 
 CONCLUSIONS 
 
 Current trials with the water-jet sys- 
 tem at Sutton Manor have proved that, to 
 some degree, all the benefits expected 
 from use of the technique, as evidenced 
 by the first trials at Middleton, can be 
 achieved. 
 
 Cutting rates have been measurably im- 
 proved, and the forces on the cutting 
 picks have been reduced, as indicated by 
 the lower specific energy requirement at 
 the cutting head. 
 
 The effect of high-pressure jets in re- 
 ducing dust make has been remarkable, and 
 this may well be a major factor in influ- 
 encing further exploitation of the sys- 
 tem, especially when considered in con- 
 junction with the observed elimination of 
 frictional sparking. 
 
 Apart from early problems with the 
 faulty sliding seal (which have since 
 been solved), the high-pressure equipment 
 has so far proved reliable in operation. 
 
 What is also important is the way 
 in which this new technology has been 
 
 readily accepted by the colliery staff. 
 Pretrial training has obviously paid div- 
 idends in that the confidence of the col- 
 liery staff has been gained; this exer- 
 cise is currently being repeated at the 
 other three trial sites. 
 
 It would be premature to forecast the 
 extent of future exploitation of high- 
 pressure water-jet assistance, operation- 
 al experience having not yet been gained 
 with the other three systems. These will 
 be operating in different conditions, a 
 fact that may well highlight problems not 
 apparent from the Sutton Manor trial. 
 Trials with the NCB type 1 and Dosco sys- 
 tems are now imminent, while trials with 
 the NCB type 2 system will follow shortly 
 thereafter. When these trials are well 
 advanced, the overall performance of all 
 four systems will be assessed. Only then 
 will any commitment on further exploita- 
 tion be made. 
 
40 
 
 DEVELOPMENT WORK FOR COAL WINNING TECHNOLOGY 
 By Dr. E. H. Henkel 1 
 
 INTRODUCTION 
 
 Worldwide, shearer-loaders and coal 
 ploughs are the predominant machine de- 
 signs for coal winning on longwall faces. 
 Even though these systems are capable of 
 high production performance under opti- 
 mized operating conditions, they do not 
 comply fully with tomorrow's expec- 
 tations, which may be summarized as 
 follows: 
 
 1. Coal winning, including high per- 
 formance, optimized web, and use on face 
 ends. 
 
 2. Adaptability to geological condi- 
 tions, including seam thickness, strength 
 of coal and adjacent strata, and working 
 through faults. 
 
 3. Working conditions including low- 
 dust operation, improved mine climate, 
 and higher safety standards. 
 
 4. Economic aspects and cost reduc- 
 tion, including coal preparation (larger 
 particle size, less fines, and reduced 
 humidity) , production (better use of en- 
 ergy, higher reliability, and wider ap- 
 plication range) , and organization (sys- 
 tematic monitoring and maintenance). 
 
 With consideration of these require- 
 ments, the present limits of practicality 
 for both types of coal winning systems 
 are set as shown on figure 1. Inde- 
 pendent of strength criteria, the appli- 
 cation range for conveyor-mounted shearer 
 loaders is in seam thicknesses of more 
 than 1.8 m. For seam thicknesses of less 
 than 1.8 m, in-web shearers may be used. 
 
 Under the conditions prevailing in German 
 coal mining, however, the performance of 
 in-web shearers is unsatisfactory. 
 
 The main application range of the 
 coal plough is found in the lower seam 
 thicknesses; however, coal plough opera- 
 tions are limited to ploughable seams. 
 Therefore, seams of hard coal and those 
 within hard adjacent strata constitute 
 a range for which, up to the present, 
 cost-effective coal winning equipment 
 for longwall faces has been nonexistent 
 worldwide. 
 
 These limits of practicality for 
 shearer-loader and coal plough operations 
 show that more concentrated energy trans- 
 mission by the coal winning tools is re- 
 quired for recovery of hard coal, selec- 
 tive mining of rock, arriving at large 
 webs, obtaining a better particle size, 
 and eventually reducing the dust release. 
 
 With respect to fulfillment of the 
 above-specified requirements, the re- 
 search for new technologies resulted in 
 three candidate systems for coal winning: 
 
 1. Use of high-pressure water jets. 
 
 2. Use of hydraulic impact devices. 
 
 3. Vibration transmission for fractur- 
 ing the mineral. 
 
 This paper discusses all three tech- 
 niques, with special emphasis on the use 
 of high-pressure water jets. 
 
 ACKNOWLEDGMENTS 
 
 The research and development work was 
 sponsored by the Bundesminister fur For- 
 schung und Technologie (Federal Ministry 
 
 1 Head of Department and Test Side Coal 
 Winning, Conveying, Face End Systems, 
 Bergbau-Forschung GmbH, Essen, Federal 
 Republic of Germany. 
 
 for Research and Technology) as well as 
 by the Minister fur Wirtschaft, Mittel- 
 stand und Verkehr (Ministry for Economics 
 and Transport) of Northrhine-Westf alia. 
 The project was set up jointly by M.A.N.- 
 GHH Sterkrade, Klockner-Becorit GmbH, 
 Ruhrkohle AG, and Bergbau-Forschung GmbH. 
 
GENERAL TESTING PROCEDURES 
 
 41 
 
 For cost reasons, the development and 
 testing of mining machinery is neces- 
 sarily done in testing installations on 
 the surface. However, one of the prob- 
 lems of surface testing is realistic sim- 
 ulation of operating conditions. This is 
 accomplished with a simulated coal block 
 that approximates the strength and rup- 
 ture behavior in terms of required cut- 
 ting forces. The volume of the mineral 
 cut must also be comparable to that of 
 the mineral encountered in actual mining 
 operations. Since these problems have 
 been dealt with in the literature, I pre- 
 fer just to give a concise report on our 
 experience. 
 
 For industrial-scale tests, blends of 
 marl, cement, and water are cast to ob- 
 tain simulated coal. The setting time of 
 these blends is approximately 3 months. 
 Good results have been obtained vary- 
 ing the components to obtain degrees of 
 hardness. However, the requirement for 
 more and more mockup coal faces necessi- 
 tated shorter setting times, requiring 
 simultaneous maintenance of controlled 
 strength properties. Accordingly, addi- 
 tives were proportioned to these blends, 
 
 Medium 
 70^db-50 
 
 PLOUGHABILITY 
 
 -Difficult 
 50— /Jb*30mm 
 
 Ab- 10 mm 
 
 I 2 3 4 56789 10 
 AV CUTTING FORCE OF A BIT(F S ) , kN 
 FIGURE!. - Applications of coal winning machines. 
 
 and these additives lead to shorter set- 
 ting periods as a result of a lower 
 water proportion of the blend. Neverthe- 
 less, the problem of determining cutting 
 forces, versus the volume of cutoff 
 mineral, remained the same. The ratio 
 cannot be established by determining 
 compressive and tensile strength run 
 on sample cubes of the same blend. For 
 comparative assessment of cuttability of 
 simulated coal face material and natural 
 coal with dirt bands, we developed a cut- 
 tability tester which measures cutting 
 force and feed thrust. In this way a 
 comparison of operating conditions can be 
 made. However, the simulation of in situ 
 rock pressures cannot be accomplished. 
 Using the cuttability tester to assess a 
 coal winning method for use in a particu- 
 lar seam was practiced in approximately 
 50 cases in the Ruhr district. 
 
 The following are remarks regarding 
 procedures followed in machine develop- 
 ment on the testing premises of Bergbau- 
 Forschung GmbH. Basically the work was 
 performed in three phases. 
 
 PHASE 1: TECHNICAL SCALE BASIC 
 RESEARCH ON A NEW CUTTING TECHNIQUE 
 
 Experimental investigations to assess 
 the efficiency of any new cutting tech- 
 nology and optimize parameters are run 
 almost entirely by Bergbau-Forschung. In 
 this phase, theoretical investigations 
 carried out are of only a complementary 
 character. If promising results are ob- 
 tained, the second development phase is 
 initiated. 
 
 PHASE 2: CONSTRUCTION AND TESTING 
 OF EXPERIMENTAL UNITS 
 
 Application of a new technique means 
 testing on the surface and underground. 
 Accordingly, experimental units are fab- 
 ricated with commercially available ma- 
 chine elements and equipment. To allow 
 assessment of coal winning capacity, 
 the experimental units correspond as far 
 as possible with a later prototype in 
 terms of designed layout, drive rating, 
 and traveling speed. In this development 
 
42 
 
 phase, a manufacturer is sought who is 
 interested in the new technique and who 
 cooperates in setting up the experimental 
 unit. Now the sometimes very long period 
 of testing and modification on surface 
 test rigs begins. If the results are 
 positive, a colliery is located where the 
 experimental unit can be tested under- 
 ground. If possible, to allow ample 
 opportunity for evaluation and modifica- 
 tion, all underground testing should be 
 conducted on nonproduction faces. If 
 good results in terms of performance, re- 
 liability, and maneuverability in under- 
 ground operations are obtained, then the 
 third phase, construction of the proto- 
 type, is begun. 
 
 PHASE 3: CONSTRUCTION AND TESTING 
 OF THE PROTOTYPE 
 
 Construction and, above all, testing 
 of the prototype necessarily require 
 cooperation of engineers from the manu- 
 facturer, the colliery, and the research 
 center. Only this cooperation enables 
 a maximum of technology transfer to take 
 place, and only in this way is it assured 
 that the participating engineers be- 
 come personally involved in the project. 
 Without these people participating, the 
 success of machine development becomes 
 rather questionable. 
 
 The new machine is designed, fabri- 
 cated, and tested on the surface accord- 
 ing to design parameters developed from 
 experimental units. Later success in 
 underground operations is to a consid- 
 erable extent a function of the testing 
 conditions on the surface, i.e., the 
 quality of definition and simulation 
 of the geological features and operating 
 conditions. 
 
 WATER-JET CUTTING TECHNOLOGY: 
 OF DEVELOPMENT 
 
 STATE 
 
 During the recent past, several reports 
 have been written about using high- 
 pressure water jets for coal winning. 
 The course of development leading up to 
 the present is as follows: 
 
 OPTIMIZATION OF CUTTING HEADS 
 
 In the course of the basic investiga- 
 tions, the cutting parameters of the 
 water-jet technology were investigated 
 for fixed and oscillating nozzles (fig. 
 2) . The tests were run on a special test 
 rig with "normally ploughable" mockup 
 coal. For measuring the cutting forces, 
 the cutting head was mounted in a special 
 frame for triaxial measurements. For a 
 pressure of 10,000 psi at the pump and a 
 flow of 150 L/min, the following opti- 
 mized cutting parameters were obtained: 
 
 Nozzle diameter (d) mm.. 
 
 Oscillating frequency (f) 
 
 Hz.. 
 
 Depth of cut (b) mm.. 
 
 Tractive effort on the 
 plough chain (F) kN. . 
 
 1.65-1.95 
 
 3-5 
 220 
 
 40 
 
 Compared to mechanical ploughing the 
 combined hard metal- jet cutting technique 
 resulted in an increase of cutting depths 
 of almost 100 pet at identical tractive 
 effort on the chain (fig. 3). These re- 
 sults were obtained for the range of coal 
 defined as "normally ploughable." 
 
 CONSTRUCTION OF AN EXPERIMENTAL UNIT 
 
 For testing the cutting technology, an 
 experimental unit was made up from exist- 
 ing machinery components, namely, coal 
 plough, guides and skids, 300-kW drum- 
 shearer loader motor, two high-pressure 
 pumps, and four cutting heads on each ma- 
 chine side. One cutting head is arranged 
 for horizontally cutting the floor. The 
 experimental unit was pulled by an hydro- 
 static motor at speeds adjustable between 
 0.1 and 0.4 m/s (fig. 4). 
 
 Subsequent to the tests on the mockup 
 coalface, operation tests underground 
 were run at the Lohberg colliery. The 
 experimental face was worked at a thick- 
 ness of M = 1.8 m and a length of L =50 
 m. The coal strength may be categorized 
 as "normally ploughable." 
 
43 
 
 Slewing / -_"^> 
 
 range | ~ z-% 
 60° 
 
 Winning direction 
 
 
 215 kW 
 
 
 
 Electric 
 motor 
 
 High- 
 pressure 
 pump 
 
 
 
 
 800 bar 
 
 High- 
 pressure 
 pump 
 
 Oil 
 
 pump 
 
 f = 3Hz 
 
 Electric 
 motor 
 
 FIGURE 2. - Jet miner, principle diagram. 
 
 
 
 20 60 100 140 180 220 260 300 340 380 420 460 
 
 CUTTING DEPTH, mm 
 
 FIGURE 3. - Comparison of mechanical cut- 
 ting and jet cutting. 
 
 FIGURE 4. - Jet-miner winning machine. 
 
 The experimental operation yielded the 
 following results: 
 
 - The coal face was undercut smoothly 
 by the oscillating high-pressure wa- 
 ter jets and subsequently broken off 
 by the hard-metal tools. 
 
 - The cutting heads exhibited no wear, 
 and in particular, no wear attributa- 
 ble to mechanical cutting work. 
 
 - The measured chain force, F = 340 kN, 
 shows that the power requirement of 
 the high-pressure pumps could be re- 
 duced from P = 300 kW to P = 220 kW, 
 and that the water flow could be re- 
 duced from 226 L/min to 170 L/min. 
 
 - At a depth of cut of b = 400 mm, a 
 traveling speed of v = 0.4 m/s was 
 obtained. 
 
 - The raw coal exhibited an excellent 
 particle size distribution. 
 
 - The quantity of dust released corre- 
 sponded to approximately 30 pet of 
 the dust produced by a shearer oper- 
 ating in the same seam. 
 
 DEVELOPMENT OF THE JET-MINER CONCEPT 
 
 After successful trials run with the 
 experimental version, the development of 
 the first Jet-Miner prototype was started 
 in cooperation with Ruhrkohle AG, M.A.N.- 
 GHH-Sterkrade, and Bergbau-Forschung 
 GmbH. Since the basic suitability of the 
 oscillating-water-jet system was proved 
 throughout the trials , the original con- 
 cept and design features of the cutting 
 heads were retained. As mentioned in the 
 introduction, the Jet-Miner was supposed 
 to be used in seam thicknesses of 1.0 to 
 1.5 m. Accordingly, a machine body of 
 1,000 mm height was designed. An array 
 of two or three cutting heads ranging in 
 height from 1.0 to 1.5 m was designed for 
 the machine. 
 
 During the underground trials , clearing 
 problems arose, resulting in the total 
 machine body of the Jet-Miner being situ- 
 ated in the space between the conveyor 
 
44 
 
 and the coal face. (The conveyor is 
 straddled by a portal structure so that a 
 good clearance profile is assured.) To 
 eliminate problems of energy and water 
 supply, a special cable guidance system 
 was developed which is supposed to allow 
 trouble-free supply via cables and hoses 
 even at traveling speeds of 0.5 m/s. 
 
 The prototype built by M.A.N.-GHH- 
 Sterkrade, subsequent to elaboration of a 
 joint concept, exhibits the following de- 
 sign data: 
 
 Length m. . 8.56 
 
 Height mined .m. . 0.98 
 
 Pump drives kW.. 215 
 
 Water flow L/min. . 162 
 
 Water pressure MN/m. . 70 
 
 Total mass kg.. 18,000 
 
 SURFACE TRIALS 
 
 The Jet-Miner prototype is designed for 
 coal winning underground. For checking 
 the overall system feasibility, a surface 
 testing program was carried out. Except 
 for the length, the surface test dupli- 
 cated all machinery components that were 
 used underground. A 35-m-long test rig 
 was set up in the test facility for coal 
 winning and coal clearance techniques at 
 Bergbau-Forschung GmbH (fig. 5). The rig 
 operates on a mockup coal face 13 m long 
 and 1.5 m high. This mockup coal face 
 had a strength corresponding to the re- 
 spective values of coal prevailing in the 
 production face envisaged. 
 
 The surface trials had the objective of 
 testing the haulage system, the hydraulic 
 drive system, the electric control in- 
 stallation, and extraction output and 
 loading trials. The cutting test result- 
 ed in a winning performance 50 pet higher 
 than with the first test rig. The 
 loading capacity could also be improved. 
 When passing horizontal and vertical un- 
 dulations, the unit showed good running 
 properties. 
 
 UNDERGROUND TRIALS 
 
 At Lohberg colliery seam R was prepared 
 for the test under production conditions. 
 The existing plough system had been re- 
 placed by the Jet-Miner. The coal face 
 was 260 m long with a seam thickness of 
 
 1.45 m. The Jet-Miner was designed in 
 such a way that it could run on any ex- 
 isting plough guides. Only the special 
 guidance system for energy and water sup- 
 ply was custom-fitted. 
 
 Only components cleared for underground 
 operation were used. The hydrostatic 
 drive system used nonflammable fluids. 
 The conveyor, Jet-Miner, machine haul- 
 age, and high-pressure pumps were con- 
 trolled from a central control consol us- 
 ing an audiofrequency system supplied by 
 Siemens. 
 
 All equipment used by Bergbau-Forschung 
 was first cleared for underground opera- 
 tion. The following parameters are mea- 
 sured and recorded by UV-recorders and 
 magnetic tape systems: Hydraulic pres- 
 sure of the hydrostatic drives (measure 
 for chain traction effort) , and speed of 
 the drives (traveling speed). 
 
 The underground tests yielded the fol- 
 lowing results: 
 
 1. The tractive efforts on the chain 
 reached maximum values of more than 600 
 kN. 
 
 2. The Jet-Miner exhibited a strong 
 climbing tendency. 
 
 3. The cutting of the roof and of dirt 
 bands was unsatisfactory. 
 
 4. The mechanical elements, e 
 high-pressure pumps, the hoses, 
 dilating mechanism for the nozzles, the 
 mechanical horizon control, etc., had 
 high failure rates. 
 
 The evaluation of these results leads 
 to the following conclusions: 
 
 1. The high tractive efforts on the 
 chain were due to — 
 
 A. Excessive friction within the 
 plough guide system and corresponding 
 high wear. 
 
 B. Unsatisfactory cutting head 
 performance due to insufficient water 
 jet pressure on the nozzles due to 
 clogging of the nozzle oscillating 
 mechanism. 
 
 2. The reason for the strong tendency 
 to climb is the arrangement of the lower 
 cutting head in a 30° position from the 
 vertical. 
 
 3. The controls of the hydrostatic 
 drives worked unsatisfactorily in terms 
 of synchronization so that uncontrolled 
 chain slackening occurred. 
 
 g., the 
 the os- 
 
45 
 
 / / 
 
 FIGURE 5. - Jet-miner test facility. 
 
46 
 
 PRESENT SITUATION 
 
 Following the underground tests, the 
 results were evaluated and an extensive 
 investigation of cutting heads was con- 
 ducted. As a result, several modifica- 
 tions were made to improve cuttability at 
 long nozzle-face distances by nozzle de- 
 sign, water conditioning, smoothing of 
 the high-pressure flow upstream of the 
 nozzle, improved water supply, and modi- 
 fication of the oscillating system. 
 
 Figure 6 shows the optimum pressure de- 
 veloped for various nozzle designs com- 
 pared with the data from the original wa- 
 ter supply system. When using curved jet 
 tubes, the oscillating system, however, 
 causes, almost inevitably, a strong pres- 
 sure drop at larger standoff distance. 
 
 PERFORMANCE SPECIFICATIONS 
 
 When designing the Jet-Miner the fol- 
 lowing performance specifications should 
 be met according to present knowledge: 
 
 1. Cut over the total worked thick- 
 ness, including roof and floor. 
 
 2. Establish horizon control by ad- 
 justment of the floor cutting system. 
 
 3. Provide yaw control for the cutting 
 heads. 
 
 4. Provide retractability of the 
 trailing head from the face. 
 
 5. Load cutoff mineral in wide-web 
 cuts at low traveling speeds. 
 
 6. Guide machine over 
 conveyor. 
 
 7. Prevent clogging 
 and plough guides. 
 
 8. Provide improved hydrostatic drive 
 control. 
 
 THE DEVELOPMENT OF 
 
 snaking 
 of cutting heads 
 
 o 
 
 70 
 
 60 - 
 
 50 
 
 LlI 
 
 en 
 
 Z) 
 CO 
 CO 
 
 £ 40h 
 
 Q_ 
 CD 
 
 z 30 
 
 I- 
 
 u 20 
 
 10 
 
 la 
 
 1 
 
 1 
 
 
 ~2a , 
 
 
 
 - 
 
 lb 
 
 • ~». ^V 
 
 
 
 -la— ^ 
 2b-- 
 
 
 N>--^^ 
 
 — ,. 
 
 — 
 
 N 
 
 
 — 
 
 lb — 
 
 \ ^v. 
 
 
 
 
 "^0\ 
 
 
 — 
 
 
 \ ^ 
 
 — 
 
 
 
 \ 
 
 ^^*" 
 
 
 
 \ 
 
 
 
 KEY 
 
 \ 
 
 
 - / Drawn 
 
 tube, 
 
 \ 
 
 \ - 
 
 300 mm long 
 
 a Optimized 
 
 
 2 Curved tube 
 
 i 
 
 b Original 
 
 1 
 
 
 
 
 50 
 
 100 
 
 150 
 
 STANDOFF DISTANCE, mm 
 
 FIGURE 6. - Cutting forces of various jet 
 tubes (tube 7 mm, nozzle 1.95 mm). 
 
 At present, tests are being run on 
 mockup coal faces in an attempt to meet 
 these sometimes contradictory performance 
 specifications. The tests mainly concen- 
 trate on loading properties, cuttability, 
 horizon control, and clogging. Another 
 aspect concerns the reliability of ma- 
 chine elements, accessibility to the in- 
 dividual components, and monitoring and 
 controlling the integrated system, name- 
 ly, the plough, the conveyor, the drives, 
 etc. 
 
 THE IMPACT PLOUGH 
 
 In the past, the function principle of 
 the pneumatic pick, i.e., mechanical cut- 
 ting by impact tools, turned out to be 
 extremely efficient. The successful use 
 of hydraulically activated percussive 
 hammers, generally known under the term 
 "impact ripper," in road headings, leads 
 to the consideration of this technology 
 also for coal winning machinery. Figure 
 7 shows the function principle of an im- 
 pact plough. According to the direction 
 of travel, the leading impact hammers 
 
 of a plough system are activated from a 
 powerpack (P = 200 kW, pressure supply 
 p = 2,000 psi) with an impact frequency 
 of 5 to 10 Hz. 
 
 The impact hammers assure a high 
 corapressive-stress buildup at the tip of 
 the pick. Accordingly, stone can be cut 
 and faults can be worked through. Fur- 
 thermore, the system can cut wide webs. 
 For experimental use and testing of this 
 technology, an experimental unit (fig. 8) 
 was set up and tested on a mockup 
 
47 
 
 coal face. The following problems were 
 encountered: 
 
 1. Guidance of the tool at high trans- 
 verse forces. 
 
 Hammer array. 
 
 Loading of the cutoff mineral. 
 
 Machine guidance along the coal 
 
 2. 
 
 3. 
 
 4. 
 face. 
 
 5. Unsatisfactory 
 hammers. 
 
 function of the 
 
 After extensive testing, the reasons for 
 the deficiencies were identified, and re- 
 medial action could be taken. At present 
 the experimental unit has been recon- 
 structed, checked, and will be run in an 
 experimental face underground. We expect 
 this development to be successful. 
 
 Hydraulic breaker 
 8 Hz -1,500 J/ blow 
 
 CCa: 
 
 CCm 
 
 Winning direction 
 
 Hydraulic breaker 
 6.5 Hz -1,200 J/blow 
 
 Electric 
 
 a 
 
 Hydraulic 
 pump 
 
 rOH 
 
 t: 
 
 FIGURE 7. - Impact plough, principle diagram. 
 
 FIGURE 8. - Impact hammer, experimental unit. 
 
48 
 
 BASIC INVESTIGATIONS ON VIBRATION TECHNOLOGY 
 
 At present, basic investigations are 
 being run within Bergbau-Forschung in 
 view of using vibrations to fracture min- 
 erals. For these investigations a test 
 rig was set up on which a cutting tool 
 has been arranged and onto which vibra- 
 tions are induced by a hydraulic ram 
 (fig. 9). The cutting tool is mounted to 
 a measuring frame which is pulled along 
 the coal face by a chain. The hydraulic 
 ram is activated by a powerpack via 
 servovalves. The oscillation frequency 
 can be adjusted between and 50 Hz. 
 Furthermore, various wave forms, e.g., 
 sinus, sawtooth, or rectangular, can be 
 selected. 
 
 The cutting tests are run on various 
 tool designs and cutting angles as well 
 as on mockup coal of varying strength. 
 Cutting forces, feed thrust, and trans- 
 versal forces are measured as assessment 
 parameters for the cutting performance 
 of this technology. From the cutting 
 force plot on figure 10 it may be seen 
 that in the case of a nonactivated tool 
 (frequency = 0) a maximum tractive effort 
 on the chain of Fs = 70 kN is recorded 
 for a cutting depth of b = 100 mm and a 
 cutting tool width of 300 mm. For an 
 identical cut, the tool vibrating at a 
 frequency of f = 20 Hz with an amplitude 
 of a = 5 mm, a cutting force of Fs = 15 
 kN was required. The cutting force re- 
 duction corresponds therefore to a factor 
 of 4 to 5. 
 
 Feed thrust (Fq) 
 
 -Vibration tool 
 
 Cutting force (F s 
 
 Tractive effort (Fk) 
 
 Measuring frame 
 FIGURE 9. - Test rig, vibrating tools. 
 
 80 
 
 ^ 60 
 
 CO 
 
 Ld 
 
 O 
 
 <r 40 
 o 
 
 LL 
 
 H 20 
 
 O 
 
 KEY 
 
 Cutting depth = 100 mm 
 Vibration amplitude = A 
 
 h*-A=0 
 
 
 
 10 
 
 20 30 40 
 
 FREQUENCY, Hz 
 
 FIGURE 10. - Cutting forces of vibrating tools. 
 
 These positive test results gave us 
 reason to develop, in a first phase, a 
 hydraulic system suited for underground 
 testing. For the next development phase 
 it is intended to set up an experimental 
 unit for surface and underground testing. 
 
 SUMMARY 
 
 Looking at present requirements for new 
 activated coal-winning machinery, the 
 necessity for such developments is point- 
 ed out. 
 
 The pattern followed for the required 
 basic investigations, the setup of ex- 
 perimental units, and the construction of 
 prototypes is discussed. 
 
 The present stage of development and 
 application of high-pressure water-jet 
 cutting technology, of impact plough sys- 
 tems, and of vibration technology is out- 
 lined. Specific problems as well as ap- 
 plication limits are explained.' 
 
49 
 
 THE WATER JET PLOW 
 By David A. Summers 1 
 
 INTRODUCTION 
 
 This meeting takes place on the longest 
 day of the year. It is, therefore, time- 
 ly as well as pertinent to begin by wish- 
 ing you "Heddwych" from the UMR- 
 Stonehenge, which was dedicated by a 
 druid of Geffodd of the British Isles at 
 sunset last night (fig. 1). 
 
 This topic is pertinent because the 52 
 rocks of this half-scale model were 
 carved, in their entirety, by high- 
 pressure water. The trilithons of the 
 inner circle (fig. 2) stand some 16 ft 
 
 high and are made of Georgia granite with 
 a compressive strength of 30,000 psi. 
 The rock was cut by water jets, at an 
 average pressure of 15,000 psi at the 
 University of Missouri — Rolla (UMR) . To 
 complete the project on time, cutting 
 rates at least twice those of convention- 
 al cutting were required, and achieved. 
 This is an interesting topic in its own 
 right, and also one that is very perti- 
 nent to the subject of the meeting today. 
 
 ACKNOWLEDGMENTS 
 
 This work was funded under contract to 
 the Bureau of Mines and the U.S. Depart- 
 ment of Energy. The detailed design of 
 the head was largely the responsibility 
 of Dr. Clark Barker of the University of 
 Missouri — Rolla, while the construction 
 was in large measure carried out by the 
 staff of the Rock Mechanics & Explosives 
 Research Center. This project was very 
 
 much a team effort, with input coming not 
 only from those of us on the project, but 
 also from the Government agencies and 
 substantially from the industrial con- 
 tacts we had with people we visited who 
 came to see the machine work. We are 
 very grateful and happy to acknowlege 
 that assistance and advice. 
 
 EQUIPMENT OPERATIONAL LIFE 
 
 Most water-jet-cutting research com- 
 prises a series of tests that are of 
 short duration and concentrate on the 
 cutting ability of the water jets. Data 
 on the problems apt to be encountered 
 during the lifetime of the equipment are 
 rarely presented. The construction of 
 the UMR megalith required that the high- 
 pressure equipment operate at a pressure 
 of 14,500 psi for approximately 1,000 h. 
 This pressure is some 50 pet higher than 
 that normally recommended for the cutting 
 of coal. To cut a smooth channel down 
 through the rock, the nozzle must be 
 fed forward after each pass across the 
 
 ' Curators' professor, Rock Mechanics 
 and Explosive Research Center, University 
 of Missouri — Rolla, Rolla, MO. 
 
 surface. This requires that a 5-cm-wide 
 slot be cut into the rock to ensure that 
 the nozzle can move freely. To cut this 
 slot, two 0.925-mm-diam jets were rotated 
 at approximately 300 r/min. The swivel, 
 located in an unsupported position at the 
 top of the cutting lance, allowed this 
 rotation, and the same unit was used 
 throughout the cutting (fig. 3). Noz- 
 zles, that cut within 1 cm of the surface 
 lasted around 20 h, with the major fail- 
 ure being because of the surrounding 
 metal holder, rather than nozzle fail- 
 ure per se. Nozzle quality was not, how- 
 ever, consistent. Rubber hoses, rated at 
 40,000 psi burst pressure, held up well 
 in the early stages of the program, 
 but after some 600 h, several had to be 
 replaced. 
 
50 
 
 FIGURE 1. - Overview of the UMR Stonehenge. 
 
 This information is provided to show, 
 in part, how far the reliability of the 
 equipment has come since 1974, when the 
 Bureau of Mines granted UMR its first 
 contract on the Hydrominer program. Al- 
 though the granite cutting unit ran for 
 
 24 h at 14,500-psi pressure on June 16- 
 17, 1984, at that time virtually no 
 equipment was available to run at even 
 10,000 psi on such a continuous basis. 
 Within this past decade water-jet equip- 
 ment has, however, come of age. 
 
 THE UMR HYDROMINER 
 
 The use of high-pressure water for cut- 
 ting coal has many potential advantages, 
 and a likely equivalent number of pit- 
 falls for the unwary. In this brief 
 presentation, it is not possible to cover 
 all of these; such a discussion is given 
 on the final report of the Hydrominer 
 project CO. 2 
 
 The Hydrominer is a water-jet-assisted 
 plow. In the original concept of the de- 
 vice (2^, water jets cut along the perim- 
 eter of the plow, cutting an access slot 
 for the wedge head to enter and wedge off 
 the central coal core (fig. 4). Follow- 
 ing laboratory tests undertaken to estab- 
 lish the basic cutting parameters of the 
 
 ^Underlined numbers in parentheses re- 
 fer to item in the list of references at 
 the end of this paper. 
 
 jet and to determine to what degree the 
 initial design would be valid, a prelimi- 
 nary unit design was developed, con- 
 structed, and field-tested in a surface 
 coal mine in the Midwest in 1976 (fig. 
 5). One initial change that had to be 
 made in that program was to ensure that 
 all the water-jet nozzles oscillated over 
 a given cutting path. In the original 
 conception, it was felt that the jets 
 would cut the required depth from a fixed 
 position on the plow body. However, be- 
 cause of the jet and slot interference 
 and the blocking of subsequent jet action 
 by the rebound of the preceding flow, 
 fixed jets do not give the performance 
 levels required. This work, since con- 
 firmed by the failure of the fixed-jet 
 plow in Germany O) , led to the simplifi- 
 cation of the device into the form used 
 
51 
 
 FIGURE 2. - 16-ft-high central trilithon, carved from granite by water. 
 
52 
 
 FIGURE 3. - Swivel detail from granite cutting unit. 
 
 FIGURE 4. - Artist's impression of UMR Hydrominer. 
 
53 
 
 r // 
 
 FIGURE 5. - Equipment on trial surface coal mine. 
 
 in the field trial. The results of that 
 trial were very encouraging, and every 
 goal set by the Bureau for our perform- 
 ance was exceeded. Potential advantages 
 resulting from the use of the Hydrominer 
 include — 
 
 1. 40-pct increase in productivity at 
 equivalent horsepower. 
 
 2. Control over product size. — Note 
 that larger coal means fewer losses 
 and increase in preparation plant 
 productivity. 
 
 3. Elimination of respirable dust 
 problem. 
 
 4. Removal of the face gas ignition 
 hazard. 
 
 5. Ability to increase web depth with- 
 out equivalent increase in horsepower. 
 
 6. Reduction in haulage horsepower 
 required. 
 
 As a consequence of that study a sec- 
 ond generation head was built; concur- 
 rently an impetus was provided for the 
 German study which has since developed 
 (4). 
 
 The effectiveness of a water-jet-mining 
 machine, however, is critically dependent 
 on making the best use of the jets that 
 cut the coal. These jets only cut a slot 
 around the perimeter of the mass being 
 removed (fig. 6), a technique proven 
 feasible by the widespread use, at one 
 time, of the Meco-Moore mining machine. 
 For most effect, this slot must run at 
 least 4 in ahead of the plow blade. Such 
 a slot depth cannot be maintained unless 
 the jets oscillate over the face of the 
 plow, but it also requires that the jets 
 be generated from an effective nozzle 
 design. 
 
54 
 
 FIGURE 6. - Cutting pattern of slots for the Hydrominer. 
 
 NOZZLE DESIGN 
 
 The UMR group, and particularly Dr. 
 Barker, spent considerable time improving 
 nozzle design (_5_) . It should be clearly 
 appreciated, from the outset, that coal 
 does not behave in a similar manner to 
 other rock under water-jet attack. In 
 most rock, adjacent cuts can be made up 
 to an intervening distance of perhaps 
 three nozzle diameters before the inter- 
 vening rib disintegrates; with coal the 
 rib is removed with a spacing between 
 cuts of up to 5 cm. 
 
 The benefit that this gives is that it 
 allows the use of a dual-orifice diverg- 
 ing jet pair to cut slots in the coal. 
 This in turn substantially improves po- 
 tential cutting performance. A single 
 jet cuts a slot of decreasing width as it 
 penetrates the material (fig. 7). Thus 
 on a second pass, over the same slot, the 
 sides of the previously cut slot erode 
 
 the sides of the cutting jet so that its 
 performance is reduced. A reduction in 
 performance of up to 50 pet may occur on 
 this second pass, depending on the rela- 
 tive efficiency and parameters under 
 which each cut is made. If, in contrast, 
 the flow is directed through two diverg- 
 ing jets, the coal between these two jets 
 will be removed as the jets make the pri- 
 mary cut (fig. 8). Thus when the nozzle 
 advances, and the second cut is now made, 
 the jets do not meet the coal until they 
 reach the back of the previous cut. In 
 this manner the jets will cut the depth 
 by which the unit has advanced, or the 
 same depth as the first cut, depending on 
 where the cut surface is relative to the 
 nozzle. This relates to the decay in jet 
 effective cutting pressure with standoff 
 distance from the nozzle. 
 
 NOZZLE POSITIONING AND CUTTING PATH 
 
 It is important to locate the nozzles 
 in the correct position on the plow head 
 to achieve optimal cutting results. This 
 pertains particularly to two aspects of 
 the design, and leads to resolution of 
 two potential problems. The cutting arms 
 
 should be so oriented that they overlap 
 in cutting to the full seam section, but 
 concurrently the face angle jet should 
 pass directly in front of the face cut- 
 ting edge of the plow. This face should 
 be a sharpened hardened metal surface, 
 
55 
 
 Material 
 
 removed on 
 
 next pass 
 
 FIGURE 7. - Slot cut by a single-jet nozzle. 
 
 Material 
 
 removed on 
 
 next pass 
 
 FIGURE 8. - Slot cut by dual-jet nozzle. 
 
 with the intention that the jets will 
 normally cut a path in the coal suffi- 
 ciently wide that the head can enter the 
 slot, with subsequent contact being made 
 on the wedge section where the angled 
 surface will cause the main coal column 
 to break off from the solid. 
 
 Where a layer of rock is present in the 
 coal, the water jets will normally remove 
 the coal from either side of the layer 
 but will not always be able to totally 
 remove the inclusion. Under these cir- 
 cumstances, the synergistic effect of the 
 water jet acting with a metal tool (the 
 water-jet-assist mode as it is known) can 
 be utilized through the combination of 
 the plow edge and the oscillating jet. 
 By such a means the Hydrominer was able , 
 in its field trials, to cut through >3- 
 in-thick lenses of pyrite. It is neces- 
 sary to cover the full seam section, giv- 
 en that one cannot predict where the 
 bands of dirt will occur. 
 
 The second important feature is to en- 
 sure that the column of coal isolated by 
 the vertical jets, cutting at the back of 
 the plow, is also cut horizontally. Two 
 different options were considered for 
 this feature. In the original Meco-Moore 
 design the column was broken at the bot- 
 tom and half way up the section; this 
 feature was changed, because of the 
 smaller web which the Hydrominer takes , 
 and also because in many coals there is a 
 need to leave either a fixed amount of 
 roof coal or a fixed amount of floor 
 coal. A positive horizon definition is 
 thus required, and therefore horizontally 
 oscillating jets are placed to cut across 
 the column at the roof and floor. This 
 arm, however, does not have the major 
 purpose of creating a cutting plane; 
 rather the intent is to break the support 
 column to the roof and thus transfer the 
 abutment load from the coal, before the 
 plow begins to fracture the coal, and 
 load it onto the conveyor. Because of 
 this feature the coal, at loading, is 
 unstressed, and with no strength in ten- 
 sion is easily broken into fragments and 
 loaded onto the conveyor. Because of 
 this feature the head becomes virtually 
 web insensitive in terms of haulage and 
 
56 
 
 cutting force. For example, in the 
 trials at Moberley, the web was increased 
 from 18 to 39 in with virtually no change 
 in the haulage force required to move 
 the machine down the face and to load 
 
 the coal. The cutting force, through 
 the jets, of course remains unchanged, 
 given that there is no change in the jet 
 system. 
 
 DESIGN OF THE SECOND-GENERATION HEAD 
 
 There were a number of substantial de- 
 fects in the design of the first- 
 generation head, which have been changed 
 in the design of the second-generation 
 unit. Apart from the need to substan- 
 tially strengthen the head to resist the 
 forces imposed in moving large tonnages, 
 the most obvious feature was the decision 
 to split the head into two modules. Each 
 module contains a vertical oscillating 
 arm and a horizontal oscillating arm 
 (fig. 9) but is designed so that the two 
 modules may be separated vertically by 
 a set of hydraulic rams , to cope with 
 
 variation in seam section (a feature we 
 were not to pursue further in our devel- 
 opment of this phase) . The modules can 
 also be adjusted horizontally so that 
 either the top or bottom section of the 
 coal can be removed first. This feature 
 is judged important since the lower force 
 required to break out the coal will allow 
 the top section of the coal to be removed 
 first and then subsequently the lower 
 section. This will allow the lower coal 
 a free surface to lift up into, and thus 
 will make loading of the coal from the 
 face a much easier operation. 
 
 FIGURE 9. - Second-generation cutting head. 
 
57 
 
 The interior features of the head were 
 simplified, in a manner detailed in the 
 contract final report (1), so that a sim- 
 ple robust head was constructed. The 
 nozzles developed were of the more ad- 
 vanced design and were fitted with guards 
 to ensure that only a slot wide enough 
 for the jets to escape existed on the 
 head of the unit. Concurrently a flush- 
 ing system was incorporated so that, at 
 the end of each path, the jet struck a 
 
 small metal surface which directed the 
 jet back into the head, to flush any coal 
 chips that had migrated back into the 
 head out of the path of the arm. A sec- 
 ond subsidiary circuit was built into the 
 head, but not used, that would allow a 
 low-pressure flow into the arm compart- 
 ment to flush any large accumulation of 
 coal out of the ports provided for that 
 purpose in the design. 
 
 REFERENCES 
 
 1. Barker, C. R. , and D. A. Summers. 
 The Development of a Longwall Water Jet 
 Mining Machine (DOE contract AC01- 
 75ET12542, Univ. MO— Rolla. July 1981, 
 199 pp.; NTIS, DOE/ET/12542-T1. 
 
 2. Summers, D. A. Water Jet Coal Min- 
 ing Related to the Mining Environment. 
 Paper in Proceedings of Conference on the 
 Underground Mining Environment (Rolla, 
 MO, Oct. 27-29, 1971). Univ. MO Press, 
 1972, pp. 183-194. 
 
 3. Henkel, E. H. , and T. Kramer. In- 
 Seam Trials With the Hydrohobel. Paper 
 in Proceedings of the First U.S. Water 
 
 Jet Symposium (Golden, CO, Apr. 7-9, 
 1981). CO Sch. Mines Press, 1982, 
 pp. III-5.1 to III-5.7. 
 
 4. Henkel, E. H. Development Work for 
 Coal Winning Technology. See pp. 40-48 
 of these Proceedings. 
 
 5. Barker, C. R. , and B. P. Selberg. 
 Water Jet Nozzle Performance Tests. 
 Paper in the Fourth International Sympo- 
 sium on Jet Cutting Technology (Univ. 
 Kent, Apr. 12-14, 1978). BHRA Fluid En- 
 gineering, Cranfield, Bedford, United 
 Kingdom, 1978, pp. A1-A12. 
 
58 
 
 DESIGN REVIEW OF JARVIS CLARK JETBOLTER 
 By William C. Griffiths 1 
 
 INTRODUCTION 
 
 The transfer of technology from the 
 world of research to the world of indus- 
 try is always a challenging task, espe- 
 cially when more than one organization is 
 involved. In December 1982, Jarvis Clark 
 saw the potential of the work being done 
 in water-jet drilling by research organi- 
 zations under Government sponsorship and 
 entered into a collaboration agreement 
 with Flow Industries, a leader in this 
 field. We took the hardware developed by 
 them and integrated it into the first 
 custom-designed water-jet roof bolter. 
 When we entered our collaboration agree- 
 ment the extent of field testing of the 
 
 water-jet-drilling concept was a 3-month 
 underground test involving a retrofit of 
 high-pressure water-jet componentry onto 
 an existing conventional hydraulic rotary 
 roof bolter. The results of this test 
 were so encouraging that design work on a 
 water-jet roof bolter began in March 
 1983. 
 
 The jetbolter is the final result of 
 one year's intensive design effort to in- 
 tegrate the high-pressure water-jet com- 
 ponentry with the most up-to-date hydrau- 
 lic and electric systems available to the 
 coal industry. 
 
 DESIGN CRITERIA 
 
 The design starting point was a self- 
 imposed set of physical constraints with- 
 in which all of the componentry had to be 
 packaged for both safety and protection. 
 These constraints were — 
 
 1. 24-in overall frame height to ena- 
 ble future low-coal versions to be de- 
 veloped with no chassis redesign. 
 
 2. 9-ft maximum overall width. 
 
 3. 24-ft maximum length. 
 
 4. Provision for adjustable ground 
 clearance and adjustable canopy. 
 
 5. 5-ft maximum tramming height. 
 
 6. Ability to drill a 6-ft hole in a 
 single pass in openings 8 to 12 ft high. 
 
 In addition to these physical con- 
 straints, the design had to recognize, 
 meet, and exceed all existing State and 
 Federal safety requirements. 
 
 Figure 1 shows the general layout with- 
 in the single-piece box frame chassis and 
 includes — 
 
 1. The operator's compartment. 
 
 2. The prime mover compartment con- 
 taining electric motors and hydraulic 
 pumps. 
 
 1 General manager, Jarvis Clark Company 
 Limited, Coal Division, Burlington, On- 
 tario, Canada. 
 
 3. The water reservoir. 
 
 4. The hydraulic oil tank. 
 
 5. A 320-f t-capacity , self-winding ca- 
 ble reel. 
 
 6. The electrical controller. 
 
 7. The intensifier box. 
 
 8. Four planetary geared, hydraulical- 
 ly powered wheel units for tramming. 
 
 This part of the machine should remain 
 unchanged irrespective of the seam height 
 the unit operates in. The Automatic Tem- 
 porary Roof Support System (ATRS) booms 
 and feeds will, of course, vary with seam 
 height, although their basic design and 
 mode of operation should remain similar. 
 
 Figure 2 is a simplified schematic of 
 the hydraulic oil and water circuits on 
 the machine , from mine water supply to 
 drill nozzle. This circuit is duplicated 
 for the other boom. 
 
 Water enters the circuit through a re- 
 verse-flushing strainer containing a mesh 
 element, which filters out any coarse 
 material in the mine water supply. Be- 
 tween the strainer and the water tank is 
 the first of the two 10-ym filters. The 
 water reservoir has a 130-gal capacity 
 and is of stainless steel construction. 
 There are internal baffles and an exter- 
 nal water level sight gauge. The tank 
 
59 
 
 ^-f clearance onATRS^^r 
 for tramming 
 
 ELEVATION VIEW 
 
 FIGURE 1. - General layout of jetbolter. 
 
 capacity is sufficient for approximately 
 4 h of drilling; however, if necessary, 
 the unit can be run with the water hose 
 continually connected. A rotary-gear- 
 type water pump delivering up to 5 gal/ 
 min at 80 psi feeds the intensifiers to 
 ensure they always work under a positive 
 head. Excess flow from the water pump is 
 diverted through an oil cooler back to 
 the water tank. 
 
 The prime mover for each hydraulic cir- 
 cuit is a 50-hp explosion-proof ac motor 
 with drive shafts at each end. The tram- 
 ming and intensifier circuit is driven 
 from the pump at the rear of the machine, 
 which is a variable- volume pressure- 
 compensated piston pump set to deliver 
 20 gal/min at 2,800 psi. On the front of 
 the motor is a smaller variable-volume, 
 pressure-compensated piston pump set to 
 deliver 17 gal/min at 1,500 psi. This 
 supplies booms, feeds, rotations, and hy- 
 draulic pilot signals. All four pumps 
 
 Drill 
 nozzle— oi/ 4^><f~ 
 
 Drill rotate 
 mechanism 
 
 Water on -off 
 valve 
 
 Water 
 
 Feed 
 
 Rotate 
 
 Sting pilot valve - 
 
 Control valve — ^ 
 
 Hydraulic 
 pump — . 
 X. 
 
 Blowdown 
 valve 
 
 Hydraulic 
 reservoir 
 
 0— Water 
 
 pump ^ er 
 
 filter 
 
 Water . \ Reverse- 
 reservoir^ f| ushing 
 
 strainer 
 
 FIGURE 2. - Jetbolter hydraulic oil and water circuits. 
 
60 
 
 draw oil from the main 150-gal reservoir 
 through a 100-mesh suction strainer. The 
 hydraulic system is filtered through five 
 6-um filters , two in the pressure line 
 and three in the return line. 
 
 The hydraulic and water circuits meet 
 at the intensifier box, which is mount- 
 ed on the outside of the chassis between 
 the wheels. This box swings out on 
 hinges to afford easy access for mainte- 
 nance. Inside the box both intensifiers 
 are on the chassis wall one above the 
 other, together with the second water 
 filter. Both water filters have a 10-ym 
 rating and have throwaway cartridges made 
 of spun polypropylene. Each filter has 
 an internal bypass system. 
 
 The intensifier is the heart of the 
 high-pressure system and is a stainless 
 steel reciprocating device, comprising a 
 double-acting cylinder with check valves 
 at either end and a hydraulic switching 
 device on top. This device is mechan- 
 ically activated. 
 
 The principle of operation of the in- 
 tensifier is shown in figure 3. At the 
 end of the piston stroke the chamber be- 
 hind the small plunger on the right is 
 full of low-pressure water. Oil then en- 
 ters the chamber behind the piston at 
 2,800 psi and during the course of its 
 
 stroke increases the water pressure by 
 the area ratio of the piston-plunger, 
 which in this case is 13:1, hence 35,000- 
 psi water. At the same time as water 
 exits the chamber via the high-pressure 
 check valve on the right at 35,000 psi, 
 water enters the opposing chamber through 
 the low-pressure check valve. The 
 switching circuit mounted on top of the 
 intensifier then reverses the oil flow, 
 and the stroke is repeated. The intensi- 
 fier operates nominally at 80 strokes per 
 minute to give an output flow of approxi- 
 mately 1-1/4 gal/min. In industrial ap- 
 plications this intensifier model series 
 has accumulated over 3 million pumping 
 hours at pressures above 30,000 psi. 
 
 The two high-pressure lines then pass 
 through the frame wall to the attenuator, 
 which is a 3-ft-long gun, drilled from a 
 stainless steel cylinder with a 2-in bore 
 and a 2-1/2-in wall thickness. This is a 
 surge-dampening device which smooths out 
 the pressure spikes to provide a continu- 
 ous flow of high-pressure water. This 
 unit is placed under the oil cooler be- 
 tween the hydraulic oil reservoir and the 
 cable reel. 
 
 From the attenuator, water flows to the 
 crossover circuit. This is a series 
 of valves enabling the two intensifier 
 
 High-pressure 
 water out 
 
 Jt 
 
 
 B 
 
 Water in 
 
 Hydraulic 
 oil out 
 
 Hydraulic 
 oil in 
 
 \ 
 
 Hydraulic 
 oil in 
 
 1 
 
 ^J 
 
 Hydraulic 
 oil out 
 
 t 
 
 Water in 
 
 A 
 
 yjM 
 
 m 
 
 nn High-pressure 
 - , i if jji^ — i water out 
 
 m 
 
 FIGURE 3. - Double-acting fluid intensifier; high-pressure water is forced to left (A) and right (S). 
 
61 
 
 outputs to remain independent or to cross 
 over or to interconnect with each other 
 to provide higher power operation to one 
 boom only. Up to this point all high- 
 pressure water has been contained in 
 steel tubing, but from the cross-over 
 circuit to the drill mast high-pressure 
 hose is used. All high-pressure steel 
 tubing is painted yellow and marked "HI 
 PRESS WATER." 
 
 The high-pressure water hose is a six- 
 wire-braid multispiral hydraulic hose 
 with a 3/16-in ID. Rated working pres- 
 sure is 35,000 psi, and burst pressure 
 is 60,000 psi. Fittings are crimped on 
 with a special crimping device which 
 virtually forms a cold weld. Hose ends 
 and connectors use high-pressure coned 
 and threaded connections which are rated 
 up to 150,000 psi. As additional protec- 
 tion for the hose from external damage, 
 it is sheathed in regular high-pressure 
 hydraulic hose. A yellow plastic sheath 
 marked "HI PRESS WATER" is then shrunk- 
 fit over the hose assembly to distinguish 
 it from other hydraulic hoses. 
 
 The hose is routed along the boom to 
 the foot of the drill mast, where it is 
 connected to the water swivel via a hy- 
 draulically operated on-off valve. This 
 valve is connected through a safety cir- 
 cuit which only allows water to flow to 
 the swivel when the mast is stung against 
 the roof. The water swivel is located 
 below the drill stem drive box and is 
 thus protected from any falling debris. 
 This water swivel contains the high- 
 pressure rotary seal that allows the pas- 
 sage of high-pressure water at drill stem 
 rotation speeds of up to 500 r/min. Seal 
 life at this speed is 40 pumping hours, 
 which is approximately 2 weeks' drilling 
 under normal conditions. 
 
 Drill stem rotation is by means of a 
 hydraulic motor and chain drive. This 
 drive produces 40 ft*lb of torque at 
 500 r/min. The roof bolt inserter drive 
 is next to the drill feed at a fixed dis- 
 tance of 6 in. After the hole is drilled 
 and the stem is withdrawn, the whole mast 
 assembly is hydraulically indexed by 6 in 
 and the bolt is installed with the in- 
 serter drive. This is also powered by a 
 hydraulic motor through a direct drive 
 system. The inserter drive produces up 
 
 to 250 ft'lb of torque. Both hydraulic 
 motors and feeds are interchangeable. 
 This system allows hands-off drilling 
 with no delays due to drill steel 
 changes. Bolts are placed in the in- 
 serter while the hole is being drilled. 
 Feed is accomplished through a chain and 
 sprocket drive, set to provide 500 lb of 
 thrust. 
 
 The drill stem is a proprietary form of 
 high-pressure tubing. The drill bit is 
 threaded onto the stem at one end; at the 
 other end, the stem is threaded into the 
 water swivel. The drill bit is similar 
 to a conventional tungsten carbide drag 
 bit with set screws set into the bit ma- 
 trix. Each set screw has a sapphire 
 jewel cemented into it with an orifice 
 drilled in it. Orifice sizes are typi- 
 cally in the 0.007-to 0.01 1-in range. A 
 fine-mesh screen at the bit-stem inter- 
 face helps protect orifice plugging from 
 any contamination introduced into the 
 system downstream of the filters. The 
 sapphire jewels are normally provided 
 predrilled and precemented into the set 
 screws for easy replacement in the drill 
 bit. 
 
 At the top of the drill mast, just 
 above the drill stem collar, is a rubber 
 boot. This collects all of the water 
 and cuttings from the hole and diverts 
 them down a 1-in hose to the ground at 
 the foot of the mast. This ensures no 
 splashback and a clean environment for 
 the operator. 
 
 Safety was a major influencing factor 
 throughout the design. One of the most 
 important safety features is the stinger 
 pilot valve. The actuator for the pilot 
 valve is an angled plate on top of the 
 mast which turns about a pivot point. 
 When the mast is stung against the roof, 
 this plate activates a hydraulic pilot 
 valve, which in turn opens the safety on- 
 off valve next to the water swivel. This 
 prevents the water jets being activated 
 whilst in a position where injury may oc- 
 cur to a second operator or a bystander. 
 When the pilot valve is fully activated 
 the plate rests against the top of the 
 mast, thus allowing the mast to carry all 
 the load. When the safety on-off valve is 
 open, the normal on-off valve at the 
 operator's station can be opened and 
 
62 
 
 FIGURE 4. - Jetbolter prototype. 
 
 drilling can commence. As an additional 
 safety feature this on-off valve is non- 
 detented. There is also a manual over- 
 ride switch for the safety on-off valve. 
 This must be depressed at the same time 
 the normal on-off valve is activated. 
 
 This is used only to check whether all 
 the jets are free and operating. There 
 is a pressure gauge at the operator's 
 station that reads intensifier oil pres- 
 sure and thus has a direct correlation to 
 water pressure. 
 
 CONCLUSION 
 
 The jetbolter prototype, shown in fig- 
 ure 4, is now at a coal property in West 
 Virginia ready to begin underground test- 
 ing. In the surface drilling tests con- 
 ducted in sandstone of about 12,000-psi 
 compressive strength, some very encourag- 
 ing results were obtained. 
 
 One-inch-diameter, 6-ft-deep holes were 
 drilled consistently at penetration rates 
 of 18 to 20 ft/min; this translates to 
 20 s per hole; which is about three times 
 the rate for a conventional rotary drill. 
 This was achieved with no dust and no wa- 
 ter splashback, and was quiet enough that 
 
 a conversation at normal levels could 
 take place at the drill operator's sta- 
 tion. During these tests over 350 ft was 
 drilled with a single bit without any 
 appreciable wear. 
 
 The potential for realizing these bene- 
 fits has been known for some time from 
 the research done in this area. The jet- 
 bolter is our attempt to make these bene- 
 fits commercially available to the coal 
 industry at a time when any potential 
 productivity increase will realize major 
 long-term benefits for the industry as a 
 whole. 
 
63 
 
 WATER- JET-ASSISTED TUNNEL BORING 
 By Dr. Levent Ozdemir 1 
 
 ABSTRACT 
 
 This paper presents and discusses the 
 results of a laboratory research pro- 
 gram designed to investigate the perform- 
 ance improvements that can be gained by 
 employing low-pressure water jets to 
 assist disk-roller-type cutters. The ob- 
 ject is to enhance hard rock boring per- 
 formance through the use of water jets to 
 increase attainable penetration rates and 
 to lengthen cutter life, thus reducing 
 
 mechanical boring costs. The technique 
 principally involves placing a low- 
 pressure jet directly in front of the 
 cutter with the jet impinging the rock 
 surface along the cutter path. The re- 
 sults obtained thus far indicate that wa- 
 ter jets designed to enhance disk cutting 
 performance in such a manner offer the 
 potential for improved boring rates and 
 reduced excavation costs. 
 
 INTRODUCTION 
 
 Mechanical tunnel boring technology has 
 realized significant advances over the 
 last two decades. A better understanding 
 of rock failure mechanism coupled with 
 invaluable knowledge and experience 
 gained from case history studies has con- 
 tributed to better design approaches with 
 resultant improvements in machine per- 
 formance and utilization. Today, tunnel 
 boring machines (TBM's) are being widely 
 used in various aspects of underground 
 excavation with favorable economics. 
 Their application to hard rock boring is 
 steadily growing as improvements in cur- 
 rent technology for machine design and 
 fabrication continue. 
 
 Despite all these advancements, how- 
 ever, TBM's still have certain limita- 
 tions for use in the excavation of very 
 hard and abrasive rock formations where 
 low penetration rates accompanied by high 
 cutter wear generally reduce their effec- 
 tiveness as a viable alternative to con- 
 ventional drill and blast methods. Since 
 no new major breakthroughs are antici- 
 pated in TBM technology in the foreseea- 
 ble future, one alternative to achieving 
 further improvements in mechanical boring 
 performance is to utilize an auxiliary 
 assisting mechanism as an integral part 
 of the machine. To this end, water jets 
 
 1 Director, Earth Mechanics Institute, 
 Colorado School of Mines, Golden, CO. 
 
 show great promise for enhancing TBM 
 performance. 
 
 A significant amount of laboratory and 
 field research has been carried out over 
 the past several years to provide infor- 
 mation for a comprehensive assessment of 
 the technical and economic feasibility of 
 using water jets to enhance TBM perform- 
 ance. The majority of this work was un- 
 dertaken by the Colorado School of Mines 
 (CSM) and by Bergbau-Forschung GmbH of 
 West Germany. The principal goal of 
 these efforts was to develop a workable 
 cutting system utilizing water jets in 
 conjunction with disk cutters for tunnel 
 boring applications. 
 
 The research effort at CSM in water- 
 jet-assisted cutting initially began with 
 an extensive series of laboratory rock 
 cutting tests using a large linear cut- 
 ting machine. Small-diameter jets with 
 pressures up to 50,000 psi were employed 
 to create slots in the rock in front of 
 or between the cutter travel paths. The 
 objective was to establish "free faces" 
 in the rock to promote rock failure and 
 chip formation. Thus, the water jets 
 were oriented to cut kerfs either between 
 or along the cutter paths , and also in a 
 combination of both. The results were 
 impressive, showing significant improve- 
 ments in the rock fragmentation effi- 
 ciency of disk cutters with jet assist. 
 To demonstrate the feasibility of the 
 
64 
 
 developed technique under field boring 
 conditions , a follow-on program was ini- 
 tiated in which a 7-ft TBM equipped with 
 disk cutters was modified to accept the 
 water-jet nozzles together with all an- 
 cillary equipment. A series of field 
 tests were run in a hard granite quarry 
 near Skykomish, WA, and a large amount of 
 test data for boring with and without jet 
 assist were gathered. Overall, a 50 -to 
 60-pct increase in TBM penetration rate 
 was observed when water jets were acti- 
 vated to assist the cutting mechanism. 
 For some tests, the water jets were found 
 to increase the penetration rate more 
 than twice. Although the field tests 
 were successful, confirming the technical 
 feasibility of water-jet-assisted cut- 
 ting, several problems likely to arise 
 from the potential application of this 
 concept on TBM's were also identified. 
 Aside from safety concerns, the long-term 
 operational reliability of the pumping 
 equipment necessary to generate the de- 
 sired pressures posed serious questions 
 about the feasibility of the system for 
 field application. 
 
 Following the Skykomish field trials, 
 tests with similar objectives were also 
 carried out by Bergbau-Forschung GmbH of 
 West Germany. An 8.5-ft-diam Wirth tun- 
 nel borer was equipped with high-pressure 
 water jets, and tests were run in a sand- 
 stone quarry. Several arrangements of 
 jet locations with respect to the cutters 
 were investigated. The pattern involving 
 a more or less uniform distribution of 
 jet nozzles over the cutterhead was found 
 to produce the greatest benefit of jet- 
 assisted cutting. In this case, the ma- 
 chine thrust required to maintain a given 
 
 penetration rate was reduced by about 57 
 pet with jet assist as opposed to mechan- 
 ical boring only. Moreover, the machine 
 power requirements were reduced by 43 pet 
 through the use of water jets. However, 
 the beneficial effects of water-jet- 
 assisted cutting were found to diminish 
 at high rates of penetration. 
 
 In spite of the fact that the applica- 
 tion of high-pressure water jets has 
 proven to be a technically feasible con- 
 cept as a means to enhance TBM perform- 
 ance in hard rock, the questions related 
 to system reliability for extended peri- 
 ods of operation under adverse field 
 conditions have prevented its full ac- 
 ceptance and utilization by the TBM manu- 
 facturers. Another shortcoming of the 
 developed concept was the requirement for 
 relatively high power, which had to be 
 added to the system to operate the water- 
 jet pumps. Also the high jet pressures 
 posed serious safety concerns. As a 
 result of these potential constraints, 
 it became apparent that the jet pres- 
 sures would have to be reduced substan- 
 tially to minimize power requirements, 
 enhance equipment reliability, and im- 
 prove personnel safety. These considera- 
 tions eventually led to new research and 
 development efforts with the objective 
 of devising a low-pressure jet-assisted 
 cutting technique for implementation on 
 TBM's. In this aspect, several research 
 programs have been conducted at CSM over 
 the last 4 years. These included jet- 
 assisted cutting in both soft and hard 
 rock formations. In this paper, only the 
 results of cutting tests in hard rocks 
 are discussed. 
 
 LABORATORY TEST RESULTS 
 
 The laboratory test program for inves- 
 tigating the effectiveness of water- 
 jet-assisted disk cutting was conducted 
 on a large linear cutting machine. Tests 
 were performed using a constant penetra- 
 tion mode of testing whereby cutter pene- 
 tration into the rock was held constant 
 and the cutter forces required to main- 
 tain this penetration depth were measured 
 and recorded. All three orthogonal cut- 
 ter force components (side, normal, and 
 
 rolling) were measured by a triaxial load 
 cell and recorded using high-speed digi- 
 tal integrators, as well as strip chart 
 recorders. Various types of pumps, in- 
 cluding axial-piston and triplex pumps, 
 were employed to supply the necessary jet 
 pressures and flow rates. 
 
 As noted previously, the jet nozzle for 
 the linear cutting tests was positioned 
 directly in front of the cutter and ori- 
 ented to impinge the rock surface along 
 
65 
 
 the cutter path. The jet nozzle was se- 
 curely attached to a fixture designed to 
 permit setting of different standoff dis- 
 tances and jet orientation angles. 
 
 As part of various research investiga- 
 tions, jet-assisted disk cutting tests 
 were carried out in samples of two rock 
 types, granite and basalt. The granite 
 samples were those of Colorado Red Gran- 
 ite, which has an average compressive 
 strength of 21,000 psi. The basalt sam- 
 ples were obtained from the Hanford 
 Site in the State of Washington, which is 
 one of the candidate locations for a 
 nuclear waste repository. The compres- 
 sive strength of the basalt samples used 
 for testing ranged from 25,000 to 50,000 
 psi. 
 
 Table 1 summarizes the test results ob- 
 tained in the Colorado Red Granite with 
 and without jet-assisted mechanical cut- 
 ting. As shown in the table, test param- 
 eters involved various combinations of 
 jet pressures and cutter penetration 
 depths. For all tests a 0.025-in jet was 
 used at a 2-in standoff and 3-in cut 
 spacing. The cutter force measurements 
 
 contained in table 1 are plotted in fig- 
 ures 1 through 3. Included in these fig- 
 ures are the normal and rolling forces 
 experienced by the cutter as a function 
 of jet pressure for the three depths of 
 cutter penetration (0.10, 0.20, and 0.30 
 in). As regards the normal force, the 
 water-jet assist is seen to produce a 
 maximum reduction of about 25 pet within 
 the levels of parameters tested. The 
 rolling force is influenced to a higher 
 degree by jet application with an average 
 35-pct reduction compared to mechanical 
 cutting only. The results do not, of 
 course, reflect the optimum cutting con- 
 ditions, meaning that additional reduc- 
 tions in cutter normal and rolling forces 
 appear feasible through optimization of 
 all pertinent system parameters. In con- 
 trast to the normal and rolling forces, 
 water-jet assist does not seem to affect 
 the side force acting on the cutter. The 
 side force data listed in table 1 exhibit 
 large scatter and therefore do not allow 
 derivation of any firm conclusions re- 
 garding this 'effect. 
 
 TABLE 1. - Results of water-jet-assisted disk cutting tests 
 with jet preceding cutter in groove 
 
 (Colorado Red Granite, 15.5 in - 90° disk cutter, 0.025-in 
 jet, 3.0-in cut spacing, 2-in jet standoff) 
 
 Cutter penetration 
 
 Jet 
 
 pressure. 
 
 psi 
 
 Average cutter forces, lb 
 
 Side Normal Rolling 
 
 0.10 in. 
 
 0.20 in. 
 
 0.30 in. 
 
 Dry 1 
 
 5,000 
 
 10,000 
 
 15,000 
 
 20,000 
 
 Dry' 
 
 5,000 
 
 10,000 
 
 15,000 
 
 20,000 
 
 Dry 1 
 
 5,000 
 
 10,000 
 
 15,000 
 
 20,000 
 
 1,569 
 1,843 
 1,610 
 1,452 
 1,843 
 
 4,010 
 4,323 
 3,607 
 4,984 
 4,278 
 
 5,177 
 7,577 
 4,143 
 3,069 
 4,251 
 
 21,343 
 17,066 
 16,651 
 17,459 
 21,563 
 
 32,441 
 29,525 
 26,273 
 23,246 
 28,266 
 
 49,674 
 42,027 
 40,753 
 38,344 
 38,763 
 
 1,366 
 702 
 864 
 742 
 963 
 
 2,320 
 2,086 
 1,916 
 1,581 
 1,809 
 
 5,266 
 4,442 
 4,030 
 3,721 
 3,703 
 
 'Mechanical cutting without jet assist. 
 
66 
 
 JET PRESSURE, 10° psi 
 
 FIGURE 1. - Colorado Red Granite, force versus 
 jet pressure, 0.10-in cutter penetration. 
 
 A series of linear cutting tests with 
 jet assist was also run in Hanford 
 basalts. This particular test program is 
 still continuing; thus only test results 
 generated to date are presented herein. 
 Figure 4 displays the normal and rolling 
 force measurements for various jet pres- 
 sures and two standoff distances at a cut 
 spacing and penetration of 2.5 and 0.15 
 in, respectively. Jet size was 0.02 in. 
 Again, the cutter forces are reduced due 
 
 
 1 
 
 1 1 1 
 
 B 
 
 M 
 O 
 
 
 
 
 ^ 
 
 
 — Mechanical cutting 
 
 
 UJ 
 
 
 
 
 u 
 
 
 
 
 cc 
 
 • 
 
 
 
 £20 
 
 
 • 
 
 • 
 
 
 CO 
 
 
 
 
 z 
 
 
 
 
 
 
 • 
 
 
 _1 
 
 
 
 
 _l 
 
 
 
 
 o 
 
 
 
 
 or 
 in 
 
 1 
 
 1 1 1 
 
 
 5 10 15 20 25 
 
 JET PRESSURE, I0 3 psi 
 
 FIGURE 2. - Colorado Red Granite, force versus 
 jet pressure, 0.20-in cutter penetration. 
 
 to application of water jets with higher 
 pressures and smaller standoff distances 
 producing greater force reductions. 
 Again, the water-jet assist influences 
 the rolling force to a higher degree than 
 it does the normal force. This finding 
 is of major importance since most TBM's 
 become torque limited before their thrust 
 capacity is ever reached. As the rolling 
 force on the cutters is the parameter 
 that determines the cutting torque on a 
 TBM, the fact that major reductions can 
 be achieved in the rolling force compo- 
 nent through the application of low-pres- 
 sure water jets emerges as a significant 
 benefit. 
 
 MECHANISM OF WATER- JET-ASSISTED DISC CUTTING 
 
 As discussed earlier, the initial ef- 
 forts toward development of a water- 
 jet-assisted cutting system for applica- 
 tion to hard-rock TBM's were directed at 
 
 using high-pressure jets to create kerfs 
 in virgin rock to promote chip formation. 
 The mechanism involved in this applica- 
 tion was a simple slotting action that 
 
67 
 
 60 
 
 ro 
 O 
 
 45 - 
 
 L±J 
 
 o 
 or 
 p 
 
 30 
 
 o 
 
 
 1 
 
 1 1 
 
 A 
 
 
 
 ^-Mechanical cutting 
 
 
 - 
 
 • 
 
 • 
 
 • 
 
 < 
 
 
 1 
 
 1 1 
 
 
 JET PRESSURE, 10^ psi 
 
 FIGURE 3. - Colorado Red Granite, force versus 
 jet pressure, 0.30-in cutter penetration. 
 
 KEY 
 CZI Normal force 
 |( S j £23 Rolling force 
 2 ksi 
 
 30 
 
 20 
 
 — 10 
 
 Water jet, 
 2- in standoff 
 
 FIGURE 4. - Normal force measurements in 
 Umatilla Basalt with and without jet assist. 
 
 made use of the high, concentrated power 
 which water jets are capable of deliver- 
 ing. The mechanism by which a low- 
 pressure jet assists the disk cutting 
 performance is quite different, probably 
 encompassing several factors. It is be- 
 lieved, however, that three factors play 
 a major role in this respect. The first, 
 and perhaps the most important, mechanism 
 is the removal of the crushed zone imme- 
 diately surrounding the cutter groove. 
 Visual observations of cutter paths to- 
 gether with photomicrographs of the 
 crushed and fractured zone beneath the 
 cutter have confirmed the occurrence of 
 such a mechanism. The second mechanism, 
 which is believed to take place with jet 
 assist, is the so-called hydrof racturing, 
 whereby the water under pressure pene- 
 trates and enlarges the subsurface cracks 
 produced due to the mechanical cutting 
 action. Some of these cracks are en- 
 larged and extended to a length suffi- 
 cient to create additional chip forma- 
 tion, increasing the total yield of rock 
 material removed by the system. Lastly, 
 the water jet appears to lubricate the 
 cutting path and provide a cooling effect 
 on the cutter. This mechanism coupled 
 with the removal of the crushed zone is 
 believed to contribute to improved cutter 
 ring life. 
 
 As previously stated, the principal at- 
 traction of low-pressure water jets is 
 their low power requirements. For exam- 
 ple, a 0.020-in-diam jet operating at a 
 pressure of 5,000 psi generates a flow 
 volume rate of about 0.70 gal/min and re- 
 quires approximately 2.5 hp at the pump. 
 In addition to these advantages compared 
 to high-pressure jets, use of low pres- 
 sure also improves equipment reliability 
 and practically eliminates most of the 
 safety concerns that are raised when con- 
 sidering the application of high-pressure 
 jets on TBM's. 
 
 It is not necessarily a requirement or 
 a feasible approach that every cutter on 
 a TBM should be fitted with a water jet 
 in order to achieve the desired level of 
 improvements in excavation rates and cut- 
 ter lives. A number of jets strategical- 
 ly placed on the cutterhead in areas 
 where the cutting action is most diffi- 
 cult, i.e., the gage and center cutters, 
 
68 
 
 may serve the purpose and provide the de- 
 gree of performance enhancement that is 
 necessary to warrant the additional cost 
 of incorporating water jets on TBM's. 
 This goal can be accomplished by carry- 
 ing out full-scale field demonstration 
 tests with a water-jet-assisted TBM for 
 determining the optimum locations of jet 
 
 nozzles on the cutterhead. Such a test 
 program can also furnish data relating to 
 the impact of jet assist on cutter wear. 
 It is very difficult to investigate the 
 wear effects in the laboratory since the 
 amount of rock cut generally is not suf- 
 ficient to produce any measurable degree 
 of wear on the cutter. 
 
 SUMMARY 
 
 The laboratory test results obtained 
 thus far indicate that low-pressure water 
 jets directed in the disk cutter path 
 offer a significant potential for en- 
 hanced TBM performance. A side benefit 
 appears to be extended cutter life, mean- 
 ing lower excavation costs. Because of 
 low pressure requirements, it is felt 
 that a water-jet-assisted cutting system 
 can be installed on a TBM without any ma- 
 jor difficulty. The pumping equipment 
 
 required to generate these low pressures 
 is commercially available with proven re- 
 liability for operation over long periods 
 of time . 
 
 Further testing is planned to improve 
 system effectiveness and to achieve the 
 optimal configuration of jet-assisted 
 disk cutting. Greater benefits of jet 
 assist than those reported in this paper 
 appear feasible through additional opti- 
 mization studies. 
 
69 
 
 INVESTIGATION OF OPTIMIZING TRAVERSE SPEED OF WATER- JET-ASSISTED DRAG PICKS 
 By R. J. Evans, 1 H. J. Handewith, 2 and C. D. Taylor 3 
 
 ABSTRACT 
 
 A cutterhead was designed and fabri- 
 cated at the Bureau of Mines Pittsburgh 
 Research Center to evaluate the rock- 
 weakening effect, when using water- 
 jet-assisted cutting, that may result 
 from increased travel speed using 
 moderate-pressure jets (3,000 to 9,000 
 psi). Two pick types, conical and flat, 
 were analyzed for speeds ranging from 30 
 to 300 ft/min. The objective was to es- 
 tablish traverse speed threshold levels 
 
 that are necessary to maintain the opti- 
 mum reduction in cutting tool forces. In 
 addition, measurements were taken to mea- 
 sure dust reduction when using water-jet 
 assist. Results indicate that when em- 
 ploying water-jet-assisted cutting, only 
 a negligible reduction in the rock- 
 weakening effect was observed at higher 
 speeds. As an added benefit, significant 
 dust reduction was evident when employing 
 water-jet-assisted cutting. 
 
 INTRODUCTION 
 
 The Bureau has initiated a research 
 program in water-jet-assisted cutting to 
 determine the improvements possible in 
 cutting performance and health and safe- 
 ty. Underground coal mining machines, 
 such as the longwall shearer and the con- 
 tinuous miner, cut with bit speeds rang- 
 ing from 400 to 800 ft/min. To measure 
 water-jet-assisted cutting effectiveness 
 at higher speeds, a full-face cutterhead 
 was designed and fabricated at the 
 Pittsburgh Research Center. It contains 
 
 six jet-assisted drag bits as shown in 
 figure 1. The cutterhead has a 36-in 
 diam and is outfitted to use either flat 
 or conical bits. The bit spacing, shown 
 in figure 2, is 2-1/2 in between each bit 
 and double tracking at the gage bits. 
 The cutterhead was designed to bring 
 high-pressure water through a swivel 
 mounted on the rear of the cutterhead. 
 The water is then transported through 
 holes drilled in the body of the cutter- 
 head to the six individual bits. 
 
 APPROACH 
 
 The traverse speed cutterhead was 
 mounted on a raise boring machine gearbox 
 (fig. 3) which was driven by a fixed- 
 displacement, variable-stroke hydraulic 
 pump. The cutterhead was flange-mounted 
 on a 5-ft section of Drilco 11-in-diam 
 drill pipe with DI-22 threaded connec- 
 tions. Rotation was varied from 1/2 to 
 40 r/min. The maximum available thrust 
 was 120,000 lbf. Torque was a demand 
 
 Supervisory civil engineer, Pittsburgh 
 Research Center, Bureau of Mines, Pitts- 
 burgh, PA. 
 
 ^Project research supervisor, Boeing 
 Services International, Inc. , Pittsburgh, 
 PA. 
 
 ^Industrial hygienist, Pittsburgh Re- 
 search Center, Bureau of Mines, Pitts- 
 burgh, PA. 
 
 function of thrust, which generated a 
 maximum hydraulic pressure of 5,000 psig 
 at full pump stroke. The water-jet sys- 
 tem was powered by two 10-gal/min posi- 
 tive displacement triplex pumps generat- 
 ing a maximum pressure of 9,500 psi. 
 Flow (pressure) control was achieved by 
 varying the running speed of the diesel- 
 engine-powered pump. The water jet was 
 mounted in front of the bit and directed 
 to impinge less than 5 mm in front of the 
 
 bit cutting tip, as shown in figure 4. 
 The water for the jet-assist cutting pro- 
 cess was filtered through a 100-um fil- 
 ter, delivered through the back of the 
 drive train gearbox, and transported 
 through the drill pipe and then through 
 the high-pressure swivel, which was lo- 
 cated in the back of the cutterhead. 
 
70 
 
 Gauge bits 
 double 
 tracking- 
 
 mammmsss 
 
 FIGURE 1. - Water-jet-assisted full-face 
 cutterhead. 
 
 FIGURE 2. - Cutterhead bit spacing (dimen- 
 sions in inches). 
 
 FIGURE 3. - Traverse speed cutterhead. 
 
71 
 
 FIGURE 4. - Water-jet-assisted cutting bit 
 and nozzle. 
 
 The test material was a German sand- 
 stone with a compressive strength of 
 19,000 psi, a bulk density of 156.6 lb/ 
 ft 3 , and 50- to 55-pct quartz content. 
 Two 4- by 4- by 2-ft-wide blocks of this 
 material were mounted on the test stand 
 and cemented together with a 3- to 4-in 
 layer of concrete around the outside, as 
 shown in figure 5. A 13-in-diam pilot 
 hole was drilled through the block to 
 guide the cutterhead as it cut through 
 the block. The cutterhead was equipped 
 with a pilot fixture that fit into the 
 pilot hole as shown in figure 6. 
 
 Dust levels were measured while cutting 
 dry and with water-jet assist by drawing 
 a portion of the dust generated from the 
 cutting surface into a dust box. While 
 in the box, respirable dust was separated 
 from nonrespirable dust using two 10-mm 
 nylon cyclones and sampling heads. Two 
 RAM-1 real-time dust sampling instru- 
 ments were used to draw respirable dust 
 from the cyclone sampling heads and to 
 
 Block I 2 ft 
 Block 2 2 ft 
 
 Typical concrete 
 case, 3 to 4 in- 
 wide 
 
 FIGURE 5. - German sandstone test block, uncon- 
 fined compressive strengths: Sandstone, 19,000 
 psi; concrete, 6,000 to 7,000 psi (est.). 
 
 Rotation 
 
 FIGURE 6. - Sandstone block and traverse speed 
 cutter test setup. 
 
 continuously measure the dust concentra- 
 tions. The concentration data from each 
 instrument were recorded by a dual-pen 
 strip-chart recorder. The areas under 
 the recorded curves were compared to de- 
 termine the relative quantities of dust 
 generated when operating with and without 
 water-jet assist. 
 
 RESULTS 
 
 Today, nearly all laboratory and some 
 field tests are conducted at a constant 
 depth of cut (DOC) with variable force 
 rates. However, in actual practice, all 
 mechanical mining machines operate with 
 
 fixed force rates and variable force or 
 penetration. The traverse rate tests 
 conducted here were closer to actual 
 practice than to laboratory testing. 
 
72 
 
 The most significant observation was 
 that the German sandstone could not be 
 cut without water-jet assist. Figure 7 
 shows the results when cutting dry for 
 less than 1 minute. The conical bit was 
 worn to the point of being unrecogniza- 
 ble. When cutting dry, grinding steel 
 rather than cutting rock was apparent. 
 However, when using 6,000-psi jet assist, 
 large chips were cut as shown in figure 8 
 with much less bit wear. Over the tra- 
 verse speed range of 35 to 300 ft/min, no 
 change in water-jet-assisted cutting ef- 
 ficiency was noted. 
 
 To measure efficiency, the use of en- 
 ergy volume (EV) as a measure of rock 
 boring rate was proposed by Ross and 
 Hustrulid 4 in 1972. This EV value was 
 used in this study to evaluate the rock- 
 weakening effect. 
 
 EV = 
 
 (2, x N x Ib) + (Tx|) 
 0.6^ D 2 x AR 
 
 where 
 
 AR = advance rate of cutter into 
 the rock sample, ft/h, 
 
 N = revolution rate of cutter- 
 head, r/min, 
 
 Energy 
 
 and 
 
 EV = tt^ — = energy per unit 
 Volume 1*4 
 
 volume of in situ 
 
 fractured rock, 
 
 (in«lbf)/in 3 , 
 
 To = cutterhead drive torque, 
 fflbf , 
 
 T = system thrust on cutterhead, 
 lbf, 
 
 D = diameter of cutterhead or 
 test bore, ft. 
 
 4 Ross, N., and W. Hustrulid. Develop- 
 ment of a Tunnel Boreability Index (U.S. 
 Bur. Reclamation contract 1 4-06-D-6849, 
 Dep. Mining, CO Sch. Mines). Feb. 1972, 
 351 pp.; NTIS REC-ERC-72-7. 
 
 FIGURE 7. - Dry cutting of a 19,000-psi sand- 
 stone with a conical pick. 
 
 Without using water-jet assist, the en- 
 ergy volume (EV) rate was greater than 
 200,000 (in«lbf)/in 3 with an instantane- 
 ous advance rate of less than 0.75 ft/h 
 as shown in figures 9 and 10, respective- 
 ly. However, when employing water-jet 
 assist at 6,000 psi, the energy volume 
 rate was less than 35,000 (in«lbf)/in 3 
 with corresponding advance rates greater 
 than 3 ft/h (figs. 9-10). The fastest 
 advance rate, 88.5 ft/h, was achieved 
 when using water-jet-assisted cutting at 
 6,000 psi. The EV was 1,150 (figs. 9- 
 10) , and the traverse rate was 40 ft/min. 
 
 There was a noticeable difference in 
 efficiency when nozzles became clogged. 
 One test had a partially plugged jet noz- 
 zle operating at 0.26 gal/min which re- 
 sulted in an EV of 77,600 (in«lbf)/in 3 
 (fig. 9). This indicated that nozzle 
 flow rates of at least 1 gal/min must be 
 sustained for optimum cutting of German 
 sandstone. 
 
73 
 
 FIGURE 8. - Rock chips when cutting with water-jet-assist. 
 
 Three tests with an advance rate in ex- 
 cess of 20 ft/h had a large departure 
 from the rest of the data, which were all 
 less than 14 ft/h as shown in figure 10. 
 The reasons for these higher advance 
 rates are not obvious. As shown in fig- 
 ure 11, advance rate is plotted as a 
 function of rotation rate. With a fixed 
 thrust force, the advance per revolution 
 steadily decreased nonlinearly as the 
 rotation rate increased. Industry has 
 always believed there is a linear rela- 
 tionship between rotation rate and ad- 
 vance rate. It has been demonstrated 
 that advance rate can be increased by 
 deeper DOC (in/r) or by increasing the 
 rotation rate. However, some other phe- 
 nomenon caused advance rates in excess of 
 20 ft/h, as shown in figure 10. Too few 
 data exist to explain this phenomenon. 
 
 In the paper by Ross and Hustrulid, 5 
 for efficient cutting it was proposed 
 that the average EV, expressed as (in 
 •lbf)/in 3 , would approximate the average 
 unconfined compressive strength of rock, 
 expressed as lbf/in 2 ). The quantity was 
 proposed as a measure of cutting effi- 
 ciency. Since dry cutting was obviously 
 not efficient, only wet cuts were evalu- 
 ated as shown in table 1 to identify the 
 average EV for all jet tests using both 
 conical and flat bits. Although the flat 
 bit was 19 pet less efficient than the 
 conical bit, the flat bit produced the 
 highest net advance rate. The reason for 
 this is beyond the scope of this report 
 and warrants more study in the future. 
 Average EV of all water-jet-assisted 
 
 ^Work cited in footnote 4. 
 
74 
 
 300 
 
 250 - 
 
 •o 200 h 
 o 
 
 UJ 
 
 _i 
 o 
 
 > 
 
 rr 
 u 
 
 Q- 
 
 >- 
 
 cc 
 
 UJ 
 
 z 
 
 UJ 
 
 150 - 
 
 100 
 
 50 
 
 1 1 
 
 1 1 
 
 D 
 
 1 
 
 
 A 
 
 
 - 
 
 KEY 
 ■ Conical bit 
 a Flat bit 
 
 □ Conical bit, dry cutting 
 a Flat bit, dry cutting 
 
 " 0.26 gal/mir 
 per nozzle — 
 
 
 
 Greater than 
 - per nozzle-, 
 
 1 gal/min 
 \ 
 
 _ 
 
 
 H 
 
 n 
 
 1.6 
 
 1.4 
 1.2 
 1.0 
 
 ui 
 o 
 
 z 
 
 o 
 < 
 
 KEY 
 
 ■ Conical bit 
 
 a Flat bit 
 
 a Conical bit, dry cutting 
 
 a Flat bit, dry cutting 
 
 Expected range 
 
 8 
 
 ^L 
 
 _L 
 
 Unexpected 
 range 
 
 4 8 12 16 20 24 28 
 
 ADVANCE RATE, ft/h 
 
 FIGURE 10. - Advance versus advance rate. 
 
 1.4 
 
 i 
 
 1 1 1 1 l 
 
 KEY 
 
 
 1.2 
 
 \ ■, 
 
 |n/r = 0.64+ (-0.18) in* rpm 
 
 
 \ 
 \ 
 
 R 2 = 0.71, conical bit 
 
 
 1.0 
 
 _ \ A *. 
 \ 
 
 In/r= 1.24+ (-0.42) in* rpm 
 
 R2 = 0.62, flat bit 
 
 - 
 
 .8 
 
 \ 
 \ 
 \ 
 \ 
 \ 
 
 * Natural logarithm 
 
 - 
 
 .6 
 4 
 
 V \ 
 
 ~ \ ^ 
 \ \ 
 
 \ \ 
 
 - 
 
 .2 
 
 AA 
 
 1 
 
 i i""^ i * 
 
 
 100 200 300 
 
 TRAVERSE RATE, ft/min 
 
 FIGURE 9. - Cutting of 19,000-psig quartz 
 sandstone. 
 
 testing was 19,490 (in«lbf )/in 3 . The re- 
 ported average unconfined compressive 
 strength for the German sandstone was 
 19,000 psi (at CSM by Ropchan), 6 sug- 
 gesting a reasonable confirmation for 
 the Ross and Hustrulid hypothesis that 
 EV approximates unconfined compressive 
 strength for efficient cutting. 
 
 6 Ropchan, D., F. D. Wang, and H. J. 
 Wolgamott. Application of Water- Jet- 
 Assisted Drag Bit and Pick Cutter for the 
 Cutting of Coal Measure Rocks (U.S. Dep. 
 Energy contract ET-77-a-01-9082, CO Sch. 
 Mines). Apr. 1980, 120 pp.; NTIS DOE/ 
 ET/1 2463-1. 
 
 TABLE 1. - Energy volume relations with water-jet assist 
 
 Conical bit, model 070, average of 4 tests (in'lbf )/in 3 . , 
 
 Flat bit, model K-107, average of 10 tests (in-lbf )/in 3 . . 
 
 Average of all 14 tests (in*lbf )/in 3 . . 
 
 Reported average unconfined compressive strength of German 
 sandstone lbf /in 2 . . 
 
 
 
 5 10 15 20 25 30 35 
 
 CUTTERHEAD ROTATION RATE, rpm 
 FIGURE 11. - Advance cutterhead rotation rate. 
 
 16,768 
 20,579 
 19,490 
 
 19,000 
 
75 
 
 To further confirm the test results, 
 scalar and force relations, and calcula- 
 tion assumptions, a comparison was made 
 with previous testing conducted in the 
 German sandstone in 1980. 7 This compari- 
 son is shown in table 2. Although there 
 were slight differences in water pressure 
 and DOC, normal, cutting, and resultant 
 forces were in good agreement for the 
 conical bit. Ropchan did not test the 
 flat bit. This confirms that scalar re- 
 lationships can be established for the 
 forces reacting on a single cutting tool 
 and on an interactive array of such cut- 
 ting tools. A significant departure from 
 the Ropchan tests was the spacing between 
 interactive cutting tools. Ropchan used 
 a tool spacing of 1.5 in, whereas the 
 spacing used here was 2.5 in. With near- 
 ly the same cutting tool force reactions, 
 the tests conducted here produced 167 pet 
 more in situ rock volume at the same bit 
 force or EV rate. 
 
 TABLE 2. - Cutting of German (19,000-psi) 
 sandstone with conical bits 
 
 
 Force, lbf 
 
 Test 
 
 Nor- 
 mal 
 
 Cut- 
 ting 
 
 Result- 
 ant 
 
 Single-tool, by CSM: l 
 
 5,000-psig water 
 iet 
 
 3,860 
 
 2,042 
 
 3,850 
 
 3,501 
 2,340 
 
 2,340 
 
 5,220 
 3,121 
 
 Multitool, by Bu- 
 Mines: 2 6,000-psig 
 
 4,500 
 
 Colorado School of Mines; depth of cut 
 was 0.5 in at a 1.5-in tool spacing. 
 
 2 Calculated from gross system forces 
 reacting on an array of 6 cutting tools; 
 depth of cut was 0.454 in at 2.5-in tool 
 spacing. 
 
 During the water-jet-assisted tests, 
 data describing several operation func- 
 tions were simultaneously monitored and 
 recorded. The dependent or controlled 
 function were — 
 
 FN(KLBF) = Normal or thrust force in 
 thousands of pounds, 
 
 'Work cited in footnote 6. 
 
 RPMs = Cutterhead revolutions per 
 minute , 
 
 PW = Water pressure, psig. 
 
 Independent functions were — 
 
 INCHES = Advance in inches of the 
 cutterhead into the test 
 rock over the test period 
 in seconds, 
 
 FT(PSIG) = Torque force measured as a 
 function of the hydraulic 
 gauge pressure, psig, 
 
 RF = Volume rate of water jet 
 flow, psig. 
 
 One conclusion reached in this study is 
 that there is a minimum threshold of 
 thrust below which the German sandstone 
 cannot be bored. This threshold was not 
 reached for dry cutting and was obviously 
 much higher than that required using 
 water-jet assist. 
 
 Tool wear, after advancing less than 
 1 in into the test block, was excessive, 
 as indicated by the conical bit shown in 
 figure 8. All six cutting tools failed 
 in this dry test. When water-jet assist 
 was used, only occasional tool failures 
 occurred. 
 
 Dust sampling results shown in figure 
 12 indicate that dust concentrations were 
 
 H 
 
 o 
 
 Z> 
 Q 
 Ld 
 
 cr 
 
 H 
 
 z> 
 a 
 
 w 
 
 c^^ 
 
 1 
 
 • 
 
 • 
 
 1 
 
 
 80 
 
 - 
 
 
 
 
 -II 
 
 60 
 
 
 
 
 • 
 
 
 40 
 
 on 
 
 ' 
 
 1 
 
 
 1 
 
 -i 
 
 
 
 30 
 
 10 20 
 
 CUTTING ROTATION RATE, rpm 
 
 FIGURE 12. - Dust reduction using water-jet- 
 assistwith flat bits (compared with dry cutting) 
 as a function of cutterhead rotation rate. 
 
76 
 
 reduced 60 to 85 pet when using water-jet 
 assist versus operating dry. The per- 
 centage reductions for these tests (con- 
 ducted with 6,000-psi water pressure, 
 
 30,000-psi thrust, and flat bits) in- 
 creased as the cutting head rotation 
 speed was reduced. 
 
 CONCLUSIONS 
 
 The German sandstone was far more dif- 
 ficult to cut than originally expected. 
 Dry cutting was impossible. Water-jet- 
 assisted cutting with 6,000 psi resulted 
 in dramatic improvement. No measurable 
 degradation in rock-weakening effect was 
 found over the tested traverse rate range 
 of 35 to 300 ft/min in German sandstone. 
 
 The following are additional pertinent 
 results: 
 
 1. With water-jet-assisted cutting, 
 the EV was nearly equal in value to the 
 unconfined compressive strength of rock, 
 indicating that cutting was in the effi- 
 cient EV range. 
 
 2. Water-jet assist was obviously ef- 
 fective in reducing bit wear and cutting 
 tool forces. 
 
 3. EV level for all dry cutting was in 
 excess of 200,000 (in'lbf )/in 3 . 
 
 4. EV levels averaged 19,490 (in«lbf)/ 
 in 3 , using 6,000-psig water-jet assist at 
 flow rates in excess of 1 gal/min and 
 0.6-mm jet nozzles. 
 
 5. Force reactions measured on a sin- 
 gle jet-assisted cutting tool in German 
 sandstone by Ropchan compared favorably 
 with those forces calculated on the in- 
 teractive array of cutting bits tested by 
 the Bureau of Mines and Boeing Services 
 International. 
 
 6. Scalar force-rate relationships can 
 be established between a single cutting 
 tool and an interactive array of cutting 
 tools. 
 
 7. The maximum instantaneous advance 
 rate recorded on one test was 88.5 ft/h. 
 
77 
 
 OPTIMIZATION OF WATER- JET SYSTEMS FOR MINING APPLICATIONS 
 By Dr. James M. Reichman 1 
 
 INTRODUCTION 
 
 Mining depends upon the ability to ef- 
 ficiently cut and drill rock so that it 
 can be economically excavated and pro- 
 cessed. Ideally, the most efficient min- 
 ing operation would be continuous. Thus, 
 much is contingent upon the longevity and 
 reliability of the equipment used. The 
 need to extend machine life is emphasized 
 by the negative effects of cutter and bit 
 wear and, indirectly, decreased equipment 
 reliability due to the higher loads re- 
 quired at wear points. In the past, at- 
 tempts to improve machine life have fo- 
 cused on the "hardening" of working 
 parts. However, metallurgy and engineer- 
 ing are rapidly approaching the limits of 
 present technology. 
 
 An alternative to "hardening" of mining 
 equipment is to develop a cutting tech- 
 nique that minimizes abrasive wear, re- 
 duces the required mechanical cutting 
 force, or decreases the amount of rock 
 cutting or drilling needed to effect 
 breakage. The use of water jets with 
 mining equipment is one method of achiev- 
 ing these goals. The optimization of 
 this approach is the subject of this 
 paper. 
 
 Water jets can be adapted to mining ap- 
 plications in various ways, including 
 pure water-jet cutting, water-jet cutting 
 with mechanical assist, mechanical cut- 
 ting with water-jet assist, and water-jet 
 cutting with abrasives. The pertinent 
 parameters involved in pure water-jet 
 cutting are shown in figure 1. Water-jet 
 cutting produces narrow kerfs in the 
 rock. To remove all the rock, kerfs must 
 be made close together; as figure 2 indi- 
 cates, rock type dictates kerf spacing. 
 
 Rock type also determine kerf depth and 
 cutting effectiveness. 
 
 Water-jet cutting with mechanical as- 
 sist uses water jets to cut kerfs at a 
 fixed spacing and then employs mechanical 
 force to break the rock between the 
 kerfs. Uncut ridges may be broken using 
 a drag-type cutter. In this method the 
 water jet accomplishes the major cutting 
 task, while the mechanical cutting is 
 secondary. 
 
 In techniques that employ mechanical 
 cutting with water-jet assist, the me- 
 chanical cutting force is generally suf- 
 ficient to cut the rock. The water jets 
 are used to reduce the required cutting 
 force, either by weakening the rock or by 
 improving the cutting conditions. As 
 shown in figure 3, the water jet can 
 weaken the rock so that it fails in ten- 
 sion. The water jet can also be used to 
 clear the cuttings away from the bit, 
 permitting the machine to apply high 
 stress directly to the rock. 
 
 The use of a water jet with an en- 
 trained abrasive adds a new dimension to 
 water- jet cutting. The introduction of a 
 high-velocity abrasive particle (fig. 4) 
 extends the cutting depth by a factor of 
 5 or more over a pure water jet. In ad- 
 dition, the sensitivity of the water jet 
 to various rock types is reduced. 
 
 The following sections discuss some ap- 
 plications of the various water-jet tech- 
 niques . To achieve the performance goals 
 and the most economical system, it is im- 
 portant to optimize the use of the water 
 jet for each application. This optimiza- 
 tion procedure will also be discussed. 
 
 WATER- JET APPLICATIONS 
 
 PURE WATER JETS 
 
 technique energy intensive. 
 
 In many 
 
 The high specific energy required 
 to excavate large amounts of materi- 
 using pure water jets 
 
 al 
 
 makes this 
 
 cases the inhomogeneity of the material 
 
 1 Director, High Pressure Technology, 
 Flow Industries, Inc., Kent, WA. 
 
78 
 
 Nozzle 
 
 25 
 
 KEY 
 
 t Standoff distance Vf Traverse velocity 
 do Nozzle diameter w Width of cut 
 P Nozzle pressure h Depth of cut 
 
 FIGURE 1. - Water-jet cutting parameters. 
 
 Side jets cutting 
 ahead of pick 
 
 Jet hitting pick 
 at contact point 
 
 FIGURE 3. 
 assist. 
 
 Mechanical cutting with water-jet 
 
 makes hydraulic mining impractical. Min- 
 ing with pure water jets makes economic 
 sense only under special conditions, such 
 as where the seam is on an angle and the 
 material is friable (as in coal mining). 
 It is, therefore, advantageous to iden- 
 tify applications where minimal material 
 removal produces the desired results. 
 
 An example of "minimal removal" is 
 disking and/or slotting of a drilled hole 
 (fig. 5). In this case the water jet is 
 
 O 
 
 1 
 
 IT) 
 
 3 
 
 en 
 
 rr 
 
 1x1 
 
 h- 
 
 UJ 
 
 < 
 
 o 
 
 UJ 
 _1 
 N 
 N 
 O 
 
 20 
 
 15 
 
 10 
 
 I ' 1 
 
 1 KEY ' 
 
 a Charcoal 
 
 • Granite 
 
 t Wilkeson Sandstone, 0.014-indiam. 
 
 ■ Wilkeson Sandstone, 0.018-in diam 
 
 _l 
 
 I 
 
 '0246 
 CUTTING VELOCITY, in/s 
 
 FIGURE 2. - Kerf spacing. 
 
 High-pressure water 
 
 
 Coherent high-velocity jet 
 
 ti Abrasives 
 
 — Patented nozzle 
 configuration 
 
 — Focused particle 
 jet 
 
 ■Target 
 
 FIGURE 4. - Abrasive water-jet schematic. 
 
 used to create slots along the side of 
 the hole. These slots allow the direc- 
 tion of fracture to be determined before 
 blasting, enabling more efficient break- 
 age of the rock. When the back of a hole 
 is disked, "boot leg" is eliminated and 
 more of the rock in a face is recovered. 
 
79 
 
 Slot fracturing 
 
 Disk fracturing 
 FIGURE 5. - Water-jet slotting and disking. 
 
 In this example, the ability of a water 
 jet to cut a rock without mechanical con- 
 tact is more important than the energy 
 required to do the cutting. This is be- 
 cause the minimal cut has a pronounced 
 effect on the overall mining process. 
 This method can be used to the best ad- 
 vantage by optimizing the configuration 
 of the blast holes to take full advantage 
 of the improved breakage. 
 
 WATER- JET CUTTING WITH 
 MECHANICAL ASSIST 
 
 In this method, the water jet provides 
 the principal means of cutting while the 
 mechanical assist is used to break the 
 rock left uncut by the jets. The thrust 
 and torque of such a cutting device are 
 much lower than for a similar mechanical 
 cutter, but the power requirements are 
 higher in many cases. Hence, the most 
 appropriate applications are when thrust 
 
 and torque reduction are of prime 
 importance. 
 
 An example of this cutting method is 
 a high-pressure water-jet drill (fig. 6). 
 In this type of drill, the cutting wa- 
 ter jets leave ridges, which are then 
 broken off as the drill progresses. The 
 drill requires thrusts of several hundred 
 pounds; the reduced cutter loads extend 
 operating life. This type of drill is 
 especially useful in abrasive rock, when 
 equipment must be light and maneuverable , 
 when hand operation is required, and when 
 a longer-than-seam-height drill is re- 
 quired. This latter application is one 
 where low torque and thrust are critical, 
 due to transmission around a curve. 
 
 Although this type of drill has many 
 inherent advantages, the energy consump- 
 tion and capital cost could be prohibi- 
 tive. It is, therefore, critical to op- 
 timize the cutting process for a particu- 
 lar application. 
 
 MECHANICAL CUTTING WITH WATER- JET ASSIST 
 
 Water jets can be used to augment the- 
 cutting process of a mechanical cutter. 
 This reduces the required cutting force 
 and allows pick or cutter spacing to be 
 increased, improving overall cutting per- 
 formance. In addition, water jets im- 
 prove the ability of a machine to effi- 
 ciently cut harder rock. This method of 
 cutting with water jets is particularly 
 useful when machine size is not the crit- 
 ical factor, since most of the cutting is 
 accomplished mechanically. 
 
 Large mining equipment for such appli- 
 cations includes longwall shearers, con- 
 tinuous miners , road headers , and raise 
 and blind shaft borers. In this applica- 
 tion the jet is used to directly assist 
 the cutter (fig. 7). In underground 
 tests, this equipment improved cutting, 
 reduced dust and wear , and eliminated 
 sparking. 
 
 To optimize this type of cutting sys- 
 tem, it is necessary to determine the 
 best method to directly assist only those 
 cutters in contact with the rock. This 
 is especially important in machines that 
 employ a rotating drum, only a portion of 
 which is actually in contact with the 
 cutting face. 
 
80 
 
 FIGURE 6. - Water-jet drill. 
 
 ABRASIVE WATER- JET CUTTING 
 
 The use of a water jet with an en- 
 trained abrasive allows a deep cut (up to 
 24 in) to be made in rock. The resulting 
 slot can be used to isolate a portion of 
 rock from the main body, enabling selec- 
 tive excavation. 
 
 Some applications of this technique are 
 improved perimeter control, as shown in 
 figure 8, selective mining, and roof and 
 floor control. Optimization involves ad- 
 justing the abrasive water jet itself for 
 the particular process, as well as inte- 
 gration of the technique with the entire 
 mining or tunneling process. 
 
 WATER-JET OPTIMIZATION 
 
 All systems utilizing water jets must 
 be optimized. This often means simply 
 identifying the pressure and flow rate 
 that most efficiently produce the desired 
 result. In other cases, optimization in- 
 volves reducing energy waste. The fol- 
 lowing subsections describe optimizations 
 for some selective applications. 
 
 WATER- JET DRILL WITH MECHANICAL ASSIST 
 
 When using water jets as the primary 
 cutting tool, the objective is to develop 
 
 a drill with minimum mechanical assist. 
 The drill should be capable of drilling 
 effectively in all rocks. However, as a 
 general rule for optimum performance, the 
 harder the rock the higher the operating 
 pressure. 
 
 To develop the drill, an acceptable 
 horsepower level and a maximum allowable 
 flow rate must be established. It is im- 
 portant to determine these parameters at 
 the outset, since the available power de- 
 termines the initial and operating cost 
 of the equipment. Also, excessive water 
 
81 
 
 Water-jet 
 nozzles 
 
 Water -jet 
 nozzles 
 
 FIGURE 7. - Water-jet shearer and roadheader. 
 
82 
 
 FIGURE 8. - Perimeter control with abrasive jet. 
 
 requirements can result in supply and 
 disposal problems , as well as floor con- 
 trol problems. By setting these para- 
 meters, the range of available pressures 
 can be determined. The actual pressure 
 at which the drill is operated should 
 be the minimum pressure required to 
 obtain an acceptable cutting speed in 
 a particular application. Minimizing the 
 pressure increases the reliability of 
 high-pressure components. 
 
 Optimizing drill performance only 
 starts with establishing the operating 
 pressure; the remainder of the process 
 involves determining the most critical 
 characteristics of the drill. This re- 
 sults from contradictory trends in the 
 drill performance. For example, if the 
 water jet is used to cut grooves which 
 are then broken off by a mechanical cut- 
 ter, groove depth must be maximized. As 
 shown in figure 9, there is an inverse 
 relationship between the depth of cut and 
 the force needed to break the uncut 
 ridge. However, it is not always possi- 
 ble to cut a deep kerf using available 
 pumps. As a result, it may be necessary 
 to use higher than desired drill thrust 
 to achieve acceptable cutting. 
 
 A second important compromise in the 
 drill design is the effect of increasing 
 the thrust on the drill. The positive 
 result is that the drill rate increases 
 dramatically with thrust (fig. 10A) . 
 However, this advantage is countered 
 by increased drill wear (fig. 10B). The 
 wear rate increase can have important 
 
 O 
 
 rr 
 o 
 
 u_ 
 
 o 
 
 z 
 
 h- 
 
 H 
 
 o 
 
 Fixed jet spacing 
 
 KERF DEPTH 
 
 FIGURE 9. - Force versus groove depth. 
 
 < 
 
 Q 
 
 a: 
 < 
 
 LlI 
 
 THRUST THRUST 
 
 FIGURE 10. - Effect of thrust on drilling rate 
 and wear (constant-diameter hole). 
 
 ramifications on the economics of the 
 drilling process that offset the in- 
 creased speed. 
 
 The optimization process can result in 
 a drill that is close to being as energy 
 efficient as a conventional drill, per- 
 forming at comparable or better drilling 
 rates while reducing bit wear by a factor 
 of 4 or 5. Drills of this type have al- 
 ready been developed for roof bolting ap- 
 plication, and hard-rock drills are cur- 
 rently being examined. 
 
 WATER- JET-ASSISTED MECHANICAL CUTTING 
 
 The application of water-jet-assisted 
 mechanical cutting is widely being exam- 
 ined for improved performance of min- 
 ing and tunneling machines. Two methods 
 of applying the jet assist have been 
 examined: direct assist on the bit and 
 
83 
 
 slotting between cutters. 2 in both meth- 
 ods the performance is optimized by main- 
 taining a high power density in the jet 
 at the rock. Retaining high power densi- 
 ty on typical mining machines is not al- 
 ways easy. 
 
 Typical mining machines using either 
 picks or disk cutters do not allow the 
 jet to be close to the cutting surface. 
 This has an adverse effect on the cutting 
 effectiveness of the jet, as illustrated 
 in figure 11. There is a dramatic de- 
 crease in depth with distance which ad- 
 versely affects performance. This can be 
 compensated for by increasing the jet 
 pressure or diameter. Increasing either 
 of these increases the power required for 
 the machine. An alternate approach is to 
 use small concentrations of polymer in 
 the jet. This has been demonstrated 3 to 
 increase jet coherence, and thus cutting 
 effect with distance is improved. This 
 could prove to be an efficient alterna- 
 tive to increasing the jet power and 
 still achieving the desired decrease in 
 cutting force. 
 
 In many mining machines only a portion 
 of the cutters are actually in contact 
 with the rock. Only a third of the cut- 
 ting bits shown on the shearer drum (fig. 
 12) are cutting at any one time; during 
 about two-thirds of the drum rotation the 
 cutters are in the air. If all the cut- 
 ters are continuously assisted with water 
 jets, two-thirds of the energy is wasted. 
 This problem can be eliminated by acti- 
 vating the jets as they come in contact 
 with the rock. This can be achieved by 
 
 o — 
 
 "•Hennecke, J., and L. Baumann. Jet As- 
 sisted Tunnel Boring in Coal-Measure 
 Strata. Paper in Fourth International 
 Symposium on Jet Cutting Technology 
 (Univ. Kent, Apr. 12-14, 1978). BHRA 
 Fluid Engineering, Cranfield, Bedford, 
 England, 1978, pp. J1 ff. 
 
 3 Franz, N. C. Fluid Additives for Im- 
 proving High Velocity Jet Cutting. Paper 
 in First International Symposium on Jet 
 Cutting Technology (Univ. Warwich, Apr. 
 5-7, 1972). BHRA Fluid Engineering, 
 Cranfield, Bedford, England, 1972, pp. A7 
 ff. 
 
 35 
 30 
 25 
 
 20 
 
 Pressure at orifice = 5,000 psi 
 Orifice diam = 10 mm 
 Traverse velocity - 61 mm/s 
 3-D nozzle 
 
 20 
 
 100 
 
 40 60 80 
 
 STANDOFF DISTANCE, mm 
 
 FIGURE 11. - Water-jet cutting effectiveness 
 with standoff. 
 
 120 
 
 FIGURE 12. - Cutting drum contact area with rock. 
 
 segmented valves , which supply water 
 to the segment of the head that is in 
 contact with the rock. Examples of each 
 are discussed below. 
 
 Flow Industries has 
 quencing system for a 
 header. The valving 
 figure 13. This particular 
 was designed so that 1 to 16 
 the head could be operated, 
 particular device was for 
 purposes, it had to operate 
 50,000 psi. The mode of operation 
 this particular system follows: 
 
 developed a se- 
 milling type road 
 system is shown in 
 arrangement 
 segments in 
 Since this 
 development 
 at up to 
 of 
 
84 
 
 O 
 
 o 
 
 o 
 
 o 
 
 o 
 
 o 
 
 o 
 
 o 
 
 FIGURE 13. - Selecting valving arrangement. 
 
 1. Pressure is applied to all the 
 valves. In this condition all the valves 
 are closed. 
 
 2. The desired segments in the valve 
 are opened to tank. This activates the 
 valves in that segment. 
 
 3. As the cutting head is rotated, the 
 valves get pressure as they leave the 
 sections that close the flow to the noz- 
 zles. At the same time, as new valves 
 enter the drained section, the valves are 
 opened. 
 
 The fluid from each on-off valve is 
 plumbed through the drive shaft to the 
 nozzles in the appropriate quadrant. 
 This is shown schematically in figure 14. 
 
 FIGURE 14. - Nozzle plumbing. 
 
85 
 
 The actual hardware has been built 
 and successfully tested. The equipment 
 is shown in figure 15. This segmental 
 control system is not practical in an 
 actual machine because of the flexibility 
 requirement . In an actual machine a far 
 simpler, smaller, and more maintainable 
 system can be developed. 
 
 A second approach to selective assist 
 is to mount control valves directly in 
 the cutter. Using such a device, the 
 jet is activated when the cutter is 
 loaded and shuts off when the load is 
 removed. The valve shown schematically 
 in figure 16 is opened by a fixed travel 
 of the cutter. The jet in this par- 
 ticular case is an integral part of the 
 cutter. 
 
 Both these control systems offer an ef- 
 ficient method of achieving the advan- 
 tages of water-jet assist while minimiz- 
 ing the power requirements and operator 
 safety and visibility. 
 
 FIGURE 15. - Actual hardware of phasing system. 
 
 High-pressure water 
 
 passage in bit 
 to nozzle 
 
 Force 
 
 W 
 
 ^-Trigger 
 V/ plate 
 
 Gap, closed by 
 bit travel 
 
 Cutting drum 
 
 High-pressure 
 water passage 
 
 in drum 
 
 FIGURE 16. - Pick-activated valve. 
 
86 
 
 CONCLUSIONS 
 
 Water jets used either alone, in com- 
 bination with mechanical cutting, or with 
 an entrained abrasive can effectively be 
 used in a mining operation. The reduc- 
 tion in cutting force, dust generation, 
 and machine vibration is beneficial for 
 continuous cutting operations. The abil- 
 ity to slot rock can lead to improved 
 blasting and ground control. Because of 
 the varying methods of applying water 
 jet, there is no good method of applica- 
 tion. To use this technique it is im- 
 portant to examine the entire mining sys- 
 tem. This allows for the opimum use of 
 improved equipment or technique for a 
 specific operation. 
 
 Once the area of application is identi- 
 fied from a system study, a parametric 
 
 evaluation is required to determine the 
 best operation conditions for the jet to 
 achieve the desired performance. It is 
 important to understand that no one oper- 
 ating condition meets all applications. 
 To take full advantage of water jet at 
 minimum energy consumption, it is neces- 
 sary to deliver the jet power with mini- 
 mum losses. In the case of many mining 
 machines sequencing valves must be used 
 to eliminate waste. 
 
 Water-jet technology is new to the min- 
 ing industry. The techniques and equip- 
 ment need to go from the laboratory into 
 the field. After experience is gained 
 with the equipment , optimization should 
 become a simpler process. 
 
 tVU.S. GPO: 1985-505-019/20,102 
 
 INT.-BU.OF MINES, PGH., PA. 28087 
 

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