A °y. 1 »'*.?- V vv ^IHl^ ' ^y A v -^ : C, iP "V 5 v/V - * «- V <£* • <> *'TVi* <0 f * A v -%. - ' A^ V 0°"°. ^ * \ 4? *^i£\ % & *T ,v v„ vTV.« .f4 V .7" A o > * j. <£„ t* •£SkV« ^ «<* ,>$«£-•- *. ^°«* V^' ****** : ^£°° * s > « o > ^ H °** ^^ : Jfev %,*♦ :*Mjfc* V>* Vifltt^ ^ ^ v /, ^v-^ ♦* ** <>.. *'...• A U ^V 4> . ^ ' • 4,, <:^ *o . » * .^ IC 883? Bureau of Mines Information Circular/1981 ^^^/(fixA Noise Control of Diesel-Powered Underground Mining Machines, 1979 Compiled by J. H. Daniel, J. A. Burks, R. C. Bartholomae, R. Madden, and E. E. Ungar UNITED STATES DEPARTMENT OF THE INTERIOR Ksj&cO JUtcfaj. &tA&*<*-> tf y?fao^. Information Circular 8837 Noise Control of Diesel-Powered Underground Mining Machines, 1979 Compiled by J. H. Daniel, J. A. Burks, R. C. Bartholomae, R. Madden, and E. E. Ungar UNITED STATES DEPARTMENT OF THE INTERIOR James G. Watt, Secretary BUREAU OF MINES if / A/z?f This publication has been cataloged as follows: Noise control of diesel-powered underground mining machines, 1979. (Information circular - Bureau of Mines ; 8837) Includes bibliographies- Supt. of Docs, no.: I 28-27:8837- 1. Mining machinery— Noise- 2- Diesel motor— Noise- 3- Noise- Physiological effect- I. Daniel, J. H. II. Series: United States- Bu* reau of Mines- Information circular ; 8837- TN295.U4 [TN345] 622s [622'.2l 8O607181 CONTENTS Page Abs tract 1 Introduction 1 Federal noise regulations 2 Machinery noise levels and worker exposure 3 Machine types and numbers in use 3 Noise doses and expo sure -weigh ted worker population 4 Noise control 5 General principles 5 Importance of attenuating dominant contributions 5 Major sources and paths 7 Reduction of noise of diesel-powered equipment 7 Airborne paths 7 S tructureborne paths 8 Machines quieted 8 Personnel vehicle 9 Source levels 9 Engine enclosure 10 Acoustically absorptive lining 11 Hole and crack sealing 12 Intake, fan, and exhaust noise 13 Results 15 Service experience 15 Load -haul -dump machine 16 Noise reduction package 17 Drive train 17 Engine 22 Cooling fan 26 Results 28 Service experience 28 Conclusions 29 ILLUSTRATIONS 1 . Getman dispatch vehicle . . . , 9 2. Sketch of removable partial engine enclosure 10 3. Removable panel for partial enclosure 11 4. Acoustic adsorption treatments 12 5. Examples of sealed holes and voids, operator vicinity 13 6 . Fan inlet modifications to prevent recirculation 14 7. Fan inlet configuration 14 8. Getman dispatch operator sound level--before and after quieting.... 15 9 . Load -haul-dump machine 16 10 . Transmission compartment cover 18 11. Transmission hood vibration isolation 19 12. Transmission front cover 20 13. Acoustical treatment for interior of fuel and water tank compartment 21 XI ILLUS TRATIONS - - Continued Page 14 . Torque converter cover 21 15. Absorptive materials applied to the interior of the torque converter compartment 22 16. Transmission vibration isolation mounting structure 23 17 . Engine enclosure , external view 23 18. Components of engine enclosure 24 19. Belly pan with cooling fan exhaust duct lining 25 20. Stiffening applied to engine frame rail 26 21. Baffle in lowered (left) and raised (right) positions 27 22. Quieted machine, shown underground at National Gypsum Mine 28 23. Comparison of above ground and underground sound pressure levels measured on load-haul-dump machines 28 TABLES 1. Permissible noise exposures 3 2. Numbers of machines found in use, by type and engine power 4 3. Typical worker-machine scenarios for noise impact over an 8-hour shift 6 4. Source levels on the Getman dispatch vehicle 10 5 . Source levels on the Wagner load -haul-dump machine 16 NOISE CONTROL OF DIESEL-POWERED UNDERGROUND MINING MACHINES, 1979 Compiled by J. H. Daniel, ] J. A. Burks, 2 R. C. Bartholomae, 3 R. Madden, 4 and E. E. Ungar 4 ABSTRACT This Bureau of Mines report presents results of a survey of underground mining equipment and of two demonstration programs showing the feasibility of quieting a load-haul-dump (LHD) machine and a personnel vehicle. Typical noise levels are presented for the major machine types used in underground mines, along with estimates of the noise overexposure of miners who operate or work near these machines. General principles of noise control are explained, and the application of these principles is illustrated in the description of modifications made to the LHD machine and the personnel vehi- cle. The noise control package installed on the personnel vehicle lowered its noise level by 14 dBA after 4 months of operation, and inspection of the LHD machine after 2% years of operation with the modifications showed its noise level 7 dBA lower than that of the unmodified machine. Noise dosimeter meas- urements indicated that both machines were in compiliance with Federal noise regulations for a typical shift. INTRODUCTION A great many machines currently used in underground metal and nonmetal mines are powered by diesel engines, which often produce relatively high levels of noise. Because Federal regulations limit the permissible noise exposure of personnel, the Bureau of Mines has sponsored studies to assess the noise exposure of workers from diesel-powered equipment and to demonstrate that engineering noise control of these machines is feasible. 1 Program manager, Branch of Health Research, Bureau of Mines, Washington, D.C. -Technical Project Officer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, Pa. Supervisory electrical engineer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, Pa. 4 ^Bolt, Beranek and Newman Inc. , Cambridge, Mass. 5 Federal Mine Safety and Health Act of 1977 (Public Law 95-164). This Information Circular summarizes the results of a survey of mining equipment and two demonstration programs that demonstrate the feasibility of quieting a load-haul-dump machine and a personnel vehicle. Details of each of these programs are available. FEDERAL NOISE REGULATIONS Miners are not usually exposed to the same noise level continuously; most commonly they experience noise levels that change throughout the working day. Since higher noise levels constitute more of a hearing hazard than lower ones, the effects of these different levels must be accounted for. The "noise dose" is a standard measure that accomplishes this accounting and also relates a worker's total noise exposure to the permissible limit. Federal regulations permit a worker to be exposed to a noise level of 90 dBA for 8 hours per day and prescribe a halving of the permissible expo- sure time for each 5-dBA increase in noise level, as shown in table 1. A miner who is exposed for C hours per day to a noise level for which the permitted exposure duration is T hours is considered to be subjected to a noise dose of C/T because of this exposure. Thus, a noise dose that exceeds 1.0 represents an excessive exposure, whereas a noise dose of less than 1.0 corresponds to an exposure that is within the permissible limits. 6 The following reports are available from the National Technical Information Service/ (NTIS) , Springfield, Va. (order by PB number) and for inspection (on open file) at the following facilities: Bureau of Mines— Denver , Colo. , Twin Cities, Minn. , Bruceton and Pittsburgh, Pa. , and Spokane, Wash. ; U.S. Dept. of Energy — Carbondale, 111., and Morgantown, W. Va. ; National Mine Health and Safety Academy, Beckley, W. Va. ; and National Library of Natural Resources, U.S. Dept. of the Interior, Washington, D. C. Huggins, G. G. , R. Madden, and B. S. Murray. Noise Control of an Underground Load-Haul-Dump Machine. BuMines Open File Rept. 125-78, July 1977, 79 pp. , contract HO262013; NTIS, PB 288 854/AS. Huggins, G. G. , and W. N. Patterson. Reducing the Operator Sound Level of a Mining Service Vehicle — A Demonstration Project. BuMines Open File Rept. 47-77, November 1975, 75 pp.; contract HO346046; NTIS PB 265 037/AS. Patterson, W. N. , G. G. Huggins, and A. G. Galaitsis. Noise of Diesel- Powered Underground Mining Equipment. Impact, Prediction, and Control. BuMines Open File Rept. 58-75, March 1975, 227 pp. ; contract HO346046; NTIS, PB 243 896/AS. TABLE 1 . - Permissible noise exposures Duration of exposure per day, hours Noise level, dBA 8 90 92 95 97 100 102 105 110 115 6 4 3 2 1.5 1 0.5 0.25 NOTE. --Noise levels are measured with a sound level meter set to slow response. Exposure to con- tinued levels above 115 dBA is not permitted. Values between those tabulated may be obtained from T = __§___,- 2(L-90)/5 where T denotes the daily exposure duration in hours and L the noise level in dBA. If a miner is exposed to different noise levels throughout the day, one may evaluate the miner's total noise dose simply by adding up all of the C/T values corresponding to the various noise levels. Commercially available instruments called noise dosimeters perform this dose evaluation automatically and continuously. MACHINERY NOISE LEVELS AND WORKER EXPOSURE Machine Types and Numbers in Use Discussions in 1975 with the regional offices of the Mine Safety and Health Administration, with State mining inspectors, and with major under- ground mine operators revealed that 2,638 specific pieces of diesel-powered equipment were being used in underground metal and nonmetal mines. This sur- vey did not cover all mines in the United States; however, extrapolation of the survey data leads to an estimate of about 4,000 for the total number of items in use. Table 2, which shows the distribution of the machines counted in the survey by type and engine power, indicates that more than 507 o of these machines had less than 100 hp and that load -haul -dump machines, ore trucks, and service trucks were the most prevalent. 7 For example, a person exposed to 90 dBA for 6 hours, to 100 dBA for 1 hour, and to 70 dBA for 1 hour per day receives a dose of (6/8) + (1/2) + = 1.25, and thus is overexposed. Similarly, a person exposed to 97 dBA for 1/4 hour, 95 dBA for 2 hours, 90 dBA for 3 hours per day, and to noise levels less than 90 dBA for the remainder of the working day receives a dose of (0.25/3) + (2/4) + (3/8) + = 0.958, and thus is not overexposed. TABLE 2. - Numbers of machines found in use, by type and engine power Types of equipment Under 100 hp 100-200 hp Over 200 hp Total Production machines: Load-haul-dumps 227 147 44 112 67 32 29 12 31 1 66 190 97 33 11 20 14 24 8 6 172 49 45 4 5 8 465 386 Front-end loaders 186 Jumbo drills Locomotives 149 78 Roof bolters and scalers Shuttle cars 52 43 Explosive buggies 36 Ram haulers 31 14 Tractor-trailer units 14 Total 702 469 283 1,454 Support Equipment: Personnel carriers 187 199 132 76 35 14 6 8 5 10 6 6 2 16 2 3 16 17 4 1 1 3 2 1 1 5 9 1 205 201 Tractors 132 80 Transit mixers and placers. . . . Motor graders 35 30 Dozers 24 17 Air compressors 15 Shotcrete machines 12 9 6 2 Total 686 63 19 768 165 170 81 416 Total 1,553 702 383 2,638 Noise Doses and Exposure-Weighted Worker Population Table 3 indicates the noise dose to which each type of machine typically subjects each operator and bystander. For each machine type, table 3 shows the typical engine power and the corresponding average noise levels at full speed (noisiest) operating conditions. The table also shows the fraction of its operating time during which a machine typically is used in its noisiest mode, and the fraction during which it is used in its next noisiest mode (called "reduced speed" in the table and assumed to be 5 dBA quieter than the full speed mode). For the remainder of the time, the machine is assumed to be used in a mode of operation that makes no contribution to the noise expo- sure of the workers. This time fraction information and the estimated total number of hours a machine is in use per shift, together with the aforementioned noise levels, permit one to estimate noise doses to which the machines subject nearby personnel. Also shown in table 3 are the numbers of operators and bystanders who usually work with each machine and the estimated number of machines in use. By adding, for a given machine type, the product of the number of operators and the operator noise dose to the product of the number of bystanders and the bystander noise dose, one finds the "exposure-weighted number of workers" for that machine. If one multiplies this number by the number of machines in use, one obtains the "expo sure -weigh ted population of workers" associated with that machine. The latter is a convenient measure of the noise exposure impact related to the given type of machine. One may conclude from table 3 that ore trucks and load-haul-dump machines have the predominant impact on personnel exposure, with personnel carriers, front-end loaders, service trucks, tractors, locomotives, shuttle cars, and air compressors (in that order) contributing to a lesser extent. The estimates shown in table 3 do not account for a worker's being exposed to noise from more than one machine at a time. Although two or more machines often are used in conjunction with each other, their operations usually are cyclic, so that only one is operating at its noisiest part of the cycle at any instant. Also, the nearest machine usually dominates a worker's exposure, so that neglecting the effects of the nearby machines results in errors in the exposure estimates that are smaller than those inherent in the data on which these estimates are based; thus, no significant error results from neglecting the effects of simultaneous exposure to more than one machine. NOISE CONTROL General Principles Importance of Attenuating Dominant Contributions In general, the noise from any one source reaches a person's ears via several paths, both direct airborne paths and reflections from various sur- faces; in addition, sound may propagate along or through structures (in the form of vibrations) . Just as repair of small holes in a leaking roof is use- less unless the large holes are closed off, reducing the noise of lesser sources and paths has practically no effect on a person's exposure unless the contributions from the dominant sources and paths are reduced. 8 An alternate method of obtaining noise dose data directly is to use a sta- tistically significant sample of noise dosimeter data. u 3 O o cd ft S •rl •i-l O a u o 154 CO O •H 54 tO 3 (U o CU 3 •H O cd e ■ u cu u o cd o •r-l a $ rJ rl O O u cd cd p g ~ 3 CD CO CU CO M a; 3 3 H ID -H p o 43 o cu o QJ X rt a o e I CD X X cdoj a (U o 54 •w 3 +j CO o O ctl P 54 X fn 0) m o co u U 0) CD 4*; I !-i 54 CU O p 4-i O CO I u u CU O O cd I >. 4J •r-l t-1 i-l M-l a, « £ o cd 43 co o -a co 3 43 a 3 O u x) O 0) 54 ft o 0) CO i-l P 3 S -f -H -I X 3 ra ^ e I T) TJ T)r4 > 3 3 3 PQ 4-) O 0) TJ CO CO ■— I 3 r-l O 1) 5-4 tfl c«>> 43 Cd I XI O S-i }-i C •rl CU O 3 O. ft 4-1 o >-. o cd co a) < > PQ QJ X 1-4 i-4 CO 0) (X D. a) 54 & x >, o o o H j: p u i-4 QJ Cd 43 4-> 6 O 3 H 3 I aj p x CJ Cd CD E XJ •i-l 5-4 4-1 - > 4-i nj 54 X i-l OJ 0) o CO v ~ / o 5-i a> M-l -i-l q-i cu E a. r-i •i-4 CD 3 X w o oj E 3 J2 •I-l 13 •rl s O O 00 O CM rs i— i is oo en o m i-i CM CN o co wo moi rl N NH O CM O & & S- ' S^ V— / on on on • • • o o o + + + oo in in m oo oo PQ xl m ■ on o + o m pq XJ m i on o + co o + oo o o in m m v£j m m m vo C3S CDS CT\ ex* 3 co cd •r-l E •* J co co r-4 5-1 CO OJ •H 5-1 60 CJJ Mr-4 3 •rl 5-1 54 -a oj CD r-l H O 4-1 Cd 43 4-) o E 3 3 43 cd 5^ OJ 4-1 CO 43 cd cu o > •h ;> i 0) 4J t4 54 -I O co O E o 4-1 O r-l CJ O p. cd O X >4 CO • 5-1 • CJ • •1-4 • 54 co 54 X cd o CJ 3 54 i-l 4J r-5 W hJ W H CQ X) 54 cd 54 cu t3 co 13 cu 3 3 cd •r-l 43 W O 54 cd cu C cu a a O -r-l CO > 54 54 CU CU P-l CO co 3 H 54 OJ 3 O 54 OJ FS O O £ •rl X CO q-t cu cd 54 co 43 B 3 O •rl QJ 4-1 43 X CJ cr) aj 3 a> 4-1 cu (J cd 54 P4 54 O a) CO o •rl IH M-l X M— 1 & 3 •H o < •r-l X) I—l pq cu X OJ CU 43 E rl o C3S •rl H H 0! CO Major Sources and Paths In diesel-powered mining equipment, the engine generally constitutes a major source of noise. Engine noise may come from the exhaust, the intake, and the casing (that is, the block and accessories attached to it); also, the cooling fan may be a significant noise source. The transmission, drive train, and hydraulic system also tend to be significant noise sources. Noise radiated from the various sources may reach the operator by propa- gation through the air, either directly or via reflections. In addition, vibrations produced by the engine and other mechanical components tend to travel through heavy structures, such as frame rails, to lighter structures that then radiate sound somewhat in the manner of a loudspeaker. The relative importance of the various noise sources and paths differs for different machine types and models. Reduction of Noise of Diesel-Powered Equipment In general, the noise exposure of a miner associated with a given machine may be reduced by obstructing the sound propagation between the important noise sources and the worker. Practical and economical considerations generally do not permit one to modify the primary noise sources or to replace them with quieter ones (except relatively early in the development cycle of new machines), Consequently, practical reduction of the noise of machines in use at mines gen- erally has obstruction of the propagation paths as its first concern. As mentioned previously, sound for a given source may reach a miner by propagation through the air, including reflections, and also by propagation along and through structures. Thus, one must deal with blocking the airborne paths and also the structural paths. Airborne Paths Full enclosures generally are the most efficient for obstructing the radia- tion of sound from such sources as engines or transmissions. The effective- ness of such an enclosure increases with the mass of its walls, and it is greater if some acoustically absorptive material is also placed within the enclosure. Where cooling or access requirements do not permit the use of complete enclosures, partial enclosures or barriers may be used. These tend to be considerably less effective than full enclosures, because they do not inter- fere with sound that is propagating in directions away from them or past their ends and that may then be reflected in the direction of concern. The effec- tiveness of a partial enclosure or barrier may be enhanced by placing acoustically absorptive material on the sides that face the noise sources. Because the noise reduction one obtains with a partial enclosure or barrier usually is not limited by the sound that passes through it, but by the sound that gets around it, increasing the barrier or enclosure mass (which reduces the sound passing through these structures) usually results in little addi- tional noise reduction. Mufflers are devices that obstruct the propagation of sound out of pipes or ducts, largely by reflecting some of the sound back toward the sources in such a way that the reflected pressure waves cancel the outgoing waves to a considerable extent. Engine exhaust mufflers must be matched to the engine so as to be effective accoustically, yet not produce excessive backpressure. Like mufflers, silencers obstruct the propagation of sound out of pipes or ducts (for example, out of air intakes). However, silencers work not by reflecting sound internally, but by absorbing sound. Thus, silencers gener- ally consist of acoustically lined pipes or ducts with baffles or louvers of acoustically absorptive material inside them. Silencers generally must be selected to provide the desired sound attenuation without excessive obstruc- tion of air flow. Structureborne Paths The propagation of vibrations along structures (vibrations that may cause structural surfaces to radiate sound in loudspeaker like fashion) usually may be obstructed efficiently by inserting vi'brat'ion- / isolation elements into the propagation path. Such elements typically need to be much softer than the structure they join; they may consist of rubber mounts placed between a vibrat- ing engine or transmission and its supports or of flexible hose inserted in a run of rigid hydraulic tubing. The remainder of this Information Circular discusses how these basic principles were applied to the noise control of two machines identified in the survey to be major contributors to the noise overexposure problem in under- ground metal and nonmetal mines. MACHINES QUIETED Diesel-powered machinery used in mines can be divided into two broad categories: loading/hauling equipment and service vehicles. Machines in both categories are noisy and numerous. The 1975 census showed that 2,200 loaders- haulers were being used in U.S. mines, and that 690 were load-haul-dump vehi- cles. Service vehicles--a term that covers all vehicles used to move personnel and equipment (lube trucks, maintenance vehicles, explosive trucks, drill carriers, and any vehicle that carries personnel are included) --ran a close second: 1,800 were in mines in 1975. The Bureau of Mines selected one machine from each of these categories for a demonstration of noise control feasibility. One was a load-haul -dump (LHD) machine, the other a personnel vehicle. Sound levels of both machines categories are high. Typical sound levels on LHD machines, measured at the operator's ear, reach 100 dBA. The average sound level of service vehicles is 96 dBA. FIGURE 1. - Getman dispatch vehicle. Personnel Vehicle A three-passenger Getman dispatch vehicle (fig. 1) was used in the noise control demonstration. This vehicle has two models , the other carrying 12 pas- sengers. Both models are the same size; the extra space on the three-passenger vehicle is used for material handling or as a portable maintenance -service facility. The vehicles are 18 ft long, with a wheelbase some- what over 9 ft. Power is supplied by a 45-hp, four- cylinder Deutz air-cooled diesel engine (Model F4L- 912W) through a four-speed manual transmission. Body metal is primarily 1/4-inch steel plate. The engine is located immediately to the operator's left, and, in the unquieted vehicles, the engine is fully exposed. Because of the exposed engine and the operator's closeness to it, the sound level at the operator's ear is considerably higher than in most service vehicles of similar horsepower. The measured sound level was 101 dBA at high idle, compared with an average 96' dBA for similar machines given in table 3. Source Levels Four different sources of noise contribute to the 101-dBA sound level at high idle of Getman dispatches : • Engine. • Intake. • Cooling fan. • Exhaus t . Measurements and diagnoses of these sources of noise indicating their levels are shown in table 4. The engine, then was by far the largest con- tributor to the total noise of the dispatch vehicle, with the intake and 9 Reference to specific makes or models of equipment is made for identification only and does not imply endorsement by the Bureau of Mines. 10 cooling fan about equal in contribution and the exhaust relatively unimpor- tant. 1 A noise control package was designed that included: Engine : • A barrier or partial enclosure around the engine. • An acoustically absorbent lining for the interior of the engine compartment. • Sealing for all holes and cracks in the engine enclosure. Intake: • Installation of a silencer in the intake line. Muffler: • Asbestos wrapping for the muffler shell. TABLE 4. - Source levels on the Getman dispatch vehicle Source Level, dBA Test condition Fan 100 89 90 <80 >High idle. - The fan received no specific noise control, because the enclosures would reduce fan, as well as engine noise. Engine Enclosure The engine partial enclosure is shown in fig- ures 2 and 3. It is con- structed of 1/8-inch-thick sheet metal. The larger door (approx- imately 6 -inch -square) pro- vides access to the oil dipstick (fig. 3B) , and the smaller door provides access to the oil filler cap (fig. 3C) . Gasket stripping was used on the edges of all panels , doors , and cover plates to ensure a tight seal. FIGURE 2. - Sketch of removable partial engine enclosure. 10 The contribution of the exhaust is low because the dispatch comes equipped with an exhaust muffler. 11 FIGURE 3. - Removable panel for partial enclos- ure. A, Enclosure; B, oil dipstick access; C, oil filler access. Although the prototype enclosure was bolted to the Getman dispatch, similar enclosures could be attached by quick-release fasteners to cut down maintenance time . Acoustically Absorptive Lining The engine compartment of the Getman dispatch was lined with acous- tically absorptive materials — fiberglass and polyure thane foam 11 in equal parts--to prevent the sound level from building up because of repeated reflec- tions of noise within the engine space. In addition, plastic foam was applied to the underside of the canopy, over the operator's head. These treatments are illustrated in figure 4. The film-wrapped fiberglass was held to the surface of the machine by the expanded grating, which in turn was bolted to the machine. i:L Although the polyurethane foam does meet the acoustic requirements, it has an exceptionally high flame spread index and emits toxic fumes when burned. It is therefore recommended that future treatments use more suitable mate- rials, such as fiberglass. 12 FIGURE 4. - Acoustic adsorption treatments. A, Fiberglass under engine head; B, foam in rear engine compartment; C , foam under operator canopy. Hole and Crack Sealing Great care was taken to seal all holes and cracks in the structure around the operator to make sure no engine noise would leak through. Figure 5 illustrates this meticulous sealing, including: • A rubber boot around the shift lever. • A steel cover plate bolted over a hole in the panel to the operator's immediate left. • A cover plate over a hole on the rear of the transmission and battery compartment. In general, any opening one-fourth inch or larger was considered a "hole", and was sealed with a steel plate to which gasket stripping had been applied. 13 Boot around gear shift Battery compartment covered Gap in rear of panel sealed Hole on operator's left sealed FIGURE 5. - Examples of sealed holes and voids, operator vicinity. Intake, Fan, and Exhaust Noise To cut air intake noise, a standard cylindrical silencer was installed between the air cleaner and the engine. This installation involved moving the filter a few feet toward the rear of the vehicle and bolting the air cleaner to the frame. The muffler was wrapped with asbestos. Since air recirculation within the enclosure could cause overheating, a metal panel and cowling were installed on the front of the engine hood. As figure 6 shows, cooling air entered the fan opening front, passed by the cylinder fins, and exited to the left of the engine. Components of the fan inlet are shown in figure 7 . 14 Entering cool air Metal panel to prevent recirculation (dashed arrow) Exiting warm air FIGURE 6. - Fan inlet modifications to prevent recirculation. Existing fan cowling Rubber transition piece FIGURE 7. - Fan inlet configuration. 15 Results When it was completely installed, the noise control package — engine enclosure, acoustically absorbent lining in the engine compartment, sealing, intake silencer, and asbestos wrapping of the muffler — cut the noise of the Getman dispatch by 14 dBA. Without the quieting package, the overall sound level of the dispatch was measured as 101 dBA; after quieting, it was meas- ured as 87 dBA. Figure 8 shows spectra recorded before and after the treat- ment. Measurements in both cases were taken to the right of the operator's right ear, with the engine at high idle. Service Experience Four months after the Getman dispatch had been put in service at International Salt's Detroit Mine, the vehicle had been used for 60 to 70 hours and had received typical periodic maintenance (engine oil change, fil- ter changes, tuneup, etc.). There had been no noticeable change in the acous- tics of the dispatch; it was as quiet as when the noise reduction package was first applied. Mine workers said they preferred to drive the demonstration vehicle "because it was quieter." They suggested that quick-release fasteners be applied to the partial enclosure, which must be removed for preventive mainte- nance every 3 months or whenever repairs are made on the engine. 100 0. a. o CM DQ "O "3 > "O c 3 O w TJ ♦* JZ. O) '55 < •a c CD J2 0) > CU u O m 90 - 80 - 70 60 50 40 i — r 1 — r t — r ~i — r T — r Overall A-weighted level j i_ 16 31.5 63 125 250 500 1,000 2,000 4,000 8,000 16,000 31,500 1/3 Octave band center frequency, Hz FIGURE 8. - Getman dispatch operator sound level— before and after quieting. 16 f>/" m FIGURE 9. - Load-haul-dump machine. Load -Haul -Dump Machine The Wagner ST-5A Scooptram (fig. 9) is one of the most widely used load- haul-dump (LHD) machines in underground mining. It is a low-profile loader, 67 inches high, with a 5-cu-yd bucket mounted on the front. Just to the rear of the bucket is the center-articulated steering wheel, which allows short- radius turns in mines. The driver sits at the side of the aft section of the vehicle, facing inward, since the vehicle has the same tram capabilities in either forward or reverse. Also located on the aft section is the air-cooled diesel engine, the torque converter, and the transmission. The diesel engine of the ST-5A is a Deutz 8-cylinder Model F8L-714, rated by the Bureau of Mines at 180 hp at 2,300 rpm. A single-stage Clark Model C-8402 torque converter is connected directly to the engine. A shaft from the torque converter drives the 4-speed Clark Model 3421 transmission, which in turn drives the front and rear differentials . Major sources of noise were-- • Drive train. • Engine. • Cooling fan. • Intake and exhaust. Measurements of these sources of noise indicating their levels (at the opera- tor's ear) are shown in table 5. TABLE 5. - Source levels on the Wagner load-haul-dump machine Source Level , dBA Test condition Drive train. 101 97 94 90 93 Rated speed in 4th gear. ^High idle. Torque converter stall. 17 Noise Reduction Package Two noise sources--the intake and the exhaust--were eliminated from further consideration. The air intake was eliminated because its noise level was already low; the exhaust was eliminated because its principal contribu- tion was in the low-frequency range and because noise reduction would have required designing a completely new muffler. The drive train, engine, and fan were left as noise sources to be quieted. The package from them included: Drive train: • Sealing holes in operator compartment. • Transmission compartment cover. • Cover on water and fuel tank. • Acoustically absorbent lining in water and fuel tank compartment. • Acoustically absorbent lining in torque converter compartment. • Cover over torque converter. • Vibration isolation of transmission. Engine : • Enclosure. • Stiffening of frame rail. Cooling fan: • Baffle on grill. • Sealing of fan area. Drive Train The principal hole that needed sealing was around the steering column. It was sealed with a shroud with an elongated hole through which the steering column can pass and can also move to the three positions. The shroud was bolted through a gasket to the existing structure. FIGURE 10. - Transmission compartment cover. Covers (fig. 10) were installed around the transmission compartment. The interior surface was lined with 1-inch- thick 2-lb/cu-ft polyure thane foam with 0.0005-inch- thick aluminized Mylar facing. The facing was covered with a 22-gage (0.031-inch) perforated steel sheet with 51% open area. These layers were held together with studs welded to the cover plate and capped with washers and nuts . The transmission hood was vibration-isolated from the main structure of the LHD at the hinge by a rubber washer, as shown in figure 11. In addition, a rubber strip, 1/4 inch thick and 1 inch wide, was glued to the other three sides of the cover. 19 1/4" ID x 1/2" OD hose, 1/2" long 1/4" UNC capscrew 1/4" Flat washer 1/8" thick x 1/2" IDx 1" OD Transmission hood 1/8" thick x 2" x 32" rubber 1/4" flat washer 1/4" lock washer 1/4" UNC nut FIGURE 11. - Transmission hood vibration isolation. The bottom of the transmission compartment was sealed with a belly pan made of 10-gage (0.139-inch) steel. A drain hole allowed transmission fluid to be emptied. Figure 12 shows the cover plate used to seal holes in the transmission compartment in the center, where the machine is pivoted. The cover was made of 10-gage steel and has 1/2 inch of polyurethane foam with 1/8-inch leaded rubber bounded to it. Another hole through which transmission noise leaked was the grate at the operator's feet. This was sealed by welding a plate underneath the grate. The water and fuel tank cover, noisy because of vibration, was quieted by adding a second cover. The second cover was vibration-isolated as shown in figure 13; it was made of 10-gage steel, with 1/2 inch of polyurethane 20 FIGURE 12. - Transmission front cover. 21 T3 o T— b CM Q CO t UJ q co i- i g ~> ! ;£ CM CM 00 ;£ CM *~ CO CM CM 1 q CO o -o c a "a; 3 *-+- *^_ o i— o 1_ CD c 1_ . o ■•— Li c E E •*— a -i— r> u E L- o -f- u n _* o c u •*- t/) 3 (1) U u D < £ LU ZD O 22 foam and 1/8-inch leaded rubber bonded to it for acoustical absorption and mass addition. The interior of the water and fuel tank compartment was treated with acoustical absorption material, as shown in figure 13. Approximately 14 sq ft of the 1-inch-thick Mylar-faced polyurethane foam was stud-welded to the front, back, and side surfaces. The torque converter was quieted with a 10-gage steel cover (fig. 14), to which 1-inch-thick Mylar-faced polyurethane foam was stud-welded. Large but- tons covered the studs and held the acoustical material in place. The interior of the torque converter compartment was lined with acousti- cal absorption material (fig. 15). Approximately 22 sq ft of the Mylar-faced polyurethane foam was stud-welded to the front, back, side, and top surfaces. Structureborne noise from the transmission was controlled by installing two Huntington M700 vibration mounts (nominal load capacity: 900 lb) on the transmission (weight: 1,100 lb), at the points where the transmission was hard -mounted to the main structure of the machine. The transmission vibration- isolation mounting strUc ture is shown in figure 16. Engine The diesel engine was quieted with an enclosure (fig. 17) that consisted of a hood, side panels, and belly pan with ducts for cooling air exhaust. Figure 18 shows the parts of the enclosure. When the air-cooled engine was FIGURE 15. - Absorptive materials applied to the interior of the torque converter compartment. 23 ■p - ■ en c ^ 24 FIGURE 18. - Components of engine enclosure. A, Hood; B, left side enclosure; C, right side enclosure; I), belly pan and cooling air exhaust ducts. 25 enclosed, there is a potential for overheating. Cooling capacity was evalua- ted during two sets of experiments. A prototype enclosure with a lined exhaust duct was designed and built, then tested by noise control engineers and also by Deutz, the manufacturers of the engine. Both groups approved the enclosure design as having sufficient cooling capacity for the engine. The hood of the engine enclosure (fig. 18A) was made of 10-gage steel hinged to the main structure, with rubber gasketing material applied to the edges to vibration isolate it from the frame of the LHD. It was lined with 1-inch- thick polyure thane foam with 0.0005-inch aluminized Mylar facing pro- tected by perforated steel. The left- and right-hand enclosures (figs. 18B and 18C) are also 10-gage steel with 2-inch- thick polyurethane foam with Mylar facing held on with studs and buttons . So that miners could reach the engine, the side enclosures were designed with removable sections attached to the fixed sections with hexhead bolts. Duct lining FIGURE 19. - Belly pan with cooling fan exhaust duct lining. 26 The belly pan and its cooling air exhaust ducts are shown in figure 18D. The pan was made of 5/8-inch-thick steel with two cutouts for exhausting the cooling air. The cutouts provided a total exhaust area of 4.7 sq ft. Fig- ure 19 shows the design of the lined ducts inside the engine enclosure. The ducts were made as separate pieces, were bolted to the belly pan, and were lined with 1-inch- thick , 2-lb/cu-ft polyurethane foam with 0.0005-inch aluminized Mylar protected by 22-gage perforated steel sheet. Structureborne noise from the engine was quieted by stiffening the frame rail. Triangular gussets, 6- by 6- by 1/2-inch, were welded to the ends of the frame rails, as shown in figure 20. Cooling Fan Figure 21 shows the treatments used to quiet the cooling fan. They included (1) sealing the entire area around the fan with 1-inch polyurethane foam with 0.0005-inch aluminized Mylar stud-welded to the structure and (2) placing a baffle on the fan grille. The baffle was covered with 1-inch polyurethane foam that "was covered, in turn, with 22-gage perforated steel plate. Engine frame rail 3" x 3" x 1 / 2 " S\ Stiffening gusset 6" x 6" x y 2 " FIGURE 20. - Stiffening applied to engine frame rail. 27 I/) o Q. c o -o o D CD CNI UJ Z> O LL 28 FIGURE 22. - Quieted machine, shown underground at National Gypsum Mine. © CM 00 ■o "53 > T3 C 3 O (/> "O 09 "5 < ■a c ro .0 > ro u O 100 90 80 70 - 60 50 - 40 i i | i r— [— l i — | — i— i— | — i i | — i — 1—| — i — r— ] — r Outdoors at Wagner dBA before noise reduction Before " After _i L j L Outdoors at National Gypsum Mine after noise . reduction J L JL I ■ ■ I 63 125 250 500 1,000 2,000 4,000 8,000 16,000 1/3 Octave band center frequency, Hz IGURE 23. - Comparison of above ground and underground sound pressure levels measured on load-haul- dump machines. Results The quieted machine is shown (fig. 22) underground at the National Gypsum Mine in Shoals, Ind. A compari- son of the spectra measured aboveground before and after noise control is presented in figure 23. In all cases, the measurement was made near the operator's right ear with the engine at high idle. Noise dosimeter meas- urements made by the Mine Safety and Health Administra- tion (MSHA) indicate that the machine is in compliance when operated underground. Service Experience Sixty days after the machine was placed in ser- vice, a second, set of noise 29 measurements was made. There was no noticeable change in the acoustical per- formance of the machine. Mine employees reported that the noise control treatments were intact and performing as expected, indicating that the treatments were sufficiently practical for the use they underwent in the mine. A visit to the mine in March 1979 showed that all treatments are still intact after 2-1/2 years of service experience. Acoustical measurements at that time indicated no degrada- tion of the performance of the noise control. (As a result of this program, the manufacturer was encouraged to offer an optional quieting package at the time of purchase.) CONCLUSIONS The major contributors to the noise overexposure of underground metal and nonmetal miners by diesel-powered equipment were identified as load-haul- dump machines and ore trucks in the production category and personnel carriers in the support equipment category. The Bureau of Mines selected one piece of equipment from each of these categories for a demonstration of the feasibility of noise control. A load-haul-dump machine was selected to represent the pro- duction category; the model chosen, a Wagner ST-5A Scooptram , was quieted by 7 dBA at the operator's position. The selected personnel carrier, an air- cooled Getman dispatch, was quieted by 14 dBA at the operator's position. Both machines were quieted to a point where they are in compliance with Fed- eral noise regulations for typical operations , and treatments on both machines are sufficiently durable to endure the mining environment. The techniques used in these demonstration programs are also applicable to the noise control of other diesel-powered underground mining machines. Mine personnel interested in implementing such noise control treatments on these machines or on others are encouraged to obtain copies of the contract reports (see footnote 6). irU.S. GOVERNMENT PRINTING OFFICE: 1981-703-002/02 int.-bu.of mines,pgh.,p a. 25163 Hjii 1 *lStLr* ^ ••••' *v *> ;•: \s :'M£-: \j> /me-. %<** .vsste. v c * v .fctei-, o_ * • A V< %. ■••»•■♦•' V^V v™>* v-IIPv % •$m: ./\ -•«• . ** v % . f» : .^ --jkk. : ^% o > °-*. *'7VT* .A ^ <• * ..».'•« « 6 o >° ... v^'^ %^^/ v-^>" v*-- t %° ;.\ c<.^^>o **.£&% /.^gjfc.% S\ti£L-\ -o*..-..t ** v % J *<♦•**&:%„ '"-^ii. - /••i-^i-\ B ^BKk r «"<* -MMM." ^f 'Mam*' ^^ • .6* V 'b^ ^o* *-♦♦ ..ab\ %/ ,^& v* .jbj. \/ ,v^, v** .-M"- \ •/ v^V < \^^-/ v-^v v-^ n ° ,4* . 3t> A* * 4 P* , r ^ at — *^-*v 4* •ilV "^6 V- v«t C.vf> *.,»• .^ *bv* < v °4» * • " ° " aV '<$>■» .V^> •>° \^- % \* h v^^* 4 / v*^?\, o • » • A iP *»s » '^^J^^ • 4o A V t *i^% o. ^-^.•y V'- T 'V ^-^Rf-o^ LIBRARY BINOINO O . ^ ^*> * /% 4^V;\°- % * '"" c" / i v - « • V .♦1m>L'* o. * V » AV