Assessment of heavy earth-moving machinery noise vis-a-vis routine maintenance

64 Noise Control Eng. J. 54 (2), 2006 Mar–Apr

Assessment of heavy earth-moving machinery noise vis-à-vis routine maintenance

Harsha Vardhana), N.C.Karmakarb) and Y.V.Raoc)

(Received 2005 August 24; revised 2005 November 08; accepted 2005 November 09)

Exposure to noise from various types of equipment/machinery has been identified as a critical health hazard for personnel working in the Indian mining industry. Heavy Earth Moving Machinery (HEMM) used in mines has been identified as a major source of noise, and several earlier investigators have proposed various types of retrofit measures on these machines to reduce noise. The present work was taken up with the objective of evaluating the noise generation characteristics of HEMM as influenced by periodic maintenance. Detailed noise measurements were carried out in a large open pit coal mine located in India. The effect of maintenance on noise production was assessed for ten dumpers and three dozers by measuring the A-weighted one-third-octave band sound pressure levels after the machines had been subjected to maintenance at the end of 300 hours, 500 hours, 750 hours and 1000 hours of use. Measurements were also carried out to assess the effect of maintaining specific HEMM systems noise characteristics at 1000 hours. Assessment of sound pressure levels at each periodic maintenance revealed major sound level reductions with 1000 hours maintenance. The data also identified the major noise generating systems in HEMM as air systems, exhaust systems, cooling systems and fuel systems. © 2006 Institute of Noise Control Engineering

Primary subject classification: 13.7; Secondary subject classification: 11.6

a) Department of Mining Engineering, National Institute of Technology Karnataka, Surathkal, P.O- Srinivasnagar, District- Mangalore (D.K), Pin- 575025, INDIA; email: [email protected]

b) Department of Mining Engineering, Institute of Technology, Banaras Hindu University, Varanasi; Pin- 221005, INDIA; email: [email protected]

c) Department of Mining Engineering, National Institute of Technology Karnataka, Surathkal, P.O- Srinivasnagar, District- Mangalore (D.K), Pin- 575025, INDIA; email: [email protected]

1 INTRODUCTION

Exposure to noise has been identified as one of the most critical health hazards for personnel working in the mining industry. The use of massive, powerful, and inherently noisy machines in various mining operations produces high sound levels by adding to sound produced by other equipment. A major cause for concern in India is that in many instances sound levels in surface mines exceed standards stipulated by regulatory authorities and lead to severe health-related impacts on mining personnel. Among the various types of machinery commonly used in the mining and quarrying industries, heavy earth moving machinery (HEMM) such as dumpers, heavy track dozers and front-end-loaders are known to be the major sources of noise1,2. Such machines are fitted with powerful diesel engine and utilize robust transmission systems and other accessories for mobility. These features combined with the combustion air intake, engine cooling fan and the combustion gas exhaust system give rise to extremely high sound levels. This noise is transmitted to the worker as airborne noise and to the operator as airborne as well as structure-borne noise. Continuous exposure to such high sound levels may have several undesirable impacts on the health of operators/workers3-11. In view of the critical nature of the problem, a number of earlier investigators have experimentally characterized noise emissions from HEMM and evaluated the efficiencies of

various retrofit treatments aimed at noise control. For instance, Daniel et al.12 evaluated the percentage of surface mine operators overexposed to noise from various types of HEMM and reported the following results: dozers- 24 %, loaders- 8.6%, haulers- 3.5 % and diesel powered shovels and draglines- 3.2 %. It was found that retrofit noise control treatments applied to dozers could reduce the overall A-weighted sound level at the operator’s position by 11.5 dB to 12 dB. Noise studies carried out by Barthalomae & Bobick13 confirm the results of Daniel et.al12. The A-weighted sound level was reported to be reduced by 6 dB on dozers by installing a windshield and a muffler and lining the underside of the falling object protective structure (FOPS) with sound absorption material. Sealing all openings and isolating dash and cowling from the vibrating engine reduced the sound level by 5.5 dB. After carrying out all the retrofit treatments, the study revealed an A-weighted sound level of 93 to 94 dB at the operator’s position in a dozer with FOPS structure only and 90 dB for dozer with cab. The most important retrofit noise control treatments applied on dozers included windshields, canopy absorption, and engine exhaust mufflers. Savich14 reported a 17-dB reduction in the A-weighted sound level when the operator’s cab was treated with foam-lead-foam material. A study carried out by Central Mining Research Station15, India, reports major noise sources in open pit mines as HEMM, engine exhausts, compressors, dozers and equipment workshops. The noise contour of different machines showed the A-weighted sound level to be 90 dB at a distance of 6 to 7 m from the machines. It was also reported that periodic maintenance or installation deficiency of HEMM does not contribute significantly to the high sound levels emitted by such machines. However, detailed results were not reported in support of this conclusion. Frequency analysis showed that the dominant sound energy was from 100 Hz to 1000 Hz in

65Noise Control Eng. J. 54 (2), 2006 Mar–Apr

case of drills, dumpers and dozers and in the range of 100 Hz to 2000 Hz in case of scrapers and pay loaders. Tomlinson16 suggested that noise from HEMM could be reduced substantially by using noise reduction kits, properly designed silencers, and noise absorbent acoustic panels attached to the sides of engine compartments and the radiator of cooling fans. A study carried out by Turner17 on scrapers revealed that the A-weighted sound level was reduced by 8 dB upon using exhaust silencers and noise absorbent, damped panels around the engine. Mukherjee18 studied the noise reducing properties of exhaust mufflers on dozers. The sound pressure levels stay consistent in the operator’s cab, whereas the sound level at different distances from the machine showed some reduction. The authors attributed this finding to the fact that noise from various machine components gets transmitted through the floor and sides of the cab to the operator. Tests were also carried out to study the noise reducing properties of acoustically treated cabs for front-end-loaders and dozers. Their results indicated 10-dB and 11-dB attenuations of the A-weighted sound level in-cab for front-end-loaders and dozers respectively. Srinivas and Rao19 also reported some positive results of retrofit noise control treatment on dozers and front-end-loaders using exhaust silencers, and acoustically treated cabs. Mukhopadhyay and Dey20,21 suggested using exhaust silencers and fitting of acoustic panels to the rear dump trucks to reduce HEMM noise. Vardhan et al.22 carried out a detailed study on the noise characteristics of HEMM with a 1000-hour maintenance schedule. The study was carried out on dumpers, dozers, drill machines, rope shovels and hydraulic shovels. Their study indicated a substantial reduction in sound pressure level with a 1000-hour maintenance schedule. A study on a total of eleven power tools, including drills, angle grinders, sanders, a circular saw and a planer, compared the sound levels ‘before’ and ‘after’ routine servicing at a commercial power tool service center in Western Australia by WorkSafe23.The average sound level at 0.5 m distance from all the machines before maintenance was 94 dB(A) and it was reduced to 92 dB(A) after maintenance. The noise reductions were up to 7 dB(A). A similar study on air compressor noise before and after maintenance indicated noise reduction on the order of 7 dB(A) at 1 m distance from the compressor indicating the importance of maintenance. Another study by Vardhan et al.24 was carried out to investigate the principal sources of sound from heavy earth-moving machinery, namely a bulldozer and a front-end loader. Major sound sources were the exhaust and air inlet for the engines and the engine cooling fan on the bulldozer. Exhaust noise was an important source at nominal one-third-octave midband frequencies from 25 Hz to 250 Hz and air inlet noise was a significant contributor in the range of midband frequencies from 25 Hz to 500 Hz. Cooling fan noise for the bulldozer was important in the frequency range from 315 Hz to 3150 Hz. For the front-end loader, the enclosed cab in which the operator sits provided good noise reduction at frequencies greater than 400 Hz up to 20 kHz. It is evident from the above discussion that sound level reductions can be achieved through a variety of retrofit

treatments, albeit with varying degrees of success. However, few studies seem to have addressed the important role played by periodic maintenance of machinery on their noise generation characteristics. It is a well-known fact that the noise emitted from a machine is a cumulative effect of noise produced by its individual components. Accordingly, an overall noise reduction may be achieved through reduction of the noise generated by the component that gives the highest sound level. It is well known that two incoherent sources producing identical sound levels increase the total sound level by 3 dB and that if the difference in the sound levels of two sources is more than 9 dB, then total sound level remains almost the same as that of the higher source. Therefore, to attenuate the overall noise from a machine, it is imperative to reduce the sound level of the individual components that generate the most noise. It is anticipated that proper maintenance of any component would bring down the noise level emanated from it to the level of its new condition. Hence, the noise spectrum of any machine/component may serve as a guide to the maintenance crew. It is thus expected that detailed investigation of noise generation before and after every scheduled maintenance would play a significant role in noise abatement. The present study was taken up to understand and evaluate the effect of maintenance on noise production in HEMM through experimental measurements of sound levels in a large open pit coal mine located in India.

2 STUDY OBJECTIVES

The present study was taken up with the following objectives:- To study the impact of maintenance on noise characteristics

after performing periodic maintenance scheduled after 300 hours, 500 hours, 750 hours and 1000 hours of operation.

- To assess the effect of component/system maintenance of HEMM on noise characteristics with a 1000-hour maintenance schedule.

- To evolve guidelines based on noise spectrum analysis to determine whether a machine would require special maintenance prior to scheduled periodic maintenance.

3 STUDY AREA

The present study was carried out in an open pit coal project located in the southern state of Andhra Pradesh, India. The total extractable coal reserve is 39.28 million tons and the estimated life of the project is 25 years. The annual coal production target is 2 million tons. While the total project is spread over an area of 4,960,000 m2, the actual area of excavation is 2,260,000 m2. The mine has 6-workable seams, with average thicknesses of 5.00 m, 4.04 m, 1.37 m, 1.21 m, 11.74 m and 3.89 m. The total depth of the quarry is 220 m and the gradient of the seams vary from 1 in 4 to 1 in 6. To extract one ton of coal, it is estimated that 4.95 m3 of waste material must be removed. The total number of workers employed in the mine is 1058.


4 MEASUREMENTS

4.1 Instruments

Sound pressure levels were measured with a Larson-Davis model 814 integrating-averaging sound level meter. The instrument was equipped with a Larson Davis model 2540 condenser microphone mounted on a model PRM904 preamplifier. The microphone and preamplifier assembly were mounted directly on the sound level meter. The acoustical sensitivity of the sound level meter is checked once a year by the local manufacturers representative. For all measurements, the sound level meter was hand held. The instrument was set to measure A-weighted, time-averaged one-third-octave-band sound pressure levels. Nominal midband frequencies ranged from 25 Hz to 20 kHz. For each measurement, the sound level meter was set for an averaging time of 2 minutes. At the end of an averaging period, the time-averaged sound pressure levels were stored in the memory of the instrument and also transferred to a file on a laptop computer for subsequent data processing. For each test condition and at each microphone location, the spectrum of the sound was determined five times in relatively rapid succession while the operator maintained the engine at the desired speed. The energy average of the A-weighted one-third-octave-band sound pressure levels from each set of five measurements was computed to yield an average spectrum for each test condition for the range of nominal midband frequencies.

4.2 Machines under study

Although all types of HEMM are potential sources of noise, in this study the effect of periodic maintenance of machines on sound levels was confined to dumpers and dozers only. Noise assessment with periodic maintenance was carried out on ten 507 kW dumpers of 85 Te capacity. This study was also carried out on two 306 kW and one 239 kW dozers. Both the dumpers and dozers were manufactured by Bharat Earth Movers Limited, India. The dozers had roll over protective structure (ROPS) and no operator cab. All the dumpers had their total hours of work at start of measurement varying from 2500 hours to 3500 hours. Similarly, all of the three dozers selected for study had total hours of work of around 3000 hours. This ensured that all machines would have similar effects of age on sound levels.

4.3 Maintenance schedule of dozers and dumpers

4.3.1 Dozer maintenance schedule

The maintenance schedule of dozers included daily checks and periodic checks after every 300 hours, 500 hours, 750 hours and 1000 hours of operation. After 1000 hours maintenance, the whole schedule is repeated, i.e., 1300 hours, 1500 hours, 1750 hours, 2000 hours and so on. During every instance, maintenance is carried out on the air system, fuel system, cooling system, lubrication system, transmission system, steering system, hydraulic system, final drive,

undercarriage assembly, dozer attachment and instrument panel. The details of the 300-hour and 1000-hour maintenance schedules are shown in Table 1 and Table 2. The 500-hour and 750-hour maintenance schedules are similar to the 300-hour schedule and differ only in some respects. For instance, the maintenance of the fuel system, cooling system, lubrication system, hydraulic system, final drive, undercarriage, dozer attachment and instrument panel is the same for 300-hour, 500-hour and 750-hour maintenance. However, in the case of air system maintenance, the air intake piping hoses and clamps are checked at 300 hours, but not after 500 hours and 750 hours. During maintenance of the transmission system, all the gear shift linkages and ‘U’ joint were greased after 300 hours, but not after 500 hours and 750 hours. Similarly, all steering linkages were greased only after 300 hours. Major maintenance and overhauling of the equipment was carried out after every 1000 hours of use.

4.3.2 Dumper maintenance schedule

The maintenance schedule of the dumpers also included daily checks and periodic checks after every 300 hours, 500 hours, 750 hours and 1000 hours of operation. After 1000-hour maintenance, the whole schedule is repeated. The detail of the 300-hour maintenance schedule is given in Table 3. The details of the 500-hour, 750-hour and 1000-hour maintenance schedules are given in Table 4. Careful observation of these maintenance schedules indicate that, at each schedule the maintenance of the earlier schedules is repeated. In addition to this, some specific maintenance is also performed at that schedule. For instance, at 500 hours maintenance, the entire 300 hours maintenance is performed besides some other maintenance which is scheduled at 500 hours only. Similarly at 750 hours, all the maintenance steps of 300 hours and 500 hours are performed apart from some specific maintenance work which is scheduled at 750 hours only.

4.4 Methodology of noise measurement

As the purpose of the study was only to analyze machine generated noise and not the noise generated due to its activity, measurements were carried out under “raised condition (fast idle)” for both dozers and dumpers. In other words, measurements were made after the machine was switched on and at high idle under neutral condition, and the machine was not performing any activity. During measurements, it was ensured that no other noise generating activity was carried out in the vicinity of the machine. A-weighted one-third-octave band SPL measurements were performed from the operators’ position for 3-dozers starting from 750 hours of work up to 1000 hours at intervals of 50 hours. These measurements were also carried out on these machines before and after 300 hours, 500 hours, 750 hours and 1000 hours maintenance to find out which maintenance schedule resulted in the maximum reduction in sound pressure level. For the dumpers, the A-weighted one-third-octave band sound pressure levels were measured at a distance of 3 m in front of the machine. The measurements were carried out for 10 dumpers starting from 750 hours of work up to 1000 hours


at intervals of 50 hours. The measurements were also carried out on 3 dumpers before and after each periodic maintenance scheduled at 300 hours, 500 hours, 750 hours and 1000 hours, similar to the measurements on the dozers.

5 RESULTS AND DISCUSSION

In the discussion that follows, the sound levels in the figures were measured with the piece of equipment operating for an averaging time of 2 minutes. The sound levels in the tables (Table 5, Table 6, and Table 9 to Table 12) are the equivalent continuous levels measured over a period of time (60 minutes).

5.1 Noise assessment of dozer and dumpers with periodic maintenance schedules

5.1.1 Dozers

The A-weighted equivalent continuous sound levels of all the three dozers with various periodic maintenance schedules are given in Table 5. The variation in sound pressure level before and after 300 hours, 500 hours and 750 hours maintenance schedule was insignificant. It was below 1 dB for all cases except for dozer-1 and dozer-3 where a 1-dB

reduction of the A-weighted sound level was observed at the 500-hour maintenance schedule. The A-weighted one-third octave band spectrum of dozer-3 at 500 hours maintenance is shown in Fig. 1. The reductions in the sound pressure levels at most of the midband frequencies was between 1 to 2 dB. All the three dozers revealed a considerable reduction in A-weighted sound pressure level at 1000 hours maintenance schedule (dozer-1: 5.6 dB, dozer-2: 3.9 dB, dozer-3: 5.6 dB). The A-weighted one-third octave band spectrum of dozer-1 at 1000 hours maintenance schedule is shown in Fig. 2. The sound pressure level was found to decrease at almost all the midband frequencies. However, the reduction of sound level up to 40 Hz was low (1.0 to 1.6 dB). From 50 Hz to 20 kHz, the noise reduction in sound pressure level varied from 1.5 to 13.4 dB.

5.1.2 Dumpers

The result of equivalent sound pressure levels of all the three dumpers with various maintenance schedules are shown in Table 6. All the three dumpers revealed a higher dB reduction in sound level with the 1000-hour maintenance schedule. Careful observation of Table 6 shows that the changes in sound pressure level at 300 hours, 500 hours and 750 hours maintenance schedule are 1 dB or less, except for dumper-3, which had a reduction in sound level of 2.3 dB at 750 hours maintenance.

Table 1 — Three hundred hours maintenance checklist for dozers

AirSystemFuel

SystemCoolingSystem

Lubrication System

Trans-mission

SteeringSystem

FinalDriveUnder

CarriageDozer

AttachmentsHydraulic

SystemInstrument

Panel

Checkconditionof air filter andclean

orchangeifnecessary.

Checkaircleaner

housingfordamages.

Checkairintakepiping

hoses&clamps.

Checkfueltankcap&

strainer.

Checkfuel

strainer.

Checkwater

separatorfor

leakages.

Checkfuel filters ‘O’rings.

Checkthrottleslinkage.

Arrestallleakages.

CheckallV-belts&tightenifnecessary.

Checkconditionofallhosesandclampsforlooseness.

Arrestcoolantleakages.

ChangeCR/addCAC.

Checkradiatorpressurerelease

valveforfunction.

Checkifradiatorcapisprovidedwith rubber

sealing.

Changelubrica-tingoil.

Changelubrica-tingoilfilters & bypass

filters & ‘O’ring.

Cleanenginebreather.

Arrestall

leakages.

Changetrans-mission

oil filters & ‘O’ring.

Arrestalltrans-

missionoilleakages.

Checktrans-mission.oilfilter cap.

Checkandtopofftrans-missionoil

ifnecessary.

Greaseallgearshiftlinkages.

Grease‘U’joints.

Checksteering

levertravelLh & Rh.

CheckbrakepedaltravelLh & Rh.

Changesteeringoilfilter & ‘O’

ring.

Arrestallsteeringoilleakages.

Greaseallsteeringlinkages.

Check final driveoil

(Lh & Rh) &supplyifrequired.

Check final driveoilleakages.

Checksprocketsegment

teethbolts&nuts.

Check final drivecovers.

Checktrack

rollers,idlers&carrier

rollersforleakagescracksorwear out.

Checktracktensionandgreasethem

forloose.

Checkcarrierroller

mountingbolts.

Lubricate diagonal

bracefittings Lh

&RH

Lubricate bladecylindersupports Lh

&RH(4pointsoneachside).

Lubricate blade linkage(10

points).

Check wear outof

cuttingedges&endbits.

Checktiltpipingguards.

Checkblademountings.

Checkhydraulicoil

cap.

Checkhydraulic

oilleakagesfromhoses,linesblade

liftcylindersandtilt

cylinders.

Checkleakages

ifanyfrombladelift

servovalve&tiltservo

valve.

Checkhydraulicoilandtopupif

required.

Checkforfunction of:

Engineoilforgauge.

Torqueconverter

temperaturegauge

Tachohourmeter.

Watertemperature

gauge.


From Table 6, it is seen that the difference in sound level before and after 300 hours maintenance schedule for dumper-1 only is 0.8 dB. The A-weighted one-third octave band spectrum of dumper-1 at the 300-hour maintenance schedule is shown in Fig. 3. A considerable reduction on the order of 1.0 to 4.8 dB was observed in the sound pressure levels with midband frequencies from 1.6 kHz to 20 kHz. The sound pressure level reduction from 25 Hz to 1.25 kHz was from 0.0 to 1.9 dB. The results of the noise assessment of dumpers at the 300-hour maintenance schedule are similar to that of dozer equipment, wherein noise reduction at the 300-hour schedule was negligible. However, all three dumpers had a reduction in sound pressure levels at the higher midband frequencies. At the 500-hour maintenance schedule, the equivalent continuous sound level of dumper-1 decreased by 0.7 dB (Table 6). The one-third-octave band spectrum revealed reductions from 1.2 dB to 4.2 dB in the sound pressure levels with midband frequencies from 6.3 kHz to 20 kHz. Similar behavior was observed for dumper-2 and dumper-3. These results are in line with that of dozers where the sound level reductions at the 500-hour maintenance schedule were negligible. Similar to the 300-hour maintenance, the one-third-octave band spectrum of

the dumpers at the 500-hour schedule reveal sound pressure level reductions at higher midband frequencies. The reduction in the A-weighted equivalent continuous sound level at the 750-hour maintenance for dumper-3 was found to be 2.3 dB (Table 6). The one-third octave band spectrum of dumper-3 at the 750-hour maintenance is shown in Fig. 4. Considerable reductions were observed in the sound pressure levels with midband frequencies from 80 Hz to 200 Hz and 1 kHz to 8 kHz. The reduction in the sound pressure levels for this dumper at lower midband frequencies may be due to proper maintenance of the exhaust system as exhaust noise is predominant in the lower frequencies up to 250 Hz24 and the reductions from 1 kHz to 8 kHz may be due to cooling system maintenance24 and tightening of various loose components25. The one-third octave band spectrum of dumper-1 at the 1000-hour maintenance schedule is shown in Fig. 5. The reduction in the A-weighted equivalent continuous sound level of dumper-1 at the 1000-hour maintenance schedule was 7.4 dB (Table 6). The one-third-octave band spectrum showed significant reductions on the order of 1.7 to 9.6 dB in the sound pressure levels with midband frequencies from 25 Hz to 5 kHz. Beyond 5 kHz, the reductions were negligible

Table 2 — Thousand hours maintenance checklist for dozers

Airsystem Fuelsystem Coolingsystem Lubrication system Transmission Hydraulicsystem Undercarriage

Checkcondition

of air filter, changeifnecessary.

Checkaircleanerhousing

fordamages.

Checkairintakepiping

hoses&clamps.

Checkfueltankcap

&strainer.

Cleanfueltankbreather.

Check water separator

forleakages.

Checkfuelfilters

O-rings.

Checkthrottlelinkage.

Arrestallleakages.

CheckallV-belts&tightenifnecessary.

Checkconditionofallhosesandclamps

forlooseness.

Arrestcoolant

leakages.

Checkradiatorpressurerelease

valveforfunction.

Checkifradiatorcapisprovided

with rubber sealing.

Checklubricationoilcondition.

Changelubricationoil filters & bypass filters & O- ring.

Cleanenginebreather.Arrestallleakages.

Checklubricationoilfilters & check for any

material.

Changetransmissionoil filters & O- ring.

Changetransmissionoil, cut & see the filter.

Changesteeringoil filter.

Cleanmagneticstrainer.

Cleantorqueconverterstrainer

&arresttransmissionoilleakages.

Greaseallsteering&transmission

linkages.

Changehydraulicoil filter, cut & see the filter.

Changehydraulicoil.

Checkbladecontrollever

valveforleaksornoise.

Checkhydraulicpipinglift&

tiltforleakages.

Checkforproperclampingof

hydraulicpiping.

Checktiltpipingcovers&guardbolts&tighten

ifnecessary.

Arrestallhydraulicoilleakages.

Greasebladeattach-ments&linkages.

Checkrollers&idlers for wearout, crack&oilleaks.

Checktracktensionforlooseness,

tightness.

Checktrackshoebolts&nuts

forlooseness.

Change final driveoil.

Lubricate all greasepoints.

Drain & fill fresh oil inalltrackroller

idlers&carrierrollers.

Check wear of rollers, idlers.Checksprocket

teethbolts&nuts&tightenifnecessary.

All air system, fuel system, cooling system, lubrication system, exhaust system, hydraulic system, transmission system and grease system components must be checked and repaired/replaced if necessary.

Clean entire engine and conduct major overhauling of all the components. High pressure and soap water mixture preferred after spraying engine with cleanser, taking care of protecting electrical system.


(0.3 dB to 1.0 dB). The noise assessment at the 1000-hour schedule for dumper-2 and dumper-3 were similar to that of dumper-1.

5.2 Noise assessment of dozers and dumpers at thousand hours schedule by

maintaining different systems

Sound level measurements were performed by maintaining a particular system of the machine, then assembling it and taking the reading using the precision sound level meter. A set of eight test conditions was defined for each earth-moving machinery. Table 7 lists test conditions A-1 through A-8 for the measurements of the sound from the dozers; Table 8 lists test conditions B-1 through B-8 for the dumpers. This was done to find out which of the systems contribute to more noise. In other words, which of the systems, if maintained properly, may result in an overall sound level reduction of the machine. For each test condition, the machine was stationary with the transmission in neutral and engine speed maintained at ‘fast idle’. This analysis was carried out on three dozers and three dumpers.

Table 3 — Three hundred hours maintenance of 85 Te dumpers

Airsystem 1. Check and clean air filter. 2. Checkaircleanerhousingandcondition. 3. Check air intake piping, hoses and clamps. 4. Drainmoistureintheairtanksandchangeautomaticdrainvalve. 5. Check leakages if any and arrest them. 6. Checkthedifferentvalvesforproperreleasing.Fuelsystem 1. Checkfueltankcapandstrainer. 2. Check water separator for leakages. 3. Change fuel filters and ‘O’ rings. 4. Checkthrottlelinkages. 5. Clean fuel tank breather. 6. Checkforleakages. 7. Check fuel filter mounting bolts.Coolingsystem 1. AddCACliquid. 2. Maintain Ph value and PPM value. 3. Check radiator cap and strainer. 4. Check for any water leakages.Lubrication system 1. Changelubricatingoil. 2. Change lubricating oil filters and ‘O’ rings. 3. Cut and examine the removed filters. 4. Checkallleakages. 5. Change super bypass filters and ‘O’ rings.Exhaust system 1. Check exhaust piping for damages. 2. Check exhaust box for repairs. 3. Check turbo charger supply hose and drain hose.Hydraulicsystem 1. Checkhydraulicoillevelandaddoilifnecessary. 2. Checkbreatherelement,clean/change. 3. Check for any leakages. 4. Checksteeringandhoistoperations. 5. Check emergency steering.Fastening 1. Checkcabinmountingbolts. 2. Checkcoolermountingbolts.

3. Check bucket hinge pin lock bolts. 4. Checkhydraulictankanddieseltankmountingbolts. 5. Check hydraulic pump mounting bolts.Suspension 1. Checkfrontsuspensionlevels. 2. Checkrearsuspensionlevels.Auto fire suppression system 1. Checkpressureincylinders. 2. Checkthehoses.Transmissionsystem 1. Check transmission filter and ‘O’ ring. 2. Cut and examine the removed filters. 3. Check for leakages. 4. Checkthedrivebolts(frontandrear). 5. Check transmission mounting bolts. 6. Cleanbreather.Finaldriveanddifferential 1. Check the final drive oil level and top up if required. 2. Cleandifferentialbreather. 3. Check the differential bolts for looseness.Greasesystem 1. Fillgreaseinthecontainer. 2. Check the working of grease pump. 3. Check all the points and injectors for proper lubrication. 4. Arresttheleakages.5. Grease the following points manually: a. Frontpropellershaft,lubricate2-points. b. Rear propeller shaft, lubricate 5- points. c. Parking brake linkage, lubricate 2- points. d. Steering column, lubricate 3- points. e. Transmissionmounting,lubricate1-point. f. Damperbearing,lubricate1-point.Tyres 1. Check tyre inflation. 2. Check wheel bolts for loosening.Brakes 1. Checktheparkingbrakes. 2. Checkandtopupthebrakeoilinthecontainer.Checkthefun

5.2.1 Dozers

The A-weighted equivalent sound pressure level of dozers for these test conditions is shown in Table 9.

Air and exhaust system maintenance (Test condition A-2)

The air and exhaust system maintenance alone reduced the A-weighted equivalent continuous sound level from 1.0 dB for dozer-3 to 2.0 dB for dozer-1 (Table 9). The one-third octave band spectrum of dozer-1 after air and exhaust system maintenance alone is shown in Fig. 6. Considerable reductions on the order of 0.2 dB to 7.3 dB were observed in the sound pressure levels with midband frequencies from 50 to 200 Hz. Dozer-2 had a reduction in the A-weighted equivalent continuous sound level of 1.1 dB after air and exhaust system maintenance alone. The one-third octave band spectrum revealed reductions of 1.4 to 5.2 dB in the sound pressure levels with midband frequencies up to 200 Hz. Similarly, dozer-3 had a reduction of 1.0 dB in the A-weighted equivalent continuous sound pressure level after air and exhaust system maintenance alone and the SPL spectrum revealed the maximum sound


pressure level reduction (0.6 dB – 6.7 dB) with midband frequencies up to 200 Hz.

This shows that sound pressure levels at lower midband frequencies can be reduced by proper maintenance of air and exhaust systems.

Table 4 — Different maintenance schedule of 85 Te dumpers

500 hours 750 hours 1000 hours

1) Repeat all maintenance steps of ‘300 hours’ check.

2) Changeengineoil.3) Change engine full flow oil filter.4) Change turbo lubrication oil filter.5) Change lubricating oil by-pass-filter elementandringrectangular.6) Clean float tank and/ or main fuel tank

breather.7) CheckcoolantpHvalueandchromate

concentration.Checkconditionofmagnesiumplate.8) Checkoillevelinhydraulicgovernor,if

provided.9) Change fuel filter element, washer and ‘O’ringofmountingbolt.Fillcleandieselto

avoidhardstarting.10)Checkoilinaneroidcontrol,ifequipped.11)Checkandadjustbelts.12)Checkallaircleanerconnections/piping for cracks chafing etc. Tighten all air intakeconnections.13) Clean crankcase breather.14)Checkthrottlelinkage.15) Check and tighten foundation bolts and flexible coupling bolts of engine andalternator.16)Recordoilpressure.

1) Repeat all maintenance steps of ‘300 hours’ and ‘500 hours’ check.

2) CheckFanhubIdler,WaterpumpIdler.3) Clean and tighten all electrical

connection.4) Checkgeneratorbrushesand

commutators.5) Check aneroid adjustment.6) Replaceaneroidbreather.7) Check heat exchanger element for leaks/operation/performance.8) Checkaircleanerevacuatorvalve,

changeifrequired.9) Cleanradiator.10) Check air compressor. Blow air throughtheradiatorcoreinopposite

direction to the normal flow of air, if working under dusty/ dirty condition.11)Changehydraulicgovernoroil/aneroidoil.Checkshaftendclearance.12)Checkvibrationdamper.Check wobble and eccentricity. Discard damperifmisalignmentismorethan1/16inch.

1) Repeat all maintenance steps of 300 hours, 500 hours and 750 hours.2) Allairsystem,fuelsystem,coolingsystem,lubrication

system, exhaust system, hydraulic system, transmission systemandgreasesystemcomponentsmustbecheckedandrepaired/replacedifnecessary.

3) Change low pressure hydraulic oil filters.4) Cleanfueltankbreather.5) Remove, clean and dry engine crankcase breathers.6) Cleanandcalibrateallinjectors.Replacerockercover

gaskets.7) Replace fuel pump filter screen and magnet.8) Checkfuelpumpcalibration.9) Replace aneroid bellows and calibrate aneroid.10) Clean turbocharger compressor wheel and diffuser.11)Checkturbochargerbearingclearances.12) Check exhaust and inlet manifold nuts and cap screws.13) Tighten all mounting bolts and nuts.14) Check crankshaft and float.15) Change coolant and de-scale cooling system if required.16)Cleanentireengineandconductmajoroverhaulingof all the components. high pressure and soap water mixture preferred after spraying engine with cleanser, takingcareofprotectingelectricalsystem.

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Figure. 1—Effect on A-weighted one-third-octave band spectrum of dozer-3 at 500 hours maintenance schedule: ▲before maintenance; ● after maintenance

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Figure. 2 —Effect on A-weighted one-third-octave band spectrum of dozer-1 at 1000 hours maintenance schedule: ▲before maintenance; ● after maintenance


Table 5 — A-weighted equivalent continuous sound levels of dozers with periodic maintenance

Equipment A-weighted equivalent continuous sound level (Leq

),dB

300 hours maintenance 500 hours maintenance 750 hours maintenance 1000hoursmaintenance

Before After Before After Before After Before After

Dozer-1 95.8 95.7 97.4 96.4 98.2 97.7 100.6 95.0

Dozer-2 93.1 92.9 93.1 92.4 94.5 93.9 96.8 92.9

Dozer-3 95.2 94.8 95.8 94.8 97.2 96.6 100.4 94.8

Table 6 — A-weighted equivalent continuous sound level of dumpers with periodic maintenance

Equipment A-weighted equivalent continuous sound level (Leq

),dB

300 hours maintenance 500 hours maintenance 750 hours maintenance 1000hoursmaintenance

Before After Before After Before After Before After

Dumper-1 98.8 98.0 98.9 98.2 99.2 98.2 102.3 94.9

Dumper-2 98.0 97.5 98.1 97.6 99.2 98.5 103.7 96.4

Dumper-3 98.3 97.6 98.4 97.7 99.5 97.2 104.9 98.2

Fuel system maintenance (Test condition A-3)

The maintenance of the fuel system was carried out subsequent to air and exhaust system maintenance. The maintenance of fuel system reduced the A-weighted equivalent continuous sound level by 1.0 dB for dozer-1 to 1.4 dB for dozer-3 (Table 9 and Test conditions A-2 and A-3). Dozer-2 had a reduction of only 0.3 dB.

The one-third-octave band spectrum of dozer-1 revealed the maximum reduction (0.3 – 6.0 dB) in the sound pressure levels with midband frequencies from 25 Hz to 315 Hz (Fig. 7). Similarly, the one-third-octave band spectrum of dozer-2 had reductions on the order of 0.4 to 3.0 dB and dozer-3 had reductions on the order of 1 to 5 dB in the sound pressure levels with midband frequencies up to 315 Hz.

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Figure 3 —Effect on A-weighted one-third-octave band spectrum of dumper-1 at 300 hours maintenance schedule: ▲before maintenance; ● after maintenance

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Figure 4 —A-weighted one-third-octave band spectrum of dumper-3 at the 750 hour maintenance schedule: ▲before maintenance; ● after maintenance


Table 7 — Test condition for investigation of dozer sound level at 1000-hours maintenance

TestCondition

Measurementofsoundpressurelevel

Before1000hrs.

maintenance

AftermaintenanceofAfter

1000hrs.maintenance

Airandexhaust system

Fuelsystem

Coolingsystem

Lubrication system

Transmissionsystem

Hydraulicsystem

A1 √ X X X X X X X

A2 √ X X X X X X

A3 √ √ X X X X X

A4 √ √ √ X X X X

A5 √ √ √ √ X X X

A6 √ √ √ √ √ X X

A7 √ √ √ √ √ √ X

A8 √ √ √ √ √ √ √

√represents measurement of sound pressure level performed for that condition

Table 8 — Test condition for investigation of dumper sound level at 1000-hours maintenance

TestCondition

Measurementofsoundpressurelevel

Before1000hrs.

maintenance

Aftermaintenanceof After1000hrs.

maintenanceAirintake

systemFuelsystem

Coolingsystem

Lubrication system

Exhaust system

Hydraulicsystem

B1 √ X X X X X X XB2 √ X X X X X XB3 √ √ X X X X XB4 √ √ √ X X X XB5 √ √ √ √ X X XB6 √ √ √ √ √ X XB7 √ √ √ √ √ √ XB8 √ √ √ √ √ √ √

√ represents measurement of sound pressure level performed for that condition

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Figure 5 —A-weighted one-third-octave band spectrum of dumper-1 at 1000 hours maintenance schedule: ▲before mainte-nance; ● after maintenance

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Figure 6 —Effect on A-weighted one-third-octave band spectrum of dozer-1 at 1000 hours schedule after air and exhaust system maintenance (Test condition A-1 and A-2): ▲ before maintenance; ● after air and exhaust system maintenance


Table 9 — A-weighted equivalent continuous sound level of dozers at 1000 hours schedule under different test conditions

EquipmentA-weighted equivalent continuous sound level (dB) under various test conditions

A1 A2 A3 A4 A5 A6 A7 A8

Dozer-1 100.6 98.6 97.6 95.6 95.1 95.1 95.0 95.0

Dozer-2 96.8 95.7 95.3 93.9 93.1 93.1 92.9 92.9

Dozer-3 100.4 99.4 98.0 95.1 94.9 94.8 94.8 94.8

Table 10 — A-weighted equivalent continuous sound level of dumpers at 1000 hours maintenance under different test conditions

EquipmentA-weighted equivalent continuous sound level (dB) under various test conditions

B1 B2 B3 B4 B5 B6 B7 B8

Dumper-1 102.3 101.0 99.2 97.5 97.4 95.0 95.0 94.9

Dumper-2 103.7 101.9 100.2 98.9 98.9 96.5 96.5 96.4

Dumper-3 104.9 103.2 101.6 100.0 100.0 98.2 98.2 98.2

Table 11 — A-weighted equivalent continuous sound level of dozers with different hours of work

EquipmentA-weighted equivalent continuous sound level (dB)

750 hours maintenance800hours 850 hours 900hours 950 hours

1000hoursmaintenance

Before After Before After

Dozer-1 98.3 97.7 98.1 98.3 99.2 99.8 100.6 95.0

Dozer-2 94.5 93.9 94.9 95.2 95.3 96.4 96.8 92.9

Dozer-3 97.2 96.6 97.2 97.4 97.8 100.0 100.4 94.8

Cooling system maintenance (Test condition A-4)

Cooling system maintenance was performed subsequent to air, exhaust and fuel systems. The maintenance of cooling system reduced the A-weighted equivalent sound pressure level by an additional 1.4 dB for dozer-2 and 2.9 dB for dozer-3. The sound pressure level reductions for dozer-1 after cooling system maintenance was on the order of 1 to 4 dB in the sound pressure levels with midband frequencies from 100 Hz to 5 kHz (Fig. 8). Dozer-2 had reductions on the order of 1.2 to 5.0 dB in the sound pressure levels with midband frequencies from 400 Hz to 2.5 kHz. The one-third-octave band spectrum of dozer-3 revealed reductions on the order of 1.6 dB to 5.0 dB in the sound pressure levels with midband frequencies from 100 Hz to 5 kHz.

Lubrication, transmission and hydraulic system maintenance (Test condition A-5, A-6, A-7)

The maintenance of the lubrication, transmission and hydraulic systems did not reveal a significant reduction in the sound levels. The one-third octave band data of dozer-1 after maintenance of the lubrication system revealed a small reduction in the sound pressure levels in the midband frequencies from 5 kHz to 10 kHz. Similar results were observed for the other dozers too.

5.2.2 Dumpers

The A-weighted equivalent continuous sound levels for the three dumpers for all the test conditions (B-1 to B-8) are shown in Table 10.

Air system maintenance (Test condition B-2)

The A-weighted equivalent continuous sound level after maintenance of the air intake system alone was reduced by 1.3 dB for dumper-1 to 1.8 dB for dumper-2 (Table 10 and Test conditions B-1 and B-2). The one-third-octave band spectrum of dumper-1 after air intake system maintenance revealed the maximum reduction (0.8 – 2.7 dB) in the sound pressure levels with midband frequencies from 25 Hz to 200 Hz (Fig. 9). The sound pressure level of dumper-2 was reduced from 1.1 dB to 2.3 dB and that of dumper-3 from 1.2 dB to 2.4 dB in the midband frequencies up to 200 Hz. The results indicate that proper maintenance of the air intake system can reduce the sound level significantly in the lower midband frequencies up to 200 Hz.

Fuel system maintenance (Test condition B-3)

The fuel system was maintained subsequent to the air intake system. The A-weighted equivalent continuous sound level after fuel system maintenance was further reduced by


1.5 dB for dumper-3 to 1.8 dB for dumper-1 (Table 10 and Test conditions B-2 and B-3). The one-third-octave band spectrum of dumper-1 after maintenance of the fuel system revealed the maximum reduction (1.0 dB – 2.4 dB) of the

sound pressure levels with midband frequencies from 25 Hz to 315 Hz (Fig. 10). For similar test conditions, dumper-2 and dumper-3 revealed a reduction on the order of 0.4 to 2.7 dB and 1.0 to 2.3 dB, respectively, in the sound pressure levels with midband frequencies up to 315 Hz. This shows that fuel system maintenance can reduce the sound level significantly in the midband frequencies up to 315 Hz. Cooling system maintenance (Test condition B-4)

The maintenance of the cooling system reduced the A-weighted equivalent continuous sound level by 1.3 dB for dumper-2 to 1.7 dB for dumper-1 (Table 10 and Test conditions B-3 and B-4). The one-third-octave band data of all the three dumpers after maintenance of the cooling system revealed the maximum sound level reduction occurred in the midband frequencies from 125 Hz to 5 kHz. In this frequency range, dumper-1, dumper-2 and dumper-3 had a sound pressure level reductions of 0.6 – 2.8 dB, 1 – 3 dB and 1.2 – 2.4 dB respectively. At all other frequencies, the reductions were negligible. The one-third-octave band spectrum of dumper-1 after cooling system maintenance is shown in Fig. 11. Cooling system maintenance can, therefore, reduce the sound pressure levels in the midband frequencies from 125 Hz to 5 kHz.

Lubrication system maintenance (Test condition B-5)

A minute reduction in the equivalent continuous sound level after maintenance of the lubrication system was observed. It varied from 0.0 dB for dumper-3 to 0.1 dB for dumper-1 (Table 10 and Test conditions B-4 and B-5).

Figure 7 —Effect on A-weighted one-third-octave band spectrum of dozer-1 at 1000 hours schedule after air, exhaust and fuel system maintenance (Test condition A-2 and A-3): ▲ air and exhaust system maintenance; ● air and exhaust + fuel system maintenance

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Figure 8 —Effect on A-weighted one-third-octave band spectrum of dozer-1 at 1000 hours schedule after cooling system maintenance (Test condition A-3 and A-4): ▲air and exhaust + fuel system maintenance; ● air and exhaust + fuel + cooling system maintenance

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Figure 9 —Effect on A-weighted one-third-octave band spectrum of dumper-1 at 1000 hours schedule after air system maintenance (Test condition B-1 and B-2): ▲ before maintenance; ● after air system maintenance


Exhaust system maintenance (Test condition B-6)

The maintenance of exhaust system caused significant reduction in equivalent sound pressure level. It varied from 1.8 dB for dumper-3 to 2.4 dB for dumper-1 (Table 10 and Test conditions B-5 and B-6). The one-third-octave band data

showed that the maximum reduction in the sound pressure levels occurred in the midband frequencies up to 200 Hz. The reduction in the sound pressure levels in the midband frequencies up to 200 Hz for dumper-1, dumper-2 and dumper-3 varied from 1.3 – 3.3 dB, 1.2 – 4.2 dB and 1.0 – 2.2 dB respectively. The one-third-octave band spectrum of dumper-1 for this condition is shown in Fig. 12.

Hydraulic system maintenance (Test condition B-7)

The reduction in the sound levels after maintenance of the hydraulic system was negligible. It was of the order of 0.0 dB for dumper-3 to 0.1 dB for dumper-1 in the equivalent sound levels, which can be neglected.

5.3 Noise assessment of dozers and dumpers with different hours of work

Sound level measurements were also taken from 750 to 1000 hours of work for both dozers and dumpers with an interval of 50 hours. The idea was to find the variation in sound level with increase in hours of work of these machines. 5.3.1 Dozers

The A-weighted equivalent continuous sound level for all the three dozers for different hours of work is shown in Table 11. A variation in sound level was noticed for all the three dozers with increase in hours of work. An increase in sound level of 2.2 dB was observed in the A-weighted equivalent continuous sound level of dozer-3 from 900 to 950 hours of work. The one-third-octave band spectrum of dozer-3 at 900 and 950 hours of work is shown in Fig. 13. An increase on

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Figure 10 —Effect on A-weighted one-third-octave band spectrum of dumper-1 at 1000 hours schedule after air and fuel system maintenance (Test condition B-2 and B-3):▲ air system maintenance; ● air + fuel system maintenance

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Figure 11—Effect on A-weighted one-third-octave band spectrum of dumper-1 at 1000 hours schedule after cooling system maintenance (Test condition B-3 and B-4): ▲air + fuel system maintenance; ● air + fuel + cooling system maintenance

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Figure 12—Effect on A-weighted one-third-octave band spectrum of dumper-1 at 1000 hours schedule after maintenance of exhaust system (Test condition B-5 and B-6): ▲air + fuel + cooling + lubrication system maintenance ● air + fuel + cooling + lubrication + exhaust system maintenance


the order of 1.5 to 4.3 dB was observed in the sound pressure levels with midband frequencies from 25 Hz to 4 kHz. The sound level in this frequency range can be reduced by proper maintenance of the air system, exhaust system, fuel system and cooling system. An increase in the sound level on the order of 1 dB was observed for dozer-2 from 900 to 950 hours of work. The one-third-octave band spectrum shows an increase on the order of 1.6 to 4.4 dB in the sound pressure levels with midband frequencies from 25 Hz to 315 Hz (Fig. 14). The sound level in this frequency range can be reduced by proper maintenance of the air system, exhaust system and fuel system. 5.3.2 Dumpers

The A-weighted equivalent continuous sound pressure levels of all the 10 dumpers with different hours of work are shown in Table 12. An increase in sound level with increase in hours of work from 750 to 1000 hours was observed. This increase ranged from 4.1 to 7.7 dB for the dumpers. However, some dumpers showed a considerable increase in sound level with increase in hours of work. For instance, dumper-3 and dumper-5 had an increase on the order of 2.9 and 1.7 dB, respectively, between the 750-hour maintenance and 800 hours of work. The one-third-octave-band spectrum for dumper-3 and dumper-5 for the above mentioned condition is shown in Figs. 15 and 16, respectively. Dumper-3 had a significant increase in the sound pressure levels with midband frequencies from 25 Hz to 200 Hz (0.7 – 5.6 dB) and 630 Hz to 8 kHz (0.8 dB – 3.0 dB) between the 750-hour maintenance and 800 hours of work. The sound pressure level reduction in the midband frequencies from 25

Hz to 200 Hz can be achieved by proper maintenance of the air intake and exhaust systems. Similarly, the sound pressure levels with midband frequencies from 630 Hz to 8 kHz can be reduced by proper maintenance of the cooling system and tightening of various loose parts/components. Dumper-5 had an increase on the order of 0.9 to 3.6 dB and 0.1 dB to 2.0 dB in the sound pressure levels with midband frequencies from 31.5 Hz to 200 Hz and 400 Hz to 20 kHz, respectively. This may be due to deterioration of the air intake system, exhaust system and cooling system. The increase in the A-weighted equivalent continuous sound level of dumper-4 was 1.3 dB from 900 to 950 hours of work and 1.9 dB from 950 to 1000 hours of work. The one-third-octave-band spectrum indicated an increase in the sound pressure levels with midband frequencies from 25 Hz to 200 Hz and 400 Hz to 20 kHz. Dumper-6 had an increase in the equivalent continuous sound level on the order of 1.6 dB from 950 to 1000 hours of work. The one-third-octave-band spectrum indicated an increase in the sound pressure levels with midband frequencies from 25 Hz to 200 Hz and 400 Hz to 20 kHz. Dumper-7 had an increase in the equivalent continuous sound level on the order of 2.7 dB from 900 to 950 hours of work. This increase was noticed in the sound pressure level spectrum in the midband frequencies from 31.5 Hz to 200 Hz and 500 Hz to 20 kHz. The equivalent continuous sound level of dumper-8 increased by 2.2 dB from 950 to 1000 hours which was observed in the sound pressure level spectrum in the midband frequencies from 25 Hz to 200 Hz and 400 Hz to 20 kHz. The difference in the equivalent continuous sound level for dumper-9 from 950 to 1000 hours was 2.5 dB. The one-

Vardham-Figure 13

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Figure. 13—Change in A-weighted one-third-octave band spec-trum of dozer-3 from 900 to 950 hours of work: ▲ 900 hours of work; ● 950 hours of work

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Figure 14—Change in A-weighted one-third-octave band spectrum of dozer-2 from 900 to 950 hours of work: ▲ 900 hours of work; ● 950 hours of work


TABLE 12—A-weighted equivalent continuous sound level of dumpers with different hours of work

Equipment

A-weighted equivalent continuous sound level, (dB)

750 hours maintenance800hours 850 hours 900hours 950 hours

1000hoursmaintenance

Before After Before After

Dumper-1 99.2 98.2 99.2 99.9 100.6 101.3 102.3 94.9

Dumper-2 99.2 98.5 99.5 99.9 101.0 102.1 103.7 96.4

Dumper-3 99.5 97.2 100.1 101.3 103.0 104.2 104.9 98.2

Dumper-4 99.1 98.2 99.2 100.5 101.7 102.9 104.9 99.1

Dumper-5 99.2 97.5 99.2 99.9 100.9 102.2 103.4 96.6

Dumper-6 99.0 97.3 98.7 100.1 101.1 102.4 104.0 97.2

Dumper-7 99.0 97.6 98.8 99.5 100.6 103.3 103.3 96.0

Dumper-8 99.3 97.8 98.5 99.3 100.4 101.2 103.4 96.4

Dumper-9 98.9 97.3 98.1 98.9 100.6 102.0 104.4 99.5

Dumper-10 99.4 97.1 98.3 99.8 101.1 103.2 104.6 98.4

third-octave-band spectrum showed the maximum increase in the sound pressure levels occurred in the midband frequencies from 25 Hz to 200 Hz and 400 Hz to 20 kHz. The equivalent continuous sound level of dumper-10 increased by 2.1 dB from 950 to 1000 hours. The maximum increase in the one-third-octave-band sound pressure level spectrum was noticed in the midband frequencies from 25 Hz to 250 Hz and 2.5 kHz to 20 kHz. The data seems to indicate that the increase in sound level with an increase in hours of work of these machines takes place in the lower midband frequencies from 25 Hz to 200 Hz and

again from 400 Hz to 20 kHz. The sound pressure level in these midband frequencies can be reduced by proper maintenance of the air system, the exhaust system, and the cooling system and tightening of various loose components.

6 CONCLUSIONS

Measurement of the sound levels of a group of dozers and dumpers after each periodic maintenance revealed a significant sound level reduction after the 1000-hour maintenance schedule. This reduction in sound level was about 6 – 7 dB

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Figure 15—Change in A-weighted one-third-octave band spectrum of dumper-3 from 750 to 800 hours of work: ▲ 750 hours of work; ● 800 hours of work

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Figure 16—Change in A-weighted one-third-octave band spectrum of dumper-5 from 750 to 800 hours of work: ▲ 750 hours of work; ● 800 hours of work


for dumpers and 4 – 5 dB for dozers. At other maintenance schedules, the reduction in sound level was below 1 dB. This is due to overhauling of the machine and replacement of certain systems/components at 1000 hours maintenance. It also appears that a larger increase in the sound levels occurs between 750 and 1000 hours. The study further revealed major noise generating systems in HEMM as the air intake system, exhaust system, cooling system and fuel systems. However, maintenance of the lubricant, transmission, and hydraulic systems bears no significant reduction in sound levels. Noise emissions from various systems lie in different frequency ranges. For example, air system and exhaust system noise is predominant at frequencies up to 200 Hz, fuel system noise is predominant from 31.5 Hz – 500 Hz and 800 Hz – 2000 Hz and cooling system noise is predominant in the frequency range of 100 Hz – 6300 Hz. The study shows that monitoring the one-third-octave band sound pressure levels following a schedule would help to quickly identify any component or system that may require maintenance prior to the scheduled periodic maintenance.

7 ACKNOWLEDGEMENTS

The authors sincerely thank the reviewers who went through the paper in depth and provided valuable comments. They also thank the management of the mine for their kind cooperation in extending necessary facilities for carrying out this work. They sincerely thank Sri Allwyn Roshan Pais, Lecturer in Department of Computer Engineering of N.I.T.K Surathkal for his help in drawing the spectral curves.

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18 R. N. Mukherjee, “Noise an occupational health hazard in Industrial activities in India”, Proceedings of the national seminar on “Environmental pollution and control in mining coal and mineral based industries”, IIT Kharagpur, Feb. 13 to 15, pp. 204 – 212, (1987).

19 P. Srinivas and Y. V. Rao, “Assessment and control of noise pollution in mining industry”, Fifth national convention of Environmental Engineers, Madras, 23 to 24 September, (1989).

20 S. Mukhopadhyay and N. C. Dey, “Noise pollution in Mining-a critical appraisal”, The Indian Mining and Engineering Journal, October, pp. 23 – 26, (1998).

21 S. Mukhopadhyay and N. C. Dey, “A comprehensive analysis of dust and noise pollution in mines”, Journal of Mines, Metals and Fuels, March, pp. 80 – 84, (1999).

22 H. Vardhan, N. C. Karmakar and Y. V. Rao, “Assessment of machine generated noise with maintenance of various heavy earth-moving machinery”, Journal of the Institution of Engineers (India), Mechanical Engineering Division, Vol. 85, October, pp. 93 – 97, (2004).

23 Department of Consumer and Employment Protection, Government of Western Australia, “Maintaining your machines”, available at http://www.safetyline.wa.gov.au.

24 H. Vardhan, N. C. Karmakar and Y. V. Rao, “Experimental study of sources of noise from heavy earth-moving machinery”, Noise Control Engineering Journal, Vol. 53 (2), March-April, pp. 37-42, (2005).

25 C. M. Harris, “Handbook of noise control”, Toronto: McGraw Hill Book Co. Inc., Chapters 20, 23 to 33, (1979).

Documents

Assessment of heavy earth-moving machinery noise vis-a-vis routine maintenance