Modified tail section reduces noise 
 

on a continuous mining machine



by A. K. Smith, J. J. Zimmerman, R. Michael and P. G. Kovalchik 

Abstract . Overexposure to noise remains a widespread, serious health hazard in the U.S.

mining industry. Most other categories of illnesses and injuries associated with mining have

improved, with the exception of hearing loss. U.S. Mine Safety and Health Administration

(MSHA) coal noise data from 2000-2004 show that the continuous mining machine (CMM) is

frst among all equipment, accounting for 35% of noise overexposures. Joy Mining Machinery,

in collaboration with the National Institute for Occupational Safety and Health (NIOSH), is

conducting research to reduce noise generated by continuous mining machines. This paper

describes a "JOY-Designed for Noise Reduction" (JOY-DNR; patent pending) tail section as a

noise control for reducing the noise overexposures of CMM operators. Underground testing

shows a 45% to 65% noise exposure reduction for the operator when comparing the JOY-DNR

tail section results to those for a standard machine. Utilizing this newly developed noise control,

along with previously proven controls, will provide CMM operators an opportunity to be within

the MSHA permissible exposure limit (MSHA-PEL).

Introduction

Exposure to industrial noise con 

tinues to be an extensive health issue 

for mine workers in the United States. 

Noise can also be an indirect safety 

hazard because it can “mask” impor 

tant sounds, such as backup alarms. 

Although noise-induced hearing loss 

(NIHL) is preventable, studies suggest 

that more than half of the nation’s mine 

workers will retire with a hearing im 

pairment (Franks, 1996). NIHL is par-

­

­

ticularly severe among underground 

mine workers, due to the operation of 

large industrial equipment in confined 

spaces. Of particular concern is the 

continuous mining machine (CMM) 

used in room-and-pillar mining. 

The CMM is one of the principal 

machines used in underground coal 

mining and is also one of the loudest. 

Analysis of noise samples collected by 

the U.S. Mine Safety and Health Ad 

ministration (MSHA) in 2006 show that 

30% of CMM operators exceeded the 

permissible exposure level (PEL), as 

stated by Title 30 of the Code of Fed 

eral Regulations (MSHA, 2008). This 

constitutes the largest group of under 

ground equipment operators that are 

overexposed to noise. Furthermore, un 

derground sound levels can range from 

78 to 109 dB (A) during typical CMM 

operation (Bauer et al., 2006). Opera 

tion of the onboard conveyor system 

has also been identified as a dominant 

noise source that significantly con 

tributes to operator exposure. Sound 

power generated by the conveyor sys 

tem can range from 118 to 120 dB (A), 

depending on how the tail section is 
 

swung (Smith et al., 2008).
 


Effective CMM noise reduction 
 

­ ­

­

­

­

­

­

­

et al., 2007). 

Recently, Joy Mining Machinery has 

made several design improvements in 

the CMM tail section to reduce noise 

and improve performance. This paper 

strategies have concentrated on ad ­

dressing the dominant noise sources. 

Acoustic beamforming has been used 

to identify components on the CMM 

conveyor system that are significant ra ­

diators of noise (Camargo et al., 2008). 

Interaction between the steel flight bar 

chain and conveyor deck excites the 

machine structure and produces most 

of the noise. Also, forces are transmit ­

ted at the tail roller and sprocket tran ­

sition points, where the conveyor chain 

transverses its path. Several engineer ­

ing noise controls have been devel ­

oped to address these noise-generating 

mechanisms (Smith et al., 2009; Camar ­

go et al., 2008; Smith et al., 2008; Smith 

examines these improvements to test 

their impact on CMM noise reduction. 

Approach

Several modifications were made 

on the tail section of a Joy Mining Machinery 14CM15 CMM to reduce noise 

generated by the conveyor system. The 

machine utilized a dual-sprocket chain 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

conveyor system. Improvements were also made to the con

veyor chain tensioning and take-up systems, as well as the 

tail roller component. The automatic hydraulic tensioning 

systems removed chain slack, which influences the noise gen

erated by the conveyor system. Tail roller components were 

constructed with various compliant materials to reduce the 

vibration transmitted to the rest of the machine. These de

sign changes were combined with a Joy Mining Machinery 

dual-sprocket conveyor chain, which has previously demon

strated the ability to reduce noise (Smith et al., 2009). 

The modified CMM was put into service at an under

ground coal mine to assess performance. Success of any 

acoustic treatment on underground mining equipment is 

determined by its ability to reduce noise and maintain dura

bility in the work environment. To evaluate the noise reduc

tion capability of the JOY-DNR tail section, noise exposure 

and task observation data were collected. Durability was 

assessed by the ability of noise treatments to survive in a 

mining environment for an extended period of time. 

CMM operator noise exposure data were collected using 

a personal noise dosimeter. The dosimeter settings were set 

to the MSHA PEL, as shown in Table 1. Dosimeters were at

tached to workers on the surface before the shift started, and 

were removed after the shift was complete. Noise exposure 

data were collected over three days for three separate work 

shifts. Dosimeters were placed on the two CMM operators 

working in a multiple-entry, split-air section. Both of the 

CMMs were Joy Mining Machinery 14CM15; one was a stan

dard build machine and the other included the JOY-DNR tail 

section. A standard tail roller was used on the JOY-DNR 

tail section for day 1, and different isolated tail rollers were 

installed for days 2 and 3 on the same machine. Task observa 

tions and production data were also collected to give context 

to the results. 

­

­

­

­

­

­

­

­

­

­

Table 1 
 

4:/( WLYTPZZPISL L_WVZ\YL SL]LS

KVZPTL[LY ZL[[PUNZ

Parameters Settings

Weighting A

Threshold level 90 dB

Exchange rate 5 dB

Criteria level 90 dB

Response Slow

Upper limit 140 dB

To achieve further noise reduction, vibration-isolated tail 

rollers were developed for the JOY-DNR tail section. The 

tail rollers had a hard plastic outer shell for wear protection with a compliant material core to absorb chain impacts. 

Two different materials for the core were examined: heavily 

damped butyl rubber and high strength natural rubber. An 

isolated tail roller installed on the JOY-DNR tail section is 

shown in Fig. 1. 

Figure 1

Joy-ONR tail section with isolated tail roller installed.

Results and discussion

Operator noise exposure data were used to evaluate a 

JOY-DNR tail section on a CMM in a working environment. 

Accumulated operator noise doses for the standard and JOY ­

DNR tail section machines were computed for each shift.The 

operator noise dose for the JOY-DNR tail section machine 

(red line) is compared to that for the standard machine (gray 

line) in Figs. 2 - 4.The total accumulated noise dose and timeweighted average for an eight-hour work shift (TWA ) (8 Hr)

are shown in the legend of each figure. An example of the 

general task observations for both machines is also shown 

in Fig. 2. Task observation data were collected for the other 

shifts, but are not shown for purposes of brevity. Production 

Figure 2

CMM operator noise exposure comparison of Joy-ONR tail

section with standard tail roller (red line) and standard tail

section machine (gray line).

Figure 3

CMM operator noise exposure comparison of Joy-ONR tail

section with tail roller #1 (red line) and standard tail section

machine (gray line).
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4

CMM operator noise exposure comparison of Joy-DNR tail

section with tail roller #2 (red line) and standard tail section

machine (gray line).

numbers were also collected for each machine during the 

work shift. 

Different tail rollers were installed on the JOY-DNR tail 

section machine in an attempt to further reduce noise and 

vibration transmitted to the rest of the machine. On the first 

day of data collection, a standard tail roller was installed on 

the JOY-DNR tail section machine. For days 2 and 3, the 

JOY-DNR tail section machine had different tail roller designs installed. The results of CMM operator exposure data 

are summarized along with production numbers in Table 2. 

The tail rollers of different compliant materials are labeled 

TR #1 and TR #2. 

Table 2 

Noise exposure results and production.

Day 1 Day 2 Day 3

STD JOY-DNR STD JOY-DNR STD JOY-DNR

(REG TR) (TR #1) (TR #2)

Shift dose 144% 85% 157% 122% 155% 90%

TWA(8 Hrs) 93 dB(A) 89 dB(A) 93 dB(A) 91 dB(A) 93 dB(A) 89 dB(A)

Production 245 ft 280 ft 240 ft 290 ft 255 ft 200 ft

There were no observed changes to the standard CMM 

noise exposure results during data collection during the three 

work shifts. In contrast, for the JOY-DNR tail section ma

chine, several observations can be made by comparing the 

accumulated operator noise exposure results. Noise expo

sure levels were consistently lower for the operator using 

the JOY-DNR tail section machine. TWA (8 Hrs) reductions of 

4 dB (A) are observed on day 1 and day 3, while a modest 

TWA (8 Hrs) reduction of 2 dB (A) is seen on day 2. These find

ings reflect a 45% and 65% noise exposure reduction for the 

CMM operator when the JOY-DNR tail section results are 

compared to those for a standard machine. Daily production 

remained relatively consistent for all shifts where data were 

collected. 

Several variables must be considered when examining 

­

­

­

these underground mining worker noise exposure 

results. Although both 

CMMs were used on the 

same working section of 

the mine, geological composition and machine operation were not exactly 

the same. Also, the operator position for the standard CMM was on the same side as the exhaust of the dust 

collection system of the standard machine. Although the 

conveyor system is a dominant noise source, noise generated by the axial-vane fan at this location could contribute to 

operator noise exposure for the standard machine operator. 

Conclusions

A JOY-DNR tail section, developed for a 14CM15 CMM, 

is the latest effort by Joy Mining Machinery to address equipment noise generation that affects mine workers. Several 

different JOY-DNR tail rollers were examined in this study. 

Modifications to their design showed promise in reducing 

worker noise exposure. Further tests are needed to confirm promising results that were observed during this underground evaluation. The JOY-DNR tail section machine 

should be examined acoustically in a laboratory environment 

to prove repeatability of the test results and reduce variance. 

Also, material properties of the compliant materials used 

in the JOY-DNR tail rollers should be further investigated. 

Implementation of this technology, along with other proven 

noise controls for CMMs, should help lessen the occurrence 

of NIHL in the underground mining industry. •

Disclosure

The findings and conclusions in this report are those of 

the authors and do not necessarily represent the views of 

the National Institute for Occupational Safety and Health. 

Mention of any company or product does not constitute endorsement by NIOSH. 

References

Bauer, E.R., Babich, D.R., and Vipperman, J.R., 2006, Equipment Noise 

and Worker Exposure in the Coal Mining Industry, Information Circular 9492, National Institute for Occupational Safety and Health, 

Pittsburgh, PA. 

Camargo, H.E., Smith,A.K., Kovalchik, P.G., and Matetic, R.J., 2008,“Noise 

source identification on a continuous mining machine,” Proceedings of 

Noise Con 2008, Dearborn, MI: INCE. 

Franks, J.R., 1996, Analysis of Audiograms for a Large Cohort of NoiseExposed Miners, Unpublished technical report. National Institute for 

Occupational Safety and Health, Cincinnati, OH. 

MSHA, 2008, MSHA Standardized Information System, Number of Noise 

Samples @90PELDose(computed)>=100 by Machine Code, 2006, 

Denver, CO: U.S. Department of Labor, Mine Safety and Health Administration, Office of Injury and Employment Information. Date 

accessed: March 20, 2008. 

Smith,A.K.,Yantek, D.S., and Peterson, J.S., 2007,“Development and evaluation of a urethane jacketed tail roller for continuous mining machines,” International Mechanical Engineering Congress & Exposition. 

Seattle, WA: ASME. 

Smith, A.K., Peterson, J.S., and Kovalchik, P.G., 2008, “Continuous mining 

machine conveyor system sound power levels,” Proceeding of Noise 

Con 2008, Detroit, MI: INCE. 

Smith, A.K, Kovalchik, P.G., Matetic, R.J., and Alcorn, L.A., 2009, “A dual 

sprocket chain as a noise control for a continuous mining machine,” 

Noise Control Engineering Journal, Vol. 57, No. 5, pp 413-419.