Noise Source Identification on a Continuous Mining Machine

Abstract

Noise Induced Hearing Loss is the most common occupational disease in the U.S. and of paramount importance in the mining industry. According to data for 2006 from the Mine Safety and Health Administration (MSHA), Continuous Miner operators accounted for 30.2% of underground mining equipment operators with noise doses exceeding the Permissible Exposure Limit (PEL). This figure becomes more significant considering that 49% of the 2006 national underground coal production was extracted using continuous mining methods. Thus, there is a clear need to reduce the sound radiated by Continuous Mining Machines. The first step towards efficient noise control of a Continuous Mining Machine requires identification of the various noise sources under controlled operating conditions. To this end, a 42-microphone phased array was used in conjunction with 4 reference microphones to sample the acoustic field of a machine in the Hemi-anechoic chamber of the Pittsburgh Research Laboratory. These data were processed using a frequency-domain beamforming algorithm to obtain acoustic maps of 5 sides of the machine. The focus of the test was on the conveyor noise since previous studies showed that operation of the conveyor is the most important contributor to the sound radiated by the machine. From the acoustic maps, the following potential areas for noise control were identified, and included: chain-tail-roller interaction, chain flight tip-side board interaction, and chain-upper deck interaction.

A noise control package for vibrating screens

“…The distributions from the humps meet at 1 kHz. As mentioned previously, prior studies showed that the frequencies below 1 kHz are attributable to screen body noise, while the frequencies above 1 kHz are due to mechanism housing noise 31,32 . A package of engineering noise controls was developed to address these noise sources, as well as spring chatter noise.…”

“…The motor and drive belts were not enclosed due to space constraints in coal preparation plants. Additionally, they were not found to be significant contributors to noise 32 . We created a modular panel-on-frame design with components that weigh less than 222 N (50 lb.)…”

“…This is due to the smaller material feed size for these particular screens. Further research in the lab, using the same make and model of screen found in the aforementioned preparation plant, showed that most of the noise due to screen vibration is radiated by the screen body and the mechanism housings 31,32 . One of these studies showed that the suspension springs were also one of the three main noise sources of the screen 31 .…”

A dual sprocket chain as a noise control for a continuous mining machine

“…However, this assumed that the operator controlled the continuous mining machine via on board controls, unlike the remote machine controls typically used by industry today. Through the use of remote controls operators are more directly exposed to the noise generated by the conveying system, which has been the focus of recent investigations 12,14 .…”

“…Noise generated by the impacts that occur between chain flight bars and conveyor components is particularly severe where the chain traverses its path; at the gear sprocket (front of machine) and tail roller (rear of machine) 14,15 . Early research conducted by BOM concentrated on treatments to reduce CMM conveyor system noise 16 .…”