Development of noise controls for longwall shearer cutting drums⁾

Noise-induced hearing loss is the second most pervasive disease in the mining industry. The exposure of miners to noise levels above the permissible exposure level results in hearing loss of approximately 80% of coal miners by retirement age. In addition, between 2002 and 2011, approximately 48% of longwall shearer operators were overexposed in coal mines in the United States. Previous research identified the two rotating cutting drums used by the longwall shearer to extract coal as the most significant sound-radiating components. In this context, the National Institute for Occupational Safety and Health conducted research to develop noise controls for longwall mining systems. To this end, structural and acoustic numerical models of a single cutting drum were developed to assess its dynamic and acoustic response, respectively. Once validated, these models were used to explore various noise control concepts including force isolation, varying structural damping and varying component stiffness. Upon multiple simulations, it was determined that structural modifications to increase the stiffness of the outer vane plates were the most practical and durable approach to reduce the sound radiated by the cutting drums. Furthermore, these modifications did not adversely affect the cutting performance, nor the loading ability of the drums. As a result, these structural modifications were implemented into an actual set of drums for evaluation purposes. Results from the underground evaluation, when the modified cutting drums were used under normal operation conditions, showed noise reduction across the entire frequency spectrum with an overall noise reduction of 3 dB in the sound pressure level at the operator location, confirming the validity of the developed noise controls.