Mingming Li

Date of Graduation

2015

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mining Engineering

Committee Chair

Yi Luo

Committee Co-Chair

Keith A Heasley

Committee Member

Rudy J Matetic

Committee Member

Victor H Mucino

Committee Member

Syd S Peng

Abstract

Noise induced hearing loss is a serious health issue among coal mine workers. The roof bolting operation is one of the noisiest underground mining operations. It is second among all equipment in underground coal mines whose operators exceed 100% noise dosage according to MSHA data. In roof bolting, the noise generated in the roof drilling normally contributes a major proportion to the noise exposure to this particular group of miners. This study is to develop a drilling control technology to reduce noise generated during roof bolting drilling.;Previous research shows that the specific energy consumed in drilling bolt holes is inversely proportional to the bite depth (i.e., penetration per drill revolution). Less specific energy at a reasonably high bite depth means less energy is wasted in the drilling process for producing heat, bit wear, and noise. Properly controlled drilling will not only maintain good drilling productivity, but also significantly reduce the sound power level, noise dosage, and the required drilling energy. Rational drilling control is implemented through properly chosen penetration and rotational rates according to the specific rock strength, drill bit, and steel.;Several efforts are investigated in this research. The first one is to explore the feasibility of the drilling control technology for reducing drilling noise. Drilling experiments have been conducted in the laboratory. Different drilling parameters (penetration rate and rotational rate) and different drill bits and steels were utilized through drilling medium hard rock. The results show that significant reduction in noise dose can be achieved at a reasonably high bite depth when drilling medium hard rock. This research indicates that through proper control of the drilling parameters with regarded to rock type, the noise exposure to the roof bolter operators can be significantly reduced. At the same time, drilling productivity is not affected or even improved. Then an algorithm has been developed for finding the rational drilling control parameters that can minimize the noise dose of the bolter operators in roof bolting drilling. Also, a mathematical model for simulating roof bolt drilling has been improved to include the noise generation. This model can be used to estimate the rock strength as well as required drilling thrust and torque, specific energy, energy efficiency, and noise dose for a given rock strength. The safety check of drilling operation is also included in this model. As an additional effect of this drill control technology, the dust size distributions of drilling at different parameters were analyzed. This noise control algorithm can be incorporated into the existing drill control unit for potential drilling automation.

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