In a rotary coal cutting system, the mined coal has to be transported through the cutting path. This transportation of mined coal through the cutting zone of a rotary cutting head is comparable to a rotary grinder. In the grinder , the mined coal particles are subjected to secondary comminution, known as regrinding. A significant amount of coal dust could be generated during regrinding. This study was undertaken to investigate the mechanisms of regrinding and dust generation, to quantify the amount of dust generated during regrinding and evaluate the effects of influencing parameters on dust generation. Three comminution mechanisms of particles in the regrinding process, namely slow compression, impact, and attrition, were recognized. Compression and dust generation were studied utilizing an electro-hydraulic servo control testing machine, with a controlled displacement rate of 0.00025 cm/s. A dynamic finite element model was employed to study impact failure. Dust generation due to impact failure was observed using a high speed video camera system. It was found that compression and impact generate dust because they create a crushed zone under the contact area. Dust generation by attrition was also investigated and it was found that attrition of coal particles generates a significant amount of dust. An Automated Rotary Coal Cutting Simulator was utilized to simulate the regrinding process. Laboratory simulation studies showed that the amount of feed particles subjected to compression and impact breakage was only 5% {dollar}\\sim{dollar} 11% and it decreased as feed particle size decreased. But the amount of dust generated during regrinding was significant and it increased as feed particle size decreased. This indicates that attrition of coal particles is the primary mechanism of the secondary dust generation. An orthogonal fractional factorial experiment was conducted to estimate the effects of the major parameters on dust generation during regrinding. Experimental results showed that the amount of dust generated increased with increasing depth of sump, cutting velocity, and grindability index of coal materials. Dust generation during regrinding can be reduced by increasing the particle size in the product of the primary cutting, reducing the depth of sump and cutting velocity
