Interaction of a coal-mining tool with rock: theory, experiment, and analysis. [Tool spacing, depth-of-cut, and kerfing with water jets]

The interaction of tool and rock has been studied using finite element and analytical models. The results indicate that fracture occurs ahead of and beneath the tool. Experimental results confirm the models; however, at shallow depths-of-cut a different mode of cutting (microfracturing) occurs which requires much larger cutting forces than expected and which removes much less material. This results in greatly increased specific energy. Slightly deeper cuts cause the chip forming mode of cutting to occur. This is more efficient and becomes even more so as the depth-of-cut increases. Kerfing (cutting slots between tools) is shown to reduce the specific energy by approximately 75% (if optimized to the depth-of-tool-cut) compared to a single tool, while optimizing tool spacing only results in approximately 30% reduction in specific energy. Cutting saturated rock reduces the cutting force by about 50%, presumably by lubrication and rock strength degradation. Petrofabric analysis of specimens which were cut in the experimental portion of this program showed that the primary mode of failure was extension or tensile fracture with little evidence of shear failure. Two types of rocks of different composition and grain size were examined and the same failure modes prevailed in both. The results of thismore » study indicate that large gains in mining efficiency, health, and safety can be made by water jet kerfing and by using deep, slow, linear cuts with water jet assisted tools.« less