Influence of cutting parameters and modes on coal fracture efficiency

Abstract

The efficiency of the process of coal cutting by coal cutting machines depends, all other things being equal, on the method of coal fracture, characterized by the number and relative location of the exposed planes, as well as by the orientation of the main plane of the cutting tool relative to the fracture surface. With greater degree of exposure of the face surface, coal fracture is easier. In this regard, the article considers various types of cutting with characteristic cross-section shapes of chips, and assesses them from the point of view of the energy intensity of the process. The main operating parameters that determine efficiency of the coal cutting process are the thickness, width and cross-section of chips, the ratio of which governs the cutting energy intensity and productivity. The patterns of the influence of operating parameters on the force and energy parameters of the cutting process are considered. It is found that for almost all types of cutting, with increasing chip thickness, the energy intensity of cutting and the degree of coal fragmentation reduce along a hyperbola and stabilize at the chip thickness exceeding 3–5 cm. The theoretical chip width conditioned by the distance between the side faces of the cutter at the height of their contact with rock mass depends on the brittleness of coal, chip thickness, type of cutting, shape of the cutting edges and surfaces of the cutting part, cutting angles, as well as on the sharpening and setting of the cutter. The formulas for determining the theoretical values of the chip width for various designs of the cutting part of the cutters are given. The joint effect of the chip thickness and width on the specific energy consumption during cutting is estimated. To analyze and quantify the effect of operating parameters on energy consumption during cutting, the face exposure coefficient is proposed, which is the ratio of the specific energy consumption at the studied values of the chip thickness and width to the energy consumption in the reference cutting mode with the same chip thickness. The theoretical dependences are obtained for determining the optimal values of the face exposure coefficient and chip width during operation of shearers and ploughs. It is found that the feed rate and cutting speeds, as well as their ratio, practically have no influence on the loads on the cutters and, therefore, can be ignored in the calculations for choosing parameters of excavating machines.