The study of high pressure water jet assisted cutting of coal samples in the laboratory
A series of experiments were conducted to invesdgate high pressure water jet assisted coal cutting. The research was sponsored by British Coal and carried out in the Department of Mining Engineering at the University of Newcastle upon Tyne. Two coals were tested: a black, coherent, anthracite; and a heavily cleated, friable, dull coloured bituminous coal. The tests modelled as closely as possible a vane pick on a two start shearer drum. The experiment was performed on a modified 50 tonne linear cutting rig at a speed of I. Im/s, using jet pressures of 35MPa, 70MPa, and 105MPa at different flow rates. A 75kW double acting intensifier type pump supplied the high pressure water for the jet. A relieved cutting mode was adopted with a line spacing of 70mm, and a 30mm nominal depth of cut. An actual production cutting tool (heavy duty 75mm radial with a HW tip) cut the coal in both the sharp and blunt states. Additional tests were also performed by pre-slotting the coal with a water jet before cutting it and by examining the effect of varying the lead and offset distances on the parameters measured below. Parameters measured were the cutting forces in three orthogonal directions; the breakout patterns; and the coal size distribution. The coal yields and specific energies were calculated from the experimental data. Both coals achieved benefit from jet assistance but at different pressures depending upon the coal type and tool wear. The breakout pattern differed between the two coals but generally fracture occurred along the major cleat planes. Both coals were easier to cut when the major cleat was orientated in the horizontal plane rather than in the vertical plane. Specific energy increased linearly with jet power. In most cases the quantity of fine coal (-0.5mm) produced decreased with jet assistance.