Abstract
Laboratory cutting experiments in Sanjome-andesite were carried out with the point attack bit assisted by high pressure water jet up to 100 MPa ahead of the bit. Reduction rate of cutting forces was determined with both water pressure and cutting speed varied.Cutting forces showed continuous increase with wear of bit, but reduction rate of forces by water jet was scarcely dependent on degree of bit wear. It was found from experimental results that reduction rate depends on water jet energy applied per unit length of cut. As far as energy reached 15 kJ/m, reduction rate increased with it up to about 12% in drag force and 32% in normal force, respectively. Beyond the value of 15 kJ/m, reduction rate no longer increased.It was also found that water jet is effective to prolong the bit life. The effect was different with different cutting speed: in the cutting speed of 0.25 m/s, the bit life became about 2.6 times with assistance of water jet;in 0.12 m/s, the effect of water jet assistance was much greater.The results obtained here were compared with those of the previous cutting experiments with water jet assistance from behind the bit. The effects of water jet on the cutting forces and the bit life were comparable whether a nozzle is installed ahead of or behind the bit, excepting the case with a severely worn bitfor which the latter seemed slightly more effective.It is supposed that the mechanism of cutting force reduction by virtue of water jet assistance may be mainly removal of crushed rock or erosion.
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