Studies in the excavation of selected rock materials with mechanical tools
This work covers laboratory studies in the excavation of selected rock materials with mechanical cutters. Cutting head design of rock excavation systems employing drag tools or disc cutters is investigated by considering their practical cutting action. Effects of tool tilt angle on the performance of roadheaders with longitudinal cutting heads are investigated in detail. Along with tilt angle, optimum tool spacing between adjacent cutters, cutting head geometry and mode of operation of roadheaders are also studied. Experiments with disc cutters covered mainly the effect of disc edge angle on disc performance. When the practical cutting action of drag tools is considered the trend of forces and specific energy becomes somewhat different from those obtained during flat rock surface cutting trials; however, the definition of optimum tool spacing with respect to drag tools confirms previous findings. Tilt angle has a significant influence on the performance of cutting tools; in particular, with corner cutting tools. It was found that individual tool forces are proportional to the cross-sectional area cut by the corresponding tool. Roadheader cutting heads with combined geometry offer better performances than those with spherical geometry when the tool spacing is kept constant around the cutting head. In arcing mode tool duties are also affected by boom length. Cyclic deepening of grooves exists when cutting with discs, discs having smaller edge angles requiring more successive passes to produce a complete breakout between adjacent grooves.