Suggested methods for optimum rotative motion of point attack type drag tools in terms of skew angles

Abstract

ABSTRACT Rotation of point attack picks in their tool holders is of crucial importance for an efficient performance of machines used for tunnelling and underground excavations of rocks and coal. With current machines, skew angle has been extensively employed to achieve tool rotation. There has, however, been no common definition and suggestion on application of skew angles, due to the differences between the results of research investigations conducted in this field. This paper sets out the findings of long-term practical research during tunnelling and underground excavation operations with roadheaders and drum shearers in order to bring a common understanding in rotation of point attack picks. Mechanism of tool rotation was discussed, and a number of formulas were derived and suggested for optimum cutting conditions for roadheaders and mechanical miners, respectively. The results showed that with drum shearers tool rotation is possible without skew angles, due to the asymmetry between adjacent grooves which generates sideways forces inducing rotative movement of picks. Skew angles were, however, found to be a must for roadheaders in consideration with tool holder damage which was significantly influenced by different settings of skew angles. Furthermore, point attack picks with small-diameter shanks were found to suffer from shank breakage resulting from high values of tool forces, when fitted on the nose portion of roadheaders cutting heads.