Theoretical considerations on pick shape in rock and coal cutting

Evan`s theory for chisel shaped picks is well known in the field of rock cutting technology. It has been widely accepted as a good mathematical description of how coal and other rocks break under the action of a simple wedge or chisel. Subsequently, Evans proposed a corresponding theory for pointed shaped picks. Theory along with experimental evidence from the laboratory has consistently shown that chisel picks are more efficient than pointed picks. Despite such evidence, however, pointed picks continue to be the preferred shape in most practical cutting applications. Even`s theory for pointed picks was developed in an attempt to shed light on this apparent incongruity. The theory although predicting forces of the right order was found to be deficient in several respects. This paper examines Evans` theory for pointed picks and proposes changes to it, which brings the theory much more into line with measured data. The issue of the relative efficiencies of chisel and pointed shaped picks is also examined on a theoretical basis and the apparent incongruity is resolved. (author). 4 tabs., 6 figs., 13 refs.