How to determine the cutting power when cutting rock, a recipe

Abstract

When estimating rock cutting projects, it is always difficult to determine the required power. Many theories are available, but which one to use. The Evans theory is suitable for tensile failure. Nishimatsu and Merchant are suitable for shear failure. But which type of failure will occur under which circumstances. The Miedema theory allows a mix of tensile failure and shear failure, named the Chip Type. This mechanism will mostly occur with medium blade angles (around 60°) and certain BTS to UCS ratios. In oil drilling with very large blade angles the Chip Type will never occur. Here a step by step approach is presented how to determine the mechanism occurring and how to determine the cutting forces, cutting power and specific energy. First of all, the required rock mechanical parameters are discussed. Then the possible mechanisms are discussed. Engineers are used to problems with one solution, however in rock cutting there are more solutions given a certain set of inputs, depending on the cutting history. So how does this work. At the end the reader is capable of carrying out a production estimation of rock cutting project.