Principles of diamond tool technology for sawing rock

Abstract

Abstract In a rock sawing operation, a single diamond particle acting as a sliding indenter expends energy by generating compression in the rock in the form of a ‘stress epicentre’ through the action of confined crushing: this compression causes the rock fracture mechanism. It is not a cutting operation per se—indeed sharp diamond particles can be a liability. The sawing requirement is for a high strength, high heat resistance indentor, with a potential for displacement that is compatible with that of the rock. Currently used tests for rock strength do not indicate energy consumption, but the Shore and Brinell hardness tests are relevant. However, the consumed energy is predictable from a new index of rock strength, called Brook hardness, which has been specifically developed for sliding diamond indenters. The ‘stress epicentre’ is located with reference to the diamond indenter through a force vector which is stable for all circular sawing velocities, but it changes with frame sawing and drilling because they operate at about a tenth of the sawing velocity. The ‘stress epicentre’ is at the location of the crushed, compacted material under the indenter. Changes in the position of the stress epicentre can increase energy efficiency by as much as 100% and reduce the generation of vertical force by as much as 70%. Drilling tests using feed/revolution as the measure of penetration are used to simulate the variable velocity of frame saws by reducing the revolutions/minute. These tests reveal a previously unrecorded sawing mechanism that can improve the use of frame saws because strong granite can now be frame sawn with diamond. This improved potential should also apply to drill bits if they use feed per revolution as the means of penetration, instead of a static bit load. By measuring diamond by volume rather than by weight, and considering alternative options, accurate tool control can now be achieved, with every aspect being predictable. Optimisation of rock sawing operations has shown that performance can be increased by 100–200% with tools removing as much as 30 tonnes in saw cuts per carat of diamond consumed. Because some rock mechanics terms used in the paper may have different meanings in the rock sawing context, a glossary of terms with further explanations is included at the end of the paper.