WEAR MECHANISMS DUE TO DIFFERENT ROCK DRILLING CONDITIONS

Abstract

Depending on the type of rock and on the drilling procedure used in rock drilling, cemented carbide is exposed to greatly differing mechanical and thermal conditions. These influence the properties of the cemented carbide required. By means of metallographical examination of rock drill inserts used under different conditions, it has been possible to determine what type of wear mechanism is critical in each case. Two kinds of mechanisms in particular were found to have a great influence on performance. When a drill is run under conditions of high mechanical stress and high temperature, which is the condition present when drilling in highly abrasive rocks, a major factor influencing performance is the creep resistance of the cemented carbide. One way of improving this property appears to be to increase the grain size. Percussive drilling in low-abrasive rock, where the mechanical stress is moderate, gives rise to another wear mechanism. In this, high thermal stresses are induced which lead to the formation of cracks and sometimes to rupture. Thus for this kind of application good thermal-crack resistance is important. During percussive drilling in rocks, with intermediate abrasivity, both mechanisms are active, making the choice of cemented carbide for this application more difficult.