WEAR OF ROCK-CUTTING TOOLS

Abstract

The conditions under which carbide-tipped rock-cutting tools are employed are very much more severe than any experienced under metal-cutting conditions, vibration of the cutting machine being very significant. Cutting rock also tends to be an intermittent process.

Once macroscopic chipping of the cutting edge has been overcome, the predominant mechanism of wear appears to be one of microfracturing of the surface layers, probably a high-strain-fatigue type of failure. For this reason pure WC–Co grades are usually employed for greater fracture-resistance, rather than other grades of cemented carbides. However, other mechanisms of wear are also probably operative, corresponding to abrasive mechanisms, and becoming more important as higher temperatures are generated. Recent hardness measurements indicate that at the temperatures generated in the carbide tip, especially when cutting quartzitic rock, grains of the rock material could well be harder than the tool material. At the wear flat, where a certain thickness of the rock has to be crushed, this can give deep scour marks.

The most significant improvements in the present range of WC–Co tools lie in the attainment of “extreme” freedom from porosity, and also in obtaining carbide grains that are structurally as perfect as possible. The latter condition is important, since it gives both a maximum resistance to fracture and also better retention of properties to higher temperatures. Other improvements are also largely directed at increasing the fracture-resistance of the carbides.

Notes

* Manuscript received 23 June 1969. Contribution to a Symposium on “Lubrication, Friction, and Wear (Tribology) in Powder Metallurgy” to be held in Eastbourne on 24-26 November 1969.