The stamp test for rock drillability classification

Abstract

With the Stamp Test the force and the penetration depth, required for a tungsten carbide button to fracture a rock surface, are determined. The indentation yields a crater in the rock surface, the volume of which is also determined. From the force and the penetration depth one may determine the piston blow velocity and the piston mass/length in a percussive machine, capable of drilling the rock material. The crater volume yields information about the expected drilling rate. Normally rock materials exhibit a decrease in the stamp strength with an increase in the stamp contact area radius. This effect is investigated experimentally for three representative rock materials. In everyday applications the standard Stamp Test radius b = 2 mm is used. Three additional representative rock materials are investigated experimentally and compared with the previous results. The stamp strength of a rock material may be used to define a non-dimensional drilling force F rel , which determines the rock drilling efficiecy. For F rel ⋍ 2 , the maximum drilling rate for constant power of a percussive rock drill is obtained. This is demonstrated in drop hammer experiments, where the rock material, drill bit type, drill bit size and drill bit state of wear are varied, together with the hammer blow velocity.