improvements are reported for all to drill with bits in one or more are reported.

摘要

911,461. Percussive tools. TIMKIN ROLLER BEARING CO. Sept. 8, 1959 [Feb. 27, 1959], No. 30599/59. Class 124. A drill bit comprising a body having an integral work-engaging end face has the workengaging portion formed of an outer layer of wear-resistant carbide material and a binder and an inner layer of tougher, shock-resistant, carbide material, the outer layer, inner layer and bit body being integrally united by fusion of the binder material therebetween. As shown, a drill bit is formed by introducing into a mould particles of a wear-resistant carbide 24a, adding particles of a shock-resistant carbide 26a, a binder material, e.g. cobalt, being present with the carbide materials, closing the mould with the bit body 28, and applying heat and pressure to form the drill bit.