Rock drill for geothermal shafts - where cutters contain peripheral row of very hard tungsten carbide inserts to improve drill life in arduous working conditions

摘要

The drill consists of a body which is rotated, and carries at least one bevel cutter (11) free to rotate on body. In each cutter (11) are several rows of inserts made of tungsten carbide (WC), including an outer row of inserts (33) in contact with the wall of the drilled hole. Inserts (33) consist of WC with average particle size (APS) above 0.5 (pref. 1-15) microns, sintered in a Ni matrix forming 6-20, esp. 6-16 wt.% of the inserts (33). Inserts (33) may contain up to 1/3 pts. wt. of tantalum carbide. Cutters (11) pref. also contain a row of heel inserts (38), made of WC with APS 0.5-10 microns, plus 3-20% Ni. Drills used in oil holes generally have a life above 100 h, but this is reduced to 40-50 hr when drilling geothermal shafts. The invention provides an improved outer row of inserts (33) increasing drill life.