| 摘要 |
1515532 Boring earth &c. HUGHES TOOL CO 2 July 1975 [3 July 1974] 27903/75 Heading E1F [Also in Division B3] In an earth boring tool e.g. a rotary percussion drill bit or a roller bit (Fig. 3), a sintered tungsten carbide insert 17 (or 36 in Fig. 3) has a surface 25 interferingly secured to the wall of a retaining hole, the surface having been finished by abrading the insert with abrasive particles having a hardness greater than 9.0 on the Mohr scale. Preferably the inserts are initially ground prior to slurry tumbling in a mixture of 100 to 325 mesh boron carbide particles and water, but other abrasive particles might be used e.g. beryllium carbide, titanium carbide, silicon carbide, aluminium boride, cast tungsten carbide, ditungsten carbide, boron carbide, boron or diamond. The inserts then have an asperity less than that formed by grinding with a diamond wheel but greater than that of the matt finish obtained by abrading with alumina, and the surface produced on the insert is such that in any lineal increment of at least 0.010 inch, there are at least 3 asperities which from peak to trough are at least 0.001 inch long and at least 0.00005 inch deep when measured with a stylus point of radius 0.0005 inch. |
