| 摘要 |
<p>A rotary drill bit is manufactured by a powder metallurgy process by placing a metal mandrel 54 in a mould 38, packing the mould 38 with particulate matrix-forming material 50, infiltrating the material with a molten binding alloy, and cooling the assembly to form a solid infiltrated matrix bonded to the mandrel 54. The mandrel 54 comprises an outer part 56 surrounded by the matrix-forming material 50 and an inner part 58, secured to the outer part 56 but out of contact with the matrix-forming material 50. The outer part 56 of the mandrel 54 is formed from a material having thermal characteristics close to those of the matrix, so as to reduce the tendency for the matrix to crack under the thermal stress, while the inner part 58 of the mandrel 54 is formed from a precipitation-hardening material, the strength and hardness of which increases in the infiltration process and the subsequent heating/cooling cycle for brazing the cutters 24 on to the drill bit. A threaded connection region of the drill bit may be formed directly on the inner part 58 since it will have sufficient strength and hardness for this purpose. <IMAGE></p> |
