| 摘要 |
<p>A method for manufacturing by a powder metallurgy process a rotary drill bit including a bit body 10 having an external surface 12 on which are mounted a plurality of cutting elements 14, and a passage for supplying drilling fluid to the surface of the bit. The method includes the known steps of forming a hollow mould 19 for moulding at least a portion of the bit body, packing at least part of the mould with powdered matrix material, and infiltrating the material with a metal alloy in a furnace to form a matrix, the method further including the step, before packing the mould with the powdered matrix material, of positioning on the interior surface of the mould one or more formers 21a-21e which project into the interior of the mould space at the desired location for a socket within the bit body, such sockets being to receive nozzles or studs on which the cutting elements are mounted. According to the invention, the formers are formed from material having a coefficient of thermal expansion not less than that of the matrix material, such as austenitic stainless steel. The formers may have a surface coating of a ceramic, such as boron nitride, or other material which does not wet or react with the binder alloy or matrix material. </p> |
