Rolling cutter bits receive predominant use throughout the world. As a result, an understanding of their design principles is essential for effective drilling operations. Common designs used by most manufacturers will be discussed with a description of various special designs when applicable. Omission of new or innovative characteristics is done for practicality until these advances have received adequate field testing.
Bit Bodies. The bit body consists of I) the threaded connection, or shank, which attaches the bit to the drillstring, 2) the bearing pins on which cones are mounted, 3) the lubricant reservoirs, which contain the lubricant supply for the bearings, and 4) the watercourses through which the drilling fluid flows to clean the cuttings from the hole. The individual body sections, including the integral bearing pins, are machined from forgings or castings of a nickel-chromium-molybdenum alloy steel of a carburizing grade. The bearing pin portion is selectively carburized (surface hardened) to provide a deep, wear-resistant case. The section is then oil-quenched hardened and tempered, resulting in wear-resistant bearing surfaces.
Each individual body component consists of a leg and bearing pin. as shown in Fig. 7—4. Three-cone bits have three segments; four-cone bits have four bit segments. The individual segments are welded together to form the complete bit body.
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