Importance

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Abstract

A roller cutter for a rotary drill bit comprising a conical roller cutter body of metal, and a plurality of cutting elements secured to the outer surface of the roller cutter body primarily by welding and being substantially free of mechanical interconnection to the roller cutter body. Each cutting element is an elongate member having a base portion at one end thereof engageable with the roller cutter body and a tip portion at the other end thereof engageable with the formation to be drilled for drilling the formation. The element is formed of a material at its tip portion which has relatively high compressive strength and good wear resistance properties, but which also has a coefficient of thermal expansion and elastic moduli significantly different from those of the metal of the cutter body thereby rendering it incapable of being satisfactorily welded thereto, and being formed of a material at its base portion which has a coefficient of expansion and elastic moduli similar to those of the metal of the cutter body thereby enabling it to be welded thereto. The cutting elements are formed of a composite material having first and second phases, with the volume fractions of these phases varying in a generally continuous composition gradient along the length thereof. In addition, a drag type drill bit, and a method of manufacturing the roller cutter and the drag bit are disclosed.

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First Claim