US 5,668,092 A · Rock bit grease composition

Abstract

A rock bit for drilling subterranean formations is lubricated with a grease composition made from a high-viscosity synthetic lubricant basestock and a combination of lubricant additives. The grease composition preferably has in the range of from 1 to 20 percent by weight polyisobutylene, in the range of from 50 to 90 percent by weight ethylene-alphaolefin, up to approximately 40 percent by weight polyalphaolefin, and in the range of from 4 to 45 percent by weight lubricant additives. The rock bit grease composition has a viscosity index in the range of from about 250 to 325, and has an absolute viscosity of greater than about 100,000 centipoise at a temperature of approximately 70.degree. F. and at a shear rate of less than about 40 seconds.sup.-1, without the use of solid metal-containing extreme pressure agents or thickening agents. The grease composition forms a lubricant film having enhanced thicknesses, when compared to conventional mineral oil-based greases, to provide excellent rock bit bearing lubrication.

Claims12

Dependent claims

A rock bit for drilling subterranean formations comprising:

a bit body including a plurality of journal pins, each having a bearing surface;
a cutter cone mounted on each journal pin and including a bearing surface;
a grease reservoir in communication with such bearing surfaces;
a solid metal free grease composition in the grease reservoir and adjacent the bearing surfaces, the grease composition having a viscosity index in the range of from 250 to 325 and comprising:
in the range of from about 55 to 95 percent by weight synthetic lubricant basestocks comprising:
in the range of from about 1 to 20 percent by weight polyisobutylene having a Flory molecular weight in the range of from 42,000 to 46,000;
in the range of from about 50 to 90 percent by weight ethylene-alphaolefin having a Flory molecular weight in the range of from 32,000 to 38,000;
and up to about 40 percent by weight polyalphaolefin having a molecular weight in the range of from 800 to 2,000;
and
lubricant additives comprising:
a 1,3,4-thiadiazole compound;
a sulfur-chloride-phosphorus compound;
an alkyl ester copolymer;
a silica gel compound:
and
a propylene carbonate compound;
and
a seal for retaining the grease in the bearing.

15 more elements

Dependencies are inferred from the claim text.

Rock bit grease composition

Life of this patent

Rock bit grease composition

Life of this patent

Abstract

Claims12