Composite diaphragm for roller cone pressure compensation system

Abstract

To address issues of durability of pressure compensation systems in roller cone rock bits, a composite diaphragm of a pressure compensation system for a roller cone drill bit includes an inner surface that defines an inner cavity and is formed of a first elastomeric material. The inner cavity is configured to serve as a lubricant reservoir. An external surface is disposed opposite the inner surface and is formed of a second elastomeric material that is different than the first elastomeric material.

What is claimed is: 
     
         1 . A composite diaphragm of a pressure compensation system for a roller cone drill bit, comprising:
 an inner surface formed of a first elastomeric material and defining an inner cavity configured to serve as a lubricant reservoir; and   an external surface disposed opposite the inner surface and formed of a second elastomeric material, the second elastomeric material being different than the first elastomeric material.   
     
     
         2 . The composite diaphragm of  claim 1  wherein the second elastomeric material is either a fluoroelastomer material or a perfluoro-elastomer material. 
     
     
         3 . The composite diaphragm of  claim 2  wherein the first elastomeric material is a hydrogenated nitrile butadiene rubber material. 
     
     
         4 . The composite diaphragm of  claim 1  wherein the second elastomeric material resists heat degradation better than the first elastomeric material. 
     
     
         5 . The composite diaphragm of  claim 1  wherein the first and second elastomeric materials are covulcanized during forming of the composite diaphragm. 
     
     
         6 . The composite diaphragm of  claim 1  wherein an adhesive bonds the first elastomeric material to the second elastomeric material. 
     
     
         7 . The composite diaphragm of  claim 1  further comprising a flange portion, the flange portion formed of a third elastomeric material having a stiffness greater than either the first or second elastomeric material. 
     
     
         8 . A composite diaphragm of a pressure compensation system for a roller cone drill bit, comprising:
 a body portion defining an inner cavity and being formed from a first elastomeric material; and   a flange portion extending radially from the body portion and being formed from a second elastomeric material, the second elastomeric material having a stiffness greater than the first elastomeric material.   
     
     
         9 . The composite diaphragm of  claim 8  wherein the second elastomeric material is a fluoroelastomer material. 
     
     
         10 . The composite diaphragm of  claim 9  wherein the body portion comprises a tip portion defining a pressure relief hole and the tip portion is formed of a hydrogenated nitrile butadiene rubber material. 
     
     
         11 . A roller cone rock bit, comprising:
 a plurality of legs, each leg supporting a shaft and a pressure compensation system;   a roller cone rotatably mounted to the shaft and supporting a plurality of cutting structures;   a seal disposed between the shaft and the roller cone; and   the pressure compensation system comprising a composite diaphragm having an inner surface and an external surface opposite the inner surface, either the inner or the external surface being exposed to a lubricant, the composite diaphragm formed of a plurality of elastomeric materials.   
     
     
         12 . The roller cone rock bit of  claim 11  wherein the inner surface is exposed to the lubricant and functions as a reservoir for the lubricant. 
     
     
         13 . The roller cone rock bit of  claim 11  wherein the composite diaphragm further comprises a flange portion, a generally cylindrical portion extending from the flange portion, and a tapered portion extending from the generally cylindrical portion. 
     
     
         14 . The roller cone rock bit of  claim 13  wherein the tapered portion of the composite diaphragm is delimited by a tip portion. 
     
     
         15 . The roller cone rock bit of  claim 14  wherein the tip portion of the composite diaphragm defines a pressure relief hole. 
     
     
         16 . The roller cone rock bit of  claim 11  wherein the plurality of elastomeric materials comprises a first elastomeric material and a second elastomeric material, and the composite diaphragm further comprises a flange portion formed of the second elastomeric material, the second elastomeric material having a stiffness greater than a stiffness of the first elastomeric material. 
     
     
         17 . The roller cone rock bit of  claim 11  wherein the plurality of elastomeric materials comprises a first elastomeric material and a second elastomeric material, and the composite diaphragm further comprises a tip portion defining a pressure relief hole, the tip portion formed of the second elastomeric material, the second elastomeric material having a tear strength greater than a tear strength of the first elastomeric material. 
     
     
         18 . The roller cone rock bit of  claim 17  wherein the second elastomeric material is a hydrogenated nitrile butadiene rubber material. 
     
     
         19 . A composite diaphragm for a roller cone rock bit, comprising:
 a body portion including a generally cylindrical portion and a tip portion;   a flanged portion disposed at a base of the body portion;   the generally cylindrical portion having an inner surface formed of a first elastomeric material and defining an inner cavity configured to serve as a lubricant reservoir and an external surface disposed opposite the inner surface and formed of a second elastomeric material, the second elastomeric material being different than the first elastomeric material; and   the tip portion defining a pressure relief hole and being formed of a third elastomeric material.   
     
     
         20 . The composite diaphragm of  claim 19  wherein the third elastomeric material is a hydrogenated nitrile butadiene rubber material. 
     
     
         21 . The composite diaphragm of  claim 20  wherein the first elastomeric material is also a hydrogenated nitrile butadiene rubber material and the third elastomeric material has a greater tear strength than the first elastomeric material. 
     
     
         22 . The composite diaphragm of  claim 21  wherein the flanged portion is formed from a fluoroelastomer material.