Texturing of the bearing surface for a roller cone rock bit

Abstract

Surface texturing is employed to modify the topography of one or more surfaces (radial or cylindrical) of the bearing system for a roller cone rock bit. The surface texturing results in a dimpled surface which retains additional lubricant helpful in reducing friction in the boundary and mixed lubrication regimes. Shot peening is disclosed as one method for texturing the desired surface.

What is claimed is: 
     
         1 . A roller cone drill bit, comprising:
 a journal bearing structure having a bearing system including a bearing surface;   at least a portion of the bearing surface having a surface texture, wherein the surface texture is formed by shot peening in a two-step process including a first shot peening action wherein the portion of the bearing surface is bombarded at a first intensity level by first small spherical media of a first average size and a subsequent second shot peening action wherein the same portion of the bearing surface is bombarded at a second intensity level by second small spherical media of a second average size, the first and subsequent second shot peening actions creating lubricant reservoirs on the same portion of the bearing surface, the lubricant reservoirs being adapted to contain lubricant for the bearing system; and   wherein the first intensity level is greater than the second intensity level and the first average size is larger than the second average size.   
     
     
         2 . The roller cone drill bit of  claim 1  wherein the bearing surface is a thrust surface. 
     
     
         3 . The roller cone drill bit of  claim 2  wherein the thrust surface is of a radial kind 
     
     
         4 . The roller cone drill bit of  claim 1  wherein the bearing surface is a journal surface. 
     
     
         5 . The roller cone drill bit of  claim 4  wherein the journal surface is of a cylindrical kind 
     
     
         6 . The roller cone drill bit of  claim 1  wherein the journal bearing structure includes a bushing and the portion of the bearing surface is one of an inside or outside surface of the bushing. 
     
     
         7 . The roller cone drill bit of  claim 1  wherein the journal bearing structure includes a shaft and the bearing surface is an outer surface of the shaft. 
     
     
         8 . The roller cone drill bit of  claim 1  wherein the portion of the bearing surface is less than an overall circumferential surface of the bearing surface. 
     
     
         9 . The roller cone drill bit of  claim 8  wherein the portion of the bearing surface is a load bearing portion of the bearing surface. 
     
     
         10 . The roller cone drill bit of  claim 8  wherein the surface textured portion of the bearing surface is formed as a plurality of strips on the bearing surface. 
     
     
         11 . The roller cone drill bit of  claim 10  wherein the surface textured portion of the bearing surface is a load bearing portion of the bearing surface and the strips align with load forces applied against the bearing surface. 
     
     
         12 . The roller cone drill bit of  claim 1  wherein the first intensity level is in a range of 0.007-0.010 inches measured on a C-type Almen strip and the second intensity level is in a second range of 0.007-0.010 inches measured on an A-type Almen strip. 
     
     
         13 . A drill bit, comprising:
 a shaft including a sealing surface and a bearing surface;   a roller cone having an annular gland and being rotatably mounted to the shaft such that a bushing on the roller cone aligns with the bearing surface and the annular gland aligns with the sealing surface, the bearing surface of the shaft or an inner surface of the bushing having a surface texture including a plurality of dimples;   wherein the plurality of dimples are formed by shot peening in a first shot peening action the bearing surface of the shaft or the inner surface of the bushing at a first intensity level by a first small spherical media of a first average size and shot peening in a second subsequent shot peening action the same bearing surface of the shaft or inner surface of the bushing at a second intensity level by a second small spherical media of a second average size;   wherein the first intensity level is greater than the second intensity level and the first average size is larger than the second average size; and   wherein the first and second subsequent shot peening actions create lubricant reservoirs on the bearing surface of the shaft or the inner surface of the bushing, the lubricant reservoirs being adapted to contain lubricant.   
     
     
         14 . The drill bit of  claim 13  wherein, following completion of the second shot peening action, more than 60% of the bearing surface of the shaft or of the inner surface of the bushing has been textured with dimples. 
     
     
         15 . The drill bit of  claim 14  wherein, following completion of the second shot peening action, 70-90% of the bearing surface of the shaft or of the inner surface of the bushing has been textured with dimples. 
     
     
         16 . The drill bit of  claim 14  wherein, following completion of the second shot peening action, substantially 100% of the bearing surface of the shaft or of the inner surface of the bushing has been textured with dimples. 
     
     
         17 . A drill bit, comprising:
 a shaft including a sealing surface and a bearing surface;   a roller cone having an annular gland and being rotatably mounted to the shaft such that a bushing on the roller cone aligns with the bearing surface and the annular gland aligns with the sealing surface;   a plurality of dimples formed on the bearing surface of the shaft or an inner surface of the bushing by:   shot peening in a first shot peening action the bearing surface of the shaft or the inner surface of the bushing at a first intensity level by a first small spherical media of a first average size;   shot peening in a second subsequent shot peening action the same bearing surface of the shaft or inner surface of the bushing at a second intensity level by a second small spherical media of a second average size;   wherein the first intensity level is greater than the second intensity level and the first average size is larger than the second average size;   wherein the first and second subsequent shot peening actions form lubricant reservoirs on the bearing surface of the shaft or the inner surface of the bushing, the lubricant reservoirs being adapted to contain lubricant for a drill bit; and   wherein the plurality of dimples provide intermittent coverage.   
     
     
         18 . The drill bit of  claim 17  wherein the intermittent coverage is provided on a region which is less than an overall circumferential surface for the bearing surface or for the inner surface of the bushing. 
     
     
         19 . The drill bit of  claim 17  wherein the intermittent coverage is provided on a region which is a load bearing portion of the bearing surface or of the inner surface of the bushing. 
     
     
         20 . The drill bit of  claim 19  wherein the intermittent coverage is formed as strips on the bearing surface or on the inner surface of the bushing. 
     
     
         21 . The drill bit of  claim 20  wherein the region is a load bearing portion of the bearing surface or of the inner surface of the bushing and the strips align with the load forces applied against the bearing surface or against the inner surface of the bushing.