Sub-surface enhanced gear

Abstract

An improved gear including a plurality of teeth defining a surface, the teeth each having a substantially continuous first subsurface stress layer located below the surface, and a second subsurface stress layer located below the first subsurface stress layer, the first subsurface stress layer comprising a thickness of compressive residual stress.

1 . A gear including a plurality of teeth extending outward from a body, each tooth being spaced apart from an adjacent tooth, the portion of the body between adjacent teeth defining a bottom land, each tooth having a tooth face and the top land, the tooth face forming a tooth fillet at the juncture with the bottom land, the top land, the bottom land and the tooth face defining a surface of the gear, the gear comprising: 
 a plurality of the teeth each having a substantially continuous subsurface stress layer which extends substantially under the tooth face and top land, the subsurface stress layer having a thickness of compressive residual stress, at least a portion of the layer of compressive residual stress being formed by a process comprising the steps of:    providing a high speed centrifugal processing apparatus having an outer housing with a central axis, and at least one inner vessel with a central axis;    placing the gear into the inner vessel;    placing abrasive media into the inner vessel; and    rotating the inner vessel about its central axis and about the central axis of the outer housing, the inner vessel rotating at high speed relative to the outer vessel, the high speed rotation causing the abrasive media to contact the surface of the gear, the contact by the abrasive creating at least a portion of the compressive residual stress in the gear.    
   
   
       2 . A gear according to  claim 1  wherein the thickness of the compressive residual stress is non-uniform.  
   
   
       3 . A gear according to  claim 1  wherein the thickness of the compressive residual stress is at least about 0.005 inches.  
   
   
       4 . A gear according to  claim 1  wherein the thickness of the compressive residual stress is at least about 0.010 inches.  
   
   
       5 . A gear according to  claim 4  wherein the thickness of the compressive residual stress is greater than about 0.012 inches.  
   
   
       6 . A gear according to  claim 1  wherein the subsurface stress layer extends substantially under the tooth fillet.  
   
   
       7 . A gear according to  claim 1  wherein the subsurface stress layer extends substantially under the tooth fillet and the bottom land.  
   
   
       8 . A gear according to  claim 1  wherein magnitude of the compressive residual stress is not uniform across the thickness.  
   
   
       9 . A gear according to  claim 1  wherein the compressive residual stress is at least about 50 ksi.  
   
   
       10 . A gear according to  claim 1  wherein the compressive residual stress is at least about 100 ksi.  
   
   
       11 . A gear according to  claim 1  wherein the compressive residual stress is at least about 175 ksi.  
   
   
       12 . A gear including a plurality of teeth extending outward from a body, each tooth being spaced apart from an adjacent tooth, the portion of the body between adjacent teeth defining a bottom land, each tooth having a tooth face and the top land, the tooth face forming a tooth fillet at the juncture with the bottom land, the top land, the bottom land and the tooth face defining a surface of the gear, the gear comprising: 
 a plurality of the teeth each having a substantially continuous first subsurface stress layer located below the surface, and a second subsurface stress layer located below the first subsurface stress layer, the first subsurface stress layer comprising a thickness of compressive residual stress, at least a portion of the layer of compressive residual stress being formed by a process comprising the steps of:    providing a high speed centrifugal processing apparatus having an outer housing with a central axis, and at least one inner vessel with a central axis;    placing the gear into the inner vessel;    placing abrasive media into the inner vessel; and    rotating the inner vessel about its central axis and about the central axis of the outer housing, the inner vessel rotating at high speed relative to the outer vessel, the high speed rotation causing the abrasive media to contact the surface of the gear, the contact by the abrasive creating at least a portion of the compressive residual stress in the gear.    
   
   
       13 . A gear according to  claim 12  wherein the thickness residual compressive stress is at least about 0.005 inches.  
   
   
       14 . A gear according to  claim 12  wherein the thickness of the residual compressive stress is greater than about 0.012 inches.  
   
   
       15 . A gear according to  claim 12  wherein the subsurface stress layer decreases in magnitude through substantially the first layer from a maximum at the surface.  
   
   
       16 . A gear according to  claim 12  wherein the residual compressive stress is at least about 50 ksi.  
   
   
       17 . A gear according to  claim 12  wherein the gear includes a layer below the surface that is carburized, and wherein the compressive residual stress extends below the surface and the carburized layer.  
   
   
       18 . A method of increasing the compressive residual stress in a gear comprising the steps of: 
 providing a high speed centrifugal processing apparatus having an outer housing with a central axis, and at least one inner vessel with a central axis;    placing a gear into the inner vessel;    placing abrasive media into the inner vessel; and    rotating the inner vessel about its central axis and about the central axis of the outer housing, the inner vessel rotating at a speed relative to the outer vessel so as to produce acceleration of the media within the vessel in excess of 10 g's, the high speed rotation causing the abrasive media to contact the surface of the gear, the contact by the abrasive creating at least a portion of the compressive residual stress in the gear.    
   
   
       19 . A method of increasing the compressive residual stress according to  claim 18  wherein the accelerations are in excess of 15 g's.  
   
   
       20 . A method of increasing the compressive residual stress according to  claim 18  wherein the inner vessel is rotated for at least 6 minutes.