Method for Imparting Residual Compressive Stress in Metal Parts

Abstract

A method of hardening metal parts, such as a rotor or drive link, and parts thus produced. Preferably the method includes imparting residual compressive stresses into the metal parts and uses various small ball type structures to create small compressions in the surfaces of the metal parts. The compressions apply residual stresses to the parts, which strengthen the metal. The substantial uniform ball type structures are pressed into the metal part to control the application of stress into the part and maintain substantial uniform properties within the metal part, which resists future stresses as the part is used in its desired machinery and/or processes.

1 . A method for producing a rotor comprising: 
 (a) providing a metal rotor having an inner surface with a plurality of internal projections and substantially spherical indenting elements; and    (b) forcibly pressing the indenting elements against the inner surface of the rotor to induce compressive stresses in the inner surface to improve the fatigue life of the rotor.    
   
   
       2 . The method of  claim 1  wherein the inner surface includes a width, and the forcibly pressing of step (b) includes forcibly pressing the entire width of the inner surface to induce compressive stresses.  
   
   
       3 . The method of  claim 1  wherein the each internal projection includes a first side and a second side, and the forcibly pressing of step (b) includes forcibly pressing the indenting elements against both sides of each internal projection to induce compressive stresses in the rotor.  
   
   
       4 . The method of  claim 1  wherein the inner surface includes a circumferential base section extending between each internal projection, and the forcibly pressing of step (b) includes forcibly pressing the indenting elements against the base section.  
   
   
       5 . The method of  claim 1  wherein the forcibly pressing of step (b) includes forcibly pressing the indenting elements against the inner surface of the rotor with a drive link having an outer surface substantially corresponding with the inner surface of the rotor to induce compressive stresses in the rotor.  
   
   
       6 . The method of  claim 5  wherein the forcibly pressing of step (b) further includes inducing compressive stresses in the outer surface of the drive link to improve the fatigue life of the drive link by forcibly press the indenting elements between outer surface of the drive link and the inner surface of the rotor.  
   
   
       7 . The method of  claim 1  wherein the forcibly pressing of step (b) includes forcibly pressing indenting elements having a diameter in the range of 0.5 millimeters to 4.0 millimeters at the inner surface of the rotor.  
   
   
       8 . A method for producing a rotor comprising: 
 (a) providing a metal rotor having an inner surface with a plurality of internal projections, a drive link having an outer surface substantially corresponding with the inner surface of the rotor, and substantially spherical indenting elements; and    (b) forcibly pressing the indenting elements between the inner surface of the rotor and the outer surface of the drive link to induce compressive stresses in the inner surface of the rotor to improve the fatigue life of the rotor.    
   
   
       9 . The method of  claim 8  wherein the forcibly pressing of step (b) further includes inducing compressive stresses in the outer surface of the drive link to improve the fatigue life of the drive link.  
   
   
       10 . The method of  claim 9  wherein the inner surface includes a rotor width and the outer surface of the drive link includes a drive link width, and the forcibly pressing of step (b) includes forcibly pressing both widths to induce compressive stresses.  
   
   
       11 . The method of  claim 10  wherein 
 (a) the inner surface includes a circumferential base section extending between each internal projection;    (b) the drive link includes an exterior circumference; and    (c) the forcibly pressing of step (b) includes forcibly pressing the indenting elements against the base section and the exterior circumference.    
   
   
       12 . The method of  claim 11  wherein the forcibly pressing of step (b) includes forcibly pressing indenting elements having a diameter in the range of 0.5 millimeters to 4.0 millimeters at the inner surface of the rotor.  
   
   
       13 . An improved rotor comprising: 
 a metal rotor having an inner surface with a plurality of internal projections, the plurality of internal projections having an initial fatigue life, wherein the fatigue life of the internal projections of the inner surface of the rotor has been increased by inducing compressive stresses in the internal projections to improve the fatigue life of the rotor.    
   
   
       14 . The rotor of  claim 13  wherein the internal projections of the inner surface of the rotor have been compressed under a static load by spherical indenting elements.  
   
   
       15 . The method of  claim 13  wherein the inner surface includes a circumferential base section extending between each internal projection, each base section including an increased fatigue life by having been compressed under a static load by spherical indenting elements.  
   
   
       16 . An improved rotor and drink link combination comprising: 
 a metal rotor having an inner surface with a plurality of internal projections, the plurality of internal projections having an initial fatigue life, wherein the fatigue life of the internal projections of the inner surface of the rotor has been increased by inducing compressive stresses in the internal projections to improve the fatigue life of the rotor; and    a metal drive link having an outer surface substantially corresponding with the inner surface of the rotor, the outer surface having an initial fatigue life, wherein the fatigue life of the outer surface of the drive link has been increased by inducing compressive stresses in the outer surface to improve the fatigue life of the drive link.    
   
   
       17 . The rotor of  claim 16  wherein the internal projections of the inner surface of the rotor and the outer surface of the drive link have been compressed under a static load by spherical indenting elements.