Process for improving fatigue life in spring-cushioned shoes

Abstract

A process for reducing heat transfer within a spring in a spring cushioned shoe, said process comprises the steps of applying a residual compressive stress to said spring, for example by shot peening, and then mounting the spring between an inner sole and an outer sole of the shoe.

1 . A process for reducing heat transfer within a spring in a spring cushioned shoe, said process comprising the steps of: 
 applying a residual compressive stress to said spring; and    mounting said spring between an inner sole and an outer sole of said shoe.    
   
   
       2 . The process of  claim 1  wherein said step of applying a residual compressive stress is selected from a group comprising shot peening, roll burnishing, knurling, compression over a mandrel, heat treating and magnaforming.  
   
   
       3 . The process of  claim 1  wherein said spring comprises a multi-turn crest-to-crest wave spring.  
   
   
       4 . The process of  claim 1  and further comprising the step of baking said spring after applying a residual compressive stress to said spring.  
   
   
       5 . The process of  claim 1  wherein the compressive stress applied to said spring is about 50% of the tensile strength of said spring.  
   
   
       6 . The process of  claim 1  wherein said step of applying a residual compressive stress comprises shot peening.  
   
   
       7 . The process of  claim 6  wherein said shot peening step creates dimples over 10 to 200% of the surface of said spring.  
   
   
       8 . The process of  claim 6  wherein said shot peening step creates dimples over 50 to 100% of the surface of said spring.  
   
   
       9 . The process of  claim 6  wherein said spring is stretched during said shot peening to expose additional surfaces for shot peening.