Coil Spring

Author:  William H. Wallace
Source:  US Patent 2,351,726
Doc ID:  1940003
Year of Publication:  1940
Abstract:  
My invention relates to coil springs and the art of treating the same to increase their useful life in comparison with similar springs as heretofore manufactured. Th invention is particularly applicable to helical compression springs such as are commonly used as vale springs in internal combustion engines and as suspension springs in automobiles and the like, which are particularly susceptible to failure due to fatigue resulting from the repeated application of stresses thereto. It is known that the fatigue life of springs that are subject to repeated flexing stresses may be increased by the cold working of the fibers at and near the surfaces of the metal, as by shot-blasting, and efforts have heretofore been made to apply this knowledge to the manufacture of coil springs by tumbling the springs in a barrel in which they are being subjected to a shot-blast. This method, however, has not been satisfactory because of lack of uniformity in the springs thus treated which results from the varying degrees of treatment that different springs received on account of the promiscuous manner in which different springs were presented to the blast of shot.