The Use Of "3m" Brand Roto Peen Product In Conditioning Metal Surfaces

Author:  Winter, P.M.
Source:  3M Company, St. Paul, MN, Oct. 1, 1968
Doc ID:  1970015
Year of Publication:  1970
Abstract:  
The residual stress condition of a metal part plays an important role in determining its useful life. Residual stresses normally exist in a heterogeneous condition caused by mechanical, thermal, or chemical treatments. The sense of the surface residual stresses is of primary importance. The highest stresses from the applied load usually occur at the surface, and the surface also has stress concentrating regions due to design geometry or metal processing. A net tensile (applied plus residual) surface stress tends to produce cracks, while a net compressive surface stress tends to prevent them. The two primary mechanisms of surface crack development, leading to ultimate failure, are fatigue and stress corrosion. Mechanical prestressing, such as cold rolling, hammer peening, and shot peening, has commonly been used to produce favorable compressive residual stresses. These methods produce residual stresses by permanently deforming only the surface layers of a metal part. Surface layers are expanded radially so that when the deforming force is removed, the elastic spring-back from the underlying material leaves the surface layers in compression. Conventional shot peening is an effective method of prestressing metal parts. However, the containment of free shot particles is a serious problem when a portable shot peening system is required. In addition, the requirement of relatively large special equipment prevents applications in certain desirable areas. To fill these needs, 3M has developed a new, portable, self-contained (bonded shot) shot peening product concept. Some typical applications for the 3M Brand Roto Peen Products are: reworking, repair, and reconditioning of critical parts; stress relieving weld joints; peening fuel tank assemblies and wing sections where contamination is intolerable; peen forming and contouring; stress relieving inside surfaces of pipes and holes; in-place peening with minimum disassembly; and repair of damaged parts in production.