Principle of strengthening technology
Strengthening process is the use of high-speed projectile flow on the impact of the metal surface due to the surface cyclic plastic strain layer, resulting in the microstructure of the layer occurred favorable change and make the surface of the introduction of residual compressive stress field. The microstructure of the surface layer and the residual compressive stress field are two strengthening factors to improve the fatigue fracture and stress corrosion cracking resistance of the metal material and its spring.
Reinforcement is a "cold treatment" process, which is different from the hot processing of metal parts at high temperature. The compressive stress layer is usually extended to the material surface under 0.005 "to 0.030" depths. If necessary, but also by changing the process parameters, such as pellet size and injection / ejection velocity, injection / ejection angle and injection / ejection time to pressure stress layer extending depth increases.
Two important parameters to evaluate the effect of reinforcement are strength and coverage. Coverage (100%, 200% or greater) is mainly relies on visual inspection and strength required representative of spring steel specimen were measured (i.e. Almen test piece