Effect of Shot Peening on Improvement of Fatigue Strength for Metal Bellows

Abstract

Generally metal bellows (it is hereafter described as a bellows) are known for a seal to defend a leak being elasticl).~ecently small size bore bellows are getting to expect to a seal of pump which was small and can use under the circumstances of high pressure.However, until now, it would be difficult to achieve the fatigue strength for required specifications in most cases. Meanwhile it was known for that shot peening had an effect on improving fatigue strength2).lt can be expected that it is difficult to obtain a large compressive residual stress on the inner surface of small bore size bellows by shot peening processh order to obtain the effect of shot peening on the inner surface of bellows, a new shot peening processes by using a air peening n~achine and a reflective plate were developed.It was found that this method can apply the shots to the inner surface of bellows effectively, to iniprove the fatig~le life of bellows, coniparing with nonshot peening one. It can be also noted that the measurements of residual stress by X-ray diffraction is not applicable to the material of bellow, SUS304 stainless steel. The measurement of residual stress is essential to dcterinine shot peening conditions. Since the structure of SUS304 bellows is mixed :x\niit!? austenite 2nd ~ t ~ ~ ~ ~ i g ( l , c c ~ d ll?art~llsite by C O ! ~ ferming the sig!?a! tn noise r a t i ~ is too small to show the peak of X-ray diffiaction. In order to solve these problems, the SUS63 1 stainless steel bellows was selected because it was a good workability and had a lot of inartensite. The optimuni shot peening conditions were decided by using residual stress of SUS63 1 bellows.