ショットピーニング加工法の研究(第3, 4報)

In the 1st. and 2nd. reports, shot peening conditions, shot speed and shot number per unit area, etc. were not related. Thus, to decide the working conditions of shot peening process, a new centrifugal type shot peening machine (for experimental use) was devised and manufactured, and the ability tested.The machine facilitated the test conditions: shot speed of 30-85m/sec, dispersion angle of 25° and shot flow rate of about 9kg/min.The residual stress and fatigue strength were measured, and the optimum conditions were studied by shot peening the spring steel (JIS sup-6) under the conditions of 0.5, 0.7, 1.0 and 1.2 mm Cut wire shot and 7.86m/min conveyor speed, in addition to the above conditions.The expeimental results are as follows:(1) Shot velocity was 1.25 times the peripheral velocity of the impeller, the shot size having no effect.(2) There is no relation between shot distribution and shot size and velocity.(3) Peening process hardly hardens quenched and tempered spring steel.(4) When the shot energy determined by the shot size and velocity is equal, the surface residual stress of the specimen is found to decrease beginning at the point of same coverage.(5) Just before the above condition is reached, when the surface residual stress begins to decrease, the fatigue strength shows the maximum value.(6) The best working condition seems to be full coverage with shots of about 1×10-4kg-m energy each.(7) Within the range, investigated the max. and min. fatigue limits under pulsating plane bending were 110kg/mm2 (0.5mm. shot, 49m/sec., 94% coverage) and 62kg/mm2 (1.2mm. shot, 82m/sec., 98% coverage) respectively.