Influence of Shot Peening on Surface Durability of Case-Hardened Steel Gears (Influences of Shot Velocity and Shot Diameter)

Abstract

In order to investigate the influence of shot peening on the surface durability of case-hardened steel gears, the case-hardened steel gears shot-peened with different shot velocities and shot diameters were fatigue-tested using a power circulating type gear testing machine. The hardness, the compressive residual stress and the surface roughness of the gears were increased by shot peening. The cause of failure of all the test gears was pitting due to surface cracking. The surface durability of the gear shot-peened under medium condition in this experimental range was higher than that of the non-peened gear. On the other hand, that of lightly or strongly shot-peened gear was just as high. Judging from the p max -N curves and also the [A(σ y /H V )] max -N curves, it is denoted in this experimental range that the surface durability of case-hardened steel gears was influenced by the hardness and the surface roughness of the gears. Therefore, it is proposed in this experimental range that the medium shot peening condition, that is, 60m/s shot velocity and 0.6mm shot diameter, should be selected in order to improve the surface durability of case-hardened steel gears.

Fatigue Strength of Steel Rollers and Gears Treated by Cavitation Peening with Short Processing Time (A Case of Processing Time of 1 min and 5 min)

“…The roughness curves of the test rollers were measured on the circumferential surface along their axial direction, and those of the test pinions were measured on the tooth surface along their tooth profile direction, using a surface roughness meter. Here, in the case of shot-peened test pinions (8) , the indentations due to steel shots appeared on the tooth surface, and the grinding marks on the tooth surface disappeared due to the SP. From the surface photographs in Fig.…”

“…The test rollers were taken as the slower rollers, and the mating rollers were taken as the faster rollers. The operating fatigue tests of the gears were performed at a test pinion rotational speed of 1800 rpm using a power circulating type gear testing machine (8) . In this experiment, the test pinions and the mating gears were used as the driven gears and the driving gears, respectively.…”

“…As in the case of the case-hardened steel rollers and gears employed in the previous papers (8), (19) , the maximum amplitude [A(σ y / 3 HV)] max of the ratio of tangential normal stress σ y to Vickers hardness HV was calculated by neglecting the effect of mean stress on fatigue and by assuming that the material strength of the test specimens is proportional to their initial hardness. In the following paragraph, the fatigue life and the fatigue strength of the test rollers and pinions were discussed by the maximum amplitude [A(σ y / 3 HV)] max (21) .…”

“…Consequently, discussing by the maximum amplitude [A(σ y / 3 HV)] max was not considered the effect of the surface residual stress. This evaluation method was the same as the previous paper (8), (21) . Figures 8 and 9 show the relations between the maximum amplitude [A(σ y / 3 HV)] max and the fatigue life N f of the test rollers and pinions, respectively.…”

Influence of density and nickel content on fatigue strength of powder-forged gears - Comparison with ingot steel and sintered steel -

“…The circumferential velocity and specific sliding of the test roller were 4.50 m/s and -25.7 %, respectively, while the corresponding values for the mating roller were 5.65 m/s and +20.5 %. Operating fatigue tests on the gears were performed at a rotational speed of the test pinion of 1800 rpm using a power circulating-type gear testing machine (Seki et al, 2007). The maximum Hertzian stress pmax (Johnson, 1987) on the roller surface and on the tooth flank at the working pitch point was adopted as the standard for loading between the contact surfaces.…”