Taku Ueno

An investigation of surface failure of surface-hardened gears by scanning electron microscopy observations

Abstract The tooth surface of surface-hardened gears often becomes grey stained under a heavy load before pitting or spalling occur. The grey-stained area increases with running time and this failure causes degradation of the tooth profile. The nature of grey staining and the influence of surface conditions on the phenomena are investigated by scanning electron microscopy observations of the surfaces of gear teeth and rollers. It is established that the grey staining consists of many microcracks and micropits. Their formation and wearing off occur successively. It is reconfirmed that surface roughness has a significant influence on grey staining.

Surface Durability of Spur Gears at Hertzian Stresses Over Shakedown Limit

Using a new type of gear-load testing machine and a disk-type rolling fatigue testing machine designed and made by the authors, the upper limits of Hertzian contact stress allowable on rolling contact surfaces were investigated. It was shown conclusively that gears and rollers made of soft carbon steels could be rotated beyond 108 revolutions at Hertzian stresses over shakedown limit (≈ 0.4 HB ). In the case of gears, pits having a pitting area ratio of 0.04 percent occurred during 1.16 × 108 rotations at a Hertzian stress of 0.50 HB . However, no pitting occurred on the roller rotated through 1.20 × 108 revolutions at a Hertzian stress of 0.71 HB , although appreciable changes in texture were observed at the subsurface. In order to rotate gears or rollers at Hertzian stresses over shakedown limit, their surface must either be very smooth initially or after a short period of running, and an oil film must be formed between contacting surfaces.

The effects of lubricating oil additives on the performance of worm gears

Abstract The effects of various types of lubricating oil additives (fatty oils, sulfurized fatty oils, metal soaps, E.P. additives) were investigated with a power circulating worm gear testing machine using hardened steel worms and phosphor bronze wheels and the following results were obtained: 1. (1) All additives used showed antiseizure properties in worm gear lubrication of steel and phosphor bronze. 2. (2) The additives affected the occurrence of pitting on the tooth surface of the worm gear; some phosphorous compounds promoted progressive severe pitting. 3. (3) The fatty oils and sulfurized fatty oils gave high gearing efficiency; the highest efficiency was over 93 %. 4. (4) The additives affected the wear and roughness of the gear tooth surface. Good results were obtained with fatty oils and some types of E.P. additives.

The Effects of Lubricating Oil on Fatigue Failure in Gears

歯車用潤滑油の耐ピッチング性能を、二円筒試験機により評価した。テストローラとして、炭素鋼およびCr-M0鋼を用い、すべり率-18%に設定し、テストローラの硬さ、表面粗さ、接触応力を変えて実験した。この結果次のことがわかった。(1)潤滑油の粘度増加、およびM0系潤滑油添加剤の作用は、耐ピッチング性能の向上に有効である。(2)磨耗が進行する実験条件下では、見かけ上ピッチング寿命が延長する。

Load-carrying Capacity of the HB〓340 (Hardened and Tempered) Gears : 1st Report, Effect of Surface Roughness on the Rolling Contact Fatigue of the Rollers and Surface Durability of the Habbed Gears

Surface durability of the HB a 340 (hardened and tempered) hobbed gears was investigated by using a 2-roller-type fatigue tester and a power circulating-type gear tester. It is found that the initial surface roughness has much more influence on the rolling contact fatigue of the HB a 340 steel than that of the HB a 150 (annealed) one, and therefore, that the pitting limit of the HB a 340 hobbed gears is Pmax a 0.2HB kgf/mm2 due to the rough initial surface. Thus, the tooth surface of the HB a 340 hobbed gears should be finished as smooth as possible in order to obtain higher surface durability by the effect of hardness.