From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Micro-examination report on a failed Hypoid Gear after a dynamometer test.
| Identifier | ExFiles\Box 136\5\ scan0257 | |
| Date | 4th June 1930 | |
| Y2066 Micro-Examination Report. M696. By: Hll/EAL4.6.30. Laboratory. c to Hs.{Lord Ernest Hives - Chair} Re Hypoid Gear marked "BH25 off Dyno.Test after running 65 miles" G70878/9. This gear was one of three which failed when run on Price's Special Black Gear Compound. The following normal hardness figures were obtained Brinell Hardness of core. Rockwell Hardness of tops of teeth. Pinion -------- 200 C59 - 60 Wheel -------- 195 - 212 C61. The hardness range quoted on the drawing, viz, 160 - 240, is, we consider, rather on the low side. Fracture tests showed that the surface of the teeth on the wheel had a granular fracture, indicating the presence of cellular cementite. This was confirmed by micro-sections which showed 0.040" of case, of which an outer layer 0.012" to 0.018" deep consisted of cells completely surrounded by free carbide. The wheel has been given only a single quench from 740 C, which explains the presence of free cementite. We understand that although half-a-dozen gears have been double-quenched for the Exptl. Dept. this treatment is not adopted for production work on account of the tooth distortion produced. Whether the large amount of cementite present has been the cause of failure or not will rest with the results of further tests on other hypoid gears which are being supplied by the Exptl. Dept. The pinion showed a similar case, but with a greater total depth, 0.050", and a thinner layer of free carbide, viz, 0.008" to 0.012". The surrounding envelopes of carbide in the case of the pinion tended to be thinner and more broken in character. Hl. HE | ||