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 comparing a failed hypoid gear wheel with two American-manufactured wheels, including hardness tests and material analysis.
| Identifier | ExFiles\Box 136\5\ scan0260 | |
| Date | 26th June 1930 | |
| Micro-Examination Report. x2066. M697. By c to Hs.{Lord Ernest Hives - Chair} H13/EA26.6.30. Laboratory. Re Hypoid Gears. Further to our report M696. We have examined three more gear wheels. One of these was marked "Result of running 125 miles on Amber A Gear Oil on Axle No.XL45". This had failed in the same way as the gear previously reported. Also two wheels of American manufacture which had given good results with Whitmore's compound have been examined. The following figures were obtained :- Brinell Hardness of core of teeth. Rockwell hardness of tops of teeth. Depth of case. Depth of cellular cementite. Failed Wheel. 216 C58 0.055" 0.020" First American Wheel. 212 C62 0.038" None present on sides of teeth. Second American Wheel. 218/234 C63 0.055" It would appear that the heat-treatment given to the American gears has been such as to ensure the retention of the carbon in a harmless form and the production of a harder surface. The difference between the two types of gear is illustrated by the accompanying photomicrographs A657 (English Gear) and A658 (American Gear). It will be noted that the core hardness of the teeth is approximately the same in both English and American Gears. It should be noted, however, that the American gear has a lower nickel content :- American Gear Analysis. Carbon ------ 0.10% Manganese --- 0.42% Nickel ------ 3.4 % Chromium ---- 0.16% H1. HE | ||