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).
Analysis of alloy hardness in bearings, focusing on silicon content, Brinell values, and casting methods.
| Identifier | ExFiles\Box 115\5\ scan0256 | |
| Date | 6th March 1939 guessed | |
| similar heat treatment of our alloy gives a Brinell of 55 to 80. The Silicon content required in these bearings, which is actually extant as an impurity in the aluminium ingot, is unusually low at .19%. This firm has cast bearings in AC 9 with a Silicon content as low as .17% in which case it was found that the Brinell was 45 as cast and 55 to 65 after heat treatment. From experience we find also that with a Silicon content of .28% the hardness is in the region of 80 Brinell. From this it will be seen that the Silicon content has a direct bearing on the hardness of the alloy, and for the purposes of rough calculation it may be said that .02% difference in the Silicon content brings about a 5 Brinell change in hardness. The Wellworthy bearing that was analysed shewed a Silicon content of .19% and Brinell figures as shewn in the Sketch I. An alloy of exactly the same composition when cast by ourselves would shew a Brinell of 65. Messrs. Wellworthy Ltd. assure us that they are most careful to cast at the correct temperature, and it would therefore appear that since the specification and casting temperature are correct, the reason for their not attaining a sufficiently high Brinell is due to method of casting and to die design. The bearings produced by Messrs. Wellworthy Ltd. are cast in the form shewn in sketch II | ||