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).
Laboratory report on the performance, hardness, and composition of bearing alloy AC7, proposing an experimental alternative.
| Identifier | ExFiles\Box 115\1\ scan0029 | |
| Date | 3rd June 1936 | |
| SWDL{Len H. Swindell}- Hile x1020 To Wor.{Arthur Wormald - General Works Manager} Hs.{Lord Ernest Hives - Chair} Er. Rm{William Robotham - Chief Engineer}/Hs.{Lord Ernest Hives - Chair} Dr. HL6/AG.3.6.36. Laboratory. Re: Bearing Alloy AC7. The above alloy has under experimental running, particularly under hot conditions, given some indications of insufficient compression strength. The alloy specification for hardness is 40 to 50 Brinell in production (as used for Bentley) but it has been found that those bearings which have given trouble in the experimental department are about 40. This hardness variation appears to be mainly due to the total hardening elements being near maximum in some casts and near minimum in others. The amount of tin also effects the hardness and strength - particularly under hot conditions of service and this probably is the most important factor since when an isolated big end failure occurred it was found that the tin on that particular bearing was 7.5% (i.e. 1.5% above max. permitted by specifications). Tests on the bearing tester suggested that the present standardised alloy behaved well under heavy load up to about 130oC. even with a soft shaft i.e. about 300 Brinell. With reduction in tin however it was found desirable to increase the shaft hardness. It may be concluded from this it should be possible to reduce the tin somewhat in the bearing alloy on account of the fact that we are now concentrating on V.C.M Crankshafts of Brinell about 580 as nitrided. If desired we could arrange with the Foundry to have some bearing pots cast with a total of tin (and antimony) of 5% which could be marked AC5 for experimental test. This alloy should be about 30% higher in compression strength than AC7 at 100 to 170oC. Hl. HC. | ||