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).
Issues with bearing hardness, heat treatment, and rejection rates for Bentley Crankcase Bearings.
| Identifier | ExFiles\Box 115\3\ scan0091 | |
| Date | 5th November 1937 | |
| -2- Another Bearing taken from a stripped engine gave a difference of 13 points in Brinell from one side of the bearing to the other checked on the back, or outside dia. This suggests that the softening was just commencing. That this metal has been under suspicion for some time is evidenced by the fact that the ageing period has been increased from 6-12 hours and again from 12-20 hours as per memos. BY/EM.36/J.6.10.37. and RHC{R. H. Coverley - Production Engineer}/EG.26/DB.{Donald Bastow - Suspensions}5.11.37. On 26th. July, 1937 the metal for Bentley Crankcase Bearings was changed from AC.7 to AC.2 and since its introduction a good deal of trouble has been experienced in maintaining the correct Brinell figure. It has been necessary to heat treat twice to obtain the required Brinell in the first heat treatment when the Bearings are in the pot stage, and again twice in the second heat treatment after further machining. From time to time Bearings which failed to respond to these treatments have been treated in the Laboratory at Hl's instigation, but have failed again and been scrapped. The rejections since introduction of this material are approximately 25%. During July of this year a large batch of bearings was heat treated which failed to respond in Brinell to second heat treatment, and were therefore rejected by Inspection Dept. The Bearings were reported to the Laboratory, who took samples and futher heat treated them in accordance with the second heat treatment. The sample bearings presumably responded satisfactorily to this treatment and authority was given by Messrs. Marriott and Gresham to pass the bulk for further machining, and heat-treatment, and passing to Production. This trouble with Pots showing low Brinell occurred again in September, and a request was made at the time for some written authority to pass Bearings at a reduced figure from that given on the drawing, viz:- 85-90. On 17.9.37. memo' Hs{Lord Ernest Hives - Chair}/JWW.6/HM.{Capt. W. Hallam - Head Repairs}17.9.37. was issued (copy attached) giving a reduced minimum Brinell figure of 73. This authority was questioned by EG. and referred back to BY/EM. and Hl who agreed to an even lower figure of 70 Brinell. However, this figure of 70 was considered rather low by RHC{R. H. Coverley - Production Engineer}/EG. who did not take advantage of it, but maintained the figure of 73 as per memo. continued over. | ||