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).
Notes on the design decisions, materials, and calculations for aluminium brake drums.
| Identifier | ExFiles\Box 159\5\ scan0088 | |
| Date | 5th November 1940 | |
| Rm.{William Robotham - Chief Engineer} from Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale} Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale}16/ML.5.11.40. ALUMINIUM BRAKE DRUMS. (Notes compiled from memory, no figures of any sort available.) 1. We decided originally to go for an aluminium case with a thin insert liner; reason - this is the lightest possible construction. 2. We decided to shrink in the liner instead of casting it in; reason - a) we thought we should have complete control of interference fit (not so in practice) b) the Hispano drum always "crazed", which would ruin the linings of a high efficiency brake system in very little time (see notes on I.M.W's "rumbled" drums.) c) cost was not of first importance in those high and far off days. 3. We first used N.M.C. steel for liner. Only one drum was made, at a cost of about £50, I should think. This drum worked fairly well due largely to the incredible time it took to make - natural ageing of aluminium. 4. We made some drums with "Birmal" austenitic iron liners, expansion co-efficient 18 X 10-6, which experience has convinced me that such a liner is bound to come loose. This is lucky because Birmal is expensive. Reason as follows :- a) Interference necessary on 12" drum to take brake torque should not be less than .012" b) Experience has shown that interference fit must disappear at about 200 deg. C. or else drum will expand plastically, resulting in reduction of interference when cool. c) Working temperature of 100 deg. C. is usual and should not be exceeded. A little calculation will show that with expansion figures of 18 X 22.4 these conditions are impossible to satisfy. For iron x RR.53c. reduction of shrink fit per 100 deg. C. For a 12" drum = (22.4-12) x 10-6 x 12" x 100° = .0125 app: For Birmal x RR.53c. = (22.4-18) x 10-6 x 12" x 100° = .0054 app: - Continued - | ||