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).
Performance, materials, and friction coefficient of brake drums and Ferodo brake liners.
| Identifier | ExFiles\Box 32\2\ Scan030 | |
| Date | 14th October 1921 | |
| R.R. 65 (500 H) (S.E. 441. 22-1-18.) Bm. 2/212/18. Handwritten: X3458 OCT 17 Md. from BY.{R.W. Bailey - Chief Engineer} c. Hs.{Lord Ernest Hives - Chair} Handwritten: X3458 X3409 Stamp: RECEIVED BY4-P14.10.21. 40/50 CHASSIS. REAR HUB & BRAKE. RE BRAKE LINERS. Further to our memo BY4-P101021, and in reply to Messrs. Ferodo Ltd. letter of the/12th inst., reference FJF/DHL, we wish to put on record a/plain statement in regard to phenomena, apart from all question of deductions we may make. When we turn out a car fitted with our present brake drums and Ferodo liners, the amount of pressure upon ones foot necessary to pull up the car is altogether different when the car is new and the Ferodo and the brake drum not polished, than what is required when the car has run some 3000 or 4000 miles and the brake used in an ordinary way, without having to negotiate during that time long down hill gradients which demand continuous use of the brake, and therefore heat up the drums. One can definitely say that from two-to-three times the amount of pressure originally required is demanded under the conditions referred to, and an examination of the brake drum and Ferodo Shoe, simply indicated that whilst in the first place these were smooth, in the second case both of these become highly polished, and in this condition there is no question as to the accuracy of the phenomena described above. With reference to Messrs. Ferodo Ltd. suggestion, that if they put the shoes in question on their standard testing machine they will discover that the co-efficient of friction will remain approximately .29, this may turn out as they expect, but obviously one of the factors which we have defined is absent, namely, the highly polished brake drum of our special material. We are pointing this out mainly with the object of interesting Messrs. Ferodo Ltd., in the actual conditions, and we suggest that the test they propose does not reproduce these conditions, as I understood the friction surface of their testing machine was cast iron, whilst the surface against which the shoe presses on our car is a .6 carbon steel of a Brinell figure between 201 and 229, the Brinell figures in question having been kept purposely low in order to avoid polishing, as we rather anticipated that this might occur, but at the same time we do know that a soft mild steel cuts up badly and does not polish. We are therefore inclined to think that somewhere between a low carbon steel of approximately .15 carbon content and our .6 carbon steel there is a carbon content which will neither polish unduly nor score unduly. contd. | ||