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).
Letter to The Morgan Crucible Co. Ltd. regarding the testing and supply of brushes for a starter motor.
| Identifier | ExFiles\Box 35\1\ scan 015 | |
| Date | 17th September 1919 | |
| X.2656 H.R. 257 a (100 T/S.SF. 576. 18-4-19) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 2354 EFC6/T. 17th Sept. 1919. The Morgan Crucible Co. Ltd., Battersea Works, Church Road, London, S.W.11 Dear Sirs, Re Brushes for R.R. Starter Motor. X.2656 ✓ We would like again to take up with you the question of brushes for our starter motor. We are sending to you three brushes to our standard design G.3901, also three samples of yours which you recently submitted to us, all of which we should be glad to receive back from you at your convenience. At the present moment you are supplying to us as standard for our present starter motor, brushes similar to the one herewith with fibre insulating rings on the leads, which you now call C.M. (but which apparently was grade C.M.1 before the War). A Sample of a brush marked C.M. which, by comparing with your recent sample, should be now called C.M.1, is also included, so also is a further brush marked C.M.4 We have experimented with brushes of these three grades on our starter motor and have found as a result of these experiments, that the first brush mentioned of present C.M. quality appears to be easily the most satisfactory of the three, and the brush marked C.M.4 easily the worst. The second mentioned, or bronze coloured brush, seems to get into trouble on the commutator fairly rapidly, and the last mentioned C.M.4 brush will scarcely give any satisfaction at all but soon allows the commutator to get into a very bad condition. We should like to have your views on the matter, and for this purpose we give below the following information:- Approx. current density in brush at instant of switching on motor 300 amps/sq" Approx. current density in motor when normally turning engine over 150 amps/sq" Approx. pressure of brush on commutator. 3 lbs/sq." Contd. | ||