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).
Chipping of dynamo and motor brushes and proposing solutions to improve bedding.
| Identifier | ExFiles\Box 50\5\ Scan334 | |
| Date | 8th July 1924 | |
| SFT {Mr Swift} /Mr. Brock. c. Mr. Davies. c. EFC. {E. Fowler Clarke - Electrical Engineer} X.4333 BY12/H8.7.24. X.4333. X.967C. X.4637. DYNAMO & MOTOR. RE BRUSHES. We have recently had an opportunity of discussing the brush question with Mr. Lawrence of the Le Carbone Company. The opportunity was of distinct advantage to us as I was able to elucidate information which undoubtedly will be helpful. In the first place, the chipping of our brushes is unquestionably due to the fact that we specify all of our parts too accurately. An examination of our brush drawings makes it clear that we specify for the surface on a commutator the exact radius of the commutator. We also definitely specify the angle of the brush holder and its position. If all these parts were accurately produced then we should get a correct result, but unfortunately it will happen that the angle of the brush holder or some other factor varies so that the brush does not bed correctly on the commutator in the first instance. To overcome this difficulty I propose to increase the radius on the curvature of the bearing surface of the brush possibly by as much as approx. 1/8". This will permit slight errors in the axis of the guide for the brush without forcing the brush to act on one extreme corner or the other. A slight amount of running with the dynamo not generating should then result in bedding the brush in. This will result in the tendency for the brush to bed on its centre surface rather than on one extreme end or the other. At the same time, a slight chamfer of .030" will be added to the leading and trailing edges of the brushes. The result of this will be that we shall not 'nip' the trailing end of the brush in the slot produced in the commutator by the clearing away of the mica. It is this 'nipping' action which breaks away the brush when the machines are being run originally. It would be of distinct advantage for us to have a scheme for 'running in' the brushes on a diameter larger than the commutator, which would be coated with fine emery cloth. We should also at the same time have some means of accurately measuring the relation of the brush holder to the commutator to make sure that the brush slides radially reckoned from the commutator itself. Contd. | ||