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 and improvements for motor brush holders and insulation.
| Identifier | ExFiles\Box 51\1\ Scan062 | |
| Date | 21th April 1922 | |
| Contd. -2- EFC1/T21.4.22. (5) The insulation between the brush holders and the end plates should completely cover the machined area, which itself should give a margin all round as compared with the corresponding surface of the brush holder. If this is not done and the insulation be made of continental bakelite the accumulation of brush dust will occur, forming a leakage path to earth, which the heat generated will carbonise the continental bakelite and the carbonisation will spread progressively between the metal surfaces until the whole brush holder becomes completely earthed. This has not happened on our own machine, but has happened on a Lucas starter motor, due to the same fault. (Regarding our previously mentioned point of the continental bakelite shrinking, this does not now appear to be the case, it having turned out to have been "paxoline" where this was experienced). (6) With the increased depth of brush we do not think that the slightly increased tension on the brush springs will be necessary. (7) We are now advocating, and apparently R.{Sir Henry Royce} has agreed to this, the use of a narrower third brush, the thickness of the brush to be such as to cover exactly one commutator segment, which of course means a narrower brush holder. At present we file the brush away to the right thickness. As the exact location of the brush is very important it is particularly necessary on any machines in use with the third brush which is thinned, to replace the brush the correct way round. In any case we think, as already mentioned, that the brush pig-tail position should be standardised as being the furthest away possible from the main body of the machine. When the new brush and brush holder details are ready, we wish to order further Le Carbone brushes in a grade as nearly similar as possible to C.M.5 Morganite which, from our experience to date, we consider to be the best so far. EFC. | ||