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).
Comparison of two grades of dynamo brushes, 'Z' and 'G3417', including a table of their properties and test observations.
| Identifier | WestWitteringFiles\Q\2-July1927-September1927\ 46 | |
| Date | 18th August 1927 | |
| Contd. -3- EFC3/T18.8.27. In view of the good result obtained with this particular grade, a set has been arranged on a dynamo on 11-G3 for test, and up to the time of writing has run 1100 miles. There is no complaint of this machine and the brushes are doing very well. We asked the Le Carbone representative for a detailed comparison of this grade with the standard Z, and received the following :- Grade "Z". Grade "G3417" Specific resistance, 0.0012 0.0006 (ohms per cu.inch). Admissible load 50 65 (amps. per sq.inch) Contact drop in volts 1.80 2.5 Maximum speed 2000 5000/6000 (feet per min.) Friction coefficient. 0.22 0.23 In this table we were a little surprised to note that the coefficient of friction given for the EG3417 was not less than that for the Z brushes, though they appear to run, when hot, as if they have a lower coefficient. This may perhaps be explained by saying that the coefficient of friction increases with the temperature of the brush more in the case of the Z grade than the EG3417. In regard to (c), my assistant reports :- "The positive brush acquired a fair polish over the leading half of its contact face, but became dull over the trailing half. The negative was fairly well polished but was slightly duller over the trailing half than the leading half. The control brush surface was moderately good. Contd. | ||