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).
Continuation of a report detailing the testing methodology for brake lining friction and temperature.
| Identifier | ExFiles\Box 121\1\ scan0074 | |
| Date | 9th November 1938 | |
| - 2 - Continuation: For the attention of Mr. A.F. Martindale. --------------------------- Except for the highest rubbing speeds, the following method of test was adopted. A single small piece of brake lining was attached to the end of a stiff lever, and pressed against the drum surface with a pressure equal to 41 lb/sq. in. The lining was run-in against the drum until it was bedded properly and the drum surface coated with a smear of the lining material, all traces of the previous lining having been removed first. The drum was driven by means of a cord wrapped around the outside several times and pulled by an electric motor. A spring balance was arranged to measure the tension in the cord. Static tests were first made at different points on the drum surface by pulling the cord by hand and reading the spring balance when slip began. A series of dynamic friction tests was then made, each at constant speed. The first test was usually made at a rubbing speed of about 0.1 ft/sec, and the speed was increased in steps up to about 12 ft/sec. For higher speeds, up to 60 ft/sec., a swinging-field dynamometer was used for driving the drum and measuring the torque. After the test at the highest speed, the speed was reduced in stages and the tests repeated, finishing with a static test. The temperature was kept low by keeping the input of work as low as possible. The area of lining in contact with the drum was only 0.61 sq. in., and in the tests up to 12 ft/sec., the number of revolutions of the drum during a test did not exceed 10. No attempt has been made to measure the surface temperature of the drum, but a thermocouple was inserted in the drum at a small depth below the rubbing surface. In the slow speed tests, this did not indicate a rise of temperature exceeding 1°C., even for linings having a high coefficient of friction, but in the high speed tests the longer running time led to temperature rises of as much as 25°C. In these high speed tests, the surface temperature may have been quite high, but the effect of temperature on the low speed tests was probably not appreciable. As with your curves A, the curve obtained with rising speed generally differed slightly from that obtained with falling speed, and the curves given in Figures 13 and 14 of our Report are the average of the rising and falling curves. You will notice that your tests have only been carried out at speeds up to about 2.5 ft/sec., so that they cannot be compared directly with ours. | ||