As a result of the general policy of the Motor Transport Corps to standardize the materials used for automotive vehicles for Army Service, in cooperation with the Bureau of Standards, the Society of Automotive Engineers and the automotive industry, the Bureau of Standards has been engaged for some time in developing a standard method for testing brake-linings. While the work is not complete, much information has been gained. This paper reports the progress of the work.
The equipment developed and the methods used for both main and supplementary tests are described. Information is given regarding the coefficient of friction, as influenced by various factors. The endurance test, showing the comparative behavior of linings under conditions similar to those of severe service, is believed to be satisfactory as developed. Further work is necessary before recommending the conditions for the other test, intended to determine the relative endurance under ordinary or light service. In work done so far with a cooled drum and over a very wide range of power absorption and speed, difficulties arising from the accumulation in the lining of particles of steel cut from the drum have persisted. Supplementary tests, covering the tendency of a lining to stick when brakes are left applied on a hot drum, and to ascertain the relative absorption of oil and water, are described. The influence of oil and water on the coefficient of friction is shown.


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