An Inertial Dynamometer Evaluation of Three Alloys for Automotive Brake Drums

Drums made of a chromium copper alloy, an aluminum alloy/cast iron composite, and conventional cast iron were compared by inertial dynamometry, using full-size linings in a Non-Servo brake system. The tests were performed with three types of linings: nonabrasive, moderately abrasive, and highly abrasive. In each test, 30 stops were made from 40 mph and 30 stops from 60 mph, using a rotational inertia of 31.4 slug-ft². Temperatures near the lining/drum interface, hydraulic line pressures, and lining wear, were measured and compared. For a given amount of work, the temperature rise near the drum surface was found to be lowest in the chromium copper drums, next lowest in the aluminum alloy/cast iron composite, and highest in the cast iron drums. This confirms earlier test results from drag dynamometry, using 1 X 1 in. samples. The average temperature rise decreased linearly with increasing thermal diffusivity of the drum material. Some surface changes were found on all three types of drums: martensite spots on the cast iron and the aluminum/cast iron composite, and work hardening on the chromium copper. The latter have the advantage of being free from metallurgical transformations in the temperature range encountered in service. The chromium copper drum with the highly abrasive lining showed the greatest increase in surface roughness. All other combinations showed only a small change in roughness. The mildly abrasive linings showed the lowest wear rate with all three types of drums, in agreement with earlier results.