The moisture adsorption kinetics of copper-free brake pads was studied to confirm an earlier finding that the adsorption weight gain follows a logarithmic path with respect to the square root of humidity exposure time. When the pad cure temperature is raised from 120 to 180 and 240 0C, the adsorption rate increases. With increased moisture adsorption, the pad compression modulus increases like the pad dynamic modulus while the ISO ‘compressibility’ determined after 3 compressions under 160 bars increases, not decreases, in contradiction. The ISO ‘compressibility’ is a hardness measurement like the Gogan or Rockwell hardness: the differences are the indenter covers the entire surface of the pad and compressing 3 times rather than once. The true compressibility must be determined by the bulk modulus as an inverse function of bulk modulus. It is recommended that the pad compression modulus should be measured under low pressures like 10, 20 or 40 bars for the purpose of determining the initial quality of virgin pads if the current ‘compressibility’ machines are to be used.

Dr. Seong Rhee, President, SKR Consulting LLC; Mr. Aman Rathee, Director, ASK Automotive Pvt., Ltd.; Mr. Shivraj Singh, Vice President, ASK Automotive Pvt., Ltd.; Mr. Devendra Sharma, Manager, ASK Automotive, Pvt., Ltd.