Friction Lining and Pad Materials
Properties of Friction Lining and Pad Materials Friction Level The coefficient of friction should be sufficiently high to limit brake pedal effort. It should not be so high that it causes grab, or in the extreme cases lock or sprag. In such a situation rotation of the drum becomes impossible. The friction material must be compatible with the degree of self-energization (Fig. 28.32). The average coefficient of friction of modern friction materials is between 0.3 and 0.5. Resistance to Heat Fade This property allows a lining or pad material to retain its coefficient of friction with an increase in rubbing temperature of the drum and shoes or disc and pads. A decrease in the coefficient of friction requires greater brake pedal effort and results in poor braking response. The changes in the coefficient of friction as a consequence of rising working temperatures are also partly caused by the additional curing of the pad due to chemical changes in the binder resin (Fig. 28.32). A progressiv