Ever since the introduction of friction brakes in vehicles, brake system designers have been striving to improve braking performance. To meet this growing demand for better brakes, lining manufacturers have evaluated numerous additives in their material formulations. These additives provide several different technical properties, the foremost being safety-related features such as frictional stability and resistance to fading. In more recent years, brake noise has become important with the elimination of asbestos fibers in linings, and there is now also a need for a higher frictional coefficient to offset increases in overall vehicle weight. Prolonging the service life of brake components, reducing pad wear, and minimizing rotor wear caused by DTV (Differential Thickness Variation) are other issues that face lining manufacturers. To address all these technical requirements, brake material formulations have become so considerably more complex that increased usage of additives is required.
Common additives used in earlier brake lining formulations were metal powders and metal sulfides. Later it was found that synergistic mixtures of various solids actually improved the tribological properties of lining materials over those using a single solid additive. More recently, considerable work has been done in improving the frictional requirements of some additives by changing their surface properties. As a result, current frictional composites use a complex (and usually proprietary) package of additives to meet the needs of modern friction brakes.
A discussion of various additives and their contribution to the development and performance of friction brake materials are presented in this paper.