BRAKE LINING

Phenohc resins are the oldest form of synthetic stmctural adhesives. Usage ranges from bonding automobile and other types of brake linings to aerospace apphcations. These adhesives have a reputation for providing the most durable stmctural bonds to aluminum. Because of volatiles, however, and the need for high pressures, the phenohc resins are used less as adhesives than the epoxy resins. 

Friction Materials. Sintered friction materials are classified as metal— nonmetal combinations (49,50). These are best manufactured by the P/M process. Clutch plates, brake bands, brake blocks, and packing compositions are examples of friction materials (see Brake linings and clutch facings). 

Friction Materials. PhenoHc friction materials are made from mol ding compounds developed to meet the extraordinary demands required by friction elements in the transportation industries. Friction materials are used for brake linings, clutch facings, and transmission bands. A moderately high coefficient of friction, which is temperature-independent, is needed. In addition, the material must be high in strength, low in wear and abrasion, and resistant to moisture and hydrauHc fluids. 

Manufacture of friction elements includes the impregnation of fabrics and subsequent lamination, the wet-dough process, and the dry-mix process. Elements from the last two are prepared by compression-molding the formulation for up to an hour at 150—175°C. Thick brake elements require a carefully controUed heating-and-cooHng cycle to minimize stresses created by expansion and contraction (see Brake linings and clutch facings Fillers). 

The preferred descriptive terms for brake or clutch friction materials according to usage are brake pads, used ia disk brakes brake linings, used ia dmm brakes brake segments, used ia medium tmck dmm brakes brake blocks, used ia large tmck dmm brakes and brake disks, used ia large aircraft brakes. Friction materials for clutches are called facings. 

Brake Linings. Substantial amounts of crystalline flake, lump, and amorphous graphite are used in brake and clutch finings, mostly in heavier duty nonautomotive situations. The graphite has been substituted for asbestos because of health considerations. The graphite proportion of the part has risen from 2 to 15% in some instances. The graphite lubricates, transfers the heat of friction away from the fining, and lowers the rate of wear. 

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