Document 9V1xxZ8dao9n6mvVgJz31xyR

2- - TV compounding of friction materials that successfully meet all these requirements is the specialty of some of the anonymous heroes of the automotive industry. The uninitiated might think that, with a stable brake design and evalua tion reduced to simple terms, the friction material compounder's job would be routine. This is far -'rom the case. The many influences on brake performance, resulting from variations in vehicle weights, climates, road conditions, vehicle equipment and driving habits, make the engineering of brake lining friction materials a most chal lenging assignment, and a highly secretive operation. The formula of a brake lining is the well-farced secret of the supplier, while other brake components are used commonly chr''ughcut the industry. SASIC DRUM AND SHOE BRAKE DESIC3J5 For purposes of clarity, all data presented herein applies to a drum and ... shoe brake o' the duo-servo type. (Fig. 1) The two other drum and shoe brake de- . signs generally employed are the two leading shoe type and two trailing shoe type. (Fig. There .s also a one leading one trailing shoe type in general use which is not shown. ORGANIC SHAKE LININGS A1. American passenger cars use organic brake linings. There are two organic linings vhich are classified by their method of fabrication. Organic dry mix in basically a gray-white compound of asbestos, filler materials and powdered resins which is choroughly mixed, preformed to shape, and placed under heat and " pressure 'until it forms a hard, slate-like board. Then it is cut and bent into in dividual arcuate segments and attached to the shoe. Organ!: wet mix is a compound of asbestos, organic fillers and liquid re sins that has a gray-brown color when blended. The compound is processed by any of several different methods which include high pressure extruding, screw extruding, calendering and other processes. Figure 2 shews a step in the high pressure extrud ing process. The extruded lining is being removed from a die that has formed it into a long slab that win he compressed to a uniform density under heat and pressure. Organic linings are generally composed of six basic ingredients. Asbestos, with its nigh heat resistance and high coefficient of friction in contact with iron and steel. :s the basic material. Friction modifiers, such as the oil of the cashew nut shell, give linings desired frv-tior. qualities. Fillers are a wide variety of materials, such as rubber scrap, which are added to. linings to control noise, wear or other brake characteristics. Curing agents and/or accelerators are added to a lining compound to pro duce recuirc`d chemical reactions in the ingredients. Materials for special effects are added to compounds to improve overall braking performance. They include powdered lead, brass chips and aluminum powders. 3-nders, which are predominantly phenolic resins, hold all the other in gredients t getter and are selected to govern the physical strength of the material at high temperatures.