Ceramic friction materials

Sintered Materials or Cermets. Heavy weights and high landing speeds of modem aircraft or high speed trains require friction materials that ate extremely stable thermally. Organic or semimetallic friction matenals ate frequendy unsatisfactory for these appHcations. Cermet friction materials ate metal-bonded ceramic compositions (see Composite materials) (12—14). The metal matrix may be copper or iron (15). 

A different type of low friction or low drag application is encountered with sliding doors or conveyor belts sliding on support surfaces. In applications like this the normal forces are generally quite small and the friction load problems are of the sticking variety. Some plastics exhibit excellent track surfaces for this type of application. TFEs have the lowest coefficient of any solid material and represent one of the most slippery surfaces known. The major problem with TFE is that its abrasion resistance is low so that most of the applications utilize filled compositions with ceramic filler materials to improve the abrasion resistance. 

Substitutes for asbestos are constantly being developed (EPA 19891). Nonasbestos friction materials are currently being used in disc brake pads, and substitutes have been developed for drum brake linings. Substitutes include fibers made of carbon, steel, cellulose, ceramics, glass, and wollastonite and organic fibers made from aramid, polyethylene, polypropylene, and polytetrafluoroethylene (USGS 2000). No single substitute was as versatile and as cost effective as asbestos. 

Polyimide materials can be used as unfilled base polymers or have graphite, PTFE and molybdenum disulphide added to further enhance the low frictional properties and can be used to replace metal and ceramic parts. Material is available as moulded stock shapes, e.g. rod, rings and plate, which can be machined to the final dimensionally accurate product. Some grades can be processed by compression moulding while other grades can be processed to produce a finished product by direct forming. 

Bonding and laminating wood, metal and a limited range or thermoplastics. Speciality use with friction materials and ceramics. 

Since SuperAurum has a high HDT of 752°F (400°C), it can replace other polyimides, ceramics, and metals. XCL3030 is a representative grade as a wear and friction material, offering... 

Because of its application in the manufacturing of porous metaUo-ceramic bearings, of friction materials, parts for machineiy, various alloys, in chemical industry, in manufacture of rechargeable batteries, etc., Fe powder is an important industrial product [55]. Significant amount of Fe powder is produced by electrochemical technique and 20% of electrodeposited Fe powders have to be blended with Fe powders produced by other procedures. The main advantage of electrodeposited Fe powder is its volumetric mass (1.5-2.2 g cm ) and its suitability for pressing, due to dendritic particle shape. 

Within the frame work of the Centre of Excellence in Research CER 483 High performance sliding and friction systems based on advanced ceramics one approach is to apply advanced ceramics as friction material for e.g. a dry running motor vehicle clutch using the ceramic specific benefits as wear and temperature resistance combined with lightweight design to fulfil today s demands as e.g. functionality, life time and reliability. 

A. Skopp and M. Woydt, Ceramic and Ceramic Composite Materials with improved Friction and Wear Properties, Tribology Transactions 38 (1995) 233-242... 

Tribological Behavior. Tribological performance of ceramics, which includes friction, adhesion, wear, and lubricated behavior of two soHd materials in contact, has been reviewed (52). 

Friction and Adhesion. The coefficient of friction p. is the constant of proportionality between the normal force P between two materials in contact and the perpendicular force F required to move one of the materials relative to the other. Macroscopic friction occurs from the contact of asperities on opposing surfaces as they sHde past each other. On the atomic level friction occurs from the formation of bonds between adjacent atoms as they sHde past one another. Friction coefficients are usually measured using a sliding pin on a disk arrangement. Friction coefficients for ceramic fibers in a matrix have been measured using fiber pushout tests (53). For various material combinations (43) ... 

---