Brake linings, bonding

In addition to aircraft applications, adhesives of this type are employed in the bonding of friction materials (e.g. grinding wheels), brake lining to brake shoes, clutch facings, etc. The cement shown in Table 22 is suitable for such diverse jobs as metal-to-metal bonding or brake lining bonding. 

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. 

Other applications for phenolics are switchgears, handles, and appliance parts, such as washing machine agitators (that s why they re usually black). Phenolics are widely used to bond plywood, particularly exterior and marine grades. Although urea-formaldehyde resins are cheaper for this purpose, they were not nearly as water-resistant and have been limited to interior grades. Abrasive wheels and brake linings also are bonded with phenolic adhesives. 

Phenolics are used in bonding wood and plywood. They are also good adhesives for automobile brake linings. A phenolic plus poly(vinyl butyral) is used to bond copper to paper or glass fiber for printed circuits. 

The high frictional coefficient (0.4 to 0.5 compared with < 0.1 for glass fibers) of asbestos fibers is crucial to its utilization in the frictional lining sector. In the manufacture of brake and clutch linings 20 to 60% asbestos is incorporated together with fillers, metal chips and preferably phenol resins and rubber into a composite material, which has to satisfy many requirements. Currently there are asbestos-free so-called semimetallic brake linings, which consist of mixtures of metal fibers, metal powders, cellulose fibers, aluminum silicate fibers and mineral wool bonded with synthetic resins. 

For example, brake linings contain finely divided, hard, abrasion resistant particles (Tab. 11-1, Chapter 11) in a complex matrix that provides the bonding in the lining itself and with the metallic supports. The formulation, containing all components, may also include such materials as metallic, mineral and, synthetic fibers. During production of the break drums, discs, or shoes, the blend is pressed onto the structural supports with specially designed presses to produce uniform, homogeneous wear pads. 

In Section 6.11.1, the manufacturing of brake linings from pre-agglomerated masses with special presses has already been mentioned. This additional processing is a further application of pressure agglomeration, yielding highly densified brake pads in which all components are well bonded. A post-treatment may be necessary to obtain final properties (Section 6.11.3). 

During World War II, synthetic rubber and resin-modified phenolics were used to bond aluminum sheets (available only in in. thickness at that time) into billets from which airplane propellers were carved, thus replacing laminated wood, which often shattered on impact with a bullet. Similar adhesives were used to bond rubber to metal in a variety of vibration-damping applications. The most successful widely known product of the new technology was the automotive bonded brake lining first introduced in 1947, and now regarded as a symbol of quality and integrity [12, p. 490]. 

In addition to molding compoimds, phenolics are used to bond friction materials for automotive brake linings, clutch parts, and transmission bands. They serve as binders for core material in furniture, the water-resistant adhesive for exterior grade pl)nvood, binders for wood particle boards, and... 

They dominate the field of wood adhesives and represent one of the largest volumes of any synthetic adhesive. Phenolics are also among the lowest-cost adhesives and may be formulated as water dispersions, to allow penetration into the cell structure of wood which is important for the formation of permanent bonds. Beyond the wood and wood products area, unmodified phenolics are used mainly as primers, to prepare metal surfaces for bonding, and as binders, for such varied products as glass wool insulation mats, foundry sand, abrasive wheels, and brake lining composites. Phenolics are supplied either as one-component, heat-curable liquid solution, as powder, or as liquid solution to which catalysts must be added. The curing mechanisms are different for these two groups. "... 

Bonding resin n. Any resin used for bonding aggregates together, e.g., holt melt epoxy, such as foundry sands, grinding wheels, abrasive papers, asbestos brake linings, and concrete masses. Plywood adhesives are sometimes called bonding resins. Skeist I (ed) (1990) Handbook of adhesives. Van Nostrand Reinhold, New York. 

Brake lining medium n. A medium for bonding together the chosen filling agent for the brake lining, e.g., asbestos. 

The sandwich construction method mentioned above involves joining metals to other materials by bonding. Further examples include the bonding of brake linings (phenolic adhesives) and compound materials in ski manufacture, where aluminum is bonded to plastics, wood, etc. (phenolic and epoxy adhesives). Highly alloyed steels, beryllium and titanium alloys, and other special metals can be bonded with adhesives (e.g., polyi-mides, polybenzimidazoles) that have comparable high-temperature resistance. 

Rubber-to-metal bonding agents are used for the production of vibration-damping members of rubber and metal, developing their adhesion to the metal during vulcanization of the rubber. The same applies to the production of shaft seals. Clutch and brake linings are applied by means of nitrile rubber - phenolic resin adhesives. 

Resistance to prolonged exposure to high temperatures is required of some adhesives for the aircraft, aerospace, and electrical industries. Many less glamorous end uses—foundry molds and cores, coated and bonded abrasives, brake linings and other friction materials, and ther-... 

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