Composite abrasion-resistant

The abrasion resistance of ionomers is outstanding, and ionomer Aims exhibit optical clarity. In composite structures ionomers serve as a heat-seal layer. 

An important appHcation of MMCs in the automotive area is in diesel piston crowns (53). This appHcation involves incorporation of short fibers of alumina or alumina—siHca in the crown of the piston. The conventional diesel engine piston has an Al—Si casting alloy with a crown made of a nickel cast iron. The replacement of the nickel cast iron by aluminum matrix composite results in a lighter, more abrasion resistant, and cheaper product. Another appHcation in the automotive sector involves the use of carbon fiber and alumina particles in an aluminum matrix for use as cylinder liners in the Prelude model of Honda Motor Co. 

Photopolymerizable compositions based on monomeric acryflc or other ethylenicaHy unsaturated acid derivatives are becoming increasingly popular. When multiftmctional derivatives are employed, three-dimensional networks having high strength and abrasion resistance are possible on exposure to light. A typical composition may contain an ethoxylated trimethylolpropane triacrylate monomer, a perester phenacjhdene initiator (69), and an acryflc acid—alkyl methacrylate copolymer as binder. 

Hardness (qv), which determines the resistance of a material to abrasion and deformation, is affected not only by composition but also by porosity and microstmcture. Higher cobalt content and larger carbide grain size reduce hardness and abrasion resistance but iacrease the toughness of cemented carbides. The trade-off of abrasion resistance and toughness enables the cemented carbide manufacturer to tailor these materials to a wide variety of metal-cutting and nonmetal-cutting appHcations. 

Alloy Compositions and Product Forms. The nominal compositions of various cobalt-base wear-resistant alloys are Hsted in Table 5. The six most popular cobalt-base wear alloys are Hsted first. SteUite alloys 1, 6, and 12, derivatives of the original cobalt—chromium—tungsten alloys, are characterized by their carbon and tungsten contents. SteUite aUoy 1 is the hardest, most abrasion resistant, and least ductile. 

Unfilled Tooth Restorative Resins. UnfiUed reskis were some of the first polymer materials iatroduced to repak defects ki anterior teeth where aesthetics were of concern. They have been completely replaced by the fiUed composite reskis that have overcome the problems of poor color StabUity, low physical strength, high volume shrinkage, high thermal expansion, and low abrasion resistance commonly associated with unfiUed reskis. 

Composite Plating. An electroless nickel matrix can be used to securely bond diamonds to cutting tools, and electroless nickel—diamond composites are also used (see Tool materials). The NYE-CARB process gives a siUcon carbide—electroless nickel composite that has extremely high abrasion resistance (49). Electroless nickel—Teflon composites are being promoted as low friction materials. 

A wide range of polyurethane-type products has become available in recent years for coating applications. These include simple solutions of linear polyurethanes, two-pot alkyd-isocyanate and polyether-isocyanate systems and a variety of prepolymer and adduct systems. The coatings can vary considerably in hardness and flexibility and find use mainly because of their toughness, abrasion resistance and flexibility. Uses include metal finishes in chemical plant, wood finishes for boats and sports equipment, finishes for rubber goods and rain-erosion-resistant coatings for aircraft. One type of coating is potentially competitive with PVC leathercloth. Both alkyd-di-isocyanate and adduct-diisocyanate compositions may be coated on to fabrics from solutions of controlled viscosity and solids content. Such coated fabrics are soft, flexible and, unlike PVC leathercloth, free from plasticisers. 

In one series of laboratory tests carried out to find the optimum wear resistance of heavy-duty epoxy resin flooring compositions, a number of different abrasion resistant materials were evaluated using BS 416, employing three different epoxy resin binders which themselves had significantly differing chemical compositions and mechanical properties. The results of this work, which was carried out under dry conditions, are given in Table 9.1. As can be seen from the table, the selection of the abrasion-resistant material and the resin matrix both influence the abrasion resistance of the system, although the abrasive material incorporated appears to play a more cmcial role. 

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. 

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