Abrasion resistance, reinforced plastics

Some aspects of plastic wear are hardly even discussed in manufacturer s literature plastic abrasivity, plastic abrasion resistance, and plastic erosion resistance. The manufacture of many plastic products involves the use of injection molding or extrusion equipment. If a plastic contains inorganic fillers such as glass or carbon fiber reinforcement, they can be veiy abrasive to parts that contact the melted plastic extruder barrels, screws, molds, and check valves. 

Because people everywhere tend to take their fun seriously, they spend freely on sports and recreational activities. The broad range of properties available from plastics has made them part of all types of sports and recreational equipment for land, water, and airborne activities. Roller-skate wheels are now abrasion- and wear-resistant polyurethane, tennis rackets are molded from specially reinforced plastics (using glass, aramid, graphite, or other fibers), skis are laminated with plastics, and so on. 

The hardness of polyurethanes can be obtained by either the density of the hard segments, the choice of curative, or the addition of plasticizer. The importance of hardness is to control the rigidity of the part (if not reinforced) or its softness to conform to the shape of some other object it passes over. For very low hardness (< 60 A) applications such as rolls, TDI esters are the most suited, whereas ether-based materials are least suited. Hard materials do have better abrasive resistance than soft materials. 

In addition to strength and stiffness, fillers offer a variety of other benefits. They include reduced cost, shrinkage reduction, exothermic heat reduction, thermal expansion coefficient reduction, improved heat resistance, slightly improved heat conductivity, improved surface appearance, reduced porosity, improved wet strength, reduced crazing, improved fabrication mobility, increased viscosity, improved abrasion resistance, hardness, and/or impact strength. Fillers also can have disadvantages. They may limit the method of fabrication, inhibit cure of certain plastics, and shorten pot life of the plastics. The particles are usually small, in contrast to those of reinforcements. 

The increasing use of plastics with abrasive fillers and reinforcements created a demand for an even more abrasion resistant barrel than the standard iron/boron type. The use of glass fiber reinforced compounds for injection molding has been the single most important factor since a fabricator would be lucky if they could reach 6 months of continuous operation. This need has been successfully answered by the development of liner materials containing metallic carbides such as tungsten carbide and titanium carbide extending their life. 

PROPERTIES OF SPECIAL INTEREST Standard emulsion SBR is a general purpose rubber. Most widely used synthetic rubber in the world. Better tire tread-wear and aging properties than natural rubber. Good abrasion resistance and crack initiation resistance. Poor in tack and heat build-up. Physical properties are poor without reinforcing fillers. Solution SBR is a speciality rubber and more expensive than emulsion SBR. Solution SBR with high vinyl and styrene levels is used in high performance tire treads to improve wet traction. Also used as impact modifier in plastics and as thermoplastic elastomers. 

Abrasion. Resistance to abrasion is adequate for many applications including footwear and can be improved hy addition of reinforcing pigments (hard clay, silicas, carbon blacks) and through use of added plastic materials such as polystyrene or polyolefins. Abrasion resistance is reduced by oils, seme resins and large-particle fillers. It is also improved with Increased molecular weight of the polymer (Table III). 

Polyurethanes find application in many areas. They can be used as impact modifiers for other plastics. Other applications include rollers or wheels, exterior body parts, drive belts, and hydraulic seals. Polyurethanes can be used in film applications such as textile laminates for clothing and protective coatings for hospital beds. They are also used in tubing and hose in both unreinforced and reinforced forms because of their low-temperature properties and toughness. Their abrasion resistance allows them to be used in applications such as athletic shoe soles and ski boots. Polyurethanes are also used as coatings for wire and cable. ... 

An alternative to rubber linings which suit corrosive environments are glass flake reinforced plastics. They combine impact, erosion and abrasion resistance and can be applied on site using a spray or brush. They are compounds of glass flakes with various corrosion resistant thermosetting resins combined in different ratios. The excellent adhesion enables bonding with steel at temperatures as high as 170 "C. 

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