And wear of plastics

The friction and wear of plastics are extremely complex subjects which depend markedly on the nature of the application and the properties of the material. The frictional properties of plastics differ considerably from those of metals. Even reinforced plastics have modulus values which are much lower than metals. Hence metal/thermoplastic friction is characterised by adhesion and deformation which results in frictional forces that are not proportional to load but rather to speed. Table 1.7 gives some typical coefficients of friction for plastics. 

Lancaster, J.K. Friction and Wear of Plastics, Chapter 14 in Polymer Science edited by A.D. 

CAUTION Potassium cyanide is very poisonous and should only be handled with great care with the wearing of plastic gloves. See Note (7), Expt 5.157, for the disposal of alkali metal cyanides. All operations should be conducted in an efficient fume cupboard. 

Lead tetraalkyl derivatives are used in catalytic systems to polymerise olefines, as catalysts of re-etherification and polycondensation, to speed up the alkylation of lateral chains of alkylbenzenes with ethylene and its derivatives. An addition of lead tetraalkyl derivatives (0.05-2% of alkylben-zene quantity) to catalysts of the liquid-phase oxidation of alkylbenzenes speeds up the oxidation. Tetraethyllead proved to be a good initiator for Diels-Alder reactions to join polymers with alkenylsiloxy chains and can be used as an additive to reduce the attrition and wear of rubbing metal parts. Tetrabutyllead is an active cross-linking agent for polyethylene and modifying agent for plastics. 

The abrasive wear of plastics occurs as a result of strong adhesive interaction, fatigue, macroshearing, abrasive action, thermal and thermooxidative interaction, corrosion, cavitation, etc. Fillers are involved in these processes because mineral... 

PV Limit - Wear of plastics is proportional to load (or pressure P) and velocity (E). Combinations of pressure and velocity are defined where the material can be used, thus alimit is defined. 

Although atomic-scale studies of friction have not been carried out until recently—because of the lack of techniques such as the AFM—several mechanisms for friction and slide that depend on the physical and chemical properties of the materials in contact have been suggested. For example, friction and wear of metal surfaces are the highest for ductile materials. This can be understood in terms of the plastic flow that occurs at the interface for these materials under normal loads. With this plastic flow, adhesion proportional to the load also occurs, leading to increased friction and wear. In addition, the oxidation of a metal at the interface can also affect the degree of the friction. If the oxide of a metal has a higher hardness value than the metal itself, measured friction coefficients will be lowered upon oxidation. If,... 

A further ISO document. ISO 6601 [102]. related to wear exists, although this is really a terminology document for both friction and wear, and ISO 6691 [lOi ] is concerned w ith the classification and designation of plastics for bearings. 

Chamley J., A. Kamangar, and M.D. Longfield. 1969. The optimum size of prosthetic heads in relation to the wear of plastic sockets in total replacement of the hip. Med Biol Eng 7 31-39. 

Gold, B. L. and Walker, P. S., Variables Affecting the Friction and Wear of Metal-on-Plastic Total Hip Joints, Clinical Orthopaedics and Related Research, Vol. 100, 1974, p. 270. 

In the injection molding process, mold leads to tribological (frictional) problems. Plastic materials while processing liberate gases, resulting in corrosion and wear of the mold material. In addition, the flow of molten plastic in contact with mold surfaces, problems of abrasion, adhesion, release, and fatigue commonly occur [28]. Appropriate surface modification... 

Wear, scoring, material flow, pitting, fracture, creep, and fatigue cause plastic and metal gears to fail. Continuous lubrication can increase the allowable bending stress by a factor of at least 1.5. However there are plastics (acetals, nylons, fluoropolymers, and others) that operate efficiently with no lubrication. There are plastics with wear resistance and durability of plastic gears makes them exceptionally useful. 

Chamley J. The wear of plastic materials in die hip. In Plastics in medicine and surgery. London The Plastics and Rubber Institute 1975.3. 

Due to the thermoplastic nature of CSM, a loading factor of 70%-75% is most effective. Highly loaded or highly plasticized compounds need to be at 75% fill factor, whereas lower loaded, high viscosity or scorchy stocks require a lower load factor. The power capabilities and wear of the mixer also dictates some further adjustment in load factors. 

It resembles polytetrafiuoroethylene and fiuorinated ethylene propylene in its chemical resistance, electrical properties, and coefficient of friction. Its strength, hardness, and wear resistance are about equal to the former plastic and superior to that of the latter at temperatures above 150°C. 

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