Wear Resistance and Frictional Properties

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. 

Coefficients of friction and relative wear rates for plastics 

The wear rate of plastics is governed by several mechanisms. The primary one is adhesive wear which is characterised by fine particles of polymer being removed from the surface. This is a small-scale effect and is a common occurrence in bearings which are performing satisfactorily. However, the other mechanism is more serious and occurs when the plastic becomes overheated to the extent where large troughs of melted plastic are removed. Table 1.7 

---

The main components in the WF series yams are glass fibres and UHMWPE. They were constructed in different mass per unit length (linear density) combinations in order to analyse a range of permutations. The composite yams were double covered with either polyester or polyamide to have a better handle and also to enable dyeing the external surface of the fabric. Polyamide 6,6 was preferred as the covering yam as it has a higher melting point (263 °C) than polyamide 6 (216 °C). Polyamide 6,6 also provides excellent wear resistance and frictional properties. ... 

The plating of composites is a recent development but one which is likely to be of increasing importance because it is found that the occlusion of solid particles into the metal deposit can greatly enhance the wear resistance and friction properties of the deposits. Solids such as AI2O3, Ti02, Si02, WC2, TiC and PTFE present in solution as particles 0.5—5.0 ixm in diameter are entrapped in a deposit by rapid electroplating. They are usually present in 2—10 vol. %. 

It was been shown that under both tension and compression, PVA-C displays nonlinear mechanical properties and viscoelastic behavior [95]. Additionally, PVA-C has been observed to have better wear resistance and friction coefficient than UHMWPE [96, 97]. 

Manganese phosphate coatings are applied when wear resistance and antigalling properties are required. Manganese phosphate also possesses the ability to retain oil, which further improves anti-friction properties and imparts corrosion resistance to the coated parts. 

Although these resins have been on the market for a number of years, volumes and appHcations remain low in spite of favorable properties including high temperature resistance, excellent wear and friction properties, good electrical properties, chemical inertness, and inherent nonflammability. ProcessibiHty and price may be the limiting factors. 

Material Characteristics Strength and Sliffness Toughness Short-Term Heat Resistance Long-Term Environ-Heat menial Resislance Resistance Dimensional Accuracy in Molding Dimensional Stability Wear and Frictional Properties Point Subtotal Cost Point Total... 

The wear resistance and coefficient of friction are suitable for tribological applications. Tribological properties for a PV of 1.75MPa.m/s are, for example ... 

The metalworking nature of the process leads to the plunge and rehll FSSW methods, with properties comparable to riveted and resistance spot-welded joints. The use of FSP to locally modify the microstructure of arc welds and castings has shown to increase strength, improve fatigue life, and remove defects. Using FSP to stir particulate materials into the surface has shown increased wear resistance and creates particulate-reinforced surface layers. Friction stir reaction processing can be used to create new materials and alloy combinations on part surfaces. 

Restricted heat and chemical resistance (swells in organic solvents, unstable to strong acids and alkalis), inflammable, resistant to alternating loads, its products display shape stability, low creep, high wear resistance, and low friction coefficient, mechanical and dielectric properties are insensitive to humidity. 

Good mechanical strength, wear resistance, low friction coefficient. Perfect dielectric properties, resistance to heat, fire, oil, gasoline, acids and corrosion. High adhesion to metals. 

These antifrictional materials of INHAM grade display higher wear resistance under friction in the liquid hostile media compared to non-inhibited plastics. For comparison, the properties of an antifrictional material based on PA6 and molybdenum disulfide without a Cl in its composition are presented in Table 4.13. Its wear resistance is seen to fall short of the INHAM materials since corrosion processes are not suppressed in the friction zone of this material with the metal. 

Hip joint replacements are the most common type of joint replacements, with 300 000 operations in the USA in 2000. The aim of this case study is to highlight the wear resistance and low friction properties of UHMWPE, to discuss the effects of sterilisation on the properties of plastics, and the effects of wear debris in the body. The order of presentation is that followed by the polymer, through fabrication, sterilisation, implantation and wear, to the reactions caused by wear debris. 

Wear and frictional properties - The ability of the plastic to resist removal of material when run against a mating metal surface. The lower the frictional values, the better the relative rating... 

---