Abrasion and wear

Polytetrafluoroethylene parts have good wear properties, as seen from the data in Table 3.27. The resistance of unfilled PTFE to wear is less than that of filled compositions. Data from tests measuring wear rate are presented in Tables 3.28-3.30. They should be viewed with an understanding that none of the techniques represent an actual wear situation. In all three methods, a new surface is exposed to abrasion during the repeated motion of the abrading surface. 

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The 3M Abrasion Test (51) is used to assess the durabUity of a protective fluorochemical finish by evaluating its resistance to abrasion and wear. The surface is abraded with an AATCC crockmeter fitted with sandpaper. 

The decorative plastic laminates widely used for countertops and cabinets are based on melamine—formaldehyde resin (see Laminates). Several layers of phenohc-saturated kraft paper are placed in a press and a sheet of a-ceUulose paper printed with the desired design and impregnated with melamine—formaldehyde resin is placed over them. Then a clear a-ceUulose sheet, similarly impregnated with the resin, is placed on top to form a clear, protective surface over the decorative sheet. The assembly is cured under heat and pressure up to 138°C and 10 MPa (1450 psi). A similar process is used to make wall paneling, but because the surfaces need not be as resistant to abrasion and wear, laminates for wall panels are cured under lower pressure, about 2 MPa (290 psi). 

White cast iron is brittle and difficult to machine. It is made by controlling the composition and rate of solidification of the molten iron so that all the carbon is present in the combined form. Very abrasive- and wear-resistant, white cast iron is used as liners and for grinding balls, dies, and pump impellers. 

Hard anodic films, 50-100/rm thick, for resistance to abrasion and wear under conditions of slow-speed sliding, can be produced in sulphuric acid electrolytes at high current density and low temperature. Current densities range from 250 to 1 000 Am , with or without superposed alternating current in 20-100g/1 sulphuric acid at —4—I- 10°C. Under these conditions, special attention must be paid to the contact points to the article under treatment, in order to avoid local overheating. 

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. 

DLC coatings are already in production in several areas (optical and IR windows) and appear particularly well-suited for abrasion and wear applications due to their high hardness and low coefficient of friction. They have an extremely smooth surface and can be deposited with little restriction of geometry and size (as opposed to CVD diamond). These are important advantages and DLC coatings will compete actively with existing hard coatings, such as titanium carbide, titanium nitride, and other thin film... 

The NR compound 4 is known to be better under low temperature conditions than the control, but worse under high temperature conditions. Chemically, NR has the lowest thermal stability of the polymers used for tread compounds in tire technology and it has therefore the highest temperature dependence of abrasion and wear. Thus, it is generally accepted that NR has a higher wear resistance in a moderate climate than, for instance, SBR but a much lower one in hot climates. This will be thoroughly documented below under tire wear. 

Friction, abrasion and wear, for instance, are - mathematically - "operators" of a system, i.e. they depend on the parameters of a system, such as the geometry of the surface, the temperature, the load, the relative velocities, the composition of the environmental atmosphere, etc. The operational character of wear, for example, depends on the physicochemical interaction of surfaces and on their interaction with the lubricant and the atmosphere. 

In the extreme case where the asperities of the harder material plough grooves into the softer material, strong abrasion and wear will occur. Since polymers are relatively soft materials, this "ploughing" term in the total friction may be important. 

Titanium dioxide is a hard, abrasive material. Coating suspensions containing titanium dioxide have been reported to cause abrasion and wear of a steel-coated pan surface, which led to white tablets being contaminated with black specks. If titanium dioxide is used as a pigment it should conform to the appropriate food standards specifications, which are more demanding than the pharmacopeial specifications. 

The wear of rubber is a technologically important phenomenon unfortunately, it is also an extremely complex one. A detailed discussion of the mechanisms of wear is beyond the scope of this review. The role of carbon black in abrasion and wear, however, is most relevant in the present context in view of the practically universal use of this pigment in automobile tire treads. 

Kraus50 has analyzed the effects of the addition of carbon black on abrasion and wear in his excellent review. He states the relation... 

In the textile field, acrylate dispermons also provide highly derirable types of finishes. Applied to cotton and rayon, they contribute a firmer hand, improved tensile and tear strength, and better abrasion and wear resistance. Th., are free from color, and remain so. They are not easily removed by wasl g, hence are characterized as permanent finishes. 

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