Friction and wear applications

A prime example of where polyamide-imides enjoy prominence is in friction and wear applications. This means not only in a system where the polymer components are meant to operate with low-friction and low-wear characteristics, but also in new applications such as brake pads and abrasion wheels, where the operating conditions require low wear with high friction, a truly demanding scenario. Polyamide-imides can achieve this due to their high softening temperature and retention of strength, stiffness, and compression properties at elevated temperatures. 

High-speed bobbins. The critical component in today s commercial lockstitch sewing machine is the rotary hook and bobbin (Fig. 12.11). These parts traditionally have been manufactured out of stainless steel, which requires constant lubrication and stitch tension adjustments. Both can play havoc with operator productivity and stitch consistency, particularly with lighter-weight or delicate fabrics. Hooks and bobbin baskets made 

Compressor vanes. Polyamide-imide compounds are being used in a number of rotating industrial equipment apphcations. One particular area of interest is in rotary vane compressors. Previously the vane materials were made from a phenolic composite construction. Although more expensive from a material of construction perspective, a polyamide-imide compound was chosen due to a dramatic extension in life and a lower lubrication requirement, both of which reduce maintenance and the overall operating cost of the compressor. In addition the compressors can operate at a higher discharge pressure due to polyamide-imide s higher-temperature capability. 

Automotive transmission components seai rings, thrust washers, check baiis. 

Many automatic transmissions on the road these days contain multiple components manufactured from injection-moldable polyamide-imide 

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AF Injection molding, extrusion Delrin 100 with 20% Teflon PTFE fibers, outstanding friction and wear properties Specialty friction and wear applications, conveyor systems... 

MP Injection molding Delrin 500P with 10% Teflon PTFE micropowder, with low-wear and low-friction properties Specialty friction and wear applications... 

Features include low water absorption, high heat resistance, high chemical resistance, hydrolysis resistance, low friction coefficient, high impact strength good fuel barrier properties, and dimensional precision. It offers an alternative to materials such as PA612 and PA 12. Its applications range from friction and wear application, automotive parts to electronic/electiical. 

Table 5.8 Characteristics, Specific Wear Rate, and Dynamic Coefficient of Friction of Various Grades of DuPont Delrin Designed for Friction and Wear Applications [3]...

A specification of parameters influencing the friction and wear applicable to the basic classes of tribometers has been established. Concepts and approaches for using tribometers to simulate... 

Applications. The capabiHties of a gc/k/ms in separating and identifying components in complex mixtures is very high for a broad spectmm of analytical problems. One area where k information particularly complements ms data is in the differentiation of isomeric compounds. An example is in the analysis of tricresyl phosphates (TCPs) used as additives in a variety of products because of thek lubricating and antiwear characteristics (see Lubrication and lubricants). One important use of TCPs is in hydrauHc fluid where they tenaciously coat metal surfaces thereby reducing friction and wear. Tricresyl phosphate [1330-78-5] (7.2 21 exists in a variety of isomeric forms and the commercial product is a complex mixture of these isomers. 

For many centuries the application of materials for low friction and wear in sliding and rolling contacts primarily involved wood, stone, leather, iron, and copper. Almost all engineering materials have since been employed at one time or another in the continuing search for the best bearing material. Final selection is commonly a judgment based on the most essential material properties, ease of appHcation, and cost. 

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. 

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... 

Brake linings and clutch facings consist of friction materials. Friction materials technology encompasses friction material types, their applications, friction and wear characteristics, raw materials, manufacturing methods, and evaluation and test methods. 

If solid polymer objects are fluorinated or polymer particles much larger than 100 mesh are used, only surface conversion to fluorocarbon results. Penetration of fluorine and conversion of the hydrocarbon to fluorocarbon to depths of at least 0.1 mm is a result routinely obtained and this assures nearly complete conversion of finely powdered polymers. These fluorocarbon coatings appear to have a number of potentially useful applications ranging from increasing the thermal stability of the surface and increasing the resistance of polymer surfaces to solvents and corrosive chemicals, to improving friction and wear properties of polymer surfaces. It is also possible to fluorinate polymers and polymer surfaces partially to produce a number of unusual surface effects. The fluorination process can be used for the fluorination of natural rubber and other elastomeric surfaces to improve frictional characteristics and increase resistance to chemical attack. 

DePalma and Tillman investigated self-assembled monolayer films from three silanes, tridecafluorooctyltrichlorosilane, undecyltrichlorosilane, and octadecyl-trichlorosilane, on silicon, a popular model substrate for such studies with great relevance to potential semiconductor coating applications. They characterized the films by ellipsometry and contact angle measurements (data for trideca-fluorooctyltrichlorosilane are included in Table 1), but more usefully from an applicational viewpoint, they carried out friction and wear measurements with a pin-on-disk device where the silicon wafer substrate, coated with monolayer, is moved under a spherical glass slider. Optical microscopy was used to assess wear. Table 2 summarizes DePalma and Tillman s data and their comparison with the classical self-assembled monolayer friction studies of Levine and Zisman [18]. 

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