Wear resistant and internally lubricated plastic compounds reduce friction between moving parts and part failure rates. Phoenix Polymer Compounding can custom formulate multi-property solutions.
Internally lubricated thermoplastics eliminate expensive, time-consuming, secondary steps associated with external surface lubrication. They keep mechanisms and components clean, enhancing long-term performance and reliability.
Thermoplastic composites can be internally lubricated with a variety of systems to improve wear resistance. PTFE and silicone, separately or in combination, provide the best improvements in wear characteristics. Graphite powder and molybdenum disulfide are also used, primarily in nylons. The PTFE lubricants are specially modified to enhance their lubricious nature in the compound. The optimum level of lubricating filler varies depending on filler type and resin, but typical ranges are:
* PTFE 15-20% * Silicone 1-5% * PTFE/silicone 15-20% * Graphite 10% * MoS2 2-5%
Polytetrafluoroethylene (PTFE) lubricants - dispersed into a thermoplastic base resin greatly improve surface-wear characteristics. Molecular weight and particle size of the PTFE lubricant are designed to provide optimum improvements in wear, friction, and PV values for selected resin systems. PTFE has the lowest coefficient of friction (0.02) of any known internal lubricant. Its static coefficient of friction is lower than its dynamic coefficient, which accounts for the slip/stick property.
Silicone fluids - are chosen for their ability to perform as boundary lubricants and for partial compatibility with a particular base resin. The silicone is sufficiently compatible with the base resin to form an alloy, yet incompatible enough to cause migration to the surface of the compound. The silicone moves to the surface of a molded or extruded part by two mechanisms: diffusion by random molecular movement, and exclusion from the matrix (migration) because of its limited compatibility. The result of the migratory action is a continuous generation of a silicone film, which serves as a boundary, or mixed-film lubricant.
Glass fibers - improve both short-term and long-term mechanical properties of a resin. The fibers also improve creep resistance, thermal conductivity, and heat-deflection temperature as well as the tribological properties of the base resin. The degree of improvement depends on the efficiency of the sizing system that bonds the resin to the fibers. Glass beads and unsized milled-glass fibers, on the other hand, increase the wear factor of the mating surface and the coefficient of friction. Glass fibers are frequently used in combination with silicone and PTFE lubricants which offset the negative wear effects that the glass fibers have on surface characteristics. The use of silicone only, in conjunction with glass fibers, is not recommended, however. PTFE provides far more protection to the mating surface and should be used (with or without silicone) if the wear rate of the mating surface is important.
Carbon fibers - added to thermoplastic resins provide the highest strength, modulus, heat-deflection temperature, creep, and fatigue-endurance values commercially available in composites. These property improvements, coupled with greatly increased thermal conductivity and low friction coefficients, make carbon fibers ideal for wear and frictional applications where the higher cost can be tolerated. In applications where the abrasive nature of glass fibers wears the mating surface, the softer carbon fibers can be substituted to reduce the wear rate. Carbon fibers can also be used in conjunction with internal lubricants to further improve surface characteristics of most thermoplastic resin system.