MODIFICATION | WEAR RESISTANCE
Figure 7: Wear results from tests depend considerably on what a material is rubbing against Source: SABIC
Figure 8: Typical wear and CoF performance for different additive and PA66 resin combinations Source: Albis
characteristic of a pair of materials under given tribological loading conditions. The amplitude of these variations is defined as the excitation power.” Eurostar and its partners wanted to evaluate the noise potential of different material pairings to avoid the risk of noise at the design stage of a shaft/bearing system. Chopin says Eurostar has put considerable effort into adjusting wear and friction properties in its Star-L range of products, with a particular goal being to meet PTFE-free trends and developing REACH PTFE regulatory requirements. “One key patented innovation has been the development a new range of compounds based on halogen-free permanent lubricant based high molecular weight polymers,” he said. The PTFE-free concept is said to have generated a great deal of interest and is now being requested by some E&E players for new developments to the EN50642 standard for Cable Management Systems. “For certain products, PTFE remains a strategic
raw material to enable low coefficient of friction. It is well known that PFOA (perfluorooctanoic acid), although not used as an intended raw material, may be detected in PTFE micropowders. REACH legislation taking effect on July 4 2020 requires less than 25 ppb PFOA level. Eurostar EP already anticipated this requirement and is already able to propose fully REACH-compliant Star L products,” Chopin said.
Beating wear LNP, a division of SABIC, has long been a player in wear resistant compounds. Erik Schwartz, Lead Scientist LNP copolymers T&I, explained that its
34 COMPOUNDING WORLD | February 2020
Lubricomp grades are traditionally lubricated compounds providing wear and friction solutions, while its Lubriloy compounds use a proprietary, fully- compatibilised alloy lubrication system to provide non-halogenated solutions based on PA 66, PC, PPO, PPA and POM. The latter compound family offers various benefits over PTFE-filled materials, the company claims, including improved impact and lower density. Wear and friction data for gears is usually based on plastic-steel contact measured in a standardised thrust washer test, which runs at room temperature with constant pressure and velocity, Schwartz said. The problem is that, with plastics, wear and friction coefficients are influenced by many parameters, including external lubricant, surface roughness, temperature, contact pressure, sliding velocity, and more. For this reason, and this was a message repeated by several speakers at the AMI conference, materials for wear applications need to be chosen on a case-by-case basis. Albis is another compounder offering a wide
range of options in wear and friction properties. Karolina Smrczkova, Product Specialist for the company’s Business Line Specialties, spoke about the different effects of various additives in PA66 compounds. Generally, among Alcom WP com- pounds for gears, she said aramid fibres improve wear properties, glass fibres improve wear and friction, silicones and PTFE have a positive impact on wear and friction coefficients, and carbon fibres reduce wear rate significantly (this is summarised in Figure 8). Providing some general indications for the use of plastics in wear applications, Smrczkova advised:
www.compoundingworld.com
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