WEAR RESISTANCE | MODIFICATION
High friction results in increased wear, reduced efficiency and unwanted noise in many sliding plastics
applications.Peter Mapleston learns how to solve the problems
Geared up for better wear performance
Plastics offer many advantages over metals in technical applications but one area where they can fall short is their resistance to wear. It is not just that plastics are typically not as hard as metals, but also that the entire physics of how plastic materials wear is not well understood. Tribology — the science of wear, friction and lubrication — is very well under- stood in the world of metals. However, when it comes to plastics the science is hardly out of its infancy. There is much is still to be learnt. In terms of learning, the Wear-Resistant Plastics
Conference in Dusseldorf last December (which was organised by Compounding World publisher AMI) provided a useful classroom. Dr Marcel Meuwissen, Senior Scientist Mechanical Properties at the DSM Materials Science Centre in The Netherlands, opened the event by pointing out that Amonton’s law of friction, which holds that the Coefficient of Friction (CoF) in any given system is constant, is just not true. Down at the level of single asperities (surface irregularities) he said CoF may
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increase or decrease with increasing force, de- pending on how much load is applied and over how big an area, for example.
Meuwissen took a deep dive into surface science as he discussed the company’s research into understanding abrasive wear of engineering plastics, especially polyamides. He concluded by saying that the links between intrinsic properties of polyamides and wear rate are simply not yet understood. “Wear and friction [are] strongly dependent on conditions at contact (pressure, temperature, surface topology, ...),” he said. “Indications are that wear is linked to toughness and fatigue, depending on testing conditions.” High-performance solid lubricants based on synthetic metal sulphides significantly improve friction and wear characteristics of engineering thermoplastics, according to lubricant supplier Tribotecc. Christian Schmied, who works in Development, Application Technology and Analytics at the company, provided an overview of
Main image: High friction surfaces
contribute to wear and noise in plastic gear systems. Careful lubricant
selection can minimise both
February 2020 | COMPOUNDING WORLD 27
IMAGE: SHUTTERSTOCK
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