Polymers in Low Friction Applications: Reducing Wear and Tear and Keeping it Smooth.
The development of faster, more durable equipment usually calls for efficiency in energy utilisation and components that can sustain either rotary or linear motion over a very long product life cycle. This problem always boils down to the management of friction. Moving parts will typically experience wear and tear due to friction, leading to both part failure and an unnecessary build up of heat (and therefore a loss of energy).
Advancements in polymer science have allowed a significant number of metal parts to be replaced with specific, high-performance plastics that combine a low coefficient of friction with a high wear rate (also called the Pressure x Velocity, or PV value). These polymers, often when combined with specific fillers, are able to perform for far longer, minimising replacement costs and boosting energy efficiency.
One of the primary advantages of polymers in low friction applications is their innate lubricating properties. Unlike traditional lubricants that require constant replenishment, polymers can provide a durable and long-lasting solution. Polymeric materials, such as polyethylene and polytetrafluoroethylene (PTFE or Teflon), have self-lubricating properties, reducing the need for external lubricants and minimizing maintenance efforts. In the case of PTFE (Teflon) and UHMWPE, the static and dynamic coefficients of friction are so low that when sliding against certain materials (for example: polished stainless steel) the coefficient could fall to as little as 0.03. In layman’s terms: it would take only 30grams of horizonal push to move a 1Kg block across the surface of the PTFE. This is something we also call ‘near rolling friction’.
In the case of PTFE, the addition of specific fillers – such as bronze, glass, carbon, or MoS2 – can further enhance the wear properties of the material, making it more robust in certain industrial applications. PTFE can itself be used as a filler in other polymers, including PEEK, POM (Delrin), PPS (Ryton) or even Nylons. The addition of PTFE micro powders into these polymers – usually in a concentration of 5-25% - gives an appreciable boost to the low-friction properties of the base polymer, while allowing the polymer to retain its other characteristics.
In addition to their lubricating properties, polymers offer excellent resistance to wear and corrosion. When used in bearings, gears, or sliding components, polymers can withstand harsh conditions and maintain their integrity over time. This resilience contributes to the longevity of the components and reduces the frequency of replacements, ultimately leading to cost savings for industries. PEEK is highly sought after in gears. The hardness of PEEK ensures that the part will not wear out over time, while PEEK’s low density (specific gravity of 1.3) gives the added benefit of weight saving in the system.
Many polymeric materials excel in low friction applications due to their lightweight nature. In industries where weight is a critical factor, such as aerospace and automotive, using polymers can lead to significant fuel savings. With specific gravities as low as 0.9, the weight saving over a metal component can be as high as 90%. Especially in aerospace applications, this is a benefit that creates immense savings for the end users. The reduced weight contributes to improved fuel efficiency and overall performance, making polymers both an eco-friendly and economically viable choice.
Medical devices also benefit greatly from the incorporation of polymers in low friction applications. Prosthetic joints, for example, often utilize polymer components to mimic the natural lubrication of human joints. The biocompatibility of certain polymers ensures that they can be safely used within the human body, providing low friction solutions for a wide range of medical applications. Similarly, PTFE tubes (usually with radiopaque fillers) are used in medical applications that require the tube to slide in and out of the patient’s body. Amplatz sheaths, for example, are used in urology wherein the tube is pushed in to make a channel through which a guidewire can be passed. The smoothness of the PTFE minimises the discomfort to the patient.
In conclusion, the use of polymers in low friction applications has ushered in a new era of efficiency, durability, and sustainability. Their innate lubricating properties, resistance to wear, and versatility make them indispensable in various industries. As technology advances and the demand for high-performance materials grows, polymers are likely to play an even more significant role in shaping the future of low friction applications.
Read More
1. PTFE Extrusion - Ram vs Paste Extruded - A comparison of features
2. Exploring the Versatile World of PVDF
3. Air Permeability Testing and Water Entry Pressure Testing in Expanded PTFE Membranes