Low Friction Coatings
As environmental restrictions on the use of lubricants grow tighter, and costs associated with disposal increase, there is a growing demand for low friction thin film coatings that allow contacting surfaces to rub against one another with reduced friction and wear. Hence the use of a low coefficient of friction coating to improve the tribological properties of tools for metal cutting and forming, and machine elements e.g. sliding bearings, seals and valves is constantly increasing. Here are some examples of applications where low friction coatings are used.
Coating forming tools with a low friction metal coating
Low friction coatings reduce the tendency to sticking and material pick up from the counter surface substantially reducing the downtime required for cleaning. Anti sticking agents may therefore be completely omitted in forming tool applications.
Coating machine components with low friction coatings
Examples of machine elements where low friction coatings are used are bearings, shafts, valves and gears. The typical operational temperatures and contact pressures for such components are 50 to 300°C and 0.5 to 3 GPa respectively. Some of these components are difficult to lubricate effectively even under normal running conditions. The low friction coating provides a low friction surface and improved performance unlubricated. Also in some cases oil or grease based lubrication can not be used such as in a vacuum / space, food processing and pharmaceutical processing, a low friction coating supplies the required lubrication and in comparison to the uncoated surface they could appear to be frictionless coatings.
Wear protection of light alloys using low friction coatings
Traditionally, machine components have been made of carbon steel or cast iron. However the trend in industry is to substitute these traditional materials for components made of lighter materials, typically aluminium, titanium and magnesium alloys to reduce weight. This phenomena is most pronounced in the automotive industry to reduce fuel consumption and increase speed. A problem with these light metal alloys is that although they are tough materials they exhibit poor tribological performance because of their low hardness and stiffness as well as a tendency to stick to the countersurface. This results in excessive plastic deformation, abrasive and adhesive wear (galling) and consequently high friction.
Excessive galling will eventually cause sliding components to seize. By coating the sliding parts with a low friction coating the light alloy surface is protected from wear and the friction is reduced lowering energy losses and improving efficiency.
Examples of the best wear resistant, low friction coatings are Graphit-iC, MoST and Dymon-iC.
These new low friction coatings offer many advantages over previous low friction coatings because of their good adhesion, hardness, wear resistance and load-bearing capability. The low friction coatings also have many advantages over conventional hard coatings because of their low friction and lubricating properties.
As a result of these tribological properties, these low friction coatings are currently in use in a wide range of applications including cutting and forming tools. The low friction coatings have also been shown to have considerable potential in heavily loaded applications, such as gears and engine parts where coatings have previously found little or no success.
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