The chemical compound tungsten disulfide, developed in the 1960s for the American space agency NASA as a dry-film lubricant, has found a number of applications in aerospace and auto racing. Although it offers excellent friction protection with only a thin surface film, existing tungsten disulfide coating methods remain too complex and expensive for most large-scale industrial uses.

But now the Swedish company Applied Nano Surfaces has patented a simple, inexpensive process for coating engine parts with tungsten disulfide. The company estimates that the reduced surface friction can lower fuel consumption by up to 2 percent, which would be equivalent to cutting carbon dioxide emissions by 500 million tons per year from Swedish-made engines for trucks and other heavy vehicles. Reduced friction also translates to less engine wear, lowering maintenance costs.

Low-friction material rubbed onto surfaces

In practice, the low-friction material is “rubbed” onto engine components. Here’s how it works:

  • The material is applied by a machine tool such as a lathe or miller. No special preparation is required.
  • A tool containing tungsten is pressed against the engine part made of steel or cast iron. A process fluid containing sulfur is then applied, causing a chemical reaction.
  • A thin film of tungsten disulfide fills in tiny irregularities in the surface.
  • The surface becomes nearly perfectly smooth, with a thickness of 1 to 2 microns (millionths of a meter).
  • The finished surface is wear- and heat-resistant, with an extremely low coefficient of friction.
Cylinder sleeves, camshafts and piston pins can be coated with the new method.

Cylinder sleeves, camshafts and piston pins can be coated with the new method.

One advantage of the new method is that it can be used with ordinary industrial equipment, producing surfaces proven to resist wear more effectively than untreated ones. The nanocomposite is chemically bound to the substrate, ensuring that the film does not flake. It also binds with oil, making it possible to use light lubricants in conjunction with the nanocomposite. This helps to further reduce friction and lessen the need for oils containing sulfur.

Engine manufacturers interested

Cylinder sleeves, camshafts and piston pins can be coated with the new method, and engine manufacturers are expressing interest in Applied Nano Surfaces, especially for use in heavy diesel engines. The market is potentially huge: some 70 million new vehicles are sold each year, including about 3 million heavy vehicles. A truck uses about 15 percent of its fuel to overcome engine friction, of which about 9 percent is lost as heat from contact between piston rings and cylinder sleeves.

Applied Nano Surfaces believes that its nanocomposite application process has the potential to significantly reduce fuel consumption in trucks, busses and passenger cars. The company aims to license its technology to major manufacturers, and the Swedish truck makers Volvo Powertrain and Scania are set to test the process in heavy diesel engines.

Applied Nano Surfaces sees a number of other industrial applications for low-friction materials, including process industry equipment, generators, compressors, plain bearings, turbines, pumps and motors.

Article published in July 2009