Less wear thanks to adapted friction coefficient of surfaces

There is so much you can achieve with structured surfaces. They add value to products, making them more competitive. Through a series of cases based on the needs of different sectors, Sirris will give you an idea about their potential. In the first one we will discuss how textures can help to cope with wear of components in the manufacturing industry.

Many products derive a large part of their functional properties from how their surfaces interact with the surroundings. These properties may vary from one industry to another. Manufacturing companies produce all kinds of components, ranging from consumer goods to machines and cars, which are subject to wear due to friction. To deal with this friction, the friction coefficient can be adapted on demand by applying textures or reduced by using certain coatings. This blog is about textures.

Customised friction coefficients

The wear of components has a large impact on the lifecycle and efficiency of machines. The wear is largely caused by the friction between moving components. This can be reduced by applying a structure on the friction surface. Certain applications may benefit more from another option, i.e. controlled friction.

Components in a wide range of applications, including cars, agricultural vehicles, airplanes and machines, are often affected by wear. This wear is one of the main factors in determining the lifespan and efficiency of these machines, and eventually, also their cost. A decisive factor is the friction coefficient of a surface: the higher the coefficient, the more friction is caused between the two surfaces and, therefore, more wear as time goes by.

It is therefore very important that we reduce the friction coefficients for components which move against each other.  Gears are an excellent example, as well as bearing seats of axes and guide rails. A special technical application, for which we want to be able to control the friction coefficient and achieve a certain dynamic behaviour instead of reducing it, are CVTs. These transmissions work by means of friction between two discs, and this friction in turn determines the behaviour of the car.

3D measurement of low-friction texture (left) and top view of this texture (right)

The use of textures makes it possible both to reduce friction coefficients and to control them. Ultra-fast pulsed lasers (fs, 10-15s) are very interesting to apply because they perform ‘cold’ laser processing: no heat is introduced into the piece, and no fusion zones with fractures are formed. This property is extremely important in components that are frequently subjected to cyclic loading. It is also perfectly possible to use femtosecond lasers in hard materials (hardened steel, carbide or ceramics) and even to work in or through coatings, regardless of the nature of these coatings.

Friction force for a milled and textured surface

Initial tests at Sirris indicate that a cavity structure with holes spaced apart at 200 µm and 150 µm and with a depth of 20 µm in an oil bath (such as, for example, gears in a gearbox or CVTs) results in a 75 per cent reduction in friction coefficient. The size of the holes, the distance between the holes and the depth play a role in this, making it possible to adjust the coefficient of friction to a particular application. In particular, it is even possible to create stick-slip effects, which means that overcoming a high static friction coefficient does not automatically result in a lower dynamic friction coefficient. 

In a next blog we will look at how friction and wear can be minimised by means of coatings. Would you like to stay up-to-date with our series about functional surfaces? Register here !