Keep rolling - secure protection for wheel hubs

Wheel hubs are a key component of the chassis and serve to guide the wheels. It is therefore all the more important that these parts are protected effectively against corrosion.

Sharp bends, potholes and uneven surfaces. The entire vehicle is subjected to great stress. This means it is especially important for all components to be high quality and fulfil their function. Wheel hubs (also known as roller bearings) have various roles to play in this: On the one hand, they guide the wheels, shafts and axles, supporting these; on the other hand they transfer forces from the wheels to the other chassis components - when cornering in particular, high axial force is exerted on them. Wheel hubs therefore represent the link between vehicle and the ground. Finally, depending on model, they deliver information to the anti-lock braking system (ABS) and/or the electronic stability programme (ESP).

Functioning wheel hubs mean a stable ride thanks to the smooth rotation of the wheels. If the wheel hubs are defective, optimal gripping of the road is no longer guaranteed. This can have negative effects when cornering in particular.

Complex structure for maximum effect

Both driven and non-driven rollers are found in cars - but the structure is the same: They comprise an outer and inner ring, rolling bodies and two so-called cages. Depending on the requirements, the actual rolling bodies are either tapered or spherical. Today, two bearings are installed opposite one another, i.e. they are greased, sealed and adjusted with tightening torque. In addition, the wheel hubs each have two seals and a flange to accept the brake disc and bolting to the cross member. In wheel hubs of the second generation onwards the hub is already applied. The roller bearings are typically made from chromium steel, very hard, but quick to rust. The high stresses and relevance for the chassis mean that the component should be corrosion resistant.

Optimal protection via zinc flake

Until now, wheel hubs were coated with zinc powder or UV coating - if at all. Increased quality requirements of low coat thickness with high corrosion resistance as well as the appearance of components have led to a rise in demand for alternatives. For production reasons, the wheel hubs must be assembled without any coating. Only afterwards is corrosion coating possible. This may not be exposed to high temperatures (max. 120°C) during the curing process, due to the fitting requirements it should ideally be only 20μm thick and offer cathodic corrosion protection where possible. The solution to these requirements is the DELTA-PROTEKT® KL170 RT zinc flake system from Dörken MKS, which hardens at room temperature. After the wheel hubs has been subjected to hot alkaline degreasing, the zinc flake coating is applied in a spraying process. Forced drying, for example at 80°C, is possible. The advantage of the system is cathodic corrosion protection of at least 720 hours in salt spray testing (in accordance with DIN EN ISO 9227). At the same time, the system has a coat thickness of just 12–15µm. A further advantage: no hydrogen is generated in the coating process and there is therefore no risk of hydrogen-induced stress corrosion cracking. This means that the zinc flake coating is particularly suitable for wheel hubs made from high-tensile steel.

DELTA-PROTEKT® KL170 RT for two different wheel hubs units in use: before the corrosion test (left) and after 720 hours in salt spray testing in accordance with DIN EN ISO 9227 (right)