Due to their structure, cast materials are susceptible to corrosion. Cast iron brake discs quickly tend to corrode whenever they are exposed to unfavourable conditions such as fog, high humidity, splash water, road salt as well as aggressive rim cleaning agents. This effect is unavoidable and does not diminish quality and is not a reason for complaint. On completion of the production process and after quality control, as a preventative measure, the brake discs are treated with an anti-corrosion agent for transportation and subsequent storage. Various methods are used for this purpose:
Treating the brake disc with anti-corrosion oil
The brake disc is coated with an anti-corrosion oil and wrapped in plastic film. Prior to installation in the workshop, it must be cleaned with a solvent (brake cleaner). The disadvantage of this treatment is that, once the oil has been removed, the complete brake disc is exposed unprotected to the adverse influences described above. As a consequence, corrosion already tends to form on the open-pored cast iron of the brake disc after a short period of time, resulting in an unsightly appearance especially on vehicles with see-through aluminium rims. If the anti-corrosion oil is not completely removed, evaporation of the oil residue can cause unpleasant odours the first time the brake disc heats up.
Coating the brake disc with a zinc-aluminium compound
The brake disc is coated with a zinc-aluminium compound which is baked in an oven. The corrosion protection layer produced in this way is resistant to road salt, brake fluid and fuel, etc. This coating greatly reduces the tendency of corrosion to form on the areas of the brake disc not used for friction pairing. The brake disc can be mounted without removing the coating. Coarse dirt on the brake disc still needs to be removed with a suitable solvent.
Special notes for bedding-in of coated brake discs:
A mandatory test run must be carried out after installing the brake to remove the coating on the brake discs by applying the brake. Initially, grinding and scraping noises may be heard. If these noises do not diminish after applying the brake several times, the brake should be checked immediately to ensure it has been fitted correctly. During the test run, the brake should be lightly applied several times at low speed. A certain distance should be covered unbraked between the braking operations to allow the removed coating material (dust) between the brake disc and brake pad to escape. The brake should remain as cool as possible while braking to remove the coating. If the brake becomes too hot, the coating material can be deposited in patches on the brake pad. Due to their metallic composition, these unwanted deposits are so hard that they can damage the brake disc (scoring). They can additionally cause the brakes to squeak.
UV lacquer coating
This coating greatly reduces the tendency of corrosion to form on the areas of the brake disc not used for friction pairing. The brake disc can be mounted without removing the coating. A bedding-in period of 300 km is recommended.