Electroplating of Brake Systems and other Cast Iron Components

Complex cast iron parts like brake calipers usually present a cleaning challenge. The UniClean® and TRI-MAX® systems are designed to completely remove soil and maximize the cleaning of ferrous-based substrates prior to zinc and zinc alloy electroplating, which is crucial for optimum adhesion of the plated metal layer.

Acid zinc processes are extensively used in caliper plating. Zylite® 11-50 is Atotech's preferred process due to its superior covering power.

High-end corrosion resistance can be achieved with a zinc-nickel coating. Zinni AC AF 210 is an acid zinc-nickel process which deposits an attractive bright coating with excellent corrosion protection due to the formation of true γ-phase structure. It has been especially designed for direct plating of cast iron and is approved by the brake caliper industry.

As Cr(VI)-free passivation on acid zinc EcoTri® HC2, the trivalent chromium based thick film passivate is the preferred process. The preferred process to passivate acid zinc-nickel is Unifix® Ni/Fe 3-10 L. Both achieve best corrosion protection and heat resistance.
Often a heat treatment procedure (2 h 150°C) prior to corrosion testing is required. It is recommended particularly for the post-treatment of brake calipers and other complex cast iron parts to use EcoTri® HC2 resp. Unifix® Ni/Fe 3-10 L in conjunction with the ion-exchange purification system Tricotect®. It ensures best process control and resulting optimum performance characteristics.

Sealers can be used to further increase corrosion protection. For brake fluid compatibility it is necessary to use inorganic based sealers that don't contain any organic lacquers. The silica-based reactive sealers Sealer 300 W and Sealer 300 WL 7 are recommended for the brake caliper application.

Typical Process Sequence with Recommended Products

Other cast iron applications include steering knuckles, which can be electroplated for enhanced corrosion protection, for example with the alkaline zinc-iron Protedur® Plus system.

Process Sequence for Silver Zinc Flake Coating of Brake Discs