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Zinc Flake Coat Protects High-Strength Steel Parts That Zinc Plating Cannot
01 Sep 2004
The Ford Motor Company Ltd has approved a new standard for coating fasteners (S442) based on the new material specification for 'DeltaProtekt', which has been on the market for only three years. This second generation micro-layer corrosion protection system is a nonelectrolytically applied zinc flake, which has been developed for corrosion protection of high-strength steel threaded parts, where traditional zinc plating methods cannot.
A recent report by Dr Rohr and Dr Stockert for Dorken MKS-Systeme GmbH, which produces Delta-Protekt and supplementary coatings, predominately for use in the motor industry, explains the benefits of using zinc flake coatings for high-strength materials.
While zinc electroplating and hot-dip galvanising provide adequate corrosion protection for non-highstrength steels, neither of these methods can be used for high-strength base materials. Electroplating cannot be used because hydrogen embrittlement occurs when hydrogen diffuses into the crystal lattice of the hardened metal. Hot-dip galvanising cannot be used because the temperatures involved are higher than those used in the original annealing process, and the hardness of the steel changes uncontrollably.
Zinc flake 'painting processes' have proved to be top-class in terms of protecting high-strength steel threaded parts against corrosion. The coatings contain flat zinc platelets which are bonded to the component with a binder system. After application, the coating is cured. The resulting layer contains about 85% metal, which is conductive and corrodes in preference to the steel when damaged by scratches.
The properties of the zinc-flake material can be extended with supplementary coatings of a top coat that can be used to optimise properties selectively such as colour, friction values, wear resistance and chemical resistance.
www.doerken-mks.com
