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Zinc plating is widely used to provide sacrificial corrosion protection to steel and is usually deposited in thicknesses varying from 5 to over 25 µm. Zinc plated coatings are usually passivated by immersing in chromate solution to increase the resistance of the zinc to corrosion, supplementary treatments can be applied after chromating to provide specific characteristics such as;

  • Sealing – to improve corrosion resistance
  • Integral lubricant – to improve torque characteristics of fasteners/threads

With suitable pre treatment zinc can be deposited on almost any substrate, though by far the most common are ferrous substrates, however certain materials such as cast iron and carbonitrided steel require processing in specific types of zinc bath.

We offer both rack and barrel plating services and a range of passivates and sealers including;

  • Clear/Blue – Trivalent chromate ELV/RoHS compliant
  • Colour/Yellow – Hexavalent chromate not ELV/RoHS compliant
  • Thick film trivalent – Trivalent chromate this class of passivate developed to approximate the corrosion resistance of the Colour/Yellow passivate as an ELV/RoHS compliant alternative
  • Torque control lubricant

The protective value of the coating is dependent upon;

  • Thickness of zinc deposit, generally the thicker the zinc deposit, once the protective value of the relevant chromate film has become exhausted, then the time to base metal corrosion or “red rust” is thickness dependent.
  • Chromate film, the type of chromate film applied influences the time to first corrosion products of zinc or “white rust” appearing.
  • Production method, zinc coatings are produced by the rack or barrel method. Barrel plating is the most economical method for bulk processing of small parts but the protective value of the relevant chromate film is less than a chromate film produced by the rack method. The main cause of this is the mechanical damage to the film that is inherent in the barrel production method.
  • Component, the substrate condition, shape of the part all have an influence on final protective value of the specific system applied.

High tensile components and components that have been hardened to specific levels of surface hardness may require baking treatments before plating (stress relief), and after plating for the relief of hydrogen embrittlement.

The baking times and temperatures are dependent upon the UTS and/or the surface hardness of the part.

High tensile or hardened parts that are not baked for the relief of hydrogen embrittlement can failure in service or even before service, more details are provided in ISO 9587 and ISO 9588.

We provide rack and barrel zinc plating with a range of passivates including ELV and RoHS compliant passivates, including processing to the following standards;

  • AMS 03-20 (Def Stan 03-20)
  • BS EN ISO 4042
  • BS EN ISO 2081 (BS EN 12329, BS 1706)

For more information download our Zinc Plating info sheet or contact us for a quote.