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Phosphate Conversion Coating

Phosphate coatings are used as a pre-treatment for paint bonding, to aid with cold forming, and to improve corrosion resistance in conjunction with supplementary treatments.

We provide Class 1 heavyweight manganese phosphate coatings and Class 3 light weight zinc phosphate coatings.

Generally the method for specifying phosphate coatings is by expressing the coatings requirements as a coating weight in either g/m2 or mg/ft2 as opposed to a film thickness.

Phosphate coatings are typically graded by class;

  • Class 1 – For maximum corrosion protection > 7.5 g/m2 coating weight – usually heavy weight manganese or zinc phsophates.
  • Class 2 – For general protective purpose > 4.5 g/m2 – usually zinc phosphate, however you can substitute a Class 1 coating for a Class 2 coating except on thin sheet material.
  • Class 3 – Pre-treatment of thin sheet steel sections zinc phosphate 1.5 to 4.5 g/m2.
  • Class 4 – Lightweight zinc or iron phosphate 0.2 to 1.5 g/m2.

Components that are high tensile or have been heat treated to certain hardness may require stress relieving before phosphating and baking after phosphating for the relief of hydrogen embrittlement.

When specifying phosphating on drawings or orders it is recommended that wherever possible national, international or defence standards are used to provide the processing instructions to us. Typically the following information should also be provided;

  • Specification reference
  • Material grade and condition (hardness, UTS)
  • Significant surfaces and areas where measurements of coating thickness are to be made.
  • Any areas that must not be used as contact points for jigging/wiring
  • Supplementary treatments such as baking, oiling.
  • Any special inspection requirements
  • Any special packing requirements

Manganese and zinc phosphating, including the processing of oilfield connections and components to customer specification, can be processed to the following standards;

  • AMD 03-11 (Def Stan 03-11)
  • BS EN ISO 9717 (BS 12476, BS 3189)

We also hold a large library of customer-specific, superseded and legacy specifications so contact us if you need any help.

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