Hohman News Blog

Hohman News Blog


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Chemical Conversion Coating- Process Spotlight

Chemical Conversion Coating is a coating process where the metal part’s surface is converted into the coating with a chemical reaction process. In general, the film thickness on the metal part is very thin and is measured in millionths of an inch (on the order of 0.00001”). It isn’t practical to measure a chemical conversion coating dimensionally so it is usually measured by coating weight (milligrams per square foot).

Also called “immersion coating” chemical conversion coatings are chemical reactions. The chemical reactions are dependent on:

  • Chemical concentration – more chemicals to react creates more energy thus producing a faster or thicker coating
  • pH – the lower the pH, the more hydrogen ions occur thereby producing more energy
  • Immersion time – keeping the part in the bath longer provides more time for the chemical reaction to occur – thus producing a faster or thicker coating.
  • Agitation – increasing the agitation puts fresh solution against the part, thus producing a faster or thicker coating

Examples of chemical conversion coatings include:

  • Chromate conversion coatings
  • Phosphate conversion coatings
  • Bluing
  • Black oxide coatings on steel

Benefits of Chemical Conversion Coating:

  • Corrosion protection
  • Retain electrical conductivity (for use in electronics)
  • Increased surface hardness
  • Color coding and decorative purposes
  • Paint primer


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