Chemical Conversion Coating
Also known as chemical film, chromate conversion coatings, chromating, alodine and alodining.
Chemical conversion coating or chromating provides economical corrosion protection and a superb surface for painting and powder coating aluminum parts.
Chemical conversion coatings also provide low electrical resistance or preserve electric conductivity as opposed to anodizing which creates a non conductive coating.
Chemical conversion coatings, unlike anodizing, do not require electricity and therefore are more economical to produce. All parts go through a multi step surface cleaning process prior to being coated.
Chromating or Alodining is typically either clear or coloured. We offer only clear.
Classifications of Chemical Conversion Coatings
Chemical conversion coatings are generally classified as follows:
- Class 1A Coatings: coatings for maximum protection against corrosion and maximum paint adhesion.
- Class 3 Coatings: coatings for corrosion (thinner than Class 1A) and intended for electrical applications where low electrical resistance is required relative to Class 1A coatings and anodizing.
Specifications of Chemical Conversion Coatings
Generally, chemical conversion coatings are specified using Military Specification MIL-DTL-5541F.
Altech Anodizing Ltd.’s standard processes for chemical conversion coating or chromate conversion coating of aluminum are generally in accordance with the process requirements of MIL-DTL-5541F.
One difference between the specification and Altech’s standard processes is the exception of paragraphs 3.6.1 and 3.6.2 of MIL-DTL-5541F. Those paragraphs require that production parts or test specimens undergo a salt spray test to determine corrosion resistance and a paint adhesion test. Those tests are not regularly performed by us for cost reasons. However, given our strict chemical and process controls, we have every reason to believe that all parts processed by us would pass those tests. We can arrange to have both the corrosion and paint adhesion testing of test specimens or your parts after processing if required.
Chemical Conversion Coating Tip
Chromating or Alodining are not intended for cosmetic enhancement of parts. Colour may vary between parts and from alloy to alloy. In some instances, the coating is clear and not detectable by visual examination.
We are pleased to announce that we have removed hexavalent gold chromate conversion coatings from our provided services. The hexavalent form of chrome found in all gold chromate solutions is a known carcinogen and simply put is bad for the environment. While Altech takes all necessary environmental and safety precautions, including waste water treatment and proper environmental disposal of solid waste by-products, we no longer viewed gold chromate as an environmentally or socially acceptable form of conversion coating.
Our decision was also an easy one in light of the fact there are other more environmentally friendly coatings which are as effective as gold chromate. One such coating which we will continue to offer is our ROHS compliant trivalent chrome conversion coating. ROHS compliance conversion coatings are an absolute requirement for the vast majority of products produced for the European market and is the direction all responsible markets are heading.