Chromic Acid Anodising

Chromic acid anodising is a specialist surface finish used primarily within the defence and aerospace sectors and industries where subsequent painting/adhesive bonding is required or in applications where crack detection is sought. Chromic acid anodising is the preferred process for the treatment of castings and other components where the minimisation of the loss of fatigue strength resulting from the anodising process is desirable.

Restrictions

• This process is not suitable for use on aluminium alloys containing a specified maximum total of 7% copper, nickel and iron or more than 6% copper.
• Chromic acid anodising is not suitable for colour dyeing due to the thin (2-3µm) coating layer as most colours will appear blotchy, however black dyeing is usually quite reliable and effective.
• The chromic acid anodising process is not suitable for welded assemblies or components with blind holes.

Painting - Adhesive Bonding

For customers that require components painted, or used in composite structures, we offer an overnight service with guaranteed availability at an agreed time the next morning, allowing you time to transport your items for finishing or manufacture before the anodised coating cures, usually within 8-16 hours.

Maximum Size Criteria

The table below outlines the maximum size criteria for chromic acid anodising:

Dimension	Clear	Black
Length	2430mm (8')	1829mm (6')
Width	910mm (3')	910mm (3')
Depth	910mm (3')	910mm (3')

Coating Thickness

Chromic acid anodising results in a thin 2-3µm coating.

Available Standards

We predominantly work to 2 specific standards as detailed below although we are happy to work to any specification provided.

• DEF STAN 03-24 (formerly DEF 151 Type 2)
• BS1615
• US MIL-A-8625 Type 1

Sealing & Dyeing

Two seals are available for application after chromic acid anodising:

• Colour dyeing prior to sealing - black
• Hot De-mineralised Water Seal