Sulphuric Acid Anodising
Sulphuric Acid Anodising Process
As aluminium “oxidises” (the natural reaction between of air and aluminium) it produces a loose dry white powder, aluminium oxide. Sulphuric acid anodising is an electrolytic process using electricity (DC current) and a sulphuric acid electrolytic solution causing oxidation of the aluminium surface to form a thin “harder” film of aluminium oxide under controlled conditions.
The passing of the current liberates high volumes of Oxygen at the surface of the aluminium thus aiding controlled formation of the oxide layer. These processes do not produce a coating but are a conversion of the surface aluminium to aluminium oxide and are therefore metallurgically bonded.
The technique produces a tight but porous layer which, because it is porous, requires a sealing process to close the pores and prevent further natural attack on the aluminium.
Sealing is carried out by immersing the component in near boiling de-mineralised water, which if required can have small quantities of other chemicals, such as Nickel acetate or sodium dichromate to further enhance corrosion resistance.
The process is the most common protective treatment for aluminium. The anodised layer forms both within the surface substrate (penetration) as well as on top of the surface, growing the size of the component.
Before sealing, immersion in specially formulated dyes can be carried out, the open pores soak up the dye which will then be locked in by the sealing process, this can produce very attractive finishes but will depend on the thickness of the anodised film as the thinner the film, the less dye will be absorbed.
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Why Choose Sulphuric Acid Anodising?
- Excellent corrosion resistance
- Electrically insulating
- Decorative qualities
- Available in a variety of colours
- Scratch resistant
- Cost effective
- 5 to 25μm coating thickness
- RoHS compliant option
Similar or obsolete designations and standards
- ISO 7599 (replaces BS 1615 and BS EN 12373-1)
- Standard Thickness:
- Def Stan 151/1 Standard - 5-7µm
- Def Stan 03-25 Standard - 5-7µm
- BS1615 Grade AA3 - 3µm
- BS1615 Grade AA5 - 5µm
- BS1615 Grade 10 - 10µm
- BS1615 Grade 15 - 15µm
- BS1615Grade 20 - 20µm
- AMS 03_25 / Def Stan 03-25 (replaces Def 151 Type 1, NWS 1005/2-1 and NES 1005/2-1)
- MIL-A-8625 Type 2 (MIL-A-8625 Type II)
- MIL-STD-171 7.2.1 and 7.2.2
- Def Stan 21-5 2-1
- JP 213 Method 1
- JP 217
- TS112 F3 + D2
- DS26.00 F3 + D2
- P&G STD 41-013
- ASTM B580 Types B, C, D, E and F
- AMS 2471
- “Type 2” anodising (North America)
Components, Applications & Industries
Here are some examples of the industries and components for which sulphuric acid anodising is common and appropriate. This is by no means an exhaustive list. Please do get in touch if you want to talk through your project.
Typical Components & Applications:
- Domestic cookware
- Hand tools
- Fascias for computers and televisions
- Automotive trim
- Base plates
- General OEM manufacture & engineering
Penta Precision is able to offer Sulphuric Acid Anodising as part of our one stop machining service in the UK. As well as our own machining expertise, we are able to access our network of approved quality suppliers for the finishing of your parts, saving you the time and effort and helping to streamline your supply chain.