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Metal Finishing Services

What Is Hard Anodising?

Anodising is the process of extending the naturally occurring oxide layer so as it becomes much thicker and adds increased wear and corrosion protection. Hard Anodising produces a thicker coating with a denser structure, and may be preferable for applications where wear, abrasion and erosion are present. Hard Anodising is suitable for Aluminium Alloys which contain less than 10% Silicon and 5% Copper.

What Is The Process?

Anodising is an electrolytic process in which components are immersed in a vat containing a Sulphuric Acid electrolyte (usually about 15%) at a low temperature and high current densities. This produces a thicker oxide layer with a denser crystalline structure. Hard Anodising produces much thicker coatings between 25 and 100 microns and it’s important to remember that Hard Anodising forms both above and below the surface of the part. (roughly half above and half below) so may affect critical dimensions. Where Natural Anodising may be used for aesthetic applications, Hard Anodising is largely a functional process and tends to be darker in colour.

What Are The Advantages?

Hard Anodising provides an excellent level of wear and abrasion resistance. The thicker the coating the greater the resistance will be, and for applications in which wear is the sole concern, leaving it unsealed is often the best option.

Hard Anodising provides a good level of corrosion resistance, it is still vulnerable to chemical corrosion in particular from Alkalis, but this performance can be improved through sealing. When sealed Hard Anodising is a popular choice for undersea and offshore applications, but hardness and abrasion resistance is lowered.

Hard Anodising provides a high electrical resistivity and may be used as barrier parts within electrical systems and also offers a good resistance to temperature.  


DEF STAN 21-5 2-3, ISO 10074,ASTM B580 Type A

What We Offer:

Please contact us today about Silchrome’s Hard Anodising services

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  • The official logos for the ISOQAR and UKAS industry regulatory bodies.