Hard Anodising

Your Guide to Hard Anodising



High quality precision machined components

Specialising in intricate, tight tolerance work

Extensive experience and high customer satisfaction

Penta Precision is able to offer hard 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.

Customers turn to us when they have had quality and delivery issues with their existing suppliers and need a reliable machining partner.

Why Choose Hard Anodising?


  • Excellent wear resistance and increased durability
  • Close tolerance control
  • Resistant to high temperatures
  • Increased corrosion resistance
  • Provides electrical insulation
  • Aesthetically pleasing finish – from clear to light grey through to black

Hard Anodising


Hard Anodising Process
Hard anodising is very similar to sulphuric acid anodising. Using a higher acid concentration, it is processed at a solution temperature of 0°C with a significantly higher voltage being applied.

A thicker oxide layer and therefore increased corrosion resistance, electrical insulation and increased wear resistance compared to standard sulphuric anodising.

As aluminium “oxidises” (the natural reaction between air and aluminium, it produces a loose dry white powder, aluminium oxide. Sulphuric acid anodising is an electrolytic process using higher voltage  (DC current) and a higher concentration sulphuric acid electrolytic solution causing oxidation of the aluminium surface to form thicker “harder” layers 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 techniques produce 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.


Most Common Specifications:

  • ISO 10074
  • MIL-A-8625 Type III
  • Def Stan 21-5 2-3
  • JP249
  • ASTM B580 Type A

Components, Applications and Industries

Hard anodising is often used in aerospace and automotive components where the hard wearing properties are most beneficial. Hard anodised aluminium can also be found in architectural and construction applications due to resistance to weathering. General engineering applications also benefit from hard anodising.


Applications: Valves | Gears | Pulleys | Swivel joints | Pistons | Sliding parts | Hinges

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    Why choose Penta Precision?


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    Client Feedback


    "Overall excellent service, parts are delivered on time to an acceptable standard. Sales and quotation team are very responsive to our enquiries."
    David  Supplier Quality Engineer
    "To be confident that an accurately manufactured part will arrive on the agreed deadline is invaluable and increasingly rare. Penta give us this confidence."
    Paul – R&D Manager
    "Penta Precision provides a near faultless service.
    They are a friendly and helpful company who I hold with very high regard.''


    John – Tooling Engineer

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