Your guide to hard anodising

The process of hard anodising allows metals such as aluminium to achieve greater performance in a number of applications within sectors such as aerospace, defence, space and precision engineering.  Below we give a brief guide on hard anodising, how it is achieved, and what the benefits are.

Hard anodising explained.

Aluminium alloys are hard anodised to produce a thick, tough and hard coating.  To put it simply, hard anodising is achieved by passing a direct current through an acid electrolyte solution between positive (anode) and negative (cathode) electrodes.  The aluminium object which is to be anodised functions as the anode.  As a result of the current passing through the solution between the two electrodes, oxygen ions are released from the solution which then combine with the aluminium atoms on the surface of the aluminium, thereby creating a coating of aluminium oxide.  The thickness of the coating depends on the strength of current and the length of time that the aluminium remains in the solution.

Because the aluminium oxide is fully integrated with the original aluminium object, it cannot chip or peel like other surface coating technologies.

PTFE can be incorporated during this hard anodising process which gives the finished object a low-friction coating which has good hydrophobic and lipophobic properties. This means that oil and water both bead in contact with the coating and will not penetrate.

The hard anodised coating is complemented at Frost by various sealing methods such as hot water, tri-valent chromate, nickel acetate and PTFE – all of which all give increased performance in respect of wear and corrosion resistance.

What are the benefits of hard anodising?

There are several benefits of hard anodising compared to that of sulphuric anodising, which include:

  • High degree of wear resistance. Hard anodised products typically have a long life span and are extremely hard wearing thanks to the higher thickness achieved during anodising. The wear resistance is increased by incorporating PTFE during the process;
  • Increased corrosion resistance in aggressive environments;
  • Resistant to temperature extremes;
  • The coating is much harder than the original metal;
  • The anodised layer prevents the substrate (the aluminium) being exposed to moisture and other contaminants which can cause damage to the metal; and
  • Additional treatments can be applied, which include dyeing.

Who should I contact to find out more about hard anodising?

When choosing a company to deliver hard anodising services for your application, you need to make sure that they have all the correct processes in place and follow necessary guidelines and directives in relation to the use of chemicals.  Frost Electroplating have been working in the surface coating industry for 130 years and are market leaders in their field.

We have achieved accreditation to Nadcap for Chemical Processing for anodising and conversion coatings, and AS9100 quality management standard for the aerospace industry.  In addition, we are also certified to both ISO 9001 quality accreditation and AS9100 aerospace standard.

We have recently built a purpose-designed facility dedicated to producing a wide range of hard anodised and sulphuric anodised coatings.  These are developed in accordance with aerospace and defence standards for durability, wear and corrosion resistance.

Our innovative processes and high-performance coatings have been developed for new industries and technologies, for customers across the globe.  These innovations are able to meet specific technical requirements for hardness, corrosion resistance and low-friction.  We work closely with our customers to find them coating solutions to meet their specific needs and help improve their products using a range of surface coating technologies.

To find out more about Frost Electroplating, hard anodising and the other services offered, please browse our website or contact one of our team on 0121 433 3091.