Three Types of Anodising

Surface treatments are a popular way of enhancing a product or extending its lifespan. There are many methods of doing so, including electroplating, painting, powder coating, and anodising.

Anodising uses an electrochemical process to alter the surfaces of metals. There are three main types of anodising: chromic acid anodising, sulphuric acid anodising, and hard anodising.

Chromic Acid Anodising

This method, unsurprisingly, utilises chromic acid. The benefits of this process include corrosion resistance, low thickness build-up, improved adhesion, and electrical insulation. The only potential disadvantages are that the coatings may crack under heavy stress, and it can be hard to achieve consistent colouring.

Due to these properties, this method is used in industries including aerospace, defence, and automotive to make components, including engine parts, wing panels, and fuselage.

Sulphuric Acid Anodising

This is perhaps the most widely used method of the three. Using sulphuric acid as the electrolyte has several benefits.

Sulphuric acid anodising can produce a uniform protective layer, enhance corrosion resistance, increase durability, improve aesthetics, and boost electrical insulation. The process is also non-toxic. However, it has limited colour options and thickness, can highlight surface imperfections, and may be porous or brittle.

This method is used across industries, including automotive, electronics, and aerospace.

Surface treatments provide a number of benefits, and specialists such as poeton.co.uk/surface-treatments/anodising/sulphuric-acid-anodising/ offer a range of options, including sulphuric acid anodising.

Hard Anodising

This method, also sometimes known as hard-coat anodising, uses sulphuric acid, but involves higher voltages and lower temperatures than the standard method.

The advantages of hard anodising are that it produces a thicker coating layer and offers excellent corrosion resistance, electrical insulation, hardness, wear resistance, scratch resistance, and surface durability. Additionally, it can offer significantly thicker coatings. However, this type of coating can affect dimensional accuracy, has limited colour options, and slightly reduces the fatigue strength.

The main applications for this method include hydraulic cylinders and landing gear for aeroplanes, brake callipers and suspension parts in cars, and equipment that may be exposed to harsh environments in industries such as oil and gas.