Anodising is the electroplating process by which the natural oxide layer on the surface of a metal is thickened. This provides a better surface for paint primers and glues to adhere to, increases the resistance to corrosion, and, additionally, cosmetic effects can be created with an anodic film. This effective, versatile process can be used for a variety of applications across many different industries. Here we will consider the four main types of anodising.
Titanium anodising
This process is specific to titanium and the process modifies the oxide layer on the surface of the metal. Titanium is used frequently in the aerospace and biomedical industries, which are where we most commonly see this anodising process. There are three forms of anodising for titanium. Type 1 is used the least frequently and is ideal for treatments at a high temperature. Type 2 protects the surface of the metal against wear and tear. Type 3 commonly helps identify different parts visually and is most often used for medical applications, though it has been used also for costume jewellery.
Sulphuric acid anodising
Sulphuric acid is the solution most often used to form an anodised coating. It is one of the most cost-effective yet versatile methods of anodising, which helps explain why it is so popular. Anodising with sulphuric acid results in a tough surface that resists corrosion. This lends itself to use within the military (such as for weapons). It can also be more easily dyed in a variety of ways as the finish is clearer than can be achieved with some other forms of anodising. Thicker coatings increase the resistance to corrosion, but beyond a certain point, it is known as hard anodising as discussed below.
Hard anodising
Hard anodising is an additional form of sulphuric acid anodising. It results in a much thicker and more robust finish, so is ideal for use on parts that undergo extreme wear and tear or need to work in harsh conditions. This often includes items such as pistons, gears or valves. Another advantage to hard anodising is the ability to further treat the surface with coatings such as the synthetic fluoropolymer, PTFE, which has the lowest known coefficient of friction. Coatings of this sort create non-stick surfaces, which are vital in many industries or products. Hard anodising PTFE, such as that seen at https://www.poeton.co.uk/standard-treatments/hard-anodising/ significantly improves the resistance to wear and tear. Hard anodising can even be seen in more mundane settings, such as bakeware, as discussed in this article from The Independent.
Colour anodising
Items that require both a durable and decorative finish could benefit from colour anodising. This effective process incorporates dyes into the process of anodising. The colour permeates any pores in the metal, sealing in colour and leading to a hard-wearing finish that cannot be scratched off. The colour available and how durable it is tends to be directly related to the cost.
Anodising is a versatile, reliable process, which can improve a wide range of products.