Anodising is an excellent way of protecting aluminium components from corrosion and deterioration. A strong, durable coating, it is formed by submerging parts in an acid solution to grow an aluminium oxide layer on the surface, and is an ideal finish for engineering, manufacturing and defence applications.
A thicker, tougher form of anodising – hard anodising – can also be applied to your aluminium parts for added wear resistance.
With both these anodising options providing durable finish options to protect your parts, what is the difference between the two – and which is suitable for your job?
Hard anodising is a much thicker aluminium oxide coating. While standard anodising is typically around 15-25 microns thick, hard anodising can range from 30 to 100 microns. This thick coating is extremely scratch resistant and is suitable for applications with high levels of abrasion or wear, such as high-speed machine parts and cookware which is frequently scraped by utensils. Standard anodising may be a better option if your application requires a thinner coating to preserve mobility or functionality of moving parts, or where parts need to be assembled tightly together.
The biggest difference between the standard and hard anodising process is the temperature at which the parts are submerged in acid to create the aluminium oxide layer. The acid used in standard anodising is typically at ambient temperature, while hard anodising involves submerging the components in an acid bath lowered to between -2 and 0°C. This low temperature solution causes a thicker aluminium oxide growth into and out of the components for an extra durable surface layer.
Standard anodising is a porous finish – and these pores require sealing to make the coating effective. Seals include nickel/cold seals and mid-temperature seals – although other materials can be used to seal anodising to give it job-specific properties, such as a Teflon seal for a frictionless finish. The pores in standard anodising can also be filled with dye to change the colour and add a decorative element to the finished product.
Hard anodising, however, creates an aluminium oxide coating with narrower pores, which does not require sealing to be effective (although seals can be applied for extra corrosion resistance in specific applications).
Depending on the alloy used, anodising colours will vary slightly. However, standard anodising is typically a light silvery grey, while hard anodising produces a dark charcoal grey colour. Both standard and hard anodising is also available in black to suit the aesthetic requirements of a project.
Anodising functions both as an attractive and functional finish. Its metallic appearance makes it popular for architectural applications such as façade panels and window frames. It also makes a protective and decorative metallic finish for computer casings and automotive bodywork. Because of its non-stick properties, it is a suitable coating for commercial cookware and food processing applications, while it gives increased corrosion and wear resistance to machine parts, increasing their lifespan.
Because hard anodising is a thicker, less porous finish and produces a darker grey colour, it is not typically used as a decorative finish. However, its high durability and wear resistance make it excellent for hardwearing and extreme applications, such as aircraft parts, high speed machine components, defence equipment and even parts for firefighting equipment.
Click to find out more about our standard and hard anodising services here, or fill out our enquiry form to speak to one of our helpful staff.
The Benefits of Hard Anodising
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