Hard Anodising is done in the same solution as ordinary sulphuric anodising but chilled down to a much lower temperatures, typically around minus 5 to 0 degrees Celsius.
This low temperature as well as the much higher voltages, causes the anodic film produced to be much denser and thicker than that on sulphuric anodising.
Typically, the thickness on hard anodised parts is around 40 to 60 microns and is naturally a dark grey in colour. This coating is extremely hard and will also withstand very high voltages without breaking down so is very good for electrical insulation and corrosion resistance purposes.
Because of hard anodisings naturally dark colour, it can only be dyed a darker colour than it already is. Think of it as using a highlighter pen over a dark shaded area on a piece of paper.
Components requiring hard anodising must be made from 6082 or 7075 type alloys.
Pricing - Hard Anodising
Hard anodising is loosely based on a pricing structure of around £20 to £25 per sq/ft total surface area per component.
This can vary on parts which are more complicated to jig or don't allow so many parts to be fitted to each jig as some other parts might.
Masking and dying requirements will also have an effect on the costing.
The minimum charge for hard anodising is currently £80.00.