Typically a sulphuric acid anodised coating is suitable for most aluminium components, however there are certain situations in which a harder coating is required.
Parts Under Heavy Sliding or Abrasive Wear
A surface layer of up to 70 microns in thickness can be achieved, with corresponding hardness, thus offering excellent wear resistance, for example on parts that slide on other parts, such as on valve bodies, pistons, and sliding rails. Other applications where hard anodizing is preferred to normal anodizing are, for example, the wear surfaces of articles such as wiping sticks, road marking machines and spreaders.
Components That Need Electrical Insulation Too
The thick layer of oxide on the surface of a component can also act as an excellent electrical insulator, thus allowing aluminium components within housings, actuators or other components to be processed with a single process to give them a surface that is both hard and insulating.
If you are looking for Hard Anodising, see https://www.poeton.co.uk/surface-treatments/anodising/hard-anodising.
Parts Exposed to Aggressive Chemicals
The dense oxide film, produced by the hard anodising process, provides excellent corrosion resistance, particularly when parts are exposed to acids, alkalis and other industrial cleaning agents. Components such as those used in the food processing industry, chemical handling and associated plant, as well as hydraulic components which come into contact with fluids, can all benefit from the improved resistance offered by the harder coating.
Where Dimensional Growth Must Be Predictable
In terms of dimension, a typical layer of hard anodising grows roughly half into the surface of the metal and half out from it. This can be designed into the metal prior to anodising and therefore accounted for at the machining stage. Hard Anodising Ltd are members of the Surface Engineering Association and are members of SEA, listed in the SEA member directory, who expect their members to supply confirmed thickness information prior to anodising.
High-Cycle or Temperature-Cycling Environments
As coating is likely to be affected by a part undergoing high cycle numbers or going through periods of high temperature and subsequent reduction in temperature, a coating that is integral to the part and that will expand and reduce in dimension with the metal is preferred to a coating that is applied on top of the part and will ‘peel off’ under such stress.
The benefits of hard anodising can far outweigh the cost of additional hard anodising of aluminium parts that wear, are exposed to chemicals or require very precise dimensions when specified from the design stage as opposed to retrofitting later.
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