Hard anodising is a high-tech, extreme engineering finish. It is extensively used in the aerospace industry on components which are subject to extreme heat and abrasion.
It also finds application in a wide range of other engineering applications for components which require a hard wearing resistant surface such as pistons, cylinders, hydraulic gear and working parts on machinery.
Another application is in the coating for the production of flame and chemically resistant surfaces. Hard anodising produces aluminium that will show a good heat resistance; a hard anodic oxide coating of 75µm will withstand short exposures to temperatures in excess of 2000 C.
Hard anodising produces a much darker coating than the normal clear anodising process. The exact shade depends upon the thickness of the coating which is usually between 25 and 75 µm and the process time which can be up 240 minutes.
Hard anodising produces darker coatings than the normal 'decorative' process, but the exact shade depends upon coating thickness and anodising conditions (which we can control), as well as alloy, thermal history, degree of hot or cold work, etc, over which we have no control. We cannot, therefore, colour match except between components from the same batch of metal. Some specifications allow the anodiser wide tolerances in his process, which must be closed down if matching is to be achieved. Matching must therefore be covered at the time of order.