If this list of Frequently Asked Questions will not answer your questions, please feel free to contact us on 01623 627700 or by email.

What is anodizing?

Anodizing is an electrochemical process that forms a protective coating of aluminium oxide on the surface of the aluminium. Raw aluminium left exposed will corrode and oxidise and become unsightly. Anodizing protects the raw aluminium, transforming it into a hard and durable weather resistant surface.

How does the process work?

Initially components to be anodized are degreased and then etched in an alkaline solution. The components are suspended on jigs into a bath of sulphuric acid which has lead sheets around the perimeter forming the cathodes. A DC current is passed through the aluminium components (which act as the anode) and during the process the surface of the aluminium is converted to form aluminium oxide. The level of current passed through, the solution temperature and the length of time determine the thickness and hardness of the film.

What is the difference between Standard and Hard Anodizing?

Standard Anodizing requires an acid solution temperature of typically 30 degrees C whilst Hard Anodizing requires a solution temperature of 0 degrees C and utilises greater voltages. Hard Anodized surfaces can be up to 8 times thicker and 10 times harder than Standard Anodizing.

What effect does anodizing have on the dimensions of the component?

During the preparation the components are etched in a caustic solution to ensure that a good key is formed on the metal surface. This process 'eats' away some of the metal but this is replaced during anodizing and an additional thickness is added which can be specified. Typical film thickness' produced are 5-15 microns for Standard Anodizing and 25-70 microns for Hard Anodizing. The growth in size of the component will be approximate 50% of the film thickness.

How durable are dyed anodized components?

Anodized films are chemically bonded to the surface and do not flake or peel. Colours are introduced by dyeing after anodizing which fill the microscopic pores in the anodized surface which are then filled with a sealer that hydrolyses the pores to create a smooth durable surface. The colours produced are long lasting and resistant to ultra violet light degradation. Certain colours are more resistant than others and if components are to be subject to a harsh environment, we will be pleased to advise on the most suitable colours.

Is the grade of aluminium critical to achieve top quality results?

Yes. Generally, the purer grades of aluminium produce better results and components produced from sheet or bar are better than cast items. Whilst there are around 34 different grades of cast aluminium alloys very few are suitable for decorative/coloured anodizing. A number of cast alloys can be Hard Anodized for increased corrosion protection and wear characteristics but the surface appearance would not be considered suitable for decorative purposes. Without definite identification of the grade of alloy it is therefore difficult to predict the resultant finish. We will be pleased to help you with your selection of a suitable alloy.

What information do I need to provide when sending in a job?

The grade of aluminium alloy used is important information, especially if Hard Anodizing is required. Components have to be suspended on jigs and at the contact point a small jig mark will be left on the finished component. This will be more noticeable on Coloured Anodizing. Normally this will be within a bore or an internal surface and therefore any critical bores or surfaces should be identified so that an alternative suspension point can be established. Similarly, when specifying Hard Anodizing, any bores or surfaces where electrical contact will be required or where there is a critical dimension, these should be specified so that these may be masked.

What about the surface finish prior to anodizing?

Obviously this depends on what the component is and if it is a decorative item, but it should be noted that anodizing will not hide any machine marks, scratches or surface blemishes - in fact it has a tendency to highlight them. Consider mirror polishing decorative components if appearance is critical.

Anything else?

Yes - any aluminium component needing anodizing cannot contain any other material such as steel rivets, brass bushes etc. Also assemblies should be split down to basic components to prevent acid entrapment and welded assembles require the use of correct specification rod to avoid colour variations.