Sulphuric (soft) anodising
We have 20+ years of experience of sulphuric anodising to a wide range of customer requirements products used in automotive, medical, high precision and architectural sectors.
What is Sulphuric Anodising?
Sulphuric anodising, sulphuric acid anodising or soft anodising is an electrolytic finishing treatment for aluminium that provides excellent protection and corrosive resistance to the part. The process leaves a clear finish on the part that when sealed provides an even more durability and extended functionality. The process produces a thin layer of aluminium oxide under conditions that can be controlled and the thickness measured using XRF equipment. Although used for a variety of requirements sulphuric anodising is typically used for decorative finishes where a level of resistance to corrosion is needed.
Sulphuric acid anodising or soft anodising results in an anodised coating of typically between 5-25µm, for greater corrosion resistance a thickness closer to the top of the range should be considered. As well as clear anodising we offer a range of different anodising colours, including black. The colour is impacted by the material grade and composition and a coating of at least 15 µm is typically applied.
Materials suitable for sulphuric anodising
We specialise in anodising aluminium materials with 6000 and 7000 grade materials being the most common. The composition of the material requiring anodising can impact significantly the results of the anodising process, the material grade and composition should be checked to ensure it is suitable, typically this is mentioned on the material’s datasheet and carried out at the design phase. Certain grades will not anodise and others may anodise but with a lesser quality finish. Please contact us if you would like to discuss the material.
Sulphuric anodising restrictions
The composition of the material requiring anodising should be checked to ensure it is suitable, certain grades may anodise but the finish is not as good as others. Anodising is typically not suitable for alloys containing more than 4% of copper or more than 7% silicon. It should be noted that sharp edges can be a problem and should have a radius and blind holes receive a lower coating thickness.
The colour is impacted by the material grade, although we have 20+ years of experience of working with coloured dye’s it cannot always be guaranteed exact colours matching between batches, although it should be okay to achieve a consistent colour matching between pre-agreed tolerances. Please contact us to discuss your requirements.
Sulphuric anodising on castings
We can carry out sulphuric acid anodising on castings however the quality of the finish is not of the same standard as with non-casted parts. Please contact us to discuss.
Maximum size criteria
At Milturn Finishing’s new 2,500 sqm site there is capacity to treat both small to large sized components in batch sizes of one to thousands. The new large anodising tanks and heavy duty crane provide the ability to anodise large size components of up to 3 meters x 1 meter x 1m in size. Please contact us to discuss.
Coating Thickness (Sulphuric Anodising)
Sulphuric acid anodising or soft anodising results in an anodised coating of typically between 5-25µm, for greater corrosion resistance a thickness closer to the top of the range should be considered. If the anodising is to be coloured a coating of at least 15 µm is typically applied.
Available standards
Anodising standards followed include BS ISO 7599 as well as other specific standards and requirements from our customers’. Please contact us if you would like to discuss any specific requirements.
Sealing
Cold seal and a drying room is available at Milturn Finishing. The sealing of the anodised aluminium is an important process in achieving the durability and extended the functionality of the anodising. For some applications where additional adhesion is necessary, such as before a painting operation, the anodising can be kept unsealed.
Surface Conditioning
There are a number of surface conditioning processes available at Milturn Finishing’s new site:
Masking
Where sections of a part do not require anodising the areas are masked allowing just the areas requiring finishing to be processed. Our capabilities allow small and fine details to be masked.
Vapour blasting
Vapour blasting also known as vapour honing and aqua blasting, can be provided as a stand-alone operation for a customer’s part or as part of the anodising process. The process uses a combination of air, water and an abrasive media to produce a smooth surface finish and can be provided as a stand-alone operation for a customer’s part or as part of the anodising process. Vapour blasting has the additional benefits of not impacting on a part’s dimensions
Pre-treatment/Etching
The etching process is used to remove any surface contaminants or oxides from a part and prepares the surface in the correct condition for the subsequent anodising stages.
Jigs
An important part of the anodising process is to ensure that the parts are held firmly on jigs to make certain that electrical contact is kept during the anodising process. We have a large range of jigs to keep parts located during the anodising process, if a part requires a jigging setup that is not available a specialist jig can be produced to meet the components requirements. To help prevent jigging marks on decorative surfaces, it may be necessary for additional holes or features to be added to the component design purely for jigging purposes. If there are jigging requirements for the part it is recommended that these are mentioned on the drawing.
Colour Dyes
As well as clear anodising we offer a range of different anodising colours, black and red being the most popular. The colour is impacted by the material grade, although we have 20+ years of experience of working with coloured dye’s it cannot always be guaranteed exact colours matching between batches, although it should be okay to achieve a consistent colour matching between pre-agreed tolerances.
Please contact us to discuss your requirements.
