Aluminium parts that require Powder Coating can be one of the following;
Aluminium Extrusions or tubes.
Aluminium Castings, either sand, gravity or die.
Aluminium Forgings.
Aluminium parts machined from solid.
Aluminium Sheet that is formed or folded.
The key issue with Powder Coating Aluminium is that it has a film of oxide on the surface formed when the metal comes into contact with oxygen.
If not correctly dealt with prior to coating this oxide film can affect the adhesion of the Powder Coated Aluminium parts.
Successful Powder Coating of Aluminium depends on the effectiveness of the cleaning method.
There are many ways to remove this oxide film and improve the adhesion and corrosion resistance of the Powder Coated Aluminium;
Linishing or rubbing down the surface with abrasive paper or Scotchbrite pads.
Chemically Etching the surface to remove the oxide film
Abrasive or Bead Blasting.
Chemical Pre-Treatments.
Anodising or Flash Hard Anodising.
Linishing or rubbing down the surface with an abrasive material.
This process involves an abrasive paper or pad being rubbed all over the surface of the aluminium to be powder coated. It can be carried out by hand or by using a power operated sanding machine or rotary linishing tool . Depending up on the grade of abrasive paper or pad the surface will be roughened and this process will remove some or all of the oxide layer depending upon how long the parts are processed for.
Chemically Etching the surface to remove the oxide film.
Using an Etch process prior to coating can successfully remove the oxide coating prior to powder coating. It usually involves parts being dipped into mild acidic solutions that will dissolve the oxide film and in the process improve the adhesion of the Powder Coating.
Abrasive or Bead Blasting.
This process mechanically removes the oxide film and roughens the surface of the Aluminium, the roughening has the added effect of increasing the surface area by virtue of the peaks and troughs caused by the indentations from the blasting process. There are various types of media that can be used to blast clean aluminium; glass beads, aluminium oxide or fine metal grit
Chemical Pre-Treatments.
This type of treatment involves what are known as conversion coatings. As part of the process the aluminium parts are etched and cleaned first and then dipped into mild acidic solutions that depending on the base chemical can produce Phosphate or Chromate conversion coatings on the surface of the aluminium. The process converts a few microns of the aluminium to a crystalline structure that improves adhesion and corrosion resistance of the powder coating.
Anodising.
Anodising is considered a very effective pre-treatment for aluminium parts. It provides greatly improved resistance to corrosion as well as improving the adhesion of the powder coated surface.
General Cleaning.
Before Powder Coating it is also important to remove all traces of oil or grease from the surface of the parts before coating. The most effective way of achieving this is by Vapour Degreasing. This process involves a heated non-flammable solvent contained within a degreasing tank. The heated material creates a hot vapour that condenses when cold work pieces are placed in the tank. The condensing action cleans the components and when removed from the degreasing tank they are dry and ready for coating.
Wether you need help with your powder coated aluminium garden furniture or powder coating aluminium in general, please don’t hesitate to get in touch or check out our services that we provide.