Powder Coating Services

Powder coating is the finishing technique of applying dry paint to a component

It can be applied either by lowering the component into a fluidised bed of the powder, which may or may not be electrostatically charged, or the powdered paint is electrostatically charged and sprayed onto the component. It is subsequently placed in an oven and the powder particles melt and coalesce to form a continuous film.

There are two main types of powder available to the surface finisher:

• Thermoplastic powders that will re-melt when heated
• Thermosetting powders that will not re-melt upon reheating. In the oven, at the curing temperature, a chemical cross-linking reaction is triggered and it is this which gives the powder coating many of its desirable properties

Preparation

The pre-treatment of the Aluminium allows the paint to stick to the component. The powder coating itself gives the component its colour. The basis of any good coating is the preparation of the aluminium; the vast majority of powder coating failures can be traced back to a lack of a suitable preparation. The preparation treatment can vary depending on materials but generally, for all applications the preparation treatment for Aluminium is as follows:

1. Etch (Acid Etch bath)
   Etch-Clean is employed to remove lightly soiled parts by using acidic cleaners containing phosphoric acid, hydrofluoric acid, glycol solvents and wetting agents. It is a convenient method of preparing aluminum surfaces for chromating or painting. An acid etch cleaned surface will provide a smooth micro-etched surface that is extremely suitable for depositing chromate conversion coating.
2. Cold Water Rinse
   The component is rinsed in cold water. Aluminum parts should be rinsed with water at room temperature. A cold water rinse minimises the chance of inconsistent chromate film formation which could be caused by temperature variations of the metal. A cold water rinse is commonly used after chromating; however a hot water rinse up to 15O°F may be used to speed drying.
3. Chromate
   After rinsing, the aluminium is dipped into a chromate or phosphate solution to form a conversion coating on the aluminium. This film is chemically attached to the aluminium.
4. Cold Water Rinse
5. Demineralised Rinse
   The aluminium is finally rinsed in demineralised water. Some non-chrome, dried in place pre-treatment is beginning to come onto the market; currently these are not recommended for exterior applications. The use of demineralised water reduces the presence of chemical salts on the aluminium surface. These salts have been found to cause filiform corrosion in humid conditions.