It is well known that aluminium and some of its alloys develop a natural oxide film which gives a degree of protection against corrosion. Under many conditions of exposure, particularly damp and humid conditions, this natural protection is inadequate and corrosion occurs.
Aluminium, even when thoroughly cleaned, does not present an ideal surface for painting. Extrusions emerging from the die at about 500oC immediately oxidise on contact with the air. The oxides of the alloying elements (magnesium, silicon, copper, manganese, etc.) swarf and extrusion 'fines' (mechanical linishing can be offered as an additional service), damage caused during handling and organic materials (dirt and oils) must all be removed to ensure adequate paint adhesion.
Metal pre-treatment, fundamentally, has two well-established aims - protection against corrosion and the preparation of a surface to which paint will adhere.
After inspection of the metal for any obvious defects which might affect the quality of the finish, the aluminium extrusions, pressings or sheet are loaded into specially designed baskets. They are then taken, under computer controlled conditions, through an 11-stage immersion process.