Before Aluminium can be powder coated it has to undergo a chemical process to strip the oxide layer from the surface . Baskets which have been received from the extrusion plant is submerged into the required chemical baths to complete the etching process.
ETCHING requires a chemical reagent to attack and roughen the surface of the metal. Alkaline and acid etchants can be used. The former are more common because they are cheaper and easier to handle. A solution of caustic soda in water is most common. Since etching lowers the resistance to corrosion by removing the natural protective oxide film formed on aluminium, another process is required to restore corrosion resistance. Chemical dipping removes metal in a controlled manner by selective chemical etching in either acid or alkaline
solutions to produce an overall reduction in metal thickness. The chemical used to create the static state, which is necessary when applying the powder, is called Chromate. As part of the chemical preparation of the aluminium before powder coating it is submerged into this Chromate solution and rinsed.
To apply powder it is necessary to hang each extrusion onto a jig which is rolled on an overhead conveyor. A small hole is drilled on both ends of each length and then tied to the jig. The jigs are moved to the spray booth where a powder spray gun is set to produce a cloud of powder particles with a strong electrostatic charge. The charged particles are attracted through the electrostatic field to the face of the aluminium and to the sides and back along the lines of force in the electrostatic field. After the powder has been applied, the extrusions are placed in the oven to cure.
The powder we use is supplied by Akzo Nobel. This polyester powder is available in a vast range of different colours with either a gloss, matt or satin finish. The most common colours requested, however, are White, Bronze, Black and Charcoal Grey.
The beams are rolled into a pre-