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Cleaning
Metals such as steel and stainless steel are some of the substrates selected for powder coating. The metal unit is then cleaned by either chemical cleaning or abrasive blasting that frees the substrate of any dirt, rust, oils and mill scale that could cause finish defects.
Pretreatment
A worker applies either zinc or phosphate-based conversion coating or a pretreatment chemical to the substrate to add protection and to help the substrate surface adhere to the powder. He then rinses the substrate repeatedly and allows it to dry completely.
Masking
The worker uses high-temperature tape, steel fixtures, plugs and caps to mask the areas where the coating will not be applied.These areas may include threaded areas that would not fit properly if coated, bearing surfaces and any spots that must be kept bare for electrical-grounding contact. Masking tapes include high-temperature polyester film and glass cloth with silicone adhesive that will not leave a residue.
Racking
The product to be coated is placed securely on a rack that allows the unit to remain stable while the coating is applied. Since the application will involve electrostatic processing, the contact points on the rack must stay clean to ensure good grounding.
Application
The most common application of powder coating is done with an electrostatic gun. The spray gun shoots an electrostatic charge into the powder and guides the powder to the grounded work piece.
Curing
After the piece is coated, it is taken to either a convection cure oven, where it is heated from 375 to 400 degrees Fahrenheit for 15 to 20 minutes, or to an infrared oven, where light energy is transmitted to the surface of the part, causing the powder to adhere in two to eight minutes.
Cooling
After curing, the piece is left to cool completely before the transfer film is applied. Cooling time depends on the type of oven used for curing. Since infrared heat does not penetrate the product itself, the product from an infrared oven cools almost immediately. The work piece from the convection oven will take a little longer, depending on the size of the piece.
Transferring the Film
To create the wood-grain effect, the product is wrapped tightly with transfer film that has been pre-printed with cellulose resin and organic photosensitive pigments. This seal must be air-tight. Vacuum suction removes any remaining air and forces the film into contact with the surface of the product.
Final Curing
The item is again taken to a curing oven and heated until the ink pigment in the film turns from its solid stage into gas and back into a solid, causing the ink to permeate into the paint layer of the substrate. The product is quickly taken from the oven and air is injected into the paper to separate it from the substrate. Hence, the result is a three-dimensional surface with a printed, one-dimensional wood-grain image.