Powder coating process
During powder coating, a negatively charged paint powder is sprayed under pressure (compressed air) onto an electrostatically grounded product. This in effect makes sure that the paint powder sticks to the product, after which the whole goes into the oven. At a temperature between 130 – 200 ° C, the powder behaves like a conventional paint, flows and forms a perfect layer around the treatment surface of the product.
Most powder coatings are 2-9 component coatings, the components only give the desired end result after 15 to 20 minutes at 150-200 ° C. This process is also called stoving. After cooling, the product is ready to use or ready for further processing. The maximum hardness of the coating or mechanical load is immediately achieved.
Before this process can take place, the product must first be properly pre-treated.
First the product is cleaned. This removes residues from, such as, sand, oil or fats, rust and welding slag. This is essential for the success of the rest of the powder coating process. Various mechanical and / or chemical methods are used for this.
Blasting is used for the mechanical removal of contamination from the surface. Kalfsvel Coating shines to a fine grain of corundum (aluminium oxide). The correct anchor pattern is now created for a good adhesion of the coating.
By applying the correct grain size and pressure to each material, the aesthetic part can also be guaranteed after powder coating. If a too coarse grain is used for blasting, the impact is so large that you can see it in the coating. If the grain is too small, the coating does not have the maximum adhesion to the surface (service life). The impact is greater if you increase the pressure during blasting and our Corundum breaks at a pressure higher than 6 bar. This in effect results in a higher roughness impact, with the result that the coating shows those contours. The selected grain size and work pressure are in direct relationship with each other, which is why this balance must be strictly maintained.
Phosphates or chromates are used in the chemical removal of surface contamination. The product is (often in several steps) bathed or the agent is sprayed onto the product. This chemical cleaning ensures that the powder adheres much better to the material. This treatment takes place in continuous ovens at other companies, but it is environmentally harmful.
The powder is sprayed onto the metal product with an electrostatic spray gun. It receives a negative electrical charge from the spray gun. The powder is sprayed on the product. Because the product is grounded, the powder is drawn to the workpiece by the electrostatic charge.
Another method is the so-called “tribo-charging”, where the powder is charged by passing it along the wall of a Teflon tube. The powder is positively charged by this frictional tension. These charged powder particles then attach to the grounded substrate. This method is not applied by Kalfsvel Coating.
Most thermosetting powders are cured at a temperature of 180 ° C for 10-15 minutes. A chemical reaction then develops, resulting in a polymer with a higher molecular weight density. This process is called crosslinking.