In the EPS (electrostatic powder spraying) process, the powder is electrostatically charged by an electrical field of high field strength on the spray nozzle. Depending on the spraying system, this involves either direct charging, which occurs in direct contact with the electrode, or ionization charging, in which the powder particles are charged through accretion of free air ions. In this case, the electrode, as the corona point, generates the required air ions. The powder particles are transported along the electrical field lines to the grounded workpiece.
The parts to be coated should be preheated to anywhere from 400 to 420 °C. Before cooling, the parts should be heated in an oven until the coating is evenly melted on them. The degree of crystallinity can be set through the cooling process. Water and sudden cooling result in amorphous and therefore transparent coatings. The crystallinity of amorphous layers can be increased by conditioning the coating. This is usually done at 200 °C in a circulating air oven. The amount of time required depends on the mass of the coated parts.
Concerning components with a large thermal mass, slow cooling rates can result in cracks in the coating. In these cases the suitable cooling rates should be determined empirically. Chilling in water can lead to thermal shock and should be avoided.
A comprehensive table with details concerning correction of defects during application of VESTAKEEP
PEEK powders is given in the brochure "VESTAKEEP
PEEK – Polyether Ether Ketone Powders".