Polymerization

After the powder paint is applied, the product is sent to the coating formation stage. It includes the melting of the lacquer layer, the subsequent formation of the coating film, its hardening and cooling. Reflow and polymerization take place in a special oven. There are many types of polymerization chambers, the design of which may vary depending on the conditions and characteristics of production in a particular company. The oven looks like a drying cabinet with electronic "filling". The control unit allows you to control the temperature regime of the oven and the dyeing time, as well as setting the timer so that the oven is automatically turned off when the process is complete. Energy sources for polymerization ovens can be electricity, natural gas, and even heating oil.
The ovens are divided into continuous and dead ends, horizontal and vertical, single and multiple passes. The speed at which the temperature rises plays an important role in cul-de-sac stoves. This requirement is best met by means of convection ovens. Conductive dielectric coating booths evenly distribute powder paint over the surface of the part. However, if used improperly, they can build up electrical charges and pose a hazard.
Melting and polymerizing takes place at a temperature of 150 to 220 ° C for 15 to 30 minutes, after which the powder paint forms a film (polymerizes). The main requirement for polymerization chambers is to maintain a constant set temperature (a temperature distribution of at least 5 ° C is allowed in different parts of the oven) for uniform heating of the product.
When the product is heated in the oven with a powder coating layer, the coating particles melt, become viscous and fuse into a continuous film, while the air in the powder coating layer is displaced. Some of the air can still remain in the film and form pores that degrade the quality of the coating. To avoid the appearance of pores, painting should be carried out at a temperature higher than the melting point of the paint, and the coating should be applied in a thin layer.
If the product is heated further, the paint penetrates deeply into the surface and then hardens. At this stage, a coating with the given properties of structure, appearance, strength, protective properties, etc. is formed.
When painting large metal parts, the surface temperature rises much more slowly than with thin-walled products, so the coating does not have time to fully cure, which decreases its strength and adhesion. In this case the part is preheated or the curing time is extended.
Curing is recommended at lower temperatures and over a longer period of time. This mode reduces the likelihood of defects and improves the mechanical properties of the coating.
The time to reach the required temperature on the surface of the product is influenced by the mass of the product and the properties of the material from which the part is made.
After hardening, the surface is cooled by extending the conveyor chain. Special cooling chambers, which can be part of the hardening furnace, are also used for this.
The appropriate mode for the formation of the coating must be selected taking into account the type of powder coatings, the characteristics of the product to be painted, the type of oven, etc. It should be noted that the temperature plays a crucial role in powder coating, especially when coating heat-resistant plastics or wood products.
At the end of the polymerization, the product is cooled in the air. After the product has cooled, the coating is ready.