At present, anodic oxidation, electrophoretic coating and powder coating are one of the three main surface treatment methods for aluminum profiles, each of which has its own advantages and occupies a considerable market share respectively. Powder spraying uses powder coating, and the process adopts electrostatic spraying, using the friction gun to make the powder particles carry a positive charge when sprayed out under the effect of accelerating wind, which produces electrostatic adsorption phenomenon in contact with the negatively charged profile, and then after high temperature curing treatment, which enhances the adsorption strength of the coating and effectively prevents the paint film from falling off.
However, a common problem that makes the powder coating technicians feel headache is the protruding particles-particles on the surface of powder coating. The particles seriously affect the decorative properties of the aluminum surface coating. About powder particle generation and how to reduce the appearance of particles, let’s learn together.
First: the material of the painted aluminum profile
When spraying, the surface of the painted workpiece should be polished smooth and flat as much as possible, and there is no oxide and microscopic pores on the surface, and if there are conditions, it can also be pre-baked, which can also effectively reduce the formation of particles.
Second: workpiece surface treatment
General powder coating aluminum workpiece needs to go through the following process: shelf – degreasing – washing – chroming – …… – curing – unloading; where impurities such as chroming residue in the surface treatment process may be attached to the workpiece, thus causing the presence of particles after film formation.
Third: the painting working environment
The production environment around the powder coating room will directly affect the surface quality of the coating film, for the corona discharge of the electrostatic spray gun coating, some dust and particulate matter in the environment is brought into the powder coating powder room, through the electrostatic effect of charged impurities adsorbed on the surface of the coating, in the powder melt flow level, become the surface particles of the coating film. A neat production environment has a good effect on product quality. The environment around the production workshop must be neat and clean, remove the mud and sand; workshop doors and windows should be opened as little as possible, exhaust fans can be installed to solve the ventilation problem; personnel entering the workshop should change into work clothes and shoes; improve the hygiene work in the workshop; often use semi-wet cloth to wipe the production equipment or use vacuum cleaners to remove the dust in various parts of the workshop.
Fourth: the thickness control of the coating film
For the spraying technicians, understand that if the coating film is too thin, in addition to particles, but also produce poor leveling, orange peel serious, and light-colored varieties of poor coverage, while the coating film of acid resistance, alkali resistance, salt resistance, water resistance and other poor performance. Properly increase the thickness of the coating film, can effectively reduce the formation of particles, the coating film should not be too thick, generally too thick then will affect the size of the coated workpiece, in impact resistance, flexibility, adhesion and other performance decline, general coating thickness control in 40 ~ 120um for normal. We can control the film thickness by the following ways: a, the number and arrangement of the guns in the powder room; b, the amount of powder and air pressure of the gun (powder, atomization, fluidization parameters); c, the running speed of the conveyor chain, i.e., chain speed; d, the way the coated workpiece is hung and arranged.
Fifth: the treatment of recycled powder
For most of the enterprises, the recovered powder generally has the following kinds of treatment: 1. In the automatic powder coating system with conveyor belt recovery, the powder is automatically recovered and sieved, and then mixed with new powder coating to continue to supply the powder gun with such recovered powder quality is relatively stable and not easy to produce particles; 2. Vibrating screen after sieving and supplying powder system circulation, the basic impact on the coating is not much, also not easy to produce particles; 3, for manual spraying of the coating system recovery of powder, because the environment of dust and impurities easily brought into the recovery of powder, after recovery must go through more than 120 mesh vibrating screen. Powder recycling and reuse, the powder adsorbed on the surface of the profile only accounts for about 1/3 of all the powder coming out of the spray gun, more powder scattered in the spray booth, the recycled powder must be mixed with the new added powder in an appropriate proportion, the effect is better, so the powder should be recycled and reused in time.
Sixth: powder coating itself has particles
The particles of powder coating can basically be divided into mechanical impurities, gelling particles. Mechanical impurities particles mainly come from the material itself, the production process and equipment wear and tear, the production process environment brought in the debris; gelling particles are mainly from the production process of extrusion process used in the resin raw materials. Therefore, we should strengthen the inspection of raw materials into the factory to prevent such a situation.