The generation of powder particles in powder spraying and how to reduce the appearance of particles

2021-12-07 by No Comments

At present, anodizing, electrophoresis coating and powder spraying are one of the three main body surface treatment methods of aluminum profiles. Each method has its own advantages and respectively occupies a considerable market share. Powder spraying uses powder coatings. 

Electrostatic spraying is used in the process. Using friction, the powder particles carry a positive charge when they are sprayed under the action of accelerated wind. Contact with negatively charged profiles produces electrostatic adsorption, and then passes through high temperature. The curing treatment enhances the adsorption strength of the paint and effectively prevents the paint film from falling off. However, a common problem that makes powder coating technicians feel headache is the protruding particles-particles on the surface of the powder coating coating. The particles seriously affect the decorativeness of the surface coating of the aluminum profile. Let’s take a look at the generation of powder particles and how to reduce the appearance of particles.

First, the material of the coated aluminum profile

When spraying, the surface of the painted workpiece should be polished as smooth and flat as possible, and the surface has no oxide scale and micropores. If possible, it can be pre-baked, which can also effectively reduce the formation of particles.

Second, the surface treatment of the workpiece

Generally, powder-coated aluminum workpieces need to go through the following process: racking-degreasing-washing-chromizing -…-curing-unloading; in the surface treatment process, impurities such as chromated residues may adhere to the workpiece. This results in the presence of particles after film formation.

The generation of powder particles in powder spraying and how to reduce the appearance of particles

Third, painting work environment

The production environment around the powder spraying room will directly affect the surface quality of the coating film. For the electrostatic coating of corona discharge, some dust and particles in the environment are brought into the powder coating powder room, and the charged impurities are caused by static electricity. It is adsorbed on the surface of the coating and becomes particles on the surface of the coating film when the powder is melted and leveled. A clean production environment has a good effect on product quality. The environment around the production workshop must be tidy and clean of mud and sand; the doors and windows of the workshop should be opened as little as possible, and exhaust fans can be installed to solve the ventilation problem; personnel entering the workshop should wear work clothes and shoes; do a good job of hygiene in the workshop; Often use a semi-damp cloth to wipe the production equipment or use a vacuum cleaner to remove dust from all parts of the workshop.

Fourth, the thickness control of the coating film

For the spraying technicians, they all understand that if the coating film is too thin, in addition to particles, poor leveling, serious orange peel, and poor hiding power of light-colored varieties will occur. At the same time, the coating film is acid and alkali resistant. , Poor salt and water resistance. Appropriately increasing the thickness of the coating film can effectively reduce the formation of particles. The coating film should not be too thick. Generally, too thick will affect the size of the coated workpiece, and the performance of impact resistance, flexibility, and adhesion will decrease. It is normal for the thickness to be controlled at 40-120um. We can control the film thickness in the following ways: a, the number and arrangement of the powder in the powder room; b, the powder output and air pressure (powder output, atomization, fluidization parameters); c, the operating speed of the conveyor chain, That is, the chain speed; d. The suspension mode and arrangement of the coated workpiece.

Fifth, the treatment of recycled powder

For most companies, the recovered powder generally has the following types of processing: 1. In the automatic powder coating system recovered by the conveyor belt, the sprayed powder is automatically recovered and sieved, and then mixed with the new powder coating to continue to be used for the powder. , The quality of this kind of recovered powder is relatively stable, and it is not easy to produce particles; 2. In the two-pole recovery system of cyclone separator and bag filter, when the powder recovered in the first stage of the cyclone separator is sieved through a vibrating screen and circulates with the powder supply system, Basically, it has little effect on painting, and it is not easy to produce particles; 3. For the powder recovered by hand-sprayed painting system, because environmental dust and impurities are easy to bring into the recovered powder, it must pass through a vibrating sieve of 120 mesh or more after recovery. . The powder is recycled and reused. The powder adsorbed on the surface of the profile only accounts for about 1/3 of the total powder output. There are more powders scattered in the spray booth. The recycled powder must be mixed with the newly added powder in an appropriate ratio. The effect is compared. Good, so the powder should be recycled and reused in time.

Sixth, the powder coating itself has particles

The particles of powder coatings can basically be divided into mechanical impurities and colloidal particles. The mechanical impurity particles mainly come from the material itself, the production process and equipment wear, and the impurities brought in by the environment during the production process; the colloidal particles mainly come from the resin raw materials used in the extrusion process during the production process. Therefore, it is necessary to strengthen the inspection of raw materials into the factory to prevent this from happening.

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