1. Coating working environment of aluminum extrusion profiles
The surrounding production environment of the powder spraying room will directly affect the surface quality of the coating film. For the coating of the electrostatic spray gun with corona discharge, some dust and particles in the environment are brought into the powder coating powder room, which is charged by electrostatic action. The impurities are adsorbed on the surface of the coating object and become 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 clean, and the aluminum extrusion profiles should be processed to remove sediment and debris; the doors and windows of the workshop should be opened as little as possible, and an exhaust fan can be installed to solve the ventilation problem; personnel entering the workshop should change into work clothes and shoes; Good workshop hygiene; often wipe the production equipment with a semi-moist cloth or use a vacuum cleaner to remove dust from all parts of the workshop.
2. The workpiece surface treatment of aluminum extrusion profiles
Generally, powder coated aluminium flat bar needs to go through the following process: racking - degreasing - washing - chroming - ... - curing - unloading; impurities such as chromed residues during surface treatment may adhere to the workpiece, This results in the presence of particles after film formation.
3. The powder coating of the aluminum extrusion profile itself has particles
The particles of powder coatings can basically be divided into mechanical impurities and gel particles. The mechanical impurity particles are mainly from the material itself, the production process and equipment wear, and the sundries brought in by the environment during the production process; the gelatinized particles are mainly from the resin raw materials used in the extrusion process in the production process. Therefore, it is necessary to strengthen the inspection of raw materials entering the factory to prevent such a situation from happening.
4. The material of the coated aluminum extrusion profile
When spraying, the surface of the coated workpiece should be polished as smooth and flat as possible, without oxide scale and micropores.
5. Thickness control of coating film of aluminum extrusion profiles
For spraying technicians, they all understand that if the coating film is too thin, in addition to particles, there will be poor leveling, severe orange peel, and poor covering power of light-colored varieties. At the same time, the coating film is resistant to acid and alkali. , salt resistance, water resistance and other poor performance.
Appropriately increasing the thickness of the coating film can effectively reduce the formation of particles. The coating film should not be too thick. Generally, if it is too thick, it will affect the size of the coated workpiece, and the performance of impact resistance, flexibility, and adhesion will decline. It is normal to control the thickness at 40~120um.
We can control the film thickness in the following ways:
a. The number and arrangement of spray guns in the powder booth;
b. The powder output and air pressure of the spray gun (powder output, atomization, fluidization parameters);
c. The running speed of the transmission chain, that is, the chain speed;
d. The suspension method and arrangement of the coated workpiece.
6. Treatment of recycled powder of aluminum extrusion profiles
For most enterprises, recycling powder generally has the following treatments:
1. In the automatic powder coating system of conveyor belt recycling, the powder sprayed from rectangular aluminium extrusion processing is automatically recovered and sieved, and then mixed with new powder coating to continue to supply powder spray gun. The quality of this recovered powder is relatively stable , it is not easy to generate particles;
2. In the bipolar recovery system of the cyclone separator and the bag filter, when the powder recovered in the first stage of the cyclone separator is sieved by the vibrating screen and circulated with the powder supply system, it basically has little effect on the coating, and it is not easy to generate particles;
3. For the powder recovered by the manual spray coating system, because the dust and impurities of the environment are easily brought into the recovered powder, it must pass through a vibrating screen with a mesh of 120 or more after recovery. In the recycling and reuse of powder, the powder adsorbed on the surface of aluminum extrusion profiles only accounts for about 1/3 of the powder output of all spray guns, and there are many powder scattered in the spray booth. The recovered powder must be mixed with the newly added powder in an appropriate proportion, whose effect is better, so the powder should be recycled in time.