Powder coatings
General
Powder coating is a dry process, where the coating materail is applied in solid form as an extremely fine-grained powder. By this coating method, you avoid the use of solvents and any emissions occurring in conjunction therewith.
Process
The fine-grained powder is applied to the work piece uniformly by suitable methods. Subsequently, the applied powder is melted (fused) in a furnace.
Coating procedure
The coating procedure is divided into the procedural steps:
- Preparation of the work piece
- Powder application
- Fusion of the powder
Preparation of the work piece
In order to achieve sufficient adhesion to the substrate, the surface areas to be coated must be prepared by first removing any grease. This is done by organic solvents of by burning out at temperatures of approx. 400°C. In the following step, the work pieces are cleaned and roughened mechanically by sand blasting. The crimping effect of the coating to the work piece substrate can be enhanced by applying an adherence agent (primer).
Powder application
The powder particles are transferred from a collector tank by pressure air, and on their way to the nozzle of the spray gun charged electro-statically. As the particles are charged by a uniform load, they repel each other in their flight and form a uniform mist cloud. The work piece to be coated is grounded, whereby an electro-static field develops between the gun and the work piece. The powder particles are attracted by the work piece, causing them to adhere to it.
Fusion of the powder
In coating technology, a principle difference is made between hot and cold coating. By hot coating the powder is applied to a substrate whose temperature is above the melting temperature of the powder material. Here the powder fuses already during application.
Cold coating is a process where the substrate temperature is lower than the powder melting temperature. Here the fusion process takes place subsequently in the furnace.