Process in industrial powder coating
The powder coating process is divided into the steps of pre-treatment of the workpiece, application of the powder coating and drying (curing). For large quantities or in series production, the use of automatic production lines is suitable - with varying degrees of automation depending on requirements. For small quantities, manual coating (e.g. PEM-X1 CG Corona cup gun) is suitable. For automatic production lines, all processes must be coordinated to achieve the desired production output. Often measured with coated area per hour or hangers per hour. Our WAGNER specialists provide profitable support with their knowledge as early as the planning discussions.
Surface coating step by step
- Pre-treatment: The condition of the surface is decisive for the quality of the coating. The aim of pre-treatment is a clean and grease-free workpiece to which the coating layer adheres well. Depending on the workpiece, sandblasting or chemical preparation is necessary. Here, sandblasting and flushing work with grease-dissolving agents. If high corrosion resistance is required, a basic wet chemical corrosion protection is applied before powder coating.
- Application: The prerequisite for powder coating is an electrically conductive substrate. Therefore, metals are ideally suited. However, wood can also be powder coated, as the moisture in the wood creates sufficient conductivity for the process. If plastics are to be powder coated, they must first be made conductive in the surface by a conductive coating. Compared to direct liquid coating, this is often uneconomical. During coating, the workpiece is electrically grounded and the powder is charged. There are two different processes for charging. With Corona charging, the powder is actively charged by a high-voltage cascade built into the powder gun. In the Tribo process, this takes place through the friction of the powder coating on friction bodies in the gun. Today, Corona charging is predominantly used. Adjustment of the charge to the coating and the ambient conditions is very flexible. For example, for thick or thin layers, in relation to the temperature and humidity conditions during processing, structural effects, gloss effects, abrasion resistance or sealing behavior of the finished coating layer. Tribo charging is used when the requirement profile is a very smooth surface or for workpieces with large and narrow recesses. Basically, both processes are used as manual or automatic powder coating.
- Cross-linking and drying (curing): At the end of powder application, the coating layer is still in powder form. Since powder is essentially a composite of plastic and color pigments, it melts when heated to temperatures of 160 to 200 degrees Celsius. Curing takes place through the hardeners contained in the composite. In technical jargon, this is referred to as curing. There are also powders that melt at lower temperatures, e.g. at 130-140 degrees Celsius. These are referred to as low-temperature powders. These powders are very sensitive to higher ambient temperatures and must be cooled during the entire process chain. This means also during production, transport and storage, e.g. at 25 degrees Celsius. The decisive factor here is the benefit, i.e. the cost-effectiveness of the energy savings during curing versus the additional costs for the required cold chain.n gegenüber den Mehrkosten für die erforderliche Kühlkette.
