CED Coating

The dip tank contains a water-soluble binder that, due to the electrical circuit, adheres to the surface of the item being coated and forms a continuous coating film.

Coating is applied in immersion tanks equipped with anodes, in which the coating material is present in a water-diluted form. The workpieces to be coated are electrically connected to the negative terminal of a rectifier and immersed in the tanks. At a voltage of up to 400 volts, a layer of paint forms on the workpiece surface within a few minutes. Since the current adjusts to the painting system due to ohmic resistance, the desired paint film thickness can be controlled by adjusting the current. An acid forms at the anodes. To maintain a constant pH level in the immersion tank, this acid is drained from the tank via special cells. While in industrial CED coating, thinner layers of around 15–30 µm typically serve as a primer, layers ranging from 35 to 50 µm are known as KTL thick coatings, which are not subsequently overcoated.

During the process, circulation pumps keep the bath fluid constantly in motion. This circuit includes both filters and coolers. These remove the unwanted heat from the immersion fluid, which is released by the ohmic resistance in the tank. After coating, the components are rinsed with demineralized water. The excess coating flows back into the immersion tank along with the rinse water. During the coating process, the coating particles coagulate on the component surface to form a web-like film composed of countless tiny beads. In the final step of the process, the microscopic spheres are melted in an oven at 180–220°C. This causes them to cross-link into a hard, uniform layer.

In general, cathodic dip coating is suitable for a wide range of materials.

• Steel and thin-gauge steel sheets
• Components made of galvanized sheet metal
• Steel and gray cast iron
• Aluminum sheets and extruded aluminum profiles
• Aluminum and zinc die-cast alloys
• Hybrid construction (e.g., steel with riveted aluminum parts)

Depending on the material and paint substrate, special cleaning steps as well as either activation or passivation are required to prepare components for CED coatings. Due to the wide variety of materials and alloys, the necessity and type of pretreatment must be assessed on a case-by-case basis. Once the parameters are set, the components typically run through the processes in the systems as standard.

In the automotive industry, as well as in commercial vehicle and agricultural machinery manufacturing, CED-coated parts meet the high requirements for corrosion protection, scratch and impact resistance, and solvent resistance. CED-treated components are also used in other sectors, such as mechanical and plant engineering, for coating pipes, in precision engineering, and in fitness, gardening, and household appliances, thanks to the fine, uniform finish of the coating. In addition, the CED coating often serves as an effective pretreatment or primer for other coating processes, such as powder coating or liquid painting.