Steel wheel e-coating line workflow: Load -> hot water rinse -> pre-degrease -> degrease -> rinse -> rinse -> surface conditioning -> phosphate -> rinse -> rinse -> pure water rinse -> e-coating -> UF1 rinse -> UF2 rinse -> pure water rinse -> drying -> powder coating/liquid coating -> curing -> unload
E-coating is improved process which provides a more uniform substrate for the top-coating process. As the environmental and performance requirement bar was raised, E-coat technologies were there to provide a process to meet industry demands.
E-coating line contains 4 stages:
- electrophoresis – the positive and negative particles movement in charged electric field.
- electrolysis – redox reaction phenomenon on the electrodes.
- electrodeposition – the process of coating film on product surface
- electro-osmosis – the process of moisture discharging from film inside, it will provide a very high resistance dense film.
Steel wheel e-coating line main components include: coating tank, e-coating power supply, oven, ultra filter machine, rinse tank
Coating line is not only setup for automotive wheels but also compatible with other hardware products within allowed sizes such as oil tank, chimney tubes and other car parts.
Understanding the technologies
There are two specific electrocoat processes, anionic and cationic, both of which are commonly used. The anionic process involves placing a positive charge on the part while the paint bath is negatively charged. This process is commonly used in the general metal industry where low cost, color control and ease of operation are the driving forces. Many parts that are in noncorrosive environments are processed through this type of system.
The cationic E-coat process is used to provide a more corrosion-resistant film. The part to be coated has a negative charge; the paint bath, a positive charge.
The process involves driving charged particles out of a water suspension to a part capable of conducting a charge. It is a rather simple electrical process of positive and negative charges being attracted to each other while like charges repel.
The electrical charge seeks out the path of least resistance and coats the exterior portions of the part or parts nearest to the counter electrode. As the process continues, the charged particles resume their search for uncoated portions of the part and begin coating areas that are not as easily reached. This ability to coat hard-to-reach areas of the part is known as the paint’s throw power.
During the deposition process, the part’s electrical resistance begins to build as the E-coat film is deposited, driving the coating process to another portion of the part or another part on the rack. The film build is controlled by the amount of voltage applied and is self-limiting. After a short dwell time, all conductive areas of the part have been coated.
There are many process advantages of electrocoating, including total coverage of densely loaded racks and complex parts with a uniform film build; transfer efficiency routinely in the 95 to 99% range; highly automated systems with high throughput and low operating costs; environmental compliance for air and wastewater emissions; high line speeds; heavy-metal-free formulas; and workplace safety.
E-coat formulas are typically based on either epoxy or acrylic chemistry. Epoxy chemistry is used in environments where corrosion protection is paramount. It inherently provides superior results in salt-spray and cycle-corrosion testing.
Acrylic systems are used in applications requiring outstanding durability or color control. Recently, coating requirements have focused on providing both superior corrosion protection and durability. These hybrid systems are finding more use in the industrial market as coating requirements change.