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What exactly is e-coating and how does it function?
What precisely is electrophoretic painting?
Electrophoretic painting (also known as electrophoretic coating or electrophoretic deposition) is a wet paint surface treatment technology that uses an electric current to attract paint particles suspended in a bath to the metal surface of a microchannel heat exchanger - aluminium.
Prior to applying paint, the heat exchanger is cleaned of oil and impurities during the pre-treatment procedure. The pretreatment process is required to optimise the electrophoretic coating's performance, provide a high quality surface finish, and keep the paint bath clean and free of dangerous pollutants. Because it gives the best corrosion resistance and paint adhesion, zinc phosphate is the favoured pretreatment choice.
Baths for electrophoresis
Electrophoresis is used to electrostatically bond the paint to the aluminium surface. As the process is self-limiting, it develops a uniform paint film and slows down when the applied paint electrically insulates the part from the bath.
The system is cathodic: which means that the heat exchanger is negatively charged in order to attract positively charged paint particles. The paint solids are first applied to the surfaces nearest to the counter electrode, and when these areas become insulated from the current, the solids are applied further out on the bare aluminium surface, ensuring total coverage (homogenising capability phenomenon).
In anodic electrodeposition coating, the positively charged anode is the component to be painted, and minute amounts of metal ions can migrate from the item into the paint layer, contaminating it and decreasing the coating's corrosion protection. Anodized coatings are less expensive and allow for lower cure temperatures.
Post-rinsing is frequently required two or three times to remove any leftover paint build-up and other loose particles. The final post-rinse stage, which is formed of deionized water, aids in the appearance of the electrophoretic paint.
Curing in an oven
Following rinsing, the electroplated heat exchanger is placed in an oven to crosslink and cure the paint film, making it hard and robust for optimal performance. The final product's quality is heavily reliant on the time spent in the oven and the application temperature (which can range from 80°C to 240°C depending on the paint technology used).
Electrophoresis can be performed using a variety of coating materials. One of these is epoxy, which provides good corrosion protection as well as resistance to salt and moisture. Epoxy electrophoresis paints, on the other hand, are less resistant to UV radiation and hence require a UV resistant topcoat to protect the epoxy primer.
Electrophoretic paints are not overly expensive when compared to other types of paint; nonetheless, electroplating lines are expensive to create and maintain, increasing the cost of the end product. Electrocoating lines are designed to run constantly with a single type of paint product. Changes in paint materials and line clean-ups are extremely costly and time-consuming, making colour changes in the electro-coated product nearly impossible.
In conclusion, electrophoresis provides significant benefits for all-aluminum microchannel heat exchangers, including
Excellent corrosion resistance.
Environmentally friendly: the electrophoretic paint process emits almost no harmful air pollutants or volatile organic compounds and complies with RoHS, OSHA, and the EPA.
Where is electrophoresis required?
Heat exchangers are used in corrosive categories C5-I (industrial areas with high humidity and corrosive environments, aluminium mass loss between 5 and 10 g/m² after one year of exposure) and C5-M (coastal areas) according to ISO 12944-5:2019 and in area C4 (e.g. industrial areas and coastal areas with moderate salinity, aluminium mass loss above 10 g/m²), high salinity offshore (facilities, aluminium mass loss loss of 2 to 5 g/m²).
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