It's freezing and raining out, and your kids want to go outside to play. Would you let them go out there without coats?

I wouldn't either.

Consider this situation: it's the same weather, but instead of your kids, it's an expensive piece of fabricated metal. That metal spends a great deal of time outside. How long before it starts corroding?

Both situations need layer protection. It's a simple solution for your kids, make them wear their coat. What's the answer for the fabricated part?

The Two-Coat Finishing Process

What is a two-coat system? The simple definition of a two-coat system is a method applying two coatings to the same component. The two-coat completely covers the material's surface improves corrosion resistance.

Although there are many ways of applying finish to a component, only one provides the best material coverage: e-coating.

What is E-Coating?

Electrophoretic deposition (e-coating) is like electroplating. The electroplating process uses electric current reducing dissolved metal cations, forming a thin, coherent metal coating.

E-coating occurs while dipping the parts in a bath of epoxy, water-based solutions, or paint while adding an electric current.

The current causes a reaction within the bath depositing floating particles on the component. The amount of time using the electric current determines the coating thickness. After coating the part, it's moved to a curing oven finishing the process.

There are many similarities between powder coating and e-coating. Both methods use electric current to bond coatings to a substrate.

E-Coating is usually a better option than powder coating because the submersion coats hard-to-reach areas of the part.

Controlling the thickness of the coating becomes easier to manage when e-coating, too. This process applies a consistent and repeatable coating over most finishing methods.

2 Common E-coating Processes

Two of the most common e-coating processes are anionic and cationic.

The anionic process applies a positive charge on the component, while the fluid in the bath is negatively charged. Anionic methods are standard in the general metal industry needing color control, easy operation, and is cheaper.

If using a component in a non-corrosive environment, the odds are the anionic process coated the part.

The cationic process provides a surface more resistant to corrosion and is the reverse of the anionic process. The component is negatively charged while the fluid is positively charged.

The chemistry involved in the cationic process is based on acrylics or epoxies.

If corrosion protection is critical, use epoxy chemistries. If applications need color control or durability, then acrylic systems are typically used.

E-Coating Evolution

General Layout of an e-coating system

With a history dating back to the 1930s, e-coating provided a coating inside steel food containers. Around 30 years later, a higher number of industrial applications starting using the e-coating system. (https://www.sharrettsplating.com/blog/industrial-uses-of-e-coating/)

Ford Motor Company was at the forefront of e-coating technology. In the early 1960s, Ford scientists created an anodic process for e-coating an assembled auto giving anti-corrosion protection. A few years later, domestic appliances and architectural aluminum successfully used the e-coating system.

In the mid-1970s, Ford advanced e-coat technology by replacing anodic with cathodic processes where a continual DC circuit in the bath applies the e-coating.

Since then, recent advancements in e-coating technology led to improved edge protection, low voltage organic compounds, and more protection from UV light. E-coating is now used when making electrical components and heavy equipment needing corrosion protection.

Typical E-Coat Process

There are four main parts to the e-coating process, including:

      Cleaning and pre-treating the component: a phosphate is applied to the surface of the component, preparing the piece for e-coating.
      Immersing the component into a bath containing direct current applying the coating to the part's surface.
      A complete rinse
      Baking the part for at least 20 minutes while the component is around 375 ºF

For a good overview of the e-coating process, watch this short video developed by PPG Industrial Coatings.

E-Coating Advantages

The debate between powder coating versus e-coating is an entirely different article. Instead of highlighting that discussion, we're only exploring the advantages of using the e-coat system.

Some of the significant advantages of using e-coating include:

      A greater coverage when a component is e-coated. Total immersion covers all the hard to reach places.
      More thickness control using varying levels of DC.
      A reduction of rework, paint usage, and VOC emission

When using e-coat as part of a two-coat system, components are protected longer. Image 1 shows a comparison between two holes that spent 1,000 hours in a spray of salt.

Image 1 introduces POWERCRON® electrocoat to our story. PPG Industrial Coatings' POWERCRON gives greater high edge protection.

Image 2 compares two edge electrocoats magnified 400 times. The high edge electrocoat provides greater rust protection than conventional electrocoats.

In Sum

The two-coat process, including e-coating, provides greater protection from rust and corrosion over other metal finishing systems. Without having a base coat, any cracks or chips in the coating reduce the aesthetics and lifespan of that component.

Despite its age, e-coating is continually evolving and improving.

If you're thinking about using a two-coat process for components, keep two importing things in mind:
      Where will the part be used? In what kind of environment?
      How much punishment will the component receive?

When considering your metal fabrication source, see if they're able to apply an e-coat themselves or if they outsource it. If the company can e-coat, ask specific questions on the process those companies follow.

Knowing these answers help make your decision process a little easier.