Q: I work for a powder coating facility, and we are trying to find information describing the differences between e-coating and underbody powder. Essentially, is underbody powder coating a viable alternative to e-coat?
A: In terms of e-coat vs. powder as an underbody coating: “It’s complicated.” Here’s why. E-coat is a great coating that is applied by immersion in an aqueous bath of electrophoretic paint. The paint gets charged cathodically and seeks a ground, which in this process is the part to be coated. Cathodically charged paint covers virtually every surface of the grounded part. For the most part, it gets into every nook and cranny. It’s difficult to get it into very narrow tubing, but other than that it coats every surface.
Also characteristic of e-coat is the amount of film build possible. E-coat typically provides a very even-thickness film that tops out around 1.2 mils. The resultant coating gives pretty good corrosion resistance, usually up to about 750 hrs salt spray if the metal has a good pretreatment (ZnPO4 is best). To summarize, e-coat gives excellent overall coverage at a relatively thin film with good corrosion resistance.
Powder coatings can be applied rather thick, easily depositing 3.0-6.0 mils in one pass. And powder coatings can provide incredible corrosion and chip resistance. In fact, epoxy-based powder over good pretreated metal can withstand up to 3,000 or more hours of salt spray resistance. The thick films are also very chip and abrasion resistant – far more than a thin coat of e-coat.
Though the electrostatic application of powder coatings provides good overall coverage, it is not as extensive as e-coat. Tight corners and channels create Faraday cages that are difficult to cover. These lightly covered areas are sites for corrosive attack.
Which is best? Like many a teenager laments: “It depends.” If your parts are relatively simple in geometry, powder over a good pretreatment is best. If your parts have intricate configurations, e-coat provides nearly (if not complete) coverage. My vote for best underbody system is:
- Good pretreatment
- Then an e-coat primer
- Followed by a nice thick coat of powder
That’s what most automotive OEMs do.