Dear Joe,

I work for a powder coating facility and we are trying to find research or any publications describing the differences between e-coating and underbody powder such as Interpon's A1000 series. Essentially, is underbody powder coating a viable alternative to e-coat? Any help you can provide would be greatly appreciated, thank you.

Caleb Cottrill

Chillicothe, OH

Hi Caleb,

Thanks for your question. It's a good one. I checked out your website - it looks like you guys do really good work. I'm impressed. As for 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). So, to summarize, e-coat gives excellent overall coverage at a relatively thin film with good corrosion resistance.

You guys seem to know powder fairly well, so I apologize if I'm telling you stuff you already know. Powder coatings can be applied as a rather thick film, easily depositing 3.0 to 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 hrs salt spray resistance. The thick films are also very chip and abrasion resistant, far more than a thin coat of e-coat. However, while 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.

So 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.

The problem is coming up with the cabbage to buy an e-coat line.

I hope this helps. BTW, I visit Chillicothe about once a month. I have a buddy who spends his time on death row there.

Please let me know if you have any further questions.

Thanks,

Joe

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