E-coat As A Primer For Powder

Q. I am a new junior design engineer for a company that manufactures construction and agricultural equipment. I recently completed a design for a component and started to research a specification for the finishing requirement. When I asked my group leader where to look, she brought up a drawing of a similar component and told me to copy the same specs to my drawing. Basically, the spec called for electrocoat as a primer and a powder coating for the top coat. We have liquid and powder coating facilities in our plant, but we will have to send the parts to a contract coater for the E-coat process. Can you tell me why the E-coat process might be required instead of a liquid process? J.J.

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A. I know the feeling. I remember having a very similar experience as a young design engineer. (That was when we actually used drawing boards and would manually draw the layouts and piece parts.) I had to learn about finishing processes on the job as well. Today knowledge related to finishing is still is basically left to be learned on the job.

OK, let’s talk briefly about why you might want to use electrocoat as a primer. For that application, the E-coat process you will be specifying will involve a cathodic epoxy electrocoat. For starters, this E-coat product provides superior levels of performance when it comes to corrosion resistance and chemical resistance and is formulated to have excellent inter-coat adhesion with powder coatings and many types of liquid top coats. A couple of characteristics that also make it desirable as a primer are its ability to find its way into the nooks and crannies of complex part configurations and the fact that it has a very consistent film thickness. The E-coat process includes an oven cure so the coating material is formulated to withstand relatively high temperatures. That property enables the film to endure the high temperatures needed to melt the powder coating over it and to be heat cured.

E-coat provides excellent primer qualities and various powders provide excellent top coating property options. I have been involved with literally hundreds of applications using that combination. The conventional wisdom commonly expressed was that combining E-coat and powder creates a quality marriage that lasts.