Alternative Coating Options and Laser Edge

Q. We currently e-coat our products and then topcoat with a powder coating line. The process is very expensive, and we were curious if there is a different method we could use to treat our products in our wash system to improve the adhesion characteristics, as well as to prevent corrosion and rust in the long term. Some of the methods we have already explored are sand blasting and topcoating, zinc-rich priming and topcoating, e-coating and topcoating, and just topcoating.

One of the other problems that is common in our product offering is scale left from our laser cutting machine. We try to cut with nitrogen as much as possible, but this seems to be the starting point of all chipping and rust formation. Do you have any experience with processes to eliminate this laser cut oxidization? The products I am concerned about are outdoor street amenities such as park benches, picnic tables and litter receptacles. —S.S.

A. Electrocoat is a very good corrosion inhibitor, especially if the surface is pretreated with zinc phosphate. There is no pretreatment chemical that can do as well as zinc phosphate plus electrocoat. You may be able to save a little by going to an autophoretic system in which the autophoretic coating can be co-cured with powder. However, the new system would be very expensive and only provide marginal savings, if any, compared to electrocoat. You could also go to a blast and zinc powder system. That may be the best alternative in terms of the process and the corrosion resistance. A blasted surface would have the added advantage of removing the laser oxide from the cut edges, and a zinc powder primer is an excellent corrosion inhibitor.

You are on the right track with the nitrogen cutting to reduce laser oxide, but using a cooler gas will not work well as you get into heavier-gauge metal. The typical options for removal of laser oxide are abrasion or acid pickling, although acid pickling is usually more challenging than a blast operation. Note that the edge breakdown may also be related to edge coverage, not just laser oxide. In that case, you can radius sharp edges or use a thicker first-coat process like the powder primer. A double-coat process is the best way to deal with sharp edges, because it results in more thickness at the critical area.