Comparing Powder Coating SuppliersWe have been buying powder coatings from three different sources, and we are working to narrow that to two or maybe even one. We hope that by locking in one supplier for most or all of our powder, we can get a better price and superior service, though each supplier we now have has provided good product at a fair price. What things should we consider as we evaluate the three suppliers? How can we compare them so that we get the best material at the most fair price possible?
Coatings have different molecular weights and hiding capabilities that will affect consumption. The color and the amount of fillers is also a determining factor on how much coverage a coating can provide.
The single most important thing to consider when evaluating powder coatings or any other types of coatings is the applied cost. Applied cost is based on the ability of a pigmented coating to hide the surface at a set film thickness while reaching physical and mechanical properties attributed to the product. That, combined with your current price per pound offerings, will give you a comparison tool. In all fairness to your current suppliers, the best way to use that tool is to compare the same color, gloss and surface type, such as textured, smooth, etc. Comparing a white against a black on that basis simply won't work.
A coating may cost less than competitors' products but have a higher applied cost because, for example, the coating's molecular weight, or specific gravity, is higher than a competitor's, thereby giving you less coverage. Molecular weight and theoretical coverage is something that can be considered, but your decision should not rest on those alone. A white pigmented coating with less pigment will provide you with better theoretical coverage but will require more film build to properly hide the surface. Because of these variables, I often see more expensive material having a lower applied cost.
Reversing Decreasing Application EfficiencyWe have been powder coating for just over one year now. We coat springs with a single color, black epoxy. Our application efficiency has gradually declined so that we have to spray a lot more powder to get the same coverage that we used to get. Our film build is less consistent, and our material usage per part has increased. We have had our application equipment vendor in, and he says there is nothing wrong with our guns. He did suggest that we keep our racks cleaner for better ground, and we have started to clean the racks more often. This seems to have helped a little, but we still feel that we are not getting the kind of coverage that we got when the system was new. Any suggestions about what to look for?
Keeping the racks clean is an excellent start. In fact, it's the basis of everything.
Poor ground affects the way charged particles will transfer to the substrate. Under these conditions, large particles will hold more static charge, and for a longer period of time. Therefore, they stand a better chance of transferring to the substrate than a much smaller powder particle. When grounding is poor, your system will start building up fines (reclaimed fine particles) that will cause orange peel and uneven and low film build, and will greatly affect powder deposition in Faraday areas.
Make sure your loading plates or diamonds that are directly attached to the conveyor are also kept clean. Check the resistance between the conveyor chain and a loaded part. I would also suggest that you get a powder particle size analysis from your supplier to determine if you are in fact working with too much fines.
In some cases, I have seen improvements when coaters use a powder with a mean value coarser than usual. It is also good to adjust the powder guns to keep the overspray to a minimum.