I manage a custom powder coating shop that does many different sizes and types of parts. We have a very large capacity 42×10-ft batch. We specialize in very heavy or large parts, although we do a lot of the same types of parts other batch shops do. The problem I would like to address is that of sealing the parts after blasting and before coating. We have a chemist here who made an acrylic sealer for us that we could spray on with an airless sprayer, which was very nice because we could work it in all of the cracks and joints and it didn’t tie up the same room in our shop as the actual powder coating. We felt like it had solved a lot of problems for us until we got complaints of chipping. Sure enough we went back and re-tested and we had adhesion loss. We then got back with the chemist who put two and two together and realized that it was not going to work, so he suggested an iron phosphate that they make for the shops that use steam cleaners. Our hope was that we could pre-heat the part and spray the phosphate on to it with the airless. The problem with this was that the phosphate solution would boil out of the cracks under the coating and make ugly marks so we had to quit using it as well. We have not pursued it any further to this point, but we really need something that we can spray on to seal the metal from exposure, especially in the cracks and joints, and that will give us an added layer of protection without double coating or priming, as the vast array of fabricators out there leave joints unsealed or if we happen to have a spot that is under mil thickness.We want to provide a top-notch product for our customers! Do you have any suggestions? J. J.
Your first problem was asking a chemist to add 2 and 2. His answer was 2+2= “iron phosphate.” Funny, I always thought 2+2=4. In this case your chemist was right; iron phosphate is your answer. However, your method of application was all wrong.
Your problem was caused by using an airless paint sprayer to apply the undiluted chemical directly to the part’s surface. Without dilution, the iron phosphate coating would be streaky, at best. Without rinsing the part afterwards, the iron phosphate would leave a powdery residue on the surface. These results would not meet your top-notch product goal.
You want to buy a cleaner/coater with iron phosphate that can be used in a spray wand (hot-water pressure washer, not steam cleaner) pretreatment machine. This chemical is designed to be applied through the pump suction siphon (chemical or soap siphon) and mixed with water and then heated by the coil. All this occurs within the pressure washer unit. This chemistry will remove any oils and apply an even iron phosphate coating to the part. Finally, rinse the part with water, using the same pressure washer, by turning off the chemical siphon. Lastly, place this part into your batch oven for at least 30 minutes at 250ºF to completely dry the part before applying the powder coating.
Following this recipe will ensure that your customer obtains a high-quality product with good corrosion protection.