Issue link: http://www.e-digitaleditions.com/i/862794
Clear coat changing to bronze color Q I'm running a bright metallic with a low gloss clear top coat. Most parts come out OK, but some come out with kind of a bronze-like color. Although some runs have good parts, some turn bronze on either the front or back line and it's sometimes only on one side and some- times both. The target is a low gloss kind of anodized clear look. The base coat is bonded and at about 80 gloss. The clear is low gloss and has a slight milky character. The oven is gas fired. Parts are not reracked; it goes around omitting the wash prior to the clear coat. When a rack turns bronze, it is the whole rack. Adjusting the heat has yet to reproduce the look. Thoughts? B.L., Holland, Mich. A Only a couple of issues would cause the color to change on the clear coat (or the basecoat for that matter). One is over cure (tem- perature or time or both). In this case, the additional temperature of time has begun to affect the appearance of the clear or basecoat, much like a white turning yellow when over cured. The second issue that would cause a color to change is oven fouling. Oven fouling is when byproducts of cure or combustion are allowed to build up in the oven, causing this contaminant to build in the coating and thus causing the discoloration. Clears often require up to 12 air changes per hour in the oven to keep fouling from occurring. You may have to clean any buildup of oven contaminants (i.e. e-cap) that have accumulated over time in addition to increasing the exhaust rate. Another possibility is contamination that is drawing into the cure oven or de- posited onto the parts on their travel through the process (two-passes). If this is the case, you are going to have to look at the surrounding manufacturing processes and general plant airstream for the root cause. Other conditions that I ruled out are compressed air fouling, because that would not "come and go," and powder formulation consistency, because that would also be consistent for the entire batch. Good luck. —N.L. Cracking powder hoses Q We've been experiencing a problem with our powder hoses cracking. It usually happens about 6 inches from our trans- fer pumps. For the past 12 to 14 years, we've never had a problem, but now we're cutting off about 6 to 8 inches of hose about four times a week or replac- ing the hoses. We've been told that it's from the charge of the powder when it goes through the hose. We were advised to ground-out the hoses, but we still are having the problem. The hoses have several small cracks, and they're not worn on the inside from impact fusion. It looks like the hose is just drying out. Is this possible? Thanks for your time and any help you can send my way. K.T., Spring Lake, Mich. A Has anything changed with the powder formulation? Are you sure? What type of powder hose are you using? Some purchasing guy didn't change feed hose suppliers to make himself look good, did he? You haven't dramatically increased powder output, have you? Have you absolutely confirmed that you have a good ground from the hose? If you've tried all these things, please let me know, and we'll see what else we can look at. —G.T. Mating two coated surfaces Q I recently had parts powder coated for a 1985 Honda A T C 1 1 0 t r i k e t h a t I ' m building. What's the best way to pro- tect the powder coat when mating two powder coated surfaces together so they don't get scratched or nicked? C.D., Los Angeles, Calif. A Masking tape is the best way to protect mating surfaces during assembly. The adhesive is easy to remove and should not affect the powder coated surface, if you selected a good coating. —N.L. Requiring respiratory examinations Q Our coaters are trained in the use and maintenance of their personal respirators. This process is also monitored for compli- ance. Are there any regulations or laws that you're aware of specifying respira- tory examinations periodically? We're also looking for the best equipment available in this area—any preferred suppliers? J.F., Fort Worth, Tex. A I'm uncertain if OSHA (the O c c u p a t i o n a l S a f e t y a n d Health Administration) re- quires any monitoring or occasional in- spections of respiratory equipment. I don't think it does, but your state may have some recommendations along this line. Even if there aren't any specific reg- ulations, you can certainly institute these requirements within your com- pany. I know of some companies that require their powder coating employees 24 POWDER COATING, August 2017 George Trigg GRT Engineering Nick Liberto Powder Coating Consultants Questions & Answers