Issue link: http://www.e-digitaleditions.com/i/715656
POWDER COATING, August 2016 25 plex. Yes, it's doable, but, yech. And yes, I did ask our design engineers if the part had to be masked. However, I got no support there, even when I told them how much it was costing us. For now, I'd just like to know what alternatives exist to eliminate masking after pretreat- ment. T.C., Milwaukee, Wis. A It's a pity that some design engi- neers don't know or care about the details of the products they design. There are probably more parts in existence than not that are difficult, if not impossible, to coat because the de- sign considerations didn't include how to finish the product. So much for the sermon, and you didn't ask for one. Maybe the good news is that you can fixture the parts in the same position every time. That means you may also fixture a method of removing un- wanted coating in a specific area. So, what I suggest is a minivacuum system that uses a very small hose to suck away the powder that is unwanted in a partic- ular area. Don't mess around with a shop-vac system. This will require a more sophisticated system than that. Check this magazine's Special Supplier Links at www.pcoating.com/suppli ers_vacuum.asp. You'll find several companies that make devices for this purpose, and they will be happy (or at least pleased) to work with you in devel- oping what you need. I don't know of another means for d o i n g w h a t y o u w a n t t o d o . Y e s , hanger-attached masks will likely have a short service life in the burn-off oven. And that dedicates the hangers to spe- cific parts. Tape is not feasible. Syn- thetic masks will probably cause a pow- der ridge and be difficult to remove. Blow-off lines will remove too much powder. Although that method is a pos- sibility, I wouldn't count on it. —G.T. Using two brands of powder coatings Q Can you use one company's clear powder over another company's base? I applied a gold made by Prismatic Powders and used a clear by ISF. I then used Pris- matic's curing schedule of curing it to 60 percent before applying the clear and then a full cure. The clear started delam- inating in less than a week. Both pow- ders cured at the same temp. B.R., Al- buquerque, N.M. A It is not so much that the brand of the powder coatings were dif- ferent, as much as the coating compatibility between the base and clear coat formulas. You must always verify with the different suppliers that these powder coating formulas can work to- gether in the total package you desire. Otherwise the results may become very unpredictable. Good luck. —N.L. Finding a way to hide an area on a part with putty Q I have a question regarding putty filling. I have some alu- minum panels 0.060 inch thick. In the middle of the panel is a big hole where a small 6-inch round duct is riveted. The customer doesn't want to see any defect or type of lining where the duct is inserted on the front surface. I've tried all kinds of aluminum putty, but nothing seems to work. After filling it with putty and sanding it smooth and applying the powder, it shows the round lining even though the surface is smooth. It seems that more powder is attracted to the metal than the round putty lining. We tried heating up the panel to 300°F and coating it, but the round lining still shows. Can you please help me out? Thank you very much. R.H., Concord, Ont. A Whatever putty you use should have some metal particulate in it to attract the powder. By your description, it seems to me that there is nothing that attracts the powder, or the attraction is poor, and the powder wants to go to the main piece. Electrostatic en- hancers are available, but generally, I think they're offered by pretreatment suppliers. I've used a product supplied by a chemical house that we sprayed on plastic to aid in electrostatic attraction, and it helped a great deal. Be certain you have continuity from the main piece to the filled-in section. This is where you're getting different film deposition, as you have found. —G.T. Stopping solution from turning purple Q In my tank #1, the degreaser solution is turning into a pur- ple solution. What can be causing this? We use an alkaline degreaser that is designed to work under tempera- tures between 45°C to 60°C. Thanks. E.D., Torreon, Coahuila, Mexico A Pretreatment chemistries are all proprietary formulas developed by each chemical company. This fact makes it extremely difficult to guess what has happened to your chem- ical bath to change the color. The only way you can sort through this problem is discuss it with the chemical company that supplies your facility. They know what is in the formula and what would cause the color change. —N.L. Lowering powder consumption during application Q How can we control powder consumption? Do you have any tips or methods we can use? S.B., Noida, Uttar Pradesh, India A This question begs a disserta- tion! So many factors are in- volved, and I don't have much information to go on, so I can only re- spond in general terms. Powder consumption can be high be- cause of too much film build on the parts you're coating. Consumption can be high because of poor hanger design. It can be high because the parts have been designed for something other than a spray application. If you have the cor- rect booth, with a reclaim system, you should be recovering the overspray and blending it with virgin material. If you have too much overspray, eventually the reclaim will be mostly fine particles, and you'll have problems with fluidiza- tion, application, and so on. Here are some things to check: Is the airflow in the booth such that it con- tains powder, or does powder escape out of the openings? Is the hanger de- sign so poor that the part surface isn't presented properly to the spray gun? Poor hanger design will cause too much overspray, and you'll likely have too