Issue link: http://www.e-digitaleditions.com/i/799392
you may have difficulty getting it out of the opening. Yes, proximity of the parts to one another on the rack could aggra- vate the issue, but that isn't the crux of the situation. Here's a suggestion, but you proba- bly won't like it. If you can find a way to insert air into the hollow por- tion of the part, the air may repel the migrating powder satisfactorily. The best way is to coat the part before running the threads. Many compa- nies do this, and it actually is the simplest way to sidestep a problem like the one you're having. Of course another method would be to chase (retap) the threads after coat- ing and curing. This seems like a duplicate operation, but you're going to have to take a deep breath and change what you're doing now. I really think you won't like putting a tight seal over the opening because of the problems you'll have removing the seal. —G.T. Finding the perfect substrate bring-up time Q How fast (ideal time) should the substrate be heated to the specified temperature? D.N., Tamil Nadu, India A Heat-up time of the substrate to the desired cure metal tem- perature is referred to as bring- up time. Most powder coatings prefer a steep ramp-up of heat on the powder surface, as the electrostatic charge is sig- nificantly reduced with heat. Because the electrostatic charge is all that holds the powder onto the part after spraying, converting the solid powder coating to a liquid coating by using heat must hap- pen as fast as possible. In fact, high intensity infrared systems often can completely cure a part in fewer than 30 seconds, so the rate of heat-up isn't a significant concern. Be careful though. Fast-heating sys- tems can be problematic because they can often overshoot and scorch the coating easily. Be sure you have proper control of your heating sys- tem, and you won't have a problem. —N.L. Determining the specific gravity of a powder coating Q I'm opening up a shop. I keep reading about specific gravity. It's in a lot of equations. My question is how do I determine the spe- cific gravity of the powder? Thank you. M.L., Henryville, Pa. A Specific gravity is calculated by the manufacturer of the pow- der coating material. You have nothing to do with it, although it's very important in figuring your cost per applied square foot. Your powder sup- plier has this information and will be happy to give it to you. You must have a copy of the powder coating Material Safety Data Sheet (MSDS) whenever you receive a shipment, and the specific gravity is listed on this sheet. It will probably change for different powder coatings and can change from supplier to supplier. Put this information very high on your priority list because it will help you figure the cost of your powder coating. —G.T. Paying a fair price for a custom powder-coating job Q Why is it that powder coating is pushed as a higher-perfor- mance finish than wet paints, yet it costs less? For example, you can get your Harley frame sandblasted and powder coated in any job shop in the country for $250. If you take that same frame to a body shop for wet paint, it costs $600 to $800. I understand that the materials and time may be less in the powder coating process, but if the fin- ished product is superior, wouldn't a customer pay at least as much, if not more, for this service? J.D., Carlock, Ill. A Powder isn't necessarily cheaper when you don't recover and reuse the over- spray, or when you have to have heated and chilled make-up air for replacement of the booth exhaust and so on. Powder applicators don't require a high level of technique to apply it to a part, so a given part can be coated quicker com- pared with liquid coating. And, as long as the customer is willing to pay for liq- uid paint, then the paint shop will charge what traffic will bear. Usually, the wet applications that I've seen on bikes are skill-intensive, such as fading colors, flames, and other fancy detailing. What bothers me in this whole scenario is that many recoaters do a poor job of metal preparation. As good as powder is, it won't last any longer or hold up against stone chips any better than a cheap liquid paint if it has poor adhe- sion to the base metal. In this situa- tion, the customer has wasted his or her money. —G.T. PC Editor's note For further reading on the problems discussed in this column, see Powder Coating magazine's website at www.pcoating.com. Click on Article Index and search by subject category. Have a question? Click on Problem Solving to submit one. George R. Trigg is pres- ident of GRT Engineer- ing, Prospect, Ohio. He has been involved in the powder coating industry for more than 40 years. He holds a BSBA degree from Muskingum Col- lege, New Concord, Ohio. Nick Liberto is presi- dent of Powder Coat- ing Consultants (PCC), a division of Ninan, Inc., 1529 Lau- rel Ave., Bridgeport, CT 06604. Established in 1988, PCC is an independent engineering firm specializ- ing in the use of powder coating technol- ogy. Nick has more than 3 decades of experience in the powder coating indus- try and is a member of many industry associations, including the Application Equipment Technical Committee of the Powder Coating Institute. A registered professional engineer in Connecticut, he holds a Bachelor of Science degree in mechanical engineering with a minor in physics. He can be contacted at 203/366- 7244; email pcc@powdercoat.com; web- site www.powdercc.com. 26 POWDER COATING, March 2017