Issue link: https://www.e-digitaleditions.com/i/1014893
28 POWDER COATING, August 2018 moisture or just plain old Mother Nature manages to affect the galvaniz- ing, it will begin to do the job it was designed to do, and the first thing that happens is a loss of adhesion between the coating and the substrate. You should get decent adhesion if you pre- treat the substrate properly. —G.T. Masking tape leaving marks on powder-coated parts Q We have problems with the masking tape (silicone tape, no adhesive) leaving marks on the powder coating when applying a second color over the base coat on the unmasked areas. Is there a surefire masking method when applying multi- ple powder colors? R.K., Albuquerque, N.Mex. A The silicone tape should work, but then a lot of things don't work that should. Could it be that the edges of the tape aren't firm enough against the base coat and as a result allow the second coat to migrate underneath? Is the gloss of the base coat inhibiting the tape from getting a good seal? I'm not aware of a material that works better than what you are using. —G.T. Conducting crosshatch adhesion and MEK tests after salt-spray tests Q How long do we have, in hours, to perform a cross- hatch test after salt-spray tests are done on our parts? We use 1008/1010 low carbon wire, and after a five-stage, iron phosphate wash with a sealer, we expect 92 hours to 168 hours to pass. Parts are coated with epoxy or triglycidyl isocyanurate-based (TGIC-based) polyester powder 2 mils to 5 mils thick. Can we also perform a crosshatch and methyl ethyl ketone (MEK) rub test after the parts cool to room temperature? N.G., Angola, Ind. A Is this testing criteria custom- er-specified, and must it be performed concurrently? Normally, these tests are performed on separate product or test panel samples. Accelerated corrosion testing (salt- spray testing) is tested to a predeter- mined time, and the coating is in- spected for corrosion (creep, bleed, or blister). Performing a crosshatch adhe- sion test on a sample that was subjected to this corrosion test isn't normally re- quired. That doesn't mean that your customer can't specify this combined test, but it's very unusual. Crosshatch and MEK (solvent resis- tance) testing can be performed on dif- ferent areas (virgin areas) of the same sample. But wait until the sample is cooled to room temperature (and then some). Waiting 24 hours before per- forming any testing is best to ensure the coating can take the punishment. —N.L. Pricing formula for powder coating jobs Q This is not a technical ques- tion but definitely involves powder coating. We have been using our powder coating system strictly for in-house production of our heavy-gauge aluminum signage. Now we have decided to provide our powder coating to outside customers in a job shop environment. We would welcome any information regarding how other powder coaters calculate pricing for their customers. We have heard every- thing from charging by the oven load to charging by the square inch based on mil thickness of the coating. Is there an industry standard? Any insight would be greatly appreciated. Thank you very much. T.B., Sarasota, Fla. A We've been asked this ques- tion several times, and I still don't have a good answer for you for the same reasons. There is such a variance at each operation that a stan- dard formula is hard to design. Your cost for powder, chemicals, utilities, labor, rent, and so forth won't be the same as the guy's down the street. I haven't heard of the by-the-ovenload method. I don't know how that could get you an accurate figure. It's fairly easy to get the cost of the pow- der coatings and the cost of the chemi- cals. Although you will need some his- tory to know the cost of utilities, you'll know your labor costs and how many people are involved in handling a par- ticular part. From all of this, you must establish data and keep records so that you don't have to do this calculation every time. And of course, you may want to modify your price per piece de- pending on the number of pieces your customer wants you to run, which is an- other factor. I know this is a pain to put together because you are running a shop and don't have time for paperwork. Or do you? Guessing at this information can put you into bankruptcy. —G.T. Powder coating zinc-plated parts Q Can you powder coat clear zinc-plated parts or will the high heat damage the plating? L.A., Corry, Pa. A The only plated surface that I've had some difficulty with is brass plating. Brass plating sometimes turns red, depending upon cure temperature and surface contami- nants under the powder coating. You shouldn't have any problems with zinc plating. Just make sure that the surface is completely clean and rinsed with vir- gin deionized water. And cure the pow- der at the lowest temperature possible. —N.L. Limiting outgassing when powder coating galvanized steel Q What, if anything, can I do to prevent or limit outgas- sing during coating of galva- nized steel (G90 and G60)? Is there anything I should be telling my steel vendors that would limit my outgas- sing? J.J., Houston, Tex. A I doubt if your steel vendors can help you, but maybe your powder supplier can. Some- times, powder suppliers can change the flow characteristics of the powder so that the gassing is prevented from reaching the surface and causing a defect. Increasing film thickness can sometimes help. This creates a higher barrier that will retard the gassing, and with just a bit more time, the powder can gel over and prevent the gaseous defect from reaching the surface. But don't expect miracles. This can help, but it won't prevent outgassing 100 percent. And too much film build can cause other problems, not the least of which is added cost. So, limit yourself