PC Home

The only technical publication devoted to the Powder Coating industry and other green finishing technologies.


Q: I’m using a clear nylon liquid primer to pretreat a metal fastener. The whole fastener is getting primed, but only the head and shank get coated with a black nylon powder. What’s the ideal method for applying the primer? Can I prime the parts by using a dip-and-spin-dry method? Will this give me a uniform primed surface? This is step one in my education of liquid primers combined with powder coatings. R.S., Macomb Township, Mich.


Q: I am having a base material bleed through on light colors. Can I stop this by applying a primer first? If so, should I bake the primer before applying the color or can the primer and color be baked at the same time? I’ve never used primer before. V.A., Houston, Tex.


Q: What’s the best way to apply zinc-rich primer and a polyester powder topcoat? I’m concerned about finish smoothness and powder adhesion between the two coats. D.V., Birdsboro, Pa.


Q: I have a big issue with peeling on aluminum. Our products are poles: The base part is casting and the body is extrusion. Somehow, the problem is only at the extrusion part (or to be exact, 90 percent of the claims). Which test can I do to try to find the reason? We have immersion tanks, which are degreaser, rinse, iron phosphate, rinse, and seal. We run aluminum, steel, and cast iron. (We have the same process for steel but different tanks.) We load the conveyor by hand, and we use only one oven to preheat and cure the pieces. We preheat the pieces to degas, but how much is enough because sometimes the pieces are really hot? We’re using polyester powder coating. The other issue is we have an electrostatic booth, but because the pieces come out of the preheat too hot, when we apply the powder coating, it’s almost cured. V.K., Tamaulipas, Mexico


Q: I’ve been trying to perfect my gloss-black parts by using less powder, but my parts still come out with orange peel. I’ve mentioned to my boss that maybe the curing time is too long and the temperature is too hot. Could you please help? D.A., Wilmington, Del.


Q: Our powder coater has been having problems powder coating our parts and has been burning off the powder coating sometimes more than once for the same part. Our parts are chair frames and are made out of 1-inch, 14-gauge carbon steel tubing. Some of the parts on the chairs are cast aluminum unions that fit into the tubing. What is the process and temperatures of burn off? How do burn off and temperatures affect the metal and aluminum? D.J., White Bear Lake, Minn.


Q: We have a high-temperature burn-off oven to burn off items that are to be recoated. The old powder coating is burned right down to the metal. Sometimes, when we recoat these items, the recoat will crack, and the coating separates from the metal and peels off in large chunks. Any idea what causes this? W., Shelburne, N.S.


Q: I’ve been struggling with our powder coating vendor on a way to properly prepare the surface of gold-plated aluminum. The powder we’re using is a low-temperature cure because of some solder on the unpainted surface of the aluminum. The gold plating doesn’t serve a purpose on the painted surface; it’s simply too costly in time and labor to mask off areas of the aluminum prior to plating. Our process so far is to use DOD-P-15328 wash-primer prior to coating. I don’t know what cleaner is being used, and I’d prefer to NOT use that wash-primer if I could get around it. The coating isn’t adhering well, and all parts have chips in the finish near the masked edges. I appreciate any help you can provide. S.S., Salt Lake City, Utah


Q: I’m new in the powder industry, and I would like to know what type of fire protection is needed in a manual-style powder booth. I’ve seen automated powder booths, and they’re equipped with ultraviolet-light (UV-light) detectors. My new employer said that because they’re not grounded to the conveyor and they’re grounded from part to part, no protection is needed. This is a modified wet paint booth with a conveyor running through it. Please advise. D.R., Goshen, Ind.


Q: My foam is not adhering to my powder coated parts. What factors could be causing this issue? Thanks. K.A., Windsor, Ont.


Q: I am a building surveyor and have a project in which some powder-coated balustrades have been damaged down to the bare metal. Can the finish be repaired in situ, and how can it be done? I would be most grateful for any advice you can offer. J.H., Chichester, West Sussex, UK


Q: I work for a company that builds mini dumpers, scissors, cranes, and related equipment. They seem to think that by putting three different metals (castings, sink, and metal) into the same washer (phosphate wash), it can all be processed together as a batch. After the wash, the metals all have to be blown off and put into ovens for 12 minutes, put back in the oven for 2.5 minutes, have a top coat applied, and finally get put back in the oven for 19 minutes. The company uses the same oven temperature on all of the work, which I think is ridiculous, but they think works perfectly fine. I am having trouble with the metal, mainly because all of the metals are on the same frame. When it gets through this batch process, there are two powder coatings on the same frame, so you are getting a buildup of powder and it is cracking when the bolts are being applied. Have you got any useful tips to help? T.E., Coleshill, Birmingham


Q: Any suggestions on how to powder coat a 1-by-4 steel grating used in an exterior application and keep it from rusting? F.B., Centralia, Wash.


Q: How fast (ideal time) should the substrate be heated to the specified temperature? D.N., Tamil Nadu, India


Q: How do I get more information on waste powder utilization? A., Auckland, New Zealand


Q: I have a customer who is making a formed sheet metal box. He wants the seams sealed shut because of airflow. Do you know of any caulking that can be applied before the coating process that will stick to powder and survive the curing cycle? The seam is very tight, so the caulking thickness has to be very thin (if applied properly and conservatively). Metal repair compounds have been mentioned, but the volume of parts makes them completely impractical. Is our best option to seal the seams after coating? Thanks. R.P., Spokane Valley, Wash.


Q: I’m trying to paint some wheels that need to have two colors. I painted the base color and then masked the wheel as needed. The problem is the wheel lip is about 0.050 wide, making it very hard for the tape to stick and not letting any of the second color get by. Does anyone have any ideas? D.L., Grand Junction, Colo.


Q: My neighbor has a powder coating business in his backyard, which is directly behind my house in Texas. We have watched him powder coat and sandblast things directly through his high-powered exhaust fan with no filter, which happens to be about 4 feet from my fence. It has gotten on our golf cart seats, motorcycles, cars, and more. Actually, the more we look, the more we find with his coatings on our belongings. It’s very inconsiderate, to say the least. Is there a way to get these coating and blasting materials off our stuff? Or should we contact an attorney to solve this matter? Help! M.E., Vidor, Tex.


Q: If I have to coat a metal part that must adhere to a PVC (polyvinyl chloride) surface, what kind of powder coating should I use? W.D., Pescara, Italy.


Q: I’m experiencing issues coating a nonconductive part. The process involves preheating the part prior to coating and then curing it. After cure, the part exhibits an uneven distribution of gloss where the edges are shinier than the center of the surface. What is the best way to maintain an even distribution of gloss? A.L., Vaughan, Ont.


Q: We’re designing an aftermarket roof rack for automobiles and sport-utility vehicles. The rack will be made from tubular steel. We want an ultraviolet-resistant crinkle finish. What do you recommend for coating this product? Should we use a primer? M.K., Atascadero, Calif.


Q: I use a variety of powders, including acrylics, polyesters, and polyester‐urethane hybrids. Over the years, I have collected a lot of expired powder rising from the overspray. Is there any way to reuse, recycle, or get rid of this outdated powder? J.A., Evansville, Ind.


Q: We’re looking at alternatives to painting steel shapes, such as H-beams, angles, and other configurations that are about 1 foot tall and wide and 40 feet long. Is powder coating a reasonable alternative? What are some of the pros and cons? J.B., Richmond, Va.


Q: How long do we have, in hours, to perform a crosshatch 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.


Q: We’ve been asked to powder coat magnesium wheels. Can they be blasted with steel shot? D.A., Yorkville, Ill.


Q: During powder coating, we have observed powder being deposited onto our hangers and fixtures. Can we avoid this by using some type of special material on our fixtures? S.C., Maharastra, India


Q: We use a silver vein powder coating. At times, it comes out flat with no structure and off-color with too much silver or black. Could this be a grounding issue? J.C., Terrell, Tex.


Q: My company is struggling with finish issues. We asked our powder supplier about these problems, and they said it all depends on the particle size of our virgin and reclaim materials. What should the particle size be for a gloss, satin, and matte finish? Our typical coating thickness is 60 microns. Thanks for your help. S.U., Chennai, India


Q: Our cure oven is a direct-fired convection system on the roof of our plant, and parts are carried through on a chain-driven conveyor. The oven shape is rectangular, measuring 22 feet by 55 feet (~1,100 square feet). The exhaust is currently located only about 5 feet away from the heat exchanger. My question is this: Would it be more efficient, and would we get a more even heat spread, if the exhaust was at the other end of the oven? F.S., Joplin, Mo.


Q: We apply white, high-gloss, smooth hybrid powder coating onto galvanized panels that are used for spray booths. Some locales require that the panels be grounded. The powder acts as an insulator. Masking specific areas to allow panels to have contact is problematic for the spraying and installation process. We plan to use a light gray powder to differentiate the panels that should be conductive. I would like to know more about using conductive powders, such as sources, issues with coating and curing, and durability. T.B., Greensboro, N.C.


Q: My question concerns the pros and cons of using aluminum bars, racks, and hooks for hanging parts. Any problems with ground? What about over a sustained period of time? J.E., Grandview, Mo.


Q: We’ve found a cobweb-like appearance on the surface of parts before and after they are cured. We apply white, glossy hybrid powder coatings on perfectly pretreated mild steel components that are hung on the conveyor for some time (15-20 minutes) before they enter the oven. Could you please tell me the cause of this problem? Gloss and other properties of the coating aren’t disturbed with this cobweb appearance. S.K., St. Louis, Mo.


Q: Can I apply a water-based paint after powder coating has been allowed to dry without scuffing the surface of the part? What prep work is involved with a powder-coated product that I would like to paint? S.L., Olympia, Wash.


Q: I passed a sample of high-gloss, white, hybrid powder coating through an infrared (IR) oven for 1 minute and a gas oven at 180°C (356°F) for 20 minutes, and the color turned yellow. When I passed the same sample through the gas oven without the IR oven, it didn’t change color. What in the formulation do I have to add to avoid this yellowish problem? S.C., Laval, Que.


Q: Is there a formula that can be used to determine the cost of an empty hook that goes through a coating system? D.S., Muscatine, Iowa


Q: Hello, I would like to know if the powder coating process induces a magnetic field in ferrous sheets and tubes. Could you provide any specific detail if so. Thanks, J.B., Austin, Tex.


Q: I’m having cast aluminum parts powder coated in China with a medium texture flat black powder. When I receive the parts, the powder coating can be scraped off, and it’s being chipped during shipment. What’s the cause of this? The coating should be more durable than this, right? Another question: Is there a flat white powder available to withstand 572°F (300°C) to 662°F (350°C)? J.E., Little Neck, N.Y.


Q: Do you have a suggestion for powder coating the inside of pipe that is of various diameters and lengths? A customer wants to use a wet primer and then powder. What type of equipment is needed? R.C., Shoshoni, Wy.


Q: I’m looking for a powder coatings manufacturer who has a highly fuel resistant powder. Do you know of any company? B.H., Spring Lake, Mich.


Q: We are into sheet metal fabrication with powder coating. For some days now, we have been facing pinhole problems in our powder coating. The diameter of the pinhole that appears on the powder-coated components starts from 0.2 micrometer in diameter to 1.0 micrometer in diameter. We have a nine-tank pretreatment process (hot process) before going to powder coating. To remove the moisture in the air, we have provided a dryer, a moisture separator, an oil separator, and an automatic drain valve. We are not able to eliminate the problem. We are looking forward to your suggestions. J.C., Coimbatore, Tamil Nadu, India


Q: Our two powder coating processes are batch done in a nonreclaim booth and an automated booth. The automated line usually runs at about 7 feet per minute with the rack hooks spaced out at 2 feet. We were considering automating the batch booth process by using operators to spray the parts going past. What line speed would you recommend for this? On average, it will take our skilled operator 51 seconds to coat 12 of our hardest parts on a rack. K.K., Jamestown, N.Y.


Q: My question is about color changes. We apply white triglycidyl isocyanurate (TGIC) and low-gloss black powders in the same booth. We reclaim. After changing from white to black, we see cross contamination as little white specs in the black. When we change from black to white, we see no contamination. We clean the booth the same for both white and black. We take about 1.5 to 2 hours per changeover. This is done three times in 24 hours. The only thing that we reuse is the booth and the cyclone. These are completely cleaned out by washing and wiping them down. The powder hoses and the reclaim hoppers are only used for their designated color. Is there any more that we could do to stop the white in the black? J.M., Adrian, Mich.


Q: Is there any such thing as a no-bake powder coating? If so, do you have any details on it? Thank you for your response. B.S., Taylor, Mich.


Q: If you had to decide between liquid or powder painting, what would be your decision and why? R.S., Distrito Federal, Mexico


Q: How can we control powder consumption? Do you have any tips or methods we can use? S.B., Noida, Uttar Pradesh, India


Q: I was recently asked how to apply two-tone powder coating to a wheel. Could you please inform me on how to address this issue. I’m kind of baffled. Will the spokes need to be removed? I’ll wait to hear back from you. Have a blessed day! L.J., Spring, Tex.


Q: I have coated several items with high-gloss clear. The clear looked great for the first couple of weeks. Now the clear is cracking in spots. I have coated two items with the same clear within 24 hours, and both items have cracked in spots. What am I doing wrong? Hope you can help with my problem. C.L., Birmingham, Ala.


Q: We have powder coating booths, and I was wondering what the regulations are to clean powder from employees in Michigan. Can you use air to blow off powder? N.H., Grand Rapids, Mich.


Q: I build large aluminum globes of the world and I have a 5-foot-diameter globe that we need to first powder coat with clear and then have the outsides of the continents painted to resemble the ‘Blue Marble’ NASA image from space. My questions would be: Beyond scuffing, what other prep do I need to do? Is there a powder type/primer chemistry that works well together? Do I need a primer? My artist will be mixing paints on a palette for the topcoat, so she can’t use high VOC or two-part paints. M.B., Chicago, Ill.


Q: I am very accustomed to working with robotic spray and dispense applications in manufacturing. However, with powder coating applications, I have only seen manual and vertical reciprocator methods used. Does anyone use robots with powder coating applications, and what are the pros and cons of using a robot? S.J., Des Plaines, Ill.


Q: One of my customers asked if he could overcoat fusion-bonded epoxy. The material is applied electrostatically in a spray booth. We apply the epoxy to AWWA (American Water Works Association) C213 standards. We manufacture carbon and stainless steel pipe couplings for the water and wastewater industry. They are from a little less than 3 inches to 240 inches in diameter. T.P., Doraville, Ga.


Q: What type of powder coating is best for exterior railing or ornamental iron work? A.L., Redwood City, Calif.


Q: Is there a process for removing the powder from silicone plugs and caps? We’re getting a buildup, which is causing a bridging effect when we reuse the plugs too many times. We roll the plugs in our hands and try to crack the powder so it falls off, which works to a point but is a tedious process. Any suggestions would really help. D.A., Ivyland, Pa.


Q: What causes starbursts in wrinkle powders? D.R., Asheboro, N.C.


Q: I have some powder left from three years ago. As long as it sprays, will there be any curing problems? M.H., Leola, Pa.


Q: I have an issue with bleed-through when using an industrial paint pen. It’s a yellow opaque ink. The application is to mark product by customer order and lay out hole locations on roll-formed and structural angle. The bleed-through happens on our light colors. Is there a product that will survive the outside elements and multiple handling but will wash off in our processor’s rinse tanks, which are industry-standard processes. Thank you in advance for any possible solutions or products to test. D.C., Dalton, Ohio


Q: Could you provide information on primers and abrasion techniques that could be used to improve adhesion of powder coating to electroless-nickel (e-nickel)? Our customer wants painted e-nickel because of the electromagnetic interference (EMI) characteristics of the e-nickel coating. The customer wants powder coating because of the added aesthetic value. Any information you could provide would be helpful in solving some of our current problems with coating e-nickel. E.H., Cedar Rapids, Iowa


Q: Is e-coating (electro-deposition coating) similar to powder coating? If different, what’s different about the applications? Is there anything different between the two applications with the Faraday cage? R.L., Oriskany, N.Y.


Q: Can powder coating replace nickel plating? We already have the equipment to apply powder coating. We’re having problems with corrosion (rust) in nickel-plated parts (housing bearings) during overseas shipments to a customer. That’s why we think we can replace the nickel plating with powder coating. The parts are sent to a vendor to be nickel-plated, but we’re having problems with the coating. The vendor is probably not doing it right, so we thought we could use powder coating to protect the parts better. The housings are made of carbon steel. C.B., El Salto, Jalisco, Mexico


Q: We currently powder coat our aluminum brake calipers red and black. They frequently see temperatures around 300°F and are subjected to hot DOT 3 brake fluid. We’re using bright red polyurethane and black polyester TGIC. We apply the colors separately and cure them at 400°F for 40 minutes. After they’ve been cured, we do a hot pot test where we submerge the caliper in hot DOT 3 brake fluid at 250°F for 2 hours, remove, and let cool, wiping off excess brake fluid. We then bake at 375°F for 20 minutes. After that time, the red is still rock hard, and the black is soft and tacky. What would cause that? C.S., Camarillo, Calif.


Q: We’re somewhat new to powder. We’re having issues with clumping due to humidity here in Indiana. We don’t always have our materials stored in our air-conditioned areas, and in some cases, we have $10-per-pound material that is used infrequently clumping between days it’s used. We’re looking for ways to rescue clumped material and any other ideas to use, such as desiccants, when the powder isn’t in the air-conditioned storage. C.J., Markle, Ind.


Q: We’ve just started a powder coating operation. We had mostly sprayed powder on structured components. Recently, a customer required a plain polyester powder coating in star white. With this type of powder, however, we had pinholes on the surface. We tried some tactics to solve the problem. For example, we checked the dryer for the powder coating plant, and it works fine. We checked the spray application equipment, and cleaned the booth and the area thoroughly. We’re still getting pinholes. Please help us. P.B., Navi Mumbai, Mahape, India


Q: I need to coat copper tubing (refrigeration) for immersion in water (tube and drum water chiller). The coating needs to be durable, yet able to flex with the copper tubing. Any ideas? Thank you. B.A., Wrangell, Ark.


Q: I apply a super-durable TGIC-based (triglycidyl isocyanurate) polyester powder on extruded aluminum parts. Currently, I claim that the coating meets American Architectural Manufacturers Association (AAMA) standard specification 2604-02. This states that a panel exposed to South Florida weathering will retain a minimum gloss of 30 percent and change a maximum of 5 delta E units over a 5-year period. Recently, I began using a new powder supplier, and I can’t wait 5 years for test results. I would like to develop a specification that uses accelerated weathering as the test method, but I’m not sure what performance objectives to claim or which accelerated test to use. Are standard specs already written for this type of weathering? If not, are there performance benchmarks I could use as a starting point (perhaps in the automotive industry)? A.G., Philadelphia, Pa.


Q: I have some automotive car parts (sheet metal fog lights) in need of powder coating. I’ve bead-blasted the housings, smoothed the surfaces with 380-grit sanding disks, and blended and smoothed with a Scotch-Brite abrasive wheel. Is it possible to fill the remaining rust pits with a metal-filled epoxy? How will the electrostatic attraction be affected, or do you have suggestions? B.P., Tampa, Fla.


Q: We’re currently using epoxy powder coating and testing for sufficient cure by using methyl ethyl ketone (MEK). We have an initiative to get MEK out of the facility for environmental health and safety reasons. We have received recommendations of toluene and xylene, which aren’t acceptable either. Do you know of any chemical that will be aggressive enough to verify cure without being a total toxic organic or a carcinogen? C.B., Reading, Pa.


Q: We’re looking for a powder that meets Mil d 24712. Do you know any suppliers who do the testing on their powder to meet this specification? M.B., Holliston, Mass.


Q: I’ve been having some trouble with clear powder coating over a veined powder coating. After the part leaves the shop, customers complain about the clear cracking or spider-webbing. I’ve talked with the powder supplier, and I was told that this is a common occurrence. Could you also discuss salt-spray testing. I would appreciate any help with this. B.C., Grants Pass, Ore.


Q: Q1: I’d like to powder coat the frame of an experimental aircraft, but I’ve heard that the powder coating process can weaken the metal. The metal involved is 6061 T-6 aluminum. I’ve also read that the temperature and cure times can be set to avoid any change in the alloy. What are the correct parameters for maintaining the structural integrity of this aluminum alloy? R.M., Bradenton, Fla. Q2: Do you have any information, recommendation, or advice regarding the concerns that powder coating and the temperatures used will weaken or affect the strength of forged rims. T.T., Kapolei, Hawaii


Q: When I apply a second coat of powder onto a part, the powder doesn’t cover the side of it. I have an inexpensive hobby-type gun, and I think the voltage isn’t enough for make a good job on the second coat. Is this possible or not? C.T., Victoriaville, Que.


Q: We’ve been custom coaters in Phoenix since the 1980s. We’ve shot powders from the RAL palette since the beginning. We’ve seen improvements in powder quality across the board from all major powder manufacturers, in all formulations. But what has not improved is the uniformity in matching RAL colors from supplier to supplier. They’re all kind of close, but all do not match. Is there any effort by powder manufacturers who sell the RAL palette to come up with standardized RAL colors (similar to Federal Standard) so they all match from supplier to supplier? R.Q., Phoenix, Ariz.


Q: I’m using sandblasting media, air blowing with compressed air to clean sand out, then cleaning with a solvent, like a paint thinner or alcohol. I then heat the part dry for 15-30 minutes at 370°F (to outgas and dry the part), and then I remove the part from the oven and let it cool to around 150°F or sometimes cooler (tried different temps). The aluminum is usually cast, mostly motorcycle parts. I’ve been told that the pinholes were caused from out-gassing so that’s why I started doing the heating before powder application. It seemed to help, but it hasn’t eliminated the problem. C.S., Windsor, Ont.


Q: I have a customer who wants us to put THREE coats of our TGIC powder paint onto his sheet metal parts. That seems like a disaster waiting to happen. We cure the paint at around 350°F (the max our oven will go to). Do three coats sound reasonable? What is the maximum paint thickness recommended with these powder paints? J.B., Tulsa, Okla.


Q: Just wondering if you can help with a problem we’re having with our powder not attracting to our parts. As far as we can tell, we’re getting a good ground on our parts that are hanging in our booth, but when we spray the powder on the parts, you can see powder just kind of falling off. And if we try to spray in corners or anywhere there is a bend, the powder won’t stick. This is causing us to overspray the parts to get full coverage, and the powder is very thick after the parts are baked. Our operator for our powder coating said it looks like the powder wants to attract directly to the booth instead of the parts. We’ve tried adjusting our settings on the powder coating machine, but nothing seems to help. Your help would be appreciated. C.M., Lewiston, N.Y.


Q: Are there cool powders? We powder coat aluminum extrusions for making doors and windows, and we want a powder that will reflect the infrared radiation, and the window will remain cool. Let me know how they work and where I can buy them. L.K., Piraeus, Attica, Greece


Q: We’re coating automotive components and are in the process of trying to complete a new order for coating shock absorber springs for motorcycles. The powder is repelling from the inner side of the spring in some areas and pin-holing. Because we try to reach the inner side to coat it, we get excessive coating on the outer portion, which isn’t acceptable to our client. What should I do to resolve the coating problem for the inner side of the spring? S.D., Aurangabad, Maharashtra, India


Q: I was wondering if you can paint over a powder-coated surface. If so, which type of paint is better–enamel or acrylic? Thanks in advance. S.J., North Ryde, New South Wales, Australia


Q: What percentage (maximum) of recovery powder can be mixed to virgin powder with the same characteristics or same appearance after baking? What are the advantages and disadvantages of recoating parts such as rejects and how many coatings could be applied? V.M., Quezon City, Rizal, Philippines


Q: We are a small effect powder coater and thermal barrier (ceramics, etc.) applier in Germany. We also sell powder coating machines as a niche product solution for small shops. We are always trying to get a perfect solution for sealing our coatings. We are now at a pretty good stage where we use an industrial one-component nano clear seal (wet paint) that is also cured at 180°C (356°F) for half an hour. Do USA coaters have experience with coatings like that? Can you tell me which powder producers supply powder coatings that produce a real chrome look that can be sealed without fading into yellow or gray? M.W., Luebeck, Germany


Q: We currently run three lines with automatic spray guns and a reclaim system. My question concerns particle size. When does the particle size become a safety concern? What’s the best method of rotating recycled powder so that it doesn’t become a safety hazard or affect the chargeability/transfer efficiency? I thank you for your assistance. J.A., Kowloon, Hong Kong


Q: I have just had my engine and exhaust powder coated. The engine is okay so far, but the down pipes have bubbled up. Why is this? Many thanks. D.D., Cirencester, England


Q: I’m interested in getting feedback on coating plastic. A lot of people are looking at coating plastic based on heating the plastic first. I think there can be irregularities not only in the film build, but also in the gloss and surface of the powder, smooth or textured. Just wanted to let you know, you give great information. C.J., Markle, Ind.


Q: I have some automotive headers and would like them to be powder-coated in flat white that will sustain header heat. I know of ceramic coatings, but that is another process. Any suggestions? B.P., St. Paul, Minn.


Q: We cut, drill, and buff extruded aluminum parts in a variety of shapes in-house and then powder coat them. We’ve had a higher number of rejects than usual lately because of aluminum chips on the parts. We paint a lot of metallic and mica powder. We installed bag filters and 250-micron filters in screens, but we still see aluminum chips on the parts (under and over the paint). We noticed aluminum flakes and other airborne dirt floating in the cure oven. The aluminum chips show up only on aluminum parts and not on steel parts. What do you recommend we do to determine the cause? Is it coming from the wash, the spray-gun tip, or oven airflow or vibration? K.M., Holland Landing, Ont.


Q: Where can I get a powder production process manual? What is the most recommended warehouse storage temperature? J.E., Apodaca, Nuevo Leon, Mexico


Q: What’s the best way to get rid of used powder when we spray to waste? Is there anyone that uses this powder? Right now we put it in the dry-off oven until it gets hard, then throw it away. J., Peoria Heights, Ill.


Q: What’s the most effective way to remove old powder coating without having to invest in chemical process equipment? I’ve tried media blasting with coal slag, chemicals called “stripper” in an aerosol can, and aircraft paint remover in a liquid form. Most of the products I powder coat are new steel or aluminum, which I prep by media blasting. This is the first time I’ve had to deal with already powder-coated parts. It’s a pain! Are there different removers for steel and aluminum? D.K., Bagley, Minn.


Q: I have a part that has two issues. First, the part is stainless steel. Second, it requires 10 to 15 mils of paint. What issues can I expect when powder coating stainless steel, and how difficult will it be to achieve the thickness spec? B.S., Toronto, Ont.


Q: What temperature should galvanized steel reach when degassing it before powder coating over it? S.M., Louisville, Ky.


Q: We’re looking for a material that could be machined and used as part of our powder racks for masking areas of product where no powder is allowed. Masking a part is too costly. We would like this protection to be part of the racks. We have the ability to machine and build special racks. We have a standard powder process with a five-stage washer. We cure parts up to 475°F in our cure oven. B.J., Jasper, Ind.


Q: After powder coating, especially with black color, the powder coating becomes white after a period of time. The parts are mild steel. M.A., Mafraq, Jordan


Q: I was wondering if you have any idea where we could have independent testing done on some aluminum parts. We have reports of the paint peeling off aluminum rails and need to find out why this is occurring. The powder we’re using is a custom color through our regular powder distributor, which is the only color we’re having trouble with. I’m hesitant to have the distributor test the powder because I’m not sure how impartial it would be. I thought of our chemical company, but if it’s a problem on that end, I may not receive accurate information either. Any information you can provide will be appreciated. B.F., Hamilton Township, N.J.


Q: We’ve had to put on some 2-inch pieces along the top rail of a trailer. When we powder coat it, we seem to blow the powder off the inside instead of making it stick. We’ve tried to move the gun farther away, and we lowered the airflow. The ground seems to be okay while the rest of the trailer is coated. I’m sort of at a loss here. It’s just a very tight space, and there isn’t a way for us to coat it unless we get the gun down inside of that space. A.B., Hugoton, Kans.


Q: Our company specializes in fabrication of aluminum doors and windows. Seven years ago we opened a powder coating plant. Now our finished product produces a ring, or crater, throughout the surface of the aluminum. My question is how to solve this problem. A.N., Dammam, Kingdom of Saudi Arabia


Q: Some of our customers ask for a color change over already powder-coated parts. We have noticed that some parts accept the deposit; others don’t. Why? Is there anything you can recommend to activate the powder coating before recoating with another coat of powder? A.M., Caguas, Puerto Rico


Q: We’re having some issues with parts that have to be spot-welded. The process creates a mark on the metal. This dragging mark bleeds through the powder coating only on light, smooth colors. We had this issue occur 2 or 3 years ago, and I blamed it on the spot-weld process. Now, I’m not sure. I hope you can give me an idea of what’s causing this. Thank you very much. N.M., Brea, Calif.


Q: What happens when you spray a powder marked tribo with a corona-charging system? I’ve special-ordered a powder from the US for a very important and rush job. The label says tribo. Just wondering if I can still spray the powder with my corona-charging system. B.D., Calgary, Alta.


Q: We’re processing cold rolled steel (CRS) panels that have been spot-welded with cosmetic spot welding tips. We prep the panels by grinding away the raised spot welds and then by finishing with 120-grit paper. We’re using a white urethane-based polyester powder coating, and our base metal temperature is 400°F for 10 minutes for full cure. The problem is we’re seeing spot welds after the coating is applied. Is there a filler that works for powders? We’ve tried some in the past with very limited success. D.W., Salt Lake City, Utah


Q: I have a problem. Some of the powder overspray has gotten on car upholstery, and I would like to know of a way to remove it. The temperature in the car was high but not enough to set the powder completely. We’ve tried many different things and nothing has worked. We need your help ASAP. R.D., Salt Lake City, Utah


Q: We currently apply wet coating systems for miscellaneous equipment in industrial markets and have batch oven capabilities for curing phenolics, epoxies, vinyl esters, and fluoropolymer-type coating systems. We’re considering getting into custom (large, heavy, non-line) powder coating systems, such as zincs, epoxies, and TGIC-based polyesters, and would like to know what the downfalls of using some of our existing processes and equipment would be. Currently, we blast-clean items to a minimum of SP10 or NACE 2. We don’t have a pretreatment system other than solvent cleaning and blasting, and our original paint booth wasn’t designed for powder applications. Based on some of the responses I’ve read before in your columns, I can just imagine what’s going through your head. Can this be done, or should we look at having two different setups for applying wet and powder materials? Looking forward to your reply. T.M., Ontario, Canada


Q: I’ve heard that powder booth cartridge filters can be cleaned and reconditioned. Is this true? If so, how good a job will they do after cleaning? Do you know of anyone who does this? N.N., Statesville, N.C.


Q: I’m having a problem with the powder coating looking like it has dirt in it. You can rub your hands across the surface and feel the imperfections. I’m preheating all my items before applying the powder. Any help would be great. R.G., Mooresville, N.C.


Q: I just had a custom lumber rack built for my truck, and the builder left out two small angle braces. Is there any way these pieces can be added, and the powder coating touched up without sandblasting the entire rack? T.S., Sebastopol, Calif.


Q: I had a lower unit for an outboard motor powder coated recently. When I picked it up, it had what looked like small busted bubbles (pores) in the coating. The guy who did it said it was from the metal (aluminum) having pores in it. Is this guy BSing me because he did a poor job, or is it true? I wasn’t satisfied with his work, but he said it was unavoidable due to the metal condition. This condition isn’t over the whole piece but just in various places (some of them in places where I know the metal was smooth). E.W., Anacoco, La.


Q: Has anyone power coated stainless steel air conditioning and power steering lines for automobiles? I want to have the stainless powder coated in a flat black finish. Any help will be appreciated. J.M., Poland, Ohio


Q: We manufacture and powder coat threaded assemblies for our finished product. We’re having trouble controlling the powder thickness on these parts. We have explored caps and tape, and would prefer a different method. Is there a liquid or paste inhibitor we can apply to the threads to keep powder from sticking to them? J.B., Cerritos, Calif.


Q: I actually have a couple of questions. First, I recently had an issue with various parts all having paint flake off. I could take a razor blade and cut and actually pull flakes up. I’ve been unable to recreate this situation. Has anyone had this happen? I’ve had the powder, chemicals, and steel all tested. Nothing is standing out. Second, in an effort to cut costs and maximize throughput, we’ve been shutting our ovens down with parts in the line. Even though nothing is currently happening, are there any unforeseen issues by doing this? J.H., Pompano Beach, Fla.


Q: Can Class A terminology be used for a part that is to be powder-coated? I know that parts can be prepped and cleaned to be Class A, but can they expect the actual paint to have any imperfections at all? As far as I know, this terminology can’t be used for powder because it can’t be controlled as easily as liquid paint can. L.E., San Jose, Calif.


Q: I’ve been coating automotive wheels for years, mostly older steel wheels from classic car restorations but also newer wheels. I’ve been hearing lately that aluminum alloy wheels shouldn’t be powder-coated because the curing temperature and dwell time make the aluminum wheels brittle. I have also seen feature articles in the magazine about companies coating wheels but no mention of this problem. Is this true and are there other coating methods that can be used to overcome this problem? K.W., Westminster, Md.


Q: We’re powder coating 18-gauge Galvannealed material. We’re cleaning with a five-stage washer and powder coating with a black wrinkle epoxy. We’re seeing bubbling and fingerprints coming back through the powder. We use infrared heat and are manually spraying the powder. Is there something we can do to prevent this? This material has given us trouble in the past. K.M., Cedar Rapids, Iowa


Q: Is it possible to apply a powder coating over satin chrome or high-polished chrome-plated parts? If we could, it would save us a lot of money in rework and scrap costs. However, some of our parts are hand-operated, and we don’t want our decorative finishes to start peeling after several years. R.C., Steeleville, Ill.


Q: We powder coat in two facilities, and our safety director is directing us not to use compressed air to clean off ourselves after applying powder. I guess OSHA (Occupational Safety and Health Administration) will site us for this practice. I’m curious how others in our industry are cleaning off afterward. I have an air-operated vacuum, but it’s so powerful, I’m afraid it would be more dangerous than compressed air. M.G., Iron Mountain, Mich.


Q: We have an aluminum frame that has gold chromate conversion coating under the powder and masking lines. We have to re-powder coat the part. The part was powder-coated twice, and the customer doesn’t like the finish. The part came out with heavy texture and a rough finish. We had to sand and re-powder coat, and the gloss ended up being dull and sandy feeling. L.B., Springfield, Mass.


Q: We recently coated machined aluminum parts with many holes of different sizes with a flat, beige polyester powder. The surface immediately surrounding the plugs was bumpy. The second time we coated this same part the customer purchased the plugs from a different vendor and cut the plugs flush with the surface, but the results were the same. We cure at 400°F for 15 minutes; we’ve had the problem with other parts and think the plugs are made from silicone. Is there a reaction between the plugs and the powder? How can we correct the problem? Thank you in advance. P.L., Cleveland, Ohio