Top Five Powder Coating Mistakes to Avoid
Recognize and prevent these common slip-ups.
Powder coating is a popular method of applying finishes to appliance parts. Unlike conventional paint or e-coat, powder coating is a solvent-free process, emitting zero or near zero volatile organic compounds (VOCs). Overspray can be recycled as well, virtually eliminating waste. Moreover, powder coating offers a wide variety of colors and textures for a uniform and long-lasting finish—that is, if the powder is properly handled, stored, and applied.
appliance DESIGN spoke to Jason Partain, technical manager at IFS Coatings, about the biggest powder coating mistakes he’s seen on the job and how to prevent them.
Failure to Prevent Contamination
“The number one defect of any defect in the appliance world is contamination,” Partain says, “something getting on the part, either before or after the powder is applied, and showing up later.” It could be lint, hair, thread, or even the tiniest speck of dirt. But outside of automotive, appliance OEMs are notoriously picky about their parts being contamination-free, Partain says, and they will notice that speck you may have tried to hide.
Most top-tier appliance OEMs often have their own coating lines and Class A facilities, Partain notes, where the technology is up-to-date and managers are proactive in ensuring that the environment is spotless. The powder coating rooms in these facilities use filtered air and positive pressure, meaning that air flows out of the room instead of into it. That way, “you’re not sucking in dirty air through the doors and windows where the parts come in and out,” Partain explains.
The tunnel going up to the oven also uses filtered air and positive pressure, Partain says, to nix the possibility of other contaminants from the outside air or from the air within the rest of the plant from coming in. Additionally, appliance OEMs often prefer gel infrared or IR ovens for the powder coating process. These ovens gel an appliance part immediately out of the powder coat booth, so if there is some debris in the air, it’s not as likely to stick to the part.
Another easy way to prevent contamination is sheltering the conveyer chain from the part below it, Partain says. Over time, dirt inevitably collects in the chain, builds up, and falls out. “To fight it, you put out a sanitary pan,” Partain says. “From the time the part comes out of pretreat to the time it gets to the oven, there should be a pan under that conveyer that would catch anything that falls out of the chain. A lot of people don’t do it, and a lot of people find dirt defects on their parts.”
Partain says he’s also seen powder applicators that run Class A services require their employees to wear lint-free jump suits and hairnets, for the simple reason of not getting lint or hair into the system. “I don’t know how many times I’ve analyzed a defect,” he says, “and I can take a guy’s jeans or hat, knock a little thread off of that, put it under a microscope, and see that it’s the exact same piece of thread in the defects that are coming out on the parts.”
Most importantly, Partain believes that any powder coating facility must take steps in advance to keep parts clean through the entire powder coating process. “Take the initiative upfront to make sure that the pretreat is filtered well; then, after pretreat, that part never needs to see the light of day,” Partain says. “That part needs to be in a controlled oven and on a controlled path with positive air pressure and filtered air, all the way to the powder room.”
Failure to Properly Clean Equipment
“Preventive maintenance is expected if you want to run a Class A facility and produce a Class A product,” Partain explains. This starts by maintaining a daily housekeeping schedule and daily maintenance requirements, and cleaning out pumps, hoses, and electrostatic guns on a routine basis. “If you don’t, you will start getting buildup in the hoses and guns,” Partain says. “And then that buildup breaks loose, shoots out of your gun, and ends up as a spot on your part.”
Partain describes seeing employees at facilities he’s visited take their pumps apart at the beginning of each shift, and insert no-go gages in them to see if the pump inserts are worn out. “They also pull their hoses out, take their guns apart,” Partain says. “For a good shop, that’s a daily routine. Sometimes it’s a by-shift routine, depending on how many shifts they have and how much volume they run.”
The regular cleaning of ovens, unfortunately, happens less often. As a former process engineer with 22 years of experience in the appliance coatings industry, Partain says he remembers when powder applicators used to clean their ovens every three months. These days, he says, people will tell him they haven’t cleaned their oven in five years.
“It just kills me that people don’t clean their ovens anymore,” Partain says. “Granted, the first day [after cleaning] is probably the biggest day of rejects, because you’ve stirred up some stuff. But I promise you: If you don’t clean your oven, you’ll get to a point where it’s the middle of the week and your defect rate is going up and up, and then you’ll be in trouble—because you’ll have to wait until the weekend to clean it, or wait until there’s downtime.”
Partain’s advice is to at least sweep or vacuum your oven every now and then, just to make sure there’s no buildup—because buildup equals defects waiting to happen.
Allowing Line Stops in Pretreatment
One of Partain’s biggest pet peeves is when people leave coating lines loaded between shifts, or leave parts on the line when they go home after their last shift.
“A pretreat is set up to run as a continuous process: to keep the part wet throughout so that each stage of the process can do its job,” he explains. “The minute you shut that down, those parts dry out and surface rust starts. There are no ifs, ands, or buts about it: The minute there’s no more water on that part, it’s going to start rusting.”
Looks can be deceiving, Partain adds, because one could take parts off the line, coat over them, and they’d still look great. “You’d never know at the end of that line whether it’s a bad part or a good part,” he says. “But throw that part on a washing machine that gets detergent and water in it constantly, and there’s a very good chance that it will fail before it should, because you have a layer of surface rust under that powder—and it’s just a matter of time before that rust is going to come through.”
Keeping an Incorrect Temperature Relative to Humidity
Seventy degrees Fahrenheit and 50 percent relative to humidity should be the goal for any powder room, Partain says, though plus or minus 5 to 10 degrees is usually okay. Eighty degrees is usually the level he calls out as being too hot for powder storage.
“Powder loves moisture; with a little humidity, the powder applies better,” Partain adds. “But when you get to too much humidity, the powder starts sticking up inside the gun, and you get impact fusion in the pumps, hoses, and guns.”
While too much humidity causes issues with powder application, so does too little—like in the wintertime, when you walk across the floor and you feel an electrostatic charge with everything you touch, Partain says. On those days, the electrostatic gun won’t emit a charge as well, which messes with the powder’s ability to stick to a part.
Fortunately, Partain has a solution to this particular problem. “I used to have my guys mop the floor in the wintertime, three times a day, and I could see a difference in a mil on our parts—most coatings are 2 to 3 mils thick in the appliance world,” he explains. “When we mopped the floor, all that moisture would evaporate into the air, which would make the powder apply better.”
Overall, Partain suggests keeping the temperature of a part consistent. “The more consistent you can make your surroundings, the more you can dial in your operations to run as efficiently and as cost-effectively as possible,” he says. Regulating the temperature to coat at precisely the right thickness, for example, can reap huge financial rewards.
“People don’t realize how much a half a mil can cost you if you apply too much coating, like if you apply 3.5 mils instead of 3, all year long,” Partain comments. “I had a $400,000 cost savings in my liquid operations for taking just a tenth of a mil off.”
Overcuring or Undercuring Parts
Discoloration is a common problem with white appliance parts, and improper curing is usually the reason why. If you overbake a white, it’s going to yellow up a bit, Partain says, while undercuring will make white parts appear bluer.
Sometimes, undercuring is not as detrimental as overcuring, as one could simply put the part back in the oven until it reaches a full cure. But with matte colors that are 30 gloss, undercuring would put them at 50 or 60 gloss. “So, yeah, you can recure it,” Partain says. “But ‘Did you recure it too much?’ becomes the question.”
Another tricky color is black stainless, which is comprised of a tinted clear coat. “You want to see through the black stainless coat: to see the substrate, the stainless steel, underneath,” Partain says. However, the thickness of the coat decides its darkness, and so it can be tough to cure to perfection with this color as well.
To combat these issues, Partain advises running constant checks: “measuring air [and metal] temperature across the whole part to make sure it’s meeting its requirements.”
And yet, as is often the case, there may be multiple different powder suppliers working side-by-side in the same facility—which presents another host of issues. “Obviously, we’re not all using the exact same products, so my cure schedule could be slightly different than theirs,” Partain explains. “Very seldom is there just one powder supplier working in one facility anymore, which again brings up the issue of contamination from one product to the next. Cross-contamination of colors—in a booth, in a room, or in an oven—is a big issue.”
Newer systems usually have multiple measurement areas for temperature within an oven, Partain notes, but in some of the older ovens, there is one point where it measures temperature, the set point. “Let’s say your set point is 380, and you have a problem over in the corner—something shifts in the duct work, or the duct work falls off,” he says. “When that happens, you can get a cold spot in the oven real quick and not know about it, without running a data pack to find out.”
One way to eliminate this annoyance, is to run data packs on a set schedule, whether that’s monthly or quarterly. “I’m running a data pack for my customer tomorrow morning,” Partain says. “All they want to know is if their oven is doing all right.”