9/7/2010
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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.
A: Coating of plastics is a challenge, and I find it interesting that some people seem to think they have an answer and others don't. Sometimes, just a minuscule thing makes the difference. When I was working on an experiment for a plastic car body, we tried a liquid spray-on material that was purported to enhance electrostatics. If it did, we didn't notice it, and preheating of the parts became a necessity. We worked many long hours trying to arrive at a proper preheat temperature. Part of the problem was, immediately after preheat, we had to get the body into the powder booth. Well, the powder booth needed to have the reclaim blower on, so it was introducing ambient air under force, which began to cool the part. Allowing for this made for a lot of trial and error on the correct preheat temperature. We sprayed powder with the electrostatics on because the fan pattern was enhanced by the electrostatic field. This effort helped in uniform distribution of the powder. The powder film was within 0.03 mil from side to side on the car body. There are companies that are applying powder coating to plastic bottles. The bottles are on a spindle and rotate, so application is relatively simple. The bottles are preheated in some cases. In other cases, they’re sprayed with the aforementioned electrostatic enhancer. Each of the companies thinks its way is best. Well, who knows. Gloss and powder surface will be affected by the thickness of the plastic because of reinforcing or just plain variances in the plastic. This will show up directly in the powder, usually where preheating is the attraction for the powder.
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8/30/2010
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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.
A. High-temperature organic materials are available. Even though these materials are designed for high temps, they’re good for only so long before they will begin to burn. That’s one of the reasons the serious show car exhibitors trailer their vehicles. The pipes never get to sustained high temps.
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8/26/2010
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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.
A: There aren’t different strippers for aluminum and steel that I know of at least. A myriad of companies claim to have metal strippers. Some work, some don't. The two most effective ways to clean cured powder from a part is by burn-off (not good for aluminum, depending upon the parts) and chemical. Stripper in a can absolutely won't work as you have apparently found out. The hot-sand method is a variant on the burn-off method. Parts are placed in a container with sand in it and a burner tube. The sand fluidizes, and the heat aids and abets the sand in removing the coating. You’re finding out why, when properly applied, powder is such a good coating. Depending upon the number of parts you have to strip, search for a stripping company in the area and have the company chemically remove the coating. Once the powder is removed from the aluminum, make sure the parts are cleaned of any residuals. Then, pretreat and paint immediately. Aluminum will begin to create its own patina very quickly, and this will negatively affect the adhesion of the paint you’ll apply.
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8/16/2010
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Q: If I’m heating angle iron that has been powder-coated, and the angle iron has to reach a temperature of 400°F before I start the hour- and 15-minute timing process, how do I know when the angle iron reaches 400°F? B.W., Bullard, Tex.
A: I'm not sure where you’re getting the hour- and 15-minute time. Typically, you powder coat the part. The oven is set at 400°F, and the part is at ambient temperature. The part is placed in the oven with a minimum of heat loss at the opening. The powder manufacturer has provided a stat sheet that states cure is 10 minutes at a certain temperature. Therefore, depending upon the size of the angle iron, you allow some minutes for bring-up time/temperature, then 10 minutes cure, and then remove the part from the oven and allow it to cool. If you have some good oven data, you can assume the part is cured. To be certain, run a solvent cure test with methyl ethyl ketone (MEK). See the article “Cure dynamics of powder coatings,” November 2008. Click on Article index, subjects, curing. See also “PCI Recommended Procedure No. 8” at [www.powdercoating.org]. Now, you either have to buy or somehow procure an oven recorder. Place the probes on the part as instructed, and put the part and the recorder in the oven to see what feedback you get. You only have to do this once or twice to get a feel for how long a given part will take to reach cure temperature and cure out. Anything less than an oven recorder, and you’ll be guessing. If you don't have access to a recorder, then you can place a part in the oven, wait 10 minutes plus (or whatever the stated cure time/temperature is), remove the part, and run the cure test. That's the old-fashioned way, but it still works. You just have to experiment. I don't know who told you an hour and 15 minutes, but that's too long, and wastes time and money.
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8/9/2010
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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
A: Stainless steel comes in several finishes. The most common is a high-gloss surface. Less common is a muted finish. I don't suppose you’re lucky enough to be coating the lower-gloss material. This material is friendlier to paint than the high-gloss finish. As a result, for a lasting finish, you should scuff-sand the area that is to be coated; otherwise, the finish will scratch easily, and the paint will begin to peel. Then the part will look awful. From a painter’s viewpoint, I don't know why people want to go to the expense of using stainless and then painting it. The combination doesn't go well together. On top of that, you need heavy film thickness. My, oh my. You realize that there will be a prominent orange peel appearance to the finish, don’t you? That will be caused by the heavy film. Okay, depending upon the designed film thickness of the powder you’re using, you’ll probably have to build the film in several passes. Trying to get the coating that thick in one pass will most likely create "starring," or kilovolt rejection. You can apply about 4 mils, maybe 5, in one pass. Place the part in the oven and set the powder, then coat again. Continue until you get the desired film thickness. It certainly would help if the powder is designed for heavy film build. If that’s the case, then you may be able to achieve the thickness in no more than two passes. If you’re going to use an off-the-shelf material, it may require multiple passes. This won’t be a cheap application. I hope that you’ve made your customer aware of the cost.
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8/3/2010
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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.
A: I know of no material that will resist powder coating and serve as a mask at the same time. The problem is that some things you could use, such as petroleum jelly (shudder), will cause horrendous problems in a powder coating shop. Will petroleum jelly keep the powder off the area? Sure, but then it has to be cleaned off, to say nothing of the contamination problems it would cause. Plastics, such as nylon and a dozen other synthetics will protect the area and survive the heat, for a while, but they have to be cleaned or tossed out and replaced. Exotic metals? They would still draw the electrostatics, and they’re too expensive. So, here are several suggestions. You probably won't like some of them. You can powder coat first and then machine. It's done all the time (on engine blocks for example). You can vacuum away the powder from the critical area. This works nicely when the person doing it cares, or if you’re lucky, you can automate. Maybe the critical area can be shielded by something on the hanger. Bad news here is if it needs to be a tight fit, it probably can't be done. And the hanger will need frequent cleaning. Don't even think of making a moving piece as part of the hanger because that will get powder coated and cease to function. I suspect you’ll just have to bite the bullet and try some version of the above mentioned items.
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7/26/2010
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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.
A: The most common reason for a coating to peel off of a substrate is poor metal pretreatment. Actually, that’s about 95 percent of the reason. If you have failure on aluminum, that percentage rises to about 99.9 percent. You have to clean aluminum before coating it. You don't say what process you’re using, if any, but a description of your current system would be enlightening. There are several sources for testing parts or panels. One is the paint guy. Another is the pretreatment guy. And another is an independent laboratory. The latter is very expensive, which makes one or both of the previous two attractive. I could find a lab for you, but be prepared to pay in the four-figure range for the lab services. If you’ll send a description of your current metal prep method, maybe I can at least eliminate some things that could be at the root of the problem.
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7/19/2010
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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.
A: That's the best way unless you can find someone who’ll buy it from you. Finding these people isn't easy because it usually requires some type of sifting or filtering system to clean up the material. If you have a lot, maybe you should consider a reclaim system for high-use powders.
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7/12/2010
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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.
A: There aren’t different strippers for aluminum and steel that I know of at least. A myriad of companies claim to have metal strippers. Some work, some don't. The two most effective ways to clean cured powder from a part is by burn-off (not good for aluminum, depending upon the parts) and chemical. Stripper in a can absolutely won't work as you have apparently found out. The hot-sand method is a variant on the burn-off method. Parts are placed in a container with sand in it and a burner tube. The sand fluidizes, and the heat aids and abets the sand in removing the coating. You’re finding out why, when properly applied, powder is such a good coating. Depending upon the number of parts you have to strip, search for a stripping company in the area and have the company chemically remove the coating. Once the powder is removed from the aluminum, make sure the parts are cleaned of any residuals. Then, pretreat and paint immediately. Aluminum will begin to create its own patina very quickly, and this will negatively affect the adhesion of the paint you’ll apply.
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7/6/2010
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Q: If I’m heating angle iron that has been powder-coated, and the angle iron has to reach a temperature of 400°F before I start the hour- and 15-minute timing process, how do I know when the angle iron reaches 400°F? B.W., Bullard, Tex.
A: I'm not sure where you’re getting the hour- and 15-minute time. Typically, you powder coat the part. The oven is set at 400°F, and the part is at ambient temperature. The part is placed in the oven with a minimum of heat loss at the opening. The powder manufacturer has provided a stat sheet that states cure is 10 minutes at a certain temperature. Therefore, depending upon the size of the angle iron, you allow some minutes for bring-up time/temperature, then 10 minutes cure, and then remove the part from the oven and allow it to cool. If you have some good oven data, you can assume the part is cured. To be certain, run a solvent cure test with methyl ethyl ketone (MEK). See the article “Cure dynamics of powder coatings,” November 2008. Click on Article index, subjects, curing. Now, you either have to buy or somehow procure an oven recorder. Place the probes on the part as instructed, and put the part and the recorder in the oven to see what feedback you get. You only have to do this once or twice to get a feel for how long a given part will take to reach cure temperature and cure out. Anything less than an oven recorder, and you’ll be guessing. If you don't have access to a recorder, then you can place a part in the oven, wait 10 minutes plus (or whatever the stated cure time/temperature is), remove the part, and run the cure test. That's the old-fashioned way, but it still works. You just have to experiment. I don't know who told you an hour and 15 minutes, but that's too long, and wastes time and money.
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6/28/2010
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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
A: Stainless steel comes in several finishes. The most common is a high-gloss surface. Less common is a muted finish. I don't suppose you’re lucky enough to be coating the lower-gloss material, which is friendlier to paint than the high-gloss finish. For a lasting finish, you should scuff-sand the area to be coated; otherwise, the finish will scratch easily, and the paint will begin to peel. Depending on the designed film thickness of the powder you’re using, you’ll probably have to build the film in several passes. Trying to get the coating that thick in one pass will most likely create "starring," or kilovolt rejection. You can apply about 4 mils, maybe 5, in one pass. Place the part in the oven and set the powder, then coat again. Continue until you get the desired film thickness. It certainly would help if the powder is designed for heavy film build. If that’s the case, then you may be able to achieve the thickness in no more than two passes. If you’re going to use an off-the-shelf material, it may require multiple passes. This won’t be a cheap application. I hope that you’ve made your customer aware of the cost.
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6/21/2010
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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.
A: I know of no material that will resist powder coating and serve as a mask at the same time. The problem is that some things you could use, such as petroleum jelly (shudder), will cause horrendous problems in a powder coating shop. Will petroleum jelly keep the powder off the area? Sure, but then it has to be cleaned off, to say nothing of the contamination problems it would cause. Plastics, such as nylon and a dozen other synthetics will protect the area and survive the heat, for a while, but they have to be cleaned or tossed out and replaced. Exotic metals? They would still draw the electrostatics, and they’re too expensive. So, here are several suggestions. You probably won't like some of them. You can powder coat first and then machine. It's done all the time (on engine blocks for example). You can vacuum away the powder from the critical area. This works nicely when the person doing it cares, or if you’re lucky, you can automate. Maybe the critical area can be shielded by something on the hanger. Bad news here is if it needs to be a tight fit, it probably can't be done. And the hanger will need frequent cleaning. Don't even think of making a moving piece as part of the hanger because that will get powder coated and cease to function. I suspect you’ll just have to bite the bullet and try some version of the above mentioned items.
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6/14/2010
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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.
A: The most common reason for a coating to peel off of a substrate is poor metal pretreatment. Actually, that’s about 95 percent of the reason. If you have failure on aluminum, that percentage rises to about 99.9 percent. You have to clean aluminum before coating it. You don't say what process you’re using, if any, but a description of your current system would be enlightening. There are several sources for testing parts or panels. One is the paint guy. Another is the pretreatment guy. And another is an independent laboratory. The latter is very expensive, which makes one or both of the previous two attractive. I could find a lab for you, but be prepared to pay in the four-figure range for the lab services. If you’ll send a description of your current metal prep method, maybe I can at least eliminate some things that could be at the root of the problem.
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