Weekly Questions and Answers

By George Trigg, GRT Engineering
and Nick Liberto, Powder Coating Consultants

Welcome to Powder Coating magazine's Weekly Questions & Answers column. Questions for this column are submitted by powder coaters just like you who are seeking ways to improve efficiencies and solve every day problems on their powder coating lines.

9/28/2015 - Q: I have a customer who has no set quality procedure in place for inspecting coated items. The customer is rejecting items for flaws in the appearance after using a flashlight to find them. Is there a procedure set by a powder coating authority that I can use to demonstrate to this customer what should be rejected and what should pass? We don’t have a clean room, and the customer isn’t willing to pay for that service. A.N., Monroe, N.C.

A: I feel sympathy for you and disgust at your customer for not having specifications. There are as many generic specifications as there are companies. I don't know of any standard that you could use for reference. Using a flashlight is completely out of line, especially with no set standards. I could say shame on you for taking on a project that has no specifications for the coating, but I won't say that. If you want to maintain this account, I recommend that you request a meeting with your customer’s pertinent personnel and state your case for the establishment of specifications. In some cases, even with specifications you can get divergent ideas on what is acceptable, so with no spec you’re aiming at a moving target. You have every right to say to the customer that without specs, whatever it is you’re coating is acceptable. If the customer wishes to create a spec, then you need to review it and confirm whether you want to coat the parts to that standard. Everyone has to be on the same page about that. You don't use a flashlight for highlight. You can view the part under standard lighting, move the part for a good view, and determine if there is a reject. Specifications can be written for what size defect is allowed and how many are allowed in an established dimension. Your customer should create this list. The customer should also be reminded that he can demand a part that is so perfect that he can't afford to have it painted. Your customer has to come to grips with his "standards" versus how much he will pay for meeting these standards. At the same time, you should review how much work there is available to justify installing a clean room. Having a clean room isn't a guarantee that all parts will be dirt-free however. —G.T.

9/21/2015 - Q: Is there a company that will come out to facilities and safety-inspect conveyor lines for stress fractures? I’m worried that as time goes on the conveyor line, which is welded to the trusses throughout the ceiling, may fail or even the ceiling itself may fail—or both. J.O., Des Plaines, Ill.

A: You could contact any of the better known conveyor companies to perform an inspection. (See the magazine’s Online Buyer’s Guide.) It will cost you whatever rate they charge for field engineering work. You could also contact a civil engineering company to do the same thing. They should be capable of determining what or if any damage has been done. Your issue is why I always strongly recommend that nothing, especially a conveyor, is ever welded to the building structure. You should use clips that bolt to columns or rafters or whatever piece of building structure you need to use.

The problem with welding to the building columns or trusses is that stress will occur from movement of the building and the conveyor. You should consider having the inspection and then modifying the connection points. While you’re at it, if you haven’t checked the conveyor rail, you should inspect all wear points and replace rail sections as necessary. Check incline and turn radii through the washer and any other places that stress may occur. —G.T.

9/14/2015 - Q: I’m interested in powder coating torsion springs in which the coils of the springs touch each other. I have two questions: 1. Will powder penetrate between the coils that are touching each other? 2. Will the powder chip off of the coils if the coated coils are rubbing against each other? J.R., Millbury, Ohio

A: Maybe. The powder may migrate between the two springs IF they are barely touching. However, even if they do touch, the motion of the springs will rub a bare spot where they touch. It doesn’t matter what type of coating you apply to the parts. When the two pieces touch, especially when driven by the weight of some type of vehicle, you’ll get only bare metal. What difference does it make anyway? The motion will always keep the metal shiny, and torsion springs as I know them will be too thick to ever rust to the breaking point. Rust would only occur if the vehicle sits idle for an extreme period of time, and the first few times the two springs move against one another, the rust will be abraded away. If you want the pieces to look pretty for a short time, you should be able to do that, but the coating won't last very long. —G.T.

9/8/2015 - Q: I need to use a palette of more than 200 customized colors on relatively large MDF (medium-density fiberboard) products. Can powder coatings be mixed to create new colors? How controllable is this? What is the minimum area of a certain color batch to make it convenient and easy to change colors? I'm afraid changing colors will take a lot of time and hence money. Thank you in advance for your reply. A.L., Montevideo, Uruguay

A: You can’t mix colors in powder coatings and achieve the kind of blended color that you can mix with liquid coatings. The powder particles don't flow together to blend into another color. Instead, you’ll get a salt-and-pepper look. For example, if you mix a black and a white, you won't get gray, you’ll get black and white. I'm not quite sure what you mean by a "certain color batch." If you mean purchasing different colors, then it would depend on the powder supplier and what standard colors are in inventory. If you want something special, it will cost you to have a color made up. If standard, off-the-shelf powder coatings would work, then it depends on availability. If you reclaim powder in your existing booth, then color-changing will be a bit time-consuming, and you’ll need a separate color module (filter section). If you’re spraying-to-waste, then it won't make any difference except for the time it’ll take to clean out the hopper, hoses, pumps, and guns. A great deal depends on the type of spray booth you now have. Time equals money, and you’ll definitely spend time cleaning up the previous color before you make a change. As a result, you’ll have lost line time while you were making the change. And if you reclaim, you’ll need another color module, as I mentioned. If you only have a few pieces, it won't be cost-effective. —G.T.

8/31/2015 - Q: I would like to know if there is an effective way to specify and accurately measure powder coating textures? I’m currently examining establishment of a worldwide powder coating standard specification for our company. How do multiple powder coating vendors worldwide control texture? S.H., Greensboro, N.C.

A: There is no standard for texture in powder coatings. There are standards for smoothness (Powder Coating Institute Smoothness Standards), but these don’t cover textures, only different degrees of orange peel. We have even tried to establish texture standards for clients by using surface roughness measurements (that is, media blast profile methods). However, these only provided the height of the texture and not the shape (sharpness or roundness) of the texture. Therefore, the only accurate way to specify the amount of texture is to use color-panel standards. This means you maintain and supply actual coated test panels that show the color and texture you require for your coating.

These standard panels are attached to the purchasing document, along with any other coating performance standards, when you’re selecting coatings or contracting for coating services. These standard panels will provide the color, gloss, and texture for your product and can be matched by the coating formulator or the coating contractor. They should be communicated to both the coating supplier and outside coating contractor, as application variables will affect the texture on your actual product.

For instance, the sharpness or roundness of a particular texture can be influenced by the applicator of the coating. Applicators can apply the coating at thicknesses that are outside the range provided by the coating formulator, causing the texture to be remarkably different than expected or formulated. Therefore, even if you have a powder that is properly formulated to provide the amount and style of texture you need, you must be sure that the applicator coats your product within stated limits to attain this final texture on your actual product. —N.L.

8/24/2015 - Q: I apply a TGIC-based (triglycidyl isocyanurate-based) polyester powder coating over electrocoat (e-coat) on a carbon steel substrate. The e-coat meets automotive specifications as this is the primary customer of my e-coat vendor. My problem is that the parts, which are mostly flat, have been coated for about 1 year, and the powder coating (not the e-coating) is losing adhesion and peeling off. What’s the proper method of cleaning and treating the e-coated parts before application of the TGIC-based powder? My e-coat vendor and powder coater aren’t the same, and I’m trying to find the answer as I'm sure one will point the finger of fault at the other. F.L., Johnson City, Tenn.

A: There shouldn’t be any issues with coating over e-coat, as if you didn't know. Most e-coat applications are designed to have some type of top applied, be it powder or liquid. My first and foremost question would be about the gloss of the e-coat. If you can get your hands on a gloss-meter, take a reading on the e-coat. Then, spray out a sample of the powder on a test panel and check adhesion. Do the same with an e-coated panel and then a powder-coated panel. I know this sounds redundant to you, but humor me. Moreover, check the material safety data sheet (MSDS) to see if the gloss rating is listed. After you know all of this, ask your e-coat supplier to visit your plant. Show the supplier the test panels and the rejects from your customer. My guess is that the material is too high in gloss so that there is no inner-coat adhesion. In my experience with this coating technology, the cured e-coat was sent directly to the powder system without washing or conditioning of any kind. Washing the e-coat won’t normally cut the gloss or condition the surface to accept and adhere to the topcoat. Sanding might get you out of trouble in the short term. If it does, that likely proves that the e-coat is the issue. —G.T.

8/17/2015 - Q: I currently have a set of very expensive magnesium wheels that were powder-coated white by a previous race team. I would like to refinish the wheels myself. Can you recommend a blast media and powder-coat process including bake times and temp for a backyard mechanic like myself? I subscribe to your magazine and would like to get started with this project but more on an entry level without investing in commercial-grade equipment. I would like to show off the car with the statement that I restored the wheels myself. P.F., Dearborn, Mich.

A: I think if I had some very expensive wheels for a show car, I would want them recoated by a professional shop. But that's just me. You should try a plastic media, or maybe glass, not metal. The media should be very small so as not to affect the surface appearance of the wheel. The bake time and temperature is the responsibility of the powder supplier. You don't want an extremely high bake temperature because of the potential effects on the magnesium. —G.T.

8/10/2015 - Q: Is there any special paint I can use to repair chips and scratches on oil-rubbed bronze powder-coated aluminum in the field? R.B., Addison, Ill.

A: Touch-up coatings are available for most powder coatings. These come in a variety of types (spray cans, liquid pens, small bottles with brushes, etc.). Selecting which touch-up device depends upon the amount of repair that is necessary. For instance, very small chips can be touched up by using the pens or small bottle/brushes, while larger areas require spray cans.

Having said all that, touch-up on rubbed bronze may be very difficult, depending upon how the look was first created. If it’s a single-coat process, then any touch-up paint provided by the supplier will work. However, if it’s a multi-step process, using a combination of plating or a different base and topcoats, performing touch-up will be near to impossible without having a noticeable repaired area. —N.L.

8/3/2015 - Q: We’re wondering if anyone has had a positive experience in high-pressure power washing of paint conveyor hooks and chain? If so, please pass on your solutions. M.L., Wyoming, Mich.

A: Be assured that high-pressure washing won’t clean powder coatings from hangers and hooks if they've been through the oven. As for the conveyor chain and rail, high pressure will clean off the uncured powder, but I wouldn't advise doing this in or near the spray booth because of the mess. As for cured powder, I'm not aware of any high-pressure wash system that will remove it. —G.T.

7/27/2015 - Q: What’s the best way to get powder to stay in tight corners, and what causes the powder equipment to shoot a glob of powder out of a gun every so often? K.G., St. Louis, Mo.

A: The powder isn’t going into the tight corner because of the Faraday cage effect. From an electrostatic point of view, the nearest point to the gun electrode will be the point to which the gun discharges, or grounds. In the case of corners, the nearest points are the sides of the part you’re spraying. To complicate things further, when you are aiming the spray gun into a corner, the atomizing air tends to blow away any accumulated powder, making the situation worse. There are various ways to improve the situation, from the no-expense side to a change in application equipment. Reducing the air and the voltage is the first and easiest way to get around the Faraday cage effect. You can also back the gun away just a tad, especially if it's an occasional issue. If you spray a lot of corners, then you may want to look at a tribo-charging gun. As for the clumps coming from the gun, there can be several reasons for this. One is moisture in the powder usually caused by not having a working air dryer on the compressed air system. High humidity in the atmosphere can cause lumping when the hopper, using good dry air, is turned off for a time, and the conditions in and around the coating application area are moist. This moisture will agglomerate the powder (make it lumpy). You may have some powder plugging in the pump, the feed hose, the gun, or the gun tip. Any or all of these will emit lumps of powder, which invariably make their way to the part and cause a defect in the coating surface. From a performance standpoint, the lumps don't really hurt anything, but they look bad and indicate a lack of maintenance to the system in most cases. —G.T.

7/20/2015 - Q: We’re currently powder coating a compressed metal seat and can’t get the powder to cover the runs in the metal. We’re using a polyester powder that should cover it. Any suggestions? We need help! J.L., Mt. Clemens, Mich.

A: If you have imperfections in the metal, such as holes or crevices or dents, or if you have ridges, pimples, or whatever, don't expect the powder to act as a metal repair kit. Any coating--powder or liquid--will only follow the contour of the part. So, if you have a crack, for instance, the powder will flow into the crack, but it won't fill it and then come out smooth. You’re going to have to prep your surface to smooth it out first before you apply the finish. —G.T.

7/13/2015 - Q: Like any shop, we do some recoats when the first coat is rejected, be it some pickup or light paint. When we do recoats, we handle it with gloves, sand it, blow off the piece, and wipe with isopropyl alcohol. When we try to repaint the piece, it appears to have streaks where the powder won’t stick (like bare spots where it was touched by hands with latex gloves or wiped). I have had this problem before, and it stopped when I heated the product up after handling and then waited for it to cool before powder coating it. I’ve tried to suggest this to my supervisor, but he thinks it’s something else and not from handling the piece. But I can see clear finger marks, and I even wrote numbers on the product with the gloves, and the paint wouldn’t sit where I did this. I’m just wondering what this is and if I’m right in saying to heat it up, or rinse it in cold water and dry it or let it sit after handling for a period of time to prevent this from happening. J.M., Langley, B.C.

A: You know the old saying: “Believe nothing that you hear and only half of what you see.” This proverb applies here, as well. However, it doesn’t say ignore what you see. To that end, if you see handprints or fingerprints under the coating, then they’re there no matter what your boss says.

Gloves often give people a false sense of security. The type of gloves and the frequency between changing them are two factors that affect the protection you obtain by using them in the first place. The best gloves are lint-free cotton gloves (preferably white in color). Change the gloves often, especially when the white color is stained or dirty. Lint-free cotton is comfortable and ensures that the operator doesn’t have an allergic reaction or deposit lint onto the surface.

Latex gloves have powder to keep them from sticking to each other and to make them easier to put on your hands. This powder can be a source of contamination. Besides, latex gloves are very uncomfortable to wear, especially when it’s warm and your hands are sweaty.

Recoats need to be handled differently than virgin parts. The surface must be completely cleaned after the defect has been removed (by sanding or stripping). Often, the entire surface needs to be scuff-sanded to ensure proper adhesion to the topcoat. All the dust must be removed and the surface completely cleaned before applying the next coat. Don’t use tack-rags, as they can often leave a residue on the part surface that will prevent the powder coating from adhering to the part (not a problem with liquid coatings, as the solvent will penetrate this contaminant).

Denatured alcohol is good, if you change the rag and solution frequently. Using a dirty rag and contaminated alcohol will just reapply the soils onto the part. Using the alcohol directly from the can on a clean rag is best, changing the rag areas often to ensure cleanliness. —N.L.

Further reading on the problems discussed in this column can be found in our Article Index and Bookstore.

George R. Trigg is president of GRT Engineering, 6314 Hughes Road, Prospect, OH 43342; 740/494-2496. He has been involved in the powder coating industry for more than 38 years. He holds a BSBA degree from Muskingum College, New Concord, Ohio. His email address is molly95@earthlink.net.

Nick Liberto is president of Powder Coating Consultants (www.powdercc.com), a division of Ninan Inc., 1529 Laurel Avenue, Bridgeport, CT 06604; 203/366-7244. He has more than 3 decades of experience in the powder coating industry. A registered professional engineer in Connecticut, he holds a bachelor’s of science degree in mechanical engineering with a minor in physics. His email address is pcc@powdercoat.com.

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