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And Now for Something Completely Different

Written by: Nick Liberto P.E., Powder Coating Consultants, Division of Ninan, Inc.

I am sure that some of you will recognize this quote from BBC program Monty pythons flying circus (circa 1970s). I was always a big Monty python fan. Their English humour was particularly witty and sophisticated. I especially liked the one show they did a skit on how to be the village idiot .It showed that no matter how absurd your profession may be .one could take pride in doing it well . That kind of describes the life of a consultant; often we don’t get much respect but solving difficult problems is a rewarding profession.

You may be asking yourself, “Why is Nick using this as the title of this month’s column?” Well it best explains the category of some questions that I get over time that are not really related to main-stream powder coating. Over the past few months when I get a question that does not fit the highly technical question and answer column format that we have established here for the last ten years, I set it aside. This issue I have decided to deal with all of them at one time. I hope you, the reading audience, get a chuckle from the humour I use to answer these slightly “off-the-wall” requests for in-formation. Now bear with me while I get a little silly.

ELECTRIC CHARGE DAMAGING GALVANIZED COATING

Q. Would the galvanized coating on a traditional chain link fence be expected to be damaged, beyond the obvious burn areas, by an electrical charge from a 7,200 volt primary electric line (30 seconds on and 30 seconds off)?

A. What???? Wait let me adjust my TV set…Nope it didn’t help. I have no idea what to say. Did you get a wrong number…this is the Powder Coating Clinic.

My only hope is readers can help me out with an answer.

POWDER COATING PERSPEX

Q. I am student at the Arts Institute at Bournemouth, currently undergoing my final major project where I am designing and making a light from Perspex pieces. I was wondering if it is possible to powder coat the pieces so color can be added? Is this possible with Perspex or does this technique only work with metal?

A. Ok, I have only one question for you—how did you get my e-mail address?

When did I loose control over my technical Q & A column for manufacturers and end-users of powder coatings. Oh well, I always wanted to be a college professor.

Ok, this one took a little research. Normally I am able to provide answers without any research, but not this time. Perspex is a product from Lu-cite and is used in a variety of applications (i.e. signage, etc.). When visiting their web site, I noticed this material is available in a wide range of colors. So this brings my first question: “Couldn’t you have just chosen the color you wanted in the first place?”

I also noticed on the Lucite web site that this plastic based material has a melt point of 110°C. This makes powder coating this material problematic since most thermoset powder coatings have melt points higher than this. Unless, of course, this is the look you want a melted coated piece of plastic?

POWDER REMOVAL USING PAINT STRIPPER

Q. I was reading your page on powder removal and was wonder if a regular automotive paint stripper would do the job. Thanks.

A. Ok. Now I sense a conspiracy…I have definitely lost control of my column.

Common automotive strippers are applied cold (ambient) and depend upon their chemical composition to soften a coating for removal. This is a problem since most powder coatings are highly chemical resistant. This is why most applicators of powder coatings use hot chemical strippers, thermal oxidation (burn-off), or mechanical stripping methods (blasting, sanding, or grinding) to remove powder coatings.

I highly doubt that you can find an over-the-counter automotive paint stripper that can remove a powder coating. But who knows, maybe you can.

SITTING ON THE FENCE

Q. I have a small fence (wire mesh) factory in Israel. I have been trying for a while to coat a garden fence with PVC powder. I built an oven and coat my product in three steps:

  1. Warming fence (so that the powder will melt on the fence).
  2. Coating with PVC powder
  3. Fence cooling

This process is different then the four-steps process I have read about in other article on the web site.

My problem is on step two. I can’t make the PVC layer to be even. There are parts of the mesh with a thick layer of coating and parts of the mesh with a thin layer of coating. I don’t use a spray gun because it’s a different process. I’m looking for some mechanism that will make the powder to hover in the small room and cover the hence in an equal layer.

I have tried to put the powder in some chamber and under the chamber to put a vent. The problem was that the powder didn’t hover: I hope you can help me.

Thank you very much for reading my e-mail.

A. I put you in this special column of “unusual questions” because your question makes me won­der how you are applying a powder that is not atomized (hovering). My imagination is running wild with thoughts of a fan and shovel to disperse the powder onto the hot part as it passes by.

The method of powder coating that you are de­scribing has been around for almost as long as the part of the world you live in. It is called fluidized bed powder coating. This process uses a fluidized bed to atomize the powder coating. A hot part is immersed into the bed, the coating is attracted to the part and melts on contact. Cooling afterwards allows this process to produce a part that is not still tacky from melted thermoplastic powder. The key component to this process, besides the oven you already have, is the fluidized bed. Without one, you cannot disperse the powder enough for even film thickness control.

A fluidized bed is a chamber that has a plenum beneath a fluidized plate (membrane). A com­pressor or a high-pressure blower introduces air into the plenum below the fluidized plate. This air passed through the plate and into the powder con­tained in the upper chamber, which will atomize it into a fluidic condition. Aggressive fluidization can create a cloud above the chamber. Wire products, like your fence, can be passed through this cloud for even powder deposition . The cloud must be controlled by an evacuation system to prevent the powder from going all over your plant. This evacu­ation system will use fabric bags or paper filters to separate the powder from the containment air, prior to reintroducing this air back into the plant.

These systems are available from a variety of manufacturers. I recommend that you purchase a complete system from someone who has the experience in designing and building these systems instead of building one yourself.

METALLIC POWDERS

Q. Is it possible to powder coat using metallic powders? If so, what powder particle size is required? Are there special set-ups for metallic powder? I want to apply nick­el and cobalt-base powders that would subsequently be ]used at around 2,200°F.

A. I am sorry, but there is no one available to an­swer your question right now. Please call back an­other time, when there is someone here. Thank you for your patience and we look forward to serving you in the future. Good-bye.

EPILOGUE

Just so that you don’t think I am a total jerk, I called the last questioner and gave him his answer on the telephone. It just does not make sense to print this answer in the magazine.

See you all next month, when my silliness fit will be over and we can get back to the more typical questions on powder coating and my usual insight­ful answers.

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