Powder Coating with a Fluidized Bed

There’s no beating the beauty and durability of a high-quality powder-coated part. There’s just something about the look and feel of the finish that goes far beyond mere painting and makes it worth the effort and expense. The typical electrostatic spray powder-coating setup can be expensive, though, and not necessarily suitable for every workpiece.

Enter the fluidized-bed powder coating chamber, perfect for limited runs of small parts, and the brainchild of [Andrew Mayhall]. With a business providing furniture kits based on iron pipe, [Andrew] needed a way to finish flanges and fittings, and powder coating provided the best look. The fluidizer he built is a great alternative to spray coating; it blows air through a bed of fine thermoplastic granules, which causes them to act like a fluid. It’s similar to the fluidized-bed hot tub we recently featured, but on a much smaller scale and with different requirements based on the ultrafine particle size and aggregation properties of the powder. [Andrew] had to add mechanical agitation to achieve a homogeneous fluid bed, and after much experimentation he’s now able to dip preheated parts into the bed and achieve one-step powder coating. The video after the break shows some of the operational details.

Does electrostatic powder-coating sound like more of your thing? No problem – DIY solutions abound, and a homebrew oven to bake your parts may be as close as the nearest file cabinet.

16 thoughts on “Powder Coating with a Fluidized Bed

    1. Redhatter, I know, I know. I filmed this quick and dirty style with my iPhone just to get it done. I’m usually not one sharing my projects but I figured I should start and just get out there. My future videos will be of better quality I prmise! Thanks for the like!

  1. too bad there is no showing of the actual powder coting with this thing. The pictured coated flange would not make me very proud.
    Do you drop in a hot part in the bed to get it to stick evenly, or is there another way yo get an even layer?

    1. Jelle,

      I plan on uploading a video soon about the process and a detailed look of the finish. Fluidized powder coating usually ends up in a thicker layer than your spray based process. This means some smaller details like embossed text, symbols, or in general small features being “washed” out.

      As for the first part of your question: Yes, the parts are hot around 260 degrees F [127 C]. Any lower than about 250 F and the powder won’t stick or won’t stick well. This changes with specific powders though so some trial and error is required. Additionally, higher temperatures usually result in better more even coverage. I did find that if the part is near the recommended cure temperature of the powder their tends to be clumps and uneven melting on the part leaving an awful finish. So there is a happy medium in there that you just need to find though experimentation.

      Thanks for the critiques!

  2. Neat project. Feels like it needs a bit more work to flesh out the practical concerns that arise from this process though if being used regularly.

    Curious about how well contained these typically polyester, hybrid or epoxy powders are being handled here. Fluidizing them can be sort of like making a powder coating machine that doubles as a particle dispensing machine. This can be mitigated in several different ways though.

    Most powder coatings are desired to have a particle size in the range of 2 to 50 μ. Breathing these in doesn’t strike me as a very good idea at all, particularly on a regular basis. Plus, the epoxy and hybrid epoxy powders mean you are probably breathing in Bisphenol A, also known as BPA. Even worse.

    Lastly, does this result in unusually heavy powder coating or is there a way to vary the coating thickness at all?

    1. Thank you!

      You point out some excellent concerns about the operation of a system like this. It is true that during the operation there tends to be a decent amount of aerosolized powder which obviously is no good. On the occasions I have used this system I am always wearing a respirator and typically using some type of fume extraction.

      In commercial systems, compressed air jets blow off any excess powder from a finished part and break up that aerosolized “cloud” of powder. Additionally, there is typically a vacuum system just above the surface of the fluidized powder to scrub the air further. These vacuums will usually employ some sort of centrifugal separator to recycle the powder with a decent efficiency.

      As for other types of powders, polyesters are by far the best for fluidizing in my experience. I have tried hybrid epoxy with some good results but these types of powders typically have very high particle and molecular interactions. Even with agitation, they have been difficult to fluidize in my setup. I am still experimenting though and I hope to have some more success in the near future.

      The finish provided by this method of powder coating is indeed heavy and thick. In my experience, there are several variables that can be adjusted to acquire tinner or thicker coatings with the temperature being the best control. 260 degrees F [127 C] is the best temperature that works with the particular powder that I am using. Higher temperatures result in more even coverage but usually provides a thicker coating as it melts more powder more rapidly. Although with lower temperatures a post-dip cure is required to flow out and cross-link the powder.

      1. Respirator or fume extraction seem like very good ideas. Commercial systems to recycle the powder seem marginally useful, depending on the amount of powder lost in use.

        My experience has been that polyester or polyurethane powder coatings work better than epoxy or hybrid ones, at least for my applications. Though I have not tried to fluidize them so I cannot really speak much about that.

        Would it be possible to vibrate (ultrasonic or mechanical) the part after coating it or work with some type of electrostatic system instead that might help with the density or powder retention? It looks like you are basically putting hot parts in and then letting it cure, rather than the more traditional methods of electrostatically applying then baking?

        Perhaps a series of very quick “dips” of a hot part in a highly fluidized bed (more like a cloud) could be useful? Sort of akin to CVD, except with powder and heated parts? Just throwing around ideas here and they may not have any merit at all.

        1. On a similar line of thought: could you wire the part to a Van de Graf or something and dip it with less heat to increase the coverage of a thinner coat then finish curing with further heat?

          1. That’s sort of what is done without a fluidized bed in traditional powder coating. You use static to adhere the “paint” particles then basically just bake the part in order to polymerize everything together.

            Until the coating is heated and allowed to cool, the coating is very easy to wipe off though. That would be my primary concern here. A fluidized bed and all of the air circulation might be enough to disrupt it from being evenly coated but it would certainly be worth trying it and seeing what it does.

            It also might be possible to quickly super coat it like this, static it and then “blow” the part to remove excess powder that had not yet melted on? I can certainly see at least a few different things worth trying here.

  3. Interesting. I’ve recently bought myself a kiln and had wondered about powder coating small parts like this but was put off because of the need for an electrostatic gun but this method seems a lot more convenient for small items (a lot less messy).
    I wonder how well the powder survives over time? (Thinking of analogous techniques but with flour on food – you often end up with random small lumps in the dry powder)

  4. Powder coating is the hot “glue” of paints. No primer, no adhesion, just sexy looks till tiny cracks and edges delaminate with rust being the zipper pull. If a primer could handle the heat?

    In a $5 million downtown project we have attractive bike racks for 2 embedded in the brick and concrete walks. The powder coating starts to show rust at exit from the surface within one year. The city breaks the racks loose and coats the pipes at the bottoms and reinstalls them like new with a black coating sticking up a few inches on the grey hammertone finish of powder coat. Within a year those coatings have failed and now bike use and locks and chains have knocked many holes into that hammertone finish which can’t be painted without stripping the plastic off first.

    How easy it is to crack thin plastics!

    1. Depends on the plastic chemistry being used and environment it is expected to be in. What type of powder did they use? Presumably a polyurethane type of powder would hold up much better to mechanical and environmental damage (such as exterior, public bike racks).

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