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 fence 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. O. S.
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.
For more than 50 years, fluidized beds have been used to coat parts with powder coatings. In this article, two industry experts tackle some common questions about the fluidized bed process…
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