Electrostatic spray is a common application method for Rilsan® Fine Powders. It allows for pinpoint control of surface thickness and ensures more comprehensive coverage of the workpiece.
What Is a Fluidized Bed Coating Process?
Powder coating is an easy way to ensure metal parts and components are protected by a paint-like coating with a premium consumer feel. A fluidized bed is one of the easiest and most efficient application methods for these powders. This coating process involves preheating and dipping a metal part into a fluid bed of the suspended polyamide 11 thermoplastic powders. The powder particles then melt onto the surface of the metal part, creating a consistent thickness on even the most complex parts and profiles.
Why Use Fluidized Bed Powder Coating?
The fluid bed method of applying a powder coating may be more advantageous than a spray application coating process. Using a fluid bed, the coating finish is highly reproducible, and the entire process can be automated to maximize productivity. The other major benefit of using a fluid bed is the incredible efficiency; 100% of the polyamide powders are transferred during the coating process. Here are the other factors to monitor when selecting this powder coating method:
Thickness of the part: Fluidized bed powder coating is ideal for parts at least 3mm thick. For smaller wire articles, a post-fusion operation may be required after the dip-coating step.
Thickness of the coating:Fluidized bed coating with Rilsan® powder allows for a coated thickness between 250 to 500 μm. If a thicker coating layer is desired, increased dipping time or successive dipping operations can be implemented.
Size of the part: The dimension of the coated part will dictate the required size of the fluid powder bed.
Nature of the substrate: A fluidized bed coating solution will work with any material that can withstand the preheating temperature requirements (280°C – 300°C).
Fluidized Bed Powder Coating Equipment
Three main pieces of equipment are required to use a fluid bed powder coating process; a fluidizing tank, an air exhaust, and a preheating oven.
Typically stainless steel, this multisection tank contains a powder chamber, porous tile membrane, and secondary chamber where ambient, clean air can be vented through the powder bed, simulating a liquid state.
It is highly recommended that a powerful exhaust fan system be installed near the top of the tank to capture any dust or powder particles that could contaminate the immediate environment.
A forced-air circulation oven is recommended for preheating metal parts prior to coating. It has a minimum air flow of 6 m/s and can heat up to 330°C for large parts and 420°C for thin parts or wire components.
Fluidized Bed — Coating Solution Process
1. Surface Treatment: Any metal parts or components should be thoroughly cleaned and primed with one of the engineered solutions from Arkema. These primers not only increase the surface adhesion of the powders, but also provide additional corrosion protection. 2. Preheating Step: To ensure proper adhesion of the nylon coating the metal parts need to be preheated in an oven to the appropriate temperature (280°C – 330°C for large parts or up to 420°C for thin parts or wires). Trial temperatures and dipping times are recommended for new processes to pinpoint the desired coating finish. 3. Masking: If there are any areas on the part that do not need to be coated, they can be masked with removable caps, tapes, pastes, or mineral fibers. 4. Handling and Coating Touch-up: The dipping hanger or jig should be fastened to the part to allow for shaking and clear movement. When possible, it is recommended to affix the hanger to a section of the part that does not require coating. It is possible to touch up hanger marks with a suitable epoxy or polyester resin coating.
Powder Coating Defects and Potential Root Causes
Insufficient surface preparation
Too little or too much primer
Incorrect preheating temperature or time
Bubbles or Bubbling
Degassing of part
Primer layer too thick
Air inclusion due to excessively long dipping time