Powder Storage

We store our powder in an open plant environment with no control of the atmosphere. We have some problems with particles in the finished film that we think are seeds. Our powder supplier says that storing the powder with no humidity control can cause agglomerations and that is part of our problem. Is this true? What temperature and humidity can the powder handle without a problem?

The plant environment that encircles the powder application process may have many contaminants that can be detrimental to a quality finish on a powder coated part. These can include airborne oils from press and machining operations, dust from grinding and packaging operations, and many other forms of particulate. Any or all of these contaminants can cause problems with quality finish and system efficiency in your powder operation.

High heat and humidity from ambient temperatures and the ovens and washer can be detrimental to the powder application and reclaim systems, creating inefficiencies and excessive maintenance. High humidity and temperature can cause the powder to stick together in clumps and resist fluidization and flow. Agglomerations in the powder may cause protrusions in the powder film.

Seeding is the formation of small agglomerates or gel particles that can form in storage or when the material is overheated during the extrusion process. Seeds can also be protrusions in the film due to small, solid contaminants that do not melt during the cure process.

To help control the environment and limit the impact of dirt and moisture, it is advisable to store and apply powder in a controlled environment. Powder application rooms are designed to isolate the powder application process from the plant environment and control the temperature and humidity. Powder coating suppliers typically recommend temperature and humidity control or 65°F to 85°F room temperature and 40 percent to 60 percent relative humidity. This prevents the powder from absorbing moisture and compacting.

If the powder is stored in an uncontrolled plant it can sometimes be dried out in the fluid hopper. A clean, dry supply of compressed air is a general requirement a powder coating system. Fluidization of the powder with clean, dry compressed air in the feed hopper can precondition the powder and break up agglomerations.

Powder Adhesion on Fillers

Do you know of any type of body filler (putty, fiberglass, bondo) that powder will stick to? I run a powder coating line and apply powder manually using a box feed system. It is baked on with a conventional gas flame oven. Hopefully you can help me out.

There are some filler materials currently available for repair of substrates to be powder coated. The repairs that can be touched up with these fillers are pits, voids, scratches, etc. The fillers are typically applied by use of a spreader or spatula, then are either air-cured or oven cured. You would have to check with the manufacturer of these products to determine their electrical conductivity and if the fillers meet the specifications that you are looking for. I'm sure that the manufacturers of these products would encourage testing before committing to the use of fillers in a production environment. Here are a few supplier suggestions with phone numbers and URL addresses to help get you started.

  • Alvin Products offers Lab Metal. Phone: 978-975-4580; Web: www.alvinproducts.com
  • Devcon offers Titanium Putty. Phone: 508-777-1100; Web: www.devcon.com/fevcon familyproduct.cfm?familyid=124
  • Dura-Chem Inc. offers Thermobond-3. Phone: 800-447-5008; Web: www.dura cheminc.com/powder coating14.html
  • National Coating Systems offers Elcon 920 Plastic Metal. Phone: 937-746-7632; Web: www.nationcoatingsystems.com/id27.html.