Costs and volatile organic compound (VOC) emissions can be reduced by using a powder coating system instead of a wet spray painting system.

Background

Powder coating is the application of a dry, powdered resin to a surface. The resin is typically a thermosetting (polyurethane, acrylic, epoxy, etc.) or thermoplastic (nylon, vinyl, etc.) resin which is electrostatically applied to the surface of a part. Application is done with a spray gun or fluidized bed. The coated part is then heated and the melted resin flows to form an unbroken film. When cool, the film exhibits properties often exceeding those achieved by conventional painting methods.

Spray Application Equipment The most common application device is the air-powered, electrostatic spray gun which uses compressed air to propel the powder from the gun to the part. The corona-charging spray gun creates an electric field between the spray gun and the workpiece. Powder passing through the electric field picks up the charge and is directed by the field. The tribo spray gun imparts a charge directly to the powder as it passes through; there is no forward-projecting electric field between the

spray gun and the workpiece. The advantage of the tribo gun is that it allows complex shapes to be painted and reduces overspray.

Powder is contained in a hopper or a barrel and is fluidized by blowing compressed air through it. While still suspended in the air, the powder is then carried to the spray gun inside a flexible hose. The most simple systems are self-contained and fit onto the top of the powder shipping drum.

Fluidized Bed Another type of application equipment is the fluidized bed. Metal parts are heated and passed through a fluidized bed of powder resin. The powder is fluidized by blowing air through it. The powder resin melts and cures to the part as it passes through the bed.

Cleaning and Pretreating Equipment When companies are considering switching from wet painting to powder coating, existing cleaning systems should be evaluated to determine their suitability. The key to choosing the correct equipment is to determine what level of cleanliness is required that will result in high quality finished parts. Some powder suppliers can perform quality tests on sample parts to determine if the finished coating meets required specifications.

Other Equipment A method of curing is required when powder coating. Curing ovens used with wet paint systems are often suitable for powder coating operations. Additionally, a burn-off oven or other hangar cleaning method will probably be needed to remove cured coating from hooks and hangars.

Equipment Costs Equipment costs can range from $2,000-$5,000 for a drum mounted powder supply and spray gun to $100,000-$200,000 for a powder coating booth with a powder recovery system.

Raw material costs for powder coating may be lower compared to wet painting, primarily due to higher utilization rates. Since the powder does not contain solvent carriers which dry in air, overspray can be recycled back into the paint system when using a paint booth. Application or utilization rates of 95 percent are achievable with powder coating compared to less than 60 percent with wet paint.

However, powder coating systems can be very time consuming to clean when color changes are required. All of the old powder must be removed from the system before the new powder can be started. Equipment duplication may be a cost-effective solution to this problem.

Energy costs associated with curing are also typically lower for powder coating operations. Since powder coating does not emit significant organic solvents when drying, the amount of air exhausted from the curing oven can be reduced.

Additionally, powder coating does not generate hazardous waste from cleanup. Cleanup of powder coating spray guns and booths usually can be done using a vacuum cleaner or compressed air instead of hazardous solvents.

Avoided hazardous disposal costs associated with cleanup can be significant. For example, a wet paint operation generating six 55 gallon drums of paint waste per month could expect to pay $40,800 annually for waste raw materials and disposal costs. (Assuming each drum contains 10 gallons of waste paint at $20 per gallon and 45 gallons of solvent at $1.50 per gallon, and a disposal cost of $300 per drum).

Finally, VOC emissions from powder coating are very low. Powdered resins contain less than one percent by weight VOCs compared to 15 percent for water-based paints and 66 percent for conventional wet paints.