POWDER COATING PAINTING SYSTEM
|Overview:||Powder coating paint systems, also
referred to as "dry painting", eliminate volatile organic compounds
(VOCs), hazardous air pollutants (HAPs), and solvents, and produce
superior surface finish.
There are four basic powder coating processes: electrostatic spraying, fluidized bed, electrostatic fluidized bed, and flame spray. Electrostatic spraying is the most commonly used powder application method. For all application methods, surface preparation (i.e., cleaning and conversion coating) is required to develop a good coating adhesion substrate. Characteristics of the four different powder coating application techniques are described below.
In electrostatic spraying, an electrical charge is applied to the dry powder particles while the component to be painted is electrically grounded. The charged powder and grounded workpiece create an electrostatic field that pulls the paint particles to the workpiece. The coating deposited on the workpiece retains its charge, which holds the powder to the workpiece. The coated workpiece is placed in a curing oven, where the paint particles are melted onto the surface and the charge is dissipated.
In a fluidized bed, powder particles are kept in suspension by an air stream. A preheated workpiece is placed in the fluidized bed where the powder particles coming in contact with the workpiece melt and adhere to its surface. Coating thickness is dependent on the temperature and heat capacity of the workpiece and its residence time in the bed. Post heating is generally not required when applying thermoplastic powder coatings. However, post heating is required to cure thermoset powder coatings completely.
Electrostatic fluidized beds are similar in design to conventional fluidized beds, but the air stream is electrically charged as it enters the bed. The ionized air charges the powder particles as they move upward in the bed, forming a cloud of charged particles. The grounded workpiece is covered by the charged particles as it enters the chamber. No preheating of the workpiece is required. However, curing of the coating is necessary. This technology is most suitable for coating small objects with simple geometry.
The flame-spray technique was recently developed for application of thermoplastic powder coatings. The thermoplastic powder is fluidized by compressed air and fed into a flame gun where it is injected through a flame of propane, melting the powder. The molten coating particles are deposited on the workpiece, forming a film on solidification. Since no direct heating of the workpiece is required, this technique is suitable for applying coatings to most substrates. Metal, wood, rubber, and masonry can be coated successfully using this technique. This technology is also suitable for coating large or permanently-fixed objects.
The choice of powders is dependent on the end-use application and desired properties. Typically, powders are individually formulated to meet specific finishing needs. Nevertheless, powder coatings fall into two basic categories: thermoplastic and thermosetting. The choice is application dependent. Generally, thermoplastic powders are more suitable for thicker coatings, providing increased durability, while thermosetting powders are often used when comparatively thin coatings are desired, such as decorative coatings. The principal resins used in thermoplastic powders are polyethylene, polyvinyl, nylon, and fluoropolymer. Thermosetting powders use primarily epoxy, polyester, and acrylic resins.
Powder coating virtually eliminates waste streams associated with conventional painting techniques. These waste streams include air emissions, waste streams generated from air emission control equipment, and spent cleaning solvents. Powder coating also greatly reduces employee exposure, and liabilities associated with liquid coating (wet solvent) use. Because the powder is dry when sprayed, any overspray can be readily retrieved and recycled regardless of the complexity of the system This results in shorter cleanup times. In all cases, the dry powder is separated from the air stream by various vacuum and filtering methods and returned to a feed hopper for reuse. Powder efficiency (powder particles reaching the intended surface) approaches 100 percent. Other advantages over conventional spray painting include greater durability; improved corrosion resistance; and elimination of drips, runs, and bubbles.
Powder coatings are somewhat limited in their application to aerospace equipment. They typically are not used with primer systems that inhibit corrosion, but they can be successfully applied over many primed and pretreated metal substrates. If primers or pretreatments are not used, the powder coating provides protection as a barrier and prevents corrosion only as long as it is intact and undamaged. The temperatures required to cure the coating are too high for many materials used in aerospace structures (primarily aluminum); however, recently developed formulations allow baking as low as 250 degrees F which enables the use of powder coating on most materials. Powder coating can be implemented in high-production facilities with highly automated application systems or on low volume, manual batch applications. The Air Force installed the first DoD high production automated powder coating facility at Kelly AFB in 1997. In addition, there is currently an initiative to use powder coatings on aircraft landing gear at Hill AFB.
|Compliance Benefit:||Use of the powder coating painting
systems results in the following compliance benefits:
Compliance benefits include: 1) reduction or elimination of recordkeeping and reporting requirements under the Title V Operating Permits Program, NESHAP Program and SARA programs; 2) reduced administrative burden associated with hazardous waste (i.e., tracking, plans, reports, training); and 3) reduced administrative burden associated with OSHA (i.e., training and recordkeeping).
The compliance benefits listed here are only meant to be used as general guidelines and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g., the amount of workload involved.
|Materials Compatibility:||Only workpieces that can be
oven heated are suitable for coating by electrostatic, fluidized bed, and
electrostatic fluidized bed application methods. Hence, these technologies
tend to be most appropriate for relatively small, metal objects. Large
standard and customized ovens are commercially available, however, for use
on components of significant size.
As with all coatings, powders require a well prepared, clean surface for optimum adhesion and protection performance. Primers and pretreatments are not necessary, but additional surface preparation (for example, iron phosphate for steel, zinc phosphate for galvanized or steel substrates, and chrome phosphate for aluminum substrates) will enhance the performance of powder coatings.
|Safety and Health:||Powder and air mixtures can be a
fire hazard when an ignition source is introduced. The concentration of
powder in air must be controlled to maintain a safe working environment.
Despite the absence of flammable solvents, any finely divided organic
material, such as dust or powder, can form an explosive mixture in air.
This is normally controlled by maintaining proper air velocity across face
openings in the spray booth. In the dust collector, where it is difficult
to maintain the powder concentration below the lower explosive limit,
either a suppression system or a pressure relief device must be
Inhalation of the powders should be avoided, as this can cause irritation to the lungs and mucous membranes. Proper personal protective equipment should be used.
Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.
|Economic Analysis:||The following economic data and
basis was provided by the Powder Coating Institute, using estimates
provided by Kelly Air Force Base concerning the amount of paint used per
year. It compares a conventional solvent-based coating system to a powder
coating system. The conventional system includes two water wash spray
Annual Operating Cost Comparison for Powder Coating System and Conventional Coating System
Economic Analysis Summary:
Click Here to view an Active Spreadsheet for this Economic Analysis and Enter Your Own Values. To return from the Active Spreadsheet, click the Back arrow in the Tool Bar.
*There are multiple MSDSs for most NSNs.
The MSDS is only meant to serve as an example. To return from the MSDS, click the Back arrow on the Tool Bar.
|Approving Authority:||Appropriate authority for making process changes
should always be sought and obtained prior to procuring or implementing any of the
technologies identified herein.|
Technical Orders are the source of authority for all paints used on aerospace equipment by the Air Force. The process for thermal plastic coatings and materials is contained in T.O.1-1-8, but the use of it requires approval by the engineering authority of the specific Weapon System Manager or Equipment Item Manager within the Air Force.
|Points of Contact:||For more information|
|Vendors:||This is not meant to be
a complete list, as there may be other manufacturers of this type of
INNOTEK Powder Coatings
Finishing Customer Support Center
300 Nordson Drive
Amherst, OH 44001
Phone: (800) 433-9319
FAX: (888) 229-4580
Service: Equipment Manufacturer
P.O. Box 88220
Indianapolis, IN 46208
Phone: (800) 628-0601
FAX: (317) 298-5010
Service: Equipment Manufacturer
|Rohm & Haas Powder Coatings|
Reading, PA 79720
Phone: (610) 775-6611
FAX: (610) 775-6645
Service: Coating Manufacturer
|Cardinal Industrial Finishes|
Powder Coating Division
1329 Potrero Ave.
South El Monte, CA 91733-3088
Phone: (626) 444-9274 or (800) 995-4431
FAX: (626) 444-0382
Powder Coating Spray System - P2 Equipment Program
Ms. Monique Speers, CH2M Hill (on-site Kelly AFB) conversation, January 2000.|
Mr. Jeff Palmer, Powder Coating Institute.
Tosko A. Miser, Powder Coatings: Chemistry and Technology, Chapter 6, Powder Coatings Application Techniques., 1991.
"Reducing Waste in Railcar Coating Operations", Graco Equipment and Emissions Update, June 1994, pp. 8-9.
Mr. Dave Ellicks, Air Force Corrosion Prevention & Control Office, November 1999.
Mr. Vern Novstrup, NFESC, November 1999.
|Supplemental:||Picture of Powder
Coating Painting System - Navy Environmental Quality Initiative (EQI)
Diagram of Powder
Coating Painting System - Navy Environmental Quality Initiative (EQI)