For this technology, an ionizing electrode, typically located at the paint gun atomizer tip, causes paint particles to pick up additional electrons and become negatively charged. As the coating is deposited on the workpiece, the charge dissipates through the ground and returns to the power supply, completing the circuit. The electrostatic field influences the path of the paint particles. Because the charged particles are attracted to the grounded workpiece, overspray is significantly reduced. Paint particles that pass a workpiece can be attracted to and deposited on the back of the piece. This phenomenon is known as "wrap".

The transfer efficiency is the percent of sprayed paint that is applied to the workpiece. Paint that is not applied to a workpiece is captured in the paint spray booth’s emission control system and ultimately disposed as waste. The typical transfer efficiency for an electrostatic paint spray system is 75%.

In conventional paint spray systems, paint atomization occurs via high velocity air jets forcing paint through small air holes in the paint gun face caps. Air pressures used in these systems range from 40 to 80 psi, with air volumes of 8 to 30 standard cubic feet per minute (scfm). The atomized paint particles travel at high velocities and have a greater tendency to bounce off the object being painted, as compared to electrostatic systems.

Paints used for electrostatic painting must be formulated with polarizable solvents. Personnel responsible for ordering the paint should coordinate with the supplier/manufacturer to ensure that they obtain the proper formulation.

No new wastes are generated when a conventional paint spray system is converted to an electrostatic paint spray system. Significant reductions in waste generation are achieved due to the electrostatic system’s increased transfer efficiency.

A potential drawback to electrostatic finishing, particularly for coating complicated surfaces, is the Faraday cage effect: a tendency for charged coating particles to deposit around entrances of cavities. The Faraday cage effect allows electric charges on a conductor to reside on the outer surface of the conductor. In the case of coating complicated surfaces, the electric charge resides on the entrances of cavities. High particle momentum can help overcome Faraday cage effects, since particles with greater momentum (larger particles or particles traveling at higher speeds) are influenced less by the electrostatic forces. However, high particle momentum also lowers efficiency.

Electrostatic paint equipment is available in three basic types: air atomized, airless, and rotating discs and bells. High-speed discs atomize the coating more finely than air atomization and direct more paint to the target. This technology is particularly efficient for the application of difficult to disperse, high-solids paints. However, the Faraday cage effect is generally greater with rotary atomizers than with air or airless types. Rotary atomizers, therefore, may not provide adequate coverage for complicated surfaces.

• Reduced emissions of volatile organic compounds (VOCs) used as solvents in paints which are associated with the formation of smog, typically regulated by state and local air pollution control districts.
• Reduced emissions of hazardous air pollutants (HAPs) used as solvents in paints and which are regulated by federal, state, and local regulations including the National Emissions Standards Hazardous Air Pollutants (40 CFR 63).
• Reduced storage and use of substances that are regulated by SARA Title III (TRI, Tier I /Tier II) if certain thresholds are exceeded (40 CFR 300, 355, 370, and 372; and EO 12856).
• Reduced occupational exposures, which are regulated under 29 CFR 1910.

Compliance benefits include: 1) reduced recordkeeping and reporting requirements under the Title V, NESHAP Program and SARA programs, and 2) reduced administrative burden associated with OSHA (i.e., training and recordkeeping).

The compliance benefits listed here are only meant to be used as a general guideline 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.

Proper design, operation, and maintenance of the equipment is required for its safe use. The spray booth must be well ventilated. Additional health concerns depend on the coating being applied. Inhalation of lead and zinc chromate based paints can irritate the respiratory system. Some lead compounds are carcinogenic. Solvent based coatings can irritate the lungs and mucous membranes. Prolonged exposure can affect the respiration system and/or the central nervous system. Proper personnel protective equipment should be worn, if required.

Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.

• Higher transfer efficiencies result in significant reductions in both paint usage and waste generated.
• Less maintenance is required for pollution control equipment serving the paint booth.

• High capital cost and more spray equipment maintenance is required.
• The electric charges tend to repel on complicated surfaces.
• Faraday Cage Effect.
• Surface imperfections are possible due to air molecules becoming trapped in the coating surface.

Assumptions:

• Gallons of paint applied to surface per year: 5,000 gallons
• Paint procurement cost: $50/gallon
• Transfer efficiency of electrostatic spray: 75 percent
• Transfer efficiency of high velocity spray: 50 percent
• Gallons of paint purchased: 6,667 gallons for electrostatic, 10,000 gallons for high velocity
• Operating hours: 145 hours for electrostatic, 200 for high velocity
• Labor rate: $45/hr.
• Waste paint collected using dry filter system.
• Dry filter replacement rate: 1.25 dry filters/hour
• Dry filter disposal cost: $1/filter

Annual Operating Cost Comparison for Electrostatic Paint Spraying and High Velocity Paint Spraying

Economic Analysis Summary

Annual Savings for Electrostatic Paint Spraying: $169,100
Capital Cost for Diversion Equipment/Process: $5,300
Payback Period for Investment in Equipment/Process: < 1 year

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The Air Force Corrosion Prevention & Control Office is an approving authority for US Air Force applications. Table of Allowance (TA) 480 provides authorization, sources, and National Stock Numbers of electrostatic paint equipment, but authority resides at the local level. US AIR FORCE Technical Order 1-1-8, "Application of Organic Coating Systems to Air Force Equipment" also authorizes the use of electrostatic spray paint systems.

*There are multiple MSDSs for most NSNs.
The MSDS (if shown above) is only meant to serve as an example.

Accuspray, Inc.
23350 Merchantile Rd.
Cleveland,  OH   44122
Phone: (800) 618-6860 
or (216) 595-6860
FAX: (216) 595-6868