| ELECTROSTATIC PAINT
SPRAY SYSTEM Revision: 9/96 methyl ketone, 2-butanone, CH3(CH2)2CH2OH Process Code: Navy and Marine Corps: ID-05-03; Air Force: PA01; Army: PNT Usage List: Navy: Medium; Marine Corps: Medium; Army: Medium; Air Force: Low Substitute for: High Velocity Paint Spray Systems Applicable EPCRA Targeted Constituents: Toluene (CAS: 108-88-3), Xylene (CAS: 1330-20-7), Methyl Ethyl Ketone (CAS: 78-93-3), Acetone (CAS: 67-64-1), n-Butyl Alcohol (CAS: 71-36-3), Lead (CAS: 7439-92-1), Chromium (CAS: 7440-47-3), Zinc Compounds Overview: An electrostatic paint spray system is a highly efficient technology
for the application of paint to specific workpieces. Negatively charged
atomized paint particles and a grounded workpiece create an electrostatic
field that draws the paint particle to the workpiece, minimizing
overspray. 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 phenomena 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
systems 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. Transfer efficiencies of 50% are typical for
conventional painting systems. 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 systems
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. Materials Compatibility: Any material that can be atomized can accept an electrostatic charge,
regardless of the coating conductivity. The workpiece must be groundable.
Metal and some wooden pieces can be painted electrostatically, but
plastic, rubber, ceramic, and glass can not. Safety and Health: Electrostatic paint spray systems operate at high voltages (30 to
150 kV). Hence, operator safety is a major concern. All items in the
work area must be grounded, including the operators, the paint booth, the
application equipment (unless applying conductive coatings), and
conveyors. Ungrounded items should be removed from the work area. Removing
paint buildup from the paint booth helps assure that workpieces are
grounded. Workers should never wear rubber- or corked-soled shoes (special
shoe-grounding devices are available.). Adequate skin contact is required
when using hand-held guns. Painters should grasp the gun with bare hands
or use gloves with finger tips and palms cut out. Consult your local industrial health specialist, your local health and
safety personnel, and the appropriate MSDS prior to implementing this
technology. Benefits:
Disadvantages:
Economic Analysis: Cost will vary, depending upon specific applications: painting/coating
type, paint volume, workpiece specifications, and technique. Generally,
electrostatic air systems cost approximately $4,000, and electrostatic
airless systems cost approximately $6,500. Installation and training are
additional costs. Assumptions:
Electrostatic Paint Spraying and High Velocity Paint Spraying
Economic Analysis Summary
Approving Authority: Navy: Approval is controlled locally should be implemented only after
engineering approval has been granted. Major claimant approval is not
required. Point of Contact: Scott Mauro Vendors: The following is a list of electrostatic spray painting system
manufacturers. This is not meant to be a complete list, as there may be
other manufacturers of this type of equipment. Accuspray, Inc. Binks Manufacturing Co. The DeVilbiss Co. Smith Eastern Corp. (AirVerter) Graco, Inc. Sources: Robinson, Frank and Dennis Stephens,
"Understanding Electrostatic Finishing," Industrial Finishing, 9/90, p
34-37. |