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| Electrostatic Painting |
 Electrostatic
painting, also known as "powder coating," uses the principal of
"opposites attract" to create a uniform and durable finish on metal
and some plastics without the sags, runs, drips and bubbles which
can occur with traditional liquid paints. It's used on many plastics
and every kind of metal. |
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| Electrostatic painting process is simple
in concept and operation. Dry powder comprised of resins and
pigments is pneumatically fed from a supply reservoir to a spray gun
where a low amperage, high voltage charge is imparted to the powder.
The part to be finished is electrically grounded. When sprayed, the
charged powder articles are firmly attracted to the grounded part's
surface and held there until melted and fused into a smooth coating
in the curing ovens. |
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| It's much more durable than liquid paint
and it's an environmentally friendly process because there are no
solvents to evaporate into the air or go down the drain.Different
formulations (epoxy, urethane, polyester or a hybrid) are determined
by the intended use of the item. For example, urethane and polyester
offer the best exterior durability while epoxy is best for corrosion
protection and chemical and solvent resistance. |
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ELECTROSTATIC PAINT SPRAY SYSTEM |
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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. |
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| 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". |
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| 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%. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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