Electrostatic Painting 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 phenomenon is known as "wrap."

The transfer efficiency is the percent of sprayed paint that is applied to the workpiece. 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 pounds per square inch (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.


Economic Analysis
Cost will vary, depending upon specific applications: painting/coating type, paint volume, workpiece specifications, and technique.

Assumptions:

Gallons of paint applied to surface per year: 5,000 gals.
Paint procurement cost: $50/gal.
Transfer efficiency of electrostatic spray: 75%.
Transfer efficiency of high velocity spray: 50%.
Gallons of paint purchased: 6,667 gals for electrostatic, 10,000 gals for high velocity.
Operating hours: 145 hrs 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/hr.
Dry filter disposal cost: $1/filter.

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

	Electrostatic	High Velocity
Labour	$6,500	$9,000
Material	$333,500	$500,000
Waste Disposal	$200	$300
Total Costs	$340,200	$509,300

Economic Analysis Summary:

Annual Savings for Electrostatic Paint Spraying: $169,100

 

Electrostatic Painting Process

First, we setup the test spraying apparatus.

 
Next, we take a black plastic sphere and place it a set distance from the spray nozzle.

Now, we spray the sphere with elctrostatics turned OFF: 1-2-3-4 seconds. (The setup is the same; the black backround was added to make the spray more visible.)

 
Notice the coverage on the target.

Finally, we turn electrostatics ON, and spray a new sphere for half the time: 1-2 seconds. (All other settings are kept constant, so half the amount of material is sprayed.)

Notice the coverage on the target. The charged droplets wrapped around, reaching the back of the sphere.

Original Sphere	Electrostatics OFF	Electrostatics ON