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Electrostatic Painting: What You Need to Know

TUESDAY, FEBRUARY 16, 2016

By Patrick Harmon

Electrostatic painting is often not well understood in the paint and coatings industry.

To help clarify the electrostatic process, I want to discuss what electrostatic painting is and how it works, things you should consider, and how to determine if it is the right fit for you.

The electrostatic method is used in liquid and powder coating, but I will focus on liquid coatings in this post.

What It Is, How It Works

Electrostatic painting is a process in which an electrostatic charge is applied to both the substrate and to the coating through the tip of the spray tool in order to achieve efficiency in painting the surface by preventing overspray.

The coating is projected by an electrostatic charge from a high-volume, low-pressure (HVLP) spray gun or airless paint sprayer to the grounded, conductive surface to be painted.

The charged paint is attracted to the charged surface in such a way that the pain essentially wraps around the target and rather than leading to overspray.

This translates into a high transfer efficiency and reduction of coating waste. Typical ranges of electrostatic transfer efficiency are anywhere from 85 to 95 percent, depending on the target type and other factors.

This paint savings is often what makes electrostatic an attractive solution, but there are a lot of things to consider with electrostatic coating, such as the coatings you use, the intended target, your equipment maintenance tendencies and safety.

Coatings and Equipment

The coatings you want to use are an important consideration because of the unique requirements of electrostatic equipment.

Binks
Binks

In the electrostatic process, the charged paint is attracted to the charged surface in such a way that the pain essentially wraps around the target and rather than leading to overspray.

Waterborne coatings, for example, require special spray guns when used for electrostatic painting. This is because waterborne coatings are conductive and tend to carry a charge that can cause issues with “grounding out” when they are sprayed.

Grounding out means that the electric charge—rather than charging the paint at the tip of the gun—simply passes back through the coating into the pressure pot and, if the pressure pot is grounded, into the earth. This provides none of the benefits of electrostatic application.

The waterborne-specific electrostatic spray gun will have an isolation block as part of the equipment to prevent the electric charge from trying to return to the pressure tank and ultimately stops the waterborne coating from grounding out.

This can be a highly expensive downside if you routinely change between solvent- and water-based coatings on your jobs because you will need two different types of electrostatic guns.

Additionally, many unique complications can occur with this specialized process, so it is always best to have someone test the equipment tested in your work area, with your coating and under your normal circumstances. Elements such as humidity, the grounded target, the coating itself and the solvent you use can vary from one work area to the next and affect the spray application.

It is also important to note that certain solvents are more likely to work well with a solvent-based electrostatic gun because they are less conductive than other solvents. See the table below for more information.

Non or Low Polarity Medium Polarity High Polarity
(Do Not Use)
Mineral Spirits Ethyl Acetate MEK
Textile Spirits Hexalin MIK
VM & P Naptha Butyl Carbitol Acetone
SC-10, Enco 100, Solvesso 100 Isophorone Isopropyl Alcohol
SC-150, Eno 150, Solvesso 150   Methyl Cellosolve
Heavy Aromatic Naptha - Han   2-Nitropropane
Xylol (Xylene)   1-Nitropropane
Toluol (Tylene)   Diacetone Alcohol
Shell 403   Ethyl Alcohol
O   Methyl Alcohol
N Butyl Acetate   Methyl Acetate


Recommended solvents: Non or Low Polarity are preferred over Medium Polarity.

Ultimately, the goal is to have the coating be as nonconductive as possible. That is why solvents like xylene and toluene are good for electrostatic painting; they are nonconductive, which minimizes the likelihood of your coating grounding out.

Keeping in mind the unique requirements of electrostatic coating, for the most part you can spray just about any coating, but certain coatings like zincs will not take a negative charge well and therefore will not be able to deliver the improved transfer efficiency electrostatic brings.

Surface Materials

The surface you intend to paint also plays a significant role in determining if electrostatic spraying is a good method to use.

Plastic, wood or fiberglass surfaces won’t conduct a charge without a preparation coating, for example. This means you will have to apply a prep coating before your intended coating to allow for electrostatic application.

Additionally, electrostatic application is subject to a phenomenon called the Faraday Cage Effect. The Faraday Cage Effect describes the tendency for negatively charged particles to want to attract to the nearest positively charged surface.

In electrostatic painting, this effect means that the paint will want to adhere to the sides of the surface material but not penetrate into any corners. With this in mind, an applicator needs to remember to turn the electricity to the gun off in order to achieve thorough coverage.

Shop and Equipment Maintenance

Another area to consider before investing in electrostatic painting is how well you maintain your shop and equipment.

Electrostatic equipment is a lot more expensive than HVLP, conventional air spray equipment or a pure airless unit, and also a bit more delicate.

Electrostatic equipment has an electrode that protrudes from the spray gun where the electric current is carried and transferred to the coating. Damage to this electrode alone can be a highly expensive repair.

The electrostatic spray gun itself is also more expensive because it is made from special composites. If the spray gun is damaged as a result of a drop, again, it is a lot more expensive to repair or replace than a traditional spray gun.

© iStock.com / Inga Dronsutaviciene

A well-grounded operator is one who is in direct contact with the earth with non-insulated shoes; the operator shouldn’t be on a platform that is not grounded or ideally should be on the ground itself.

Overall, the savings in paint costs can be extraordinary with the electrostatic coating method. However, it is important to evaluate your shop cleanliness and equipment maintenance habits to determine if you will lose any savings to equipment repairs or replacement.

Safety

Safety is paramount for electrostatic painting because an electrostatic gun has a high electric charge, which can cause a spark and start a fire. A spark can occur, for instance, if the gun is applying a charge too close to a grounded target, which might cause the charge to “jump” to the ground.

Electrostatic spray guns do have safety features in place to prevent this from happening, however. Built-in voltage detectors, for example, will shut off the power to the spray gun if a ground is determined to be too close.

The risk of creating a spark is increased if you do not use proper solvents (discussed above) or do not ensure the operator is well grounded.

A well-grounded operator is one who holds the electrostatic spray gun with his or her bare hand (no gloves or other obstacles should be in the way) and is in direct contact with the earth with non-insulated shoes. The operator shouldn’t be on a platform that is not grounded and ideally should be on the ground itself.

If the operator is not grounded, the negative charge will not be able to disperse into the ground and instead will accumulate in the operator. When the operator moves toward a grounded object, the negative charge can jump to the grounded object, potentially causing a spark or shock.

Is It Right for You?

In the end, electrostatic may be the perfect solution for you if:

  • You find you use a particular coating type routinely (water- or solvent-borne);
  • Have a good record of maintaining equipment well;
  • A heavy enough production load that it would benefit from reducing your coating use; or
  • A significant need to control overspray.

Before going forward with purchasing an electrostatic outfit, as mentioned earlier, I recommend having someone demonstrate the equipment with your typical coatings to ensure it will work properly with your paints and in your work environment.

By following these guidelines, you should be able to determine if electrostatic painting is a good fit for you and ensure the investment in electrostatic equipment will significantly lower your painting costs.

ABOUT THE BLOGGER

Patrick Harmon

Patrick Harmon works with Pittsburgh Spray Equipment Company, a distributor for painting and sandblast equipment to industrial fabricators and manufacturers. There, he helps clients solve problems related to coating application challenges, finish quality problems, production limitations and proper equipment for desired finish end results. Patrick is pursuing his MBA while working in the field with customers and their finishing equipment challenges. Equipment Insights covers the most common questions and considerations encountered when evaluating finishing equipment. Contact Patrick.

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Tagged categories: Electrostatic spray; Paint application; Paint application equipment

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