Now for a post in English about electrostatic application. We’ll ask some basic questions and then provide the answers. Hopefully, this exercise will either bring you up to speed or perhaps refresh your knowledge of this finishing technique. Let’s start:
1. What is the advantage of electrostatic air spray?
Electrostatic air spray offers greater product transfer efficiency than both conventional airmix and airless, and a much higher finish quality than airless. If the product is currently sprayed airless and a higher efficiency is needed, electrostatic air assisted airless technology can be considered. The operator can use the same pump/system as their old airless and all that is needed is a small air compressor for the gun.
2. How does electrostatic spray work?
The coating is electrostatically charged as it passes through an electrostatic field produced between the electrode on the front of the gun and a grounded object. The charged particles of coating are attracted to the grounded (neutral) object and form an even coating.
3. Does electrostatic application work only when spraying metal pieces?
No, nearly any piece can be sprayed electrostatically. If the electrostatically charge paint “sees” a conductive grounded surface it will be attracted to it. A nonconductive piece can be sprayed electrostatically by either putting it between the applicator and a conductive grounded surface or spraying the piece conventionally with a conductive primer.
4. Can electrostatic application be used to paint something other than metal? If so, will the same benefits as spraying metal electrostatically be achieved?
Almost any product can be finished electrostatically. Some may require pretreatment with chemical sensitizers to produce a conductive surface. With some products, a metal object may be placed behind the part to create a ground image for attraction. Many black rubber items have enough carbon content to be sprayable. Others, such as wood parts, sometimes have enough moisture to produce a ground sufficient to spray electrostatically. The many advantages and savings associated with electrostatic spraying justify the application of a pretreatment or preparation product. Material, maintenance, labour and filter savings may alone justify an electrostatic application, not to mention increased production.
5. Why should an electrostatic spray gun be selected over a conventional spray gun?
Although an electrostatic gun may cost more, it has many advantages over a conventional spray gun. An electrostatic gun has a very high transfer efficiency (40-98 %) which results in a lower paint cost, less VOCs, less cleanup and faster production.
6. Will painting electrostatically provide better adhesion?
Painting electrostatically will give better transfer efficiency (more paint on the part) but not better adhesion. Adhesion depends on the condition of the substrate and the properties of the paint. Painting, in general, electrostatic or conventional, requires the same type of properly prepped surface before applying paint. Proper preparation is an important key to a good finish.
7. Is special paint required for electrostatic spraying?
Most standard solvent based coatings can be sprayed electrostatically. The materials, solvents, and reducers used in the manufacture of the coatings determine the “resistivity” of the coating. This can be measured with a paint probe meter which measures megohms per centimeter of resistance. The best electrostatic results are achieved when the resistivity of the coating is between 25 and 50 megohms per centimeter. Some adjustment to paints can be made in the field using “polar” or “non polar” solvents to adjust the resistivity of the paint but care must be taken not to seriously affect the quality of the coating.
8. Can waterborne paints be sprayed electrostatically?
Yes. Waterborne paints are the most conductive paints made. This makes them ideal for electrostatic applications. However, when spraying waterborne paint electrostatically, the charge will be carried back to the fluid-supply system. Therefore, spraying waterborne paint electrostatically requires isolating the paint-supply system from contact with people. Special hardware is required, such as an isolation stand and cage or voltage-blocking system. Various types of isolation devices are available, depending on the application and manufacturer.
9. Why should equipment geared specifically for a waterborne paint be purchased?
Waterborne paints are highly conductive. As a result, the paint supply and fluid lines must be isolated. Power supplies must also be designed to accommodate for the inherit high current draw of waterborne paints. Spraying waterborne paint through a solventborne system is dangerous and may result in equipment damage.
10. What needs to be grounded when using electrostatic guns?
All of the equipment, personnel and target parts in the spray booth area must be grounded. Any ungrounded object, or person, in the spray area can become electrically charged. Improper grounding can result in static sparking which can cause fire or electric shock.
An earthing scheme example is as follows:
11. What is the best way to check the voltage of an electrostatic gun?
There are several ways to check the voltage of an electrostatic gun. The best way to check the voltage is to have an electrostatic test equipment kit. With this kit, accurate voltage measurements of both the electrostatic gun and power supply are assured.
12. What is the difference between a cascade and a classic type power supply?
A cascade type power supply sends out a low voltage that is then stepped up at the transformer on the gun. A classic type immediately sends out the required high voltage.
13. Where does electrostatic not work so well?
Spraying outside is difficult unless the area can be shielded from any wind. Wind can carry the paint away from the part before the coating can be attracted to the grounded object.
14. Is electrostatic spraying safe?
Yes. The guns incorporate a built in current limiter which automatically reduce the guns output voltage to safe levels when the gun’s tip approaches a grounded object.
15. What are the safety recommendations to take in account?
The person in charge of the workshop should ensure that personnel are properly trained in the use of this kind of equipments.The equipment must only be used in well ventilated areas to prevent health risks to the operators and to prevent the risk of fire or explosion in the workshop. Spraying certain products can be dangerous, so full protection for operators in the form of masks and protective cream must be provided at all times.
- Spraying and cleaning must be carried out in an adequately ventilated place.
- The power supply unit must be located outside the spraying area. It must be at least 4 m / 13 ft from any source of inflammable vapour.
- All metal parts, paint pumps, solvent containers and any other conductive article – located within 3 m / 10 ft of the gun air cap – must be grounded.
- Do not store paint or solvent near the spraying area.
- Keep the spraying area clean. Remove all unnecessary components or waste materials.
- The part to be painted must be connected to the ground continuously.
- Paint must not be allowed to accumulate on the suspension hooks.
- Keep the gun perfectly clean.
- Do not use the equipment if there is an air leak from the gun or in the hoses when the system is not operating.
- Be sure that hooked parts on the conveyor must not come closer than 15 cm / 6″ from the gun air cap.
- Before plugging in the power supply unit, be certain gun air cap and tip are installed.
- The electric power supply must be interrupted before any cleaning operation (power supply unit switched to the off position).
- When shutting off the high voltage, in case of intervention on the gun, wait for a few seconds so that the electric charge has time to reach the ground.
- Do not soak or immerse the gun or any plastic part in the solvent. This could result in damage and impair the safety circuits. If necessary, clean the plastic parts with a soft brush soaked in solvent and dry them immediately.
- Before disconnecting the hose, ensure that the circuit is no longer pressurized and that the electric current is switched off.
- After any repair – prior to turning on the power supply – always make sure gun air cap and tip are installed onto the gun.