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Electrostatic Spraying Technologies

There are several key factors that must come together in order to use electrostatic guns effectively. First you must select the right atomization technology for your coating application needs. There are several electrostatic atomization technologies to choose from. The oldest and probably most common are the air spray electrostatic guns. These guns use compressed air as their primary and sole means of atomizing the coating. These guns are most commonly used in applications that require a “Class A” automotive finish. The guns offer a lot of control at the gun such as fluid flow by use of the fluid needle adjustment knob and fan control through the use of the fan adjustment knob. In addition, the amount of fluid can be controlled by how far back the operator pulls the trigger. AirPods Pro Case This is referred to as “feathering” the gun.

The main source of fluid control is determined by the fluid pressure from a low-pressure pump, the air going into a pressure pot or by a fluid regulator mounted near, or in the spray booth. The viscosity of the coating and the size of the fluid nozzle also affect the fluid flow. Although air spray electrostatic guns have great atomization, they are also the least efficient of the electrostatic guns. This is due to the potential use of high air pressure to atomize the coating. The use of high air pressure can defeat the electrostatic attraction by forcing the charged particles of paint past the part or by creating excessive bounce back or overspray.

A variation of the air spray electrostatic gun is the HVLP electrostatic gun. The gun operates almost identically to the air spray gun except that it uses less atomizing air pressure. Instead, the gun uses more cubic feet of compressed air or CFM. The result is a softer spray pattern which lowers the velocity at which the paint particles travel. This allows for more of the charged particles to remain in the electrostatic field which helps to improve transfer efficiency. Like any HVLP gun, some coatings may be too viscous or the application rate may be too high, which may make it difficult for the HVLP electrostatic gun to provide high productivity and acceptable finish quality for some applications. In addition, HVLP guns usually require more CFM which can lead to increased electrical costs for compressed air.

For the application of very viscous materials or for very high application rates, some manufacturers use airless electrostatic guns. These guns use pumps to create very high fluid pressure which is the primary means of atomizing the coatings. When the gun is triggered, the high fluid pressure is allowed to escape into the atmosphere through a tungsten carbide tip that is cut to form an elliptical spray pattern. The size of the pattern and the amount of fluid leaving the gun are controlled by the tip. The viscosity of the coating and the fluid pressure used also affects the application rate.

In general, airless technology does not provide the same level of atomization as air spray or HVLP electrostatic guns but they work well for some coatings, especially when spraying large products at high rates of speed. Tip plugging can be an issue when spraying materials that contain an aggregate such as silica or zinc. Air-assisted airless electrostatic is a hybrid version of the airless electrostatic and the air spray electrostatic. These guns use both fluid pressure and air pressure to atomize the coating. Pumps are needed to create the fluid pressure. Since these types of guns use lower fluid pressure than airless and less air pressure than air spray, they can offer companies a good compromise between the speed of an airless and a finish quality closer to the air spray electrostatic. The best part is that this technology is usually more efficient than either the air spray or the airless electrostatic guns. In some cases they are even more efficient than the HVLP electrostatic guns.

However, air assisted airless electrostatic guns do not offer the same level of control at the gun as the air spray or HVLP electrostatic guns. This is because the fluid pattern cannot be fully adjusted from very narrow to very wide without changing the tip. Also, like the airless electrostatic gun, the operator cannot feather the gun. This could be problematic when spraying very complex substrates where the operator needs that kind of control at the gun. Tip plugging can also be an issue with some aggregate filled materials.

The most efficient manual electrostatic spray gun is a hand held rotary atomizer. These guns use centrifugal forces and a very high voltage electrostatic field to atomize the material. Since there is no atomizing air the paint particles travel very slowly through the electrostatic field. The result is very high transfer efficiency. However, the gun puts out a doughnut shaped spray pattern which does not work well for most production finishing applications and is used mostly for the on-site refinishing industry.

Michael V. Michalski
President
Advanced Finishing Technologies, Inc.
Manufacturers Representative for the Industrial Finishing Industry
adfintec@optonline.net
We have over 30 years of experience in selling industrial paint and powder application equipment to manufacturers and equipment distributors for use in the application of paint and powder in the wood, metal and plastics industries. In addition we have experience in environmental and safety regulations such as NESHAP and OSHA for spray finishing operations. We have also developed a comprehensive Operator Training Program for finishers.

 

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