Types of Electrostatic Liquid Spray Guns
The Electrostatic Liquid Spray Gun is a device that creates static electricity by creating a small amount of static charge on the target. It works by using two disc electrodes, shown in Figures 14 and 15. These discs are attached to a wooden or metal frame and a cord is connected between the two ends. To start spraying, a small amount of water is placed on one of the disc electrodes and the spray is released from the other. The amount of static charge created will depend on the humidity level in the room.
Figure 14 shows the basic shape of the Electrostatic Liquid Spray Gun. In this embodiment, the left side elevating view shows an electric circuit on the top surface of the disc and the right side elevating view shows the bottom surface. The right disc electrode has a black rectangular mark in its center. The electrical connections are depicted in white. The electrical contacts in figure 1 are located at the left side of this figure.
A coating of some sort is placed over the surface of the frame in figure 13 to serve as an insulator for the particles that fly through it. This coating is typically aluminum oxide, but other coatings have also been developed. In this type of electrostatic spray gun, the particles create an electrostatic field just as they do in the electrostatic fields created by the real field created by a magnet.
An electrostatically charged liquid particle may enter the frame when the wire or cord is pulled into the gun’s chamber. Then the gun’s nozzle provides a constant stream of powdered metal or tungsten carbide. The metal or tungsten carbide powder passes through a tube that has a small hole in the middle of it. This is designed to allow only small particles to enter the chamber from either side. The entrance of these particles is prevented by a second, larger hole in the tube called a passageway.
As the gun is primed, the primer creates a charge within the electrostatic spray gunpowder. This charge pushes against the coating particles and causes them to be accelerated out of the gun’s chamber into the passageway. The particles then enter the hole in the tube, where they deposit themselves and settle. After a bit, the particles de-load back into the gun and the cycle begins all over again. This is why there is no continuous feeding of gunpowder.
There are two different kinds of electrostatic waterborne electrostatic guns – those that are primed with a liquid and those that are non-poured. Although both use the same materials to coat the inside of their barrels, the way they spray the metal or tungsten carbide into the air differs. The non-poured types use compressed CO2 and air to generate charges, which are then sprayed onto the coated surface of the barrel at a low velocity to electrostatically charge the coated particles.
The compressed air part of these types of guns use a grounded article or a charged metallic surface as an electrode. When the air spins around the grounded article, it causes the charged particles to be accelerated out of the barrel, into the passageway, and then into the room. Because the particles are accelerated out of the barrel, they don’t stay on the ground and mix with any other particles present. A good coated piece of metal, such as a tubular steel pipe, acts as the ground or grounded article.
The second type of electrostatic gun uses a liquid-to-air or powder-to-gas discharge method. In this method, the gas (usually nitrogen) is blown over the electrode and into the chamber where the charged particles are expected to be deposited. The pressure in the chamber is controlled by a variable valve. The particle flows out of the nozzle at a high velocity. A powder deflector and electrode are also used in this type of electrostatic chamber. Because the chamber is filled with a different liquid than the previous method, it may take longer to deposit the charged particles.