Electrostatic Spray Nozzle Illustrations and Concepts
The electrostatic spray nozzle is one of several new innovations in industrial coatings. The invention relates to electrostatic spray systems and especially to a single system of this kind with a novel electrostatic spray nozzle that functions at relatively low charge levels, gives a fine stream of fine particles at a high static-charge spray-target charge, and is completely safe, easy, rugged, and reliable. This novel system has the ability to give superior spray quality even at very low charge levels and to deliver very accurate spray coverage over a wide area. The charge controllers include a linear actuator that controls the amount of charge variation between a high and low level. Spray nozzles that use this actuator have been well-designed to deliver even spray coverage without any surface irregularities. The result is an impressive level of control that allows for an extremely wide range of applications.
The electrostatic spray nozzle was invented by A.J. Geary and was first patented in 1938 by W.C. Fisher and Company. The patent was later renewed by W.C. Fisher and Company and then promptly patented in the United States by W.C. Fisher again.
The invention is easily related to electrostatic spraying because it involves the application of a charged source to produce electrostatic charges at an elevated spray target. This charge source can be a static charge produced when a fluid stream is charged while being sprayed or it can be a charged build up of charge on a positively charged base such as the coating of a metal component. The application occurs when a nozzle sprayer is used. The sprayer is designed to deliver the liquid stream to an area where it will be electrostatically attracted to the charged base component.
The basic design of an electrostatic spray nozzle includes a positive charge electrode which is located above the nozzle and an electrical discharge coil situated below the electrode. As the liquid stream is propelled into the discharge coil, the charged particles are forced to flow along the surface of the coil. The surface of the coil may be a thin film, semi-permeable or a conductive metal. The diagram illustrates a small portion of the inside of a coil. As the charged particles move along the coil, they produce a localized electric field which is an electrical charge.
Fig. 4 is a view of a portion of a non-metallic surface at right angles to the direction of motion of the charged particles. The surface has a fine boundary where the charged particles are formed. The electrostatic spray nozzle forms the electric field by passing a concentrated stream of gas through the fine boundary area. As described, the electrostatic forces do not form a sharp edge or corners as the result of the formation of fine boundary areas.
A second common type of electrostatic spray nozzle comprises a high velocity airstream. This system produces much smaller droplets than the first type. The high velocity airstream may use compressed air, argon or nitrogen in the fuel mix to produce the droplets. The size of the droplets depends on the size of the high velocity airstream and the ambient temperature. A third variation of the electrostatic spray nozzle comprises a vacuum spray.
A very interesting type of electrostatic force is the induced electrostatic forces. In this system, the size of the droplets produced is controlled by an induction electrode. The electrode is usually a rod of flexible glass or plastic. Fig. 5 is a view of a typical induction electrode installed in a chamber.
Here, it is shown that the induced electric field imparts motion to the rod which generates droplets of water vapor and ice. Thereafter, a permanent magnetic field coming from the chamber’s walls imparts movement to these droplets causing them to stick to the rod. The induced electric fields also create large amounts of heat, which in turn melts the plastic coating of the induction electrode. The coating is known as the insulator. It is evident from the passage 22 that the induced droplets are made by the application of a static charge.