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Electrostatic coating is a manufacturing process that employs
charged particle In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can also be an electron or a proton, or another elementary particle, ...
s to more efficiently paint a workpiece. Paint, in the form of either powdered particles or atomized liquid, is initially projected towards a conductive workpiece using normal spraying methods, and is then accelerated toward the work piece by a powerful
electrostatic charge Electric charge is the physical property of matter that causes charged matter to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons respectiv ...
.''Manufacturing Processes Reference Guide'', 1st ed. , Robert H. Todd, Dell K. Allen, and Leo Alting, 1994 An addition to the electrostatic coating (or e-coating) process is dipping electrically conductive parts into a tank of paint that is then electrostatically charged. The ionic bond of the paint to the metal creates the paint coating, in which its thickness is directly proportional to the length of time the parts are left in the tank and the time the charge remains active. Once the parts are removed from the paint tank, they are rinsed off to remove any residual paint that is not ionically bonded, leaving a thin film of electrostatically bonded paint on the surface of the part.


Process characteristics

* Uses a
high voltage High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant spec ...
electrostatic charge which is applied to both the workpiece and the sprayer mechanism * Uses 95% of sprayed paint due to reduced over-spray and better wrap-around * Paint materials can be either powdered or liquid * Process can be either automatic or manual * Workpieces ''must'' be conductive * Workpieces are usually baked after coated * The baked on paint adheres extremely well and is difficult to remove without aggressive means of removal.


Process

The workpiece travels down a
conveyor belt A conveyor belt is the carrying medium of a belt conveyor system (often shortened to belt conveyor). A belt conveyor system is one of many types of conveyor systems. A belt conveyor system consists of two or more pulleys (sometimes referred to ...
towards a paint booth, or paint tank, where it is sprayed with, or dipped into, electrostatically charged paint
particles In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, from s ...
. Integrated into a powder paint booth is a powder recovery unit, which recovers between 95% and 100% of the paint over-spray coatings. After the workpiece is coated, it continues on the conveyor belt to an
oven upA double oven A ceramic oven An oven is a tool which is used to expose materials to a hot environment. Ovens contain a hollow chamber and provide a means of heating the chamber in a controlled way. In use since antiquity, they have been us ...
, where the paint is cured. The benefits to the process of electrostatic coating are the ability to recover the little over-spray and having the process automated which will cut costs. The reason for the little overspray is the paint particles that do not hit the piece will turn in the air and go back to the piece. There are also some drawbacks to the process: everything in the area of the coating must be grounded to prevent static buildup and can easily arc, damaging the hanging devices and/or the locations where the hanging devices rest on the conveyor. All hangers, conveyors, etc. must be cleaned often to ensure a good ground and prevent anyone in the area from getting a severe shock. In an airborne system, any recesses on the piece that is being coated can be missed because the electrostatic paint is more attracted to corners and sharp edges; this means that another process for coating can be a better option if the piece has recesses. In the dipping process, air entrapment can occur in blind holes and deep recesses, so the positioning of the part as it enters the paint tank is critical in removing any trapped air that will restrict paint coverage.{{cite web, url=http://www.etfinancial.com/coatingsequip%2Ehtm , accessdate=January 11, 2009 , url-status=dead , archiveurl=https://web.archive.org/web/20090118064613/http://www.etfinancial.com/coatingsequip.htm , archivedate=January 18, 2009 , title=Coating Equipment & Processes


Workpiece geometry

The
geometry Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...
of the workpiece is limited only by the size of the paint booth or tank. Using electrostatic coating, it is possible to apply paint in various thicknesses being limited only by the paint's tendency to run and therefore ruin the coating if applied in too thick a manner. It is usually preferred to apply many thin coats as opposed to one thick coat.


Setup and equipment

The job may be delivered to the coating booth or hangers in any fashion, most commonly using either hands or
pliers Pliers are a hand tool used to hold objects firmly, possibly developed from tongs used to handle hot metal in Bronze Age Europe. They are also useful for bending and physically compressing a wide range of materials. Generally, pliers consist ...
. After passing through the booth, or tank, and getting coated, the workpiece then either goes into a baking oven or out into the open air to allow the paint to cure on the part. In spray coating, many different spray nozzles may be used depending on the desired paint consistency and the shape of the workpiece.


Typical tools and geometry produced

There are a wide variety of
spray nozzle A spray nozzle is a device that facilitates the dispersion of a liquid by the formation of a spray. The production of a spray requires the fragmentation of liquid structures, such as liquid sheets or ligaments, into droplets, often by using ki ...
s available for use in electrostatic coating. The type of nozzle used will largely depend on the shape of workpiece to be painted and the consistency of the paint.


References


External links


How the process of electrostatic coating is used in the finishing process during their construction. Example is during the final minute of the video
Painting techniques Electrostatics