A rotary atomizer is an automatic electrostatic

paint Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture. Paint can be made in many ...

applicator used in high volume, automatic

production Production may refer to: Economics and business * Production (economics) * Production, the act of manufacturing goods * Production, in the outline of industrial organization, the act of making products (goods and services) * Production as a stati ...

painting environments. Also called a 'paint bell', "rotary bell atomizer" or 'bell applicator', it is preferred for high volume paint application for its superior transfer

efficiency Efficiency is the often measurable ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without ...

, spray pattern consistency, and low

compressed air Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...

consumption, when compared to a paint spray gun. It can be mounted in a fixed position, reciprocating arm, or an

industrial robot An industrial robot is a robot system used for manufacturing. Industrial robots are automated, programmable and capable of movement on three or more axes. Typical applications of robots include welding, painting, assembly, disassembly, pick a ...

Transfer Efficiency

Rotary atomizers Rotary atomizers use a high speed rotating disk, cup or wheel to discharge liquid at high speed to the perimeter, forming a hollow cone spray. The rotational speed controls the drop size. Spray drying and spray painting are the most important and ...

can provide highest transfer efficiency of any paint applicator at approximately 95%. This means that the applicator puts an

electric 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 respe ...

on each droplet of paint to attract it to the part being sprayed. Rotary atomizers are able to get higher transfer efficiency compared to other spray guns because of its unique spinning bell cup. The bell cup inside the applicator, spins the material at 20,000 to 60,000 revolutions per minute. Due to the high rotation speed, the paint is subjected to high

centrifugal force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is paralle ...

. This forces the paint to flow along the edge of the spinning cup. When it reaches, the edge of the cup, the paint is broken apart into a fine cloud of fluid particles. The droplet size is finer and more consistent than other atomization methods like air spray. The cloud of paint droplets is directed or shaped by the shaping air coming out of the air cap. This allows us to shape and propel the pattern towards the part. This leads to higher transfer efficiency. In order to achieve maximum transfer efficiency, electrostatic effect is added. The electrostatic charge within the bell cup is formed from the power supply within the rotary atomizer. Each paint particle is charged as it spins inside the bell cup, causing the paint to be attracted to a part that is grounded. This drastically reduces overspray and wasted paint. Electrostatics also help the paint to wrap around the paint and can be very helpful in reducing the number of passes needed to paint a part.

Assemblies

The typical bell applicator consists of five major assemblies: the

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...

module, the bell cup, the

turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...

, the shaping air

shroud Shroud usually refers to an item, such as a cloth, that covers or protects some other object. The term is most often used in reference to ''burial sheets'', mound shroud, grave clothes, winding-cloths or winding-sheets, such as the famous Shr ...

, and the

electrostatic Electrostatics is a branch of physics that studies electric charges at rest (static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for amber ...

system. The valve module is a manifold consisting of passages for paint,

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

, and

, and valves to control the flow of materials for paint delivery, cleaning and purging with solvent, and management of compressed air to the valves, turbine, and shaping air shroud. The bell cup is a conical or curved disc fixed to the shaft of the turbine. Paint is injected into the center of the rear of the disc, and is atomized by being forced out to the edge of the cup by

centrifugal Centrifugal (a key concept in rotating systems) may refer to: *Centrifugal casting (industrial), Centrifugal casting (silversmithing), and Spin casting (centrifugal rubber mold casting), forms of centrifigual casting *Centrifugal clutch *Centrifug ...

forces. The flow of the paint over the cup and off the edge breaks up the paint into atomized droplets. The turbine is a high speed, high precision air motor that rotates the bell cup at speeds ranging from 10,000rpm to 70,000rpm, depending on the cup diameter, atomization desired, and physical properties of the paint. Typical turbines for this application use an

air bearing Air bearings (also known as aerostatic or aerodynamic bearings) are fluid bearings that use a thin film of pressurized gas to provide a low friction load-bearing interface between surfaces. The two surfaces do not touch, thus avoiding the tradit ...

, where the spinning shaft is suspended in a cushion of flowing compressed air, with virtually no frictional resistance. The shaping air shroud, or shaping air ring, is simply a ring with passages for air to flow out the front of the atomizer, outside of the cup diameter, to manage the size of the spray pattern produced. As more air is forced through the shroud, the atomized paint is forced into a smaller pattern. The electrostatic system can be internal or external (or direct or indirect charge), and supplies high

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...

(30,000 to 100,000 volts DC) charge to the applicator, or the air surrounding it. This has the effect of negatively charging the paint, while causing a region of

positive 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 ...

to form on the workpiece, resulting in electrostatic attraction between the paint and the workpiece. The electrostatic system is visible only on an external (or indirect) charge applicator, where it appears as a series of 4-8 forward-facing

electrodes An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

in a circular array around the bell. It is typically called a 'candelabra' for its resemblance to one. The bell is also used in

powder coating Powder coating is a type of coating that is applied as a free-flowing, dry powder. Unlike conventional liquid paint which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or ...

. Although the bell looks different from a topcoat bell.

Applications

Bell applicators are used in wide variety of industries because of its ability to integrate well into automated production environments. Each industry provides its own unique challenges that rotational bell painting can solve. Some of these include: mold release, non-destructive testing, agriculture &

construction equipment Heavy equipment or heavy machinery refers to heavy-duty vehicles specially designed to execute construction tasks, most frequently involving earthwork operations or other large construction tasks. ''Heavy equipment'' usually comprises five e ...

, backlit displays,

electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

, automotive components and parts, wheels and rims, aerospace and defense,

wood products Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin t ...

and furniture, industrial components, architectural panels and extrusions, cylinders and tanks, cosmetics, glass coating,

cookware Cookware and bakeware is food preparation equipment, such as cooking pots, pans, baking sheets etc. used in kitchens. Cookware is used on a stove or range cooktop, while bakeware is used in an oven. Some utensils are considered both cookware ...

, footwear and apparel.

References

* * {{DEFAULTSORT:Rotational Bell Painting Painting techniques