Rotational bell painting

Last updated

A rotary atomizer is an automatic electrostatic paint applicator used in high volume, automatic production 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, spray pattern consistency, and low compressed air consumption, when compared to a paint spray gun. It can be mounted in a fixed position, reciprocating arm, or an industrial robot. [1]

Contents

Transfer Efficiency

Rotary atomizers can provide highest transfer efficiency of any paint applicator at approximately 95%. This means that the applicator puts an electric charge 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. 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. [2]

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 module, the bell cup, the turbine, the shaping air shroud, and the electrostatic system.

The valve module is a manifold consisting of passages for paint, solvent, and compressed air, 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 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, 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 (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 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 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. 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, backlit displays, electronics, automotive components and parts, wheels and rims, aerospace and defense, wood products and furniture, industrial components, architectural panels and extrusions, cylinders and tanks, cosmetics, glass coating, cookware, footwear and apparel. [3]

Related Research Articles

Pump Device that imparts energy to the fluids by mechanical action

A pump is a device that moves fluids, or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they use to move the fluid: direct lift, displacement, and gravity pumps.

Spray drying

Spray drying is a method of changing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals, or materials which may require extremely consistent, fine particle size. Air is the heated drying medium; however, if the liquid is a flammable solvent such as ethanol or the product is oxygen-sensitive then nitrogen is used.

Four-stroke engine Internal combustion engine type

A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

  1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing vacuum pressure into the cylinder through its downward motion. The piston is moving down as air is being sucked in by the downward motion against the piston.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust valve.
Airbrush Small, air-operated tool that atomizes and sprays various media

An airbrush is a small, air-operated tool that atomizes and sprays various media, most often paint but also ink and dye, and foundation. Spray painting developed from the airbrush and is considered to employ a type of airbrush.

Powder metallurgy Process of sintering metal powders

Powder metallurgy (PM) is a term covering a wide range of ways in which materials or components are made from metal powders. PM processes can reduce or eliminate the need for subtractive processes in manufacturing, lowering material losses and reducing the cost of the final product.

Spray painting Painting technique in which a device sprays coating material through the air onto a surface

Spray painting is a painting technique in which a device sprays coating material through the air onto a surface. The most common types employ compressed gas—usually air—to atomize and direct the paint particles.

Nebulizer Drug delivery device

In medicine, a nebulizer or nebuliser is a drug delivery device used to administer medication in the form of a mist inhaled into the lungs. Nebulizers are commonly used for the treatment of asthma, cystic fibrosis, COPD and other respiratory diseases or disorders. They use oxygen, compressed air or ultrasonic power to break up solutions and suspensions into small aerosol droplets that are inhaled from the mouthpiece of the device. An aerosol is a mixture of gas and solid or liquid particles.

Inlet manifold Automotive technology

In automotive engineering, an inlet manifold or intake manifold is the part of an engine that supplies the fuel/air mixture to the cylinders. The word manifold comes from the Old English word manigfeald and refers to the multiplying of one (pipe) into many.

Shot peening Cold metal working process to produce compressive residual stress

Shot peening is a cold working process used to produce a compressive residual stress layer and modify the mechanical properties of metals and composites. It entails striking a surface with shot with force sufficient to create plastic deformation.

Vaneless ion wind generator

A vaneless ion wind generator or power fence is a device that generates electrical energy by using the wind to move charged particles across an electric field.

Dust collector

A dust collector is a system used to enhance the quality of air released from industrial and commercial processes by collecting dust and other impurities from air or gas. Designed to handle high-volume dust loads, a dust collector system consists of a blower, dust filter, a filter-cleaning system, and a dust receptacle or dust removal system. It is distinguished from air purifiers, which use disposable filters to remove dust.

Rotary-screw compressor Gas compressor using a rotary positive-displacement mechanism

A rotary-screw compressor is a type of gas compressor, such as an air compressor, that uses a rotary-type positive-displacement mechanism. These compressors are common in industrial applications and replace more traditional piston compressors where larger volumes of compressed gas are needed, e.g. for large refrigeration cycles such as chillers, or for compressed air systems to operate air-driven tools such as jackhammers and impact wrenches. For smaller rotor sizes the inherent leakage in the rotors becomes much more significant, leading to this type of mechanism being less suitable for smaller compressors than piston compressors.

A coalescer is a device which induces coalescence in a medium. They are primarily used to separate emulsions into their components via various processes, operating in reverse to an emulsifier.

Spray nozzle Device that facilitates dispersion of liquid into a spray

A spray nozzle is a precision device that facilitates dispersion of liquid into a spray. Nozzles are used for three purposes: to distribute a liquid over an area, to increase liquid surface area, and create impact force on a solid surface. A wide variety of spray nozzle applications use a number of spray characteristics to describe the spray.

Ultrasonic nozzle

Ultrasonic nozzles are a type of spray nozzle that use high frequency vibrations produced by piezoelectric transducers acting upon the nozzle tip that create capillary waves in a liquid film. Once the amplitude of the capillary waves reaches a critical height, they become too tall to support themselves and tiny droplets fall off the tip of each wave resulting in atomization.

Electrostatic coating is a manufacturing process that employs charged particles 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.

Spray (liquid drop) Dynamic collection of drops dispersed in a gas

A spray is a dynamic collection of drops dispersed in a gas. The process of forming a spray is known as atomization. A spray nozzle is the device used to generate a spray. The two main uses of sprays are to distribute material over a cross-section and to generate liquid surface area. There are thousands of applications in which sprays allow material to be used most efficiently. The spray characteristics required must be understood in order to select the most appropriate technology, optimal device and size.

Internal combustion engine Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber

An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to. This replaced the external combustion engine for applications where the weight or size of an engine was more important.

Patternation is the specialized technical art of performing quantitative measurements of specific properties of particles within a spray and visualizing the patterns of this specific property within the spray. In order to understand patternation, we need to consider the role sprays play in our daily lives.

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 common uses of this technology.

References

  1. ↑ "Rotary Bell Applicator Basics". www.graco.com. Retrieved 2021-06-14.
  2. ↑ "How a Rotary Bell Atomizer Works - Rotary Applicator". www.graco.com. Retrieved 2021-06-14.
  3. ↑ "Paint Automation – Robotic Paint Systems". www.graco.com. Retrieved 2021-06-14.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.