Spray painting

Spray painting is a painting technique where a device sprays a coating (paint, ink, varnish etc.) through the air onto a surface. The most common types employ compressed gas — usually air compressed by an air compressor — to atomize and direct the paint particles. Spray guns developed from airbrushes and the two are usually distinguished by their size and the size of the spray pattern they produce — with airbrushes being hand held and used instead of a brush for very fine work such as photo retouching, painting nails or fine art.

Types

Canned spray paint

The most common type in the consumer market are cans of aerosol paint. A metal aerosol can contains the highly pressurized paint which becomes atomized into a fine spray when the paint is released through a valve operated by depressing it with the finger. These aerosol cans are inexpensive, small, easily transported and easily operated. This technology enabled and became synonymous with graffiti, but it is also widely used by private persons for small paint work.

Conventional

A spray gun combines the coating (paint) and compressed air from a separate air compressor in order to atomize the coating and direct it to the target surface. The coating is held either in a small bottle or container attached to the spray gun or in a separate pressurised container attached to the spray gun with a hose.General rule of thumb is that this type of gun puts 1/3 of the coating on the substrate being coated and 2/3 into the air.

HVLP (High Volume Low Pressure)

This is similar to a conventional spray gun using a compressor to supply the air, but the spray gun itself requires a lower pressure (LP). A higher volume (HV) of paint is therefore applied at a lower air pressure. This results in more paint landing on the target surface instead of staying airborne.A regulator is often required so that the air pressure from a conventional compressor can be lowered for the HVLP spray gun.

As a rule of thumb puts 2/3 of the coating on the substrate and 1/3 in the air. True HVLP guns use 8 – 20 cfm and a minimum 5 hp industrial compressor is required. HVLP spray systems are used in the automotive, marine, architectural coating, furniture finishing, and cosmetic industries.

LVLP (Low Volume Low Pressure)

Like HVLP, these spray guns also operate at a lower pressure (LP), but they apply a low volume (LV) of coating (paint). This is a further effort at increasing the transfer efficiency (amount of coating that ends up on the target surface) of spray guns.

Electrostatic spray painting

When the powdered paint is forced through the barrel of the paint gun it rubs against the side of the barrel and builds up an electrostatic charge. This means the paint particles repel each other, and spread themselves evenly as the exit the spray nozzle. The object being painted is charged oppositely, or grounded. The paint is then attracted to the object giving a more even coat than wet spray painting, and also increasing the percentage of paint that actually sticks to the object. This method also means that paint covers hard to reach areas. The whole is then baked to properly attach paint. Car body panels and bike frames are two examples of where electrostatic spray painting is often used.

Rotational bell

With this method the paint is flung into the air by a spinning metal disc ("bell"). The metal disc also imparts an electrical charge to the coating particle.

Electric fan

There are a variety of hand-held paint sprayers that either combine the paint with air, or convert the paint to tiny droplets and accelerate these out a nozzle.

Air Assisted Airless spray guns

These use air pressure and fluid pressure (300 – 3000 psi) to achieve atomization of the coating. This equipment provides high transfer and increase application speed but is best used with flat line applications. Commonly found in factory finish shops.

Airless spray guns

These operate connected to a high pressure pump commonly found using 300 – 7500 psi pressure to atomize the coating using different tip sizes to achieve desired atomization and spray pattern size. This type of system is used by contract painters to paint heavy duty industrial,chemical and marine coatings and linings.

Such Advantages of airless spray are:

Coating penetrates better into pits and crevices.

A uniform thick coating is produced, reducing the number of coats required.

A very "wet" coating is applied, ensuring good adhesion and flow-out.

Most coatings can be sprayed with very little thinner added, thereby reducing drying time and decreasing the solvent release into the environment.

Automated Linear Spray Systems

Manufacturers who mass produce wood products use a Automated Spray system, that allows them to paint materials at a very high rate as well as at a minimum of personnel. Automated Spray Systems usually incorporate a paint saving system, this eliminates waste. Commonly, linear spray systems are when products are on are laying flat on a conveyor belt and then enters into a linear spray system, where automated spray guns are stationed above, and when the material is directly below the guns, the guns then begin to paint the material. Materials consist of window frames and any other material that is simple in design.

Automated Flatline Spray Systems

Mass produced material is loaded on a conveyor belt where it is fed into one of these flatline machines. Flatline machines are designed to specifically to paint material that is complex in shape. For example a kitchen cabinet. Spray guns are aligned above the material and the guns are in motion in order to hit all the grooves of the material. The guns are can be moving in a cycle or can be moving back and forth in order to apply paint evenly across the material. Flatline systems are typically large and can paint doors, kitchen cabinets, and other plastic products.

Applications

One of the applications is graffiti. Spray-painting has also been used in fine art (using airbrush type), for both painting and sculpture as in the art of Jules Olitski, Dan Christensen, Peter Reginato, Sir Anthony Caro, and Jean-Michel Basquiat.

See also

*Airbrush
*Primer (paint)
*Spray paint art
*Huffing
*Frederick William Lawrence

More Spray Painting Resources

* [http://www.normanchigier.com/DepositionofPaintonCarsAutomobiles-AtomizationandSprayTechnology.html Spray Painting of Automobiles - Problems and Solutions]
* [http://www.plasti-kote.co.uk/how_to/ Plastikote] - How to spray paint
* [http://www.finishingequipmentandsupplies.com/paint-preparation-system.htm How To Video - 3M Paint Preparation System] Available in Spanish and English
* [http://www.danleodesign.com Danleo Design] - Dublin Spray Artist
* [http://www.advancedequipmentsys.com/overview-spray.html Advanced Equipment Systems] - Automated Spray System Overview