Spray painting: Difference between revisions

'''Spray painting''' VANDALISM 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 compressor|air]]—to atomize and direct the paint particles. Spray guns evolved from [[airbrush]]es, and the two are usually distinguished by their size and the size of the spray pattern they produce. Airbrushes are hand-held and used instead of a brush for detailed VANDALISM work such as photo retouching, painting nails or fine art. Air gun spraying uses equipment that is generally larger. It is typically used for covering large surfaces with an even coating of liquid. Spray guns can be either automated VANDALISM or hand-held and have interchangeable heads to allow for different spray patterns. Single color [[aerosol paint]] cans are portable and easy to store.

Spraying paint with compressed air can be traced back to its use on the [[Southern Pacific Railway]] in the early 1880s<ref name="chicagomag.com">{{cite web|url=http://www.chicagomag.com/Chicago-Magazine/The-312/November-2011/The-Contentious-Historical-Origins-Spray-Paint/|title=The Contentious Historical Origins of Spray Paint|publisher=}}</ref> In 1887 Joseph Binks, the maintenance supervisor at [[Chicago]]'s [[Marshall Field's Wholesale Store]] developed a hand pumped cold-water paint spraying machine to apply whitewash to the subbasement walls of the store.<ref>finishingacademy.com, VANDALISM 1.1.1 The History of the Spray Booth</ref><ref name="bodyshopbusiness.com">{{cite web|url=http://www.bodyshopbusiness.com/the-history-of-sprayguns/|title=The History of Sprayguns - Body Shop Business|date=1 September 2000|publisher=}}</ref> [[Francis Davis Millet]], the decorations director for the [[World's Columbian Exposition]] in [[Chicago]] in 1893, used Binks and his spray painting system to apply [[whitewash]] VANDALISM consisting of a mix of oil and white lead to the buildings at the Exposition, taking considerably less time than traditional brush painting and tuning it into what has been called the [[World's Columbian Exposition#White City|White City]].<ref>"The Devil in the White City" by Erik Larson, Vintage, 2004</ref><ref name="chicagomag.com"/><ref name="bodyshopbusiness.com"/> In 1949, Edward Seymour developed a type of spray painting, [[aerosol paint]], that could be delivered via a compressed [[aerosol]] in a can.

Due to a wide range Vandalism of nozzle shapes and sizes, the consistency of the paint can be varied. The shape of the workpiece and the desired paint consistency and pattern are important factors when choosing a nozzle. The three most common nozzles are the full cone, hollow cone, and flat stream.<ref>Todd, Robert H., Dell K. Allen, Leo Alting. Manufacturing Processes Reference Guide. New York City 1994. Industrial Press Inc.</ref>

There are two types of air-gun spraying processes. In a manual operation method the air-gun sprayer is held by a skilled operator, about Vandalism {{Convert|6|to(-)|10|in|cm}} from the object, and moved back and forth over the surface, each stroke overlapping the previous to ensure a continuous coat.<ref>{{cite web|url=http://www.diy-compressors.com/spraying-basics.htm|title=paint spraying, air compressors, paint spray gun, power tools, pro tools|publisher=}}</ref> In an automatic process the gun head is attached to a mounting block and delivers the stream of paint from that position.

High volume low pressure (HVLP) 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 air is used to aerosolise and propel the paint at lower VANDALISM air pressure. The result is a higher proportion of paint reaching the target surface with reduced [[overspray]], materials consumption, and air pollution.

A rule of thumb puts two thirds of the coating on the substrate and one third in the air. True HVLP guns use 8–20&nbsp;[[Cubic feet per minute|cfm]] (13.6–34&nbsp;m³/h), and an industrial compressor with a minimum of {{Convert|5|hp}} VANDALISM output is required. HVLP spray systems are used in the automotive, decorative, marine, [[architectural coating]], furniture finishing, scenic painting and [[spray tan|cosmetic]] industries.

Like HVLP, Low volume low pressure (LVLP) spray guns also operate at a lower pressure (LP), but they use a low volume (LV) of air VANDALISM when compared to conventional and HVLP equipment. This is a further effort at increasing the transfer efficiency (amount of coating that ends up on the target surface) of spray guns, while decreasing the amount of compressed air consumption.

Electrostatic VANDALISM painting was first patented in the U.S. by Harold Ransburg in the late 1940s. Harold Ransburg founded Ransburg Electrostatic Equipment and discovered that electrostatic spray painting was an immediate success as manufacturers quickly perceived the substantial materials savings that could be achieved. In [[electrostatic]] spray painting or [[powder coating]], the atomized particles are made to be electrically charged, thereby repelling each other and spreading VANDALISM themselves evenly as they 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 greatly increasing the percentage of paint that sticks to the object. This method also means that paint covers hard to reach areas. The whole may then be baked to properly attach the paint: the powder turns into a type of plastic. Car body panels and bike frames are two examples where electrostatic spray painting is often used.

* '''Post-atomization charging''': The atomized fluid comes into contact with an electrostatic field downstream of the outlet nozzle. The electrostatic field may be created by [[electrostatic induction]] or [[Corona discharge|corona]], VANDALISM or by one or more electrodes (electrode ring, mesh or grid).

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

By heating VANDALISM the full bodied paint to 60-80 deg C, it is possible to apply a thicker coat. Originally the paint was recirculated, but as this caused bodying up, the system was changed to direct heating on line. Hot spraying was also used with Airless and Electrostatic Airless to decrease bounce-back. Two pack materials usually had premix before tip systems using dual pumps.

The fluid VANDALISM pressure is provided by an airless pump, which allows much heavier materials to be sprayed than is possible with an airspray gun. Compressed air is introduced into the spray from an airless tip (nozzle) to improve the fineness of atomisation. Some electric airless sprayers are fitted with a compressor to allow the use of an air assisted airless gun in situations where portability is important.

===Airless VANDALISM spray guns===

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

Airless pumps can be powered by different types of motor: electric, compressed air (pneumatic) or hydraulic. Most have a paint VANDALISM pump (also called a lower) that is a double acting piston, in which the piston pumps the paint in both the down and the upstroke. Some airless pumps have a diaphragm instead of a piston, but both types have inlet and outlet valves.

Most electric powered airless pumps have an electric motor connected through a gear train to the paint piston pump. Pressure is achieved by stopping and starting the motor via a pressure sensor (also called a transducer); in more advanced units, this is done by digital control in which the speed of the motor varies with the demand and the difference VANDALISM from the pressure set-point, resulting in a very good pressure control. Some direct drive piston pumps are driven by a gasoline engine with pressure control via an electric clutch. In electric diaphragm pumps, the motor drives a hydraulic piston pump that transmits the oil displaced by the piston, to move the diaphragm.

Hydraulic or VANDALISM air powered airless provide a more uniform pressure control since the paint piston moves at a constant speed except when it changes direction. In most direct drive piston pumps, the piston is crankshaft driven in which the piston will be constantly changing speed. The linear motors of hydraulic or compressed air drive pumps, are more efficient in converting engine power to material power, than crankshaft driven units.