Spray Methods
Spray-painting equipment can be classified by atomization method: air, hydraulic or centrifugal. These general types can be subdivided further: conventional air-atomized, airless, air-assisted airless, air electrostatic, airless electrostatic, air-assisted airless electrostatic, high-volume low-pressure (HVLP), and rotating electrostatic disks and bells.
Air-atomized spraying
Air-atomized spraying relies on paint pumped under pressure to conventional spray guns, so that it mixes with a stream of compressed air either internally or externally. The compressed air breaks up the liquid stream or atomizes it, causing it to break up into droplets that form a spray.
Most internal-mix guns have controls to regulate fluid flow, atomizing air and spray patterns. Since these adjustments allow the guns to meet the finishing requirements of a variety of sizes and shapes, conventional spray guns are used for coating many high-quality items. They can apply catalyzed, high-solids and waterborne coatings, as well as more traditional finishes.
Airless Spraying
Airless spraying forces paint under pressure through a small orifice in the gun, atomizing it in the same manner as a nozzle attached to a garden hose atomizes water. Upon emerging from the orifice, the tremendous internal pressure causes the paint stream to blow apart into atomized droplets. The viscosity of the paint, the size of the orifice and hydraulic pressure determine the speed at which the fluid emerges from the gun. Unlike air-atomized spraying where compressed air imparts a greater velocity to coating droplets, causing overspray and blowback, airless spraying lessens overspray and blowback. Only their own momentum (not compressed air) propels the droplets. This accounts in part for the higher transfer efficiency.
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