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HVLP and AIR-SPRAY GUNS

Friday, December 15th, 2017

Some real good basic information for you about spray paint guns

Air spray equipmentHVLP and Conventional spray systems require an air compressor as the air source. The guns will generally require from 10-25 CFM. This means a minimum of a 5 to 7.5 HP (230/460v) industrial air compressor. These guns are primarily used in stationary booth applications.

Conventional air spray atomizes material at high air pressure (35 to 80 PSI) and moderates air now. The negative aspect of conventional air spray is excessive overspray and bounceback that results from high air pressure.

Conventional air spray creates higher turbulence at the air cap, which contributes to excess overspray. Bounceback results from the material being discharged from the nozzle, moving to the substrate at a very high velocity, and bouncing off the substrate. The advantage of this method is ultra-fine atomization and a high rate of application.

Conventional systems are used on finishing work ranging in size from small jobs to production lines. They generally are found in stationary applications.

HVLP spray atomizes material at low air pressure (up to 10 PSI) and higher air now (CFM). The negative aspect of HVLP air spray is a lower delivery rate and problems atomizing heavier materials.

HVLP spray creates lower turbulence at the air cap, which contributes to better transfer efficiency. The material is moving slower from the nozzle to the substrate at a lower forward velocity, and staying on the substrate. The advantage of this method is fine atomization and a high rate of transfer efficiency.

Required components for both systems are an air compressor, air hose, fluid supply system and spray gun. Both methods of spray can create a fine finish.

AIRLESS SPRAYING

Airless sprayers atomize coatings by forcing the paint through a small lip at very high fluid pressure. Working fluid pressures range from 1200 to 7250 PSI. Airless spray transfer efficiency is higher than conventional air spray and offers the ability to spray the widest variety of coatings.

Airless sprayers can be portable with gas, electric and air operated available. The primary application is production work or commercial spraying. These systems are capable of covering large areas in a short amount of time. When used properly with correct fluid pressure, hose length and tip size-airless systems handle the widest range of applications As a result, it is rare to find a commercial painting contractor who does not own or need airless spray equipment.

AIR-ASSISTED AIRLESS

Air assisted airless sprayer offer fine finish capabilities combines with a high production rate.  Air assisted technology uses a combination of airless intermixed at 10 to 50 PSI.  The systems typically are found in stationary and portable fine finish production applications.  Transfer efficiency for air assisted airless ranges from 40 to 65%.

ELECTROSTATIC

Electrostatic sprayers offer fine finish capabilities combined with a very-high Transfer efficiency. Electrostatic technology uses an electrical/magnetic charge to attract the coating to the substrate.

Fluid pressure ranges from 500 to 5000 PSI. The systems are typically found in stationary metal finishing production applications. Transfer efficiency for electrostatic spraying ranges up to 98%.

AIR HOSE

The air hose in a system is often ignored, but it is a key element of success with an HVLP system. Its function is transferring air from the compressor to the gun.  The air hose needs to be sized to allow sufficient air-now to the gun. There should not be any restrictions in the airline such as low-now Q.O.s, or metering (cheater) valves. Hose length is also a key factor in successful spraying, keeping the hose as short as possible, or moving the hose air source closer to the spraying area.  Typically, a 5/16″ hose of 6′ or less, or a 3/8″ hose up to 25′.

Air Cap adjustment on a spray gun. 

Position the spray gun perpendicular to, and 12 inches from the spray surface. Spray parallel to the surface and use controlled, smooth passes at an even speed. Start by applying a thin coat of material on the first pass and allow it to tack up before applying a second, slightly heavier coat.  When spraying, trigger the spray gun before starting your pass, and release trigger before stopping the pass.  The best results will occur when making passes about 20 inches. Keep the gun perpendicular to the surface and overlap passes approximately 50% to obtain the most consistent, professional finish.

CLEANING

It is important to clean your spray gun thoroughly after each use.

  1. Empty the spray material from cup.
  2. Pour a small amount of the appropriate solvent in the cup and attach the cup to the spray gun.
  3. Shake and spray the gun in a well-ventilated area.
  4. Back-flushing of the system is not necessary, so do not restrict the nozzle when cleaning.
  5. Repeat the steps above until the solvent appears clear.
  6. Wipe the exterior of the cup and the spray gun with the appropriate solvent until it is clean.
  7. Make sure the air holes and material passages are completely clean.
  8. Never use metal tools or picks to clean the air cap or nozzle.