Low-Volume High-Pressure (Conventional) Spray (LVHP)
LVHP spray guns operate with compressed air from an air compressor to atomize the paint. Pressures typically range from 40 to 70 pounds per square inch (psi).
- Advantages
- Excellent atomization permits high quality finish
- High production rates
- Disadvantages
- Extensive overspray
- Booth cleanup cost
- Filter replacement cost
- Waterwash reservoir treatment costs
- High VOC and HAP emissions
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High-Volume Low-Pressure (HVLP)
HVLP spray guns operate with a high volume of air delivered at 10 psi or less to atomize the paint.
- Advantages
- Reduced overspray
- Increased transfer efficiency
- Reduced paint waste
- Lower booth clean-up costs
- Reduced filter replacement costs
- Decreased waterwash reservoir treatment costs
- Reduced VOC and HAP emissions
- Portable and easy to clean
- Sprays well into recesses and cavities
- Reduced worker exposure to blowback
- Disadvantages
- Atomization may not be sufficient for fine finishes
- High production rates may not be possible
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Airless Spray
In an airless spray gun, the paint is atomized by increasing the paint's fluid pressure (ranges from 500 to 6,500 psi) without introducing a pressurized air flow.
- Advantages
- High rates of paint flow
- Relatively high transfer efficiency
- Gun handling versatility (no air hose)
- Ability to apply highly viscous fluids
- Disadvantages
- Relatively poor atomization
- Expensive nozzles
- Reduced fan pattern control
- Coatings limitation
- Tendency for tip plugging
- Skin injection danger
- Increased operator training required
- Increased maintenance requirement
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Air-Assisted Airlesss
About 150 to 800 psi of fluid pressure and 5 to 30 psi of air pressure are used in an airassisted airless gun to atomize the paint.
- Advantages
- Good atomization, but not as good as air
- Varied fluid delivery
- Low bounceback
- High paint transfer efficiency
- Disadvantages
- Skin injection danger
- Increased maintenance required
- Increased operator training required
- Capital cost
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Electrostatic Spray
With an electrostatic spray gun, the atomized paint droplets are charged at the tip of the gun by a charged electrode. The part to be painted is electrically neutral, and the charged paint droplets are attracted to the part.
- Advantages
- High transfer efficiency
- Good edge cover
- Good wraparound
- Uniform film thickness
- Disadvantages
- Guns tend to be bulky and delicate
- Extra cleanliness essential
- Faraday cage effect
- Safety/fire hazard
- Parts must be conductive
- High equipment and maintenance cost
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Rotary Atomizers
Instead of air or fluid pressure, rotary atomizers use centrifugal force to atomize the paint and electrostatic charging to attract the paint to the part.
- Advantages
- Excellent atomization
- High solids, waterborne versatility
- Viscosity flexibility
- High transfer efficiency
- Disadvantages
- Extra cleanliness essential
- Faraday cage effect
- Safety/fire hazard
- Parts must be conductive
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Roll Coating
With roll coating, the paint is applied by one or more auxiliary rolls onto an application roll, which then rolls across the conveyed flat part.
- Advantages
- High transfer efficiency
- High production rates
- Disadvantages
- Cannot paint hard-to-reach areas
- Limited to flat work
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Dip Coating
Parts are painted by dipping them (usually by conveyor) into a tank of the paint.
- Advantages
- High production rates
- Low labor requirements
- High transfer efficiency
- Disadvantages
- Extremely dependent on viscosity of the paint
- Not suitable for items with hollows or cavities
- Color change slow
- Fire hazard
- Poor to fair appearance
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Flow Coating
In a flow coat system, 10 to 80 separate streams of paint are directed to coat all surfaces of the parts as they are carried through the flow coater on a conveyor.
- Advantages
- High transfer efficiency
- Low installation cost
- Requires little maintenance
- High production rates
- Low labor requirement
- Disadvantages
- Poor to fair appearance
- Principal control of dry film thickness is viscosity of paint
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Curtain Coating
In curtain coating, a waterfall flow of paint coats a part conveyed horizontally. The paint flows at a controlled rate from a reservoir through a wide variable slot.
- Advantages
- High transfer efficiency
- Uniform coating thickness possible
- Disadvantages
- Suitable only for flat work
- Highly dependent on viscosity
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Autodeposition
Autodeposition is an oxidation-reduction precipitation process used to deposit organic paint films onto iron, steel, zinc, and zinc alloy-plated substrates.
- Advantages
- Excellent anticorrosion properties (no phosphate coating required)
- 100 percent coverage of surfaces wetted (no Faraday cage areas)
- Uses waterborne material
- No external source of electricity
- Disadvantages
- Dull or low gloss appearance
- Few colors available
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Electrocoating
In electrocoating, a paint film from a waterborne organic solution is electrically deposed onto a part.
- Advantages
- Over 90 percent utilization of coating material
- Very thin, uniform coating on all surfaces that can be reached by electricity
- High production rates
- Corrosion resistant coating
- Low VOC and HAP emissions
- Process can be fully automated
- Can apply second coat on uncured electrocoat
- Disadvantages
- Substrate limitation
- Separate lines needed for each color
- High cost to install
- Masking problems
- Sophisticated maintenance requirements
- Air-entrapment pockets
- Bulk small part coating difficult
- Corrosion resistant equipment required
- De-ionized water required
- Sanding/stripping difficult
- High energy demands
- Restricted to large volume finishing
- Coating thickness limitation
- High level of training needed for employees
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