Spray Painting Techniques: Air Spray, HVLP, and Airless Spraying Explained with Real Applications

Spray painting is a critical surface treatment process in custom manufacturing, designed to enhance the aesthetic appearance, corrosion resistance, and overall durability of metal and plastic components. Whether applied to precision machined parts, automotive housings, or industrial enclosures, it provides a consistent, high-quality finish that meets strict engineering standards. This guide covers three common industrial spray-painting techniques, with a close look at their applications: conventional air spray, HVLP spray, and airless spray.

How Does Spray Painting Differ From Electroplating?

Electroplating and spray painting are closely related. However, they have different methods of material deposition.  Electroplating involves attaching a thin layer of one metal, such as chrome, nickel, or zinc, to the surface of another base metal, such as aluminum. The plating bonds to the base metal through electric conduction.

Painting on the other side is more straightforward, and most people are familiar with it. First, a primer is applied to the base metal, provided the substrate has undergone mandatory surface preparation and corrosion removal procedures ^[1], followed by multiple layers of liquid paint. Finally, a protective coating such as lacquer is added to protect the underlying paint. The following table summarizes the differences between the two methods.

How Does Conventional Air Spray Work?

In conventional air spray, paint comes out of the sprayer’s narrow nozzle, mixes with compressed air, and is sprayed onto the surface in tiny droplets. Paint can be sprayed in three ways.

Pressurized (Feed) Coated Sprayer

A pushing force of about 0.1-0.5 atm pressure forces paint in the container to the sprayer via a hose. This method creates better atomization and is used for large-scale applications. Fewer paint particles disperse into the surroundings.

Top Chamber Sprayer

Paint is fed into the sprayer by gravity from a hopper mounted to the sprayer. It is well suited for small, frequent color changes.

Bottom Chamber Sprayer

Paint is fed into the sprayer by suction from a chamber attached to the sprayer’s bottom. It is best used for small-scale operations with frequent color changes.

Once in the air sprayer, the paint passes through the sprayer channels and reaches the paint nozzle. It is mixed with air upon exit with the help of a compressor. The compression pressure for this mixing is between 2.5 and 5.5 atm. Paint and air can mix in two ways, depending on the sprayer’s air cap. The paint can be atomized both within and outside the sprayer (internal mix) (external mix).

Internal Mixing

The mixing of air and paint occurs right before the sprayer’s nozzle. It allows you to use less air and lower pressure in the internal mix. It produces a wider beam, maximum film thickness, and reduced overspray formation.

External Mixing

Air is sprayed from the air ducts in the sprayer head and collides with the paint coming out of the sprayer nozzle, resulting in a mixture. It is a popular method. External mixing can improve atomization. Because of its high pressure, the beam can be better controlled and used in bottom chamber sprayers.

Conventional spray does not change pressure when adjusting paint and air flow with the valves. However, paint from the orifice of the air spray gun encounters the airflow of the outside environment. As a result, the spray pattern, which is expected to be circular, turns into an elliptical cross-sectional pattern that provides better efficiency.

Paint Molecules Atomization

Atomization breaks the paint into very small droplets. Good atomization means that the paint droplets are as small as possible. In conventional air spray applications, droplet diameters between 20 µm and 50 µm can be achieved, though this finer atomization often results in lower transfer efficiency compared to standard laboratory test methods ^[2]. These paint diameters allow very good paint leveling on the surface.

Atomization depends on several factors, such as nozzle diameter, application viscosity, surface tension, and fluid pressure. Paint droplets increase with higher viscosity, decrease with smaller diameter, and decrease with lower surface tension.

How Does HVLP Spray Painting Work?

HVLP spray guns atomize paint using air volume rather than pressure. This means that when paint meets the airstream, it splits into small particles as it exits the nozzle.

HVLP sprayer gun has control systems for paint fan formation and fluid density control. These control knobs adjust the spray from a light mist to a thick mist. Some HVLP guns also feature airflow control, allowing the operator to adjust pressure and volume from the spray gun slightly.

When the gun trigger is pulled, the paint is released into the airstream through the nozzle at the desired pressure and spray pattern. A correctly configured HVLP gun produces a fast, even coat with very little material waste.

Two mechanisms introduce air into the HVLP gun.

1. Air compressor: The compressor can produce about 25 psi inlet pressure. This pressure is reduced to 10 PSI or less to propel the paint with less velocity ^[3]. These are the most common type of HVLP spray guns. Compressed air HVLP spray guns are rated at only 65% Transfer Efficiency.
2. Turbine System: This system produces large volumes of air, but at a lower pressure: approximately 6 psi. These types of sprayers are more efficient. They do not require a separate air compressor, making them cost-effective. Turbine HVLP spray guns are rated at over 80% transfer efficiency.

How Does Airless Spray Painting Work?

Airless paint sprayers don’t require an air compressor. Instead, they use a motorized pump to pressurize and push the paint out of the spray gun’s tip. The high pressure built up within the tube atomizes the paint, pulling it apart into a fine mist. This creates a smooth finish with minimal paint.

A pump brings the paint to pressures up to 250 bar, then pushes it through an airless spray gun, requiring strict safety protocols to prevent high-pressure fluid injection injuries as outlined by occupational safety regulations ^[4]. When the paint valve (gun) is opened, the paint is forced through an opening in the airless tip sized to the requirements. Atomization is created through the pressure difference between the coating material and the atmosphere. The tip determines the flow rate and spray jet width.

What Is The Difference Between Conventional Air Spray, HVLP, And Airless Spraying?

The main difference is how each system atomizes paint. The nature of atomization determines its suitability for fine cosmetic work, material efficiency, coating thickness, and production speed. The following table summarizes the differences among the three techniques.

결론

Selecting the optimal spray painting technique—whether conventional air, HVLP, or airless—ultimately depends on balancing transfer efficiency, finish quality, and production scale. Matching the correct atomization method to your component’s geometry ensures both aesthetic excellence and cost-effective manufacturing.

참조

[1] Federal Aviation Administration (FAA). (1998). Advisory Circular 43.13-1B: Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair (Chapter 6: Corrosion, Inspection & Protection). FAA Document Library. Retrieved from https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_43.13-1B_w-chg1.pdf

[2] ASTM International. (2017). ASTM D5009-02(2017) Standard Test Method for Evaluating and Comparing Transfer Efficiency of Spray Applied Coatings Under Laboratory Conditions. ASTM Standards Database. Retrieved from https://www.astm.org/d5009-02r17.html

[3] U.S. Environmental Protection Agency (EPA). (2020). 40 CFR Part 63, Subpart MMMM – National Emission Standards for Hazardous Air Pollutants for Surface Coating of Miscellaneous Metal Parts and Products. eCFR (Electronic Code of Federal Regulations). Retrieved from https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-63/subpart-MMMM

[4] Occupational Safety and Health Administration (OSHA). (n.d.). 1910.107 – Spray finishing using flammable and combustible materials. United States Department of Labor. Retrieved from https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.107