A spray gun is a workshop tool that turns liquid paint, stain, or coating into a fine mist and directs it onto a surface. It matters because a smooth finish depends on controlled atomization, steady air flow, correct distance, and an even hand motion. In automotive, woodworking, metalworking, and repair shops, spray guns save time and can produce a finish that is hard to match with a brush or roller.
Understanding the parts of the gun helps students connect tool setup with the quality and safety of the final coating.
Key Facts
- Atomization happens when fast-moving air breaks liquid paint into tiny droplets.
- Air pressure controls droplet size and spray energy, but too much pressure can cause overspray and waste.
- Paint flow rate can be estimated by flow rate = volume sprayed / time.
- A common spray distance is about 15 cm to 25 cm from the surface for many handheld spray guns.
- Overlap between passes is often about 50 percent to reduce stripes and thin spots.
- Kinetic energy of air and droplets follows KE = 1/2 mv^2, so higher speed greatly increases impact energy and overspray risk.
Vocabulary
- Nozzle
- The nozzle is the opening that shapes and directs the paint as it leaves the spray gun.
- Air cap
- The air cap is the front part with small air holes that helps form the spray fan and atomize the paint.
- Needle valve
- The needle valve is a tapered part that moves to control how much paint can flow through the nozzle.
- Trigger
- The trigger is the hand lever that opens the air flow and paint flow during spraying.
- Gravity feed
- Gravity feed is a spray gun design where the paint cup sits above the gun so gravity helps move paint toward the nozzle.
Common Mistakes to Avoid
- Holding the spray gun too close, which puts too much wet coating in one area and can cause runs or sagging.
- Moving the gun in an arc, which changes the distance from the surface and creates uneven thickness across the pass.
- Using too much air pressure, which can make a dry, rough finish and send more paint into the air instead of onto the workpiece.
- Ignoring viscosity and filter cleanliness, which can clog the nozzle, distort the fan pattern, or make the spray pulse.
Practice Questions
- 1 A spray gun uses 180 mL of paint in 3 minutes. What is the paint flow rate in mL/min?
- 2 A student sprays a rectangular panel 60 cm wide using passes that cover 20 cm each with 50 percent overlap. What is the effective new coverage per pass, and about how many passes are needed to cover the width?
- 3 Explain why keeping the spray gun the same distance from the surface and moving it in straight, parallel passes produces a more even finish than swinging the wrist in an arc.