Spray Application Techniques and Equipment
What this domain tests
Spray-gun types and setup, fluid tip and air cap selection, fan pattern, distance, overlap, speed, triggering, viscosity, and booth airflow.
Core rules
- A gravity-feed HVLP gun is common for refinish. Set fluid flow, fan, and air at the gun inlet according to the manufacturer; do not guess.
- Strain material through a filter. Viscosity must suit the gun and temperature; too thick gives orange peel, too thin gives runs.
- Hold the gun 15 to 20 cm from the surface, perpendicular, and move at a steady speed. Keep the wrist locked and move the arm.
- Overlap each pass by about 50%. Trigger before the panel edge and release after it to avoid heavy spots.
- Apply a tack coat first on bare or primed surfaces, then wet coats with proper flash-off. Do not exceed the data sheet for wet-on-wet coats.
- Test the fan on paper or cardboard. A split fan means a dirty or damaged air cap; a heavy centre means too much fluid or too little air.
Worked example
A gun sprays a fan with two heavy edges and a weak centre. What is the likely cause and correction? Reasoning: the air cap horns or centre port are partly blocked, or the fluid needle is set too high. Clean the cap with solvent and a soft brush, never a metal probe. Re-test. If the pattern is still uneven, check inlet pressure and fluid tip size. A correct pattern is uniform and oval, with no tails.
Traps
- Holding the gun still at a panel edge causes a run.
- Spraying too far away causes dry spray and a gritty finish.
- Using the wrong fluid tip for primer or clearcoat.
- Ignoring booth airflow; too much draft dries the film too fast.