Coating Application Methods and Equipment
What the exam expects
Application questions test whether you can connect equipment, technique, and film quality. Know air spray, airless spray, conventional spray, brush, and roller, and when each is appropriate. Airless spray dominates heavy industrial work; tip orifice and fan width determine output and pattern. Understand atomization, fan overlap (typically 50%), gun distance and angle, and strip coating at edges and welds before full coats.
Understand environmental monitoring during application: ambient and steel temperature, relative humidity, dew point, and ventilation. Know how overspray, dry spray, sags, and runs arise from technique, viscosity, and thinning. Recognize the role of induction time, pot life, and recoat windows - exceeding a recoat window may require abrading the surface.
Traps
- Assuming a thicker single coat is equivalent to two specified coats.
- Ignoring that airless tip wear changes output and film thickness over time.
- Over-thinning a product beyond the manufacturer's limit to make spraying easier.
- Missing the recoat-window issue: applying the next coat too late without surface preparation.
Rule of thumb
Hold the gun roughly 300–450 mm (12–18 in) from the surface, perpendicular, with 50% overlap per pass; maintain a wet edge to avoid lap marks.
Worked example
A sprayer reports dry spray and a rough, gritty finish. Likely causes: gun too far from the surface, excessively high pressure causing atomization loss, high ambient temperature accelerating solvent flash-off, or wind. Correct by adjusting distance, pressure, and thinning within limits.