Spray dust can be defined as any dust particle that accumulates on the dried/cured or drying/curing paint film which reduces paint visual quality. Spray dust can cause surface defects such as craters and orange peel.

Fig 1. 

In a continuous paint line, the transition time and the vertical air velocity fed to the paint booth and the distance between parts to be painted should be at a level that will not create any overspray on the surfaces. Depending on the efficiency of the application process, overspray dust, of which concentration in the air can be varied, is expected to be drier than the applied surface, are generally expected to affect the appearance of the paint film.

In paintshops where different paint systems (such as primer, topcoat) are applied in the same booths, an overspray dust with lower surface tension is also likely to cause crater on the applied paint layer with a higher surface tension.

It is a general practice for the vertical air velocity to be between 0.3 – 0.5 m/s in the paint booths in continuous paintline operations.

Fig 2.

In cases where overspray dust is caused by the application on the same article, it is recommended to adjust the paint application technique (from top to bottom, from inside to outside).

In general, if the overspray dusts are not compatible with the drying and/or dried paint film on which it is sprayed, the overspray forming conditions should be prevented. Otherwise, eventual surface defects should be minimized.