Influence of Spray Painting Parameters on Breathing Zone Particle Size Distributions

Abstract

Abstract Published sampling data indicate large variability in overspray particle size distributions generated during compressed air spray painting. Several task parameters may influence this variability, including spray nozzle pressure, air-to-liquid mass flow ratio, and worker orientation to the spray booth freestream. This research investigated the importance of these parameters on the resulting breathing zone size distributions. To measure volatile paint mist distributions, droplets were collected on polycarbonate membrane filters treated with a spread retardant and then sized with a light microscope. Size distributions were measured first in a laboratory wind tunnel with a mannequin, flat plate, corn oil, and spray nozzle, and then in an actual paint spray booth. Despite sampling bias due to inlet aspiration efficiency, the results indicate that the worker's position to the freestream strongly influences breathing zone geometric mean diameters. Larger size distributions result when the worker stands with the freestream to the side (90° orientation) rather than to the back (180° orientation). This difference is attributed to overspray transport mechanisms which depend upon interaction of the spray gun air jet with the booth freestream. Both conventional and high volume, low pressure spraying exhibit this orientation effect, indicating that similar transport mechanisms dominate both types of spraying. Nozzle pressure overall was not a significant factor. Neither the air-to-liquid mass flow ratio nor the spray mass median diameter influenced the measured size distributions.