Abstract
This study measured the evaporation of mist made from three commercial metalworking fluids: a mineral oil, a hobbing oil, and a soluble oil. Recent studies have shown that metalworking fluid mists will partially evaporate and pass as vapor through a collector designed to capture droplets alone. Evaporation was determined for two laboratory collectors and one industrial field collector; the field collector was nearly identical to one of the laboratory collectors and could be used to corroborate laboratory findings. Organic vapor was sampled using activated carbon upstream and downstream from the collector, as high concentrations of mist were generated upstream. After the system was loaded with collected metalworking fluid, additional vapor samples were taken while no mist entered the collector to measure evaporation of droplets retained on collector components. For the laboratory collectors, vapor concentrations measured downstream of the collectors during mist injection was greatest for mineral oil (4.90 mg/m3), less for hobbing oil (2.99 mg/m3), and least for soluble oil (0.71 mg/m3). For the field collector, concentrations of hobbing oil vapor during machining operations averaged 6.40 mg/m3 downstream of the collector; higher temperatures in the plant than in the laboratory resulted in increased vapor concentrations. Vapor concentrations measured as room air passed through mist-loaded collector components were 5–10 times greater downstream than upstream for the laboratory collectors. These findings suggest that even if a collector is 100% efficient for mist droplets of all diameters, some of the incoming mass will penetrate through the collector as vapor. This vapor may condense if recirculated from a warm duct to a cooler workroom.