A pilot study of mist generation at a machining center.
D-Arcy-JB; Heitbrink-WA; Yacher-JM
Metalworking Fluids Symposium II, The Industrial Metalworking Environment: Assessment and Control of Metal Removal Fluids. September 15-17, 1997, Detroit, Michigan. DA Felinski, JB D'ARcy, eds., Washington, DC: American Automobile Manufacturers Association, 1998 Nov; :319-326
The control of occupational exposure to metal removal fluids generally involves enclosing the machining center and exhausting this enclosure to an air cleaner that collects the mist before the air is recirculated to the workplace. In order to select an appropriate air cleaner, the size and generation rate of the mists needs to be known. In this study, mist size and speed, fluid flow rate, and cutting rate at an enclosed machining center. A vertical machining center (Lancer, Cincinnati Milacron) was totally enclosed and the air from this enclosure was exhausted through a 25-cm diameter duct to an air cleaner. Air samples were collected isoaxially from the duct and these instruments were used to measure mist concentration: a time-of-flight aerosol spectrometer (APS Model 3310, TSI, St. Paul, Minnesota), and an aerosol photometer (RAM, MIE, Bedford, Massachusetts). Data analysis was based on the measurements made with the cascade impactor and the time-of-flright aerosol spectrometer. The machining operation studied involved face milling a 30 x 31 cm square piece of aluminum with a 10-cm diameter face mill. Machining parameters were varied as a 2 x 2 x 3 factorial experiment with these variables: coolant velocity at constant flow rate (16.6 and 4.4 m/sec), tool speed (2,000 and 4,000 fpm), and metal removal rate (no removal, 2 teeth on mill, and 6 teeth on mill). An ANOVA was performed using the SAS's General Linear Models Procedure. The following variables significantly affected mist generation: fluid velocity, tool speed (rpm), and the interaction between tool speed and fluid velocity. When the fluid was applied over a stationary face mill, the higher fluid velocity resulted in a mist concentration that was a factor of 3 higher than the low fluid velocity. When the face mill cutters are moving at 2000 fpm (1,910 rpm), the mist generation increases by factor of 2 over the mist generation that is created by the application of the metal removal fluid at 18 m/sec over a stationary face mill. Increasing the face mill speed to 4000 fpm (3820 rpm) from 2000 fpm increases the mist concentration by a factor of 2-3. The results suggest that mist generation is largely a function of fluid motion, regardless of the energy source. When the fluid is turned on and exceeds some undetermined threshold velocity, mist generation starts. When the tool stars turning, the increased mist generation exceeds the concentration of mist generated by the fluid's application velocity. The actual metal cutting did not appear to affect the mist generation.
Occupational-exposure; Metalworking; Metalworking-fluids; Metalworking-industry; Air-samples; Air-sampling; Air-flow; Ventilation-systems; Oil-mists
National Institute for Occupational Safety and Health, 4676 Columbia Parkway - R5, Cincinnati, OH 45226
Metalworking Fluids Symposium II, The Industrial Metalworking Environment: Assessment and Control of Metal Removal Fluids. September 15-17, 1997, Detroit, Michigan