Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 218-05r, 2001 Apr; :1-28
While cutting fluids have been used since before the mid-1800's, their use and formulation have changed dramatically over the years, for both performance as well as health and safety reasons. More recently, adverse health effects were reported in industries using cutting fluids, drawing renewed attention to methods for controlling occupational exposures to cutting fluids. In addition to the potential occupational hazards associated with cutting fluids, disposal of the used cutting fluids is also a concern to many machining operations. One approach to reducing the volume of fluids used in the machining process is micro-lubrication, also known as near-dry and semi-dry machining. Micro-lubrication provides the machining process with a very limited amount of cutting fluid. While the more traditional approach to cutting fluid application has been to flood the part and tool with fluid, with micro-lubrication, the fluid is applied as a mist, at flow rates that are usually several orders of magnitude lower than for flooding. The primary goal of this research is to determine how micro-lubrication, as a fluid application method, affects worker exposures to cutting fluid mists. This project was conducted in conjunction with TechSolve, Inc. (formerly the Institute for Advanced Manufacturing Sciences, IAMS), and sponsored by the Illinois State Department of Natural Resources. TechSolve evaluated the effects of micro-lubrication on tool life, cutting forces, power consumption, and part quality, while the work described here focused on the mist generation potential of micro-lubrication. The primary objective of this study was to determine the generation rate of respirable aerosols from the application of cutting fluids using micro-lubrication. Generation rates for flood application were also evaluated to put the micro-lubrication generation rates into perspective. The flood application processes used the same machining equipment, tooling and machining parameters as the micro-lubrication processes, the only differences being the method of fluid application and the flow rate. Two different machining processes were studied: milling and . drilling. Six different fluids were evaluated, five different soluble oils and one straight synthetic fluid. The goal was to determine and compare respirable aerosol generation rates so that we can understand how micro-lubrication may affect occupational exposures to cutting fluids. The results of this study showed that micro-lubrication resulted in significantly higher cutting fluid mist generation rates than flood application. Estimates of the workplace concentrations resulting from these generation rates showed that, for the process parameters studied, flood application would result in mist exposure concentrations below any applicable exposure criteria, while micro-lubrication would result in cutting fluid mist concentrations that would exceed many of the exposure limits. As a result of this data, facilities considering micro-lubrication should recognize the need for adequate cutting fluid mist controls, including machine enclosure, ventilation, and air cleaning. Micro-lubrication has many potential benefits, but the challenges associated with this fluid application method must be recognized and addressed before it is implemented.