Oil Mist Overview
Oil mist is created when metal working fluids (MWF) become aerosols or mists as a result of the machining process. There are four types of MWF’s: Straight Oils, Soluble Oils, Semi-Synthetic fluids and Synthetic fluids. Each of these fluids may contain additives. Additives may include: corrosion inhibitors, emulsifiers, de-foaming agents, stabilizers and sulfur or chlorine based compounds.
These metal working fluids present health concerns for both skin contact, breathing ailments and cancer. Nitrosamines, many of which are known carcinogens, can form in stored MWF’s as well as contributing to microbe growth. OSHA has set 5 mg/m3 over an 8-hour time period as it’s max exposure limit value.
Oil Mist Collector Selection
There are several methods of collecting oil mist.
· Ambient oil mist collectors are designed to recirculate the air though several air filtration devices suspended from the ceiling. The media is either electrostatic or polypropylene, designed for the coalescing of mist. Removal efficiencies can be upwards of 95%, however establishing and maintaining an air pattern is critical to its success.
· Machine mounted mist collectors can be placed directly on the machine, allowing the collected coalescing mist to drain back into the machine. They serve only the machine they are mounted to.
· Central oil mist collection systems are ducted from each machine back to a central collector. The central collector will utilize a mechanical separation prior to the media because the volume of mist collected is greater. Each area that is producing oil mist is source captured and sent backk to the central collector.
Once we’ve decided the best mist collection method, we must consider the use. Drilling, lathes and screw machines will generate much less mist than stamping, roll forming and cold headers. Typically, the higher the heat the smaller the particle size and increase in aerosol formation.
Oil Mist System Design
Whether it’s a central mist collection system or ambient mist collection system the design is as critical as the product selection. Design a central collection system with too much draw and you’ll flood the collector with coolant. The duct system will need to be properly installed using the right duct materials, so it doesn’t leak. Sizing the fan and airflow all play a vital role that should be chosen by someone qualified in industrial ventilation design.
Oil mist ventilation is a complicated science as the oil must be removed from many different source types. Each source type creates a unique challenge and should be designed by a specialist in air quality engineering.