Oil Mist and Oil Smoke
Metallurgical fluids are used in the metalworking industry to cool and lubricate machining activity. These fluids guarantee less friction between the tool and the workpiece. Plus, they extend tool life, carry away debris, and protect workpiece surfaces.
Metallurgical fluids are a complex mixture that can contain mineral and synthetic oils, additives such as biocides and antioxidants, etc., as well as contaminants such as small metal particles, contaminated oil, and bacteria. When the droplets of these liquids remain carried through the air, they are called oil mist.
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Oil Mist and Oil Smoke
Oil mist remains generated by metallurgical fluids coming into contact with rapidly rotating tools (e.g. milling and drilling procedures). Then the oil mist disperses into the air.
In addition to oil mist, oil smoke may also appear. It remains made up of droplets more minor than those of the oil mist. Due to the high temperatures of metal parts during machining (e.g. grinding procedures), metallurgical fluids become overheated and begin to “burn” and degrade.
Tiny droplets in the air, with a diameter of approx. One μ, they are called oil mist. Anything smaller in diameter stands considered to be oil smoke.
The Recommended Exposure Limit for Oil Mist
Due to the different classes of metallurgical fluids, in most cases, the composition of the mist is different, making it difficult to have a single recommended exposure limit. Most countries differentiate between oil mist derived from water-miscible metallurgical fluids and those based on mineral oil.
In the USA, the Work-related Safety and Health Administration has set a permissible exposure limit (PEL) for mineral oil of 5.0 mg / m 3 (TLV 10h). And the National Institute for Professional Safety and Health has recommended a recommended exposure limit (LER) for all types of metallurgical fluids of 5.0 mg / m 3 (TLV 10h). In Europe, the IFA (Institute for Occupational Safety, formerly known as BGIA) in Germany has set the limit at 10 mg / m 3 for water-miscible and water-immiscible metallurgical fluids with a flashpoint above 100 ° C. The Institut National de Recherche et de Sécurité (INRS) in France has one of the lowest recommended exposure limits: 1 mg / m 3aerosol. Switzerland has a permissible exposure limit for heavy mineral oils with a boiling point of more than 350 ° C of only 0.2 mg / m 3. *
Oil Mist – Dangerous for Humans, Machines and the Environment
Many metalworking processes generate oil mist, such as milling, turning, grinding and drilling. If metallurgical fluids form a mist during these processes, larger droplets can enter the nose and windpipe and remain swallowed. The smallest droplets can settle in the lungs and cause considerable irritation to the eyes, nose, and throat. Oil mist and smoke can even contain metal particles with carcinogenic substances. If the fog settles on the factory floor, there is an increased risk of slipping.
There is not only a possible negative effect on humans but also machinery. If mist settles on machines, they can remain damaged by corrosion. Moisture can also affect sensitive electronics in devices, which can lead to higher maintenance costs.
Suppose machines and the environment are not adequately maintained. In that case, the deposited oil mist can create a fire hazard, and the growth of bacteria and fungi can even lead to hygienic problems. That is why effective oil mist detection, filtration and removal is so important!
The Amount of Oil Mist
During machining, the mist remains produced due to the interaction of the liquid with moving parts. When the liquid collides with rapidly moving parts, it is repelled and dispersed in fine droplets. The gaseous state of any liquid remains formed when molecules leave (evaporate) from the surface of the liquid. Evaporation increases with a low boiling point of the liquid and an increase in its temperature. In a water-based emulsion, evaporation will increase the humidity in the factory. The generation of mists depends fundamentally on:
Higher tool speed = higher mist generation
The volume, flow rate and supply point of the metallurgical liquid at the cutting edge
Higher workpiece temperature = higher oil smoke generation.
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