In metal processing such as vehicles, milling, drilling, and grinding, a large amount of oil mist particles are formed in the air due to the use of metal cutting fluids. This phenomenon has caused widespread concern over the issue of air quality in the breathing zone of workers. Because long-term exposure to this kind of oil mist is very unfavorable to the health of workers, according to the National Institute of Occupational Safety and Health (NIOSH), there are as many as 1.2 million workers exposed to oil mist every year. Therefore, the study of oil mist in metal cutting fluid is a significant issue.
1 The production of metal cutting fluid mist
1.1 The mechanism of oil mist production
In order to effectively lubricate, cool, and clean, metal cutting fluids undergo pumping cycles, jets and high-speed rotating tools or workpieces, such as intense impact and high temperature evaporation, during the process of use, which determines the cause of its oil mist is very complex. Mechanical, physical and chemical factors are intertwined and work together. However, not all factors have a decisive influence on the production of oil mist. The formation of oil mist from the metal cutting fluid during processing can be mainly attributed to two mechanisms: atomization and evaporation: atomization is the conversion of mechanical energy into droplet surface energy. The process is mainly due to the fierce impact of the liquid on the fixed and rotating units in the machine tool system. It is broken up by the liquid and forms fine droplets floating in the working environment; the evaporation occurs due to the large amount of heat generated in the cutting area. The liquid makes its temperature significantly higher than the saturation temperature, boiling occurs on the solid-liquid contact surface and steam is generated. These vapours then condense with small droplets or other particles in the surrounding air as the core, forming an oil mist. Figure 1 shows the mechanism of oil mist formation during processing.
1.2 The existence of oil mist
The metal cutting process can produce the following three types of oil mist:
(1) Clean oil mist produced by jet impact without solid dust;
(2) Smoke resulting from evaporation or burning due to the high temperatures of heating or high speed cutting;
(3) Oil mist containing grinding dust generated by metal cutting fluid during grinding.
The way in which oil mist is generated is different, and its particle diameter range is also quite different. Under normal circumstances, the oil mist produced by the mechanical atomization process mainly exists in the form of droplets, and the droplet diameter range is wide, usually 2 to 10 um. The oil vapor produced by evaporation will also form a very small diameter condensed suspension in the condensation process, and the particle size is usually 2um or less. Medical studies have demonstrated that oil vapour and large droplets are relatively harmless to human lungs. Oil mists in the form of oil vapors are drawn into the lungs and exhaled. They are not captured by the alveoli, and large droplets of oil cannot enter the lungs through the nose and bronchi. Only in the form of droplets, oil mist particles with a diameter of less than 5um can reach the alveoli successfully and precipitate in the lungs, thus causing greater harm to the human body.
2 The harm of oil mist from metal cutting fluid
The presence of oil mist in metal cutting fluids increases the risk of fire hazards slipping on oily floors. For example, fogging air exits the workshop and can also cause environmental pollution. The greatest danger of oil mist is that the cutting fluid is also exposed to contact. ring. Long-term exposure of workers to oil mist in metal cutting fluids can cause diseases such as systemic diseases, allergic skin diseases, and malignant tumors to increase, and may cause hereditary effects. The composition of metal cutting fluids is complex. Additives and contaminants may be used as stimuli to induce sudden asthma, worsen the condition of existing asthma, or cause airway discomfort in patients without asthma. Soluble and pure oils are associated with asthma in four types of metal cutting fluids. Three types of pure oils, soluble oils, and synthetic oils have been identified because the inhalation process can cause workers' airway dysfunction and respiratory diseases. Even if the concentration of oil mist is only 0.41 to 0.55 mg/m, workers' long-term exposure to such oil mist will still cause chronic bronchitis, chest discomfort, and airway irritation. Earlier research on allergic pneumonia was not conducted on workers exposed to oil mist from metal cutting fluids. However, due to the recent surge in the number of workers suffering from allergic pneumonia, the fact that prolonged exposure to oil mist can cause pneumonia has been studied and studied. Confirmed. Research data on the effect of metal cutting fluid on the lung function of workers is still lacking. One of the reasons for this is that most of the decline in lung function that can be observed is irreversible. In addition, the decline in lung function is related to the amount of oil mist that is in contact with it. This is a long-term accumulation. However, animal-based studies have shown that dogs exposed to 5 to 100 mg/m oil mist for more than 12 months experience fat-containing alveolar and macrophage adipose granuloma, as well as respiratory tissue morphological changes.
Another major hazard of metal cutting fluid mist is its carcinogenicity. The carcinogenicity of metal cutting fluids mainly depends on the concentration of its additives, contaminated conditions and conditions of use. There is currently no research on the carcinogenicity of metal cutting fluids for humans, and experimental studies on animals have found that oil mists in cutting fluids can cause skin tumor/skin cancer, lung cancer, and pancreatic cancer. There are still many controversies about the carcinogenicity of oil mist in cutting fluids. Although many epidemiological studies have reported the carcinogenic tendency of metal cutting fluids and oil mists, the incubation period of cancers is particularly long. Epidemiological Research often can only evaluate the damage caused by a substance 20 to 30 years ago. To this end, researchers pointed out that the composition of metal cutting fluids decades ago completely failed to represent today's cutting fluid. In particular, the oil refining process has undergone tremendous changes that have largely removed polycyclic aromatic hydrocarbons and other undesirable components. Therefore, it is not appropriate to extend the original proven carcinogenic tendency to current cutting fluids. However, due to the complexity of the metal cutting fluid composition, it is very difficult to simply prove that it is not carcinogenic. Compared with studies on other aspects of health hazards, the study of genetic effects of cutting fluid mists is minimal. According to the results of the 1995 Fuchs J et al. study, the IARC (United Nations Agency for International Oncology Research) characterizes N-nitrosodiethanolamine (NDELA) as a 2B carcinogen (possibly carcinogenic to humans). NDELA strongly influences the breakage of mononuclear blood cell DNA strands. Workers exposed to air at concentrations greater than 500 mg/m NDELA significantly increased the number of DNA strand breaks exposed to concentrations below 50 mg/m. Although the EPA (United States Environmental Protection Agency) has banned NDELA as an additive for metal cutting fluids, triethanolamine (TEA) and diethanolamine (DEA) can still react under the action of nitrosating agents in metal cutting fluids. Generate NDELA.
3 Metal cutting fluid mist control
3.1 Traditional methods
The concentration of oil mist in the control shop atmosphere is mainly mechanical and chemical. Mechanical methods include the installation of exhaust fans, oil mist traps, protective covers or splash guards around the machine. These methods are widely used because they are easy to implement and have obvious effects. However, these methods have their own inadequacies. Although the exhaust fan is simple and effective, a simple exhaust device is not desirable. It merely moves a large amount of oil mist from the interior to the outside and is an extremely irresponsible behavior to the environment. It is a reliable practice to install oil mist traps or oil mist separators in the workshop and purify or recover the gas containing oil mist.
3.2 Centrifugal (simple and economical) Recommended Products: Oil mist filter
CRD series oil mist filter applies precision filtration and centrifugal separation technology, and the filtration effect of mist is up to 99.8%. The application range is wide, and it can be water or oil mist.
How does CRD work?
A. The inhaled mist and dust enter the oil mist filter first and collide with the inertial collision plate, and then a secondary filter removes the large particle mist.
B. Coarse granulation of the mist under the action of the impeller to improve the filtering effect of the next filter.
C. The third filter is a high-efficiency filter, which can filter out fine oil mist better.
Features:
· High smoke collection efficiency, oil mist filter for mist collecting efficiency up to 99.8%
• Easy to maintain, plug-in installation.
·The equipment running noise is low, less than 68dB (A).
· Safe and reliable operation, setting up phase-to-phase and overheat protection functions. The device has no exposed power and the operation is safe.
·The oil mist filter has a wide range of applications and is suitable for the purification of various water-soluble and oily mists.
3.3 Electronic (no consumables) Recommended Product: Oil mist cleaner (electrical ion)
The working principle of the oil mist cleaner is to ionize the air by means of corona discharge, so that the oil smoke particles in the air are charged, and the charged particles are moved to the discharge electrode under the action of the electric field force through the electric field, and are accumulated after discharge. Recycling (recovered oil mist can be reused for the factory to reduce the economic expenditure of coolant), while the discharge is clean air.
The oil mist cleaner includes four parts: a wind farm, electrical control, and a collection area. Oil fumes and oil mist enter the electric field under the negative pressure of the induced draft fan. They are first ionized by the electric field and charged (this process is called “chargingâ€). Charged ions are trapped under the electric field (this process is called “Dust collectionâ€). Charged particles release charge on the collecting electrode and aggregate into oil droplets and finally recover in the oil collection area.
The oil mist cleaner can purify smoke of various properties, including acid gas and alkaline gas. The collection efficiency is more than 99% and the minimum filtration precision is 0.01UM. It is an ideal equipment for the metal processing industry and the factory clean production of the machining industry.
Features:
· Efficiency and energy saving, oil mist recovery efficiency is greater than 99%.
· Improve the working environment and achieve cleaner production.
· Protect the physical and mental health of employees and reduce the occurrence of occupational diseases.
· Reduce the impact of smoke and oil mist on the machine's circuit system and control system and reduce the cost of machine maintenance.
• The oil mist cleaner can recycle the part of the cooling oil that the machine tool generates smoke, reducing production costs.
Function and Application of Oil Mist Collection and Purification Equipment
Reduce the impact on employees: 0.3 ~ 3.5UM oil mist particles will remain in the body, posing a health hazard.
Reducing work accidents: The deposition of oil mist makes the work area, floor, and walkway slippery and can easily cause wrestling accidents.
Reduce the risk of fire danger: Oil deposits on the walls, ceilings, and equipment pose potential fire hazards.
Reducing the consumption of coolant: The recovered oil mist can be reused for the plant to reduce the economic expenditure of the coolant.
Range of application: It can be used for oil mist, water mist generated during cutting of oil, diesel oil and synthetic coolant.
Application examples: CNC lathes, washers, cylindrical gears, surface grinders, gear hobbing machines, milling machines and gear machines, vacuum pumps, spray test chambers, EDM machines, and CNC machining centers.
Selection instructions:
Closed cavity: inner cavity volume (M3) coefficient (1/min) air flow rate (M3/min) [Length*Width*Height] *Functional coefficient = Required air volume.
Example: CNC lathe, inner cavity size 1.1m wide 1.05m high 1m [1.1*1.05*1]*4=4.6 M3/min
According to the formula above, it is most suitable to use CRD-400 to calculate the air volume.
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