Ecological and Physiological Aspects of Utilizing Cooling Lubrication
Health Hazards
Contact with cooling lubricants bears the risk of cancer as well as respiratory tract and skin diseases, which can be caused by direct skin contact, swallowing, inhaling, or by contact with fogs and vapors [61], [62],[63] and [64]. Relevant substances for physical danger include emulsifying agents, which at times have a degreasing effect on the skin [65]; corrosion inhibitors, of which some are toxic and therefore should no longer be used [65]; preservatives such as formaldehyde [66]; and heavy metals. In particular, chlorine leads to chlorine acne and also causes issues in relation to correct disposal [63] and [65]. Additional health hazards arise from reaction products such as nitrosamines, microorganisms and their metabolic products[38] and [67], solid materials that can cause microdamages, dissolved toxic material elements such as nickel or cobalt, and personal hygiene [65] and [68]. The risk of skin irritation usually increases with a high pH-value and a rising concentration when using water-mixed cooling lubricants.
Ecological Damage
The use of cooling lubricants can lead to ground, air, and water contamination. Regarding their disposal and water damage, emulsions and solutions are most problematic. Due to their comparatively short service life, which is mostly limited by bacterial infestation, a relatively high quantity accumulates for disposal. The durability of alloyed mineral oils is longer, and possible service life depends on contaminations.
The lowest risk of ecological damage arises from biologically decomposable cooling lubricants such as esters, which can be characterized as ecologically neutral. However, lower disposal expenditures must make up for the often higher acquisition costs. In this regard an efficiency analysis is recommended for the selection of an optimal cooling lubricant under consideration of all limiting quantities, whereas criteria of the objectives should be mathematically combined with the capacity to fulfill these objectives [39] and [59]. An exemplary application of said efficiency analysis recommended the use of an ester as cooling lubricant based on its good ecological behavior [59].
Approach to the Reduction of Cooling Lubricant Volume
To solve the ecological, physiological, and economic problems caused by using cooling lubricants, the most promising step is to completely avoid the usage of cooling lubricants by dry machining. In addition to avoiding health hazards and ecological damages, the major advantages of dry machining are the avoidance of purifying, drying, or disposal processes for workpieces and chips, as well as the cooling lubricant itself, and therefore the saving of related expenses. These advantages lead to higher process flexibility and better recycling of cutting products [38], [61], [62], [63] and [69]. However, these advantages are opposed by problems that result from the absence of the primary functions—cooling, lubricating, and rinsing—of cooling lubricants. For these reasons, dry grinding has only been applied in a scientific context until now[64] and [70]. Yet, a diminishment in the necessary circulation amount of cooling lubricant can be realized by optimizing the lubrication feed process in the active zone [38], [61], [62], [71] and [72]. These optimizations are mainly accomplished by improved nozzle designs and adjustments (e.g. needle nozzles, shoe nozzles, or Rouse nozzles). Another approach is transporting the cooling lubricant directly to the active zone by tool types with internal cooling [63]. In an extreme case, the necessary cooling lubricant is determined so precisely by minimal-amount cooling lubrication systems that it is completely used up through vaporization. The low amount of necessary cooling lubricant as well as the fact that the cooling lubricant is, due to its singular use, not in constant circulation through the system are the major advantages of this cooling lubrication technique. As a result, high expenses for the control, maintenance, and disposal of cooling lubricants can be saved. So far, knowledge about the effects of cooling lubricant fog released into the air as well as corresponding countermeasures are not available however [61], [71], [72], [73], [74], [75],[76] and [77]. Additionally, significant quantities of cooling lubricants can be saved by discontinuous feed or delivery pumps regulated by the machine control system to exactly adjust the amount, time, and location of necessary cooling lubricant to the process. Furthermore, this technology allows a reduction of energy consumption [63].
4.6. Environmental issues
Michael Weismiller
Introduction
Manufacturing processes can be evaluated using four criteria:
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Producible dimensions and shapes
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Dimensional and surfaces accuracy
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Economic efficiency
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Human-environment technology [78] and [79]
The consideration of the human-environment technology condition is relatively new to the manufacturing industry. In many ways, investors and users of the technologies were not aware of many of the environmental hazards and did not provide enough resources to maintain minimum environmental standards. Over the past 10 years, however, government regulations, often the result of public opinion, have forced the manufacturing industry to account for environmental risks [80].
As the manufacturing industry has worked to protect the environment and employees from the effects of wastes, disposal costs have increased. Some examples of these efforts include formulating fluids to minimize harmful effects on worker health, extending the sump life of the grinding fluid, and minimizing the generation of waste by recycling [81].
Environmental Health and Safety
As with all metalworking fluids, grinding fluids can negatively affect worker health. Although respiratory effects may occur, occupational dermatitis (skin) problems are the most common. In fact, of all occupational diseases, approximately 50% are related to the skin [82] and [83]. One form of dermatitis is skin irritation and accounts for approximately 70% of the dermatitis cases. It is damage caused by skin exposure to the grinding fluid and is almost always curable. A second more severe form of dermatitis is skin sensitization (allergic) dermatitis and accounts for approximately 30% of the cases. It is damage caused by a worker’s allergic reaction to the chemical(s) in the fluid, is normally not curable, and may become worse with repeated exposure to the chemical(s) [84]. Unfortunately, the worker may need to be relocated to a different job to keep away from all exposure to the fluid [85].
The chemical properties of the grinding fluid and contaminants may lead to many of the skin irritation problems. For example, the grinding fluid is basic and has a pH of approximately 9. This level can irritate human skin, which has a pH of approximately 6. Grinding fluids also have chemicals (surfactants) that can remove the oil from workers’ skin, causing irritation with extended use. Bacterial contamination of the fluid can also irritate the skin. Finally, during the grinding process, metals (nickel, chromium, and lead) can enter into the fluid and irritate the skin [86].
Identifying and correcting skin irritation issues can be difficult because more than one cause may be to blame, or the issues may have resulted from the use of chemicals outside the workplace. For example, a rash may have resulted from working with the grinding fluid or from working in the garden (pesticides), working in the home garage (gasoline), using home bathroom cleaners, or using cosmetic products [82]. Also dry winter months can increase the possibility of dermatitis [83]. Therefore, employee hygiene and manufacturing site cleanliness and air quality are important factors in controlling dermatitis [84].