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Figure 1 Deionized water equipment Deionized water application
Figure 2 Calcium on the Grob machine tool holder Conclusion
Application of deionized water in powertrain production
In traditional powertrain companies, water-based cutting fluids are often mixed with tap water. Since the formula of water-based cutting fluid is mostly from abroad, and the products produced have certain uniformity, although the chemical producers will consider the difference of water quality around the world as much as possible, research and development or select targeted products for practical applications, but due to water The characteristics of each of the basic cutting fluids are mutually constrained, the actual operating conditions of different sites are different, and the actual requirements of different operating phases are different. If all the actual requirements are met, it is a very difficult technical problem. How to improve the service life of cutting fluid, reduce the impact of cutting fluid on processing and even the whole enterprise production, and reduce the environmental impact of sewage discharge is the basis of our discussion of deionized water.
1. Definition of deionized water
Deionized water refers to pure water after removal of impurities in the form of ions. The “deionization†defined by ISO/TC 147 is defined as: “Deionized water completely or incompletely removes ionic substances, mainly refers to the treatment method using ion exchange resin.†The current process is mainly made by RO reverse osmosis. The ion exchange resin is used to remove anions and cations from the water, but there are still soluble organic substances in the water, which can contaminate the ion exchange column and reduce its efficacy. The deionized water is also likely to cause bacterial growth after storage.
2. How to get deionized water
There are several processes for deionized water. At present, the widely used process in powertrain enterprises is a combination of reverse osmosis water treatment equipment and ion exchange equipment to obtain deionized water, as shown in Figure 1. The basic process is: raw water → quartz sand filter → activated carbon filter → resin exchange (treatment of calcium and magnesium ions) → precision filter → high pressure pump → reverse osmosis equipment → pure water tank → pure water pump → water point.
The quartz sand filter is used to filter out the iron, aluminum and silica gel bodies present in the tap water, intercept the fine particle impurities in the water, reduce the turbidity of the raw water, and control the raw water pollution index. Activated carbon filter is used to remove organic matter such as residual chlorine, chloroform and volatile phenols in tap water, odor and odor, and adsorb some toxic and harmful metal elements, such as hexavalent chromium and lead, and finally reduce the turbidity and chroma of raw water. The original water taste makes the raw water quality meet the requirements of the inlet water quality of the reverse osmosis unit after pretreatment. Resin exchange is used to remove calcium and magnesium ions from water, reduce the hardness of raw water, and protect rice reverse osmosis membrane components. The fine filter is used to filter out fine particles leaking from the foreline equipment.
The core of the process is reverse osmosis, and reverse osmosis is the reverse process of penetration. There is a membrane in nature called semi-permeable membrane, which can only pass through water and cannot pass through other solutes. If the semi-permeable membrane of fresh water and salt water is separated, fresh water will naturally pass through the semi-permeable membrane to the side of the brine. This phenomenon is called infiltration. When the permeation proceeds to a level on the side of the brine to a certain level to generate pressure, thereby inhibiting the fresh water from further penetrating into the brine to reach equilibrium, the equilibrium pressure is called osmotic pressure. In this case, if a pressure greater than the osmotic pressure is applied to the brine side, the molecules in the brine will pass through the semipermeable membrane to the fresh water side from the brine side. This phenomenon is called reverse osmosis.
As can be seen from the above process, the deionized water equipment processing process is relatively simple, basically a straight line process, no feedback.
Combined with the application experience of the current engine factory and transmission factory, according to the experience of the famous German washing machine manufacturer Dürr, the conductivity of deionized water can be controlled at ≤50us/cm. In fact, we have several basic requirements and precautions when considering the planning of deionized water equipment:
(1) Raw water indicators, raw water indicators directly determine the design of subsequent equipment.
(2) Deionized water index, the acceptance requirement of new equipment is ≤10us/cm, and the control period is within 50us/cm. It needs regular maintenance and maintenance.
(3) Equipment processing capacity needs to be designed according to specific demand. Pay special attention to the influence of water temperature on the output of the whole system.
(4) Concentration of concentrated water should be considered when selecting the location of the plant equipment.
In view of the existence of these problems, the application of deionized water has practical value. Deionized water is used to compensate for the adverse effects of different water quality and actual operation conditions on the cutting fluid. Below we will conduct detailed analysis and research based on the application of deionized water in powertrain production.
1. Application in water-based cutting fluid control
Taking the engine factory as an example, the engine factory is mainly based on machining, and the heat treatment process is less. Therefore, we pay more attention to the water-based cutting fluid that has a great influence on machining.
The main factors affecting the stability of water-based cutting fluids are the hardness of the raw water and the cumulative hardness of the cutting fluid for long-term operation. Here, we take a cutting fluid centralized filter engine factory cast iron cylinder processing as an example. During the period from 2006 to 2009, the problem of using one product is less than one year. When the actual processing is less than 60,000 pieces, the cutting fluid will be unstable and stratified, the amount of supplement will increase sharply, and the defoaming property will be The rust-proof performance is reduced, and there are a series of problems such as frequent bacteria and a large amount of precipitates on the surface of the machine tool.
In view of the doubt about the quality of the cutting fluid itself, the company chose the high quality product Quaker QUAKERCOOL 3755 BIO. The actual operation effect, when using 200,000 pieces per year, the hardness rapidly rises to about 1000ppm, and the cutting fluid has delamination problems. It is not allowed to carry out half-slot adjustment, and the service life is extended for another 9 months. Although the quality of the cutting fluid has been improved qualitatively, the problem of calcium and magnesium ion precipitation (Fig. 2) is apparent in the cutter head and other positions of the Grob machine tool, which affects the normal operation of the equipment and plagues the production of the enterprise.
Based on the above phenomenon, the factory and Quaker Chemical Company jointly studied and analyzed the reasons. Since the tap water inlet hardness is between 120 and 150 ppm, the hardness is not high, and the cutting fluid itself does not contain calcium and magnesium. The main reason for the instability of the emulsion is that the evaporation is too fast (the amount of water added per day in winter is 17-20 m3/day, In summer, 13 to 15 m3/day), the hardness of the cutting fluid accumulates too fast. To this end, it is necessary to add a deionized water device to ensure the stability of the cutting fluid operation, reduce the influence of hardness accumulation on the cutting fluid, prolong the service life of the cutting fluid, and reduce the impact on the machine tool and production.
The actual use effect is very obvious. In the most recent use cycle, the Quaker QUAKERCOOL 3755 BIO has not undergone any major adjustments, and the continuous use of 650,000 pieces in 19 months. Before the replacement, the hardness of the cutting fluid was still controlled at about 300 ppm. The product did not have delamination problems, and no abnormal precipitation occurred on the machine. The cost per part of the cutting fluid is reduced by 20% to 30%. At the same time, the hidden costs of sewage treatment costs and the impact on machine tools and tools have not been evaluated.
The above situation is only for the actual situation of the factory. Our control index is to control the hardness of the cutting fluid to 120~250ppm. If the local tap water quality is basically normal at 120-150ppm, considering the limitation of the amount of deionized water produced by the deionized water and the effect of hardness on the defoaming property of the cutting fluid, it is recommended to use tap water when initializing. When the hardness of the cutting fluid rises to a certain extent, it starts to be added. Ionic water. For the northern part with high water hardness, the climatic dry water evaporates faster. It is recommended to add deionized water when the cutting fluid is initially matched. It is beneficial to improve the stability and service life of the cutting fluid from the perspective of hardness control. Compared with centralized filtration, the application effect of deionized water on a single-filter device with higher turnover rate will be more obvious. If the hardness is well controlled, the service life can be greatly extended and the cost of regular replacement can be reduced.
2. Application of deionized water in cleaning
In transmission plants where shafts and gears are mainly used, the application of deionized water is more directed to the field of cleaning.
Due to the large number of heat treatment processes in the shaft and tooth processing, in order to ensure the quality of mass production and reduce the scrap rate of the heat treatment process, the workpiece needs to be cleaned before the workpiece enters the heat treatment equipment. In addition to removing particulate impurities from the metal surface, the purpose of cleaning is to minimize the residue of the salt component to improve the quality of the heat treatment. Therefore, in the transmission factory, the washing machine mostly uses deionized water for dosing, which can greatly reduce the adverse effects of various types of ion residues in the water on the heat treatment surface.
Earlier we mentioned the influence of the hardness of the cutting fluid on the machine tool. The actual deionized water is also very beneficial to the cleaning equipment. The cleaning machine generally has a high cleaning temperature of 50° to 60°, and the water evaporates faster. During long-term use, it was found that there was a significant scaling problem on the inner wall of the washing machine using tap water. With an electrically heated washing machine, the heating rod will also burn out due to the accumulation of scale for a long time.
3. Effect of deionized water on rust prevention
Because of the many factors involved in rust prevention, such as humidity, electrolytes, surface cleanliness and packaging of the workpiece, purely from the water point of view, deionized water has low conductivity and low chloride and sulfate ion content in water. It is used in tap water, so it is good for rust prevention work. However, due to the many factors affecting rust prevention, the effect of deionized water on rust prevention is not very obvious. However, for the vast southern regions and coastal areas, especially during the yellow-summer rainy season in the Yangtze River Delta, the chloride ion content of tap water will increase significantly in addition to moisture, causing problems such as rusting of parts (especially cast iron and steel parts) and finished parts. The use of deionized water still has a certain effect.
Deionized water plays an important role in the application and control of cutting fluids in powertrain enterprises, and will be more widely used in major machining plants. After our company used deionized water to achieve certain effects, Shanghai Volkswagen and FAW-Volkswagen's engine plant also put deionized water equipment into the overall planning of the filtration equipment to ensure the quality of the water-based cutting fluid in actual operation and improve the operation. Efficiency, reduced consumption and sewage discharge. However, it should be noted that in the application process, professionals are required to monitor and analyze the data to avoid misuse.