The washing process of electrophoresis coating

1 Before the
electrophoresis coating line has a lot of washing process, but also a lot of water use, water consumption process. With the shortage of water resources and the need to build a conservation-oriented society in China, as well as environmental protection, sewage discharge and other regulations are increasingly valued, sewage treatment costs are also rising, electrophoresis coating line how to rationally formulate the washing process, in order to ensure the quality of workware cleaning under the premise of rational use of water, minimize water consumption and sewage discharge, improve the utilization rate of water, is a more and more attention.
2 electrophoresis coating washing
electrophoresis coating line conventional process design is: pre-cleaning (spraying→ pre-skimming → skimming→ washing (spraying) → wash (spraying) → surface →phosphorusing→ washing (spraying) → washing (impregnation) → cycle cleansing (Spray) → pure water wash (impregnation→ clean pure water spray →electronic swimming→0 spray → cycle ultrafiltration water wash 1→ cycle ultrafiltration water wash 2→ cycle ultrafiltration water wash 3→ clean ultrafiltration cleaning (spraying→ pure water wash→ clean pure water spray
China
. In electrophoresis coating, the main washing process is before and after degreasing, phosphation, electrophoresis after the water (ultrafiltration fluid) wash. In the actual coating line, due to the work parts shape, requirements or equipment investment factors vary, the number of washing processes, working methods may vary, there is spray, impregnation, or spray combination.
2.1 Pre- and post-skimming washing
2.1.1 Process Description
(1) pre-cleaning process. It is generally used to spray with high flow, also known as "flood cleaning". The pre-cleaning groove is used to flush the resurfaced work parts, the newly removed coated hangers (in order to ensure good conductivity), the long-standing dust-covered workstations, etc., while removing the solder slag, particles, etc. on the work pieces, in order to reduce the pollution level of the degreasing tank, reduce the filtration load of subsequent processes and the frequency of replacement of the filter bags, and prevent fouling of the spray pipe nozzle. The water level of the pre-flushing tank is kept extremely low and the water circulation can be maintained, i.e.
can be picked out of the pre-flushing tank in time due to the suspension of work items that are not firmly flushed down. This process in the previous electrophoresis coating line design is generally not, but in recent years the level of coating development needs, has been increasingly set in the new coating line. From the actual use of the situation, the improvement of electrophoresis coating quality, equipment management, etc. have brought more benefits. On some car coating lines, even before going online, the work parts are rinsed manually with a high pressure water gun at a pressure of about 0.6MPa.
(2) after degreasing the washing process. Mainly to clean the surface of the work parts, the inner cavity, etc. carried by the degreasing liquid and other impurities, to prevent the work parts with liquid string grooves, pollution of the next process, affecting the quality of treatment. Generally after degreasing there is 1 or 2 washes, can be sprayed, can also be impregnated (if only 1 wash, requires the use of impregnated water wash). In the design, it is worth noting that the interval between skimmed work and washing should not be too long, that is, before entering the washing process, not only to ensure that the work parts have sufficient leaching time, but also to ensure that the surface of the skimmed work parts can not appear a large area of drying phenomenon. The interval between the washing of the work parts and the entry into the next process should not be too long, preventing the rusting of the work pieces and affecting the quality of subsequent treatment. In addition, the bottom of the water sink design should have tilt angle, or other design forms, to ensure that a small amount of precipitation converges to the bottom of the sewage pipe, to help clean the groove.
Most automotive coating lines have now installed filters on washing cycle lines, and some car coating lines are also fitted with cyclone separators and magnetic filters to capture 95% of iron powder particles of more than 20mm, which can greatly reduce particles, ash particles and other ills on the surface of the work parts coating. At the same time, it is helpful to clean the work parts after the washing tank does not have foreign object attachment, secondary pollution and other conditions.
2.1.2 Water management
the cleaning quality of the work parts, in addition to equipment factors, and cleaning water quality also has a great relationship. In order to improve the quality of cleaning, cleaning water needs to be constantly replaced and updated, so it is also an important part of water and drainage.
As shown in Figure 1, to achieve reasonable water in the pre-skimming tank, degreasing groove between the connecting tube 1 outside, in the pre-cleaning and water tank between the addition of connecting tube 2, and keep the liquid surface of the wash tank higher than the liquid surface of the pre-flushing tank. Add a drain branch to the water sink cycle line, which can be controlled by valve F to add water from the sink to the skimming tank. Only the last sink is equipped with a tap water pipe, remove the tap water from the other tank. The water in the water wash tank can be replenished with valve control, or the pre-skimmed tank (the degreasing tank fluid is reduced due to high temperature evaporation and the consumption of work parts is carried), can also be used to condition the degreasing tank solution, flushing the pre-skimming tank and the degreasing tank. Daily water level difference through the connecting tube 2 to supplement the pre-cleaning tank required cleaning water, and by the pre-cleaning tank discharge, to complete the multi-recycling of water.
2.2 Phosphate after washing
2.2.1 washing process
phosphate washing is mainly to clean the surface of the work parts, the inner cavity with phosphate liquid, phosphate slag, metal ions and other impurities ions, etc. , while ensuring that the water and electricity conductivity after the cleaning of the work piece to meet the requirements of the electrophoresis tank into the tank work, to prevent contamination of the electrophoretic tank liquid. The effect of workware cleaning directly affects the quality of electrophoresis coating and the stability of electrophoresis tank fluid. After phosphate washing generally has tap water spray cleaning, tap water impregnation cleaning, pure water impregnation cleaning, pure water spray washing, clean pure water spray cleaning and other processes.
In the design, the general work piece out of the phosphate tank will have a phosphate spray line, for the initial cleaning of the surface of the work piece phosphate slag, which in practice proved to be able to play a better effect. The first washing after phosphate is generally designed to work by spraying, so that the volume of the tank body is generally relatively small, in order to facilitate the updating of washing water, improve the cleaning effect. In the design, should also pay attention to the work parts before entering the electrophoresis tank, the outer surface should not appear semi-dry and semi-wet situation, so as not to produce paint film ills. If such problems occur, it is recommended to increase the wetting or blow-drying of the workware and its equipment before entering the slot. For each sink, it is recommended to also install a filtration device. There are many benefits to prevent the adsorption of phosphate slag on the work piece and to avoid particles, ash particles, etc. on the surface of the work piece.
2.2.2 Water management
As can be seen from Figure 2, after phosphation to electrophoresis before the washing process, each tank has a connected pipe, should be used reverse rehydration method, improve the utilization rate of water.
Clean pure water spray work, cleaning water back to the pure water sink, pure water sink water overflow to the front of the tap water sink, and then overflow to the front of the tap water spray tank, through the spray tank discharge, to achieve water reuse. Control the discharge and replacement of cleaning water by detecting the pH and conductivity of each tank of water. In daily production management, when all the pure water sink needs to be replaced, you can replace the tap water sink with the water of the pure water sink, or when changing the water sink, rinse the water tank with the water in the pure sink.
2.3 After electrophoresis washing
after electrophoresis washing mainly cleans the inside and outside surface paint, lacquer liquid in the mezzanine, improve the appearance quality of the paint film, recycle the lacquer liquid, improve the utilization rate of paint liquid. Work parts from the electrophoresis tank will inevitably bring out part of the lacquer liquid, this part of the paint if washed as wastewater direct discharge, not only increased the load of wastewater treatment, but also greatly reduced the utilization rate of coatings, correspondingly increased coating costs. The use of ultrafiltration liquid as water washing, can achieve closed cycle cleaning, improve the utilization rate of coatings, reduce wastewater emissions, save pure water use.
after electrophoresis washing system from the process selection can be multi-level choice, in theory, the more ultrafiltration water wash section, the higher the efficiency of paint recovery. However, the more wash segments that are not ultrafiltration in actual production, the better. Because each additional level of ultrafiltration washing, equipment length, equipment investment costs and operating costs are increased, and the improvement of paint recovery efficiency is limited, in the design of ultrafiltration washing step, should take into account several factors, usually choose three-level ultrafiltration washing can achieve satisfactory results. As shown in Figure 3.
In the arrangement of the coating line electrophoresis after the washing process, most of the use of spray washing and immersion combined way, and more by 2 levels of spray washing and 1 level of immersion composed of 3 levels of recycled washing and 1 level of clean washing. Because of the 3-stage cycle washing has 3 kinds of arrangement, that is, spray-immersion-spray, immersion-spray-spray and spray-spray-immersion.
based on Ted Mooney's theory, water consumption is independent of the way the work is arranged in order to achieve the same cleaning effect. However, from the actual situation, as long as the impurities attached to the work piece after a long time without becoming difficult to clean, in order to facilitate production control, the baptist process should be as far as possible in the last place. Therefore, it is recommended to choose the spray-spray-immersion arrangement.
Of course, the effect of workware cleaning and recovery efficiency is also related to the electrophoresis ultrafiltration equipment ultrafiltration fluid through the amount, with the increase in the amount of ultrafiltration, the cleaning effect of work parts, paint recovery efficiency significantly improved. But that doesn't mean the larger the ultrafiltration, the better. Because the larger the amount of ultrafiltration fluid through, the higher the investment of the corresponding ultrafiltration equipment, and when the ultrafiltration fluid permeation increases to a certain extent, the trend of recovery efficiency tends to flatten. Paint recovery efficiency is typically maintained at 95% without the need to increase unnecessary investment in the one-sided pursuit of extremely high recovery efficiency. In general, the ultra-filter through the quantity selection according to the needs of each square meter of work (1.3 to 1.8) L ultrafiltration fluid to calculate. Ultrafiltration water washing, work parts also need pure water cleaning, generally have pure water immersion, coupled with a clean pure water spray cleaning process, but also the use of reverse flow reuse water, that is, clean pure water cleaning work parts, returned to pure water wash tank, and then through the pure water tank overflow discharge.
The above-mentioned process, there are some cleaning water discharge, but ultrafiltration equipment and special reverse osmosis equipment combination (i.e. EDRO) used in electrophoresis coating after flushing, forming a complete and complete closed-circuit cleaning, but also more and more accepted by the vast number of coating lines, especially environmental protection increasingly strict today, its application value is growing.
3 Conclusion
The washing process and water use of electrophoresis coating have an important impact on improving cleaning quality and saving water and reducing costs. Through the rational formulation of cleaning process, management methods, can change the past water added to the pressure or manual control of water pipes, but also can change the amount of water by the process to prescribe on-time discharge and other practices. By formulating the detection index and method of cleaning water, formulating a reasonable water quality range and adapting it to the coating production of different work parts, the reuse rate of water can be improved under the premise of ensuring the quality of coating, saving water and reducing the cost of coating.