Coating knowledge: water saving technology in the process of automobile coating

Core tip: because there are many chemical treatment processes and water washing processes in the coating production line, it is a process that consumes a lot of water On the other hand, the shortage of water resources in a large scale is becoming more and more serious in our country The shortage of water resources has become an important factor restricting the economic and social development of our country With the improvement of China's environmental protection laws and regulations and sewage discharge laws and regulations, environmental protection issues have been highly valued, sewage discharge standards are increasing, and sewage treatment costs are also increasing How to design and develop a reasonable coating production process, under the premise of ensuring product quality, reasonable water use, water conservation, and Paint knowledge | precautions for wall paint color selection Recommended introduction: when painting the wall, the owner sometimes has difficulty in choosing what color of the wall paint to paint In fact, there is no ugly color in the wall paint, only the disharmonious color matching The use of wall color contains the knowledge of health Too strong color will stimulate people's perception, make people have a sense of fidgety, affect people's mental health Grasp the basic principles of wall color and paint a colorful space 1、 Wall paint color selection notice 1 Light color is generally used for the top surface Light colors make people feel light, dark colors make people feel heavy Usually, the treatment of rooms is from top to bottom, from shallow to deep For example, the ceiling and walls of rooms are white and Paint Home News: because there are many chemical treatment processes and water washing processes in the coating production line, it is a process that consumes a lot of water On the other hand, the shortage of water resources in a large scale is becoming more and more serious in our country The shortage of water resources has become an important factor restricting the economic and social development of our country With the improvement of China's environmental protection laws and regulations and sewage discharge laws and regulations, environmental protection issues have been highly valued, sewage discharge standards are increasing, and sewage treatment costs are also increasing How to design and formulate a reasonable coating production process, under the premise of ensuring product quality, reasonable water use, water conservation, and the maximum reduction of water consumption and sewage discharge are not only related to the survival and development of enterprises, but also to the national economy and people's livelihood 1 main water equipment and waste water source of coating production line The main water consumption equipment of the coating production line includes pretreatment equipment, electrophoresis equipment and wet paint spraying equipment, among which the former treatment and electrophoresis equipment are the main water consumption points, accounting for about 80% of the total production water consumption of the coating workshop; based on the production beat of 1 set / min and the treatment area of the body of (80-100) m2 / set, the water consumption of the production line per hour reaches 30t, and the sewage discharge volume is roughly equivalent to the water consumption The pretreatment waste water comes from the waste water discharge of degreasing, phosphating, surface adjustment and water washing processes, and the electrophoresis waste water comes from the cleaning process of the floating paint attached to the cleaning workpiece and the process tank; the spray booth waste water comes from the process of the wet spray booth water mixed with the air in the spray booth operation area to absorb, the paint mist in the air and the organic solvent mixed into the water 2 The main water-saving technology of the coating line is to save water In the planning and design of the coating line, it can be considered from the aspects of improving the process scheme, improving the equipment functions, and adopting new technologies and materials 2.1 after degreasing or phosphating, in order to clean the chemical agent attached to the surface of the workpiece, it is necessary to wash it several times In order to save water, two water-saving units are designed for each water washing process of the pretreatment, so that the cleaning water will be discharged from each process tank separately into a unit The water supply of the back section and the overflow water supply of the front section are adopted, and finally the water is discharged to the trench, which improves the utilization rate of the cleaning water In the process design of some coating production lines, the water for degreasing and phosphating is supplemented by the water after cleaning respectively, and fresh industrial water is not added directly, so as to achieve the purpose of further water saving At present, this water-saving method has become a general method of water washing design for coating line 2.2 reasonable use of new equipment to reduce the renewal cycle of tank liquid by taking the following measures to reduce the renewal cycle of tank liquid and achieve the purpose of water saving a High pressure water gun pre cleaning is added in the manual pre cleaning station to reduce the processing burden of subsequent processes b In the hot water washing and pre degreasing process, a suspension separation device is added to remove the iron powder, sediment and other impurities in the tank liquid in time This not only ensures the cleaning effect of the workpiece, but also maintains the cleaning of the bath liquid c In the pre degreasing and degreasing process, the oil-water separation device is added to separate the grease in the degreasing tank in time, thus prolonging the service life of the degreasing solution d The bag filter is added to filter the impurities in the tank liquid and keep the tank liquid clean 2.3 to reduce the amount of liquid carried between processes, by improving the structure of the processed parts, changing the mounting and conveying methods, the phenomenon of liquid carried in the process of pretreatment and electrophoresis can be eliminated as much as possible, and the amount of liquid carried on the workpiece can be reduced, which can greatly reduce the water consumption of pretreatment and post electrophoresis washing The main measures are: check the workpiece, open the process hole at the liquid holding part to eliminate the phenomenon of liquid holding; ensure the reasonable drainage time between each process during the process design; adopt the latest rotary dip conveying technology (RO dip conveying technology or multi-functional shuttle) when the investment allows, which can greatly reduce the liquid carrying capacity of the workpiece 2.4 membrane separation technology is adopted to realize the recycling and reuse of wastewater (discharge water) Nth = "12" iscdate = "false" islunadate = "false" day = "30" > 2.4.1 pretreatment of discharge water The final discharge water of the two water-saving units, degreasing and phosphating, is treated by RO reverse osmosis device, and the RO water generated can be respectively used for the last fresh water spray washing before the meter adjustment and the last fresh pure water spray washing after phosphating, so as to realize no wastewater discharge or a small amount of discharge in the pretreatment Due to the different requirements for water quality between degreasing water washing and phosphating water washing, the first level reverse osmosis device is generally used for degreasing water-saving unit, and the second level reverse osmosis device must be used for phosphating water-saving unit Figure 2 is the schematic diagram of pretreatment ro recycling system Nth = "12" isrocdate = "false" islunardate = "false" day = "30" > 2.4.2 the current electrophoresis system adopts UF filter recovery technology, which realizes the closed cycle of electrophoresis and UF liquid water washing system However, the last stage of pure water washing still has a large amount of wastewater discharge due to the fresh pure water spray supplement and overflow discharge of pure water tank At present, there are two ways to reuse the discharged water from electrophoresis equipment (1) RO reverse osmosis device is added in the electrophoresis system, and UF ultrafiltration is used as the raw water of ed-ro system After ed-ro reverse osmosis system, concentrated water is added to UF3 tank, the pure water produced is used as the last fresh spray water, and the overflow water of pure tank is also added to UF3 tank, so as to realize the closed cycle of all electrophoresis processes and zero discharge of waste water (2) The overflow discharge water of pure water washing is used as the raw water of RO system After RO reverse osmosis system, the concentrated solution is added to UF3 tank, and the regenerated pure water is used as the last fresh spray water It can be seen from Fig 3 and Fig 4 that UF ultrafiltration system and RO reverse osmosis system form a complete closed cycle system for electrophoresis and post washing, and the recovery rate of electrophoretic paint can reach 99% ～ 100%, while minimizing the water consumption of the electrophoresis system Nth = "12" iscdate = "false" islunardate = "false" day = "30" > 2.4.3 treatment of water discharged from paint spraying equipment Particles, solvents, salts, etc are separated, which greatly reduces the discharge of wastewater, and the effective components of paint can be recycled 2.5 recovery and utilization of concentrated water in pure water plant the preparation equipment of pure water is one of the auxiliary equipment of automobile coating line, among which the two-stage RO reverse osmosis pure water preparation equipment is the most widely used The principle is that the filtered water enters the reverse osmosis desalination system for desalination, mainly removing dissolved ions and small molecular organic matters in the water By adopting two-stage reverse osmosis, the desalination rate, recovery rate and water quality can be more effectively guaranteed Therefore, concentrated water with high inorganic salt will be produced in the process of preparation of pure water, which is directly discharged by most domestic coating lines At present, the comprehensive water production rate of two-stage RO pure water equipment is generally about 70%, and the rest 30% is directly discharged, which is a great waste of water resources Considering the current situation of domestic coating equipment, there are three possible low-cost recycling measures for this part of waste water, which can be selected in the planning and design stage (1) As the supplementary water for pretreatment production, it is used in a heavy truck coating line with an annual output of 60000 vehicles in China The actual test shows that this part of waste water from pure water equipment can be used for the production of several tanks before the phosphating process The author personally presided over the transformation of this part of concentrated water recovery After the transformation, the concentrated water produced by the pure water equipment is all used in each process before the pre-treatment of phosphating, saving the consumption of industrial water Because the water quality of tap water varies greatly from place to place, and the chemical composition of the concentrated water is also quite different, whether this scheme can be used for recycling needs to be confirmed by relevant tests This kind of recycling method is generally used in the coating production line of auto parts, and is not recommended in the coating line of car body (2) It is proved that the concentrated water produced by the pure water equipment can be used as the supplementary water for the circulating water pool of the wet spray booth, which has little effect on the condensation of the paint mist (3) As the flushing water for the toilet of the workshop in the planning and design stage, a water storage tank needs to be set at a higher position of the workshop 2.6 new materials are used to extend the service life of the tank liquid At present, most of the pretreatment lines still use solid meter adjustment, which has poor thermal stability, and the tank liquid is required to be less than 30 ℃; the tank liquid has a short service life, generally less than 2 weeks, and needs to be changed frequently The new generation of meter regulator is liquid product When the bath temperature is 50 ℃, the colloid is still stable, without refrigeration system Usually, only the bath liquid taken by the workpiece needs to be supplemented, and the renewal cycle of the bath liquid can be up to 6 months, greatly reducing the water consumption of the bath liquid renewal The VOC emission of traditional solvent based medium and surface coatings is very large, which causes serious pollution to the environment Therefore, the paint industry in developed countries is engaged in the research and development of water-based coatings, powder coatings and high solid coatings that can reduce environmental pollution, especially for powder coatings, because of the use of dry spraying equipment and the cancellation of circulating water system, water-saving and energy-saving are completely achieved Purpose Home of coatings is specialized in coatings, diatom mud, paint coating, coating technology, fire retardant coating news and coating, diatom mud, paint coating, coating technology, fire retardant coating decoration knowledge and decoration renderings,