Automotive component spraying production line
Painting line design of car plastic bumper
Car bumper is an important exterior decoration of car, with the continuous improvement of car painting requirements, bumper painting is also more and more attention by professional factories. Car bumpers are mainly made of plastic material, paint is difficult to attach on its surface, in addition to the plastic parts of the thermal deformation temperature is low, the general production of the selection of paint drying temperature is lower than the metal parts of the paint drying temperature, so plastic parts painting and metal parts painting in the process and coating materials are very different, bumper painting is generally not body painting mixed line production. At present, some large automobile manufacturers in China have taken the injection molding and painting of the bumper as an important part of the vehicle production, and the construction of the bumper injection molding and painting workshop in the planning of the new factory, such as Japan's Toyota in the domestic construction of the factory has a resin workshop (that is, the injection molding and painting workshop of the bumper and other plastic parts). The bumper of some domestic automobile manufacturers is provided by a large professional plastic parts processing plant, and the domestic large automobile plastic parts production plant has Jiangyin Molding and Shanghai Yanfeng Westone.
The design of a number of domestic bumper coating lines has absorbed the experience and technology of Japan and South Korea, Europe and the United States, etc. These coating production lines have many different places in the process, equipment layout and mechanization form. In order to reduce the processing cost of plastic bumpers and improve its coating quality, people have carried out a lot of research in coating materials, coating process and coating equipment, and achieved certain results, so the design of the coating line has undergone great changes in recent years.
1 Overall layout of coating line
The overall layout of large painting lines tends to be regionalized and three-dimensional. The same or similar equipment and processes should be arranged in the same area as far as possible to facilitate the organization and management of production. The first floor mainly arranges the upper and lower parts station, pre-treatment, grinding, inspection, modification and auxiliary equipment; The second floor is mainly arranged with spray painting room, drying room and air conditioning platform area. This three-dimensional, equipment partition arrangement is more conducive to improving the cleanliness of the spray clean area, which is of great help to improve the qualified rate of product parts. The whole painting workshop is a fully enclosed workshop, and the manual operation is on the side of the production line when the upper and lower parts are standing on the side of the production line. The bumper painting adopts the form of combining automatic spraying and manual spraying. The exhaust gas of the painting room adopts the centralized high-altitude emission or the exhaust gas is discharged after centralized incineration.
2 Coating materials
Plastic bumper heat resistance is poor, easy to deformation at high temperature, so the bumper painting generally can not choose the drying temperature is too high paint, the current domestic use of paint drying temperature is roughly 80±5℃ and 120±5℃. The bumper coating is a composite coating, that is, primer + color paint + varnish. The primer has two components and one component. The color paint is mostly single-component paint, and the varnish is mostly two-component paint. The two-component primer has a good covering power after baking, and can be polished for paint defects such as surface particles, especially for the poor appearance of the plastic part itself, but the electrical conductivity of the two-component primer in the wet film state is generally poor, such as the primer is not dried on the spray paint will affect the adhesion of the color paint. Compared with single component varnish, two-component varnish has the advantages of less pollution and easy adjustment. The coating with two-component primer and varnish system has the disadvantages of large investment in equipment and complex maintenance of paint conveying pipeline, but the paint itself is easy to adjust and it is easy to obtain a good surface state of the paint film.
3 Coating process
3.1 Main process forms of coating line
The commonly used painting process for plastic bumpers is as follows: upper part → pretreatment → moisture drying → strong cooling → flame treatment → upper shielding → removing static electricity → spraying primer → leveling → primer inspection/polishing → removing static electricity → spraying color paint → leveling → spraying varnish → leveling → Top paint drying → strong cooling → checking and modifying → Lower part → repairing unqualified products. The above process is three spray and two drying (3C2B) process, and there is a three spray and one drying (3C1B) coating process (the "primer drying" in the above process to the primer after the "electrostatic removal" process is canceled). The 3C1B process can save the one-time investment of equipment and the later equipment operating costs, and the plastic bumper coating line with larger production capacity in China has adopted this process form, and has been put into mass production, and the operation is relatively stable. Considering that 3C1B coating process is rarely used in domestic coating production line design, and 3C1B process has certain risks in coating construction parameter control, coating site management, coating performance guarantee, product qualification rate guarantee, etc. At the same time, most European and American automobile manufacturers require 3C2B process for bumper coating. Therefore, some domestic coating production lines can also realize 3C1B process while 3C2B process design and construction.
3.2 Pre-Processing
The pretreatment of plastic bumper before painting is mainly to remove dust, oil and residual release agent on the surface of the workpiece, and at the same time, activate the surface. Poor pre-treatment is easy to cause defects such as poor adhesion, shrinkage and particles. There are two forms of pretreatment, one is automatic spray, and the other is manual wiping. Automatic spraying is to hang the workpiece on the conveying equipment through the pre-treatment spray line, the main process is: pre-degreasing → degreasing → washing 1→ washing 2→ fresh DI washing → blowing water → water drying → strong cold; Manual wiping is mainly to manually wipe the entire surface of the workpiece with solvents, which can reduce the one-time investment of the equipment and its operating costs. The large number of plastic bumper painting lines in China mostly use automatic spray, and the small batch bumper painting and small parts painting mostly use manual wiping.
3.3 Flame Treatment
Flame treatment can further activate the workpiece surface. The robot sprayed the flame to the surface of the workpiece. After the flame treatment process, manual and automatic electrostatic removal processes were set up to enhance the bonding force between the workpiece and the coating film.
3.4 Top Masking
The upper shielding is mainly to shield some areas on the surface of the workpiece that do not need to be sprayed, and it is generally more difficult to shield on the line, and more off-line shielding is used.
3.5 Spray Painting
Workpiece spraying is mostly a combination of robot automatic spraying and manual spraying, first automatic spraying, and then manual inspection and spray. Some production lines can be fully automated spraying when commissioning into mass production, automatic painting is mainly used robot spraying, the general primer is mostly used air spray gun, color paint 2 workstations generally use rotary cup workstation + spray gun workstation, varnish 2 workstations generally use spray gun + rotary cup workstation.
4 Painting equipment
The equipment of the plastic bumper coating line mainly includes mechanized conveying equipment, pre-treatment equipment, flame treatment equipment, spray painting room equipment, drying furnace and artificial work area equipment.
4.1 Mechanized conveying equipment
There are many forms of mechanical conveying equipment for plastic bumper spray line, including ordinary suspension conveying chain, reverse stacking chain and skid conveying form. Skid conveying form layout is flexible and changeable, many domestic production lines built in recent years have adopted skid conveying, and the Japanese bumper coating line mainly uses reverse stacking chain. Considering that some equipment of the pre-treatment process conveying system has the requirements of water resistance and corrosion resistance and the temperature influence of the drying process, the drive device of the skid conveying system in the pre-treatment and drying process is generally external.
4.2 Pre-processing Devices
Pre-treatment equipment mainly includes non-standard equipment, circulation system and exhaust system. The degreasing fluid of the plastic bumper is acidic (pH value is generally about 6.4), which is different from the degreasing fluid of the body, so the pre-treatment equipment should consider acid resistance, and it is recommended that the pre-treatment closed chamber body and the tank body use stainless steel material. The top of the pre-treatment equipment room body is equipped with exhaust fans to avoid the diffusion of gas to the outside of the room. It is recommended that the inspection platform be set on one side of the pre-treatment room body, the inspection door be set up in the room body, and the inspection door be equipped with cantilever searchlight to facilitate the relevant personnel to repair and maintain the equipment.
4.3 Spray booth
The existing painting production lines in China have Wenshi spray painting room, water spin spray painting room and water curtain spray painting room, and most of them use Wenshi spray painting room. The spray booth supply and exhaust air system has two types: full fresh air mode and circulating air mode. The full fresh air method is that the air supply air conditioning unit takes air from outside the room, passes through the multi-stage treatment of the air conditioning unit and sends it into the spray painting room, and the air is used through the spray painting room exhaust fan and discharged into the atmosphere. The circulating air mode is the air recycling of the spray painting room (that is, the air enters the spray painting room through the air supply air conditioner, and then returns to the air supply air conditioner through the circulating air treatment equipment for reuse). The air in the spray painting room is not completely discharged, but only partially discharged and partially supplemented. The amount of air supply and exhaust air should be calculated according to the balance of the air volume of the spray painting chamber, the explosion limit concentration of the exhaust gas in the spray painting chamber and the performance requirements of the paint, and the air volume supplement of some production lines is designed to be 10% and 30% of the total circulation air volume. The air volume of exhaust air and make-up air in the spray painting room should not be too low, too low will lead to high organic solvent content in the circulating wind, easy to cause the paint film surface loss of light, and the control of spray construction parameters is difficult. The concentration of exhaust gas in the spray booth with circulating air is higher (exceeding the requirements of national environmental protection standards), and the exhaust gas needs to be incinerated into the atmosphere (the exhaust gas after incineration can meet the national environmental protection requirements). The temperature of the painting room is generally required to be controlled at about 23 ° C, heat transfer in winter and refrigeration in summer, and the energy consumption of the painting production line in the form of full fresh air is large. The use of circulating air conditioning can reduce the energy consumption of the production line (comprehensive energy consumption can be reduced by more than 30%, the installed power of related equipment can be reduced by 40%) and save operating costs. The spray booth adopts circulating air supply, and the corresponding spraying form should be automatic spraying, because the harmful gas content in the circulating air is high, it is not suitable for manual operation, such as manual spraying to wear clothing and masks with anti-gas function.
4.4 Drying furnace
The main forms of drying oven are straight-through type, bridge type and P type 3. The mechanized conveying of Japanese painting production line mostly adopts the form of reverse stacking chain, and the drying furnace is bridge type drying furnace. The European and American system adopts light skid conveying system, and the drying furnace is P type drying furnace. The drying furnace mainly adopts the double stroke drying furnace, which can reduce the heat dissipation area of the drying room and reduce energy consumption.
4.5 Paint Supply system
There are two kinds of paint supply system, one is the centralized paint supply system, that is, all the paint is concentrated in a specific area for deployment, the centralized paint supply system should be arranged as far as possible in the place close to the three spray rooms, reduce the pressure loss and temperature loss caused by the length of the paint supply pipe, and avoid the difficulty of pipeline cleaning; The other is the line edge system, that is, the paint conveying equipment is placed near the spray room. The paint supply tank volume used by the line edge system is much smaller than that of the centralized paint supply, so the line edge system is also called a small system. The advantage of the small system is that it can meet the spray production under the condition of small paint feeding, which is used for infrequently produced color paints, new color trial production and temporary color adjustment painting; The centralized paint supply system is used for primers, varnishes and several large quantities of color paints.
5 Closing remarks
The state attaches more and more importance to environmental protection work, the State Environmental Protection Administration has issued the relevant cleaner production standards, the requirements of the painting line exhaust gas emissions will be more and more stringent, the body painting production line has been developing in the direction of water-based paint, bumper painting is also bound to develop in the direction of water-based painting, the domestic bumper painting line has been painted with water-based paint.
