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. 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).
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