Process flow of automobile bumper spraying production line:

Workpiece online → pre-treatment (pre-degreasing → degreasing → washing ① → washing ② → pure water washing → blowing water) → moisture drying → cooling → transfer → cleaning, polishing → flame treatment → electrostatic dust removal → spray primer → leveling →Spray finish→leveling→spray over varnish→leveling→curing and drying→inspection, polishing, inspection→workpiece offline.

(1) Pre-treatment

The pre-treatment is directly related to the spraying quality of the bumper. On the one hand, the pre-treatment can improve the anti-corrosion performance of the coating film and prolong the service life of the workpiece. On the other hand, it can improve the adhesion of the coating film to the substrate, and it can also make the bumper coating film have uniform performance.

(2) Moisture drying

The purpose of moisture drying is to fully dehydrate the pre-treated bumper surface to obtain a solid substrate for surface spraying operations. But the drying temperature should not be too high, because excessive dehydration will cause the coating performance to drop significantly.

(3) Surface spraying

Usually the bumper surface coating is composed of multiple coating films with different functions. Nowadays, wet spraying is often used, which can save energy, simplify the process, and meet the needs of mass production lines.

At present, the more advanced painting line is composed of paint spraying robot, two-component paint supply, automatic color change, workpiece identification, synchronization, master control and other subsystems. It has functions such as automatic color change, automatic identification, synchronous movement, and offline simulation. Multiple robots move in sequence to complete the processes of polishing, flame treatment, electrostatic dust removal, primer, topcoat and finishing paint spraying at one time. Of course, completely using robots, which are fully automatic operation methods, to carry out operations in various processes, and the investment and operating costs are relatively large; currently, it has not been applied in most domestic production enterprises.

(4) Polish and clean

After pre-treatment, the bumper enters the next polishing process. This process can be determined according to the actual situation of the surface of the workpiece. However, when the surface of the workpiece is uneven or has other damages, it must be passed through this process.

(5) Flame treatment

Flame treatment uses high temperature (above 3000##) gas flame to oxidize the surface of the plastic. Generally, surface tension or surface energy is used to measure the ability of the substrate to absorb liquid. If the surface energy of the substrate is at a high level, the liquid will become more wetted on its surface and have good ductility. This is the substrate adsorption Liquid foundation. Flame treatment can increase the surface tension of the substrate, making the bonding strength of the substrate and the coating tend to be greater, making it easier to spray.

Flame treatment involves a series of complex physical and chemical reactions. On the one hand, the high-temperature flame transfers energy to the oil and impurities attached to the surface of the substrate, causing it to evaporate when heated, and play a role in cleaning the surface of the substrate. On the other hand, the flame contains a large number of highly oxidizing ions. These ions react with the surface of the object to be treated at high temperature, so that a layer of charged polar functional groups is formed on the surface of the object to be treated, which improves the substrate’s performance. Surface energy, which also improves its ability to absorb liquids.

Maintaining a certain flame temperature and distance, and performing this pre-spraying treatment on the surface of the workpiece at an appropriate moving speed can reduce the surface stress of the workpiece, improve the surface adhesion of the workpiece, and improve the quality of spraying.