Common shrinkage hole defects and countermeasures in painting workshop

Abstract: Shrinkage hole is one of the common defects in painting shop, because it is difficult to repair online, often cause rework. There are many causes of shrinkage holes, this paper mainly introduces the types, causes and solutions of several shrinkage holes in actual production, and provides some references for the analysis and solution of similar problems in other sites.

introduction

In the painting process, the shrinkage hole defect is difficult to avoid and the repair work is large.There are many reasons for shrinkage, such as defects of the electrophoretic layer, pollution of the electrophoretic layer, pollution of the environment before spraying, pollution of the spraying equipment, pollution after spraying, paint problems, etc.The occurrence of shrinkage holes not only increases the rework cost, but also takes time and effort and is not easy to solve. Therefore, it is a very meaningful research direction to improve the level of coating process and reduce production cost to analyze the causes of shrinkage holes in automobile painting process, find corresponding solutions and eliminate shrinkage holes as much as possible.

Causes of shrinkage holes

1.1 Introduction to coating process

After the BIW enters the painting workshop for pre-treatment electrophoresis, the sealant process is carried out, and then the BIW arrives at the electrophoresis grinding station, where some paint slag, residual glue, welding slag and other defects affecting the next top paint process are disposed of, and then the biW enters the spray booth for spraying.

The spray painting process uses the IP2 process, also known as the no-medium paint process, in which the color paint coating is BC1 primer layer and BC2 color paint layer, BC2 spray into the flash dry oven, then spray varnish, and finally into the top paint oven.

1.2 Form of shrinkage hole

Defect description: The crater on the surface of the paint film (see Figure 1), which can be large or small in diameter, usually between 0.2-1.0mm visible to the naked eye. Foreign bodies can be observed in some depressions, but not in others. Some shrinkage holes can be observed in the wet film state.

The difference between the shrinkage hole and the pinhole: 1) the shrinkage hole is generally larger than the pinhole, the boundary is clear, and the depth is shallower than the pinhole; 2) Pinhole holes are small. Like a hole pierced with a needle, the center looks black when observed because of its small and deep; 3) Pinholes are generally caused by the ejection of air bubbles or solvent bubbles formed by the paint layer.

1.3 Causes of shrinkage holes

The main reason for shrinkage holes is that foreign pollutants (dripping, splashing, purging, volatilization, etc.) cause changes in the surface tension of the substrate or coating, resulting in uneven film formation. It is generally divided into the following aspects: 1) there is pollution in the paint; 2) There is environmental pollution in the process; 3) personnel introduce pollution; 4) Cleaning supplies pollution; 5) Replacement of relevant materials (such as compressed air, chamber glass glue); 6) Introduction of non-standard materials; 7) No certified oil or grease is used.

1.4 Several conventional material shrinkage evaluation test methods

The test methods generally include: rubbing the sample with the test plate or coating it on the test plate, spraying it and observing the wet film state; Dry film test; Sample and paint mixing test; There are also differences in factory methods such as contamination testing after mixing samples with solvents. The general test process is to simulate the situation and conditions of the sample to be tested in actual use.

2.Problem Solved

1) For the indoor and outdoor spray painting departments, the top paint engineer takes the lead and involves several departments including production, maintenance, cleaning and planning to jointly develop the inspection list and conduct detailed investigation from five aspects: human, machine, material, method and environment;

2) It was found that there was reconstruction construction under the conveyor chain from electrophoresis grinding to painting booth by the planning department, which was carried out only during the day and stopped after 17:00, which basically coincided with the occurrence of shrinkage hole defects. Moreover, after finishing, cleaning and standardized operation of the construction site, the proportion of shrinkage holes decreased significantly, and the same problem was solved.

03 Conclusion

Shrinkage problems are common in actual production, and they are always in the cycle of problem occurrence, investigation and solution. The special feature of shrinkage hole problem is that we can not always find the real root cause and eliminate the defects from the source, but the solution of the problem cannot be stopped. Only by constantly summarizing experience, summarizing methods, looking for rules, and sorting out the problem solving process can we not be busy when encountering problems and accurately find the starting point.

The more common cause of shrinkage problems is pollution, whether it is the electrophoretic layer, the conveying environment, the spraying material, the spraying environment, the spraying equipment will have pollution (especially silicone) problems, in these links need to make great efforts to manage.

1) Materials and accessories: including the use of Vaseline, lubricants, robot overalls, pipes, sealing materials replacement, use, brand change, etc., should be recorded and documented. Paint material is also a very key one, factory shrinkage test is to ensure the shrinkage of the material problem is the first checkpoint, materials into the factory after the system, daily spot inspection and observation of equipment operation, circulation system temperature, pressure is also essential;

2) Personnel management: the wearing of gloves at key stations, the use of skin care products, and the standardization of personnel operations. The maintenance of equipment, whether it is spraying robots or conveying equipment, should be carried out in accordance with the requirements of regular maintenance, cleaning, inspection and other work;

3) Environment: The cleanliness of the environment is the first important event for painting, which is not only very important for avoiding shrinkage defects, but also the most important for common coating defects such as particles and fibers.

In short, the management of shrinkage hole defects is a system management problem, involving all aspects, and a lot of work needs to be done before the problem occurs. After the problem occurs, we should be patient to sort out, look for changes, and improve and solve the problem.