As we all know, the coating of epoxy wire mesh can be customized and can even be processed into regular lines. At the same time, based on the configuration characteristics of powder, it can have products of the same color but different gloss, such as high gloss, semi gloss, matt etc.
What we are going to talk about today is the color inconsistency of dots, blocks or a larger proportion of the mesh surface after the epoxy coating process is completed.
The composition of the product is substrate wire mesh + electrostatic spray coating. The coating is made by charging the solid epoxy powder with the electrostatic spray gun, and then adsorbing it together with the grounded substrate wire mesh, and through the process of preheating, heat preservation and cooling to form a dense coating. This is to say, the abnormal processing technology will cause inconsistent color.
There are two cases, one is transparent coating treatment, the other is non-transparent coating treatment. For the first case, the color difference of substrate wire mesh is also an important factor causing color inconsistency. In this article, we only analyze the factors of the second situation.
1. When changing the powder, the powder room of the coating system is not cleaned up, resulting in the mixing of new powder and residual powder, which will lead to spotted color difference. Even due to different powder systems, it will lead to incomplete curing of the coating, decreased adhesion, unqualified performance and other problems. Therefore, when changing the powder, it is required to fully start the powder spraying and recovery system. First, blow the system from the powder pump to the spray gun with compressed gas one by one; Secondly, close the screening system, blow the powder in the powder room and recovery pipeline into the recovery system, close the system, manually clean the pulse filter element and funnel, and finally manually clean the powder barrel.
2. If the curing temperature or heat preservation time exceeds the limit of the melting requirements of the coating itself, it will cause the embrittlement of the coating, massive yellowing, low gloss and other problems. For example, the coating requires 160 ℃ for 2min, which will be caused if the actual operation is 200 ℃ or 4min in the spraying process. Therefore, during the coating process, it is necessary to ensure that the temperature curve in the furnace is between ± 5 ℃, the circulating air keeps the temperature in the furnace uniform, and the temperature control probes in each temperature zone must be calibrated regularly. In case of long-term shutdown or failure, the spraying line needs to be shut down in time, and the operation can be started after the failure is eliminated, so as to avoid uneven coating color. (Note: products that are not cured completely can be cured again with the same parameters)
3. There is grease on the surface of the substrate metal mesh . The volatilization of grease during the melting process of the coating will affect the leveling of the coating, resulting in dense pits on the mesh surface after curing, and even the exposure of the metal mesh. The grease mainly comes from the lubricant in the process of wire drawing and weaving. Therefore, on the one hand, volatile lubricants such as aviation kerosene are required to be used in the process of metal mesh weaving, on the other hand, the metal mesh needs degreasing pretreatment (i.e. cleaning).
4. Uneven coating thickness will also cause reflective color difference, and thick areas have higher gloss. The lines formed by different spray gun arrangements are also different. The reciprocating spray gun is easy to form a "W" shape and thick on both sides, and the fixed gun spraying will form a vertical uneven shape. For example, when the thickness of the same area is 30um and 50um, the color will be inconsistent. Therefore, before coating, the spray gun system (especially the powder tube inside the reciprocating machine shall be adjusted smoothly without bending. At the same time, the workpiece chain speed, reciprocating frequency and the number of spray guns must be calculated and verified) shall be comprehensively checked to keep it smooth. At the same time, the powder output state of each spray gun in the powder room shall be observed regularly and adjusted in time.
Recommended monitoring methods for the above problems: micrometer, hand-held photometer and 50x magnifying glass.
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