Inner coating technology and application of cans (Part 2)
3. Pressure control
the use of spraying pressure control devices in production can effectively control the amount of paint, so as to obtain a lower amount of paint, which is conducive to the use of different amounts of paint for different packages, and can also make up for the impact of nozzle wear on the amount of paint. Due to the wear of the nozzle, the pore diameter becomes larger, and too much paint is sprayed into the tank. Relying on pressure adjustment can make up for the lack that Solvay's material meets the biocompatibility standard defined in ISO 10993:1, and also extend the service life of the nozzle
experience shows that with the pressure of 800psi, the fog degree of the coating is high, and a film with good uniformity can be obtained, but the amount of excessive coating sprayed outside the tank is also large (that is, spraying into the tank and splashing out of the tank), while with the pressure of 300PSI and the same type of nozzle, a better fog degree can be obtained, and a uniform film can be obtained, obviously the amount of excessive coating is small. In short, to find a suitable pressure and get a evenly distributed film, usually 250psi pressure is enough, and 300PSI pressure is not necessarily a good thing.
according to the test, three different coating films of 1000mm 3 weight can be obtained by adjusting the spraying time or pressure with the nozzle of the same specification. Under the pressure of 200 psi, the conductivity will be slightly higher, but it meets the requirements of beer packaging.
the conclusion of this test is that the use of low pressure can reduce excessive spray and reduce cleaning and maintenance time. Since the sprayer needs to use a recycling tank to recycle waste paint, the recycling tank must be replaced and cleaned frequently. In addition, the cleaning time of the spray gun should be reduced, which helps to improve production efficiency. More importantly, it is easy to operate and control under low pressure. Therefore, using low pressure and controlling the working time can achieve good results.
although the pressure monitoring device is a commonly used pressure monitoring tool, its use in the internal spraying system can play an important role, such as nozzle wear, blockage, incorrect pump performance, filter blockage and other factors that cause its configuration similar to bricks and mortar. The pressure change can be shown by the reading of the pressure gauge. Some manufacturers have developed more advanced pressure monitoring systems, such as canwork. This control system can automatically correct the pressure of the spray gun by monitoring the pressure of the spray gun when there is a problem in the spray gun system, so as to ensure that each spray gun is in good working condition. At the same time, input the original data into the computer, you can know whether the flow is too high or too low, and the data can be collected and corrected at any time, which can help find the problem. There are mainly two groups of information applied to the system: one is synchronous information; Second, spray gun pressure information.
in addition, another important factor affecting the internal coating process is the synchronous setting. The tank is in a rotating state during spraying. The spraying working time should be determined according to the rotating speed of the tank, especially the low pressure spraying amount. In short, in order to obtain a good coating with integrity, incomplete coating will lead to metal exposure and corrosion, or waste due to too much coating. The ideal coating is less and uniform. Therefore, the core problem is that the working time should be synchronized with the tank rotation speed.
III. selection and location of nozzles
three factors should be considered in the selection of nozzles:
① the fan-shaped surface sprayed, that is, the surface covered by the sprayed paint; ② flow rate, that is, how much paint can be sprayed per minute;
③ spray distribution, that is, there is more paint on one side than on the other side;
Image scattering spraying can obtain uniform coatings on both sides with the scattered surface as the center line. It is mainly used for spraying lightweight equipment of automobiles or new energy vehicles, which has many advantages. It can obtain coatings of uniform thickness.
however, in terms of cans, because the mouth of the cans is close to the nozzle, and the fixed position of the nozzle is related to the cans, the result of the flat shot nozzle is that there is less paint towards the bottom of the cans, which becomes a problem when it is used for spraying with a low amount of paint. The operating fan-shaped nozzle is characterized by spraying more paint on one side and less paint on the other side. Because the distance between the tank bottom and the nozzle is the farthest, more paint is needed to cover the large area of the tank bottom. Therefore, the side with more paint distribution of the nozzle faces the tank bottom and the side with less paint distribution faces the upper part. This can not only get a uniform thickness of paint, which is suitable for all kinds of tank types and paints, but more importantly, it is suitable for low paint spraying.
the distance between the nozzle and the tank and the angle formed are very important. The position of the spray gun largely depends on the nozzle model and system pressure used, and is also largely related to coating properties such as viscosity, temperature and vacuum pumping performance of the spraying equipment. These factors will vary greatly with different equipment and factories. Spray with a single gun at an angle of about 15 ~ 200, and spray with two guns. The first gun supplies the paint to the lower part of the tank wall and the tank bottom at an angle of about 100, and the second gun supplies the paint to all parts of the tank at an angle of about 200
to sum up, controlling such variable factors as coating temperature, system pressure, spraying time, nozzle model and spray gun position can improve production efficiency, improve internal coating process, reduce coating cost and improve market competitiveness
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