Select advanced technology to improve the surface treatment quality of steel drum
Zhuzhou City Metal Packaging Factory Liu Hongshun
There are many ways to improve the quality of steel drum spraying, and some use excellent performance coatings and advanced spraying equipment. In addition, some have taken effective measures from the spraying construction to ensure the quality and coordination between the processes.
In recent years, China's anti-corrosion coatings have developed rapidly, and various internal and external anti-corrosion coatings suitable for steel drum spraying have been developed. For example, the anti-corrosion coatings for high-corrosion properties are PVCD (polyvinylidene chloride) and PVF (polyvinyl fluoride), which are suitable for packaging chemical and pesticide products. Another example is the development of a special coating for the food and honey export packaging barrels - EPR type resin series coatings. In addition, there are two-component high-temperature anti-corrosion coatings that cure at room temperature.
In the field of spraying equipment, the emergence of advanced electrostatic powder coating equipment also shows a bright future for the improvement of steel drum spraying quality. At present, the widely used high-pressure airless spraying equipment and electrostatic spraying equipment can also achieve excellent spraying quality for steel drums.
Steel drums are also difficult to obtain good spray quality if there are only high-performance paints and advanced spray equipment without a construction process that ensures the quality of the steel drum. The main factors affecting the fluctuation of steel drum spraying quality are the cleaning quality of the steel before the spraying, the surface of the barrel and the drying method of the coating film. In the baking process of the coating film, the baking temperature and time should be within the standard temperature, and change according to the thickness of the coating film, so as to complement each other, flexible mastering is essential. For example, baking PVC coating film must be controlled at 230-260 ° C, baking time should be flexible according to the thickness of the coating film, in the range of 15 to 18 minutes.
The reason for the unstable quality of the steel drum spraying is that the spraying process is not tight enough, especially the surface of the steel drum is pre-sprayed. For example, for cold-rolled steel drums, some plants only use trichloroethylene for pre-treatment, and some plants use chemical degreasing. After the steel drums are dried, they are then sprayed. The two methods described above are only suitable for removing oil stains on the metal surface, but the rust removal effect is not good. Another example is that some factories use mechanical cleaning methods. This method is not only inefficient, but also difficult to stabilize quality, and workers have poor working conditions. It can ensure the process quality of the surface cleaning of the steel drum before spraying, Only the rust-passivation process, or the rust-phosphorization process.
The surface of the inner coated steel drum of our factory was cleaned before the rust-passivation solution promoted by the metal anti-corrosion plant of Huaibei Mineral Bureau. The process is as follows:
1) Cold rolled steel plate steel barrel semi-finished products
Degreasing -> hot water washing -> derusting -> washing -> passivation -> furnace drying -> surface cleaning -> spraying PVF -> baking coating.
2) Hot rolled steel plate steel barrel semi-finished products
Rust removal -> Washing -> Neutralization -> Passivation -> Furnace drying -> Surface cleaning -> Spray PVF -> Baking coating.
According to the above process, various process quality indicators of the steel drum coating film can be ensured. However, in the derusting-passivation process, the passivation film is dense, but the passivation film is thin, and it must be sprayed and coated in 24 hours to ensure the stability of the spraying process. If the semi-finished steel drum is not dried in time, due to the influence of residual liquid in the straight seam of the barrel, the part will first rust, which will also affect the stability of the coating process quality.
If the rust-phosphating process is used, the surface cleaning effect before spraying is better. This is because the phosphating film is thick and stable, but the process is complicated, and the operating specifications and total acidity and free acidity of the bath must be strictly controlled. Here, let me introduce the use of room temperature phosphating solution provided by our factory with the Dayong Experimental Factory of China Modern Physics Institute. The class is about 120. Processing time is 8-10 minutes. The process of hot-rolled steel drum semi-finished products is as follows:
Rust removal -> Washing -> Neutralization -> Washing -> Phosphating -> Supplementary treatment -> Drying or natural drying -> Surface cleaning -> Spraying PVF -> Baking PVF coating.
At the beginning of the construction, I did not use the supplementary treatment. After drying, there were residual white powder on the surface of the steel drum, and there were light rust marks on the straight seam of the barrel. After adding the supplementary treatment for 1 to 2 minutes, not only the white powder on the treated surface disappears, but also the straight seam portion of the barrel body, that is, the natural drying without rust marks. Thereby ensuring the stability of the quality of the surface cleaning process, the user reflects the corresponding problem of the quality of the inner coating steel drum.
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