Application of the hottest chrome plated steel she

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Application of chromium plated steel sheet in food can storage and packaging. The United States, Europe and Japan have more and more applications, replacing some tinplate materials. The application of this material in China is relatively few, which requires a correct understanding of this material and some technical and ideological analysis

I. Development and characteristics of chromium plated plate

chromium is a hard metal with silver white luster. It has good hardness, wear resistance, matrix adhesion and high heat resistance. As early as the 1920s, the chromium plating process was used in industrial production. In 1940, the United States began to study chromium plated plates, which were treated with chromic acid for chemical treatment and electrolytic chromic acid treatment, and then transferred to mass production. Since 1955, Japan has studied chromate passivation methods and achieved many results. For example, Hitop chrome plated plate of Toyo steel plate company entered industrial production in 1961; Fuji iron Institute has also successively produced con copper chromium plated plates; In 1972, bright coat chrome plated plate was produced by Japan steel pipe (Zhuzhou) Co., Ltd. European countries also successively produced chromium plated plates in the 1970s

the original plate and tinplate used for chromium plating are the same, both of which are low-carbon structural steel sheets, but the chromium plating layer is very thin (1.3 μ m) The process is the same as that of tinplate. Therefore, generally, the original tin plating production line can be used for tin plating or chromium plating only by slightly modifying and adding chromium plating tank

the structure of chromium plated plate has four layers: steel substrate, metal chromium layer, hydrated chromium oxide layer and oil film. As the substrates are the same, their mechanical properties are the same as those of tinplate, but they have some own characteristics in application:

1 The cost is about 10% lower than that of tinplate, and the appearance luster is not as good as that of tinplate

2. The corrosion resistance is not as good as tinplate, the coating is thin and the pinhole rate is high, so the internal and external surfaces should be coated when using

3. Chrome plate has strong adhesion to organic coatings, which is 3 ~ 6 times stronger than tin plate. The resistance to vulcanization corrosion is also stronger than that of tinplate

4. The chromium plated plate cannot be tin welded, but can only be welded by overlapping resistance welding or bonding

5. The coating is thin and has poor toughness, and the can making is easy to crack, so it is not suitable to flush the can, and can be used for deep flushing

6. Chrome plated plate has strong high temperature resistance. Generally, there is no obvious change in color and hardness at 5000 ℃, and it begins to soften at 7000 ℃

II. Main problems in the application of chromium plated plates in food can making

from the above understanding, there are two main technical problems restricting the application of chromium plated plates in food can making industry:

the first is corrosion resistance. This problem can be studied from the improvement of chromium plating technology and coating after plating. It should be noted that cost should be considered for any technical improvement in order to maintain the advantages of chromium plated plate. At present, although the corrosion resistance of chromium plated plate is not as good as that of tin plated plate, it also has certain corrosion resistance, which is suitable for the packaging of weak acid food. This kind of food has a large market, such as meat, fish, poultry, dairy products, vegetables, carrots, wrist beans, beets, potatoes, as well as various drinks and soups. If the technical guarantee for the coating is strict, some pH is 3 7 to 4 5 acid foods can also be packaged with chromium plated plates, such as fruits, pickles, etc. It is worth mentioning that the study on the corrosion resistance of chromium plated plates should not rest on the general concept that chromium has a good corrosion protection effect on iron. Chromium plated plates are cathodic coatings and cannot play an electrochemical protection role. Under the condition of large porosity, the alloy effect between steel substrate and chromium layer is worth studying. Someone tested the corrosion resistance of chromium steel in seawater and found that chromium can improve the corrosion resistance of carbon steel after short-term (within 2 years) immersion; However, long-term immersion (after more than 2 years) is not only unhelpful, but also accelerates corrosion

the second is the can making process. The chromium plated plate is thin and poor in toughness, lacking the stamping lubricant like tin, so the stamping process needs to be carefully studied. At present, it is feasible to adopt deep drawing process for two-piece tank. Since tin welding is not possible, fusion welding or bonding must be used when making three piece cans. If tin plate and chromium plate are used together, tin plate for tank body and chromium plate for tank bottom cover are also used. In addition, the sealing between the tank body and the cover should not be double rolled into the process, otherwise it must be repaired

III. ideological understanding of the application of chromium plated plate

the above analysis shows that although the application of chromium plated plate in food packaging has its limitations, it also has its characteristics and advantages, and has a relatively broad market, so it is worth promoting and developing. However, from the current reality of our country, there are still two cognitive problems in the process of development

first, the manufacturing industry of chromium plated steel plate in China is almost blank. Since the reform and opening up, China's iron and steel industry has developed rapidly. At the end of the last century, China has become the world's four largest iron and steel producers. In 2002, the steel output reached 1. 5% 2.7 billion tons. But in terms of its variety and quality, it is quite different from the developed countries in the world. Only about 40% of the products can meet the needs of variety and quality, 30% of the products are insufficient in quantity, 20% of the products are poor in quality, and 10% of the products cannot be produced. In fact, China's steel products are mainly made of wire rod and this round of adjustment, which is really a fundamental warming, or the short-term repair of steel products lags behind another falling range, which still needs to be verified by the market. Profiles are the main types, and plates and pipes are in short supply. While 25% of the steel manufacturers are small enterprises, and 33% of the steel manufacturers are small enterprises. Their equipment is old, their technology is backward, and the composition of raw materials is unstable. Large enterprises are also facing a period of system reform and technological upgrading. Therefore, on the whole, the quality gap of steel products in China is still large, the chemical composition fluctuates greatly, the performance is unstable, the dimensional accuracy of finished products is not high, and there are many surface defects, obviously causing a high scrap rate for users. Many enterprises have imported foreign advanced equipment, but they have to import materials because domestic raw materials are not applicable. From the point of view of steel sheet materials, although the annual growth is very fast, in 2002, China made 1903 810000 tons, a year-on-year increase of 10 20%, but the performance consumption reached 39.23 million tons. Therefore, the gap of sheet steel in China is very large. It is conceivable that in this context, the packaging industry can only rely on imports if it wants to use chrome plated steel plates. It is worth mentioning that the current production capacity of tinplate in China is surplus. Unfortunately, most of them are low-grade production lines, and the products can only be used for dry food packaging. High grade tinplate for cans and beverage packaging still depends on import. It can be seen that raw materials themselves restrict the development and progress of food packaging, which involves many scientific management and coordinated development issues in our progress

second, how Chinese food canning enterprises understand their packaging containers. At present, canned food processing enterprises mainly use tinplate. Their food technology, canned goods sales, corresponding equipment and mechanism are all based on tinplate. Any technological transformation and innovation involves the benefit of the enterprise and the reputation of the market. Therefore, the application of chromium plated plates is a risk for them. Only with scientific economic analysis, reliable conditions and enterprisers with reform spirit can they have the courage to try. Whether foreign countries have ready-made experience and equipment to adapt to China's new energy vehicles is a national ldquo; 1035 rdquo; The current situation of the key development direction countries should be carefully discussed. The author has learned about some factories. Due to the limitations of the enterprise mechanism, the factory director dare not take risks, because this is a major transformation. It can be seen that Chinese enterprises have the problems of conditions and ideological understanding in the connection of new things to the 1025 development plan of the plastic machinery industry. The key is to establish a mechanism for enterprises to constantly explore and improve. Especially after China's entry into WTO, it must be strengthened in the face of market internationalization. It is urgent to meet the technical requirements of hydraulic system cylinder configuration

reprinted from: China canning business

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