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Continuous strip line

- Sep 07, 2018 -


     Strip steel continuous hot plating details 1GI, galvanneale d and GA, galvanneale d have excellent corrosion resistance and relatively low cost. With the improvement of hot-dip galvanizing technology, their surface quality and galvanneale d can be compared with electrogalvanizing products, thus they are widely used in cars. At present, most Japanese cars are made of GA board, and the automobile manufacturing industry in Europe and America is constantly improving the use of hot-dip galvanized steel. Automobile plate, especially automobile outside plate is in demand ceaselessly increase while, to hot galvanization product surface quality and the respect such as molding sex also put forward higher and higher requirement, it is exactly this kind of market demand ceaselessly raise to promote the progress of continuous hot galvanization technology of strip steel greatly.Continuous hot galvanizing process and its improvement & the continuous hot galvanizing process of NBSPL includes three kinds: sensemir method, modified sensemir method and United States method. Semilier process and modified semilier process are simple and low cost. However, the use of direct flame heating can burn off the rolling oil on the surface of steel plate, which affects the surface quality of strip steel and is not conducive to the production of thin specification products. The cleaning section is set up before the annealing furnace by using electrolytic degreasing, which can remove the oil on the surface of the steel belt. Although the process is relatively complex and low in thermal efficiency, it can produce hot-dip galvanized steel sheet with better surface quality and thinner thickness. Moreover, it can reduce the H2 content in the furnace and improve safety. Therefore, most of the newly-built hot-dip galvanizing units adopt American steel association method.The typical technological process of continuous galvanizing of modern cold rolled steel strip is as follows: loading - uncoiling - clamping, straightening - welding cleaning - inlet looper - annealing - galvanizing -(alloying)- cooling - middle looper - flat,- tension leveling - post-processing - exit looper - inspection coiling. With the use of the middle looper, the machine can be replaced and the process section can operate normally. In this way, the unit speed can not only increase the output, but also control the uniformity of the coating thickness. In addition, when producing galvanizing products with strict requirement of surface roughness, it is necessary to change the working roller of the leveling machine frequently, and it is also necessary to use the middle looper.In recent years, continuous hot galvanizing of hot-rolled steel strip has developed rapidly. There are several hot-rolled steel strip continuous hot galvanizing production lines in Japan, and a similar production line has been built at handan iron and steel co., ltd. in China. The typical process of continuous hot galvanizing of hot rolled steel strip is as follows: hot rolled pickling, incoming material - fear of receiving one cleaning one inlet looper - annealing one galvanizing - leveling - drawing correction - passivation - exit looper - take-up. It can be seen that according to the characteristics of hot-rolled base plate and the use of hot-rolled strip galvanized products, this process is simplified on the basis of cold-rolled strip hot-dip galvanizing process, which not only saves the investment, but also greatly reduces the operating cost. Its development trend is towards short process, low energy consumption and high efficiency, and online pickling is also a development direction. In German S tahlwerkeBr emen works, the hot-dip galvanizing line of hot-rolled pickling board is formed after the hot-rolled strip is welded and the galvanized strip is flat, and then a pull and stretch straightening system is set up. The leveling stretching and straightening system can further improve the flatness of the final product and adjust the mechanical properties of hot galvanized sheet within a certain range by adjusting the stretching and leveling.In order to solve the hot rolled strip continuous hot galvanizing process caused by the original plate containing Si more leakage points plating, plating is poor and poor surface smoothness, developed a called South Korea's posco acid free choose hot rolled steel with continuous hot galvanizing process, namely the hot-rolled steel belt without acid directly into the reduction furnace, and to increase the reduction furnace temperature to 650-750 ℃, holding time increased to 120-400 - s, protective gas hydrogen content up to more than 10%. Under this condition, hot rolled steel with cracks and pores due to the expansion of the iron oxide, hydrogen gas can be introduced into, by these cracks and pore f scale become composed of pure Fe and FeO porous layer, when the hot dip galvanized, the porous layer can promote the diffusion of zinc and aluminium to form a soft texture of Fe - A1 - zinc alloy layer, so as to improve the adhesion of the coating, and eliminate plating leakage point. Cleaning process usually includes alkali cleaning and electrolytic degreasing, which can remove impurities such as iron layer and oil on the surface of cold rolled steel sheet. New hot galvanizing unit cleaning section of some factory including alkali soaking, lye scrub, electrolytic cleaning, hot water cleaning, hot water rinse, drain cleaning and dry cleaning, can put the amount of residual oil and residual carbon steel strip surface control under the 20 m g/m2 (single), reached the requirements of quality of hot dip galvanized auto outer surface cleaning, also USES the brush roll with Si02 grits, when cleaning on the strip surface grinding, can improve adhesion of coating of GA products. It was also suggested that the future direction of cleaning section should be the development and utilization of ultrasound widely used in other fields