Development status of continuous hot galvanizing technology for strip steel
- hot pure zinc plating (GI, galvanized) products and alloying (GA, galvanneale d) product has excellent corrosion resistance, costs are relatively low, and with the progress of hot galvanizing technology, the product surface quality, quantity and are comparable to those obtained with electric galvanized products, thus has been widely used in the car. At present, Japanese cars are mainly made of GA board, and the automobile manufacturing industry in Europe and the United States is also increasing the use of hot-dip galvanized steel plate. , car plate, especially in practical auto outer panel demand increased at the same time, the surface quality of hot dip galvanized products and formability, etc, also put forward higher request, it is the requirement of this market is increasing greatly promoted the strip continuous hot galvanizing process technology, the progress of the operation.Continuous hot galvanizing process of strip steel and its improvement  1 hot galvanizing process strip steel continuous hot galvanizing process, there are three kinds of process: sengimil method, improved sengimil method and United States steel link method. Jimmy, Jimmy's method and the improved sen method is simple, the product cost is low, but as a result of using direct flame heating, although plate on the surface of the rolling oil can burn, but affect strip table, surface quality, is unfavorable to produce thin specifications products. Steel union law set up in front of the annealing furnace cleaning section, using electrolytic degreasing, can be, steel strip surface oil completely get rid of, in addition, the process using total radiation tube reduction furnace heating strip, and the galvanized layer surface quality, is good. The process is relatively complex, thermal efficiency is low, but it can produce better surface quality, the thickness of the thinner galvanized, steel plate, and can reduce the H2 content in the furnace, improve security, and therefore most new hot galvanizing unit using the steel!Link ". Modern cold rolling with typical technological process of the continuous hot galvanizing is: feeding a open book a pinch, straightening, welding cleaning the entry loop, a galvanizing annealing (alloying) - cooling - the middle loop, a pull a post-processing masking smooth export, and set a check coiling. The use of intermediate sleeve can make the whole machine to replace the work roll when the unit's process section can run normally, such machine!The high speed can not only improve the output, but also control the uniformity of plating thickness. In addition, when producing galvanized products with strict surface roughness, it is necessary to change the working roll of the planer frequently. In recent years, continuous hot galvanization of hot-rolled steel strip has developed rapidly. There are several hot rolled steel bands in Japan that have been continuously galvanized and produced lines. The typical process flow of hot rolling steel strip continuous hot galvanizing is: hot rolling acid-washing incoming material is welded, cleaned, inlet sleeve - annealed, galvanized - leveled, stretched, passivated and outlet sleeve is rolled. Can, see, according to the characteristic of hot rolling baseplate and the purpose of the hot rolled strip steel galvanized products, the process on the basis of cold-rolled strip steel hot galvanizing technology made to simplify, this not only save investment, but also greatly reduces the operating costs. Its development trend is towards short process, low energy, consumption and high efficiency. In addition, online pickling is also a development direction. Germany StahlwerkeBr emen factory in the hot-rolled pickling plate hot galvanizing line in hot rolled strip steel and galvanized strip steel flat after welding of 1, after straightening system, after the welding machine set tension leveling system is for the sake of porous oxide, improve the efficiency; After leveling, the tensile straightening system can further improve the flatness of the final product, and the mechanical properties of hot-coated galvanized sheet can be adjusted within a certain range by adjusting the tensile straightening elongation.In order to solve the hot rolled strip continuous hot galvanizing process caused by the original plate containing Si more leakage points plating, coating adhesion is poor and poor surface smoothness, developed a called South Korea's posco without pickling hot-rolled steel with continuous hot galvanizing process, namely the hot-rolled steel belt without pickling directly into the reduction furnace, and the reduction furnace temperature rise, to 650-750 ℃, holding time increased to 120-400 - s, protective gas hydrogen content up to more than 10%. In this case,, hot rolled steel with cracks and pores due to the expansion of the iron oxide, hydrogen gas can be introduced into and through the cracks and pores, oxide skin become composed of pure Fe and FeO porous layer, in hot dip galvanizing, this publication quality layer can promote more zinc and aluminum, diffusion and the formation of a quality of a material soft Fe - A1 - zinc alloy layer, so as to improve the adhesion of the coating, and eliminate plating leakage point. 2 cleaning process usually includes lye scrub and electrolytic degreasing cleaning, it can clear the iron layer on the cold rolled steel sheet surface and oil pollution, impurities, to produce high surface quality and high bonding strength galvanized products is vital. A new hot-dip galvanizing unit has been built in a factory. The washing section includes alkaline leaching, alkaline cleaning, electrolytic cleaning, hot water scrubbing, hot water rinsing, washing and drying- in order to control the total amount of residual oil and carbon on the surface of strip steel below 20m g/m2(single surface) and achieve the cleaning of hot-dip galvanized automobile exterior platesQuality requirements, in addition to using the S i02 abrasive brush roller, when cleaning the strip surface grinding, can improve GA products, coating adhesion. It is also suggested that the future direction of cleaning section should be to develop and utilize ultrasonic cleaning or high-pressure cleaning widely used in other fields. In order to further ensure the strip surface is clean, no. 4 hot galvanizing unit is South Korea's posco, the cleaning system, in addition to the normal entrance before looping pre-cleaning, steel belt gateway after looping, electrolytic cleaning is carried out again.The cleaning section is usually arranged before the inlet sleeve or after the inlet sleeve to achieve constant speed cleaning.