(1) Roller strip steel system. The roller strip steel system mainly includes: sinking roller, stabilizing roller, correction roller and six arms that support the three rollers immersed in the zinc pot, usually called "three rollers and six arms", and air knives and adjustment devices. According to different strip specifications, materials, tension and zinc pot temperature, combined with the detection of the zinc layer thickness after cooling, adjusting the horizontal movement distance of the correction roller can increase the strip tension to suppress the swing of the strip, thereby achieving the correction plate shape purpose. During this process, the strip needs to go through two processes: annealing and hot-dip galvanizing. First, the strip needs to go through three stages of heating, constant temperature, and cooling in the annealing furnace. Then it passes through the tension roller and enters the zinc pot. It passes through the sinking roller and the stabilizing roller. The roller reaches the air knife. Each link in the middle will have a certain impact on the quality of galvanized strip, so how to control it has always been a problem.
(2) Continuous annealing furnace. Before the strip passes through the tension rollers, it needs to be annealed. The quality of annealing directly affects the mechanical properties of the strip, thereby having a certain impact on the thickness, uniformity and final product quality of the galvanized layer. At present, continuous strip annealing furnaces are divided into two types: horizontal annealing furnaces and vertical annealing furnaces. The hot core unit equipment introduced in my country in the early days is generally a horizontal annealing furnace. The horizontal annealing furnace uses the Sendzimir method and uses an open flame for direct and rapid heating. , using high temperature to evaporate the grease on the strip steel surface. The horizontal annealing furnace has a simple structure and low investment. However, it is difficult to create the oxygen-free environment required in the furnace, and the high temperature also causes excessive oxides to be produced on the surface of the strip, affecting the quality of galvanizing. Secondly, the horizontal annealing furnace occupies a large area and has low space utilization. At present, it is mainly used in the production of building materials and other products that do not require high product quality.
The vertical annealing furnace uses the US Steel Union method to remove surface grease from the strip through electrolysis. Compared with the horizontal annealing furnace, the surface quality of the strip produced by the vertical annealing furnace is high, with good economic benefits and high space utilization. Since the vertical annealing furnace uses radiant tubes for indirect heating throughout the entire process, there are P-type, U-type, W-type and other thermal radiant tubes. Among them, the W-type has the highest thermal radiation efficiency, and the oxides generated during the annealing process are significantly reduced compared to the Sendzimir method. At the same time, multiple pairs of rollers in the vertical annealing furnace have a tensioning effect on the strip, which solves the problem of strip deviation in the horizontal annealing furnace.
(3) Zinc liquid temperature. There is a certain temperature difference between the strip steel and the zinc liquid. Generally speaking, the strip steel temperature is 30 to 40°C higher than the zinc liquid temperature, which plays the role of indirectly heating the zinc liquid. The temperature difference between the two should not be too large. On the one hand, the strip steel temperature is high. Above the temperature of the zinc liquid, the galvanizing process tends to produce too much aluminum-iron alloy, which accumulates scum on the surface of the zinc liquid. On the other hand, the strip temperature is lower than the zinc liquid, which will cause the coating to solidify prematurely, which will affect the thickness and uniformity of the subsequent coating. Big trouble.
(4) Roller system. The strip steel needs to pass through the tension roller before entering the zinc pot. Generally, only one tension roller is installed. The structure is simple, but there are certain problems. Changing one tension roller to two tension rollers can prevent the strip steel from deflecting and improve The quality of galvanized coating. The sinking roller in the zinc pot has been immersed in high-temperature zinc liquid for a long time. At the same time, it is continuously driven to rotate by friction with the strip. The wear resistance of the sinking roller affects the strip shape, and the surface quality affects the galvanizing effect. Therefore, the sinking roller needs to be replaced regularly to ensure the quality of galvanizing. The sinking roller made of SUS16 steel used in the initial stage had poor wear resistance and short replacement cycle. Nowadays, sinking rollers made of 1Cr13, SUS316L and other materials are commonly used to improve product quality and extend the replacement cycle. Secondly, the improvement of the surface coating of the sinking roller is also extremely important. The innovation of new materials and new technologies will definitely bring huge economic benefits to the hot-dip galvanizing industry.
The strip passes through the sinking roller and then reaches the stabilizing roller. The stabilizing roller is in the zinc liquid above the sinking roller. The working conditions are the same as the sinking roller. For a single stabilizing roller, it only has the function of advancing the strip and cannot solve the possible warping phenomenon of the strip. Adding a correction roller can suppress the warpage of the strip. This needs to be based on simulation experiments or practical experience. If the amount of push-up is too small, the effect of suppressing the warpage of the strip may not be obvious. If the amount of push-up is too large, the strip will warp in the direction. For strips of different specifications and materials, the upward push amount of the correction roller is adjusted to achieve the best effect. Secondly, the stabilizing roller and correction roller have the same material requirements as the sinking roller, so it is particularly important to reduce the frequency of replacement.
(5) Air knife aspect. The air knife is the core to ensure the quality of coating. The influence of the air knife on the quality of galvanizing mainly includes the lip shape and gap of the air knife, the position of the air knife, the angle of the air knife, and the blowing pressure of the air knife. The lip shape of the air knife determines the air flow. In production, straight air knives are often used to facilitate adjustment of the gap between the upper and lower lips of the air knife. In addition, double air knives inhibit the generation of new ripples on the surface of the strip compared to a single air knife. At the same time, the inner wall of the air knife The finish is also very important. The air knife gap needs to be adjusted according to the actual situation. Due to the progress of the production process, the air knife gap will change due to changes in blowing pressure and temperature. Adjustments should be made in time to ensure the quality of the zinc layer.
The position of the air knife can be divided into the height of the air knife and the distance between the air knife and the strip. The height of the air knife is generally set between 200 and 400mm, which not only avoids the possibility of zinc liquid sputtering when the galvanized layer has good fluidity, but also avoids the risk of galvanizing. It is difficult to ensure the thickness and uniformity of the zinc layer after cooling. The distance between the air knife and the strip also needs to be determined according to the production situation. If the distance is too large, the injection pressure on the strip will be small. If the distance is too small, the zinc liquid will sputter and increase the probability of clogging the knife lip. The air knife angle refers to the angle between the air knife and the strip steel. The selection of the angle can increase the zinc wiping ability of the air knife. The air knives on both sides should be staggered, and ±4o is appropriate.
The air knife blowing pressure directly affects the thickness of the zinc layer and is a key factor in the quality of galvanizing. As the pressure increases, the thickness of the zinc layer decreases. The injection pressure is also affected by the strip speed and needs to be adjusted according to the strip speed. The faster the speed, the greater the injection pressure. The air knife adjustment relies on production experience and data to adjust the air knife parameters in a timely manner and the synergy of each part to achieve the best effect of the galvanized layer.
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