Galvanizing Kettles

The galvanizing kettle for hot-dip galvanizing of steel structures is usually called the galvanizing kettle, and most of it is welded with steel plates. The steel galvanizing kettle is not only easy to make, but also suitable for heating with various heat sources. It is also very convenient to use and maintain. It is especially suitable for the supporting use of large steel structure hot-dip galvanizing production line.The quality of hot-dip galvanized coating and the level of production efficiency. It is closely related to the process technology used and the life of the zinc pot. If the zinc pot is corroded too fast, it will lead to premature damage or even perforation and leakage of zinc, which will result in great direct economic losses and indirect economic losses due to shutdown. Therefore, how to improve the service life of the galvanizing kettle is of great concern to hot-dip galvanizing workers. We will introduce and analyze the material, processing, structure, temperature rise, galvanizing kettle temperature, heating intensity and other factors that mainly affect the service life of the galvanizing kettle.

When selecting the zinc kettle material, the first thing to see is its ability to resist the corrosion of zinc liquid, while the requirements for its strength, oxidation resistance and other properties are relatively secondary. Because the increase of carbon content and silicon content in steel will cause the increase of iron loss (in other words, accelerate the corrosion rate of zinc liquid to zinc kettle), the steel with low carbon content and silicon content is selected as the raw material for making zinc pot in practical application. Adding a small amount of carbon and manganese (C ＜ 0.1%, Mn ＜ 0.5%) to the steel has little effect on the corrosion resistance of the steel to the molten zinc, but can improve the strength of the steel. The chemical composition of zinc pot steel provided by W.PILLING, a famous zinc kettle manufacturer in Germany, is: C ≤ 0.08%, Si ≤ 0.02%, Mn ≤ 0.50%, P ≤ 0.015%, S ≤ 0.010%. The steel with this composition has been confirmed as the special steel for zinc kettle.The corrosion rate of zinc liquid on the zinc kettle, the hydrostatic load of zinc liquid on the zinc pot wall, the strength of zinc pot wall material at operating temperature, and the supporting force provided by surrounding bricks and other strengthening elements on the zinc pot wall are considered comprehensively; The silicon content of the steel plate used to manufacture the zinc pot shall be controlled below 0.002%, and the wall thickness of the zinc pot shall be 50mm~60mm.In addition to the requirements for the chemical composition of steel, it should also be emphasized that the composition segregation and local macro defects (porosity, slag inclusion, folding, porosity, etc.) of steel plate may cause great harm to the zinc pot. Therefore, it is necessary to strictly inspect the steel plate for zinc pot and the manufacturing quality of zinc kettle.

The shape of the zinc pot shall be conducive to reducing the possibility of internal stress and strain generated by the zinc pot during manufacturing and use to a minimum. The zinc pot is generally made into a cuboid shaped container, which is most suitable for practical hot-dip galvanizing production. Sometimes a zinc pot with complex shape is used for easy operation, but such a zinc pot may have high thermal stress and is generally not recommended.The size of the zinc pot shall first be determined according to the needs of the product. The minimum size (length, width and depth) of the zinc pot must ensure that a single large workpiece or a certain number of small workpieces can be easily immersed in the pot.Due to the large heat dissipation of the zinc bath surface, the length and width of the zinc pot should be minimized to save energy on the premise that the workpiece can be conveniently placed. Reducing the heat dissipation of the zinc bath surface can reduce the heat transfer through the zinc pot wall, which can also reduce the heating intensity of the zinc pot, which is conducive to extending the service life of the zinc pot. The zinc bath surface is small, and the zinc ash produced by oxidation of the zinc bath surface will also be reduced.After the length and width of the zinc pot are determined, it can be considered to increase the depth of the zinc pot appropriately. Increasing the depth of the zinc pot has the following advantages:1) When the workpiece is immersed in a deep zinc pot, it is not easy to contact and stir the zinc slag at the bottom of the pot, which is conducive to sediment. The surface of the workpiece produced in the zinc bath with good sediment is smooth, and the zinc layer is thin and uniform.2) Increase the zinc capacity of the zinc pot, that is, increase the heat capacity of the zinc bath, and reduce the temperature fluctuation of the zinc bath when the workpiece is immersed.3) Under the same input power, the heating intensity of the pot wall will decrease, which can reduce the temperature difference between the inner wall of the zinc pot and the zinc bath, which is crucial to improve the life of the zinc pot.In production practice, the proportion range of width and depth of zinc pot is usually 1: (1.3~2).The thickness of steel plate used for making zinc pot is usually 50-60mm. According to the connection mode between each facade of the zinc pot and between the facade and the bottom, the structure of the zinc pot can generally be divided into the following two forms:1) The middle part of the zinc pot in the length direction is composed of one or more sections of pre bent U-shaped steel plates. The preformed end plate of the zinc pot includes the end elevation of the zinc pot and a small part of the side elevation and bottom surface. The transition between these surfaces is circular arc, and the two bottom corners of the end form a spherical crown surface. Then, weld the end plate and the middle U-shaped section, as shown in the figure. Such a structure can greatly reduce the tendency of stress concentration in the dangerous area of the zinc pot, including the junction between the bottom and the elevation, and the junction between the end elevation and the side elevation. At present, the large zinc pot adopts this structure.2) The wall of the zinc pot is composed of two flat side vertical panels and two prefabricated U-shaped end vertical panels. All vertical panels are welded on one flat bottom plate, as shown in the figure. The weld between the vertical panel and the bottom plate is fillet weld, and electroslag welding is not possible. The corner at the bottom of the zinc pot with this structure is at a right angle, and the weld area at this part will become the dangerous area and weak point with the maximum stress. For the zinc pot with a large depth, this situation deserves more attention and vigilance. It is generally believed that this type of structure is not suitable for zinc pots with a depth of more than 2m.

First of all, we choose the special steel plate for zinc pot with the same composition as the steel for zinc pot provided by W. PILLING of Germany as the raw material to manufacture the zinc pot, which is resistant to corrosion of zinc liquid. The zinc pot is made into a container with rectangular round bottom and round corner shape, so that the thermal stress of the zinc pot is small. In addition, a fully automatic PLC controlled galvanizing furnace is used to heat the zinc pot to control the furnace temperature evenly, and the heating intensity is set to be lower than 24kW/m2 to prevent local over erosion on the inner wall of the zinc pot. The service life of zinc pot can reach 8-10 years if the above points are achieved.