Method for controlling zinc flow lines on surface of matt zinc-aluminum-magnesium plated narrow strip steel

Abstract

The invention discloses a method for controlling zinc flow lines on the surface of matt zinc-aluminum-magnesium-plated narrow strip steel, belongs to the technical field of metal coatings, solves the technical problems that a coating on the surface of the zinc-aluminum-magnesium-plated narrow strip steel is not uniform and the zinc flow lines are easy to generate, and adopts the technical scheme that the temperature of zinc liquid, the temperature of the narrow strip steel entering a zinc pot, the opening degree of a knife lip of an air knife and the production speed are increased; and the distance from the air knife to the narrow strip steel and the height from the air knife to the zinc liquid are reduced. By adjusting technological parameters, the phenomenon that zinc flow lines are generated on the surface of the zinc-aluminum-magnesium-plated narrow strip steel can be effectively controlled, the surface cleanliness of the produced zinc-aluminum-magnesium-plated narrow strip steel is high, and the zinc-aluminum-magnesium-plated narrow strip steel can be put into service without finishing operation of a finishing machine.

Description

Technical Field

[0001] The invention belongs to the technical field of metal plating, and in particular relates to a method for controlling zinc flow lines on the surface of a non-polished galvanized aluminum-magnesium narrow strip steel. Background Art

[0002] Galvanized aluminum-magnesium products are widely used in photovoltaics, animal husbandry, pipe making, automobiles, home appliances and other fields. The zinc-aluminum-magnesium coating is made by adding aluminum and magnesium elements to the molten zinc liquid, so that the coating has excellent corrosion resistance, wear resistance and processability. Increasing the content of aluminum and magnesium elements within a certain range can make the corrosion resistance of zinc-aluminum-magnesium coated steel plates several to dozens of times higher than that of ordinary galvanized plates.

[0003] Among the galvanized aluminum-magnesium products, the photovoltaic industry has the largest demand, mainly used to make photovoltaic brackets. The service life of photovoltaic panels is 25 years, and the anti-corrosion period of photovoltaic brackets is required to reach more than 25 years. Therefore, the weight of the coating metal per square meter is an important indicator of the surface coating of photovoltaic brackets. 2 . Generally, the preparation process of galvanized aluminum-magnesium narrow strip steel is as follows: first, the narrow strip steel is heated to above 700℃ in an annealing furnace, and the internal microstructure of the narrow strip steel completes recovery and recrystallization; second, the zinc pot is filled with zinc liquid, which contains three alloy elements: zinc, aluminum, and magnesium. After annealing, the narrow strip steel is cooled to the zinc pot temperature by a cold spray fan. In order to improve the wettability of the narrow strip steel in the zinc liquid, the zinc pot temperature is generally close to the zinc liquid temperature; third, after the galvanizing is completed in the zinc pot, the zinc liquid adheres to the surface of the narrow strip steel and enters the air knife with the narrow strip steel; finally, when the galvanized aluminum-magnesium narrow strip steel passes through the air knife, the nitrogen sprayed from the knife lip blows away the excess zinc liquid on the surface of the coating, thereby achieving the coating thickness required by the order. The air knife not only has the function of controlling the thickness of the zinc layer, but also has the effect of cooling the coating, so that the coating temperature drops below the melting point faster, thereby solidifying the coating. Compared with coil products, narrow strip galvanized aluminum-magnesium products have disadvantages such as poor raw material shape, poor surface quality, and low production line configuration. Therefore, the production of 275g / m 2 The zinc flow phenomenon on the surface of narrow strip steel is serious during coating and cannot meet product requirements.

[0004] Through 275g / m 2 The zinc flow pattern sample was used for defect observation. Horizontal zinc flow pattern defects appeared on the surface. They were obvious visually and felt severe, showing irregular morphology. The zinc flow pattern defects appeared as zinc protrusions under a 50x metallographic microscope (such as Figure 3As shown). The coating thickness of the raised part of the zinc flow pattern is 5μm-10μm thicker than that of the normal part. The reason is that when the narrow strip steel leaves the zinc pot, a large amount of zinc liquid will be attached. Before entering the air knife, the zinc liquid is in liquid state. Because the zinc liquid brought out by the steel plate cools naturally before reaching the air knife, its viscosity becomes higher and its fluidity decreases. Due to the flow caused by the zinc liquid's own weight and the cooling effect of the gas reflux, the waves formed by the flow of the zinc liquid cool below the solidification line, forming zinc flow patterns. The zinc flow pattern is manifested as zinc undulations and zinc waves in the macroscopic sense, and uneven coating thickness in the microscopic sense. In general production lines, the zinc flow pattern can be greatly improved by configuring a skin pass machine for leveling, but it is only a temporary solution. If a skin pass machine is configured, the floor space of the production equipment will be expanded, and the production cost will be increased. Therefore, to solve the technical problem of zinc flow pattern on the surface of galvanized aluminum-magnesium narrow strip steel, it is necessary to start from improving the fluidity of zinc liquid on the coating surface and controlling the cooling temperature of the coating, so as to ensure the uniformity of the coating. Summary of the invention

[0005] In order to overcome the deficiencies in the prior art and solve the technical problems of uneven coating on the surface of galvanized aluminum-magnesium narrow strip steel and easy generation of zinc flow lines, the present invention provides a method for controlling zinc flow lines on the surface of unfinished galvanized aluminum-magnesium narrow strip steel.

[0006] The design concept of the present invention is: (1) Properly increase the temperature of the zinc liquid: The temperature of the zinc liquid directly affects the solidification effect of the zinc liquid on the surface of the narrow strip steel. The higher the temperature of the zinc liquid, the better the fluidity of the zinc liquid. However, the higher the temperature of the zinc liquid, the better. As the temperature of the zinc liquid increases, the solubility of iron in the zinc liquid will increase accordingly. At the same time, the increase in the temperature of the zinc liquid will accelerate the chemical reaction in the zinc liquid, which will lead to an increase in the slag discharge rate and cause cost waste; (2) Appropriately increase the temperature of the narrow strip entering the zinc pot: After the temperature of the narrow strip entering the zinc pot is increased, it is released to the zinc liquid through the core heat dissipation, thereby increasing the temperature of the zinc liquid on the surface of the narrow strip and improving the fluidity of the zinc liquid. The higher the temperature of the narrow strip entering the zinc pot, the better. Too high a temperature will affect the wettability of the zinc liquid and cause the risk of dezincification and leakage plating; (3) Increase the opening of the air knife lip: When the air knife opening is low, the pressure is relatively concentrated, the jet force is large, and the cooling capacity is strong, which causes the zinc liquid to cool suddenly and reduces the fluidity of the zinc liquid. After increasing the opening of the air knife lip, the airflow is relatively gentle, the cooling capacity decreases, and the zinc layer cools slowly and evenly; (4) Reduce the distance between the air knife and the narrow strip steel: When the coating thickness is constant, the closer the air knife is to the narrow strip steel, the smaller the required gas pressure, and the lower the air flow cooling capacity, which is conducive to maintaining the fluidity of the zinc liquid. The closer the air knife is to the narrow strip steel, the better. If it is too close, it is easy to cause the zinc liquid to fly into the air knife and block the knife lip, resulting in a new defect of air knife streak; (5) Lower the height of the air knife from the zinc liquid surface: The cooling effect of the air knife on the coating is mainly reflected in the reflux of the airflow. The closer the air knife is to the zinc liquid, the smaller the reflux impact area is, and the more conducive to the stability of the coating thickness. The lower the height of the air knife from the zinc liquid surface is, the better. If it is too low, zinc slag will fly into the air knife and block the knife lip, resulting in new defects such as air knife streaks; (6) Properly increase the production speed: After increasing the production speed, the residence time in the gas recirculation zone of the air knife is shortened, which not only reduces the cooling capacity of the air knife airflow, but also reduces the impact of the recirculation influence zone on the uniformity of the zinc layer. When the production speed is too high, it will cause a variety of problems such as narrow strip jitter, deviation, incomplete annealing, etc., so it is necessary to choose the optimal speed suitable for the production line.

[0007] The present invention is achieved through the following technical solutions: A method for controlling zinc flow lines on the surface of unfinished galvanized aluminum-magnesium narrow strip steel, wherein: (1) Increase the temperature of the zinc liquid: increase the current zinc liquid temperature by 10°C-30°C to 455°C to ensure the fluidity of the zinc liquid; (2) Increase the temperature of the narrow strip steel entering the zinc pot: The narrow strip steel is preheated to 455°C before being sent into the zinc pot to ensure that the core heat of the narrow strip is released, which will heat the zinc coating and improve the fluidity of the zinc solution; (3) Increase the opening of the air knife lip: the width of the air knife is 800mm, and the opening of the air knife lip is 1.0mm-1.2mm; (4) Reduce the distance between the air knife and the narrow strip steel to 8 mm; (5) Lower the air knife to a height of 110 mm from the zinc liquid; (6) Increase production speed: Set the TV value to 130, where TV value = the value of the narrow strip thickness × the value of the production speed.

[0008] The beneficial effects of the present invention are: The invention can effectively control the phenomenon of zinc flow lines on the surface of galvanized aluminum-magnesium narrow strip steel by adjusting process parameters. The produced galvanized aluminum-magnesium narrow strip steel has high surface cleanliness and can be delivered for use without the need for finishing operation of a finishing machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 The schematic diagram of zinc-aluminum-magnesium coating on narrow steel strip; Figure 2 This is a macroscopic morphology of the unpolished galvanized aluminum-magnesium narrow strip steel prepared in Comparative Example 1; Figure 3 This is a microstructure morphology of the non-pass galvanized aluminum-magnesium narrow strip steel prepared in Comparative Example 1; Figure 4 This is a macroscopic morphology of the non-pass galvanized aluminum-magnesium narrow strip steel prepared in Comparative Example 2; Figure 5 This is a microstructure morphology of the non-pass galvanized aluminum-magnesium narrow strip steel prepared in Comparative Example 2; Figure 6 This is a macroscopic morphology of the unpolished galvanized aluminum-magnesium narrow strip steel prepared in Example 1; Figure 7 This is the microstructure morphology of the unpolished galvanized aluminum-magnesium narrow strip steel prepared in Example 1. DETAILED DESCRIPTION

[0010] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0011] According to product requirements, the thickness of the coating in the finished product of the unpolished galvanized aluminum-magnesium narrow strip steel in this specific implementation manner is 2.5 mm.

[0012] Comparative Example 1 like Figure 1 A method for controlling zinc flow lines on the surface of unpolished galvanized aluminum-magnesium narrow strip steel is shown, wherein: (1) The zinc liquid temperature is 430°C; (2) The temperature of the narrow strip entering the zinc pot is 430°C; (3) The width of the air knife is 800 mm, and the opening of the air knife lip is 0.4 mm-0.5 mm; (4) The distance between the air knife and the narrow strip steel is 26 mm; (5) The height of the air knife from the zinc liquid is 130 mm; (6) Increase production speed: Set the TV value to 120, where TV value = the value of the narrow strip thickness 2.5 × the value of the production speed 48; The macroscopic morphology and microstructural morphology of the non-pass galvanized aluminum-magnesium narrow strip steel prepared in this comparative example 1 are as follows: Figure 2 , Figure 3 shown.

[0013] Comparative Example 2 like Figure 1 A method for controlling zinc flow lines on the surface of unpolished galvanized aluminum-magnesium narrow strip steel is shown, wherein: (1) The zinc liquid temperature is 440°C; (2) The temperature of the narrow strip entering the zinc pot is 440°C; (3) The width of the air knife is 800 mm, and the opening of the air knife lip is 0.7 mm-0.9 mm; (4) The distance between the air knife and the narrow strip steel is 16 mm; (5) The height of the air knife from the zinc liquid is 120 mm; (6) Increase production speed: Set the TV value to 125, where TV value = the value of the narrow strip thickness 2.5 × the value of the production speed 50; The macroscopic and microstructural morphologies of the unpolished galvanized aluminum-magnesium narrow strip steel prepared in this comparative example 2 are as follows: Figure 4 , Figure 5 shown. Example 1

[0014] like Figure 1 A method for controlling zinc flow lines on the surface of unpolished galvanized aluminum-magnesium narrow strip steel is shown, wherein: (1) Increasing the temperature of the zinc liquid: increasing the current zinc liquid temperature by 10°C-30°C. In this embodiment 1, the zinc liquid temperature is 455°C. (2) Increasing the temperature of the narrow strip steel entering the zinc pot: In this embodiment 1, the narrow strip steel is preheated to 455°C before being fed into the zinc pot; (3) Increase the opening of the air knife lip: The opening of the air knife lip gradually increases from the middle to both sides. The width of the air knife is 800mm, and the opening of the air knife lip is 1.0mm-1.2mm; (4) Reduce the distance between the air knife and the narrow strip steel to 8 mm; (5) Lower the air knife to a height of 110 mm from the zinc liquid; (6) Increase production speed: Set the TV value to 130, where TV value = the value of the narrow strip thickness 2.5 × the value of the production speed 52; The macroscopic and microstructural morphologies of the unpolished galvanized aluminum-magnesium narrow strip steel prepared in Example 1 are as follows: Figure 6 , Figure 7 shown.

[0015]

[0016] By comparing comparative example 1, comparative example 2 and embodiment 1, it can be seen that the improvement effect of zinc flow pattern on the surface of the unpolished galvanized aluminum-magnesium narrow strip steel in embodiment 1 is very obvious and can meet the use requirements of customers.

[0017] right Figure 3 , 5 ,7 After testing the zinc flow microstructure, it can be seen that Figure 3 The zinc of the sample fluctuates obviously and the zinc flow defect is serious. After optimizing and adjusting the relevant processes, Figure 5 , Figure 7 The zinc fluctuation characteristics of the samples were greatly reduced; Figure 7 The sample coating Figure 5 Better, good overall uniformity, no obvious zinc flow defects.

[0018] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for controlling zinc flow lines on the surface of non-pass galvanized aluminum-magnesium narrow strip steel, characterized in that: (1) Increase the temperature of zinc liquid: the temperature of zinc liquid is 455℃; (2) Increase the temperature of the narrow strip steel entering the zinc pot: the narrow strip steel is preheated to 455°C before being sent into the zinc pot; (3) Increase the opening of the air knife lip: the width of the air knife is 800mm, and the opening of the air knife lip is 1.0mm-1.2mm; (4) Reduce the distance between the air knife and the narrow strip steel to 8 mm; (5) Lower the air knife to a height of 110 mm from the zinc liquid; (6) Increase production speed: Set the TV value to 130, where TV value = the value of the narrow strip thickness × the value of the production speed.

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