A method for producing a thin-gauge thin-zinc-layer large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit

Abstract

The application belongs to the technical field of steel metallurgy, and particularly discloses a method for producing thin-gauge thin-zinc-layer large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit, which comprises acid combined rolling, alkali tank scrubbing, electrolytic degreasing, annealing, zinc plating and cooling. In view of the problem that the current extremely thin-gauge strip steel cannot produce uniform large zinc flowers, the application precisely realizes one-side 22-28 g / m 2 of the thin-zinc-layer control of the strip by strictly limiting the content of Pb in the zinc liquid and precisely controlling the Al and Sb ratio, thereby inhibiting the excessive thickening of the zinc-iron alloy layer; meanwhile, the multiple slow cooling means are adopted in combination with the segmented gradient cooling to reduce the supercooling degree of the zinc liquid, so that the stable production of 8-16 mm uniform and clear large zinc flowers is realized, and the problem that the extremely thin-gauge strip steel cannot produce uniform large zinc flowers due to the excessively fast cooling rate and large plate temperature measurement error when the zinc-aluminum-magnesium unit rolls the thin-gauge strip steel in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a method for producing thin-gauge, thin-zinc-layer, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit. Background Technology

[0002] The formation of zinc flowers on the surface of hot-dip galvanized coatings is essentially a competition between nucleation and grain growth during the solidification stage of molten zinc. Following the basic theory of metal solidification: the greater the supercooling of the molten zinc, the more nuclei are formed per unit volume, and the grain growth rate is significantly suppressed, resulting in small zinc flowers. Conversely, reducing the supercooling and decreasing the number of nuclei allows zinc dendrites to grow fully, resulting in large zinc flower coatings with coarse size and clear morphology. The coating cooling rate is the most crucial process variable controlling the supercooling and determining the size of the zinc flowers. Simultaneously, alloying elements in the molten zinc, the surface condition of the substrate, and the temperature at which the strip enters the pot all synergistically alter the solidification kinetics, ultimately determining the uniformity and appearance of the zinc flowers. There is a rigid market demand for large zinc flowers in conventional galvanized steel sheets used in building decoration, requiring a zinc flower diameter of no less than 6mm, uniform distribution of snowflake-like dendrites on the sheet surface, and the absence of localized micro-zinc flowers, zinc scars, air knife streaks, and other appearance defects.

[0003] Currently, mature large zinc spangle production technologies fall into two categories, but neither can be adapted to the extremely thin specifications and thin zinc layer conditions of zinc-aluminum-magnesium units, exhibiting the following problems: 1. Traditional lead-containing large zinc spangle process: This relies on adding metallic lead to the zinc melt to reduce the nucleation rate and delay grain solidification and growth, thus stably producing large-sized zinc spangles. However, lead is a heavy metal pollutant, subject to strict domestic and international environmental regulations. The production process involves risks of heavy metal emissions from flue gas and zinc slag, and solid waste disposal costs are high, making it unsuitable for green mass production. 2. Lead-free antimony-based conventional large zinc spangle process: This uses a zinc-antimony binary alloy system to control the zinc spangle, but it is only suitable for thicknesses greater than 0.5mm and single-sided zinc layer weights ≥30g / m². 2 Medium-thickness steel plates. This process does not have a temperature control, slow cooling, and air knife coordination strategy for the conditions of thin strip with fast heat dissipation and thin zinc layer. If it is directly used to produce ultra-thin strip steel with a diameter of ≤0.31mm, the cooling rate after plating cannot be effectively reduced. Even if the antimony content is adjusted, it is still difficult to suppress the formation of a large number of crystal nuclei, resulting in a continuously small zinc flower size.

[0004] In summary, to solve the above problems, it is necessary to design a method for producing thin-gauge strip with thin zinc layer and large zinc flower based on a zinc-aluminum-magnesium mill. This method can address the issue that, under existing technology, when rolling thin-gauge strips with zinc-aluminum-magnesium mills, the excessively fast cooling rate and large plate temperature measurement error prevent the production of uniform large zinc flower in extremely thin-gauge strips. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing thin-gauge strip with a thin zinc layer and large zinc flowers based on a zinc-aluminum-magnesium mill, in order to solve the problem that, under the existing technology, when rolling thin-gauge strip with a zinc-aluminum-magnesium mill, the excessively fast cooling rate and large plate temperature measurement error result in the inability to produce uniform large zinc flowers in extremely thin-gauge strip.

[0006] To achieve the above objectives, the basic solution provided by this invention is: a method for producing thin-gauge, thin-zinc-layer, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit, comprising the following steps: S1: Pickling and rolling: First, the strip steel is immersed in the pickling tank, and the iron oxide scale on the surface of the strip steel is removed by the hydrochloric acid in the pickling tank. Then, the pickled strip steel is sent to the cold rolling mill for cold rolling. S2: Degreasing: First, the strip steel is immersed in the alkaline solution tank and brushed with a brush roller. Then, the strip steel is used as an electrode and energized. Subsequently, the strip steel is passed through multiple sets of anode and cathode plates in the electrolytic cell to remove the grease on the strip steel through electrolysis. Then, the strip steel is rinsed with pure water to remove the alkaline solution adhering to the surface of the strip steel. S3: Annealing: First, the cold-rolled strip is transported to the annealing furnace and passes through the PH section, NOF section, RTF&SF section, JCF section, LTH section and TDS section in sequence for preheating, heating, heat preservation and cooling, so that the transverse temperature difference of the strip is reduced to within ±3℃. Then, the strip tension is controlled by the hot tension rollers in the TDS section to prevent the strip from deviating. S4: Galvanizing and Cooling: First, the strip steel is fed into the zinc pot through the hot tension roller and immersed in the zinc liquid. Then, the strip steel passes through the submerged roller and exits the zinc pot vertically upward. Subsequently, the surface of the strip steel is purged with nitrogen air knife to remove excess plating liquid. After that, the strip steel is cooled so that the high-temperature liquid coating on the strip steel solidifies.

[0007] The beneficial effects of the present invention are as follows: (1) The present invention adopts the Zn-Al-Sb environmentally friendly alloy system, strictly limits the Pb content in the zinc liquid, and solves the problems of pollution and high waste treatment costs in lead-containing process production; at the same time, it precisely controls the Al and Sb ratio, Sb can reduce the nucleation rate of zinc liquid and promote the growth of large zinc flower dendrites, and Al can improve the fluidity of zinc liquid and accurately achieve 20g / m on one side. 2 The thin zinc layer control can also suppress the excessive thickening of the zinc-iron alloy layer, making it suitable for ultra-thin plates with a thickness of ≤0.31mm. This makes up for the shortcomings of traditional alloy formulas, which are only suitable for plates with a thickness of 0.5mm or more, and realizes low-lead clean production. (2) This invention forms a complete solution by coordinating temperature control throughout the entire process of annealing, immersion plating, and post-plating cooling; during the annealing stage, most of the JCF cooling fans are shut down, the dew point is controlled to ensure full restoration of the plate surface, and the plate temperature entering the zinc pot is increased in stages according to the unit speed to increase the superheat of the zinc liquid and prolong the solidification time of the liquid phase; by setting up a heat insulation cover above the zinc pot to reduce the initial heat dissipation, combined with segmented gradient cooling, low-speed slow cooling is used in the solidification stage to reduce the supercooling, while the cooling speed is accelerated in the solidification stage to take into account the production capacity; multiple slow cooling methods work together to reduce the supercooling of the zinc liquid, significantly reduce the nucleation rate, thereby stably producing 8-16mm uniform and clear large zinc flowers, and broadening the process window for the production of large zinc flowers of the thinnest strip steel; (3) By adjusting the existing process parameters such as acid rolling plate shape, degreasing, annealing, zinc liquid, air knife, and post-plating tension, and with minor optimization of the submerged roll shape, it can be implemented. The equipment modification cost is low, the on-site operation is simple, and it can be directly adapted to the existing continuous hot-dip galvanizing unit.

[0008] Option 2, an optimal choice from the basic option, involves a strip surface cleanliness of 65±5% after pickling, a strip thickness of 0.305-0.275mm after cold rolling, and a strip surface roughness of 0.6-1.2μm. This cleanliness balances descaling efficiency with substrate surface condition, preventing rolling pitting. Narrow-range roughness control reduces degreasing load while ensuring the mechanical bonding strength of the zinc-aluminum-magnesium coating, preventing cracking during stamping.

[0009] Option 3, an optimal choice from the basic option, involves using S2 where the temperature of the low-temperature degreasing agent is 45±7℃, the electrolytic cell current is 2300±200A, and the number of free alkali points in the alkaline solution is 26-30ml. This ensures uniform electrolytic gas generation on the board surface, effectively removing microscopic oil and iron powder; the electrolytic intensity is stable, guaranteeing no over-corrosion risk for ultra-thin strips, and resulting in high consistency in board surface cleanliness.

[0010] Option 4, an optimal choice from the basic option, involves adding 1.5 kg of low-temperature degreasing agent to the alkaline solution in the electrolytic cell for every 1 ton of strip degreasing completed in S2. This ensures long-term stability of the alkaline solution concentration in the electrolytic cell, reduces the frequency of titrations, and minimizes reagent waste.

[0011] Option 5, which is the preferred option of the basic option, in S3, the strip temperature at the exit of the PH section is 300-360℃, the strip temperature at the exit of the NOF section is 680-730℃, the strip temperature at the exit of the RTF&SF section is 750-770℃ with a holding time of 20-30s, the strip temperature at the exit of the JCF section is 450-470℃, and the strip temperature at the exit of the LTH section is 455-465℃.

[0012] Option 6, an optimal choice from the basic option, in S3, uses ZG0Cr18Ni9 cast steel as the material for the hot tension roll. The roll surface is coated with an LC1C coating with a thickness of 0.08-0.15 mm. The thickness deviation of the LC1C coating on the same roll surface is ≤ ±0.01 mm, and the roll crown is 30±5 μm. The ZG0Cr18Ni9 material provides resistance to high-temperature creep, making it suitable for the high-temperature conditions at the annealing furnace exit and ensuring long-term roll shape stability. The coating extends the wear life of the roll, reducing the frequency of roll grinding and replacement. The roll crown compensates for the tension distribution of ultra-thin strip steel, counteracting the double-sided waves caused by insufficient tension at the strip edges and preventing strip breakage.

[0013] Option 7, an optimal choice from the basic option, specifies the following zinc bath composition in S4: Al content 0.4-0.8%, Sb content 0.18-0.22%, impurity elements Pb content ≤0.004%, Fe content ≤0.003%, Cd content ≤0.002%, Sn content ≤0.001%, with the balance being Zn; the zinc bath temperature is 475±5℃. This design features extremely low impurity limits, minimal zinc pot slag, and significantly reduces surface pressure defects.

[0014] Option 8, an optimized version of the basic option, specifies the following: In S4, the distance between the nitrogen air knife and the strip is 8-15mm, the nitrogen air knife heating temperature is 100-150℃, the nitrogen air knife pressure is 100-150kPa, the angle between the front and rear nitrogen air knives is -4° to -5°, and the angle difference between the front and rear nitrogen air knives is >0.5°. This ensures that the ultra-thin strip is free of zinc fly ash and air knife streaks during high-speed operation, thereby guaranteeing a uniform zinc layer thickness.

[0015] Option 9, an optimal choice from the basic option, involves using a 1.0-2.5m long insulation cover for the post-plating cooling section of the strip steel in S4. A two-stage cooling system is employed: the first stage is the solidification stage with a cooling rate of 3-8℃ / s, and the second stage is the curing stage with a cooling rate of 8-15℃ / s. This segmented, differentiated cooling method ensures stable production of uniform and clear large zinc flowers while preventing a decrease in the corrosion resistance of the coating. Detailed Implementation

[0016] The present invention will be further described in detail below through specific embodiments: Example 1 A method for producing thin-gauge, thin-zinc-coated, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit includes the following steps: S1: Pickling and Rolling: First, the strip steel is immersed in a pickling tank, where hydrochloric acid dissolves the iron oxide scale on the surface of the strip steel plate. Then, it is rinsed with clean water and dried to prevent the strip steel from rusting during rolling. The cleanliness of the strip steel plate surface after pickling is 68%. Subsequently, the pickled strip steel is sent to the cold rolling mill for multi-pass cold rolling to produce a strip steel with a thickness of 0.305mm. During the cold rolling process, emulsion is sprayed onto the rolls of the cold rolling mill to cool the rolls and lubricate the strip steel. The surface roughness of the strip steel plate after cold rolling is 0.85μm. S2: Degreasing: First, the strip steel is immersed in an alkaline solution tank to cause the grease on the strip steel to undergo saponification and emulsification. Then, the strip steel is brushed with a brush roller to remove iron powder and grease embedded in the fine pits on the strip steel surface. Next, the strip steel is used as an electrode and immersed in the alkaline solution and energized. Then, the strip steel is passed through multiple sets of anode and cathode plates in the electrolytic cell and the electrolytic cell current is set to 2380A. The grease on the strip steel is removed by the low-temperature degreasing agent in the alkaline solution of the electrolytic cell and electrolysis. The temperature of the low-temperature degreasing agent is 45±7℃. Then, the strip steel is rinsed with pure water to remove the alkaline solution adhering to the surface of the strip steel. Then, it is dried. The number of free alkali points in the alkaline solution of the electrolytic cell is 28-29ml (e.g., take 5ml of alkaline solution sample and titrate with 0.05mol / L sulfuric acid, the number of milliliters of acid consumed = the number of free alkali points). For every 1t of strip steel degreasing completed according to the above degreasing process, the system automatically adds 1.5kg of low-temperature degreasing agent to the alkaline solution of the electrolytic cell. S3: Annealing: First, the furnace is purged with nitrogen to reduce the oxygen content to <1%. Then, the strip is conveyed to the PH section (exhaust gas preheating section) of the annealing furnace, and the high-temperature flue gas generated by combustion in the NOF section (non-oxidizing heating section) flows counter-currently through the PH section furnace to preheat the strip. The strip temperature at the PH section outlet is 300-360℃. Subsequently, the strip enters the NOF section (non-oxidizing heating section) and is heated to 680-730℃. Then, it enters the RTF&SF section (radiant tube heating homogenization section) and continues to be heated to 750-770℃, followed by holding at that temperature for 20-30 seconds. Once the overall temperature of the strip is uniform and stable, it is sent to the JCF section (gas jet cooling section). Then, all cooling fans in the JCF section are turned off, or two cooling fans are symmetrically turned on. The furnace is cooled by a blower, which allows the nitrogen-hydrogen protective gas inside the furnace to slowly convect and exchange heat, and controls the dew point inside the furnace at -30 to -50℃. When the strip cools to 450-470℃, it enters the LTH section (equilibrium section) to reduce the temperature difference between the edge and the middle of the strip, so that the transverse temperature difference of the strip converges to within ±3℃. Finally, the strip temperature is stabilized at 455-465℃ and then sent to the TDS section (exit hot tension roll section). The strip tension is controlled by the hot tension roll to prevent the strip from deviating. The hot tension roll is made of ZG0Cr18Ni9 cast steel, and the surface of the hot tension roll is coated with LC1C with a coating thickness of 0.08-0.15mm. The thickness deviation of the LC1C coating on the same hot tension roll surface is ≤±0.01mm, and the crown of the hot tension roll is 30±5μm. S4: Galvanizing and Cooling: First, the strip steel is fed into the zinc pot via hot tension rollers and immersed in the molten zinc. The molten zinc contains 0.6% Al, 0.22% Sb, and impurities of Pb ≤0.004%, Fe ≤0.003%, Cd ≤0.002%, Sn 0.001%, with the balance being Zn. The temperature of the molten zinc is 470℃. The speed of the zinc-aluminum-magnesium unit is 125 m / min. The steel strip enters the zinc pot at a temperature of 580℃. It then passes vertically upwards through the submerged rollers and exits the zinc pot. The surface of the strip is then purged with nitrogen gas to remove excess plating solution, followed by cooling to solidify the high-temperature liquid plating layer. Simultaneously, the strip tension is adjusted to 1350 DaN. The submerged roller diameter is 602.6 mm, the groove pitch is 24 mm, the groove depth is 1.5 mm, and the strip plating weight is 22-28 g / m². 2 The distance between the nitrogen air knife and the strip is 12mm, the nitrogen air knife heating temperature is 120℃, the nitrogen air knife pressure is 120kPa, the angle of the front nitrogen air knife is -4°, and the angle of the rear nitrogen air knife is -5°. The length of the insulation cover of the cooling section after strip plating is 1.5m, and a two-stage cooling method is adopted. The first stage is the solidification stage, which cools the strip temperature to 400℃ at a cooling rate of 6℃ / s. The second stage is the curing stage, which cools the strip temperature to 300℃ at a cooling rate of 12℃ / s.

[0017] The galvanized steel strip produced by the above method has a specification of 0.305mm×1250mm and a steel grade of DX51D+Z. The zinc flower size is 8-13mm, the zinc flower morphology is uniform and has a typical snowflake shape. The zinc layer has good adhesion and no zinc layer peeling off after a 180° bending test.

[0018] Example 2 A method for producing thin-gauge, thin-zinc-layer, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit, the steps of which are the same as those in Example 1, the difference being: S1: Pickling and rolling: The pickled strip is then fed into the cold rolling mill for multiple passes of cold rolling to produce a strip with a thickness of 0.285 mm. During the cold rolling process, emulsion is sprayed onto the rolls of the cold rolling mill to cool the rolls and lubricate the strip. The surface roughness of the strip after cold rolling is 0.95 μm. S2: Degreasing: Then the strip steel is passed through multiple sets of anode and cathode plates in the electrolytic cell, and the current of the electrolytic cell is set to 2390A. The grease on the strip steel is removed by electrolysis. Then the strip steel is rinsed with pure water to remove the alkaline solution attached to the surface of the strip steel. Then it is dried. The number of free alkali points in the alkaline solution of the electrolytic cell is 28ml. S4: Galvanizing and Cooling: First, the strip steel is fed into the zinc pot by hot tension rollers and immersed in the zinc liquid. The zinc liquid contains 0.65% Al, 0.18% Sb, 0.003% Pb, ≤0.003% Fe, ≤0.002% Cd, and 0.001% Sn, with the balance being Zn. The zinc liquid temperature is 475℃. The speed of the zinc-aluminum-magnesium unit is 118m / min, and the temperature of the strip steel entering the zinc pot is 590℃. The distance between the nitrogen air knife and the strip steel is 14mm, the nitrogen air knife heating temperature is 140℃, and the nitrogen air knife pressure is 135kPa. The length of the insulation cover of the strip steel cooling section after galvanizing is 2.0m, and a two-stage cooling method is used. The first stage is the solidification stage with a cooling rate of 5℃ / s, and the second stage is the curing stage with a cooling rate of 10℃ / s.

[0019] The galvanized steel strip produced by the above method has a specification of 0.285mm×1000mm and a steel grade of DX51D+Z. The zinc flower size is 9-14mm, the zinc flower morphology is uniform and has a dendritic structure; the zinc layer has good adhesion and no zinc layer peeling off after a 180° bending test.

[0020] Table 1: Summary of Optimal Ranges for Some Process Parameters

[0021] Example 3 A method for producing thin-gauge, thin-zinc-coated, large-zinc-flower strip steel based on a zinc-aluminum-magnesium mill, the steps and process parameters of which are all conventional, the difference being: S1: Pickling and rolling: The pickled strip is then fed into the cold rolling mill for multiple passes of cold rolling to produce a strip with a thickness of 0.275 mm. During the cold rolling process, emulsion is sprayed onto the rolls of the cold rolling mill to cool the rolls and lubricate the strip. The surface roughness of the strip after cold rolling is 0.75 μm. S2: Degreasing: Then the strip steel is passed through multiple sets of anode and cathode plates in the electrolytic cell, and the current of the electrolytic cell is set to 2400A. The grease on the strip steel is removed by electrolysis. Then the strip steel is rinsed with pure water to remove the alkaline solution attached to the surface of the strip steel. Then it is dried. The number of free alkali points in the alkaline solution of the electrolytic cell is 28-29ml. S3: Annealing: The strip is then cooled by nitrogen and hydrogen protective gas and enters the LTH section (equilibrium section) to reduce the temperature difference between the edge and the middle of the strip, so that the transverse temperature difference of the strip converges to within ±3℃. Finally, the strip temperature is stabilized at 585℃ and then sent to the TDS section (exit hot tension roll section). After passing through the TDS section (exit hot tension roll section), the temperature is stabilized at 577-581℃. The dew point of the reduction section of the annealing furnace is controlled at -40℃. S4: Galvanizing and Cooling: First, the strip steel is fed into the zinc pot via hot tension rollers and immersed in the molten zinc. The zinc liquid contains 0.8% Al, 0.13% Sb, and impurities of Pb ≤0.004%, Fe ≤0.003%, Cd ≤0.002%, Sn 0.001%, with the balance being Zn. The zinc liquid temperature is 473℃. The speed of the zinc-aluminum-magnesium unit is 135m / min, and the temperature of the strip steel entering the zinc pot is... 560℃; the diameter of the submerged roller is 601.5mm, the groove pitch is 24mm, the groove depth is 1.5mm, the distance between the nitrogen air knife and the strip is 7mm, the heating temperature of the nitrogen air knife is room temperature (≈30℃), and the pressure of the nitrogen air knife is 135kPa; the length of the insulation cover of the cooling section after strip plating is 0.5m, and a two-stage cooling method is adopted. The first stage is the solidification stage with a cooling rate of 10℃ / s, and the second stage is the curing stage with a cooling rate of 20℃ / s.

[0022] The galvanized steel strip with specifications of 0.275mm×1250mm and steel grade DX51D+Z produced by the above method has a zinc flower size of ≤0.5mm, and is in a state of micro zinc flower or no zinc flower, and does not have the appearance characteristics of large zinc flower.

[0023] In summary, the final single-sided coating weight produced through Examples 1 and 2 is 22-28 g / m². 2 The first example produces a thin zinc coating on the strip, while ensuring the zinc flower size is 8-14mm, with a clear morphology and a uniform dendritic or snowflake-like structure. The zinc layer adhesion is excellent, and there is no peeling after a 180° bending test, and the strip shape meets the standards. The second example uses conventional process parameters, resulting in only micro-zinc flowers ≤0.5mm or even no zinc flowers on the strip, failing to meet the requirements for large zinc flower appearance. These three examples demonstrate that the synergistic combination of process conditions such as Sb-Al alloy ratio, zinc bath temperature, pre- and post-plating slow cooling, heated nitrogen air knife, and differentiated nitrogen air knife angle is ideal for strips with a thickness ≤0.31mm and a single-sided coating weight of 22-28g / m². 2 The key to the stable production of uniform large zinc flowers in thin-layer zinc strip steel.

[0024] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for producing thin-gauge, thin-zinc-coated, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit, characterized in that, Includes the following steps: S1: Pickling and rolling: First, the strip steel is immersed in the pickling tank, and the iron oxide scale on the surface of the strip steel is removed by the hydrochloric acid in the pickling tank. Then, the pickled strip steel is sent to the cold rolling mill for cold rolling. S2: Degreasing: First, the strip steel is immersed in the alkaline solution tank and brushed with a brush roller. Then, the strip steel is used as an electrode and energized. Subsequently, the strip steel is passed through multiple sets of anode and cathode plates in the electrolytic cell. The grease on the strip steel is removed by the low-temperature degreasing agent in the alkaline solution of the electrolytic cell and electrolysis. Then, the strip steel is rinsed with pure water to remove the alkaline solution adhering to the surface of the strip steel. S3: Annealing: First, the cold-rolled strip is transported to the annealing furnace and passes through the PH section, NOF section, RTF&SF section, JCF section, LTH section and TDS section in sequence for preheating, heating, heat preservation and cooling, so that the transverse temperature difference of the strip is reduced to within ±3℃. Then, the strip tension is controlled by the hot tension rollers in the TDS section to prevent the strip from deviating. S4: Galvanizing and Cooling: First, the strip steel is fed into the zinc pot through the hot tension roller and immersed in the zinc liquid. Then, the strip steel passes through the submerged roller and exits the zinc pot vertically upward. Subsequently, the surface of the strip steel is purged with nitrogen air knife to remove excess plating liquid. After that, the strip steel is cooled so that the high-temperature liquid coating on the strip steel solidifies.

2. The method for producing thin-gauge, thin-zinc-coated, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit according to claim 1, characterized in that, In S1, the surface cleanliness of the strip after pickling is 65±5%, the thickness of the strip after cold rolling is 0.305-0.275mm, and the surface roughness of the strip is 0.6-1.2μm.

3. The method for producing thin-gauge, thin-zinc-layer, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit according to claim 1, characterized in that, In S2, the temperature of the low-temperature degreasing agent is 45±7℃, the current of the electrolytic cell is 2300±200A, and the number of free alkali points in the alkaline solution of the electrolytic cell is 26-30ml.

4. The method for producing thin-gauge, thin-zinc-coated, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit according to claim 1, characterized in that, In S2, for every 1 ton of strip steel degreasing completed, 1.5 kg of low-temperature degreasing agent is added to the alkaline solution in the electrolytic cell.

5. The method for producing thin-gauge, thin-zinc-layer, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit according to claim 1, characterized in that, In S3, the strip temperature at the exit of the PH section is 300-360℃, the strip temperature at the exit of the NOF section is 680-730℃, the strip temperature at the exit of the RTF&SF section is 750-770℃ with a holding time of 20-30s, the strip temperature at the exit of the JCF section is 450-470℃, and the strip temperature at the exit of the LTH section is 455-465℃.

6. The method for producing thin-gauge, thin-zinc-coated, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit according to claim 1, characterized in that, In S3, the material of the hot tension roll is ZG0Cr18Ni9 cast steel. The surface of the hot tension roll is coated with LC1C with a coating thickness of 0.08-0.15mm. The thickness deviation of the LC1C coating on the same hot tension roll surface is ≤±0.01mm. The crown of the hot tension roll is 30±5μm.

7. The method for producing thin-gauge, thin-zinc-coated, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit according to claim 1, characterized in that, In S4, the zinc liquid composition is as follows: Al content is 0.4-0.8%, Sb content is 0.18-0.22%, impurity element Pb content is ≤0.004%, Fe content is ≤0.003%, Cd content is ≤0.002%, Sn content is ≤0.001%, and the balance is Zn; the zinc liquid temperature is 475±5℃.

8. The method for producing thin-gauge, thin-zinc-coated, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit according to claim 1, characterized in that, In S4, the distance between the nitrogen gas knife and the strip is 8-15mm, the nitrogen gas knife heating temperature is 100-150℃, the nitrogen gas knife pressure is 100-150kPa, the angle between the front and rear nitrogen gas knives is -4° to -5°, and the angle difference between the front and rear nitrogen gas knives is >0.5°.

9. A method for producing thin-gauge, thin-zinc-layer, large-zinc-flower strip steel based on a zinc-aluminum-magnesium unit according to claim 1, characterized in that, In S4, the length of the insulation cover for the cooling section after strip galvanizing is 1.0-2.5m, and a two-stage cooling mode is adopted. The first stage is the solidification stage with a cooling rate of 3-8℃ / s, and the second stage is the curing stage with a cooling rate of 8-15℃ / s.

Images