Air knife for hot-dip production of steel strip and method for controlling the edge of a zinc-aluminum-magnesium coated steel strip

Abstract

The application belongs to the technical field of metallurgy, and particularly discloses a gas knife for hot-dip production of strip steel and a thick edge control method for a zinc-aluminum-magnesium plated strip steel. The gas knife comprises a gas knife body, an upper knife lip and a lower knife lip mounted on the gas knife body. The upper knife lip and the lower knife lip are longitudinally spaced apart at the front end to form a knife lip gap. The knife lip gap is narrow in the middle and wide at both sides. The knife lip gap comprises a constant gap section in the middle and increasing gap sections at both sides. The increasing gap sections at both sides are symmetrically arranged with the constant gap section as the center, and the gap of the increasing gap sections increases in a semi-parabolic form. The gas knife can effectively inhibit the generation of thick edge defects of the hot-dip production strip steel.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to an air knife for hot-dip galvanizing strip steel production and a method for controlling the thickness of zinc-aluminum-magnesium coated strip steel. Background Technology

[0002] With the implementation of the "dual-carbon, clean, and energy-saving" strategy, the photovoltaic power generation industry has become a major pathway for China's energy transition and has experienced rapid development. Photovoltaic arrays are the core components of photovoltaic power generation, requiring installation on photovoltaic brackets in sunny outdoor environments. Due to the harsh outdoor environment subject to intense sunlight and rain, and the design requirements for photovoltaic power stations exceeding 25 years, the corrosion resistance of photovoltaic brackets is extremely high. Prior to zinc-aluminum-magnesium plating technology, the manufacturing method for photovoltaic brackets involved first processing steel plates into parts, then hot-dip galvanizing them, requiring a plating thickness of 55μm (800g / m² for double-sided plating). 2 The above methods are not only costly and wasteful, but also environmentally unfriendly and energy-inefficient. Against this backdrop, zinc-aluminum-magnesium alloy coating technology has developed rapidly thanks to advancements in coating technology.

[0003] Hot-dip galvanized aluminum-magnesium products possess excellent corrosion resistance, 3 to 15 times that of ordinary hot-dip pure zinc coatings. They also offer advantages such as superior surface quality, good processability, and strong economic applicability, making them widely used in the automotive, home appliance, construction, highway guardrail, solar panel mounting systems, photovoltaic systems, and livestock industries. In particular, with the implementation of the national clean energy strategy, the photovoltaic power generation industry has become a major pathway for China's energy transition and has experienced rapid development. To ensure long-term use, photovoltaic mounting systems are required to withstand corrosion for more than 30 years. This necessitates an ultra-thick zinc coating for protection.

[0004] Producing ultra-thick zinc-coated products is challenging, with the key issue being the thick edges. Thick edges reduce the uniformity of the coating, affecting its corrosion resistance. In severe cases, this can lead to defects such as bulging at the coiled section, edge waviness, or even trumpet-shaped curls, rendering the product unusable for customers. Furthermore, thick edges can cause coating peeling in the ultra-thick areas, impacting the corrosion resistance of the zinc-aluminum-magnesium coating. The main causes of thick edges include: poor substrate edge quality, rapid cooling of the strip edge, high zinc liquid viscosity, low pressure at the air knife connection point, and turbulent flow, all ultimately resulting in poor zinc liquid flow and the thick edge defect. Currently, most methods control this by increasing the unit speed and air knife pressure; however, these methods are limited by unit capacity and are ineffective at low speeds for thick strip steel.

[0005] Existing technologies disclose some methods for producing zinc-aluminum-magnesium coated steel sheets or some methods for improving the quality and performance of aluminum-magnesium-zinc coatings, such as: CN115233132A discloses a method for controlling the edge thickness of hot-dip galvanized steel without spangles. The method employs an air knife gap with a baseline of 1.2–1.3 mm in the middle, increasing towards both ends in increments of 0.03–0.04 mm until reaching 1.4–1.6 mm. The air knife upper beam spray angle is -2–0°, the lower beam spray angle is -1–1°, and the distance between the air knife baffle and the strip is 2–3 mm. Furthermore, measures such as finishing and staggered coiling are used to eliminate the impact of thick edges on subsequent processing.

[0006] CN116288104A discloses a method for preparing a thick steel plate with a zinc-aluminum-magnesium coating and the coated steel. The method employs a first temperature of 439-445℃, a second temperature of 430-436℃, a speed of 30-45 m / min, an air knife pressure of 65-70 mbar, an air knife opening of 1.1-1.2 mm, an air knife height of 190-210 mm, and a distance of 35-40 mm between the air knife and the steel plate. When the strip thickness is ≥4.0 mm, a zinc-aluminum-magnesium coating with a thickness of ≥275 g / m² can be formed, and the surface quality of the zinc-aluminum-magnesium coating is high.

[0007] CN113755773B discloses a method for controlling the surface quality of thick-gauge, thick-coated zinc-aluminum-magnesium strip steel. By controlling the plating bath temperature to 470–495℃ and adjusting the strip's entry temperature into the zinc bath, air knife distance, and air knife pressure according to the strip's thickness, zinc-aluminum-magnesium strip steel with a thickness of 1.8–3.0 mm and a coating thickness ≥275 g / m² is produced. The horizontal lines of the coating and the oblique crystal lines at the edges are well controlled, ensuring excellent surface quality of the product.

[0008] CN114107866B discloses a production method for eliminating black spot defects on the surface of thick-gauge, thick-coated steel plates. The method describes a thick-gauge, thick-coated steel plate with a plating solution composition of 1-3% Al and 1-3% Mg, with the remainder being Zn and unavoidable impurities. The finished coated steel plate has a thickness ≥1.5mm, an air knife lip gap of 1.0-1.3mm, a lip-to-strip distance of 14-25mm, and an air knife height of 180-210mm. The air knife uses N2 purging at a pressure of 120-150mbar. The cooling rate of the first fixed cooling fan is controlled at 15-25℃ / s; the second cooling fan at 18-26℃ / s; and the third cooling fan at a power greater than or equal to 30℃ / s. The strip temperature is controlled to be less than 200℃ at the top roller. This method achieves the goal of eliminating black spot defects on the surface of thick-gauge, thick-coated zinc-aluminum-magnesium steel plates.

[0009] While the aforementioned patent CN115233132A discloses a method for controlling the edge thickness of hot-dip galvanized steel without spangles, it does not completely eliminate the thick edge defect, only mitigating the impact of the thick edge on subsequent processing. Furthermore, it is a galvanized product, significantly different from hot-dip galvanized aluminum-magnesium alloy coatings, and therefore cannot be used to guide or reference the treatment of thick edge defects in photovoltaic zinc-aluminum-magnesium alloys. Although the other patents mentioned above can produce thick-gauge, thick-coated hot-dip galvanized aluminum-magnesium steel sheets or eliminate black spot defects, they do not explain methods for eliminating edge thickness defects, nor do they address improvements specifically for thick edge defects. Thick edge defects are common and persistent defects with significant impact on users during the production of thick-gauge, thick-coated hot-dip galvanized aluminum-magnesium alloys. Therefore, this invention is proposed. Summary of the Invention

[0010] The purpose of this invention is to provide an air knife for hot-dip galvanized strip production that aims to solve the above-mentioned problems, and a method for controlling the thickness of zinc-aluminum-magnesium coated strip.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: According to a first aspect of the present invention, an air knife for hot-dip galvanizing strip steel is provided. The air knife includes an air knife body and an upper cutting lip and a lower cutting lip mounted on the air knife body. The front ends of the upper cutting lip and the lower cutting lip are longitudinally spaced to form a cutting lip gap. The cutting lip gap is narrow in the middle and wide at both sides, including a constant gap section in the middle and gap increasing sections on both sides. The gap of the constant gap section is constant, and the gap increasing sections on both sides are symmetrically arranged with the constant gap section as the center, and the gap of the gap increasing sections increases in a semi-parabolic form.

[0012] According to one embodiment of the present invention, the constant gap section occupies 1 / 5 to 3 / 5 of the length of the air knife.

[0013] According to one embodiment of the present invention, the gap of the constant gap section is set to 1.0 to 1.2 mm.

[0014] According to one embodiment of the present invention, the air knife is provided with a plurality of gap adjustment points evenly spaced along the length of the air knife. The gap at each gap adjustment point in the gap increasing segment is set as a function of the gap of the gap constant segment and the gap adjustment point number. The gap adjustment points are numbered sequentially from smallest to largest according to their distance from the gap constant segment.

[0015] According to one embodiment of the present invention, the gap at the gap adjustment point located in the gap increasing segment is set according to the following formula: hn=h0+0.05*n(n+1) / 2, where hn is the gap at the nth gap adjustment point, h0 is the gap of the gap constant segment, and n is the gap adjustment point number.

[0016] According to one embodiment of the present invention, the air knife is provided with 11 gap adjustment points evenly spaced along the length of the air knife, the constant gap section includes 5 gap adjustment points, and the increasing gap section (single side) includes 3 gap adjustment points.

[0017] According to a second aspect of the present invention, a method for controlling the thickness edge of zinc-aluminum-magnesium coated steel strip is provided, the method comprising: using an air knife as described in the first aspect of the present invention to purge the plating solution on the surface of the zinc-aluminum-magnesium coated steel strip.

[0018] According to one embodiment of the present invention, the strip temperature entering the zinc pot is set to 460-480°C, the plating bath temperature is set to 460-480°C, the strip tension in the zinc pot section is set to 4000 DaN-6500 DaN, the pressing amount of the correction roller is set to 25-35 mm, the strip C-curvature value at the air knife is controlled to be ≤5 mm, the strip inclination value is controlled to be ≤8 mm, the lateral distance between the edge baffle of the air knife and the edge of the strip is controlled to be 2-4 mm, and the longitudinal deviation between the edge of the edge baffle and the edge of the strip is controlled to be between 0-1 mm.

[0019] According to one embodiment of the present invention, the thick edge of the strip is eliminated by moving the air knife laterally by 0-15cm and utilizing the high-impact part with a large gap in the blade lip. The other thick edge of the strip is eliminated by moving the air knife close to the strip from the other side.

[0020] According to one embodiment of the present invention, the plating solution composition is set as follows: by weight percentage, it includes 8-15% Al, 0.2-0.5% Si, 2.0-3.0% Mg, and the remainder is zinc and unavoidable impurities.

[0021] According to one embodiment of the present invention, the thickness control method is applicable to strip thickness ≥ 2.0 mm, unit speed of 40–65 m / min, and coating thickness ≥ 275 g / m. 2 Thick-coated zinc-aluminum-magnesium coated steel strip.

[0022] By adopting the above technical solution, the present invention has at least the following beneficial effects: The air knife for hot-dip galvanizing strip steel provided by this invention adopts a blade lip gap that is narrow in the middle and wide on both sides. The gap in the middle section is constant, while the gap in the two sides increases in a semi-parabolic manner. The airflow ejected through this blade lip gap can act evenly on the surface of the strip steel. While ensuring the uniformity of the coating in the middle of the strip steel, it can also compensate for the pressure loss at the edges, increase the blowing impulse of the air knife, and improve the zinc scraping ability of the air knife at the edges, thereby effectively preventing the generation of thick edge defects.

[0023] The method for controlling the thickness of zinc-aluminum-magnesium coated steel strip provided by this invention can improve the uniformity of the coating thickness on the surface of the steel strip and effectively eliminate the thickness defect. Attached Figure Description To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 A schematic diagram of an air knife used for hot-dip galvanizing strip production provided by the present invention; Figure 2 This is a schematic diagram of the air knife blade lip gap; Figure 3 This is a schematic diagram of the C-curvature value of the strip at the air knife location; Figure 4 This is a schematic diagram showing the inclination value of the strip at the air knife location. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] Specific embodiments of the invention are disclosed herein as needed; however, it should be understood that the embodiments disclosed herein are merely examples of the invention that may be implemented in various alternative forms. In the following description, various operating parameters and components are described in several contemplated embodiments. These specific parameters and components are provided as examples only and are not intended to be limiting.

[0027] A first aspect of the present invention provides an air knife for hot-dip galvanizing strip production. For example... Figure 1 As shown, the air knife includes an air knife body 10 and an upper cutting lip 20 and a lower cutting lip 30 mounted on the air knife body 10. The front ends of the upper cutting lip 20 and the lower cutting lip 30 are longitudinally spaced to form a cutting lip gap 40. Figure 2 As shown, the blade lip gap 40 is narrow in the middle and wide at both ends, including a constant gap section in the middle and increasing gap sections on both sides. The gap in the constant gap section is constant, while the increasing gap sections on both sides are symmetrically arranged around the constant gap section, and the gap in the increasing gap sections increases in a semi-parabolic manner. The airflow ejected through the blade lip gap 40 can act evenly on the strip surface, ensuring the uniformity of the coating in the middle of the strip while compensating for pressure loss at the edges, increasing the air knife blowing impulse, and improving the air knife's ability to scrape zinc at the edges, thereby effectively preventing the generation of thick edge defects.

[0028] In some embodiments, preferably, the constant gap section occupies 1 / 5 to 3 / 5 of the air knife length. In some embodiments, preferably, the constant gap section is located at 3 / 10 to 7 / 10 of the air knife length. Air knife length refers to... Figure 2 The dimension from the left edge to the right edge. In operation, the length direction of the air knife corresponds to the width direction of the strip.

[0029] In some embodiments, preferably, the gap of the constant gap section is set to 1.0 to 1.2 mm. The fixed and narrow gap of the constant gap section has the beneficial effect of ensuring the uniformity of the coating in the middle, while increasing the pressure of the air knife cavity, improving the pressure uniformity of the air knife cross-section, and reducing the pressure loss at the edge.

[0030] In some embodiments, the air knife has multiple gap adjustment points evenly spaced along its length. The gap at each adjustment point in the gap increasing segment is set as a function of the gap in the constant gap segment and the gap adjustment point number. The gap adjustment points are numbered sequentially from smallest to largest distance from the constant gap segment. A "gap adjustment point" refers to a location where the gap size can be adjusted. For example, in... Figure 1 In the embodiment shown, the gap adjustment point is the location of the adjusting bolt 5, and the gap size can be adjusted by adjusting the adjusting bolt 5.

[0031] In some embodiments, preferably, the gap at the gap adjustment point located in the gap increasing section is set according to the following formula: hn=h0+0.05*n(n+1) / 2, where hn is the gap at the nth gap adjustment point, h0 is the gap in the gap constant section, and n is the gap adjustment point number. The beneficial effects of using this parabolic blade lip gap are that it rapidly increases the airflow rate of the blade seam, compensates for edge pressure loss, increases the air knife blowing impulse, improves the air knife's ability to scrape zinc from the edge, and prevents the formation of thick edge defects.

[0032] exist Figure 2 In the illustrated embodiment, there are a total of 11 gap adjustment points along the entire length of the air knife. The constant gap section contains 5 adjustment points, while the left and right gap increasing sections each contain 3 adjustment points.

[0033] A second aspect of the present invention provides a method for controlling the thickness of zinc-aluminum-magnesium coated steel strip, comprising: purging the plating solution on the surface of the steel strip using an air knife as described in the first aspect of the present invention. Purging the plating solution on the surface of the steel strip using the aforementioned air knife helps to improve the uniformity of the coating thickness on the steel strip surface and effectively eliminates thickness defects.

[0034] In some embodiments, the thick edge defect of zinc-aluminum-magnesium coated strip can also be eliminated by comprehensively controlling processes such as the temperature of the strip entering the zinc pot, the temperature of the plating solution, the state of the strip in the zinc pot section, and the air knife control.

[0035] In some embodiments, the temperature of the strip entering the zinc bath is set to 460–480°C. Preferably, the temperature of the strip entering the zinc bath is slightly higher than the temperature of the plating solution, which improves the fluidity of the plating solution and prevents thick edge defects caused by poor fluidity of the plating solution.

[0036] In some embodiments, the plating bath temperature is set to 460–480°C, which is 40–50°C higher than the alloy's complete melting temperature. This helps improve the plating bath's fluidity and prevent thick-edge defects. Depending on the composition, the alloy's complete melting temperature is 420–430°C.

[0037] In some embodiments, the plating solution composition is: by weight percentage, comprising 8-15% Al, 0.2-0.5% Si, 2.0-3.0% Mg, with the remainder being zinc and unavoidable impurities.

[0038] In some embodiments, the strip tension in the zinc pot section is set to 4000 DaN to 6500 DaN, and the pressing amount of the straightening roll is set to 25 to 35 mm. The purpose of setting these strip tension and straightening roll pressing amounts is to control the strip C-curvature value at the air knife to be ≤5 mm and the strip inclination value at the air knife to be ≤8 mm. Controlling the strip C-curvature and inclination values ​​aims to prevent the strip edge from being too far from the air knife and to prevent insufficient gas purging force leading to thick edge defects due to the airflow not being perpendicular to the strip edge.

[0039] Figure 3 The figure shows a schematic diagram of the C-curve value of the strip at the air knife location. 1 represents the strip, 2 represents the line connecting the edges of the strip, and the height ΔC in the figure is the C-curve value, which is the distance from the middle of the strip to the line connecting the edges of the strip.

[0040] Figure 4 The figure shows a schematic diagram of the strip inclination value at the air knife. 1 represents the strip, 2 represents the unit centerline, and the height Δh in the figure is the inclination value, that is, the distance between the edge of the strip and the unit centerline.

[0041] In some embodiments, the lateral distance between the edge baffle of the control air knife and the edge of the strip is 2-4 mm, and the longitudinal deviation between the edge of the control edge baffle and the edge of the strip is 0-1 mm. This effectively isolates the strip from airflow disturbances on both sides, preventing thick-edge defects. It should be noted that the longitudinal deviation between the edge of the control edge baffle and the edge of the strip is easily overlooked.

[0042] In some embodiments, the air knife used is an air knife with a lateral movement function. During production, the air knife can be lateralized by 0-15cm, utilizing the high-impact portion of the large gap in the blade lip to remove the thick edge on one side of the strip, and the other side of the strip can be removed by moving the other side of the air knife closer to the strip. Here, "the other side of the air knife is close to the strip" means tilting the air knife at a certain angle so that the other side of the air knife is closer to the strip.

[0043] In some embodiments, a nitrogen gas knife is used.

[0044] In some embodiments, preferably, the above-described method for controlling the thickness of zinc-aluminum-magnesium coated steel strip is applicable to strip thickness ≥ 2.0 mm, unit speed of 40–65 m / min, and coating thickness ≥ 275 g / m. 2 Thick-coated zinc-aluminum-magnesium coated steel strip.

[0045] The method for controlling the thick edge of zinc-aluminum-magnesium coated steel strip described in this invention has good reproducibility and repeatability, enabling stable and continuous production of high-quality zinc-aluminum-magnesium coated steel strip, such as zinc-aluminum-magnesium alloy coated steel sheets / strips for photovoltaic brackets. The zinc-aluminum-magnesium coated steel strip produced using this method not only possesses excellent corrosion resistance and coating processability, but also exhibits superior surface quality, free from thick edge defects. This avoids defects such as edge waviness, bulging at the coiled portion, coating peeling, and flared curling caused by thick edge defects, as well as the resulting reduction in coating uniformity and corrosion resistance. This meets the surface quality, corrosion resistance, and processing requirements of photovoltaic power plants for high-quality brackets. The method described in this invention addresses the thick edge defect in thick-gauge, thick-coated zinc-aluminum-magnesium products by eliminating it through technological innovation and reasonable matching of process parameters without modifying existing equipment, thereby meeting the usage requirements of photovoltaic brackets in photovoltaic power plants.

[0046] The zinc-aluminum-magnesium coated steel strip described in this invention takes the photovoltaic bracket manufacturing industry as an example. Its application includes, but is not limited to, the photovoltaic bracket manufacturing field, and also includes various production and manufacturing fields with high requirements for product surface quality, corrosion resistance and processability.

[0047] The present invention will be further described below with reference to specific embodiments.

[0048] Example 1 The present invention relates to a method for controlling the thickness of thick-coated zinc-aluminum-magnesium alloy strips and for producing steel strips with the following characteristics: strip thickness 2.0 mm, coating thickness 275 g / m. 2 The strip temperature in the zinc bath is 470℃, the plating solution composition is 8.5% Al, 0.25% Si, 2.55% Mg, and the remainder is zinc and unavoidable impurities. The plating solution temperature is 475℃, the strip tension in the zinc bath section is 4200 DaN, the correction roll infeed is 25mm, the strip C-curvature value is 2mm, the strip inclination value is 5mm, the air knife h0=1.1mm, h1~h3 are 1.15mm, 1.25mm, and 1.40mm respectively, the air knife lateral movement is 0cm, the lateral distance between the edge baffle and the strip edge is 2mm, and the longitudinal deviation of the alignment with the strip edge is 0mm.

[0049] In this embodiment, the continuously hot-dip galvanized aluminum-magnesium alloy coated steel sheet / strip coated steel sheet is free from thick edge defects and the resulting edge waviness, coiling bulge, coating peeling, and horn-shaped curling problems. The coating is uniform and of good quality, meeting the requirements for high-quality photovoltaic brackets.

[0050] Example 2 The present invention relates to a method for controlling the thickness edge of a thick-coated zinc-aluminum-magnesium alloy and for producing steel strips with the following characteristics: steel strip thickness 2.3 mm, coating thickness 320 g / m. 2 The strip temperature in the zinc bath is 468℃, the composition of the plating solution is 9.53% Al, 0.28% Si, 2.75% Mg, and the remainder is zinc and unavoidable impurities. The plating solution temperature is 465℃. The strip tension in the zinc bath section is 5100 DaN. The correction roll infeed is 35mm. The strip C-curvature value is 3mm. The strip inclination value is 6mm. The air knife h0=1.0mm, h1~h3 are 1.05mm, 1.15mm and 1.30mm respectively. The air knife lateral movement is 0cm. The lateral distance between the edge baffle and the strip edge is 2mm. The longitudinal deviation of the edge baffle from the strip edge is 0mm.

[0051] In this embodiment, the continuously hot-dip galvanized aluminum-magnesium alloy coated steel sheet / strip coated steel sheet is free from thick edge defects and the resulting edge waviness, coiling bulge, coating peeling, and horn-shaped curling problems. The coating is uniform and of good quality, meeting the requirements for high-quality photovoltaic brackets.

[0052] Example 3 The present invention relates to a method for controlling the thickness of thick-coated zinc-aluminum-magnesium alloy and producing steel strips with the following characteristics: steel strip thickness 2.5 mm, coating thickness 350 g / m. 2 The strip temperature in the zinc bath is 475℃, the composition of the plating solution is 11.35% Al, 0.32% Si, 2.83% Mg, and the remainder is zinc and unavoidable impurities. The plating solution temperature is 478℃. The strip tension in the zinc bath section is 5900 DaN. The correction roll infeed is 33mm. The strip C-curvature value is 1mm. The strip inclination value is 4mm. The air knife h0=1.2mm, h1~h3 are 1.25mm, 1.35mm and 1.50mm respectively. The air knife lateral movement is 0cm. The lateral distance between the edge baffle and the strip edge is 3mm. The longitudinal deviation of the edge baffle from the strip edge is 1mm.

[0053] In this embodiment, the continuously hot-dip galvanized aluminum-magnesium alloy coated steel sheet / strip coated steel sheet is free from thick edge defects and the resulting edge waviness, coiling bulge, coating peeling, and horn-shaped curling problems. The coating is uniform and of good quality, meeting the requirements for high-quality photovoltaic brackets.

[0054] Example 4 The present invention relates to a method for controlling the thickness edge of a thick-coated zinc-aluminum-magnesium alloy and for producing steel strips with the following characteristics: steel strip thickness 3.0 mm, coating thickness 350 g / m. 2The strip steel enters the zinc pot at a temperature of 470℃. The plating solution composition is 14.65% Al, 0.45% Si, and 2.92% Mg, with the remainder being zinc and unavoidable impurities. The plating solution temperature is 468℃. The strip steel tension in the zinc pot section is 6300 DaN. The correction roller infeed is 30 mm. The strip steel C-curve value is 2 mm. The strip steel tilt value is 6 mm. The air knife h0=1.0 mm, h1~h3 are 1.05 mm, 1.15 mm, and 1.30 mm respectively. The air knife lateral movement is 13 cm. The lateral distance between the edge baffle and the strip steel edge is 2 mm. The longitudinal deviation between the edge baffle and the strip steel edge is 1 mm.

[0055] In this embodiment, the continuously hot-dip galvanized aluminum-magnesium alloy coated steel sheet / strip had a slight thick edge due to both the steel strip and the coating exceeding the unit's limits. By moving the air knife 13cm laterally towards the operating side and using the high-impulse airflow with a large lip gap on the air knife drive side to eliminate the thick edge on the drive side, while simultaneously moving the air knife closer to the operating side to eliminate the thick edge on the operating side, the steel strip was ultimately free of thick edge defects on both sides, as well as the resulting edge waviness, coiling bulges, coating peeling, and horn curling problems. The coating was uniform and of good quality, meeting the requirements for high-quality photovoltaic brackets.

[0056] Example 5 The present invention relates to a method for controlling the thickness of thick-coated zinc-aluminum-magnesium alloy strips and for producing steel strips with the following characteristics: strip thickness 2.0 mm, coating thickness 275 g / m. 2 The strip temperature in the zinc bath is 480℃, the plating solution composition is 8.5% Al, 0.25% Si, 2.55% Mg, and the remainder is zinc and unavoidable impurities. The plating solution temperature is 460℃, the strip tension in the zinc bath section is 6500 DaN, the correction roll infeed is 25mm, the strip C-curvature value is 5mm, the strip inclination value is 5mm, the air knife h0=1.1mm, h1~h3 are 1.15mm, 1.25mm, and 1.40mm respectively, the air knife lateral movement is 0cm, the lateral distance between the edge baffle and the strip edge is 4mm, and the longitudinal deviation of the alignment with the strip edge is 0mm.

[0057] In this embodiment, the continuously hot-dip galvanized aluminum-magnesium alloy coated steel sheet / strip coated steel sheet is free from thick edge defects and the resulting edge waviness, coiling bulge, coating peeling, and horn-shaped curling problems. The coating is uniform and of good quality, meeting the requirements for high-quality photovoltaic brackets.

[0058] Example 6 The present invention relates to a method for controlling the thickness of thick-coated zinc-aluminum-magnesium alloy strips and for producing steel strips with the following characteristics: strip thickness 2.0 mm, coating thickness 275 g / m. 2The strip temperature in the zinc bath is 460℃, the plating solution composition is 8.5% Al, 0.25% Si, 2.55% Mg, and the remainder is zinc and unavoidable impurities. The plating solution temperature is 480℃, the strip tension in the zinc bath section is 4000 DaN, the correction roller infeed is 25mm, the strip C-curvature value is 2mm, the strip inclination value is 8mm, the air knife h0=1.1mm, h1~h3 are 1.15mm, 1.25mm, and 1.40mm respectively, the air knife lateral movement is 0cm, the lateral distance between the edge baffle and the strip edge is 2mm, and the longitudinal deviation of the alignment with the strip edge is 0mm.

[0059] In this embodiment, the continuously hot-dip galvanized aluminum-magnesium alloy coated steel sheet / strip coated steel sheet is free from thick edge defects and the resulting edge waviness, coiling bulge, coating peeling, and horn-shaped curling problems. The coating is uniform and of good quality, meeting the requirements for high-quality photovoltaic brackets.

[0060] Comparative Example 1 A method for controlling the thickness edge of a thick-coated zinc-aluminum-magnesium alloy strip and for producing steel strips of the following specifications: strip thickness 2.0 mm, coating thickness 275 g / m. 2 Using the process of Example 1, in order to verify the influence of the pressing amount of the correction roll and the C-curvature value of the strip on the thick edge defect, the pressing amount of the correction roll was adjusted to 18mm, the C-curvature value of the strip was 8mm, and other processes remained unchanged.

[0061] In this comparative production, the strip steel at the zinc pot exhibited severe C-curving, and the produced continuous hot-dip galvanized aluminum-magnesium alloy coated steel sheet had obvious thick edge defects, no trumpet coils, and wavy shape when uncoiling. Zinc shavings fell off during user processing, which could not meet the requirements for photovoltaic bracket use.

[0062] Comparative Example 2 A method for controlling the thickness edge of a thick-coated zinc-aluminum-magnesium alloy strip and for producing steel strips of the following specifications: strip thickness 2.0 mm, coating thickness 275 g / m. 2 Using the process of Example 1, in order to verify the influence of strip tension and strip inclination on thick edge defects in the zinc pot section, the strip tension in the zinc pot section was adjusted to 3000 DaN and the strip inclination was 11 mm, while other processes remained unchanged.

[0063] In this comparative production, the strip steel at the zinc pot was severely tilted, and the produced continuous hot-dip galvanized aluminum-magnesium alloy coated steel sheet had obvious thick edge defects, no trumpet coil, no wavy shape when uncoiling, and zinc shavings fell off during user processing, which could not meet the requirements of photovoltaic brackets.

[0064] Comparative Example 3 A method for controlling the thickness edge of a thick-coated zinc-aluminum-magnesium alloy strip and for producing steel strips of the following specifications: strip thickness 2.0 mm, coating thickness 275 g / m. 2Using the process of Example 1, in order to verify the influence of the longitudinal deviation of the alignment between the edge baffle and the strip edge on the thick edge defect, the longitudinal deviation of the alignment between the edge baffle and the strip edge was adjusted to 3mm, while other processes remained unchanged.

[0065] In this comparative production, the edge baffles and strip steel have large longitudinal deviations. The produced continuous hot-dip galvanized aluminum-magnesium alloy coated steel sheets have obvious thick edge defects, flared coils during winding, and wavy shapes during unwinding. They are rejected by the factory and cannot meet the requirements for photovoltaic brackets.

[0066] Comparative Example 4 A method for controlling the thickness edge of a thick-coated zinc-aluminum-magnesium alloy strip and for producing steel strips of the following specifications: steel strip thickness 2.5mm, coating thickness 350g / m. 2 Using the process of Example 3, in order to verify the influence of the air knife lip gap curve on the thick edge defect, the air knife lip gap was adjusted from h0=1.2mm, h1~h3 were 1.25mm, 1.35mm, and 1.50mm respectively, to h0=1.2mm, h1~h3 were 1.25mm, 1.30mm, and 1.35mm respectively, while other processes remained unchanged.

[0067] In this comparative production, the air knife lip gap was not parabolic but linear. The airflow impulse at the edge of the strip was small, resulting in a decrease in zinc scraping ability. The produced continuous hot-dip galvanized aluminum-magnesium alloy coated steel sheet had obvious thick edge defects on both sides, no trumpet coil, and wavy shape when uncoiling. Users reported that zinc shavings fell off, which could not meet the requirements of photovoltaic brackets.

[0068] Tables 1-4 below show the process parameters and quality characterization of Examples 1-4 and Comparative Examples 1-4.

[0069] Table 1 Hot-dip galvanizing process for strip steel

[0070] Table 2 Zinc Pot Section Process

[0071] Table 3 Air Knife Process

[0072] Table 4 Comparison of Quality Status

[0073] As shown in Table 4, Examples 1-6, using the method of the present invention, produced products without thick edge defects, exhibiting good quality and meeting the requirements for high-quality photovoltaic brackets. Comparative Examples 1-4 show differences in the strip C-curvature value at the air knife, strip inclination value at the air knife, air knife lip gap curve, air knife lateral movement, and edge baffle process compared to the method of the present invention. Compared to the zinc-aluminum-magnesium steel sheet produced by the present invention, these exhibit problems such as thick edges, flared coils, uncoiling waviness, and zinc shavings during processing, indicating a certain gap in quality compared to the technology of the present invention.

[0074] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0075] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0076] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. An air knife for hot-dip galvanizing strip steel production, comprising an air knife body and an upper cutting lip and a lower cutting lip mounted on the air knife body, wherein the front ends of the upper and lower cutting lips are longitudinally spaced to form a cutting lip gap, characterized in that, The blade lip gap is narrow in the middle and wide at both sides, including a constant gap section in the middle and gap increasing sections on both sides. The gap of the constant gap section is constant, and the gap increasing sections on both sides are symmetrically arranged with the constant gap section as the center. The gap of the gap increasing sections increases in a semi-parabolic form. The air knife has multiple gap adjustment points evenly spaced along its length. The gap at each gap adjustment point in the gap increasing section is set as a function of the gap of the constant gap section and the gap adjustment point number. The gap adjustment points are numbered sequentially from smallest to largest distance from the constant gap section. The gap at the gap adjustment point in the gap increasing section is set according to the following formula: hn=h0+0.05*n(n+1) / 2, where hn is the gap at the nth gap adjustment point, h0 is the gap of the constant gap section, and n is the gap adjustment point number.

2. The air knife for hot-dip galvanizing strip steel production according to claim 1, characterized in that, The constant gap section occupies 1 / 5 to 3 / 5 of the air knife length.

3. The air knife for hot-dip galvanizing strip steel production according to claim 1, characterized in that, The gap of the constant gap section is set to 1.0 to 1.2 mm.

4. The air knife for hot-dip galvanizing strip steel production according to claim 1, characterized in that, The air knife has 11 gap adjustment points evenly spaced along its length. The constant gap section contains 5 gap adjustment points, and each increasing gap section contains 3 gap adjustment points.

5. A method for controlling the thickness of zinc-aluminum-magnesium coated steel strip, characterized in that, include: The plating solution on the surface of the zinc-aluminum-magnesium coated steel strip is purged using an air knife according to any one of claims 1-4.

6. The method for controlling the thickness of zinc-aluminum-magnesium coated strip steel according to claim 5, characterized in that, The strip temperature entering the zinc pot is set to 460-480℃, the plating bath temperature is set to 460-480℃, the strip tension in the zinc pot section is set to 4000DaN-6500DaN, the pressing amount of the correction roller is set to 25-35mm, the strip C-curvature value at the air knife is controlled to be ≤5mm, the strip inclination value is controlled to be ≤8mm, the lateral distance between the edge baffle of the air knife and the edge of the strip is controlled to be 2-4mm, and the longitudinal deviation between the edge of the edge baffle and the edge of the strip is controlled to be between 0-1mm.

7. The method for controlling the thickness of zinc-aluminum-magnesium coated strip steel according to claim 5, characterized in that, By moving the air knife laterally by 0-15cm, the thick edge on one side of the strip is eliminated by utilizing the high-impact section with a large gap in the blade lip, and the other thick edge on the strip is eliminated by moving the air knife close to the strip from the other side.

8. The method for controlling the thickness of zinc-aluminum-magnesium coated strip steel according to claim 5, characterized in that, The plating solution composition is set as follows: by weight percentage, it includes 8-15% Al, 0.2-0.5% Si, 2.0-3.0% Mg, and the remainder is zinc and unavoidable impurities.

9. The method for controlling the thickness of zinc-aluminum-magnesium coated strip steel according to claim 5, characterized in that, The aforementioned thickness control method is applicable to strip thickness ≥ 2.0 mm, unit speed of 40–65 m / min, and coating thickness ≥ 275 g / m. 2 Thick-coated zinc-aluminum-magnesium coated steel strip.

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