A method for producing hot-dip galvanized automotive exterior panels

Abstract

This invention relates to the field of hot-dip galvanized automotive steel technology, specifically disclosing a production method for hot-dip galvanized automotive outer panels, comprising the following steps: 1) setting the operating status requirements of the galvanizing unit; 2) setting the production organization and scheduling sequence of the galvanizing unit: including unit stabilizing material, pre-feeding material, grinding and slag removal material, transition material, and target outer panel material; 3) full-process control of the galvanizing process: including galvanizing cleaning process, continuous annealing furnace and furnace nose gas control, zinc pot process, and finishing machine control; 4) establishing a surface quality inspection and evaluation mechanism for finished steel strips; The production method for hot-dip galvanized automotive outer panels designed in this invention effectively improves the guarantee capability and production efficiency of product surface quality, reduces surface defects such as zinc slag and pitting, and improves the yield index of hot-dip galvanized automotive outer panels. This technology has been industrialized and mass-produced stably in a US Steel continuous hot-dip galvanizing unit, and has good promotion and application value.

Description

Technical Field

[0001] This invention relates to the field of metallurgical hot-dip galvanized automotive steel technology, specifically to a method for producing hot-dip galvanized automotive outer panels. Background Technology

[0002] As people's standards for automobile quality and aesthetics gradually improve, hot-dip galvanized steel for automotive exterior panels is increasingly widely used in domestic and joint-venture automobiles due to its excellent surface quality, mechanical properties, and corrosion resistance.

[0003] Hot-dip galvanizing boasts advantages such as low production cost, ease of implementation, cathodic protection, strong coating, and attractive appearance, making it widely used in high-tech fields and industries like automobiles and home appliances. It has experienced rapid development over the past 20 years; according to incomplete statistics, the total number of wide strip steel hot-dip galvanizing units in my country reached over 730 in 2022. However, the production process for hot-dip galvanized automotive outer panels is complex and technically challenging. Currently, few units possess the capacity for continuous and stable production of automotive outer panels. The requirements for unit operation, production organization and scheduling, selection of transition materials, control of key galvanizing processes, and surface quality inspection of steel strips are extremely high. Improper control in any of these areas can result in a large number of defective products, severely impacting the production efficiency and cost of the galvanizing unit.

[0004] CN 114875224 A discloses a method for manufacturing automotive outer panels with high surface quality and high formability. This method primarily achieves excellent adhesion and surface quality through control of raw material surface morphology and appropriate coating processes, including setting the zinc pot composition and temperature, and controlling post-plating cooling. However, this invention only controls a few key parameters such as roughness and does not manage the galvanizing unit status, upstream material requirements, or the entire process flow.

[0005] CN 112159926 A discloses an economical hot-dip galvanized steel for automotive outer panels with excellent comprehensive mechanical properties and its production method. The main chemical element composition and mass percentage content are: C: 0.001~0.005%, Si: 0.09~0.15%, Mn: 0.40~0.55%, Ti: 0.05~0.07%, Als: 0.02~0.06%, P: 0.035~0.055%, S≤0.015%, N≤0.005%, Nb: 0.001~0.006%, B≤0.0015%, with the balance being Fe and unavoidable impurities. This invention mainly focuses on the production control of a specific steel grade throughout the entire process of steelmaking, hot rolling, and cold rolling, ultimately achieving the development of outer panel products. In contrast, this patent focuses on the unit status control, pre-feed preparation, and key process control of galvanizing the target material for galvanized outer panels, highlighting a significant difference between the two.

[0006] CN 108531819 A discloses a hot-dip galvanized steel sheet that meets the requirements for paint-free automotive outer panels. Its chemical composition (wt%) is: C 0.0015%–0.0040%, 0 < Si ≤ 0.02%, Mn 0.15%–0.25%, P 0.005%–0.015%, 0 < S ≤ 0.01%, Al 0.03%–0.06%, 0 < Cr ≤ 0.03%, Nb 0.002%–0.008%, Ti 0.002%–0.008%, 0 < N ≤ 0.003%, with the balance being Fe and unavoidable impurities. This invention mainly focuses on the key process control of hot rolling and cold rolling of 180MPa grade bake-hardening outer panel steel, which is significantly different from the control focus of this patent.

[0007] CN 103769431 A discloses a method for producing automotive outer panels. By controlling the surface roughness of chilled steel sheets before annealing and performing two-pass leveling treatments after annealing, a very low surface waviness W-(CA) can be obtained while ensuring that the average surface roughness Ra value of the steel sheet meets the stamping requirements. This is beneficial for improving the coating quality of automotive outer panels, enhancing stamping performance, reducing product defect rates, and meeting the usage requirements of automotive manufacturers. This invention mainly controls roughness and waviness parameters to ultimately achieve the surface quality of the outer panel, but does not describe the galvanizing unit status, pre-feed requirements, or the entire process.

[0008] CN 115354107 A discloses a method for preparing IF steel for galvanized automotive outer panels, including converter smelting, tapping, RH refining, and casting. This method effectively solves the technical problem that existing preparation methods cannot effectively control oxide inclusions in IF steel products. This invention mainly optimizes and controls the steelmaking process to improve the cleanliness of molten steel and reduce oxide inclusions, which is significantly different from the control focus of this patent.

[0009] CN 109097714 A discloses a hot-dip galvanized steel sheet for automotive panels and its production method. The hot-dip galvanized steel sheet contains an alloy layer between the hot-dip galvanized coating and the substrate. The high-hardness alloy layer solves the technical problem of increased microscopic unevenness after stamping deformation of the galvanized steel sheet, which is significantly different from the control focus of this patent.

[0010] This invention improves the surface quality of hot-dip galvanized automotive outer panels and reduces quality re-judgment and cutting losses by implementing production scheduling for galvanizing units, controlling key processes throughout the galvanizing process, and establishing a surface quality inspection and evaluation mechanism for finished steel strips. It is suitable for stable production in large-scale industries. Summary of the Invention

[0011] In view of the problems existing in the prior art, the purpose of this invention is to provide a method for producing hot-dip galvanized automotive outer panels.

[0012] The technical solution adopted by this invention to solve its technical problem is: a method for producing hot-dip galvanized automotive outer panels, comprising the following steps:

[0013] 1) Set the operating status requirements for the galvanizing unit;

[0014] 2) Set the production organization and scheduling sequence for the galvanizing unit: including the unit stabilizing material, the pre-feeding material, the grinding and slag removal material, the transition material, and the target outer plate material;

[0015] 3) Full-process control of galvanizing: including galvanizing cleaning process, continuous annealing furnace and furnace nose gas control, zinc pot process, and bright finishing machine control;

[0016] 4) Establish a surface quality inspection and evaluation mechanism for finished steel strips.

[0017] Specifically, the operating status requirements for the galvanizing unit in step 1) are as follows: automobile outer panel production is organized within 3 to 10 days after the submerged roller in the zinc pot is replaced; there is no downtime of more than 4 hours within 24 hours before feeding; no downtime of more than 2 hours within 16 hours before feeding; and no downtime of more than 0.5 hours within 8 hours before feeding.

[0018] Specifically, the production organization and scheduling sequence of the galvanizing unit in step 2) is as follows:

[0019] S1. Stabilizing feed for the unit: 1185-1220 tons of DX51 or IF steel, of which IF steel accounts for no less than 20%, with a thickness of 0.7-1.2mm;

[0020] S2, Lead material: 980-1030 tons of IF steel, thickness 0.65mm~1.2mm, width greater than the target outer sheet material;

[0021] S3, Grinding and Slag Removal Material: 190-205 tons of IF steel, non-passivated, with a thickness similar to the target outer plate and a width greater than the target outer plate material;

[0022] S4, Transitional material: 22-26 tons, same grade and specification as the target outer sheet material;

[0023] S5, target outer panel material: the single production volume is controlled within 3,000 tons, and the material is switched to transition material when removing slag during the process.

[0024] Specifically, the galvanizing cleaning process in step 3) is as follows: alkaline immersion washing, alkaline brush washing, electrolytic circulation tank temperature 80±5℃, rinsing section temperature 65±5℃; alkaline immersion washing and alkaline brush washing conductivity 30~50μs / cm, electrolytic section conductivity 40~60μs / cm, rinsing conductivity ≤30μs / cm; the surface reflectivity of the steel strip after cleaning is ≥90%.

[0025] Specifically, in step 3), the dew point of the preheating, heating, homogenizing, slow cooling, and rapid cooling sections of the continuous annealing furnace is ≤-35℃, and the dew point of the equalization section is ≤-25℃; the oxygen content inside the furnace is ≤10ppm; and the furnace nose humidification system uses 10~20Nm 3 The wet nitrogen flow rate is / Hr, and the nose dew point is -10 to 0℃.

[0026] Specifically, in step 3), the temperature of the zinc liquid in the zinc pot is controlled at 455±2℃; the effective aluminum content in the zinc pot is 0.225-0.235%, and the iron content is <0.008%; the zinc pot liquid level is controlled at -80±2mm; the purging air knife angle is -1.0 degree, the air knife height is 200-260mm, and the distance between the air knife and the steel strip is 6-10mm.

[0027] Specifically, in step 3), the finishing mill work rolls are chrome-plated rolls with a diameter of Φ600mm~650mm, a surface roughness (Ra) of 2.0~2.2μm, and a peak value (Rpc) of 100~120 pieces / cm; the finishing solution concentration is 2.3~2.7%; the finishing rolling force is controlled at 2000-4000KN; the surface requirements of the finished steel strip are: Ra=0.8-1.2μm, Rpc≥80 pieces / cm, and waviness Wsa1-5≤0.35μm.

[0028] Specifically, the surface quality of the finished steel strip in step 4) is checked using the following three methods:

[0029] (1) When the steel strip is stationary, visual inspection is required. The better side should be free of zinc dross or other defects that affect the surface quality. The other side should not have zinc dross with a diameter greater than 0.5 mm, and the number of zinc dross particles with a diameter not greater than 0.5 mm should not exceed 5 per m. 2 ;

[0030] (2) After polishing with a sandpaper or oilstone, visual inspection is required. Ideally, one side should be free of visible zinc dross or other defects that affect surface quality. The other side should not have zinc dross with a diameter greater than 0.8 mm, and the number of zinc dross particles with a diameter not greater than 0.8 mm should not exceed 5 per m. 2 ;

[0031] (3) After micro-stamping, visual inspection of grinding is performed. After stamping a 700*700mm sample to a depth of 10-15cm, the upper 1 / 3 of the sample is ground with a sanding mesh and the lower 2 / 3 is ground with an oilstone. After grinding, the surface of the steel strip is not allowed to have bright spots or pits with a diameter greater than 1.0mm.

[0032] The present invention has the following beneficial effects:

[0033] The hot-dip galvanized automotive exterior panel production method designed in this invention effectively improves the product surface quality assurance capability and production efficiency, reduces surface defects such as zinc dross and pitting, and improves the yield index of hot-dip galvanized automotive exterior panels. This technology has been industrialized and produced in large quantities stably in a continuous hot-dip galvanizing unit of US Steel, and has good promotion and application value. Attached Figure Description

[0034] Figure 1 This is a production organization and scheduling flowchart for the galvanizing unit of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0036] A method for producing hot-dip galvanized automotive outer panels improves the surface quality of hot-dip galvanized automotive outer panels and reduces quality re-judgment and cutting losses by implementing production scheduling of galvanizing units, key process control throughout the galvanizing process, and a surface quality inspection and evaluation mechanism for finished steel strips.

[0037] The production method for hot-dip galvanized automotive outer panels requires that outer panel production be organized within 3 to 10 days after the submerged rollers in the zinc pot of the galvanizing unit are changed. There should be no downtime of more than 4 hours within 24 hours before feeding; no downtime of more than 2 hours within 16 hours before feeding; and no downtime of more than 0.5 hours within 8 hours before feeding, to ensure stable operation of the unit and good circulation in the zinc pot.

[0038] like Figure 1 As shown, the production method of hot-dip galvanized automotive outer panels involves the following steps: First, 1200 tons of stabilizing material (DX51 or IF steel, with IF steel accounting for no less than 20%, and a thickness of 0.7–1.2 mm) are produced. Then, 1000 tons of pre-leading material (IF steel, with a thickness of 0.65 mm–1.2 mm and a width greater than the target outer panel material) are produced. Next, 200 tons of polishing and slag-removing material (IF steel, without passivation, with a thickness similar to the target outer panel material and a width greater than the target outer panel material) are produced. Then, 25 tons of transition material (of the same grade and specification as the target outer panel material) are produced. Finally, the target outer panel material is produced, and the production volume per batch is controlled within 3000 tons (the transition material is switched during slag removal).

[0039] The production method for hot-dip galvanized automotive exterior panels involves a continuous annealing furnace with a dew point ≤ -35℃ in the preheating, heating, homogenizing, slow cooling, and rapid cooling sections, and a dew point ≤ -25℃ in the equalization section; the oxygen content inside the furnace is ≤ 10ppm. The furnace nose humidification system uses a 10-20Nm... 3 The wet nitrogen flow rate is / Hr, and the nose dew point is -10 to 0℃.

[0040] The production method of hot-dip galvanized automotive exterior panels involves controlling the temperature of the zinc bath at 455±2℃; the effective aluminum content in the zinc bath is 0.225-0.235%, and the iron content is <0.008%; the zinc bath level is controlled at -80±2mm; the air knife angle is -1.0 degree, the air knife height is 200~260mm, and the distance between the air knife and the steel strip is 6~10mm.

[0041] The production method of hot-dip galvanized automotive outer panels uses chrome-plated rolls with a diameter of Φ600mm~650mm on the finishing machine, with a surface roughness (Ra) of 2.0~2.2μm and a peak value (Rpc) of 100~120 per cm. The finishing solution concentration is 2.3~2.7%. The finishing rolling force is controlled at 2000-4000KN. The surface requirements of the finished steel strip are: Ra = 0.8-1.2μm, Rpc ≥ 80 per cm, and waviness Wsa1-5 ≤ 0.35μm.

[0042] The production method of hot-dip galvanized automotive outer panels, the surface quality of finished steel strips is inspected in the following three ways: (1) Visual inspection when the steel strip is stationary, it is required that there are no visible zinc dross or other defects affecting the surface quality on one side, and no zinc dross with a diameter greater than 0.5 mm on the other side, and no more than 5 zinc dross with a diameter not greater than 0.5 mm per m2; (2) Visual inspection after grinding with sandpaper or oilstone, it is required that there are no visible zinc dross or other defects affecting the surface quality on one side, and no zinc dross with a diameter greater than 0.8 mm on the other side, and no more than 5 zinc dross with a diameter not greater than 0.8 mm per m2; (3) Visual inspection after micro-stamping and grinding, take a 700*700mm sample, stamp it to a depth of 10-15cm, grind the upper 1 / 3 of the sample with sandpaper, and grind the lower 2 / 3 with oilstone. After grinding, no bright spots or pits with a diameter greater than 1.0 mm are allowed on the surface of the steel strip.

[0043] Example 1

[0044] A method for producing hot-dip galvanized automotive outer panels, wherein the steel strip is DX56D+Z with a specification of 0.7*1455mm.

[0045] (1) Production schedule: Production is organized within 5 days after the submerged roller is changed in the zinc pot of the galvanizing unit. The unit operates stably and there are no downtimes within 24 hours before feeding. Priority is given to producing 860 tons of DX51D+Z, followed by 360 tons of 0.7-1.2mm stabilizing material of DX53D+Z, then 1030 tons of (0.7-1.0)*(1620-1500)mm leading material of DX53D+Z, then 195 tons of 0.7*1500mm non-passivated grinding and slag removal material of DX54D+Z, then 26 tons of 0.7*1455mm transition material of DX56D+Z, and finally the target material of DX56D+Z for hot-dip galvanized automotive outer panels, with a single production of 650 tons.

[0046] (2) The dew point inside the continuous annealing furnace and at the furnace nose is as follows: -38℃ in the preheating section, -45℃ in the heating section, -45℃ in the soaking section, -42℃ in the slow cooling section, -40℃ in the rapid cooling section, and -37℃ in the equalization section. The oxygen content inside the furnace is 6 ppm, and the wet nitrogen flow rate of the furnace nose humidification system is 17 Nm³. 3 / Hr, the dew point at the furnace nose is -6℃.

[0047] (3) Galvanizing process: The temperature of the zinc liquid in the zinc pot is 455℃; the effective aluminum content in the zinc pot is 0.228% and the iron content is 0.006%; the zinc pot liquid level is -81mm; the blowing air knife angle is -1.0 degrees; the air knife height is 235mm; and the distance between the air knife and the steel strip is 7mm.

[0048] (4) Finishing process: The finishing machine work roll is a chrome-plated roll with a diameter of φ636mm, a surface roughness Ra of 2.15μm, a peak Rpc of 116 pieces / cm, a finishing solution concentration of 2.5%, and a rolling force of 3120~3200KN; the surface Ra of the finished steel strip is 1.06μm, the Rpc is 92 pieces / cm, and the waviness Wsa1-5 is 0.28μm.

[0049] (5) Surface inspection: When the steel strip is stationary, visual inspection is performed. The better side has no visible zinc dross or other defects that affect the surface quality, and the other side has 2 zinc dross particles with a diameter of 0.3mm per m2. After grinding with a sandpaper or oilstone, visual inspection is performed. The better side has no visible zinc dross or other defects that affect the surface quality, and the other side has 3 zinc dross particles with a diameter of 0.4mm per m2. After micro-punching and grinding, visual inspection is performed. There are no bright spots or pits with a diameter greater than 1.0mm on the surface of the steel strip.

[0050] Example 2

[0051] A method for producing hot-dip galvanized automotive exterior panels, wherein the steel strip is DX54D+Z with a specification of 0.8*1250mm.

[0052] (1) Production schedule: Production is organized within 9 days after the submerged rollers are changed in the zinc pot of the galvanizing unit. The unit operates stably, with no downtime of more than 4 hours within 24 hours before feeding and no downtime within 16 hours before feeding. Priority is given to producing 920 tons of DX51D+Z, followed by 290 tons of 0.7-1.2mm stabilizing material of DX53D+Z, then 980 tons of (0.8-1.1)*(1500-1300)mm leading material of DX53D+Z, then 205 tons of 0.8*1300mm non-passivated grinding and slag removal material of DX53D+Z, then 25 tons of 0.8*1250mm transition material of DX54D+Z, and finally the target material of hot-dip galvanized automotive outer panels DX54D+Z, with a single production of 1190 tons.

[0053] (2) The dew point inside the continuous annealing furnace and at the furnace nose is as follows: -45℃ in the preheating section, -51℃ in the heating section, -52℃ in the soaking section, -49℃ in the slow cooling section, -48℃ in the rapid cooling section, and -42℃ in the equalization section. The oxygen content inside the furnace is 9ppm, and the wet nitrogen flow rate of the furnace nose humidification system is 12Nm³. 3 / Hr, the dew point at the furnace nose is -2℃.

[0054] (3) Galvanizing process: The temperature of the zinc liquid in the zinc pot is 456℃; the effective aluminum content in the zinc pot is 0.233% and the iron content is 0.007%; the zinc pot liquid level is -80mm; the blowing air knife angle is -1.0 degrees; the air knife height is 256mm; and the distance between the air knife and the steel strip is 7mm.

[0055] (4) Finishing process: The finishing machine work roll is a chrome-plated roll with a diameter of φ612mm, a surface roughness Ra of 2.04μm, a peak Rpc of 103 pieces / cm, a finishing solution concentration of 2.6%, and a rolling force of 2060~2180KN; the surface Ra of the finished steel strip is 0.86μm, the Rpc is 83 pieces / cm, and the waviness Wsa1-5 is 0.33μm.

[0056] (5) Surface inspection: When the steel strip is stationary, visual inspection is performed. The best side has no visible zinc dross or other defects that affect the surface quality, and the other side has 3 zinc dross particles with a diameter of 0.4 mm per m2. After grinding with a sandpaper or oilstone, visual inspection is performed. The best side has no visible zinc dross or other defects that affect the surface quality, and the other side has 3 zinc dross particles with a diameter of 0.5 mm per m2. After micro-punching and grinding, visual inspection is performed. There are no bright spots or pits with a diameter greater than 1.0 mm on the surface of the steel strip.

[0057] Example 3

[0058] A method for producing hot-dip galvanized automotive exterior panels, wherein the steel strip is DX53D+Z with a specification of 0.9*1600mm.

[0059] (1) Production schedule: Production is organized within 3 days after the submerged roller is changed in the zinc pot of the galvanizing unit. The unit operates stably and there are no downtimes within 24 hours before feeding. Priority is given to producing 905 tons of DX51D+Z, followed by 280 tons of 0.7-1.2mm stabilizing material of DX53D+Z, then 990 tons of (0.7-1.2)*(1730-1600)mm leading material of DX53D+Z, then 190 tons of 0.85*1600mm non-passivated grinding and slag removal material of DX54D+Z, then 22 tons of 0.9*1600mm transition material of DX53D+Z, and finally the target material of DX53D+Z for hot-dip galvanized automotive outer panels is produced, with a single production of 2620 tons.

[0060] (2) The dew point inside the continuous annealing furnace and at the furnace nose is as follows: -40℃ in the preheating section, -42℃ in the heating section, -43℃ in the soaking section, -40℃ in the slow cooling section, -39℃ in the rapid cooling section, and -27℃ in the equalization section. The oxygen content inside the furnace is 8 ppm, and the wet nitrogen flow rate of the furnace nose humidification system is 15 Nm³. 3 / Hr, the dew point at the furnace nose is -9℃.

[0061] (3) Galvanizing process: The temperature of the zinc liquid in the zinc pot is 453℃; the effective aluminum content in the zinc pot is 0.226% and the iron content is 0.006%; the zinc pot liquid level is -78mm; the blowing air knife angle is -1.0 degrees; the air knife height is 208mm; and the distance between the air knife and the steel strip is 9mm.

[0062] (4) Finishing process: The finishing machine work roll is a chrome-plated roll with a diameter of φ645mm, a surface roughness Ra of 2.12μm, a peak Rpc of 110 pieces / cm, a finishing solution concentration of 2.4%, and a rolling force of 3510~3600KN; the surface Ra of the finished steel strip is 1.17μm, the Rpc is 95 pieces / cm, and the waviness Wsa1-5 is 0.3μm.

[0063] (5) Surface inspection: When the steel strip is stationary, visual inspection is performed. The better side has no visible zinc dross or other defects that affect the surface quality, while the other side has 4 zinc dross particles with a diameter of 0.3mm per m2. After grinding with a sandpaper or oilstone, visual inspection is performed. The better side has no visible zinc dross or other defects that affect the surface quality, while the other side has 3 zinc dross particles with a diameter of 0.4mm per m2. After micro-punching and grinding, visual inspection is performed. There are no bright spots or pits with a diameter greater than 1.0mm on the surface of the steel strip.

[0064] The hot-dip galvanized automotive outer panels of (0.7~0.9)*(1250~1600)mm specifications DX56D+Z, DX54D+Z, and DX53D+Z obtained using the above method have good surface quality and can meet the requirements of automobile manufacturers.

[0065] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0066] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A method for producing hot-dip galvanized automotive exterior panels, characterized in that, Includes the following steps: 1) Set the operating status requirements for the galvanizing unit so that the production of automotive outer panels is organized within 3 to 10 days after the replacement of the submerged roller in the zinc pot. There should be no downtime of more than 4 hours within 24 hours before feeding; no downtime of more than 2 hours within 16 hours before feeding; and no downtime of more than 0.5 hours within 8 hours before feeding. 2) Set the production sequence for the galvanizing unit: Before producing the outer sheet, first produce 1185-1220 tons of DX51 or IF steel, of which IF steel accounts for no less than 20% of the weight and is a stabilized material with a thickness of 0.7-1.2mm; then produce 980-1030 tons of IF steel, with a thickness of 0.65mm-1.2mm and a width greater than the target outer sheet material as a pre-treatment material; then produce 190-205 tons of IF steel, without passivation, with a thickness similar to the target outer sheet material and a width greater than the target outer sheet material as a grinding and slag removal material; then produce 22-26 tons of transition material of the same grade and specification as the target outer sheet material; finally, produce the target outer sheet material, and control the single production volume to within 3000 tons, switching to transition material during slag removal. 3) Full-process control of galvanizing: including galvanizing cleaning process, continuous annealing furnace and furnace nose gas control, zinc pot process, and finishing machine control; the galvanizing cleaning process includes alkaline immersion washing, alkaline brush washing, electrolytic circulating tank temperature of 80±5℃, and rinsing section temperature of 65±5℃; the conductivity of alkaline immersion washing and alkaline brush washing is 30~50μs / cm, the conductivity of the electrolytic section is 40~60μs / cm, and the conductivity of rinsing is ≤30μs / cm; the surface reflectivity of the steel strip after cleaning is ≥90%; the dew point of the preheating, heating, homogenizing, slow cooling, and rapid cooling sections of the continuous annealing furnace is ≤-35℃, and the dew point of the equalization section is ≤-25℃; the oxygen content in the furnace is ≤10ppm; the furnace nose humidification system uses 10~20 Nm 3 The wet nitrogen flow rate is / hr, and the furnace nose dew point is -10~0℃; the zinc pot temperature in the zinc pot process is controlled at 455±2℃; the effective aluminum content in the zinc pot is 0.225-0.235% by mass, and the iron content is <0.008% by mass; the zinc pot liquid level is controlled at -80±2mm; the purging air knife angle is -1.0 degree, the air knife height is 200~260mm, and the distance between the air knife and the steel strip is 6~10mm; the finishing mill work rolls are chrome-plated rolls with a diameter of ɸ600mm~650mm, Ra=2.0~2.2μm, Rpc=100~120 pieces / cm; the finishing solution concentration is 2.3~2.7% by mass; the finishing rolling force is controlled at 2000-4000KN; the surface requirements of the finished steel strip are: Ra=0.8-1.2μm, Rpc≥80 pieces / cm, and waviness Wsa. 1-5 ≤0.35μm; 4) Establish a surface quality inspection and evaluation mechanism for finished steel strips; the surface quality of finished steel strips shall be inspected using the following three methods: (1) When the steel strip is stationary, visual inspection is required. One side should be free of zinc dross defects that affect the surface quality and no zinc dross with a diameter greater than 0.5 mm is allowed on the other side. The number of zinc dross particles with a diameter not greater than 0.5 mm should not exceed 5 per m. 2 ; (2) After polishing with a sanding mesh or oilstone, visually inspect the surface. There should be no visible zinc dross on one side that affects the surface quality. On the other side, there should be no zinc dross with a diameter greater than 0.8 mm, and the number of zinc dross particles with a diameter not greater than 0.8 mm should not exceed 5 per m. 2 ; (3) After micro-stamping, visual inspection of grinding is performed. After stamping a 700×700mm sample to a depth of 10~15cm, the upper 1 / 3 of the sample is ground with a sanding mesh and the lower 2 / 3 is ground with an oilstone. After grinding, the surface of the steel strip is not allowed to have bright spots or pits with a diameter greater than 1.0mm.

Images