Analysis and control method for oblique scar defect of hot substrate super-thick zinc layer product

Abstract

The invention relates to an analysis control method for oblique scar defects of a hot substrate ultra-thick zinc layer product, and belongs to the technical field of metallurgy control methods. The method comprises the following steps: analyzing the macroscopic morphology of defects, controlling the temperature of a furnace area in an annealing furnace process, controlling the temperature and components of molten zinc in a zinc pot process, and controlling an air knife and an air knife baffle in an air knife process. According to the method, the inclined scar defect of the hot substrate super-thick zinc layer product without spangles of 720 g / m < 2 > or above can be effectively inhibited.

Description

Technical Field

[0001] The invention relates to an analysis and control method for oblique scar defects of a super-thick zinc layer product on a hot substrate, belonging to the technical field of metallurgical control methods. Background Art

[0002] At present, some of the ultra-thick zinc layer products used in the market are hot-dip galvanizing. This type of galvanizing process is to make the finished structural parts pass through the traditional hot-dip galvanizing to achieve the requirements of corrosion resistance, but there are problems such as poor surface quality, low production efficiency and serious environmental pollution; some are traditional large zinc flower products. Due to the presence of zinc flowers, such products are prone to intergranular corrosion of the zinc layer; and some are zinc flower-free continuous galvanizing products. Such products have been mass-produced in recent years and are superior to hot-dip galvanizing and zinc flower galvanizing. They are characterized by no zinc flowers on the surface of the product, a large coverage of the zinc layer weight, and the use of improved Sendzimir heating process or electric heating process, high production efficiency and low processing cost. However, the increase in the thickness of the zinc layer of the galvanized sheet has greatly increased the difficulty of production. In the hot-dip galvanizing production process, "oblique scar" defects often occur. This defect is irregularly distributed on the edge surface of the strip, and the inclined scars that appear randomly on the edge of the strip feel like a hand, which is manifested as a local zinc layer that is too thin. It is necessary to provide a control method for its defects. Summary of the invention

[0003] The purpose of the present invention is to provide a method for analyzing and controlling the oblique scar defect of the ultra-thick zinc layer product of the hot substrate. Through the analysis of the defect macroscopic morphology and the defect microscopic morphology, the plate temperature of the annealing furnace process is controlled, the zinc pot process controls the zinc liquid temperature and the zinc liquid composition, and the air knife process controls the gap between the air knife and the air knife lip, and the air knife baffle manufacturing and air knife baffle production and installation control can effectively suppress the zinc flower 720g / m 2 The generation of oblique scar defects in products with ultra-thick zinc layers on (double-sided) and above hot substrates effectively solves the above-mentioned problems existing in the background technology.

[0004] The technical solution of the present invention is: A method for analyzing and controlling the oblique scar defect of a super-thick zinc layer product on a hot substrate comprises the following steps: (1) Description of defect type: During the production process of ultra-thick zinc layer products, inclined scars randomly appear on the edge of the strip, which feel like a hand mark, indicating that the local zinc layer is too thin; (2) Analyze the causes of defects and conduct defect morphology analysis; (3) Defect control, including plate temperature control in the annealing furnace process, zinc liquid temperature and zinc liquid composition control in the zinc pot process, and air knife and air knife lip gap control in the air knife process.

[0005] (4) Air knife baffles, including air knife baffle manufacturing and air knife baffle production and installation control.

[0006] In the step (2), the defect morphology is a tendency scar that randomly appears on the edge of the strip along the running direction of the strip, and the defect at one end of the edge of the strip is wider, while the defect at the middle end is thinner.

[0007] In step (2), the cause of the defect is analyzed. If the strip has C-warping at the air knife, the oblique scar only appears on the concave side. There are relatively more 50 meters from the head to the tail of the strip, and the single one is less common, and the pairs or multiple consecutive ones are more common.

[0008] From the curve of the zinc layer thickness gauge, the thinner the zinc layer on the edge of the strip, the more oblique scars appear. The wave shape will lead to an increase in the number, but oblique scars will also appear even if the plate shape is good, so the plate shape is one of the reasons. Analyzing from the shape of the defect and the actual thin zinc layer phenomenon, the cause is airflow disturbance. According to the location where the airflow disturbance is formed, it can be divided into the inside of the air knife cavity and the outside of the air knife cavity. According to the cause of the airflow disturbance, it can be divided into air knife equipment reasons and raw material substrate reasons. The places where air knife equipment is prone to airflow disturbance include improper installation or deformation of the baffle, uneven knife lip gap, small deviation of the angle of the front and rear air knives, and back blowing. Under the blowing of the air knife airflow, the surface of the plating solution can be significantly disturbed to form a local thin area, which is consistent with the actual situation of the defect.

[0009] In the step (3), the plate temperature of the furnace process is controlled by controlling the plate temperature zone by zone: the plate temperature of the open flame section is 690±10°C, the plate temperature of the radiation tube section is 670±10°C, the plate temperature of the soaking section is 630±10°C, and the plate temperature of the cooling section is 452±5°C.

[0010] In the step (3), the zinc pot process controls the temperature and composition of the zinc liquid. The zinc liquid temperature is 450-455°C, the mass content of AL in the zinc liquid is 0.20-0.21%, and the mass content of Fe is ≤0.02%.

[0011] In the step (3), in the air knife process, the air knife lip gap is 1.3 mm in the middle, and increases by 0.01 mm on both sides, and is 1.4 mm on the outermost side.

[0012] In the step (3), in the air knife process, the air knife angle is -1 to 0°, the air knife pressure is ≤50 mbar, the air knife distance is ≥31 mm, and the air knife height is ≤100 mm.

[0013] In the step (4), the air knife baffle is manufactured with a material of SUS304, a thickness of 5 mm, a baffle height of 290 mm, and a baffle length of 720 mm.

[0014] In the step (4), the air knife baffle is produced, installed and controlled, and the air knife baffle is aligned and parallel to the steel strip, and is 2 mm away from the steel strip.

[0015] The ultra-thick zinc layer product is zinc-free 720g / m 2 And above hot base plate ultra-thick zinc layer products.

[0016] The beneficial effects of the present invention are: The present invention controls the plate temperature of the annealing furnace process, controls the zinc liquid temperature and zinc liquid composition in the zinc pot process, controls the gap between the air knife and the air knife lip in the air knife process, and controls the air knife baffle manufacturing and air knife baffle production and installation through defect morphology analysis, which can effectively suppress the zinc flower 720g / m 2 The generation of oblique scar defects in products with ultra-thick zinc layer on hot substrates (double-sided) and above. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a defect morphology diagram of the present invention; Figure 2 The zinc layer at the oblique scar defect is thin; Figure 3 This is a front view of the air knife baffle. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the invention implementation cases clearer, the technical solutions in the implementation cases of the present invention will be clearly and completely described below in conjunction with the drawings in the implementation cases. Obviously, the implementation cases described are only a small part of the implementation cases of the present invention, rather than all the implementation cases. Based on the implementation cases in the present invention, all other implementation cases obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0019] A method for analyzing and controlling the oblique scar defect of a super-thick zinc layer product on a hot substrate comprises the following steps: (1) Description of defect type: During the production process of ultra-thick zinc layer products, inclined scars randomly appear on the edge of the strip, which feel like a hand mark, indicating that the local zinc layer is too thin; (2) Analyze the causes of defects and conduct defect morphology analysis; (3) Defect control, including plate temperature control in the annealing furnace process, zinc liquid temperature and zinc liquid composition control in the zinc pot process, and air knife and air knife lip gap control in the air knife process.

[0020] (4) Air knife baffles, including air knife baffle manufacturing and air knife baffle production and installation control.

[0021] In the step (2), the defect morphology is an oblique scar that randomly appears on the edge of the strip along the running direction of the strip, and the defect at one end of the edge of the strip is wider, while the defect at the middle end is thinner.

[0022] In step (2), the cause of the defect is analyzed. If the strip has C-warping at the air knife, the oblique scar only appears on the concave side. There are relatively more 50 meters from the head to the tail of the strip, and the single one is less common, and the pairs or multiple consecutive ones are more common.

[0023] From the curve of the zinc layer thickness gauge, the thinner the zinc layer on the edge of the strip, the more oblique scars appear. The wave shape will lead to an increase in the number, but oblique scars will also appear even if the plate shape is good, so the plate shape is one of the reasons. Analyzing from the shape of the defect and the actual thin zinc layer phenomenon, the cause is airflow disturbance. According to the location where the airflow disturbance is formed, it can be divided into the inside of the air knife cavity and the outside of the air knife cavity. According to the cause of the airflow disturbance, it can be divided into air knife equipment reasons and raw material substrate reasons. The places where air knife equipment is prone to airflow disturbance include improper installation or deformation of the baffle, uneven knife lip gap, small deviation of the angle of the front and rear air knives, and back blowing. Under the blowing of the air knife airflow, the surface of the plating solution can be significantly disturbed to form a local thin area, which is consistent with the actual situation of the defect.

[0024] In the step (3), the plate temperature of the furnace process is controlled by controlling the plate temperature zone by zone: the plate temperature of the open flame section is 690±10°C, the plate temperature of the radiation tube section is 670±10°C, the plate temperature of the soaking section is 630±10°C, and the plate temperature of the cooling section is 452±5°C.

[0025] In the step (3), the zinc pot process controls the temperature and composition of the zinc liquid. The zinc liquid temperature is 450-455°C, the mass content of AL in the zinc liquid is 0.20-0.21%, and the mass content of Fe is ≤0.02%.

[0026] In the step (3), in the air knife process, the air knife lip gap is 1.3 mm in the middle, and increases by 0.01 mm on both sides, and is 1.4 mm on the outermost side.

[0027] In the step (3), in the air knife process, the air knife angle is -1 to 0°, the air knife pressure is ≤50 mbar, the air knife distance is ≥31 mm, and the air knife height is ≤100 mm.

[0028] In the step (4), the air knife baffle is manufactured with a material of SUS304, a thickness of 5 mm, a baffle height of 290 mm, and a baffle length of 720 mm.

[0029] In the step (4), the air knife baffle is produced, installed and controlled, and the air knife baffle is aligned and parallel to the steel strip, and is 2 mm away from the steel strip.

[0030] The ultra-thick zinc layer product is zinc-free 720g / m 2 And above hot base plate ultra-thick zinc layer products.

[0031] In practical applications, no zinc flower 720g / m 2 The difficulty of the analysis and control method of the oblique scar defect of the ultra-thick zinc layer product on the hot substrate (double-sided) and above lies in the defect cause analysis and defect control.

[0032] In the defect description and morphology analysis of the present invention, Figure 1 Along the running direction of the strip, there are random tendon scars on the edge of the strip. The defect at one end of the strip is wider, and the defect at the middle end is thinner. Figure 2 The zinc layer is thin at the oblique scar.

[0033] After defect analysis, it was found that there was no zinc flower 720g / m 2 The analysis and formation of oblique scar defects in products with ultra-thick zinc layer on hot substrates (double-sided) and above are closely related to the plate shape and the airflow at the air knife.

[0034] Defect control includes defect control of annealing furnace process, zinc pot process, air knife process and air knife baffle.

[0035] In the annealing furnace process of the present invention, the plate temperature in the open flame section is 690±10°C, the plate temperature in the radiation tube section is 670±10°C, the plate temperature in the soaking section is 630±10°C, and the plate temperature in the cooling section is 452±5°C. The plate temperature in the annealing furnace process has a certain influence on the plate shape of the strip when it leaves the zinc pot. If the temperature is too low, the surface defects such as pinhole plating leakage and zinc slag will appear on the surface of the strip. If the temperature is too high, the substrate will appear wavy, and the gas knife will form a slant scar defect.

[0036] In the zinc pot process of the present invention, the zinc liquid temperature is 450-455°C, the mass content of AL in the zinc liquid is 0.20-0.21%, and the mass content of Fe is ≤0.02%. When the zinc liquid temperature and the Al content in the zinc liquid are too high, the zinc liquid has high fluidity, the strip is more affected by the airflow, and the airflow disturbance will increase the edge scars. When the zinc liquid temperature and the Al content in the zinc liquid are too low, the zinc pot inductor heater continues to work at high power, stirring the bottom slag and suspended slag, which sticks to the strip and is affected by gravity to destroy the zinc layer and cause the scar defect.

[0037] In the air knife process of the present invention, the gap of the air knife lip is 1.3mm in the middle, and increases by 0.01mm on both sides, and the outermost side is 1.4mm. The air knife angle is -1 to 0°, the air knife pressure is ≤50mbar, the air knife distance is ≥31mm, and the air knife height is ≤100mm. Due to the thick zinc layer, the zinc liquid is not solidified when the strip exits the air knife, the outer shell of the zinc layer is solidified while the inside is in a liquid state. When the air knife pressure is too large and the air knife distance is too small, the air flow disturbance is too large, the outer shell is blown, the internal zinc liquid flows out, and an oblique scar is blown out. The air knife angle of -1 to 0° can avoid the splashing of zinc liquid and the generation of zinc slag when the air knife is at a low height. This air knife lip gap matches the air knife parameters, reduces air flow disturbance and prevents the generation of oblique scars on the edges.

[0038] The air knife baffle of the present invention is made of SUS304, with a thickness of 5 mm, a baffle height of 290 mm, and a baffle length of 720 mm. Figure 3. Production and installation control of the air knife baffle, the air knife baffle is aligned and parallel to the strip steel, and the distance from the strip steel is 2mm. The air knife baffle is an important tool for controlling the oblique scar on the edge. The air knife baffle needs to be aligned and parallel to the strip steel, and cannot be deformed by heat, so it is made according to this material, thickness and size. Due to the thick zinc layer, the zinc liquid has not solidified when the strip steel leaves the air knife, the outer shell of the zinc layer solidifies and the inside is in a liquid state. The best distance between the air knife baffle and the strip steel is 2mm. When the distance is greater than 2mm, serious edge thickness defects will occur. When the baffle distance is less than 2mm, because the strip steel will shake slightly and move left and right when it leaves the zinc pot, and because the zinc layer is thick, the air knife wind pressure is too small, and the zinc slag is more likely to stick to the edge of the strip, causing the air knife baffle to stick to the slag, destroying the outer shell of the zinc layer on the edge, and causing oblique scar defects on the edge. Example 1

[0039] The DX51D+Z raw material with a substrate thickness of 2.0mm is rolled up and galvanized to produce a zinc-free 720g / m 2 (Double-sided) zinc-coated products.

[0040] In the annealing furnace process, the plate temperature is controlled zone by zone: the plate temperature in the open flame section is 680℃, the plate temperature in the radiation tube section is 660℃, the plate temperature in the soaking section is 620℃, and the plate temperature in the cooling section is 447℃.

[0041] In the zinc pot process, the zinc liquid temperature is 450℃, the zinc liquid composition has an AL content of 0.20% by mass and an Fe content of 0.01% by mass. During production, the zinc liquid level is controlled to be stable and the slag is removed frequently.

[0042] In the air knife process, the gap between the air knife lips is 1.3mm in the middle, increasing by 0.01mm on both sides, and 1.4mm on the outermost side.

[0043] The air knife angle is -1 to 0°, the air knife pressure is 48 mbar, the air knife distance is 31 mm, and the air knife height is 100 mm.

[0044] The finished product is obtained through the above process, and no oblique scar defects are produced during the whole roll. Example 2

[0045] The DX51D+Z raw material with a substrate thickness of 2.0mm is rolled up and galvanized to produce a zinc-free 750g / m 2 (Double-sided) zinc-coated products.

[0046] In the annealing furnace process, the plate temperature is controlled zone by zone: the plate temperature in the open flame section is 690℃, the plate temperature in the radiation tube section is 670℃, the plate temperature in the soaking section is 630℃, and the plate temperature in the cooling section is 452℃.

[0047] In the zinc pot process, the zinc liquid temperature is 453 ℃, the zinc liquid composition AL mass content is 0.205%, Fe mass content is 0.014%. During production, the zinc liquid level is controlled to be stable and the slag is removed frequently.

[0048] In the air knife process, the gap between the air knife lips is 1.3mm in the middle, increasing by 0.01mm on both sides, and 1.4mm on the outermost side.

[0049] Air knife angle -1~0°, air knife pressure 45mbar, air knife distance 32mm, air knife height 90mm.

[0050] The finished product is obtained through the above process, and no oblique scar defects are produced during the whole roll.

[0051] Example 3 The DX51D+Z raw material with a substrate thickness of 2.0mm is rolled up and galvanized to produce a zinc-free 820g / m 2 (Double-sided) zinc-coated products.

[0052] In the annealing furnace process, the plate temperature is controlled zone by zone: the plate temperature in the open flame section is 700℃, the plate temperature in the radiation tube section is 680℃, the plate temperature in the soaking section is 640℃, and the plate temperature in the cooling section is 457℃.

[0053] In the zinc pot process, the zinc liquid temperature is 455 ℃, the zinc liquid composition AL mass content is 0.21%, Fe mass content is 0.016%. During production, the zinc liquid level is controlled to be stable and the slag is removed frequently.

[0054] In the air knife process, the gap between the air knife lips is 1.3mm in the middle, increasing by 0.01mm on both sides, and 1.4mm on the outermost side.

[0055] The air knife angle is -1 to 0°, the air knife pressure is 42 mbar, the air knife distance is 33 mm, and the air knife height is 80 mm.

[0056] The finished product is obtained through the above process, and no oblique scar defects are produced during the whole roll.

[0057] The above examples prove that the technical solution of the present invention can effectively suppress the zinc spangle 720g / m 2 The generation of oblique scar defects in products with ultra-thick zinc layer on hot substrates (double-sided) and above.

Claims

1. A method for analyzing and controlling the oblique scar defect of a super-thick zinc layer product on a hot substrate, characterized in that: The following steps are involved: (1) Description of defect type: oblique scars appearing on the upper and lower edges of the strip during the production process of ultra-thick zinc layer products, showing that the local zinc layer is thin; (2) Defect cause analysis: perform defect morphology analysis; (3) Defect control: including controlling the plate temperature in the annealing furnace process, controlling the temperature and composition of the zinc liquid in the zinc pot process, and controlling the gap between the air knife and the air knife lip in the air knife process; (4) Air knife baffle control: including the control of air knife baffle manufacturing and the production and installation of air knife baffles.

2. The method for analyzing and controlling the oblique scar defect of a super-thick zinc layer product of a hot substrate according to claim 1 is characterized in that: In the step (2), the defect morphology is random oblique scars appearing on the edges of the upper and lower surfaces of the strip, and the number and size are random.

3. The method for analyzing and controlling the oblique scar defect of a super-thick zinc layer product of a hot substrate according to claim 1 is characterized in that: In the step (3), the annealing furnace process controls the plate temperature zone by zone: the plate temperature in the open flame section is 690±10°C, the plate temperature in the radiation tube section is 670±10°C, the plate temperature in the soaking section is 630±10°C, and the plate temperature in the cooling section is 452±5°C.

4. The method for analyzing and controlling the oblique scar defect of a super-thick zinc layer product of a hot substrate according to claim 1 is characterized in that: In the step (3), the zinc pot process controls the temperature and composition of the zinc liquid. The zinc liquid temperature is 450-455° C., the mass content of AL in the zinc liquid is 0.20-0.21%, and the mass content of Fe is ≤0.02%.

5. The method for analyzing and controlling the oblique scar defect of a super-thick zinc layer product of a hot substrate according to claim 1 is characterized in that: In the step (3), in the air knife process, the air knife lip gap is 1.3 mm in the middle, and increases by 0.01 mm on both sides, and is 1.4 mm on the outermost side.

6. The method for analyzing and controlling the oblique scar defect of a super-thick zinc layer product of a hot substrate according to claim 1 is characterized in that: In the step (3), in the air knife process, the air knife angle is -1 to 0°, the air knife pressure is ≤50 mbar, the air knife distance is ≥31 mm, and the air knife height is ≤100 mm.

7. The method for analyzing and controlling the oblique scar defect of a super-thick zinc layer product of a hot substrate according to claim 1 is characterized in that: In the step (4), the air knife baffle is manufactured with a material of SUS304, a thickness of 5 mm, a baffle height of 290 mm, and a baffle length of 720 mm.

8. The method for analyzing and controlling the oblique scar defect of a super-thick zinc layer product of a hot substrate according to claim 1 is characterized in that: In the step (4), the production and installation of the air knife baffle is controlled so that the air knife baffle is aligned and parallel to the steel strip and is 2 mm away from the steel strip.

9. The method for analyzing and controlling the oblique scar defect of a super-thick zinc layer product of a hot substrate according to claim 1, characterized in that: The ultra-thick zinc layer product is zinc-free 720g / m 2 And above hot base plate ultra-thick zinc layer products.

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