Process for producing super-thick zinc layer products from a hot-rolled sheet blank with endless rolling

Abstract

This invention discloses a process for producing ultra-thick zinc-coated products from hot-rolled thin slabs using endless rolling raw materials, belonging to the steel production field. The galvanizing process includes hot-dip galvanizing and air knife purging. In the hot-dip galvanizing, the temperature rise and holding time of the strip in the induction heating furnace are controlled; the heating rate is 100±5℃ / s during the rapid heating stage; during the heating and holding stage, the temperature is reduced to an entry temperature of 445-450℃ before galvanizing. In the air knife purging, the air knife lip gap is adjusted, adopting a gradually increasing lip gap pattern; the air knife-strip spacing is set according to the lip gap; the strip speed is controlled within the range of 130-150m / min. Compared with existing technologies, this process features a stable zinc coating and high surface quality.

Description

Technical Field

[0001] This invention relates to a hot-based continuous galvanizing process, and more particularly to a production process suitable for hot-rolled endless rolling mills that produces ultra-thick zinc-coated products from raw materials through pickling and galvanizing. Background Technology

[0002] Continuous hot-dip galvanizing involves pre-treatment and induction heating of the strip steel, followed by a series of parameters such as air knife blowing pressure, air knife-strip spacing, and air knife height. After closed-loop control by a zinc layer thickness gauge, the parameters of the air knife are further adjusted.

[0003] Because a thicker zinc layer requires a lower air knife pressure, if the air knife pressure is too low, the strip cannot solidify quickly after exiting the air knife, resulting in zinc flow marks or edge feathering defects, affecting the galvanized surface quality and zinc layer thickness. Therefore, in current production, the thickest zinc layer in conventional continuous hot-dip galvanizing production is generally controlled below 600g. If the zinc layer is too thick, it is impossible to effectively control the sheet surface quality and zinc layer thickness.

[0004] In addition, conventional hot-dip galvanizing requires specific heating temperatures in the furnace, necessitating performance improvements. However, the speed is limited; the lower the speed, the lower the blowing pressure of the air knife, making surface defects more likely to occur. Summary of the Invention

[0005] The technical objective of this invention is to address the shortcomings of the prior art by providing a process for producing ultra-thick zinc-coated products from hot-rolled thin slabs using endless rolling raw materials, achieving stable industrial production of 1020g ultra-thick galvanized products, improving the corrosion resistance of galvanized products, and meeting the market demand for galvanized products.

[0006] The technical solution of this invention to solve its technical problem is: a process for producing ultra-thick zinc-coated products from hot-rolled thin slabs without end rolling raw materials, characterized in that: the galvanizing process includes hot-dip galvanizing and air knife purging; in the hot-dip galvanizing, the temperature rise and holding of the strip in the induction heating furnace are controlled; the heating rate is 100±5℃ / s in the rapid heating stage; in the heating and holding stage, the temperature is reduced to the entry temperature of 445-450℃, and then galvanizing is performed; in the air knife purging, the air knife lip gap is adjusted, and an air knife lip gap pattern with gradually increasing edges is adopted; the air knife-strip spacing is set according to the lip gap; the strip speed is controlled within the range of 130-150m / min.

[0007] Furthermore, in the aforementioned rapid heating stage, the plate temperature upon entering the induction heating furnace is 30-40℃, and the target heating temperature of the strip steel is 500±5℃.

[0008] Furthermore, in the aforementioned rapid heating stage, two 6000kW electromagnetic induction heating stages are employed.

[0009] Furthermore, in the aforementioned heating and heat preservation stage, electric radiant tubes are used for heating and heat preservation.

[0010] Furthermore, the aforementioned air knife lip gap pattern with gradually increasing edges is characterized by a flat blade in the middle section, with the lip gap gradually increasing at both ends.

[0011] Furthermore, the above-mentioned air knife blade lip gap pattern is as follows: the middle 1 / 2 uses a flat blade with a blade lip gap of 1.25±0.05mm, and the blade lip gap is gradually increased to 1.45±0.03mm starting from the 1 / 4 on each side.

[0012] Furthermore, in the above-mentioned air knife purging process, the air knife-strip spacing is set to 8-10 times the gap at the middle position of the blade lip.

[0013] Furthermore, the aforementioned raw material is a 0.6-1.5mm hot-rolled thin slab endless rolled steel plate.

[0014] Compared with the prior art, the present invention has the following outstanding advantages:

[0015] 1. Stable production of ultra-thick galvanized steel, with a zinc layer thickness of up to 1020g, improving the corrosion resistance of galvanized products, meeting the market demand for galvanized steel, and increasing profit per ton of steel;

[0016] 2. The zinc coating has a high pass rate, and the product surface quality is good. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the air knife blade lip gap of the present invention.

[0018] Figure 2 This is a schematic diagram of the gap between the flat blade lip of the air knife in control group 2.

[0019] Figure 3 This is a schematic diagram of the gap between the curved blade lip of the air knife in control group 1.

[0020] Figure 4 This is a surface quality diagram of the steel product of this invention.

[0021] Figure 5 This is a surface quality diagram of steel product from control group 1.

[0022] Figure 6 This is a surface quality diagram of steel product 2 from the control group. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] For the purposes of the following detailed description, it should be understood that the invention may take various alternative variations and sequences of steps unless explicitly stated otherwise. Furthermore, except in any operational instance or where otherwise indicated, all figures representing quantities of ingredients as used, for example, in the specification and claims, should in all cases be understood to be modified by the term “about.” At least, and without attempting to limit the application of the principle of equivalents to the scope of the claims, each numerical parameter should be understood at least according to the number of significant figures reported and by applying common rounding techniques.

[0025] Although the numerical ranges and parameters illustrating the broad scope of the invention are approximate, the values ​​described in the specific examples are reported as precisely as possible. However, any numerical value inherently contains some error that is necessarily caused by the standard deviation found in its corresponding test measurement.

[0026] It should also be understood that any range of values ​​stated herein is intended to include all subranges included therein. For example, the range “1 to 10” is intended to include all subranges between (and including) the stated minimum value of 1 and the stated maximum value of 10, that is, a minimum value equal to or greater than 1 and a maximum value equal to or less than 10.

[0027] In this application, unless otherwise specified, the use of the singular includes the plural and the plural encompasses the singular. Additionally, in this application, unless otherwise expressly stated, the use of "or" means "and / or," even if "and / or" may be explicitly used in certain circumstances. Furthermore, in this application, unless otherwise specified, the use of "a" or "an" means "at least one / a." For example, "an" first material, "an" coating composition, etc., refer to one or more of any of these items.

[0028] This invention relates to a process for producing ultra-thick zinc-coated products from hot-rolled thin slabs using endless rolling raw materials, which can achieve stable industrial production of 1020g ultra-thick galvanized products.

[0029] The galvanizing process includes hot-dip galvanizing and air knife blasting.

[0030] 1. Hot-dip galvanizing process

[0031] Control the temperature rise and heat preservation of the strip steel in the induction heating furnace.

[0032] (1) Electromagnetic induction rapid heating

[0033] The target temperature for heating the strip is 500±5℃, and the heating rate is 100±5℃ / s.

[0034] The heating range of the strip depends on the strip's running speed and the energy supply of the induction heating. Generally, after pickling and rinsing, the strip temperature is 30-40℃ when it enters the induction heating furnace, and it needs to be above 460℃ when it enters the zinc pot. However, the energy supply of the induction heating method in the current technology is limited, so the strip's running speed must be reduced. The lower the speed, the less quickly the strip can solidify at the air exit knife, resulting in zinc flow marks or edge feathering defects, which affect the quality of the galvanized surface and the thickness of the zinc layer.

[0035] Therefore, this process uses two 6000kw electromagnetic induction heating stages to heat the strip steel to 500±5℃ at a rate of 100±5℃ / s.

[0036] (2) Heating and insulation of electric radiant tube

[0037] After the strip steel reaches 500±5℃, it is heated and kept warm by electric radiation tubes. The surface is reduced by hydrogen in the furnace, and the iron oxide scale on the surface of the strip steel is reduced into a spongy state that is easy to galvanize.

[0038] After passing through the radiant tube, the strip steel is heated only on the surface due to electrical induction, and some of the heat is transferred to the core. During this process, the temperature of the strip steel drops to the 445-450℃ temperature required for entering the galvanizing process, and then it is galvanized.

[0039] Furthermore, since strip steel is a hot-rolled raw material, cold rolling results in crystallization hardening, requiring the strip steel to be heated to 720℃ for annealing and reduction for at least 10 seconds. This makes it impossible to meet the requirements for rapid heating and heat holding, which is detrimental to the ultra-thick zinc layer in the subsequent galvanizing process. The ESP hot-rolled headless continuous casting and rolling process can control the minimum thickness to 0.6mm. Using this hot-rolled substrate to produce ultra-thick zinc layer hot-dip galvanized products with specifications below 1.5mm offers high heating efficiency, fast processing speed, and guaranteed zinc layer quality.

[0040] The target heating temperature of 500℃ for the strip and the excessively high temperature of the plate entering the pot will affect the strip speed. The essence of increasing the speed lies in providing a relatively wide process channel for the air knife pressure.

[0041] 2. Air knife purging process

[0042] In addition to existing parameter controls, the following controls also need to be implemented:

[0043] like Figure 1 As shown, adjust the air knife lip gap using a gradually increasing lip gap pattern at the edges. That is, the middle section is flat, and the lip gap gradually increases towards both ends.

[0044] In this embodiment, the middle half uses a flat blade (blade lip gap of 1.25±0.05mm), and the blade lip gap is gradually increased to 1.45±0.03mm starting from each of the two sides in the first quarter.

[0045] like Figure 2 As shown, a standard air knife blade lip gap of 1.1-1.25mm is used for flat blades, which meets the production requirements of 60-600g zinc layers. However, if producing a 1020g zinc layer, the air knife blade lip gap needs to be increased to ensure the air knife pressure.

[0046] During the production of ultra-thick zinc layers, feather-like defects easily form at the edges of the strip due to airflow diffusion. To control these edge defects, a specialized design for the air knife lips is required. This design must ensure a sufficiently large gap between the air knife lips and that edge cooling is greater than that in the center. A fully flat blade arrangement (with the air knife lips maintaining a consistent width throughout) can lead to airflow loss at the edges during thick zinc layer production, resulting in localized excessive thickness of the zinc layer at the edges and thick-edge defects. A gradually widening curve, such as... Figure 3 As shown, although this method can effectively reduce the thick-edge defect caused by excessive zinc layer thickness, the zinc layer is unevenly distributed along the width of the strip, and even feather-like defects appear. Furthermore, the edge gap needs to be increased to over 1.8mm under the full-curve gradient method to solve the thick-edge defect. However, during operation, a large difference between the middle and edge of the air knife lip causes fluctuations in the airflow, affecting the stability of the strip's operation. These fluctuations cause the strip to shake, leading to slag adhesion defects when the strip exits the zinc pot.

[0047] 3. Air knife parameter settings

[0048] Adjust the air knife pressure, air knife-strip spacing, and strip speed to achieve a parameter balance that ensures both the quality of the zinc coating and the surface quality of the product.

[0049] The specific parameter adjustment method is as follows:

[0050] S1. Set the air knife-strip spacing according to the blade lip clearance.

[0051] The air knife-strip spacing should be controlled to be 8-10 times the gap at the center of the blade lip.

[0052] S2. Adjust the air knife pressure according to the air knife-strip gap.

[0053] To meet the requirements of producing ultra-thick zinc layers, the minimum air knife pressure is designed to be 35 mbar. Based on this, the air knife pressure is adjusted according to the distance between the air knife and the strip to achieve zinc layer thinning and cooling effects, preventing zinc flow defects caused by unsolidified molten zinc. For the same zinc layer thickness, the further the strip is from the air knife, the higher the required air pressure.

[0054] S3. Further adjust the air knife pressure according to the strip running speed.

[0055] The strip speed is limited by the heating temperature, and must be maintained at the required heating temperature. The strip speed is controlled within the range of 130-150 m / min.

[0056] The faster the strip speed, the more zinc needs to be blown off, and the greater the required air pressure.

[0057] S4. Thickness measurement feedback further adjusts air knife pressure.

[0058] After measuring the zinc layer thickness with a zinc layer thickness gauge, the air knife pressure is adjusted to meet the zinc layer thickness requirements.

[0059] Since the unit's online thickness gauge is designed to measure a maximum thickness of 600g, it cannot detect zinc layers exceeding this thickness, so manual measurement is required. Ultimately, it was determined that the 1020g ultra-thick zinc layer could be produced with a thickness range of 0.8-1.5mm.

[0060] Setting parameters in the above order allows for mutual influence and restriction among the parameters, which is beneficial for production and quality control. Widening the gap between the air knife blade lips can increase air pressure and volume. While ensuring that the zinc layer weight meets order requirements, the large air volume allows for rapid cooling, thus avoiding quality defects such as feather-like edges.

[0061] To better compare the method of this application with the prior art, comparative experiments were conducted.

[0062] To ensure baseline consistency, the thickness of each hot-rolled substrate is 1.5mm.

[0063] Each set of embodiments represents the process of this application.

[0064] The comparative example process is an improvement on the technology in our company's earlier application "A process for producing ultra-thick zinc-coated hot-dip galvanized steel strip" (CN201910099535.1), which is used to produce double-sided 720mm ultra-thick zinc-coated hot-dip galvanized steel strip.

[0065] The process parameters for each group are as follows:

[0066]

[0067] Test results for each group:

[0068]

[0069] As can be seen from the table above, the various embodiments using the technology of this application, by adjusting the heating rate and the air knife lip method, achieve an increase in the strip running speed, and can produce strips that meet the zinc coating requirements of orders, and as... Figure 4 As shown, the curling has no local bulging, good uniformity, and qualified surface quality.

[0070] Comparative Example 1, using the current heating method, had a relatively low heating rate, preventing the strip speed from reaching 130 m / min. Even with a gradient air knife lip, uneven width, bulging at the outer quarter of the rolled strip, and slag adhesion defects occurred, rendering it unqualified. Comparative Example 2 adjusted the heating rate, increasing the unit speed, but the air knife was not adjusted, resulting in edge feathering defects and zinc flow lines on the strip surface. Although Comparative Examples 1 and 2 met the order requirements for total zinc coating, as... Figure 5-6 As shown, the quality does not meet the usage requirements and is therefore deemed unqualified.

[0071] It should be noted that the specific embodiments of the present invention have been described in detail. For those skilled in the art, various obvious changes made to it without departing from the spirit and scope of the present invention are within the protection scope of the present invention.

Claims

1. A process for producing ultra-thick zinc-coated products from hot-rolled thin slabs using endless rolling raw materials, characterized in that: The galvanizing process includes hot-dip galvanizing and air knife blasting; In the hot-dip galvanizing process, the temperature rise and heat preservation of the strip steel in the induction heating furnace are controlled; the heating rate is 100±5℃ / s in the rapid heating stage; the temperature is reduced to the entry temperature of 445-450℃ in the heating and heat preservation stage, and then galvanizing is performed. During the air knife purging process, the air knife lip gap is adjusted to adopt an air knife lip gap pattern with gradually increasing edges; the air knife-strip spacing is set according to the lip gap. The strip speed is controlled within the range of 130-150 m / min; the air knife lip gap pattern with gradually increasing edges is that the middle section is flat, and the lip gap gradually increases at both ends; the air knife lip gap pattern is that the middle 1 / 2 uses a flat knife with a lip gap of 1.25±0.05 mm, and the lip gap gradually increases to 1.45±0.03 mm at each of the two sides in the 1 / 4.

2. The process for producing ultra-thick zinc-coated products from hot-rolled thin slabs using endless rolling raw materials according to claim 1, characterized in that: During the rapid heating stage, the plate temperature upon entering the induction heating furnace is 30-40℃, and the target heating temperature of the strip steel is 500±5℃.

3. The process for producing ultra-thick zinc-coated products from hot-rolled thin slabs using endless rolling raw materials according to claim 2, characterized in that: During the rapid heating stage, two 6000kW electromagnetic induction heating systems are used.

4. The process for producing ultra-thick zinc-coated products from hot-rolled thin slabs using endless rolling raw materials according to claim 2, characterized in that: During the heating and heat preservation stage, electric radiant tubes are used for heating and heat preservation.

5. The process for producing ultra-thick zinc-coated products from hot-rolled thin slabs using endless rolling raw materials according to claim 1, characterized in that: In the air knife purging process, the air knife-strip spacing is set to 8-10 times the gap at the middle position of the blade lip.

6. The process for producing ultra-thick zinc-coated products from hot-rolled thin slabs using endless rolling raw materials according to claim 1, characterized in that: The raw material is a 0.6-1.5mm hot-rolled thin slab rolled into a headless steel plate.

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