A galvannealing system for hot-dipped galvanized steel strip

Abstract

The application discloses an alloying treatment system for hot galvanizing strip steel, which is arranged above a zinc pot along the running direction of the strip steel, and comprises an induction heating section, a direct-fired heating section arranged above the induction heating section along the running direction of the strip steel, wherein the direct-fired heating section is provided with a plurality of rows of flat-flame flameless burner groups arranged along the running direction of the strip steel, each row of the flat-flame flameless burner groups comprises a plurality of flat-flame flameless burners arranged along the width direction of the strip steel, each flat-flame flameless burner has a plurality of injection holes arranged in the circumferential direction of the burner, and the axial direction of the flat-flame flameless burner is perpendicular to the surface of the strip steel, a direct-fired soaking section arranged above the direct-fired heating section along the running direction of the strip steel, a heat preservation section arranged above the direct-fired soaking section along the running direction of the strip steel, and a cooling section arranged above the heat preservation section along the running direction of the strip steel.

Description

Technical Field

[0001] This invention relates to an alloying system, and more particularly to an alloying system for hot-dip galvanized steel sheets. Background Technology

[0002] In the hot-dip galvanizing process of steel strip, after galvanizing, an alloying heat treatment is performed to cause an alloying reaction between the zinc layer and the steel substrate, forming a hot-dip galvanized zinc-iron alloy coating. This process is called hot-dip galvanizing alloying, or GA (Galvannealing). The iron content in this alloy coating is typically 7–15% (mass fraction), and the coating consists of a coarse zinc-iron alloy phase δ1 and a small amount of ξ phase. This zinc-iron alloy layer significantly improves the corrosion resistance and weldability of the steel, while also increasing the hardness and wear resistance of the coating.

[0003] Currently, the annealing treatment of hot-dip galvanized products is completed in an alloying furnace. As the most critical piece of equipment in the alloying process, the alloying furnace has a direct impact on the quality of hot-dip galvanized alloyed GA products.

[0004] Among these factors, the heating method, capacity allocation, and heating location of the alloying furnace are the most important factors affecting whether the coating temperature meets the requirements of the coating annealing curve and the quality of the alloyed coating. Inadequate heat loss will cause the temperature inside the alloying furnace to drop. Current alloying systems have the following main drawbacks:

[0005] 1) Inappropriate heating method. Existing alloying furnaces use induction heating. For high-strength GA steel plates, due to the high alloy content and austenite content in the substrate, their magnetic permeability decreases. Induction heating is extremely inefficient, and the plating temperature cannot reach the alloying temperature after induction heating. The unit can only maintain production by reducing its speed, severely impacting unit efficiency. Furthermore, production performance analysis shows that even when the induction heating equipment is operating at full capacity, incomplete alloying and under-alloying still occur.

[0006] 2) Inappropriate distribution of heating capacity. In the existing process, the alloying heating of strip steel can only be completed by extremely rapid induction heating. For BH steel, which requires a higher alloying temperature, higher power output from induction heating is required to maintain a certain production speed. However, rapid heating can easily lead to local overheating of the zinc layer surface, causing the zinc layer to crack and resulting in alloying on the strip steel surface.

[0007] 3) Inappropriate heating location. In existing alloying furnace structures, the induction heating section is relatively short and located at the bottom of the furnace, while the homogenization gas injection zone is typically located in the middle. Due to the chimney effect, the hot gas in the middle has difficulty flowing downwards. Since induction heating itself does not generate hot gas, there is a significant area of ​​insufficient heating capacity between the induction heating zone and the middle hot gas injection zone. In these areas, the strip steel is prone to temperature drops after reaching the reaction temperature in the induction heating section, ultimately leading to insufficient alloying. Summary of the Invention

[0008] The purpose of this invention is to provide an alloying treatment system for hot-dip galvanized strip steel, which can flexibly combine induction heating and direct heating according to the annealing process curve, the heat supply capacity distribution and the heat supply location requirements before homogenization, so as to uniformly and efficiently achieve alloying of coatings on various hot-dip galvanized strip steel while ensuring the surface quality of the strip steel.

[0009] To achieve the above objectives, the present invention provides an alloying treatment system for hot-dip galvanized strip steel, which is disposed above a zinc pot along the running direction of the strip steel, wherein the running direction of the strip steel is from bottom to top, and the alloying treatment system includes:

[0010] Induction heating section;

[0011] The direct-fire heating section is arranged above the induction heating section along the running direction of the strip. The direct-fire heating section is provided with several rows of flat flameless burner groups arranged along the running direction of the strip. Each row of flat flameless burner groups includes several flat flameless burners arranged along the width direction of the strip. Each flat flameless burner has several nozzles arranged in the circumferential direction of the burner. The axial direction of the flat flameless burner is perpendicular to the surface of the strip.

[0012] The direct heating and soaking section is located above the direct heating section along the running direction of the strip.

[0013] The heat preservation section is located above the direct heating and soaking section along the running direction of the strip.

[0014] The cooling section is located above the insulation section along the running direction of the strip.

[0015] The alloying system described in this invention employs a vertical alloying furnace. The strip runs from bottom to top, and along the running direction of the strip, it sequentially includes: an induction heating section, a direct-fire heating section, a direct-fire soaking section, a holding section, and a cooling section. After the strip is galvanized in the zinc pot, it enters the induction heating section for rapid heating to complete the first stage of temperature rise. Then, it enters the direct-fire heating section to rapidly heat to the alloying reaction temperature. The alloying reaction continues in the direct-fire soaking section and the holding section until the cooling section completes the entire alloying heat treatment process.

[0016] The process consists of several sections: an induction heating section for rapidly raising the temperature to or below the alloying reaction temperature (for conventional strip steel); a direct heating section for rapidly increasing the furnace temperature and strip temperature to the alloying reaction temperature, thus completing the heating process; a soaking section for uniformly heating the strip using the furnace temperature; a holding section for allowing the strip to complete the coating alloying reaction at a relatively stable and suitable process temperature; and a cooling section for forming the lattice layer of the alloyed coating, thus completing the alloying process.

[0017] The flat flameless burner used in this invention, because the nozzle is parallel to the strip, the high-temperature flue gas is not sprayed vertically onto the strip, but forms a uniform high-temperature surface close to the strip surface. The strip is mainly heated and heated by the convection heat transfer and radiation heat of the high-temperature flue gas, so the heating is uniform and will not affect the surface quality of the strip.

[0018] Furthermore, in the alloying system described in this invention, the flat flameless burner has 3-12 of the aforementioned nozzles.

[0019] Furthermore, in the alloying system described in this invention, the angle between the axial centerline of the nozzle and the axis of the flat flameless burner is 45-90°.

[0020] Furthermore, in the alloying system described in this invention, the distance between the nozzle and the strip surface is 150-550 mm.

[0021] Furthermore, in the alloying system described in this invention, the working mode of the flat flame flameless burner can be switched between a flame combustion mode and a flameless combustion mode. When the value is higher than a set threshold, it switches to the flameless combustion mode, and when the value is lower than the set threshold, it switches to the flame combustion mode.

[0022] Furthermore, in the alloying system described in this invention, the set threshold is selected within the range of 800-900°C.

[0023] Furthermore, in the alloying system described in this invention, an inlet plate thermometer and / or an inlet regulating baffle are provided at the inlet of the direct heating section, wherein the inlet plate thermometer is used to measure the temperature of the strip at the inlet of the direct heating section, and the inlet regulating baffle adjusts the size of the inlet of the direct heating section.

[0024] Furthermore, in the alloying system described in this invention, the direct-fire heating section is equipped with at least one of the following: a heating section furnace temperature thermocouple, a burner thermocouple, a direct-fire heating section inlet thermocouple, and a direct-fire heating section inlet pressure gauge.

[0025] Furthermore, in the alloying system described in this invention, the direct-fire soaking section has a first cooling air system for introducing external cold air and a soaking section furnace temperature thermocouple for measuring the furnace temperature.

[0026] Furthermore, in the alloying system described in this invention, the direct heating and soaking section is provided with at least one of the following: a soaking section furnace temperature thermocouple, a soaking section outlet thermocouple, and a soaking section outlet pressure gauge.

[0027] Furthermore, in the alloying treatment system described in this invention, the heat preservation section has a second cooling air system for introducing external cold air.

[0028] Furthermore, in the alloying system of the present invention, the heat preservation section has at least one of the following: heat preservation section outlet pressure gauge, heat preservation section outlet thermocouple, heat preservation section furnace temperature thermocouple, heat preservation section plate temperature gauge, and heat preservation section furnace internal pressure gauge.

[0029] The alloying treatment system for hot-dip galvanized strip steel described in this invention has the following advantages and beneficial effects:

[0030] The alloying system described in this invention is applicable to various hot-dip galvanized steel strips and has a very wide range of adaptability, wherein:

[0031] For conventional strip steel, if the induction heating capacity is sufficient, it can be heated to the alloying reaction temperature. The subsequent flat-flame flameless oxidation direct heating section, soaking section, and heat preservation section mainly serve the function of heat preservation to complete the coating alloying. Furthermore, for conventional strip steel, a combination of induction heating and flat-flame flameless oxidation direct heating can be adopted according to the unit operation and product process requirements to rationally allocate heat supply and reduce the cost of induction heating.

[0032] For bake-hardening (BH) steel, which has a high alloying reaction temperature and is prone to defects such as alloying spots and "zinc bursting" on the coating surface, the strip heating process is completed by a combination of induction heating and direct heating with a flat flame or flameless oxidation process. While increasing heating capacity, the heating rate of the strip in the induction heating section can be controlled. The strip temperature after induction heating should be lower than the alloying reaction temperature, and then it is rapidly heated to the alloying reaction temperature in the direct heating section to complete the alloying process. This effectively avoids defects such as "zinc bursting" on the coating surface.

[0033] For high-strength steel, the heating process is completed by a combination of induction heating and direct-fired oxidation heating with a flat flame. Because the induction heating efficiency of high-strength steel is low, the power of the induction heating section can be reduced, and the alloying process is mainly completed by subsequent direct-fired oxidation heating with a flat flame to the alloying reaction temperature. This combination of induction heating and direct-fired oxidation heating provides sufficient heating capacity, eliminating the need to reduce the machine speed during the production of high-strength steel coatings. It also reduces induction heating costs and avoids the problems of low induction heating efficiency and under-alloying of the coating caused by magnetic permeability. Attached Figure Description

[0034] Figure 1 A schematic diagram of one embodiment of the alloying treatment system for hot-dip galvanized strip steel described in this invention is shown.

[0035] Figure 2 The direct-fire heating section of the alloying treatment system for hot-dip galvanized strip steel described in this invention is shown in one embodiment.

[0036] Figure 3 for Figure 2 Side view.

[0037] Figure 4 This invention illustrates a flat flameless burner in one embodiment of the alloying treatment system for hot-dip galvanized strip steel described in this invention.

[0038] Figure 5 Showing Figure 4 Axial end face view.

[0039] Figure 6 The annealing curves for various alloying processes are shown in comparison. Detailed Implementation

[0040] The alloying treatment system for hot-dip galvanized strip steel described in this invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. However, this explanation and description do not constitute an undue limitation on the technical solution of this invention.

[0041] Figure 1 A schematic diagram of one embodiment of the alloying treatment system for hot-dip galvanized strip steel described in this invention is shown.

[0042] In one specific implementation, such as Figure 1 As shown, the present invention provides an alloying treatment system for hot-dip galvanized strip steel. The strip steel runs from bottom to top and is positioned above the zinc pot 1 along the running direction of the strip steel 2. The alloying treatment system includes: an induction heating section 100, a direct heating section 200, a direct heating homogenization section 300, a heat preservation section 400, and a cooling section 500.

[0043] The system comprises several sections: an induction heating section 100 rapidly heats the strip to or below the alloying reaction temperature (for conventional strip steel); a direct heating section 200 rapidly increases the furnace and strip temperatures to the alloying reaction temperature, completing the heating process; a soaking section 300 utilizes the furnace temperature to uniformly heat the strip; a holding section 400 ensures the strip completes the alloying reaction at a relatively stable and suitable process temperature; and a cooling section 500 forms the lattice layer of the alloyed coating, completing the alloying process. In some more specific embodiments, the alloying system employs a vertical alloying furnace.

[0044] In this manner, after the strip steel 2 is galvanized in the zinc pot 1, it enters the induction heating section 100, where it is rapidly heated by the induction heating device 3 to complete the first stage of temperature rise. Then it enters the direct heating section 200, where it is heated to the alloying reaction temperature at a relatively fast speed through the direct heating zone 9. The alloying reaction continues in the direct heating zone 12 of the direct heating zone 300 and the heat preservation zone 15 of the heat preservation zone 400 until the entire alloying heat treatment process is completed in the cooling section 500 through the cooling device 20.

[0045] Figure 2 The direct-fire heating section of the alloying treatment system for hot-dip galvanized strip steel described in this invention is shown in one embodiment.

[0046] Figure 3 for Figure 2 Side view.

[0047] like Figure 2 and Figure 3 As shown, in some embodiments, the direct-fire heating section is provided with several rows of flat flameless burner groups arranged along the running direction of the strip, wherein each row of flat flameless burner groups includes several flat flameless burners 10 arranged along the width direction of the strip.

[0048] Figure 4 This invention illustrates a flat flameless burner in one embodiment of the alloying treatment system for hot-dip galvanized strip steel described in this invention.

[0049] Figure 5 Showing Figure 4 Axial end face view.

[0050] like Figure 4 and Figure 5 As shown, each of the flat flameless burners has several nozzles 32 arranged in the circumferential direction of the burner at its flame end 33, and the axial direction of the flat flameless burner is perpendicular to the surface of the strip steel 2.

[0051] In this way, the flat flameless burner used in this invention, because the nozzle is parallel to the strip, the high-temperature flue gas is not sprayed vertically onto the strip, but forms a uniform high-temperature surface close to the strip surface. The strip is mainly heated and heated by the convection heat transfer and radiation heat of the high-temperature flue gas. Therefore, the heating is uniform and will not affect the surface quality of the strip.

[0052] In some more specific embodiments, a single flat flameless burner 10 has 3-12 nozzles 32.

[0053] In some more specific implementations, such as Figure 4 As shown, the angle α between the axial centerline of the nozzle 32 and the axis of the flat flameless burner is 45-90°.

[0054] In some more specific implementations, such as Figure 4 As shown, the distance L between the nozzle 32 and the surface of the strip 2 is 150-550mm.

[0055] In some embodiments, the flat flame flameless burner 10 can switch between a flame combustion mode and a flameless combustion mode according to the furnace temperature. Flame combustion occurs at low furnace temperatures, and flameless combustion occurs at high furnace temperatures. For example, it switches to flameless combustion mode when the temperature is above a set threshold, and switches to flame combustion mode when the temperature is below the set threshold.

[0056] In some more specific implementations, the set threshold can be selected within the range of 800-900°C.

[0057] In some more preferred embodiments, such as Figure 1 As shown, an inlet plate thermometer 4 and an inlet adjusting baffle 5 can be installed at the inlet of the direct heating section 200. The inlet plate thermometer is used to measure the temperature of the strip at the inlet of the direct heating section, and the inlet adjusting baffle 5 can adjust the size of the inlet of the direct heating section, so as to adjust the size of the bottom strip channel opening according to the strip specifications and minimize the area for cold air intake.

[0058] In some more specific implementations, such as Figure 1 As shown, the inlet regulating baffle 5 can be directly and sealed to the bottom of the direct-fire heating section via a retractable high-temperature expansion joint 6.

[0059] In some implementations, such as Figure 1 As shown, the direct-fire heating section 200 may also be equipped with a maintenance manhole 7 and a furnace flame observation window 8.

[0060] like Figure 1As shown, in some embodiments, the direct-fire heating section 200 may also be provided with at least one of the following: heating section furnace temperature thermocouples 28-1 and 28-2, burner thermocouples 29-1 and 29-2, direct-fire heating section inlet thermocouples 31-1 and 31-2, and direct-fire heating section inlet pressure gauge 30.

[0061] These thermocouples are used to control and detect furnace temperature and flame temperature. The inlet pressure gauge 30 of the direct-fire heating section detects the furnace pressure. The set pressure of the inlet pressure gauge of the direct-fire heating section can be -50 to 50 Pa.

[0062] Continue reading Figure 1 In some embodiments, the direct-fire soaking section 300 has a first cooling air system 13 for introducing outside cold air and a soaking section furnace temperature thermocouple 27 for measuring the furnace temperature.

[0063] When the furnace temperature is detected to be too high, the first cooling air system 13 can send cold air into the furnace through an external fan and piping to regulate the furnace temperature.

[0064] In addition, in some embodiments, the direct-fire heat-spreading section 300 may also be equipped with at least one of the following: heat-spreading section furnace temperature thermocouple 27, heat-spreading section outlet thermocouples 25-1 and 25-2, and heat-spreading section outlet pressure gauge 26.

[0065] In some more specific embodiments, a row of 3-15 heat exchanger thermocouples 11 can be symmetrically arranged on both sides of the strip along the width direction to detect changes in furnace temperature along the width direction.

[0066] Continue reading Figure 1 In some embodiments, the insulation section 400 has a second cooling air system 14 for introducing outside cold air, and may also be provided with a stabilizing roller 16.

[0067] In some embodiments, the insulation section may also include at least one of the following: insulation section outlet pressure gauge 21, insulation section outlet thermocouple 22, insulation section furnace temperature thermocouple 23, insulation section plate temperature gauge 17, and insulation section furnace internal pressure gauge 24.

[0068] When the furnace temperature is detected to be too high, the second cooling air system 14 of the insulation section can send cold air into the furnace through an external fan and piping to regulate the furnace temperature. The second cooling air system 14 is also equipped with a waste gas emission system 18, which includes a high-temperature fan and piping, and plays the role of discharging waste gas from the furnace and controlling the furnace temperature and pressure.

[0069] In some embodiments, a sealing system 19, including a fan and piping, may be installed above the exhaust gas system 18, which can control the furnace pressure and furnace temperature.

[0070] The alloying system described in this invention is applicable to various hot-dip galvanized steel strips and has a very wide range of adaptability, wherein:

[0071] For conventional strip steel, if the induction heating capacity is sufficient, it can be heated to the alloying reaction temperature. The subsequent flat-flame flameless oxidation direct heating section, soaking section, and heat preservation section mainly serve the function of heat preservation to complete the coating alloying. Furthermore, for conventional strip steel, a combination of induction heating and flat-flame flameless oxidation direct heating can be adopted according to the unit operation and product process requirements to rationally allocate heat supply and reduce the cost of induction heating.

[0072] For bake-hardening (BH) steel, which has a high alloying reaction temperature and is prone to defects such as alloying spots and "zinc bursting" on the coating surface, the strip heating process is completed by a combination of induction heating and direct heating with a flat flame or flameless oxidation process. While increasing heating capacity, the heating rate of the strip in the induction heating section can be controlled. The strip temperature after induction heating should be lower than the alloying reaction temperature, and then it is rapidly heated to the alloying reaction temperature in the direct heating section to complete the alloying process. This effectively avoids defects such as "zinc bursting" on the coating surface.

[0073] For high-strength steel, the heating process is completed by a combination of induction heating and direct-fired oxidation heating with a flat flame. Because the induction heating efficiency of high-strength steel is low, the power of the induction heating section can be reduced, and the alloying process is mainly completed by subsequent direct-fired oxidation heating with a flat flame to the alloying reaction temperature. This combination of induction heating and direct-fired oxidation heating provides sufficient heating capacity, eliminating the need to reduce the machine speed during the production of high-strength steel coatings. It also reduces induction heating costs and avoids the problems of low induction heating efficiency and under-alloying of the coating caused by magnetic permeability.

[0074] Figure 6 The annealing curves for various alloying processes are shown in comparison.

[0075] Figure 6 Curve I in the diagram represents the ideal alloying annealing curve, curve II represents the alloying annealing curve using existing equipment, and curve III represents the alloying annealing curve using the present invention. From... Figure 6 As can be seen from the above, the alloying annealing curve of the alloying device described in this invention is closer to the ideal alloying annealing curve.

[0076] It should be noted that the prior art portion of the protection scope of this invention is not limited to the embodiments given in this application. All prior art that does not contradict the solution of this invention, including but not limited to prior patent documents, prior publications, prior public uses, etc., can be included in the protection scope of this invention.

[0077] Furthermore, the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0078] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. An alloying treatment system for hot-dip galvanized strip steel, wherein the system is positioned above a zinc pot along the running direction of the strip steel, characterized in that, The alloying system includes: Induction heating section; The direct-fire heating section is arranged above the induction heating section along the running direction of the strip. The direct-fire heating section is provided with several rows of flat flameless burner groups arranged along the running direction of the strip. Each row of flat flameless burner groups includes several flat flameless burners arranged along the width direction of the strip. Each flat flameless burner has several nozzles arranged in the circumferential direction of the burner. The axial direction of the flat flameless burner is perpendicular to the surface of the strip. The direct heating and soaking section is located above the direct heating section along the running direction of the strip. The heat preservation section is located above the direct heating and soaking section along the running direction of the strip. The cooling section is located above the insulation section along the running direction of the strip.

2. The alloying system as described in claim 1, characterized in that, The flat flameless burner has 3-12 nozzles.

3. The alloying system as described in claim 1, characterized in that, The angle between the axial centerline of the nozzle and the axis of the flat flameless burner is 45-90°.

4. The alloying treatment system as described in claim 1, characterized in that, The distance between the nozzle and the strip surface is 150-550mm.

5. The alloying treatment system as described in claim 1, characterized in that, The flat flameless burner switches between a flame combustion mode and a flameless combustion mode. When the flame level is above a set threshold, it switches to the flameless combustion mode; when the flame level is below the set threshold, it switches to the flame combustion mode.

6. The alloying treatment system as described in claim 5, characterized in that, The set threshold is selected within the range of 800-900℃.

7. The alloying system as described in claim 1, characterized in that, An inlet plate thermometer and / or an inlet regulating baffle are provided at the inlet of the direct-fire heating section. The inlet plate thermometer is used to measure the temperature of the strip at the inlet of the direct-fire heating section, and the inlet regulating baffle adjusts the size of the inlet of the direct-fire heating section.

8. The alloying treatment system as described in claim 1, characterized in that, The direct-fire heating section is equipped with at least one of the following: a heating section furnace temperature thermocouple, a burner thermocouple, a direct-fire heating section inlet thermocouple, and a direct-fire heating section inlet pressure gauge.

9. The alloying treatment system as described in claim 1, characterized in that, The direct-fire homogenizing section has a first cooling air system for introducing external cold air and a homogenizing section furnace temperature thermocouple for measuring furnace temperature.

10. The alloying system as described in claim 1, characterized in that, The direct-fire homogenization section is equipped with at least one of the following: a homogenization section furnace temperature thermocouple, a homogenization section outlet thermocouple, and a homogenization section outlet pressure gauge.

11. The alloying system as described in claim 1, characterized in that, The insulation section has a second cooling system for introducing cold air from the outside.

12. The alloying system as described in claim 1, characterized in that, The insulation section has at least one of the following: insulation section outlet pressure gauge, insulation section outlet thermocouple, insulation section furnace temperature thermocouple, insulation section plate temperature gauge, and insulation section furnace internal pressure gauge.

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