The hot galvanizing annealing furnace adopts the process method of electromagnetic induction body rapid heating annealing

Abstract

This invention relates to the field of pretreatment technology for hot-dip galvanizing of steel plates, specifically disclosing a process method for rapid heating and annealing in a hot-dip galvanizing annealing furnace using an electromagnetic induction heater. The process includes: a rapid heating stage where an induction heating unit acts as the core, and the steel plate continuously passes through the induction heating zone at a set speed, heating the steel plate from room temperature to 720°C; a temperature homogenization stage where the heated steel plate enters a reheating zone, where the surface and internal temperature of the steel plate are corrected through thermal radiation; a cooling adjustment stage where the temperature-homogenized steel plate enters a cooling section, reducing the temperature from 720°C to a set target temperature range of 450°C-460°C; and a thermal equilibrium stabilization stage where the cooled steel plate enters an equilibrium section, which is an insulated channel, ensuring uniform temperature throughout the steel plate. This invention employs a combination of electromagnetic heating and thermal radiation reheating, which is environmentally friendly, produces clean steel strip surfaces free of iron oxide scale, and improves the unit's operating speed.

Description

Technical Field

[0001] This invention relates to the field of pretreatment technology for hot-dip galvanizing of steel plates, specifically to a process method for rapid heating and annealing in a hot-dip galvanizing annealing furnace using an electromagnetic induction device. Background Technology

[0002] Before hot-dip galvanizing steel sheets enter the zinc bath, the temperature of the steel sheets needs to be strictly controlled, requiring processes such as heating, cooling, and holding in an annealing furnace. However, conventional annealing furnaces generate high-temperature flames through gas combustion, transferring heat to the strip steel via "direct flame heating + air convection within the furnace." Due to the characteristics of "localized high temperatures and uneven overall distribution" in flame heating, heat must be indirectly transferred through air, with a large amount of heat being dissipated by the furnace body and carried away by exhaust gases, resulting in low heating efficiency (typically less than 50%). This low efficiency leads to the consumption of more gas for heating the same workpiece, and the high costs of gas procurement and storage result in high operating costs. Furthermore, the combustion of gas (mainly containing methane) inevitably produces CO2, and inefficient combustion increases additional gas consumption, leading to high carbon emissions. The air convection within the furnace carries away iron oxide scale and dust, which easily adhere to the surface of the rotating furnace rollers at high temperatures, accumulating over time and failing to be automatically cleaned, causing nodules on the furnace rollers, which in turn lead to scratches on the workpiece surface and production interruptions. To overcome the problems of low heating efficiency, severe nodule formation on furnace rollers, safety issues in gas-fired annealing furnaces, and high carbon content in exhaust emissions, this invention provides a process method for rapid heating and annealing of hot-dip galvanizing furnaces using electromagnetic induction. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention aims to provide a process method for rapid heating and annealing of hot-dip galvanizing annealing furnace using electromagnetic induction, achieving green, efficient, and low-cost energy use. The method uses electromagnetic induction to rapidly heat the strip steel, and then uses radiant rollers for heat supplementation and insulation to anneal the cold substrate, so that the strip steel gradually transforms from fine, deformed, and broken grains into coarse, complete equiaxed grains, thereby realizing the transformation of strip steel properties.

[0004] The technical solution adopted by this invention to solve its technical problem is: a process method for rapid heating and annealing of hot-dip galvanizing furnace using electromagnetic induction, comprising the following steps:

[0005] S1. Rapid heating stage: The induction heating unit serves as the heating core, and the steel plate continuously passes through the induction heating area at a set speed, heating the steel plate from room temperature to 720℃.

[0006] S2, Temperature homogenization stage: The heated steel plate enters the heat compensation zone, which corrects the surface and internal temperature of the steel plate through thermal radiation, so that the overall temperature of the steel plate is kept in a uniform state of 720℃±5℃.

[0007] S3, Cooling and Adjustment Stage: After the steel plate has reached a uniform temperature, it enters the cooling section to reduce the temperature of the steel plate from 720℃ to the set target temperature range of 450℃-460℃.

[0008] S4. Thermal equilibrium stabilization stage: After cooling, the steel plate enters the equilibrium section, which is an insulated channel, and the overall temperature of the steel plate is uniform.

[0009] Specifically, the induction heating unit in step S1 uses four 6000kW induction heating elements, which are arranged in series along the running direction of the steel plate. The distance between adjacent induction heating elements is 1.2m, which together form an induction heating area. Rapid heating is achieved inside the steel plate through electromagnetic induction effect.

[0010] Specifically, the induction heating area in step S1 is designed to be 20m long, and the strip steel is heated from room temperature to 720℃ by electromagnetic cutting over a length of 20m.

[0011] Specifically, in step S1, when the set speed of the steel plate is 200 m / min, the time to pass through the induction heating area is 6.0 s; when the set speed is 150 m / min, the time to pass through the induction heating area is 8.0 s; and when the set speed is 100 m / min, the time to pass through the induction heating area is 12.0 s.

[0012] Specifically, in step S2, the heat replenishment area is equipped with five radiant heating tubes. The radiant heating tubes are evenly arranged along the width and length of the steel plate. The radiant heating tubes are gas-fired radiant tubes and are arranged at equal intervals of 0.8m along the running direction of the steel plate. Each radiant heating tube covers the entire width of the steel plate. The heat replenishment area is located on the outlet side of the induction heating area and is connected to the outlet of the induction heating area through a sealed channel. The steel plate directly enters the radiant heat replenishment area from the induction heating area. The heat replenishment area is 125m long. Through the 125m heat uniformity, the internal temperature of the steel plate is made more uniform.

[0013] Specifically, when the running speed of the steel plate in the heating zone is set to 200 m / min, the time it takes to pass through the induction heating zone is 37.5 s; when the running speed is set to 150 m / min, the time it takes to pass through the induction heating zone is 50.0 s; and when the running speed is set to 100 m / min, the time it takes to pass through the induction heating zone is 75.0 s.

[0014] Specifically, the cooling section in step S3 includes a cooling channel, a fan cooling system, and temperature control nozzles; the cooling section uses nitrogen as the cooling medium and sprays cooling gas onto the steel plate surface through the temperature control nozzles; the inlet of the cooling channel is connected to the outlet of the heat replenishment area, and multiple sets of temperature control nozzles are evenly distributed along the upper and lower surfaces of the steel plate inside; the fan cooling system is connected to the temperature control nozzles through pipes and is equipped with a temperature sensor and a fan power regulating valve to adjust the fan power of the fan cooling system according to the real-time temperature of the steel plate.

[0015] Specifically, when the running speed of the steel plate in the cooling section is set to 200 m / min, the time it takes to pass through the induction heating zone is 15.0 s; when the running speed is set to 150 m / min, the time it takes to pass through the induction heating zone is 20.0 s; and when the running speed is set to 100 m / min, the time it takes to pass through the induction heating zone is 30.0 s.

[0016] Specifically, the heat-insulating channel in step S4 is a double-layer heat-insulating shell structure, with high-temperature resistant insulation cotton laid inside the shell; the inlet of the equalization section is sealed to the outlet of the cooling section, and the outlet of the equalization section is directly connected to the inlet of the zinc pot, forming a closed temperature stable channel to ensure that the temperature of the steel plate does not fluctuate before entering the zinc pot.

[0017] Specifically, when the running speed of the steel plate in the equalization section is set to 200 m / min, the time it takes to pass through the induction heating zone is 16.5 s; when the running speed is set to 150 m / min, the time it takes to pass through the induction heating zone is 22.0 s; and when the running speed is set to 100 m / min, the time it takes to pass through the induction heating zone is 33.0 s.

[0018] The present invention has the following beneficial effects:

[0019] This invention designs a hot-dip galvanizing annealing furnace that employs a rapid heating annealing process using electromagnetic induction. The heating method combines electromagnetic heating with thermal radiation supplementation. All heating is electrically converted, resulting in high heating efficiency. The electromagnetic heating method achieves a heat transfer efficiency of up to 80%, while thermal radiation provides insulation, ensuring thorough heating of the strip steel's interior after electromagnetic heating. Furthermore, there are no carbon emissions, making it environmentally friendly. Because there is no oxygen environment required for gas-fired heating, the strip steel surface remains clean and free of iron oxide scale, avoiding the nodule formation problem common in conventional annealing furnaces. Moreover, this heating method offers rapid heat transfer, and the strip steel speed is not limited by heat transfer, significantly increasing the unit's operating speed. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be described clearly, completely, and in further detail below. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] Example 1

[0022] A hot-dip galvanizing annealing furnace employs a rapid heating annealing process using an electromagnetic induction unit. This process is applied to a hot-dip galvanizing production line for steel strips at a steel plant. The preheating process before hot-dip galvanizing of the steel plates is mainly achieved through a continuous heating unit. The core steps, in the order of steel plate operation, are as follows:

[0023] 1. Rapid heating stage: Four induction heating elements with a power of 6000kW are used as the heating core. The steel plate passes through the induction heating area continuously at a set speed. Through the electromagnetic induction effect, the steel plate is rapidly heated from room temperature to 720℃.

[0024] The induction heating section is designed to be 20m long. The main consideration is the arrangement of the induction elements. The strip steel is rapidly heated from room temperature to a maximum of 720℃ through this 20m electromagnetic cutting process.

[0025] 2. Temperature Homogenization Stage: After rapid heating, the steel plate enters the reheating zone. This zone is equipped with five radiant heating tubes, evenly distributed along the width and length of the steel plate. These tubes correct for surface and internal temperatures through thermal radiation, eliminating the temperature differences generated during the rapid heating stage and maintaining a uniform overall temperature of 720℃. This radiant heating system is 125m long. Considering that electromagnetic heating of the strip only generates surface heat, this 125m heating element ensures a more uniform internal temperature and provides a certain degree of reheating capability.

[0026] 3. Cooling and Adjustment Stage: After the steel plate has reached a uniform temperature, it enters the cooling section. The cooling section uses nitrogen as the cooling medium. Cooling gas is sprayed onto the surface of the steel plate through temperature-controlled nozzles. According to the subsequent zinc pot temperature requirements, the temperature of the steel plate is reduced from 720℃ to the set target temperature range, usually 450℃-460℃.

[0027] 4. Thermal equilibrium stabilization stage: After cooling, the steel plate enters the equilibrium section, which is an insulated channel structure that maintains a stable temperature environment. The steel plate moves slowly in this area to further eliminate local temperature fluctuations that may occur during the cooling process and ensure that the overall temperature of the steel plate is uniform.

[0028] The set steel plate running speed, running time, zone length, and temperature for each stage are shown in Table 1:

[0029] Table 1 Production setup of strip steel at each stage

[0030]

[0031] The core equipment for realizing the above process is the "continuous steel plate heating unit", and its structural composition and the relationship between its components are as follows:

[0032] Induction heating unit: It consists of 4 6000kW induction heating elements, which are arranged in series along the running direction of the steel plate. The distance between adjacent heating elements is 1.2m, which together form a rapid heating zone. Each induction heating element is equipped with an independent power control system, which adjusts the output power in real time according to the thickness of the steel plate and the running speed to ensure a stable heating rate.

[0033] Radiant heating unit: It contains five radiant heating tubes, which are gas-fired radiant tubes, and are arranged at equal intervals (0.8m spacing) along the running direction of the steel plate. Each radiant tube covers the entire width of the steel plate. The radiant heating unit is located on the outlet side of the induction heating unit and is connected to the outlet of the induction heating unit through a sealed channel. The steel plate enters the radiant heating unit directly from the induction heating unit.

[0034] Cooling unit: consists of a cooling channel, a fan cooling system and a temperature control nozzle group; the inlet of the cooling channel is connected to the outlet of the radiant heating unit, and multiple sets of temperature control nozzles are evenly distributed along the upper and lower surfaces of the steel plate inside; the fan cooling system is connected to the nozzle group through pipes, and is also equipped with a temperature sensor and a fan power regulating valve to adjust the fan power according to the real-time temperature of the steel plate.

[0035] Equalization unit: It has a double-layer insulated shell structure with high-temperature resistant insulation cotton laid inside the shell; the inlet of the equalization unit is sealed to the outlet of the cooling unit, and the outlet is directly connected to the inlet of the zinc pot, forming a closed and stable temperature channel to ensure that the temperature of the steel plate does not fluctuate before entering the zinc pot.

[0036] The process method of this invention uses electromagnetic induction heating, which is more efficient and energy-saving than gas radiation heating; moreover, electromagnetic heating allows the strip steel to be heated quickly, and the unit operates at a high speed.

[0037] Gas consumption is directly positively correlated with CO2 emissions (methane combustion formula: CH4 + 2O2 = CO2 + 2H2O). This heating method does not require gas heating, thus solving the problem of "high gas consumption and high carbon emissions in conventional furnaces".

[0038] This invention designs an "inert gas (such as nitrogen) circulation system" to replace the original air convection, which isolates oxygen and prevents iron oxide scale and dust from flowing with the airflow; it solves the problem of "conventional furnace air convection causing impurities to adhere to the furnace rollers", ensuring that the surface of the furnace rollers remains clean and free from nodules, thus avoiding scratches on the workpieces.

[0039] This embodiment, compared with conventional heating furnaces, reduces power consumption and heating furnace cost per ton of steel by approximately 17 yuan / ton, resulting in an annual benefit of 500,000 * 17 = 8.5 million yuan.

[0040] 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.

[0041] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A process for rapid heating and annealing in a hot-dip galvanizing annealing furnace using an electromagnetic induction device, characterized in that, Includes the following steps: S1. Rapid heating stage: The induction heating unit serves as the heating core, and the steel plate continuously passes through the induction heating area at a set speed, heating the steel plate from room temperature to 720℃. S2, Temperature homogenization stage: The heated steel plate enters the heat compensation zone, which corrects the surface and internal temperature of the steel plate through thermal radiation, so that the overall temperature of the steel plate is kept in a uniform state of 720℃±5℃. S3, Cooling and Adjustment Stage: After the steel plate has reached a uniform temperature, it enters the cooling section to reduce the temperature of the steel plate from 720℃ to the set target temperature range of 450℃-460℃. S4. Thermal equilibrium stabilization stage: After cooling, the steel plate enters the equilibrium section, which is an insulated channel, and the overall temperature of the steel plate is uniform.

2. The hot-dip galvanizing annealing furnace according to claim 1, characterized in that, The induction heating unit in step S1 uses four 6000kW induction heating elements, which are arranged in series along the running direction of the steel plate. The distance between adjacent induction heating elements is 1.2m, which together form an induction heating area. Rapid heating is achieved inside the steel plate through electromagnetic induction effect.

3. The hot-dip galvanizing annealing furnace according to claim 1, characterized in that, The induction heating area in step S1 is designed to be 20m long, and the strip steel is heated from room temperature to 720℃ by electromagnetic cutting over a length of 20m.

4. The hot-dip galvanizing annealing furnace according to claim 1, characterized in that, In step S1, when the set speed of the steel plate is 200 m / min, the time it takes to pass through the induction heating area is 6.0 s; when the set speed is 150 m / min, the time it takes to pass through the induction heating area is 8.0 s; and when the set speed is 100 m / min, the time it takes to pass through the induction heating area is 12.0 s.

5. The hot-dip galvanizing annealing furnace according to claim 1, characterized in that, In step S2, the heat replenishment area is equipped with five radiant heating tubes. The radiant heating tubes are evenly arranged along the width and length of the steel plate. The radiant heating tubes are gas-fired radiant tubes and are arranged at equal intervals of 0.8m along the running direction of the steel plate. Each radiant heating tube covers the entire width of the steel plate. The heat replenishment area is located on the outlet side of the induction heating area and is connected to the outlet of the induction heating area through a sealed channel. The steel plate directly enters the radiant heat replenishment area from the induction heating area. The heat replenishment area is 125m long. Through 125m of heat uniformity, the internal temperature of the steel plate is more uniform.

6. The hot-dip galvanizing annealing furnace according to claim 5, characterized in that, When the running speed of the steel plate in the heating zone is set to 200 m / min, the time it takes to pass through the induction heating zone is 37.5 s; when the running speed is set to 150 m / min, the time it takes to pass through the induction heating zone is 50.0 s; and when the running speed is set to 100 m / min, the time it takes to pass through the induction heating zone is 75.0 s.

7. The hot-dip galvanizing annealing furnace according to claim 1, characterized in that, The cooling section in step S3 includes a cooling channel, a fan cooling system, and temperature control nozzles. The cooling section uses nitrogen as the cooling medium and sprays cooling gas onto the surface of the steel plate through the temperature control nozzles. The inlet of the cooling channel is connected to the outlet of the heat replenishment area, and multiple sets of temperature control nozzles are evenly distributed along the upper and lower surfaces of the steel plate inside. The fan cooling system is connected to the temperature control nozzles through pipes and is equipped with a temperature sensor and a fan power regulating valve to adjust the fan power of the fan cooling system according to the real-time temperature of the steel plate.

8. The hot-dip galvanizing annealing furnace according to claim 7, characterized in that, When the running speed of the steel plate in the cooling section is set to 200 m / min, the time it takes to pass through the induction heating zone is 15.0 s; when the running speed is set to 150 m / min, the time it takes to pass through the induction heating zone is 20.0 s; and when the running speed is set to 100 m / min, the time it takes to pass through the induction heating zone is 30.0 s.

9. The hot-dip galvanizing annealing furnace according to claim 1, characterized in that, The heat-insulating channel in step S4 has a double-layer heat-insulating shell structure, with high-temperature resistant insulation cotton laid inside the shell; the inlet of the equalization section is sealed to the outlet of the cooling section, and the outlet of the equalization section is directly connected to the inlet of the zinc pot, forming a closed temperature stable channel to ensure that the temperature of the steel plate does not fluctuate before entering the zinc pot.

10. The hot-dip galvanizing annealing furnace according to claim 9, characterized in that, When the running speed of the steel plate in the equalization section is set to 200 m / min, the time it takes to pass through the induction heating zone is 16.5 s; when the running speed is set to 150 m / min, the time it takes to pass through the induction heating zone is 22.0 s; and when the running speed is set to 100 m / min, the time it takes to pass through the induction heating zone is 33.0 s.

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