A high temperature annealing device and cooling method for oriented silicon steel ring furnace steel coil

Abstract

The present invention discloses a high-temperature annealing device and cooling method for steel coils in an annular furnace for oriented silicon steel. It includes a trolley for carrying heated steel coils; a base placed on the trolley for supporting a bottom plate; a bottom plate for placing heated steel coils; an inner cover covered on the trolley for covering the area where the steel coils are located, and a protective gas is passed through the inner cover; a protective gas inlet pipe, through which protective gas is passed to prevent the steel coils from being oxidized; a furnace gas circulation device, which is installed outside the furnace body, rotates synchronously with the trolley, and is connected to the inner cover, and is used to speed up the gas flow speed in some areas of the inner cover. The present invention increases the flow rate of the gas in the inner ring area of ​​the steel coil, and the low-temperature gas reduces the temperature of the inner ring strip steel of the steel coil, thereby reducing the thermal stress of the outer ring strip steel of the steel coil, improving the shape quality of the strip steel after annealing, reducing the time required for cooling the steel coil, and improving the production efficiency of the unit.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment of steel coils in the metallurgical industry, and specifically relates to a high-temperature annealing device for steel coils in an annular furnace for oriented silicon steel and a cooling method. Background Art

[0002] Oriented silicon steel is an important soft magnetic functional material that is indispensable in the power and electronics industries. It has the characteristics of high magnetic induction and low iron loss. At present, the most commonly used equipment for high-temperature annealing of oriented silicon steel is the silicon steel high-temperature ring annealing furnace. The steel coil is placed vertically on a trolley in a coiled shape. The outer cover of the steel coil is made of a heat-resistant alloy. During the annealing process, protective gases such as N2 and H2 are introduced into the inner cover according to the process requirements. The gas pressure in the inner cover is controlled to be greater than the gas pressure in the furnace to ensure that the steel coil is in a neutral or reducing atmosphere and the strip is not oxidized. After the oriented silicon steel coil is subjected to primary heating, low insulation, secondary heating, and high insulation treatment in sequence, the steel coil enters the cooling stage. Compared with the single-shell annealing furnace, the silicon steel high-temperature ring annealing furnace can save energy and reduce the annealing cycle.

[0003] The steel coil is placed vertically in the furnace in a coiled shape. There is a certain gap between the steel strips and they are coated with inorganic powders such as MgO as an isolation agent. The thermal conductivity of the steel coil in the radial direction is much smaller than that in the vertical direction. However, it still causes a temperature difference in the radial direction of the steel coil. The faster the temperature rise and fall speed of the steel coil in the furnace, the greater the radial temperature difference of the steel coil, and the greater the thermal stress on the strip. When the thermal stress on the strip in the steel coil exceeds a certain critical value, it may cause various plate defects, such as edge waves, ship shape, flanged edge on the upper end of the steel coil, and inner convexity of the inner circle on the upper end of the steel coil.

[0004] When the steel coil is annealed at high temperature in the furnace, except for the strip steel on the bottom plate side (lower end face) of the steel coil, the main source of stress on the strip steel at other positions in the steel coil is the temperature difference of various parts in the steel coil. That is, the outer ring flange defect located on the upper end face of the steel coil, the inner convex defect of the inner ring of the upper end face of the steel coil, and the buckling defect in the middle part of the steel coil (width direction) are only related to the thermal stress inside the steel coil during annealing. The faster the temperature rise and fall speed of the steel coil, the more serious the plate shape defect of the steel coil. At present, most of the technologies for improving the plate shape of the strip steel after annealing are to control the thermal stress inside the steel coil by controlling the temperature rise and fall speed of the steel coil. These measures effectively improve the plate shape quality of the steel coil, but these technologies lead to longer annealing time and lower production efficiency. In the silicon steel ring furnace, the main heat transfer mode between the strip steel in various parts of the steel coil and the furnace body is radiation heat transfer. When the temperature of the strip steel in the steel coil drops below a certain level, the heat transfer capacity of the strip steel to the outside of the inner cover by radiation drops sharply, which also leads to insufficient cooling speed of the steel coil at low temperature.

[0005] For example, Chinese patent CN112853052A discloses a method for controlling the average cooling rate of steel coils in sections, which reduces the shape defects of oriented silicon steel after high temperature annealing. However, the production efficiency of this section control is still relatively low.

[0006] For example, Chinese patent CN103987863A proposes a cylindrical inner cover, which uses external airflow to cool the inner wall of the inner cover and then cool the inner ring of the steel coil. This inner cover is more complicated and easily damaged during lifting. It is necessary to add a fixed cooling air pipe on the top of the furnace body, which is not suitable for intermittently rotating silicon steel ring furnaces.

[0007] For example, Japanese patent JPS60221521A wraps the outer ring or the inner and outer rings of the steel coil with heat insulation materials to reduce the radial heat transfer of the steel coil, reduce the radial temperature difference of the steel coil, and improve the shape of the strip after annealing. Heat insulation materials are mostly made of oxides, and in a reducing atmosphere, their service life is short, the cost of use is high, and the operation is also more troublesome.

[0008] For example, Japanese patent publication JP2014025102A uses heat insulation materials of different thicknesses or different thermal conductivities along the radial direction on the upper and lower ends of the steel coil to reduce the radial temperature difference of the steel coil and improve the shape of the steel coil after annealing. Heat insulation materials are mostly made of oxides, and their service life is short and the cost of use is high in a reducing atmosphere. In addition, the use of heat insulation materials reduces the heat transfer capacity of the steel coil, prolongs the cooling time of the steel coil, and reduces the production efficiency of the unit.

[0009] In a silicon steel ring furnace, the main heat transfer method between the strip steel in each part of the steel coil and the furnace body is radiation heat transfer. When the strip steel temperature in the steel coil drops below a certain level, the heat transfer capacity of the strip steel to the outside of the inner cover by radiation drops sharply, which leads to insufficient cooling speed of the steel coil at low temperatures.

[0010] Chinese patent CN 112029985A discloses an indirect water cooling device for an annular furnace. The device is located in the fast cooling section of the annular furnace. By spraying water on the inner cover, the temperature of the inner cover is lowered, and the cooling of the steel coil is accelerated. By lowering the temperature of the inner cover, the radiation absorbed by the steel coil to the inner cover can be reduced, but the amount of radiation that the strip can radiate at low temperatures is limited, and the cooling rate of the steel coil is limited. In addition, the use of cooling water sprayed on the inner cover to lower the temperature of the inner cover causes a sharp increase in the internal thermal stress between the oxide film on the surface of the inner cover and the substrate. When the thermal stress is greater than the bonding force between the oxide layer and the substrate, the oxide film will collapse and expose the inner cover substrate, causing the oxidation rate of the inner cover to accelerate during the subsequent annealing process.

[0011] When the oriented silicon steel coil is annealed in a high-temperature annealing furnace, it is subjected to different thermal stresses due to the different heating conditions of each part. When the thermal stress on the strip exceeds a certain critical value, it may cause various plate defects, such as edge waves, ship shape, flanged edge on the upper end of the steel coil, and inner convexity of the inner circle on the upper end of the steel coil. At present, a good strip shape is mostly obtained by controlling the heating and cooling speed of the steel coil. However, the time required for annealing the steel coil is extended and the production efficiency is reduced. In addition, since the outer cover of the steel coil is protected, the heat transfer method between the steel coil and the furnace is mainly thermal radiation. When the temperature of the steel coil is low, the efficiency of radiation heat transfer is low, which also causes the steel coil to take more time to cool. Summary of the invention

[0012] The purpose of the present invention is to solve the shortcomings of the above-mentioned background technology and provide a high-temperature annealing device and cooling method for oriented silicon steel ring furnace steel coils, improve the plate quality of oriented silicon steel coils after high-temperature annealing, and improve the production efficiency of steel coils.

[0013] The technical solution adopted by the present invention is: a high temperature annealing device for oriented silicon steel ring furnace steel coil, comprising

[0014] A trolley for carrying the heated steel coil;

[0015] A base, placed on the trolley, for supporting the bottom plate;

[0016] A bottom plate, used for placing the heated steel coil, the steel coil is placed vertically on the bottom plate;

[0017] An inner cover, which is mounted on the trolley and is used to cover the area where the steel coil is located, and a protective gas is passed through the inner cover;

[0018] The protective gas inlet pipe is used to prevent the steel coil from being oxidized;

[0019] The furnace gas circulation device is installed outside the furnace body, rotates synchronously with the trolley, and is connected to the inner cover to speed up the gas flow speed in some areas of the inner cover.

[0020] The furnace gas circulation device includes a circulating gas inlet pipe, a first circulating gas outlet pipe, a second circulating gas outlet pipe, a high-temperature circulating fan (the high-temperature circulating fan is used to transport high-temperature gas of 200-900°C), a first cooler and a second cooler, a first pipeline valve and a second pipeline valve; one end of the circulating gas inlet pipe is connected to the space surrounded by the upper part of the trolley in the inner cover and the inner circle of the base, and the other end is connected to the input end of the high-temperature circulating fan, one end of the first circulating gas outlet pipe is connected to the center of the inner circle of the steel coil in the inner cover close to the upper end surface of the steel coil, one end of the second circulating gas outlet pipe is connected to the space surrounded by the upper part of the trolley in the inner cover, the outer circle of the base and the lower end surface of the bottom plate, the other end of the first circulating gas outlet pipe or the second circulating gas outlet pipe is connected to the output end of the high-temperature circulating fan, the first cooler is arranged on the first circulating gas outlet pipe, the second cooler is arranged on the circulating gas inlet pipe, the first pipeline valve is arranged on the first circulating gas outlet pipe 7, and the second pipeline valve is arranged on the second circulating gas outlet pipe.

[0021] The outer side of the inner cover is covered with a heat insulation material layer.

[0022] The thermal insulation material layer is 600-1200 mm wide and 3-10 mm thick.

[0023] The upper end surface of the steel coil is covered with a cover plate with a thickness of 0.2-2.0 mm.

[0024] The cover plate is made by cutting a steel plate with a magnesium oxide or aluminum oxide isolation coating on the surface, and is not bonded to the upper end surface of the steel coil.

[0025] A plate temperature thermocouple is arranged in the inner cover.

[0026] The high-temperature circulation fan, the first pipeline cooler and the second pipeline cooler are installed outside the furnace body and rotate synchronously with the trolley.

[0027] A cooling method for a high-temperature annealing device for annular furnace of oriented silicon steel coils comprises the following steps:

[0028] Step 1: Hoist the steel coil onto the bottom plate and place it vertically;

[0029] Step 2: The flow rate into the inner cover is 10-20Nm 3 / h of pure nitrogen, the gas pressure in the hood is controlled to be 100-300pa;

[0030] Step 3: The steel coil is running with the trolley. When the trolley enters the secondary heating stage, start the high-temperature circulation fan and open the second pipeline valve on the first circulation gas outlet pipe. The gas flow direction of the inner circle of the steel coil is: first circulation gas outlet pipe → upper end face of the inner circle of the steel coil → lower end face of the inner circle of the steel coil → circulation gas inlet pipe → high-temperature circulation fan → first circulation gas outlet pipe. Adjust the air volume of the high-temperature circulation fan to 10-20Nm 3 / H, control the temperature of the upper end surface of the inner ring of the steel coil ≤ the average temperature of the upper end surface of the steel coil. When the annular furnace is about to turn, the furnace gas circulation device is closed; when the annular furnace completes the turning operation, the high-temperature circulation fan is started again. The temperature of the circulating gas flowing into the hood is low, the temperature of the strip at the upper end surface of the inner ring of the steel coil is reduced, the radial compressive stress it is subjected to is reduced, and the probability of the occurrence of the inner convex defect is reduced;

[0031] Step 4: When the steel coil enters the high-temperature insulation stage, turn off the high-temperature circulation fan;

[0032] Step 5: After the steel coil has completed high-temperature insulation and entered the cooling stage, the inner ring gas circulation of the steel coil is started again. The gas flow direction of the inner ring of the steel coil is: the first circulating gas outlet pipe → the upper end face of the inner ring of the steel coil → the lower end face of the inner ring of the steel coil → the circulating gas inlet pipe → the high-temperature circulating fan → the first circulating gas outlet pipe. As the temperature of the steel coil drops, the air volume of the high-temperature circulating fan gradually increases to control the inner ring strip temperature of the steel coil to be lower than the outer ring strip temperature of the steel coil;

[0033] Step 6: When the trolley enters the third cooling stage, the protective gas in the furnace is pure nitrogen, the furnace temperature is ≤700℃, open the first pipeline valve on the second circulating gas outlet pipe, and control the air volume of the high-temperature circulating fan to 200-2000Nm 3 / h, the main gas flow direction in the inner cover is: the second circulating gas outlet pipe → the outside of the base → the outside of the bottom plate → the outside of the steel coil → the upper end face of the steel coil → the inner side of the inner circle of the steel coil → the inner side of the bottom plate → the inner side of the base → the inner circle circulating gas inlet pipe → the high-temperature circulating fan → the second circulating gas outlet pipe, the second circulating gas outlet pipe is connected to the gas flow distributor, which can evenly distribute the gas to all directions of the lower end face of the inner cover, so that the gas flow from all directions in the inner cover to the upper end face of the steel coil is more uniform. Since the circulating gas temperature flowing into the cover is low and the circulating gas temperature flowing out of the cover is high, the overall cooling speed of the steel coil is accelerated, and the time required for the steel coil to cool in the third stage is reduced;

[0034] Step 7: After the steel coil is out of the furnace, turn off the high-temperature circulation fan, open the inner cover, and lift the steel coil to the cooling area outside the furnace. After the steel coil is cooled to a certain temperature, it is sent to the stretching and leveling unit for production.

[0035] The present invention increases the flow rate of gas in the inner ring area of ​​the steel coil by a high-temperature circulating fan, and the low-temperature gas reduces the temperature of the strip steel in the inner ring of the steel coil, thereby reducing the thermal stress of the strip steel in the outer ring of the steel coil, improving the plate shape quality of the strip steel after annealing, reducing the time required for cooling the steel coil, and improving the production efficiency of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the structure of the present invention;

[0037] Figure 2 It is a schematic diagram of stress analysis of steel coil;

[0038] Figure 3 Schematic diagram of radial pressure distribution of steel coil layer by layer after unloading the steel coil under different coiling tensions;

[0039] Figure 4 It is a schematic diagram of the temperature distribution curve of the longitudinal section of the steel coil during the heating stage;

[0040] Figure 5 It is a schematic diagram of the temperature distribution curve of the longitudinal section of the steel coil during the cooling stage;

[0041] Figure 6 It is a schematic diagram of the temperature distribution curve of the longitudinal section of the steel coil during the trolley cooling stage of the present invention.

[0042] In the figure, 1-trolley; 2-support; 3-bottom plate; 4-inner cover; 5-insulating material layer; 6-steel coil; 7-first circulating gas outlet pipe; 8-cover plate; 9-second circulating gas outlet pipe; 10-high-temperature circulating fan; 11a-first pipeline cooler; 11b-second pipeline cooler; 12a-first pipeline valve; 12b-second pipeline valve; 13-circulating gas inlet pipe; 14-protective gas inlet pipe; 15-plate temperature thermocouple. DETAILED DESCRIPTION

[0043] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments to facilitate a clear understanding of the present invention, but they do not constitute a limitation on the present invention.

[0044] The internal stress of the steel coil during high temperature annealing treatment is analyzed.

[0045] In the decarburization annealing process, the steel coil is coiled on a coiler.

[0046] The steel coil is then rolled by the coiler and transported to be placed vertically on the bottom plate. Before annealing begins, the stress condition in the steel coil is simplified to a plane axisymmetric problem for stress analysis, such as Figure 2 As shown in the figure: σ θ : tangential stress; σ r : radial stress; r0: inner diameter of steel coil; r n : outer diameter of steel coil; d θ : Polar angle; According to the formula:

[0047] r(dσ r / dr)+σ r -σ θ =0

[0048] In the formula, σ r and σ θ are radial stress and tangential stress respectively, r is the radius of the steel coil, r0≤r≤r n .

[0049] When the influence of thermal stress can be ignored at room temperature, the internal stress of the steel coil is redistributed after unloading. Figure 3 As shown in the figure, an isolation agent composed of MgO powder and the like is applied between each layer of the steel coil, and the radial forces between the steel strip layers in the steel coil are all compressive stress. The radial compressive stress of the steel strip of a certain thickness in the innermost circle of the steel coil is 0. As the number of steel strip layers increases, the radial compressive stress between the layers of the inner circle steel strip increases rapidly; after reaching the increased value, the pressure between the steel strip layers gradually decreases. As the diameter of the steel strip approaches the outer circle of the steel coil, it decreases rapidly as the number of steel strip layers increases, and the radial compressive stress on the steel strip of the outermost circle of the steel coil is 0.

[0050] When the steel coil is annealed at high temperature in a ring furnace / bell furnace, the influence of the temperature field must also be considered. The relationship between the radial strain and stress of the steel coil can be expressed by the following formula:

[0051]

[0052] Where, E-elastic modulus of material;

[0053] μ-Poisson's coefficient of the material;

[0054] ε r - radial strain of the strip;

[0055] εn - Additional strain caused by contact between the strips;

[0056] α- radial thermal expansion coefficient of the material;

[0057] T-strip temperature;

[0058] The internal temperature distribution of the steel coil during the heating stage is as follows Figure 4 As shown, the outer ring nth layer strip temperature T n Than the n-1th layer strip temperature T n-1 , so the radial strain of the n-th layer of strip steel is greater than the radial strain between the n-1-th layer of strip steel, so Δε r，n >0, that is, the gap between the outer ring strip steel increases during the heating stage, and the radial compressive stress of the outer ring strip steel decreases. For the inner ring steel strip, the opposite is true, Δε r，n <0, that is, the gap between the inner ring strip steel decreases during the heating stage, resulting in an increase in the radial compressive stress between the inner ring strip steel. In particular, the upper end surface of the steel coil is directly subjected to the radiation heat transfer of the burner on the furnace body, and the radial compressive stress between the strip steel increases rapidly. When the radial compressive stress of the inner ring strip steel is too large, it is easy to form an inner convex defect (heart-shaped coil). Therefore, lowering the inner ring temperature of the steel coil during the heating stage is conducive to reducing the occurrence of inner convex defects (heart-shaped coils).

[0059] The internal temperature distribution of the steel coil during the cooling stage is as follows Figure 5 As shown, the outer ring is strip steel T n <T n-1 , Δε r，n <0, the gap between the outer ring strip steel decreases, resulting in an increase in the radial compressive stress of the outer ring strip steel. When the radial compressive stress of the outer ring strip steel increases, its tangential stress increases accordingly. When the tangential stress is greater than the yield strength of the strip steel, the strip steel undergoes plastic deformation. When the plastic deformation is too large and the leveling unit cannot eliminate it, the oriented silicon steel product will be warped. Inner ring strip steel T n >T n-1 , radial displacement difference of strip steel between adjacent layers Δε r，n >0. When the cooling speed of the inner ring of the steel coil is accelerated, the interlayer temperature difference ΔT between the inner ring strip steel n Increase, Δε r，n Increase, the gap between the strip layers increases, and the radial compressive stress decreases. Therefore, accelerating the cooling of the inner ring strip of the steel coil will not lead to the deterioration of the shape quality of the inner ring strip of the steel coil. When the cooling speed of the inner ring of the steel coil is accelerated, the temperature distribution inside the steel coil is as follows Figure 6 As shown in the figure, the hot spot in the steel coil moves outward, the thermal stress on the outer ring of the steel coil is reduced, and the shape degradation of the outer ring of the steel coil is suppressed. That is, in the cooling stage, accelerating the cooling speed of the inner ring of the steel coil is conducive to improving the shape of the outer ring of the steel coil.

[0060] According to the analysis results, it is proposed to increase the gas flow rate in the inner ring area of ​​the steel coil during the cooling stage, accelerate the cooling speed of the inner ring strip of the steel coil, reduce the tangential stress of the steel coil strip, and reduce the plastic deformation of the strip during the cooling process. The present invention is further described below in conjunction with specific embodiments.

[0061] like Figure 1 As shown, the present invention provides a high temperature annealing device for oriented silicon steel ring furnace steel coil, comprising:

[0062] A trolley 1, used for carrying a heated steel coil 6;

[0063] A base 2 is placed on the trolley 1 and is used to support a bottom plate 3;

[0064] The bottom plate 3 is used to place the heated steel coil 6, and the steel coil 6 is placed vertically on the bottom plate 3;

[0065] An inner cover 4 is mounted on the trolley 1 and is used to cover the area where the steel coil 6 is located. A protective gas is passed through the inner cover 4.

[0066] The protective gas inlet pipe 14, the protective gas passed inside is one of N2 and H2 or a mixture of N2 and H2 mixed in a certain ratio, which is used to prevent the steel coil from being oxidized;

[0067] The furnace gas circulation device is installed outside the furnace body, rotates synchronously with the trolley 1, and is connected to the inner cover 4, so as to speed up the gas flow speed in a part of the area inside the inner cover 4.

[0068] The furnace gas circulation device includes a circulating gas inlet pipe 13, a first circulating gas outlet pipe 7, a second circulating gas outlet pipe 9, a high-temperature circulating fan 10, a first cooler 11a and a second cooler 11b, a first pipeline valve 12a and a second pipeline valve 12b; one end of the circulating gas inlet pipe 13 is connected to the space enclosed by the upper part of the trolley 1 in the inner cover 4 and the inner circle of the base 2, and the other end is connected to the input end of the high-temperature circulating fan 10, and one end of the first circulating gas outlet pipe 7 is connected to the inner circle center of the steel coil 6 in the inner cover 4 close to the upper end of the steel coil 6 At the surface, one end of the second circulating gas outlet pipe 9 is connected to the space enclosed by the upper part of the trolley 1 in the inner cover 4, the outer circle of the base 2 and the lower end surface of the bottom plate 3, the other end of the first circulating gas outlet pipe 7 or the second circulating gas outlet pipe 9 is connected to the output end of the high-temperature circulating fan 10, the first cooler 11a is arranged on the first circulating gas outlet pipe 7, the second cooler 11b is arranged on the circulating gas inlet pipe 13, the first pipeline valve 12a is arranged on the first circulating gas outlet pipe 7, and the second pipeline valve 12b is arranged on the second circulating gas outlet pipe 9.

[0069] The outer side of the inner cover 4 is covered with a heat insulation material layer 5 .

[0070] The heat insulating material layer 5 is 600-1200 mm wide and 3-10 mm thick.

[0071] The upper end surface of the steel coil 6 is covered with a cover plate 8 with a thickness of 0.2-2.0 mm.

[0072] The cover plate 8 is made by cutting a steel plate with a magnesium oxide or aluminum oxide isolation coating on the surface, and is not bonded to the upper end surface of the steel coil 6.

[0073] A plate temperature thermocouple 15 is provided in the inner cover 4 .

[0074] The high-temperature circulation fan 10 , the first duct cooler 11 a and the second duct cooler 11 b are installed outside the furnace body and rotate synchronously with the trolley 1 .

[0075] There are two furnace gas circulation paths in the present invention. In circulation mode 1, the air inlet of the device is set in the space enclosed by the upper part of the trolley 1 and the inner circle of the base 2, and the air outlet of the circulation device is set at the center of the inner circle of the steel coil 6 close to the upper end surface of the steel coil 6, mainly to accelerate the flow of gas in the inner circle of the steel coil 6. When the temperature of the steel coil 6 is high during the heating stage and the cooling stage, circulation mode 1 is used; circulation mode 2, the air inlet of the device is set in the space enclosed by the upper part of the trolley 1 and the inner circle of the base 2, and the air outlet of the circulation device is set in the space enclosed by the upper part of the trolley 1 and the outer circle of the base 2 and the lower surface of the bottom plate 3, which accelerates the flow of gas in the entire inner cover 4. When the temperature of the steel coil 6 is low during the cooling stage, circulation mode 2 is used. The air inlet is set in the space enclosed by the upper part of the trolley 1 and the inner circle of the base 2, which can avoid the occurrence of a low-pressure area at the sand seal of the inner cover 4 and prevent the diffusion of gas outside the inner cover 4 into the inner cover 4.

[0076] The existence of the cover plate 8 reduces the heat radiation efficiency between the top of the steel coil 8 and the furnace top, reduces the radial temperature difference of the upper end surface of the steel coil 6, and reduces the temperature gradient of the strip in the vertical direction. After annealing, the upper end surface flange defect, the upper end surface edge wave and the inner convex defect of the inner ring of the steel coil are reduced, and the final product yield rate is improved.

[0077] In the present invention, the presence of the heat insulating material layer 5 on the outer side of the inner cover 4 reduces the heat radiation heat transfer efficiency on the outer side of the steel coil, and reduces the radial temperature difference of the steel coil during the heating and cooling process.

[0078] Embodiment: The cooling method of the present invention comprises:

[0079] Step 1: The trolley 1 is in the loading area, the protective gas pipeline is purged, the high-temperature circulation fan 10 is started, and the circulation pipeline condition test is completed respectively. After the test is completed, the high-temperature circulation fan 10 is turned off.

[0080] Step 2: hoist the steel coil 6 onto the bottom plate 3 and place it vertically. Cover the upper end of the steel coil 6 with a 0.3 mm thick cover plate 8 coated with MgO. The cover plate 8 is annular or composed of multiple sector plates and can cover the upper end of the steel coil 6.

[0081] Step 3: Buckle the inner cover 4. The outer side of the inner cover 4 corresponding to the steel coil 6 is wrapped with a 600-1200mm wide and 3-10mm thick insulation material layer 5, and the flow rate is 10-20Nm 3 / h of pure nitrogen to drive out the air in the cover, and adjust the insertion depth of the inner cover 4 into the sealing sand by knocking and vibrating the inner cover 4 to control the gas pressure in the cover to 100-300Pa.

[0082] Step 4: The steel coil 6 is operated with the trolley 1, and the heating, heat preservation, protective gas introduction and other operations are carried out according to the process requirements. When the trolley 1 enters the secondary heating stage, the high-temperature circulation fan 10 is started, and the second pipeline valve 12b on the first circulation gas outlet pipe 7 is opened. The gas flow direction of the inner circle of the steel coil is: the first circulation gas outlet pipe 7 → the upper end face of the inner circle of the steel coil 6 → the lower end face of the inner circle of the steel coil 6 → the circulation gas inlet pipe 13 → the high-temperature circulation fan 10 → the first circulation gas outlet pipe 7, and the air volume of the high-temperature circulation fan 10 is adjusted to 10-20Nm 3 / H, control the temperature of the upper end surface of the inner ring of the steel coil 6 ≤ the average temperature of the upper end surface of the steel coil 6. When the annular furnace is about to turn, the furnace gas circulation device is closed; when the annular furnace completes the turning operation, the high-temperature circulation fan 10 is started again, the temperature of the circulating gas flowing into the cover is low, the temperature of the strip at the upper end surface of the inner ring of the steel coil 6 is reduced, the radial compressive stress it is subjected to is reduced, and the probability of the occurrence of the inner convex defect is reduced.

[0083] Step 5: When the steel coil 6 enters the high-temperature insulation stage, the high-temperature circulation fan 10 is turned off.

[0084] Step 6: When the steel coil 6 completes high-temperature insulation and enters the first cooling stage, the inner ring gas circulation of the steel coil 6 is started again. The inner ring gas flow direction of the steel coil 6 is: the first circulating gas outlet pipe 7 → the upper end face of the inner ring of the steel coil 6 → the lower end face of the inner ring of the steel coil 6 → the circulating gas inlet pipe 13 → the high-temperature circulating fan 10 → the first circulating gas outlet pipe 7. As the temperature of the steel coil 6 decreases, the air volume of the high-temperature circulating fan 10 gradually increases, and the temperature of the inner ring strip of the steel coil 6 is controlled to be lower than the temperature of the outer ring strip of the steel coil 6. At this time, the hot spot of the steel coil 6 moves outward, and the radial compressive stress and tangential tensile stress of the outer ring strip of the steel coil 6 are reduced. Therefore, the critical cooling speed of the steel coil 6 at each temperature in the first cooling stage and the second cooling stage without buckling defects increases, and the time required for the steel coil 6 to go from high-temperature insulation to exit the second cooling stage is reduced.

[0085] Step 7: When the trolley 1 enters the third cooling stage, the protective gas in the furnace is pure nitrogen, the furnace temperature is ≤700℃, the first pipeline valve 12a on the second circulating gas outlet pipe 9 is opened, and the air volume of the high-temperature circulating fan 10 is controlled to 200-2000Nm 3 / h, the main gas flow direction in the inner cover 4 is: second circulating gas outlet pipe 9→outside of base 2→outside of bottom plate 3→outside of steel coil 6 circle→upper end face of steel coil 6→inside of inner circle of steel coil 6→inside of bottom plate 3→inside of base 2→inner circle circulating gas inlet pipe 13→high temperature circulating fan 10→second circulating gas outlet pipe 9, the second circulating gas outlet pipe 9 is connected to the gas flow distributor, which can evenly distribute the gas to all directions of the lower end face of the inner cover 4, so that the gas flow from all directions in the inner cover 4 to the upper end face of the steel coil 6 is more uniform, because the circulating gas temperature flowing into the cover is low and the circulating gas temperature flowing out of the cover is high, the overall cooling speed of the steel coil 6 is accelerated, and the time required for the steel coil 6 in the third cooling stage is reduced.

[0086] Step 8: After the steel coil 6 is taken out of the furnace, the high-temperature circulation fan 10 is turned off, the inner cover 4 is opened, and the steel coil 6 is hoisted to the cooling area outside the furnace. After the steel coil 6 is cooled to a certain temperature, it is sent to the stretching and leveling unit for production.

[0087] Table 1 Experimental conditions of the embodiments and comparative examples of the present invention

[0088]

[0089] In this embodiment, the annealing device of the present invention is used for annealing of samples No. 1 and No. 2. The bottom plate temperatures of the two steel coils when entering and exiting the cooling section are similar, but the cooling rate of sample 1 in the cooling section is about 4°C / h faster than that of sample 2, and its residence time in the cooling section is about 8 hours less than that of embodiment 2.

[0090] Table 2: Defects of the steel coil after stretching and annealing in the embodiment of the present invention

[0091]

[0092] As can be seen from the table, the plate quality of sample 1 and sample 2 is better. Although the cooling time of sample 1 is 8 hours less than that of sample 2 in the embodiment, there is no obvious difference in the plate quality of the two samples.

[0093] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A high temperature annealing device for oriented silicon steel ring furnace steel coil, characterized in that: include A trolley (1) for carrying a heated steel coil (6); A base (2) is placed on the trolley (1) and is used to support the bottom plate (3); A bottom plate (3) for placing the heated steel coil (6); An inner cover (4) is covered on the trolley (1) and is used to cover the area where the steel coil (6) is located, and a protective gas is passed through the inner cover (4); A protective gas inlet pipe (14) is provided to allow protective gas to flow therein to prevent the steel coil from being oxidized; A furnace gas circulation device is installed outside the furnace body, rotates synchronously with the trolley (1), and is connected to the inner cover (4), and is used to accelerate the gas flow speed in a part of the area inside the inner cover (4); The furnace gas circulation device comprises a circulating gas inlet pipe (13), a first circulating gas outlet pipe (7), a second circulating gas outlet pipe (9), a high-temperature circulating fan (10), a first cooler (11a) and a second cooler (11b), a first pipeline valve (12a) and a second pipeline valve (12b); one end of the circulating gas inlet pipe (13) is connected to the space enclosed by the upper part of the trolley (1) inside the inner cover (4) and the inner circle of the base (2), and the other end is connected to the input end of the high-temperature circulating fan (10); one end of the first circulating gas outlet pipe (7) is connected to the center of the inner circle of the steel coil (6) inside the inner cover (4) close to the upper end surface of the steel coil (6) , one end of the second circulating gas outlet pipe (9) is connected to the space enclosed by the upper part of the inner trolley (1) of the inner cover (4), the outer ring of the base (2) and the lower end surface of the bottom plate (3); the other end of the first circulating gas outlet pipe (7) or the second circulating gas outlet pipe (9) is connected to the output end of the high-temperature circulating fan (10); the first cooler (11a) is arranged on the first circulating gas outlet pipe (7); the second cooler (11b) is arranged on the circulating gas inlet pipe (13); the first pipeline valve (12a) is arranged on the second circulating gas outlet pipe (9); and the second pipeline valve (12b) is arranged on the first circulating gas outlet pipe (7); The cooling method of the high-temperature annealing device of the oriented silicon steel ring furnace steel coil comprises the following steps: Step 1: hoist the steel coil (6) onto the bottom plate (3) and place it in a vertical position; Step 2: The flow rate into the inner cover (4) is 10-20Nm 3 / h of pure nitrogen, and the gas pressure in the hood is controlled to be 100-300Pa; Step 3: The steel coil (6) is operated along with the trolley (1). When the trolley (1) enters the secondary heating stage, the high-temperature circulation fan (10) is started, and the second pipeline valve (12b) on the first circulation gas outlet pipe (7) is opened. The gas flow direction of the inner circle of the steel coil (6) is: first circulation gas outlet pipe (7) → the upper end surface of the inner circle of the steel coil (6) → the lower end surface of the inner circle of the steel coil (6) → the circulation gas inlet pipe (13) → the high-temperature circulation fan (10) → the first circulation gas outlet pipe (7). The air volume of the high-temperature circulation fan (10) is adjusted to 10-20Nm 3 / h, control the temperature of the upper end surface of the inner ring of the steel coil (6) ≤ the average temperature of the upper end surface of the steel coil (6), and when the annular furnace is about to be turned, the furnace gas circulation device is closed; when the annular furnace completes the turning operation, the high-temperature circulation fan (10) is started again, the temperature of the circulating gas flowing into the cover is low, the temperature of the strip at the upper end surface of the inner ring of the steel coil (6) is reduced, the radial compressive stress it is subjected to is reduced, and the probability of the occurrence of the inner convex defect is reduced; Step 4: When the steel coil (6) enters the high-temperature insulation stage, the high-temperature circulation fan (10) is turned off; Step 5: When the steel coil (6) has completed the high-temperature insulation and entered the cooling stage, the inner ring gas circulation of the steel coil (6) is started again. The inner ring gas flow direction of the steel coil (6) is: first circulating gas outlet pipe (7) → upper end surface of the inner ring of the steel coil (6) → lower end surface of the inner ring of the steel coil (6) → circulating gas inlet pipe (13) → high-temperature circulating fan (10) → first circulating gas outlet pipe (7). As the temperature of the steel coil (6) decreases, the air volume of the high-temperature circulating fan (10) gradually increases to control the inner ring strip temperature of the steel coil (6) to be lower than the outer ring strip temperature of the steel coil (6); Step 6: When the trolley (1) enters the third cooling stage, the protective gas in the furnace is pure nitrogen, the furnace temperature is ≤700°C, the first pipeline valve (12a) on the second circulating gas outlet pipe (9) is opened, and the air volume of the high-temperature circulating fan (10) is controlled to 200-2000Nm 3 / h, the main gas flow direction in the inner cover (4) is: the second circulating gas outlet pipe (9) → the outer side of the base (2) → the outer side of the bottom plate (3) → the outer side of the steel coil (6) circle → the upper end surface of the steel coil (6) → the inner side of the inner circle of the steel coil (6) → the inner side of the bottom plate (3) → the inner side of the base (2) → the inner circle circulating gas inlet pipe (13) → the high-temperature circulating fan (10) → the second circulating gas outlet pipe (9), the second circulating gas outlet pipe (9) is connected to the gas flow distributor to evenly distribute the gas to all directions of the lower end surface of the inner cover (4), so that the gas flow in all directions in the inner cover (4) toward the upper end surface of the steel coil (6) is more uniform. Since the circulating gas flowing into the cover has a low temperature and the circulating gas flowing out of the cover has a high temperature, the overall cooling speed of the steel coil (6) is accelerated, and the time required for the steel coil (6) to cool in the third stage is reduced; Step 7: After the steel coil (6) is taken out of the furnace, the high-temperature circulation fan (10) is turned off, the inner cover (4) is opened, and the steel coil (6) is hoisted to the cooling area outside the furnace. After the steel coil (6) is cooled, it is sent to the stretching and leveling unit for production.

2. The device for high temperature annealing of oriented silicon steel coil in annular furnace according to claim 1, characterized in that: The outer side of the inner cover (4) is covered with a heat insulation material layer (5).

3. The device for high temperature annealing of oriented silicon steel coil in annular furnace according to claim 2, characterized in that: The thermal insulation material layer (5) is 600-1200 mm wide and 3-10 mm thick.

4. The device for high temperature annealing of oriented silicon steel coil in annular furnace according to claim 1, characterized in that: The upper end surface of the steel coil (6) is provided with a cover plate (8) having a thickness of 0.2-2.0 mm.

5. The device for high temperature annealing of oriented silicon steel coil in annular furnace according to claim 4, characterized in that: The cover plate (8) is cut and made from a steel plate with a magnesium oxide or aluminum oxide isolation coating on its surface, and is not bonded to the upper end surface of the steel coil (6).

6. The device for high temperature annealing of oriented silicon steel coil in annular furnace according to claim 1, characterized in that: A plate temperature thermocouple (15) is provided in the inner cover (4).

7. The device for high temperature annealing of oriented silicon steel coil in annular furnace according to claim 1, characterized in that: The high-temperature circulation fan (10), the first pipeline cooler (11a) and the second pipeline cooler (11b) are installed outside the furnace body and rotate synchronously with the trolley (1).

Images