Steel strip manufacturing apparatus, continuous annealing facility and manufacturing method

Abstract

A steel strip manufacturing device related to the present invention comprises a first water tank unit for storing cooling water for immersing and cooling a steel strip, a water cooling nozzle unit installed in the first water tank unit and spraying cooling water onto the surface of the steel strip, a second water tank unit connected to the first water tank unit through a connector, an opening and closing door for opening and closing the connector, and a conveying control unit for conveying the water cooling nozzle unit so that the water cooling nozzle unit passes through the connector and is positioned somewhere between a cooling water spraying position in the first water tank unit and a non-water cooling standby position in the second water tank unit.

Description

Technology Field

[0001] The present invention relates to a steel strip manufacturing apparatus, a continuous annealing facility, and a manufacturing method. Background Technology

[0002] In the continuous annealing process of steel strips, controlling heat treatment conditions such as heating and cooling is crucial to impart the required mechanical properties to the strips. In particular, controlling the cooling rate of the steel strip is important for controlling the microstructure of the steel by actively utilizing the characteristics of the steel's phase transformation. Generally, a continuous annealing line for carrying out the continuous annealing process of steel strips is equipped with a heating zone, a cracking zone, and a cooling zone. Cooling methods for the steel strip in the cooling zone include water quenching, roll cooling, steam-water (mist) cooling, and gas jet cooling, and an appropriate cooling method is selected to control the material properties of the steel strip. Particularly in the manufacture of high-strength steel sheets, the water quenching method is frequently used because it allows for a rapid cooling rate and reduces the addition of alloying elements to increase strength. In the water quenching method, the steel strip is immersed in cooling water, and the strip is cooled by cooling water sprayed from a water cooling nozzle unit installed in the cooling water.

[0003] However, when switching the cooling method of a steel strip from the water quenching method to another cooling method, it is necessary to protect the water cooling nozzle unit from heat because the interior of the cooling strip may become relatively high temperature in cooling methods other than water quenching. For this reason, when switching the cooling method of a steel strip from the water quenching method to another cooling method, at least the operation of removing the water cooling nozzle unit from the furnace is carried out. However, when removing the water cooling nozzle unit from the furnace, it is necessary to open a part of the furnace to the atmosphere, remove the water cooling nozzle unit from the furnace, and then replace the atmosphere inside the furnace with a non-oxidizing gas, so a lot of time is required to switch the cooling method. Against this background, Patent Document 1 proposes a steel strip manufacturing apparatus capable of supplying cooling gas to the water spray nozzle while providing a reflector that suppresses radiation or heat conduction from the steel strip between the water spray nozzle and the steel strip. According to this steel band manufacturing device, even when switching from a water quenching method to another cooling method, the task of removing the water spray nozzle from the furnace can be omitted, so the time required to switch cooling methods can be shortened. Prior art literature

[0004] Japanese Patent Publication No. 5891857 The problem to be solved

[0005] However, in cooling methods other than water quenching, the temperature of the steel strip in the cooling zone becomes high, exceeding 200°C, and the operating time becomes long. For this reason, even with the steel strip manufacturing apparatus described in Patent Document 1, there is a problem in that the lifespan of the water spray nozzle is shortened due to heat. In addition, when switching from the water quenching method to another cooling method, it is necessary to supply cooling gas to dry the water spray nozzle, and the dew point inside the furnace may fluctuate during the time until the water spray nozzle is dried. Therefore, there is room for improvement in that a long time is required to stabilize the heat treatment conditions of the steel strip after switching the cooling method.

[0006] The present invention is made to solve the above problem, and its purpose is to provide a steel strip manufacturing apparatus, a continuous annealing facility, and a manufacturing method that can reduce the time required to switch between a water-cooling method and a non-water-cooling method. means of solving the problem

[0007] A steel strip manufacturing device related to the present invention comprises a first water tank unit for storing cooling water for immersing and cooling a steel strip, a water cooling nozzle unit installed in the first water tank unit and spraying cooling water onto the surface of the steel strip, a second water tank unit connected to the first water tank unit through a connector, an opening and closing door for opening and closing the connector, and a conveying control unit for conveying the water cooling nozzle unit so that the water cooling nozzle unit passes through the connector and is positioned somewhere between a cooling water spraying position in the first water tank unit and a non-water cooling standby position in the second water tank unit.

[0008] The above water cooling nozzle unit is supported by a support connected to the above return control unit, and the support may be provided with a sunshade that closes the connection when the water cooling nozzle unit is located at the cooling water spray position.

[0009] The above water cooling nozzle unit may be equipped with a water spray nozzle that sprays cooling water onto the surface of the steel strip, in addition to a restraining roll that restrains the steel strip by at least one pair of rolls.

[0010] The continuous annealing facility for steel strips related to the present invention is equipped with the steel strip manufacturing device on a cooling plate.

[0011] A reducing gas or a non-oxidizing gas may be supplied to the above cooling zone.

[0012] A method for manufacturing a steel strip related to the first aspect of the present invention is a method for manufacturing a steel strip using a steel strip manufacturing apparatus related to the present invention, comprising: a non-water cooling step of cooling the steel strip without spraying cooling water on the surface of the steel strip in the first water tank section; a water supply step of supplying cooling water to the first water tank section and the second water tank section after the completion of the non-water cooling step; an opening step of opening the opening / closing door of the connector; a nozzle unit loading step of conveying the water cooling nozzle unit so that the water cooling nozzle unit passes through the connector section and moves from the non-water cooling standby position to the cooling water spraying position; and a water cooling step of immersing the steel strip in cooling water stored in the first water tank section while spraying cooling water on the surface of the steel strip using the water cooling nozzle unit.

[0013] A method for manufacturing a steel strip related to a second aspect of the present invention is a method for manufacturing a steel strip using a steel strip manufacturing apparatus related to the present invention, comprising: a water cooling step of immersing and cooling the steel strip in cooling water within a first water tank while spraying cooling water onto the surface of the steel strip using the water cooling nozzle unit; a nozzle unit withdrawal step of returning the water cooling nozzle unit so that, after the completion of the water cooling step, the water cooling nozzle unit passes through the connector and moves from the cooling water spraying position to the non-water cooling standby position; a closing step of closing the opening and closing door of the connector; a draining step of draining the cooling water within at least the first water tank; and a non-water cooling step of cooling the steel strip without spraying cooling water onto the surface of the steel strip in the first water tank.

[0014] The method for manufacturing a steel strip related to the present invention manufactures a steel strip using a continuous annealing facility for the steel strip. Effects of the invention

[0015] According to the steel strip manufacturing apparatus, continuous annealing facility, and manufacturing method related to the present invention, the time required to switch between a water-cooling method and a non-water-cooling method can be reduced. Brief explanation of the drawing

[0016] FIG. 1 is a schematic diagram showing the configuration of a continuous annealing facility, which is an embodiment of the present invention. Figure 2 is a diagram showing the thermal history of a steel strip during the annealing and reheating processes. Figure 3 is a side view showing the configuration of a water-cooled cooling device. Figure 4 is a front view and a top view showing the configuration of a water-cooled cooling device. Figure 5 is a drawing showing an example of the configuration of the opening of the connector. FIG. 6 is a side view showing the configuration of a modified example of the cooling device shown in FIG. 3. Figure 7 is a side view showing the configuration of a non-water-cooled cooling device. FIG. 8 is a front view and a top view showing the configuration of a non-water-cooled cooling device. FIG. 9 is a drawing for explaining a method of switching from a non-water-cooling method to a water-cooling method, which is an embodiment of the present invention. FIG. 10 is a drawing for explaining a method of switching from a water-cooled method to a non-water-cooled method, which is an embodiment of the present invention. Specific details for implementing the invention

[0017] Hereinafter, with reference to the drawings, an apparatus for manufacturing a steel strip, a continuous annealing facility, and a manufacturing method according to an embodiment of the present invention will be described. Furthermore, the apparatus for manufacturing a steel strip according to an embodiment of the present invention constitutes part of a continuous annealing facility that performs heat treatment on a steel plate whose thickness has been reduced to a predetermined plate thickness through a hot rolling process, a pickling process, and a cold rolling process. Also, since the steel plate is wound into a coil and then heat treatment, etc. is performed at least after the hot rolling process, the steel plate is referred to as a "steel strip" in this specification.

[0018] [Continuous Annealing Equipment]

[0019] First, with reference to FIGS. 1 and FIGS. 2, the configuration of a continuous annealing facility, which is an embodiment of the present invention, will be described.

[0020] FIG. 1 is a schematic diagram showing the configuration of a continuous annealing facility according to one embodiment of the present invention. As shown in FIG. 1, a continuous annealing facility (1) according to one embodiment of the present invention is a facility for manufacturing cold-rolled steel sheets and is installed in a continuous annealing line (CAL) that performs a manufacturing process of cold-rolled steel sheets including an annealing process. In this embodiment, the continuous annealing facility (1) is equipped with an inlet facility, a furnace body, and an outlet facility.

[0021] The inlet side equipment is equipped with a payoff reel, a welding machine, an electrolytic cleaning device, and an inlet side looper. The furnace body is equipped with an annealing section and a reheating section. The annealing section is equipped with a heating zone (2), a cracking zone (3), and a cooling zone (4), and may also have a preheating zone upstream of the heating zone (2). The reheating section is equipped with a reheating zone, an overaging zone, and a final cooling zone, and an induction heating device (5) is arranged in the reheating zone. The outlet side equipment is equipped with an outlet side looper, a temper rolling facility, an inspection facility, and a tension reel.

[0022] The annealing process is a process of raising the temperature of a steel strip from near room temperature, maintaining it at a predetermined temperature, and then lowering the temperature to near room temperature. In the continuous annealing facility (1) shown in FIG. 1, the annealing process is performed in the heating zone (2), the cracking zone (3), and the cooling zone (4). The reheating process is a process of performing over-aging treatment on the steel strip (S) that has passed through the cooling zone (4). In the continuous annealing facility (1) shown in FIG. 1, the reheating process is performed in the reheating zone, the over-aging zone, and the final cooling zone.

[0023] The heating zone (2) is a facility for raising the temperature of the steel plate (S), and heats the steel plate (S) to a preset temperature within a range of about 600 to 900°C depending on the steel type. In the heating zone (2), a direct flame or radiant combustion burner is used as a heating device. Since these heating devices have a large heating capacity and a relatively fast response, it is easy to change the temperature rise history when changing the heat cycle. The cracking zone (3) is a facility for maintaining the steel plate (S) at a predetermined temperature, and is a facility with a heating capacity sufficient to supplement the heat radiated from the furnace body, etc.

[0024] The cooling unit (4) is a facility for cooling the steel plate (S) to a predetermined temperature, and water cooling (water quench), gas jet cooling, roll cooling, and mist cooling (gas-liquid mixed cooling) are used as cooling means. Water cooling is a cooling means that cools the steel plate (S) by immersing it in an immersion tank installed downstream of the cracking unit (3). Gas jet cooling is a cooling means that cools the steel plate (S) by spraying gas onto the surface of the steel plate (S) from a nozzle. Roll cooling is a cooling means that cools the steel plate (S) by bringing the steel plate (S) into contact with a water-cooled roll. Mist cooling is a cooling means that cools the steel plate (S) by spraying water in the form of fine mist and absorbing the heat of vaporization.

[0025] In this embodiment, a cooling method using water cooling as the cooling means is called a water cooling method, and a cooling method using other cooling means is called a non-water cooling method. In addition, mist cooling uses water as a refrigerant, and since the size of the sprayed water droplets is very fine (about 0.1 to 1 mm) and the refrigerant vaporizes upon impact with the steel strip (S), a water tank for recovering water is not required, so this is included in the non-water cooling method. That is, in this embodiment, using an immersion tank as a cooling method for the steel strip (S) and immersing the steel strip (S) in the immersion tank is called a water cooling method, and cooling by other methods is called a non-water cooling method. In addition, gas jet cooling, roll cooling, and mist cooling, which are included as non-water cooling methods, may be combined in two or more ways in the cooling tank (4) to cool the steel strip (S), and such cases are also included in the non-water cooling method. However, if a non-water cooling method is combined with a water cooling method using an immersion tank, the water cooling method shall be used.

[0026] The reheating zone is positioned downstream of the cooling zone (4) and reheats the steel strip (S) to a temperature of about 300 to 400°C using an induction heating device (5). The overaging zone is a facility for performing an overaging treatment by maintaining the reheated steel strip (S) for a predetermined time. The final cooling zone is a facility for finally cooling the steel strip (S) that has undergone the overaging treatment to near room temperature. However, a continuous annealing facility that does not have a reheating zone may also be used.

[0027] FIG. 2 is a diagram showing the thermal history of a steel strip during an annealing process and a reheating process. In FIG. 2, the horizontal axis represents time, and the vertical axis represents the temperature of the steel strip. The temperature of the steel strip is, for example, the surface temperature of the steel strip (S). An annealing process is performed by a heating zone (2), a cracking zone (3), and a cooling zone (4), and thereafter, a reheating process is performed by a reheating zone, an overaging zone, and a final cooling zone. In order to suppress material non-uniformity depending on the longitudinal position of the steel strip (S), the conveying speed (line speed) of the steel strip (S) during the annealing process is maintained constant. However, if steel strips (S) with different thicknesses, widths, steel grades, etc. are welded together, the conveying speed may change while the welded part passes through the continuous annealing facility. The operating conditions of the continuous annealing facility, including the operating conditions of the cooling device, are set by a control computer that oversees the operation of the continuous annealing facility and are appropriately reset according to changes in the conveying speed, etc.

[0028] A mixed gas containing hydrogen, nitrogen, and water vapor is supplied to the interiors of the heating zone (2), cracking zone (3), and cooling zone (4) where the annealing process is performed, thereby controlling the atmosphere of the annealing process. Since the atmosphere of the annealing process affects oxides, etc. formed on the surface of the steel band (S), the composition and flow rate of the supplied gas are adjusted. For example, a reducing gas or a non-oxidizing gas is supplied to the cooling zone (4). As the reducing gas, a H2-N2 mixed gas is typically used, and, for example, a gas having a composition consisting of H2: 1 to 20 volume%, with the remainder being N2 and unavoidable impurities (dew point: about -60°C) is supplied. Also, as the non-oxidizing gas, a gas having a composition consisting of, for example, N2 and unavoidable impurities (dew point: about -60°C) is used.

[0029] In the cooling zone (4), gas controlling the atmosphere inside the furnace is supplied from inlets at two or more points in the height direction and two or more points in the length direction of the cooling zone (4) so ​​that reducing gas or non-oxidizing gas is supplied evenly. Also, since the gas supplied to the heating zone (2), cracking zone (3), and cooling zone (4) contains water vapor, the atmosphere in the annealing process is adjusted not only in the gas composition but also in the dew point. Because of this, a certain airtightness is ensured so that the atmosphere inside the heating zone (2), cracking zone (3), and cooling zone (4) is maintained as an atmosphere different from the atmosphere outside the furnace.

[0030] [Water-cooled cooling device]

[0031] Next, with reference to FIGS. 3 to 6, the configuration of a water-cooled cooling device will be described.

[0032] FIG. 3 is a side view showing the configuration of a cooling device when cooling a steel bar (S) by a water cooling method in a cooling unit (4). As shown in FIG. 3, the cooling device (10) is equipped with a water cooling nozzle unit (11) equipped with a water spray nozzle, an immersion water tank (12), and deflector rolls (13a, 13b). In addition, a pressing roll (14) is installed in the cooling device (10) to suppress deviation of the steel bar (S). In this cooling device (10), the steel bar (S) that has passed through the immersion water tank (12) has cooling water (W) attached to its surface removed by a water removal roll (15), is dried by a drying oven (16), and then sent to a reheating unit.

[0033] Additionally, the water removal roll (15) is preferably a metal roll to ensure sufficient heat resistance even when a non-water cooling method is used. However, instead of the water removal roll (15), a gas-type wiping device that sprays gas onto the surface of the steel strip (S) may be used. Also, in order to suppress the rise in temperature of the cooling water (W) stored in the immersion tank (12) and to control the temperature of the cooling water (W) within a predetermined range, the cooling device (10) may be equipped with a cooling chiller that circulates and cools the cooling water (W) in the immersion tank (12).

[0034] The water cooling nozzle unit (11) cools the steel band (S) by spraying cooling water onto the steel band (S). In the water cooling nozzle unit (11), a pair of water spray nozzles are arranged in multiple stages on the surface side of the moving steel band (S) to spray cooling water onto the surface side of the moving steel band (S). By spraying cooling water onto the surface side of the steel band (S) from the multiple stages of water spray nozzles, the steel band (S) that has passed through the cracked band (3) can be cooled.

[0035] The immersion tank (12) is shaped like a container to store cooling water (W) for immersing and cooling a steel bar (S). Additionally, the immersion tank (12) is equipped with a water supply valve for supplying cooling water (W) to the inside of the immersion tank (12) and a drain valve for discharging cooling water (W) stored inside the immersion tank (12). In this embodiment, the immersion tank (12) is equipped with a water supply and drainage device (20) that shares the water supply valve and the drainage valve, and the height of the liquid level of the cooling water (W) stored in the immersion tank (12) is adjusted by adjusting the opening of the water supply and drainage valve. However, the adjustment of the liquid level of the cooling water (W) may be performed by the operating operator visually adjusting the opening of the water supply valve or drain valve, or a liquid level control unit that controls the opening of the water supply valve or drain valve using a liquid level gauge may be provided.

[0036] The deflector rolls (13a, 13b) change the conveying direction of the steel strip (S) while restraining the steel strip (S) and applying a predetermined tension to the steel strip (S). As a result, the steel strip (S) immersed in the cooling water (W) stored in the immersion tank (12) is guided upward above the liquid level of the cooling water (W). In this case, at least one of the deflector rolls (13a, 13b) is positioned to be immersed in the cooling water (W) of the immersion tank (12).

[0037] FIGS. 4(a) and (b) are a front view and a top view showing the configuration of a cooling device that cools a steel strip (S) by a water cooling method. Additionally, the immersion tank (12) constituting the cooling device (10) is referred to as the first tank section (12) below. As shown in FIGS. 4(a) and (b), in this embodiment, a second tank section (22) having a connecting member (21) between it and the first tank section (12) is disposed on the side of the first tank section (12). The side of the first tank section (12) refers to the side of the steel strip (S) in the conveying direction, and refers to the direction called the machine side of the so-called continuous annealing facility. In this case, the second tank section (22) may be disposed on the machine side of the working side of the continuous annealing facility or on the machine side of the driving side.

[0038] The second water tank section (22) is also shaped like a container to allow for the storage of cooling water (W). Additionally, the second water tank section (22) is equipped with a water supply valve for supplying cooling water (W) inside and a drain valve for discharging the cooling water (W) stored inside. The connector (21) is open to allow the cooling water (W) stored in the first water tank section (12) and the second water tank section (22) to flow between each other. Additionally, the connector (21) has an opening through which the water cooling nozzle unit (11) is transported and can move between the first water tank section (12) and the second water tank section (22). The shape, size, and number of the openings are not a concern as long as the water cooling nozzle unit (11) can pass through them.

[0039] In this embodiment, the water cooling nozzle unit (11) is provided with a surface nozzle unit (11a) that sprays cooling water (W) onto the front side of the steel plate (S) and a back nozzle unit (11b) that sprays cooling water (W) onto the back side, and the connector (21) is provided with two openings through which each nozzle unit can pass. Additionally, the opening of the connector (21) may be a single opening through which both nozzle units can pass. However, the opening of the connector (21) needs to be positioned at a height lower than the liquid level when the cooling water (W) for performing water cooling is stored in the first water tank (12). That is, the opening of the connector (21) is arranged so that when cooling water (W) is stored in the first water tank (12) and water-cooling is performed, the entire opening can be submerged in the cooling water (W).

[0040] FIG. 5 is a drawing showing an example of the configuration of an opening of a connector (21) through which a surface nozzle unit (11a) and a back nozzle unit (11b) pass. FIG. 5 illustrates the state of the opening viewed from the side of the first water tank section (12). Furthermore, the method of connecting the first water tank section (12) and the second water tank section (22) is not limited to a form in which the wall blocking the first water tank section (12) and the second water tank section (22) is opened. For example, the first water tank section (12) and the second water tank section (22) may be connected by a tubular member in the shape of a steel pipe or a square pipe, and the water cooling nozzle unit (11) may pass through the interior of the tubular member.

[0041] As shown in FIG. 5, in this embodiment, the connecting member (21) between the first tank section (12) and the second tank section (22) is equipped with an opening / closing door (23) for opening and closing the opening. The means of the opening / closing door (23) is not a problem as long as it can close the opening so that the cooling water (W) does not move between the first tank section (12) and the second tank section (22), and also open the opening so that the cooling water (W) can move between them. However, it is preferable that the opening / closing door (23) be equipped with a shutter mechanism capable of automatic opening and closing by external operation. As for the material constituting the opening / closing door (23), heat-resistant steel or stainless steel is preferably used, similar to the material constituting the furnace wall of the annealing furnace.

[0042] Additionally, the opening / closing door (23) is preferably airtight to block the gas atmosphere inside the furnace from the atmospheric atmosphere outside the furnace when performing the non-water-cooling method of cooling described later. For example, it is preferable to use a sealing material such as packing or gasket made of graphite or metal with excellent heat resistance. Furthermore, the opening / closing door (23) is preferably equipped with a mechanism that presses the opening / closing door (23) against the wall surrounding the opening using hydraulic or pneumatic pressure to improve the airtightness of the opening. However, a method in which the opening / closing door (23) is pressed against the wall surrounding the opening by means of a squall vise or screw fixing may also be adopted. Also, to further improve airtightness, a double or triple opening / closing door may be used instead of a single opening / closing door as the opening / closing door (23).

[0043] Returning to FIG. 4. As shown in FIG. 4(a), the water cooling nozzle unit (11) is provided with a conveying control unit (24) that conveys the water cooling nozzle unit (11) so that it passes through a connector (21) and is positioned somewhere between a cooling water spraying position and a non-water cooling standby position. In this embodiment, the water cooling nozzle unit (11) is supported by a support member (25), and the conveying control unit (24) conveys the water cooling nozzle unit (11) by moving the support member (25). Additionally, the support member (25) may support the water cooling nozzle unit (11) in a cantilevered manner in the direction in which the water cooling nozzle unit (11) moves back and forth. Furthermore, the means for moving the support member (25) back and forth may be arbitrary, such as conveying it by hydraulic or pneumatic pressure, or moving it in a straight line using an electric motor and a rack and pinion. Additionally, the support member (25) may have wheels formed thereon to reciprocate the support member (25) on the track. FIG. 4(a) shows an example of a conveying control unit (24) that supports the support member (25) in a suspended manner and reciprocates the water cooling nozzle unit (11) on the track.

[0044] The return control unit (24) controls the water cooling nozzle unit (11) to be positioned somewhere between a cooling water injection position and a non-water cooling standby position. The cooling water injection position of the water cooling nozzle unit (11) refers to the position where cooling water is sprayed onto the surface of the steel strip (S) by the water injection nozzle of the water cooling nozzle unit (11) when cooling water (W) is stored in the first water tank (12) to perform water cooling. That is, by positioning the water cooling nozzle unit (11) at the cooling water injection position, normal water cooling can be performed. The position of the water cooling nozzle unit (11) shown in FIG. 4(a) and (b) is the cooling water injection position, and the water cooling nozzle unit (11) is in a state where it is inside the first water tank (12). Meanwhile, the non-water-cooled standby position of the water cooling nozzle unit (11) refers to the position where the water cooling nozzle unit (11) is placed when performing the non-water-cooled cooling method described later, and refers to the state where the water cooling nozzle unit (11) is inside the second water tank (22). That is, it means a position where the opening and closing door (23) can be closed by placing the water cooling nozzle unit (11) inside the second water tank (22).

[0045] The water spray nozzle constituting the water cooling nozzle unit (11) can be appropriately selected according to the cooling rate required to secure the material of the steel strip (S) being manufactured. Since the cooling rate of the steel strip (S) depends on the spray flow rate of the cooling water sprayed from the water spray nozzle, the cooling rate can be increased by using one with a high spray flow rate. However, when the cooling rate exceeds a predetermined value, the cooling rate does not increase significantly even if the spray flow rate is increased. Specifically, if the spray flow rate is, for example, 2 m / s or more, the cooling effect is not improved even if the spray flow rate is increased, and the change in the cooling rate of the steel strip (S) becomes almost unchanged. On the other hand, the lower the temperature of the cooling water sprayed from the water spray nozzle, the greater the cooling rate can be. Therefore, in order to obtain a higher cooling rate, it is desirable to keep the temperature of the cooling water sprayed by the water cooling nozzle unit (11) low. For example, it is desirable to set the temperature of the cooling water sprayed from the water spray nozzle to be between 10°C and 40°C, and to control it to, for example, about 30°C using a cooling chiller.

[0046] Here, it is preferable that the cooling device (10) can adjust the liquid level of the cooling water (W) using a water supply and drainage valve when the cooling water (W) is stored in the first water tank section (12) and the second water tank section (22). Also, it is preferable that the water cooling nozzle unit (11) is equipped with a mechanism that can adjust the height position so that the height at which the water cooling nozzle unit (11) is positioned relative to the liquid level can be adjusted. For example, a guide section capable of sliding in the up and down direction is installed on the water cooling nozzle unit (11) so that the height position relative to the support section (25) can be adjusted. This is because the material of the steel strip (S) or the shape during cooling can be adjusted by adjusting the timing of the cooling start of the steel strip (S) by the cooling water. For example, by installing a portion of the water spray nozzle constituting the water cooling nozzle unit (11) at a position higher than the liquid level, pre-cooling by the water spray nozzle can be performed immediately before rapid cooling by the first water tank unit (12). Therefore, the deterioration of the shape of the steel strip (S) due to thermal shrinkage or phase transformation can be suppressed, and a steel strip (S) with a good shape can be manufactured.

[0047] Additionally, the water cooling nozzle unit (11) may be equipped with a restraining roll that restrains the steel band (S) by at least one pair of rolls together with the water spray nozzle. For example, as shown in FIG. 6, a restraining roll (26) that applies pressure toward the steel band (S) may be provided between a plurality of water spray nozzles constituting the water cooling nozzle unit (11). By installing the restraining roll, the shape of the steel band (S) can be suppressed from being distorted by the transformation expansion when the steel band (S) undergoes a phase transformation. However, the number or installation position of the restraining rolls may be appropriately changed according to the cooling conditions applied to the steel band (S). When such a restraining roll is provided in the water cooling nozzle unit (11), it is preferable that the restraining roll be integrated with the water cooling nozzle unit (11), supported by a support member (25), and conveyed together with the water cooling nozzle unit (11) by a conveying control member (24).

[0048] [Non-water-cooled cooling device]

[0049] Next, with reference to FIGS. 7 and FIGS. 8, the configuration of a non-water-cooled cooling device will be described.

[0050] FIG. 7 is a side view showing the configuration of a cooling device when cooling a steel plate (S) in a non-water cooling manner in a cooling unit (4). As shown in FIG. 7, the cooling device (10) when cooling a steel plate (S) in a non-water cooling manner is configured by a cooling means that is gas jet cooling, mist cooling, or a combination thereof. When cooling a steel plate (S) in a non-water cooling manner, a non-water cooling nozzle unit (27) is arranged to cool the steel plate (S) by spraying gas or mist onto the steel plate (S). In the non-water cooling method using gas jet cooling, a non-water cooling nozzle unit (27) is used in which a pair of gas injection nozzles are arranged in multiple stages on the front and back sides of the moving steel plate (S). Meanwhile, in a non-water cooling method using mist cooling, a non-water cooling nozzle unit (27) is used in which a pair of mist spray nozzles are arranged in multiple stages on the front and back sides of the moving steel bar (S). Also, in a non-water cooling method using roll cooling, an internal water-cooled roll is placed on the cooling platform (4) instead of the non-water cooling nozzle unit (27). Furthermore, in the example shown in FIG. 7, only one set of non-water cooling nozzle units (27) is shown, but normally, multiple non-water cooling nozzle units (27) are arranged along the cooling platform (4). In the example shown in FIG. 7, only a part thereof is shown.

[0051] In a cooling device capable of switching between a water-cooling method and a non-water-cooling method as in the present embodiment, it is desirable to switch the cooling method without changing the configuration of the device as much as possible. This is because the more devices whose configurations are changed, the longer the time required to switch between the water-cooling method and the non-water-cooling method. For this reason, in the example shown in FIG. 7, the deflector rolls (13a, 13b), the pressing roll (14), the water removal roll (15), and the drying oven (16) are used in common in both the non-water-cooling method and the water-cooling method. Also, the immersion tank (12) and the non-water cooling nozzle unit (27) do not need to be moved when switching the cooling method and are placed in a fixed position. In that case, in the water-cooling method, cooling water (W) is stored in the immersion tank (12), and in the non-water-cooling method, cooling water (W) is discharged from the immersion tank (12).

[0052] In the non-water cooling method, the non-water cooling nozzle unit (27) sprays a refrigerant toward the steel sheet (S) from a gas injection nozzle or a mist injection nozzle, but in the water cooling method, it basically maintains a state where it does not spray a refrigerant. Also, even if movement is performed such that the injection nozzle facing the surface of the steel sheet (S) and the injection nozzle facing the back surface are separated from each other, the non-water cooling nozzle unit (27) is not removed from the furnace. Also, in the non-water cooling method, the water removal roll (15) does not necessarily need to be used, so if water removal is not performed, the steel sheet (S) may be passed through with the opposing rolls separated. Likewise, in the non-water cooling method, the steel sheet (S) may be dried as needed, and if drying is not performed, the steel sheet (S) may be passed through with the output of the drying furnace (16) lowered. Anyway, the cooling device (10) for performing non-water cooling shown in FIG. 7 is a device configuration in which at least a water cooling nozzle unit (11) is removed, with respect to the device configuration for performing water cooling.

[0053] When gas jet cooling is performed by a non-water cooling nozzle unit (27), the injection pressure of the gas injection nozzle is usually set to about 0 to 10 kPa so that non-water cooling is performed. If the injection pressure exceeds 10 kPa, even if the injection pressure is increased, an improvement in cooling capacity cannot be expected to the extent corresponding to the increase in the power cost of the blower. Also, because the vibration of the steel band (S) increases due to the increase in gas flow rate caused by the increase in injection pressure, there is a risk of non-uniformity in cooling. The shape of the gas injection opening in the gas injection nozzle may be a round hole shape or a slit shape. The shape of the gas injection opening can be appropriately selected according to the cooling capacity of the steel band (S) and the uniformity of cooling required for non-water cooling. Meanwhile, when mist cooling is performed by a non-water cooling nozzle unit (27), the gas pressure that atomizes the droplets varies greatly depending on the type and structure of the nozzle, but a gas pressure of approximately 3 to 1000 kPa is used as the appropriate value. The shape of the mist sprayed from the mist cooling nozzle may be conical or fan-shaped, and can be appropriately selected according to the cooling capacity or uniformity of cooling required to obtain the target material of the steel strip (S).

[0054] FIG. 8 is a front view and a top view showing the configuration of a cooling device when performing non-water cooling. In addition, the first water tank section (12), the connector (21), the second water tank section (22), the opening / closing door (23), the conveying control section (24), and the support section (25) are identical to those in a cooling device when performing water cooling. However, when performing non-water cooling, cooling water (W) is not stored in the first water tank section (12) and the second water tank section (22). Also, the water cooling nozzle unit (11) is positioned in a non-water cooling standby position, and the opening of the connector (21) is closed by the opening / closing door (23). As a result, the atmosphere inside the furnace body of the cooling unit (4) is isolated from the ambient atmosphere, and an atmosphere inside the furnace suitable for the annealing process is maintained.

[0055] As described above, in a cooling device (10) which is an embodiment of the present invention, when water cooling is performed, cooling water (W) is stored in the first water tank section (12) and the second water tank section (22), so that the connecting port (21) between the first water tank section (12) and the second water tank section (22) is filled with cooling water (W). Because of this, even when the opening / closing door (23) of the connecting port (21) is opened, the atmosphere inside the furnace and the ambient atmosphere outside the furnace are blocked by the cooling water (W). Thus, even when the water cooling nozzle unit (11) is moved between the cooling water injection position and the non-water cooling ambient position using the return control unit (24), the atmosphere inside the furnace can be maintained in a state where it is blocked from the atmosphere. Meanwhile, when performing non-water cooling, the water cooling nozzle unit (11) is positioned in a non-water cooling standby position, and the opening / closing door (23) between the first water tank (12) and the second water tank (22) is closed. Thus, even when the cooling water (W) stored in the first water tank (12) and the second water tank (22) is drained, the connection port (21) is closed by the opening / closing door (23), so the atmosphere inside the furnace can be maintained in a state where it is isolated from the atmosphere.

[0056] That is, according to the cooling device (10) of one embodiment of the present invention, when switching the cooling method between a water-cooling method and a non-water-cooling method, the atmosphere inside the furnace is maintained in a state isolated from the atmosphere. As a result, work such as gas replacement is unnecessary when bringing the water-cooling nozzle unit (11) into the furnace or taking it out of the furnace as in the conventional method, so the time required to switch the cooling method can be significantly reduced. Also, when performing non-water-cooling cooling, there is no need to keep the water-cooling nozzle unit (11) inside the furnace, so fluctuations in the dew point inside the furnace caused by moisture attached to the water-cooling nozzle unit (11) can be suppressed. In addition, since the water-cooling nozzle unit (11) is not left inside the furnace when performing non-water-cooling cooling, the lifespan of the water-cooling nozzle unit (11) can be extended, and the cost of renewing the equipment can be reduced.

[0057] Additionally, it is preferable that the support member (25) be provided with a sunshade that can close the connector (21) when the water cooling nozzle unit (11) is positioned at the cooling water spraying position. Specifically, as shown in FIG. 4(a) and (b), the sunshade (25a) is a member fixed to the support member (25) that supports the water cooling nozzle unit (11), and has a shape that covers the opening of the connector (21) of the first water tank (12) and the second water tank (22). Also, the sunshade (25a) is positioned on the support member (25) so as to close the opening of the connector (21) when the return control member (24) positions the water cooling nozzle unit (11) at the cooling water spraying position.

[0058] The sunshade section (25a) has the function of suppressing the free movement of cooling water (W) between the first water tank section (12) and the second water tank section (22) in water-cooling cooling. In the first water tank section (12), since the high-temperature steel strip (S) is continuously immersed in the cooling water (W), the temperature of the cooling water (W) gradually rises when water-cooling cooling is performed. Since the cooling capacity of the steel strip (S) decreases when the temperature of the cooling water (W) rises, it is desirable to provide a cooling chiller that suppresses the rise in temperature of the cooling water (W) while circulating the cooling water (W) in the first water tank section (12). However, when the opening / closing door (23) is open, it is necessary to cool the entire cooling water (W) stored in the first water tank section (12) and the second water tank section (22) by the cooling chiller. If the movement of cooling water (W) between the first water tank (12) and the second water tank (22) is suppressed by the sunshade (25a), the cooling chiller only needs to have the ability to circulate and cool the cooling water (W) inside the first water tank (12), and thus the running cost can be suppressed. In addition, as for the member constituting the sunshade (25a), heat-resistant steel or stainless steel can be used, just like the opening / closing door (23). However, it is not necessary to have airtightness (sealing) that blocks the atmosphere inside the furnace and the atmosphere outside the furnace when performing non-water cooling, as with the opening / closing door (23). In water cooling, when the opening / closing door (23) is in an open state, it is sufficient to ensure a degree of sealing that suppresses the movement of cooling water (W) between the first water tank (12) and the second water tank (22) to some extent. Because of this, there is an opening in some parts, so it is acceptable for some cooling water to move between the first tank section (12) and the second tank section (22).

[0059] [How to Switch from Non-Water Cooling to Water Cooling]

[0060] Next, with reference to FIG. 9, a method for switching from a non-water cooling method to a water cooling method in a cooling device which is an embodiment of the present invention will be described.

[0061] The transition from a non-water cooling method to a water cooling method begins with a non-water cooling step in which cooling is performed using the non-water cooling method shown in FIG. 9(a). Additionally, it is desirable to reduce the line speed of the continuous annealing facility at the end of the non-water cooling step. This is because, during the transition of the cooling method, material variation occurs in the steel strip (S) passing through the cooling zone (4), thereby allowing the length of the steel strip (S) where material defects occur to be shortened. More preferably, the line speed of the continuous annealing facility is reduced to the minimum speed. In that case, it is desirable to reduce the output of the combustion burner of the heating zone (2) or cracking zone (3) according to the line speed and reset the operating conditions of the annealing process so that the steel strip (S) is not overheated. However, in cases where it is difficult to adjust the burner output, such as when using a direct-fired burner, it is necessary to transport the steel strip (S) at a constant line speed or higher. In addition, it is not desirable to stop the transport of the steel band (S) during the switching of the cooling method. This is because if the transport of the steel band (S) is stopped, it is necessary to lower the furnace temperature of the heating zone (2) and the cracking zone (3) in order to suppress overheating of the steel band (S), and it takes time to raise the temperature to a predetermined furnace temperature when the transport of the steel band (S) is started again.

[0062] After the non-water cooling step is completed, the process transitions to a water supply step in which water is supplied to the first water tank section (12) and the second water tank section (22). The water supply step is a step of storing cooling water (W) by operating the water supply valves of the first water tank section (12) and the second water tank section (22), respectively. As shown in FIG. 9(b), the water supply to the first water tank section (12) and the second water tank section (22) is carried out such that the liquid level of the cooling water (W) is above the position of the opening of the connector (21). However, when performing water cooling, if there is a pressure difference between the pressure inside the cooling tank (4) and the atmospheric pressure, there may be a difference between the liquid level of the first water tank section (12) and the liquid level of the second water tank section (22). For this reason, it is desirable to adjust the liquid level of the cooling water (W) so that it is higher than the position of the opening during normal operation, taking into account such a pressure difference. Since the water supply to the first tank section (12) and the second tank section (22) is carried out with the opening / closing door (23) closed, water is supplied individually by each water supply valve. In that case, it is desirable to adjust the liquid level so that the liquid level position of the first tank section (12) and the liquid level position of the second tank section (22) are roughly the same. This is because when the opening / closing door (23) is opened, resistance due to water pressure occurs when the liquid level position of the first tank section (12) and the liquid level position of the second tank section (22) are different, creating a pressure difference inside. Meanwhile, while the non-water cooling method is being executed, the water supply to the second water tank (22) may be performed in advance, and the water supply to the first water tank (12) may be performed after the non-water cooling method is finished. This is because the water supply time can be shortened. In that case, when the water cooling nozzle unit (11) is in the non-water cooling standby position, air is mixed into the water spray nozzle, so water is sprayed in the non-water cooling standby position and the air inside the water spray nozzle is discharged in advance.In addition, when supplying cooling water (W) to the first water tank (12), it is preferable that the temperature of the steel strip (S) passing through the first water tank (12) be 400°C or lower. If the temperature of the steel strip (S) is in a high temperature state exceeding 400°C, the contact position between the cooling water (W) in the supply water and the steel strip (S) changes. This is because there is a risk that the thermal deformation of the steel strip (S) may occur significantly at the boundary between the part where the cooling water (W) is supplied and the part where it is not supplied, thereby causing the condition of the plate to become unstable.

[0063] When the cooling water supply step is completed, the process proceeds to the opening step of opening the opening / closing door (23), as shown in FIG. 9(c). In the opening step, by opening the opening / closing door (23) that blocks the space between the first water tank section (12) and the second water tank section (22), the cooling water (W) becomes flowable between the first water tank section (12) and the second water tank section (22). However, since the opening of the connector (21) is filled with cooling water (W), there is no case where the gas inside the furnace and the gas outside the furnace move to each other through the connector (21). Therefore, the atmosphere inside the furnace of the cooling unit (4) and the atmosphere in contact with the liquid surface of the second water tank section (22) are kept blocked. When the opening step is completed, the process proceeds to the nozzle unit loading step. As shown in FIG. 9(d), the nozzle unit loading step is a step in which the water cooling nozzle unit (11) is loaded so that it passes through the connector (21) opened by the opening step and moves from a non-water-cooled standby position to a cooling water injection position. The transfer of the water cooling nozzle unit (11) to the cooling water injection position is executed by the transfer control unit (24). Thus, the water cooling nozzle unit (11) is placed at the cooling water injection position, and becomes capable of performing water-cooling cooling by the cooling water (W) stored in the first water tank (12). Then, when the nozzle unit loading step is completed, the line speed of the continuous annealing facility is increased to perform water-cooling cooling. Then, the output of the combustion burner of the heating zone (2) or the cracking zone (3) is also controlled so that the annealing condition is preset for the steel band (S) that is subjected to water-cooling cooling, and the operation of the continuous annealing facility that performs water-cooling cooling is executed.

[0064] [How to Switch from Water-Cooled to Non-Water-Cooled System]

[0065] Next, with reference to FIG. 10, a method for switching from a water-cooling method to a non-water-cooling method in a cooling device which is an embodiment of the present invention will be described.

[0066] The transition from a water-cooling method to a non-water-cooling method begins with a water-cooling step in which cooling is performed using the water-cooling method shown in FIG. 10(a). When the water-cooling step is completed, it is desirable to reduce the line speed of the continuous annealing facility. This is because, during the execution of the transition of the cooling method, a variation in material occurs in the steel strip (S) passing through the cooling zone (4), thereby allowing the length of the steel strip (S) where material defects occur to be shortened. More preferably, the line speed of the continuous annealing facility is reduced to the minimum speed. In that case, it is desirable to reduce the output of the combustion burner of the heating zone (2) or cracking zone (3) according to the line speed and reset the operating conditions of the annealing process so that the steel strip (S) is not overheated. However, in cases where it is difficult to adjust the burner output, such as when using a direct-fired burner, it is necessary to transport the steel strip (S) at a constant line speed or higher.

[0067] After the water cooling step is completed, the process proceeds to the nozzle unit withdrawal step. As shown in FIG. 10(b), the nozzle unit withdrawal step is a step in which the water cooling nozzle unit (11) withdraws from the cooling water injection position to the non-water cooling standby position by passing through the connector (21) that is open during the water cooling step. The return of the water cooling nozzle unit (11) to the non-water cooling standby position is executed by the return control unit (24). Thus, the water cooling nozzle unit (11) is placed in the non-water cooling standby position. After the nozzle unit withdrawal step is completed, the process proceeds to the closing step in which the opening / closing door (23) is closed, as shown in FIG. 10(c). According to the closing step, by closing the opening / closing door (23) that blocks the space between the first tank section (12) and the second tank section (22), the flow of cooling water (W) between the first tank section (12) and the second tank section (22) is stopped. Then, when the closing step is completed, as shown in FIG. 10(d), the process proceeds to a drainage step in which the cooling water (W) stored in the first tank section (12) and the second tank section (22) is drained.

[0068] The drainage step is a step of draining the cooling water (W) using the respective drain valves of the first tank section (12) and the second tank section (22). Since the connection port (21) is blocked by the opening / closing door (23), drainage from the first tank section (12) and the second tank section (22) is performed individually. However, it is not necessary to drain the cooling water (W) stored in the second tank section (22). This is because if the cooling water (W) stored in the first tank section (12) is drained, the cooling water (W) used for immersion cooling is removed, so non-water cooling can be performed on the steel plate (S). In this case, the cooling water (W) stored in the second tank (22) may be kept stored until the next water-cooling method is transitioned, or the cooling water (W) stored in the second tank (22) may be drained while the non-water-cooling method is performed. By keeping the cooling water (W) stored in the second tank (22) during the draining step, the water supply to the second tank (22) can be omitted during the water supply step when switching to the next water-cooling method.

[0069] Then, in the drainage step, when drainage from at least the first water tank section (12) is completed, the line speed of the continuous annealing facility is increased to perform non-water cooling. Then, the output of the combustion burner of the heating zone (2) or the cracking zone (3) is also controlled to become a preset annealing condition for the steel zone (S) that is subjected to non-water cooling, and the process transitions to an annealing process in which the cooling zone (4) is operated in a non-water cooling manner. As a result, in each step of the transition from a water cooling method to a non-water cooling method, the space between the first water tank section (12) and the second water tank section (22) is always blocked by stored cooling water (W) or an opening / closing door (23). Thus, the transition of the cooling method can be performed while maintaining a state of isolation between the atmosphere inside the furnace of the cooling zone (4) and the atmosphere outside the furnace. In addition, the operation of each device during the transition from a non-water cooling method to a water cooling method and from a water cooling method to a non-water cooling method is configured to be carried out by a control computer that controls the operation of the continuous annealing facility. Alternatively, the switching operation of the cooling device may be executed by installing a cooling device switching unit that controls the switching operation of the cooling device.

[0070] [Method of manufacturing steel rods]

[0071] In a method for manufacturing a steel strip according to one embodiment of the present invention, by manufacturing a steel strip (S) using a continuous annealing facility (1), the steel strip (S) can be divided into a steel strip (S) cooled by a water cooling method and a steel strip (S) cooled by a non-water cooling method as a cooling method. In the water cooling method and the non-water cooling method, different cooling rates can be applied to the steel strip (S) heated in the heating zone and the cracking zone, so the thermal history of the steel strip (S) during continuous annealing can be changed. As a result, the degree of freedom for controlling the microstructure of the steel strip (S) is improved, and a steel strip having various quality characteristics can be manufactured.

[0072] Examples

[0073] The present invention will be described in more detail below using examples. In this embodiment, a continuous annealing facility that operates by switching between a water cooling method and a non-water cooling method (gas jet cooling method) as a cooling unit was switched from a non-water cooling method to a water cooling method. As shown in FIGS. 4 and FIGS. 8, the cooling device used in this embodiment is equipped with a water cooling nozzle unit (11) that sprays cooling water (W) onto the surface of a steel strip (S), and a first water tank unit (12) that stores cooling water (W) for immersing and cooling the steel strip (S). Additionally, the cooling device used in this embodiment is provided with a second water tank (22) that is positioned on the side of the first water tank (12) and has a connecting port (21) between it and the first water tank (12), and an opening / closing door (23) that opens and closes the connecting port (21) between the first water tank (12) and the second water tank (22). Additionally, the cooling device used in this embodiment is provided with a return control unit (24) that returns the water cooling nozzle unit (11) so that the water cooling nozzle unit (11) passes through the connecting port (21) and is positioned somewhere between a cooling water spraying position and a non-water cooling standby position.

[0074] In this embodiment, the transition from a non-water cooling method to a water cooling method was carried out by each step shown in FIGS. 9(a) to (d). The time required for each step is shown in Table 1 below. The time required for the preparation for the cooling method transition (at the end of the non-water cooling step) in Table 1 is the time required to prepare for the cooling method transition after the normal operation (normal operation) using the non-water cooling method as the cooling method has ended. That is, it indicates that the time required to change the operating conditions of the furnace to maintain the temperature of the steel strip passing through the cooling bed at 400°C or lower by reducing the burner output of the heating bed along with decelerating the line speed of the continuous annealing facility was 0.2 hr. Next, the water supply step is a process of supplying cooling water (W) to the first water tank section (12) and the second water tank section (22), and the time required was 0.5 hr. After the cooling water (W) is stored so that the connector (21) is submerged by the water supply step, the opening step is executed, and the time required to open the opening / closing door (23) is 0.1 hr. Subsequently, in the nozzle unit loading step, 0.1 hr is required until the water cooling nozzle unit (11) is returned to the cooling water injection position by the return control unit (24). Then, as preparation for the water cooling operation (at the start of the water cooling step), the line speed of the continuous annealing facility is increased, and 0.2 hr is required until the output of the combustion burner of the heating zone or cracking zone reaches the pre-set annealing condition for the steel band undergoing water cooling. As described above, in this embodiment, the transition from non-water cooling to water cooling is carried out in a time of 1.1 hr.

[0075] Meanwhile, as a comparative example, the time required to switch from a non-water-cooling cooling method to a water-cooling cooling method without using the equipment of the above example is shown in Table 2 below. In this case, since it is necessary to open the furnace of the cooling unit, 2.0 hours were required for the preparation for the cooling method switch (at the end of the non-water-cooling step). In this case, since it is necessary to open a part of the cooling unit to the atmosphere, the line of the continuous annealing equipment is temporarily stopped to open the furnace. In addition, a relatively long time is required to lower the furnace temperature so that the high-temperature atmosphere inside the furnace does not have an adverse effect on the equipment or workers outside the furnace. Furthermore, even after the furnace temperature is lowered, 1.0 hour was required as an air exchange step to perform air exchange and gas concentration measurement for a certain period of time before carrying out the switch operation, considering the safety of workers working around the continuous annealing equipment. In addition, in the nozzle unit loading step, since the water cooling nozzle unit return control unit is not provided as in the equipment of the present embodiment, the removal of the water cooling nozzle unit requires a worker to enter the furnace to perform the work, requiring 2.0 hours. Afterwards, 1.0 hour was required for the gas exchange step, in which the furnace cover is closed and the atmosphere inside the furnace is replaced with a non-oxidizing atmosphere. The time required for supplying water to the immersion tank for immersion cooling was 0.5 hours, which is equivalent to the above embodiment; however, for the preparation of the water cooling method operation (at the start of the water cooling step), 5.0 hours were required until the atmosphere temperature inside the furnace, which had dropped to room temperature, was raised and line operation was resumed. Thus, in the comparative example, 11.5 hours were required to switch from a non-water cooling method to a water cooling method.

[0076] In addition, regarding the nozzle unit loading step, even if a conveying control unit for the water-cooled nozzle unit is provided as in the present embodiment, the time required for the nozzle unit loading step is reduced from 2.0 hr to 0.1 hr. Consequently, the total required time becomes 9.6 hr, which is longer than the method of switching by isolating the atmosphere inside and outside the furnace as in the present embodiment. On the other hand, since the same amount of time is required for switching from the water-cooling method to the non-water-cooling method, manufacturing facilities that switch between the water-cooling and non-water-cooling methods can significantly reduce the time required for switching cooling methods compared to conventional methods. In particular, in a continuous annealing facility that operates by switching between the water-cooling method and the non-water-cooling method (gas jet cooling method) as a cooling bed, the production capacity of steel strips can be improved.

[0077]

[0078] Explanation of the symbols

[0079] 1 : Continuous annealing facility 2 : Heating zone 3 : Rift zone 4: Cooling zone 5: Induction heating device 10: Cooling device 11: Water cooling nozzle unit 11a: Surface nozzle unit 11b: Rear nozzle unit 12: Immersion tank, 1st tank section 13a, 13b: Deflector roll 14 : Press Roll 15: Water removal roller 16: Drying oven 20: Water supply and drainage device 21 : Connector 22: Second Water Tank Section 23 : Opening and closing door 24 : Return control unit 25 : Support 25a : Sunshade 27: Non-water cooling nozzle unit S : Gangdae W: Coolant

Claims

Claim 1 A steel strip manufacturing apparatus comprising: a first water tank unit for storing cooling water for immersing and cooling a steel strip; a water cooling nozzle unit installed in the first water tank unit and spraying cooling water onto the surface of the steel strip; a second water tank unit connected to the first water tank unit through a connector; an opening and closing door for opening and closing the connector; and a conveying control unit for conveying the water cooling nozzle unit so that the water cooling nozzle unit passes through the connector and is positioned somewhere between a cooling water spraying position within the first water tank unit and a non-water cooling standby position within the second water tank unit, wherein the water cooling nozzle unit is supported by a support unit connected to the conveying control unit, and the support unit is provided with a sunshade unit that closes the connector when the water cooling nozzle unit is positioned at the cooling water spraying position. Claim 2 A steel strip manufacturing apparatus according to claim 1, wherein the water cooling nozzle unit comprises, in addition to a water spray nozzle that sprays cooling water onto the surface of the steel strip, a restraining roll that restrains the steel strip by at least one pair of rolls. Claim 3 delete Claim 4 A continuous annealing facility for steel strips, comprising a steel strip manufacturing device described in claim 1 or 2, equipped in a cooling bed. Claim 5 In claim 4, a continuous annealing facility for steel strips in which a reducing gas or a non-oxidizing gas is supplied to the cooling zone. Claim 6 A method for manufacturing a steel strip using a steel strip manufacturing apparatus described in claim 1 or 2, comprising: a non-water cooling step of cooling the steel strip without spraying cooling water on the surface of the steel strip outside the first water tank section; a water supply step of supplying cooling water to the first water tank section and the second water tank section after the completion of the non-water cooling step; an opening step of opening the opening / closing door of the connector; a nozzle unit loading step of conveying the water cooling nozzle unit so that the water cooling nozzle unit passes through the connector and moves from the non-water cooling standby position to the cooling water spraying position; and a water cooling step of immersing the steel strip in cooling water stored in the first water tank section while spraying cooling water on the surface of the steel strip using the water cooling nozzle unit. Claim 7 A method for manufacturing a steel strip using a steel strip manufacturing apparatus described in claim 1 or 2, comprising: a water cooling step of immersing and cooling the steel strip in cooling water within a first water tank while spraying cooling water onto the surface of the steel strip using the water cooling nozzle unit; a nozzle unit withdrawal step of returning the water cooling nozzle unit so that, after the completion of the water cooling step, the water cooling nozzle unit passes through the connector and moves from the cooling water spraying position to the non-water cooling standby position; a closing step of closing the opening and closing door of the connector; a draining step of draining the cooling water within at least the first water tank; and a non-water cooling step of cooling the steel strip without spraying cooling water onto the surface of the steel strip outside the first water tank. Claim 8 A method for manufacturing a steel strip by using a continuous annealing facility for steel strips described in Clause 5.

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