Cast piece manufacturing method and cast piece manufacturing apparatus

Abstract

To provide a method and an apparatus for manufacturing a cast slab capable of cooling the cast slab in an appropriate mode.SOLUTION: A cooling step of cooling the slab by water cooling. The cooling step includes a first cooling step of spraying water onto the cast slab, and a second cooling step of discharging flowing water onto the cast slab. The second cooling step is started after the first cooling step is started. According to the method for producing a cast slab and the like of the present invention, since the second cooling step is started after the first cooling step is started, the cast slab can be cooled in an appropriate manner. Accordingly, the slab may be manufactured while minimizing warpage.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for producing a slab, which include a cooling step of cooling the slab by water cooling. [Background technology]

[0002] Continuously cast slabs and other cast pieces are transported by ships, trailers, etc. From the viewpoint of handling, the cast pieces are cooled before being transported.

[0003] Conventionally, castings have been cooled by water spraying. For example, Patent Document 1 discloses that slabs whose sides have been allowed to cool until they reach a predetermined temperature are stacked, and water is sprayed on both sides of the slabs except for a predetermined area from the top surface of the topmost slab.

[0004] Furthermore, Patent Document 2 discloses a method of cooling a slab after continuous casting by repeatedly spraying water on the slab and then stopping the spraying of water. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-055865 A [Patent Document 2] JP 2008-200685 A Summary of the Invention [Problem to be solved by the invention]

[0006] A continuously cast slab is at a high temperature. When a high-temperature slab is cooled, warping may occur depending on the cooling method. The methods disclosed in Patent Documents 1 and 2 still have room for improvement because warping may occur in the slab. Furthermore, the method disclosed in Patent Document 2 has a problem in that the time required to cool the slab is long because the water spraying process is stopped periodically.

[0007] The present invention has been made in view of the above problems, and has an object to provide a method and an apparatus for manufacturing a slab that are capable of cooling the slab in an appropriate manner. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention has the following features.

[0009] [1] A method for producing a cast slab, comprising a cooling step of cooling the cast slab by water cooling, The cooling step a first cooling step of spraying water onto the slab; a second cooling step of discharging running water onto the slab, The method for producing a cast slab, wherein the second cooling step is started after the first cooling step is started. [2] The method for producing a slab according to [1], wherein the second cooling step is started after the temperature of the slab has reached 450°C or lower. [3] The cast pieces are stacked in plurality, The method for producing a cast slab according to [1] or [2], wherein the second cooling step is started after the temperature of the side surface of at least one of the plurality of cast slabs has reached 450°C or less. [4] The method for producing a slab according to any one of [1] to [3], wherein pressure is applied from an upper surface of the slab toward a lower surface of the slab in the first cooling step and the second cooling step. [5] A casting manufacturing apparatus including a cooling unit that cools a casting by water cooling, The cooling unit is a first cooling section that sprays water onto the slab; a second cooling section that discharges running water onto the slab; A casting manufacturing apparatus comprising: [6] a water cooling control unit that controls the start of the spray by the first cooling unit and the start of the discharge by the second cooling unit; The apparatus for manufacturing a cast slab according to [5], wherein the water cooling control unit starts the spraying by the first cooling unit and then starts the discharge by the second cooling unit. [Effects of the Invention]

[0010] The method for producing a slab of the present invention includes a first cooling step in which water is sprayed onto the slab, and a second cooling step in which running water is discharged onto the slab. The second cooling step is initiated after the first cooling step is initiated. This allows the slab to be cooled in an appropriate manner. This allows the slab to be produced with minimal warpage. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing an outline of a casting manufacturing apparatus. [Figure 2] FIG. 2 is an explanatory diagram showing an installation mode of a cooling unit of a cast slab manufacturing apparatus. [Figure 3] FIG. 1 is a flow diagram of a method for manufacturing a cast slab. [Figure 4] FIG. 4 is an explanatory view showing an aspect of the installation step of FIG. 3. [Figure 5] FIG. 3 is an explanatory view showing an aspect of the first cooling step in FIG. 2. [Figure 6] FIG. 3 is an explanatory view showing an embodiment of the second cooling step in FIG. 2. [Figure 7] FIG. 10 is a block diagram showing an outline of a modified example of a cast slab manufacturing apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a cast slab manufacturing apparatus 100. The cast slab manufacturing apparatus 100 of FIG. 1 includes a continuous casting machine 10 that forms a slab, which is a cast slab, and a cooling section 20 that cools the slab formed by the continuous casting machine 10. The cast slab is not limited to a slab, and for example, a billet, a bloom, or the like may also be used. In this embodiment, an example in which a slab is used as the cast slab will be described. The cast slab may also be formed by a casting method other than continuous casting.

[0013] The continuous casting machine 10 has a mold (not shown) for cooling the molten steel supplied from the tundish, and a cutting section (not shown) for cutting the steel billets formed by cooling in the mold into predetermined lengths.

[0014] The slab formed into a plate shape by the continuous casting machine 10 is transported to a yard (not shown), which is provided with a cooling section 20. The slab is cooled by water in the cooling section 20 until it reaches a predetermined temperature.

[0015] Fig. 2 shows an installation mode of the cooling section of a casting manufacturing apparatus. As shown in Fig. 2, a yard 30 is provided with a plurality of slabs stacked in the thickness direction, i.e., a plurality of slabs stacked one on top of the other. The cooling section 20 cools the stacked slabs as the cooling object 40 by water cooling. In this embodiment, the cooling object 40 is configured by stacking a plurality of slabs, but this is not limited to such an embodiment, and the cooling object 40 may be configured by a single slab.

[0016] The objects to be cooled 40 are arranged, for example, at predetermined intervals in the yard 30. The installation position of the cooling unit 20 is not particularly limited as long as it is provided at a position where the objects to be cooled 40 can be water-cooled. In the example shown in FIG. 2, the cooling unit 20 is arranged between the objects to be cooled 40.

[0017] The cooling unit 20 has a first cooling unit 21 that sprays water onto the object 40 to be cooled, and a second cooling unit 22 that discharges running water onto the object 40 to be cooled.

[0018] The first cooling section 21 is provided with a nozzle (not shown) that sprays water. The nozzle of the first cooling section 21 is arranged facing the cooling target 40. In the example shown in Fig. 2, the nozzle is provided so as to spray atomized water W1 toward one cooling target 40. The first cooling section 21 is provided with a valve (not shown) that adjusts the amount of water sprayed from the nozzle.

[0019] It should be noted that the manner in which the nozzle of the first cooling section 21 is provided is not limited to this manner, and the nozzle may be provided facing in multiple directions so as to spray mist-like water W1 toward two or more cooling targets 40.

[0020] The second cooling section 22 is provided with a nozzle (not shown) that discharges running water. The nozzle of the second cooling section 22 is arranged facing the cooling target 40. In the example shown in Fig. 2, the nozzle is provided so as to discharge running water W2 toward one cooling target 40. In other words, the nozzle of the first cooling section 21 and the nozzle of the second cooling section 22 provided in one cooling section 20 are arranged facing the same cooling target 40. The second cooling section 22 is provided with a valve (not shown) that adjusts the amount of running water discharged from the nozzle.

[0021] Furthermore, the manner in which the nozzle of the second cooling section 22 is provided is not limited to this manner, and the nozzle may be provided in multiple directions so as to eject flowing water W2 toward two or more cooling targets 40.

[0022] 2, one cooling section 20 is used for one cooling target 40. The cooling mode of the cooling target 40 is not limited to this mode, and multiple cooling sections 20 may be used for one cooling target 40. For example, four cooling sections 20 may be used so as to surround one cooling target 40. By cooling the slab 42 from multiple directions in this way, temperature unevenness can be reduced.

[0023] Fig. 3 shows a flow of the method for producing a slab. As shown in Fig. 3, in the method for producing a slab, a continuous casting process is performed in a continuous casting machine 10 to form a slab (step S01).

[0024] The slab formed in the continuous casting process in step S01 is placed in the yard 30, and a placing process is carried out (step S02).

[0025] After the installation process of step S02 is performed, a cooling process is performed to cool the slab 42 by water cooling as follows: That is, the first cooling section 21 performs the first cooling process by spraying atomized water W1 toward the slab installed in the yard 30 (step S03).

[0026] When the first cooling process of step S03 is performed and the temperature of the slab 42 reaches a predetermined reference temperature, the second cooling section 22 performs the second cooling process by ejecting running water W2 toward the slab installed in the yard 30 (step S04).

[0027] The reference temperature is set to a temperature at which the possibility of warping occurring when the second cooling step is started is low. The reference temperature is set depending on the dimensions of the slab, the thermal conductivity of the slab, etc. For example, if the dimensions of the slab 42 are a width of 1100 to 1500 mm, a length of 8000 to 10000 mm, and a thickness of 150 to 350 mm, the reference temperature should be set to 450°C, preferably 430°C, and more preferably 400°C.

[0028] By starting the second cooling process after the reference temperature has been reached, it is possible to suppress the occurrence of warping of the slab 42 and minimize the impact on operations due to the generation of steam in the yard 30. Furthermore, by starting the second cooling process after the reference temperature has been reached, it is possible to optimize the cooling efficiency of the slab 42.

[0029] The temperature of the slab 42 is, for example, the temperature of its side surface, and the maximum temperature obtained by measuring the temperatures of the side surface in the longitudinal direction and the cross section along the longitudinal direction at multiple points can be used. The temperature of the side surface of the slab 42 can be measured using, for example, a radiation thermometer. The temperature of the cross section of the slab 42 can be calculated from the measured temperature of the side surface using a known calculation method.

[0030] Furthermore, the slab 42 to be the object of temperature measurement is not particularly limited, but for example, if the cooling object 40 is formed by stacking multiple slabs 42, it is preferable to measure the temperature of the slab 42 located in the middle of the cooling object 40 in the height direction. The slab 42 located in such a position is presumed to have the highest temperature among the multiple slabs 42. Therefore, when the temperature of the slab 42 at that position reaches the reference temperature, there is a high probability that the other slabs 42 have also reached the reference temperature.

[0031] Fig. 4 shows the installation process of step S02 in Fig. 3. As shown in Fig. 4, a plate-shaped base 41 is provided in the yard 30. Four slabs 42 are stacked on the base 41 in the thickness direction.

[0032] A pressure member 43 is provided on the slab 42 located at the topmost stage, applying pressure from the upper surface of the slab 42 towards the lower surface of the slab 42. The pressure member 43 is not particularly limited, but for example, a slab cooled to near room temperature can be used. Providing the pressure member 43 can reduce the occurrence of warping of the slab 42. Furthermore, using a slab cooled to near room temperature as the pressure member 43 allows the required load to be applied evenly to the cooling target 40.

[0033] Furthermore, by providing a pressure member 43 on the top tier of the cooling target 40, it is possible to prevent the upper surface of the slab 42 arranged on the top tier from being exposed to the flowing water W2 in the second cooling step. This makes it possible to prevent temperature deviations in the slab 42 arranged on the top tier. This also makes it possible to prevent warping of the slab 42. Note that in the first cooling step of step S03 and the second cooling step of step S04, pressure is preferably applied from the top surface of the slab 42 to the bottom surface of the slab 42, i.e., a pressure member 43 is preferably installed. Furthermore, it is preferable that the pressure be started before the first cooling step of step S03 is started and ended after the second cooling step of step S04 is finished.

[0034] Fig. 5 shows an aspect of the first cooling step of step S03 in Fig. 3. As shown in Fig. 5, the first cooling section 21 is formed in a columnar shape extending along the height direction of the cooling target 40.

[0035] The first cooling section 21 has nozzles provided in accordance with the number of slabs 42, the height of the cooling target 40, etc. The number of nozzles provided is not particularly limited, but in the example shown in Fig. 5, five nozzles are provided.

[0036] As shown in Figure 5, when the first cooling section 21 sprays the water mist W1, the cooling target 40 is covered with the water mist W1. The water mist W1 is easily vaporized due to its small volume. Therefore, the cooling target 40 is cooled by the heat of vaporization of the water mist W1. This lowers the temperature around the cooling target 40, allowing the slab 42 of the cooling target 40 to be uniformly cooled, thereby enabling the slab 42 to be cooled while suppressing warping of the slab 42.

[0037] Fig. 6 shows an aspect of the second cooling step of step S04 in Fig. 3. As shown in Fig. 6, second cooling section 22 is formed in a columnar shape extending along the height direction of cooling target 40.

[0038] The second cooling section 22 has nozzles provided in accordance with the number of slabs 42, the height of the cooling target 40, etc. The number of nozzles provided is not particularly limited, but in the example shown in Fig. 6, five nozzles are provided.

[0039] 6, in the second cooling step, for example, after the spraying by the first cooling unit 21 is stopped, the second cooling unit 22 discharges running water W2. As the running water W2 is discharged from the second cooling unit 22, the cooling target 40 is exposed to the running water W2. That is, in the second cooling step, the cooling target 40 is cooled with a stronger intensity than in the first cooling step. In other words, the rate at which the temperature of the cooling target 40 decreases in the second cooling step is faster than in the first cooling step.

[0040] The second cooling step is started after the first cooling step is completed, which can avoid a sudden temperature change in the slab 42. This makes it possible to cool the slab in an appropriate manner, and suppress the occurrence of warpage in the slab 42.

[0041] That is, if flowing water cooling is used in the first cooling step, the cooling difference becomes large at different positions in the slab, and austenite structure (γ), ferrite structure (α), etc. are generated non-uniformly in the slab depending on the location.

[0042] When the austenite structure (γ) transforms into the ferrite structure (α), the coefficient of linear expansion changes significantly, causing contraction and expansion within the slab. As a result, warping of the slab occurs. By using water spray cooling (mist cooling) in the first cooling process, differences in the formed structure within the slab are less likely to occur. As a result, warping of the slab can be suppressed. Furthermore, by using running water cooling in the subsequent second cooling process, the slab temperature can be efficiently reduced. This reduces the time required to transport the slab to the next process.

[0043] In the above embodiment, an example has been described in which spraying by the first cooling unit 21 is stopped when the discharge of running water is started by the second cooling unit 22. The cooling mode of the slab 42 is not limited to this mode, and for example, the discharge of running water by the second cooling unit 22 may be started without stopping the spraying by the first cooling unit 21.

[0044] In this case, spraying by the first cooling section 21 may be performed while the second cooling section 22 is discharging the flowing water, or the spraying by the first cooling section 21 may be stopped at any timing after the second cooling section 22 has discharged the flowing water. The timing at which the spraying by the first cooling section 21 is stopped may be determined taking into consideration the temperature of the slab and the operating cost of the first cooling section 21.

[0045] In the above-described embodiment, an example has been described in which the first cooling section 21 and the second cooling section 22 are configured as separate members. However, the first cooling section 21 and the second cooling section 22 are not limited to this configuration, and may be configured using, for example, a nozzle that can switch between discharging a spray and discharging running water. Even when the first cooling section 21 and the second cooling section 22 are configured in this manner, the same effects as those of the above-described embodiment can be obtained.

[0046] (Variation) The operation of the first cooling section 21 and the second cooling section 22 of the water cooling unit 20 may be controlled by water cooling control that controls the operation of these sections. Note that the same components as those in the above-described embodiment are denoted by the same reference numerals and descriptions thereof will be omitted.

[0047] Fig. 7 shows the configuration of a modified example of a slab manufacturing apparatus 200. As shown in Fig. 7, the cooling unit 20 is connected to a water-cooling control unit 50 that controls the operation of the water-cooling unit 20. The water-cooling control unit 50 is connected to a temperature measurement unit 60 that measures the temperature of the slab 42.

[0048] The temperature measurement unit 60 is provided so as to be able to measure the temperature of the slab 42 installed in the yard 30. The temperature measurement unit 60 is not particularly limited as long as it is capable of measuring the temperature of the slab 42, but for example, a radiation thermometer can be used. The temperature measurement unit 60 transmits the measured temperature to the water cooling control unit 50 as needed.

[0049] The water cooling control unit 50 is a computer including a CPU. The water cooling control unit 50 controls the operation of the water cooling unit 20 based on the temperature measured by the temperature measurement unit 60, for example.

[0050] For example, when the slab 42 is transported from the continuous casting machine 10 to the yard 30, a temperature change of 100°C or more is observed at the location where the slab 42 is placed. When the water cooling control unit 50 detects such a sudden temperature change, it operates the first cooling unit 21 to perform the first cooling step.

[0051] When the temperature of the slab 42 reaches a predetermined reference temperature, the water cooling control unit 50 operates the second cooling unit 22 to perform the second cooling process. That is, the water cooling control unit 50 starts the spraying by the first cooling unit 21 and then starts the discharge by the second cooling unit 22. Operating the water cooling unit 20 in this manner can also achieve the same effects as those of the above-described embodiment. [Example]

[0052] (Test example 1: Slab warpage and cooling time comparison test) The slabs shown in Table 1 were cooled by water to check the occurrence of warpage and the cooling time. The results are shown in Table 1.

[0053] [Table 1]

[0054] The temperature of the slab was measured at multiple points on the longitudinal side and longitudinal cross section, and the maximum temperature was recorded. The temperature of the slab at the start of cooling was measured when it was transported from the continuous casting machine to the yard. The temperature of the slab at the start of cooling was approximately 550°C in all cases. The second cooling step was started at the temperature shown in Table 1. When the second cooling step was started, the first cooling step was stopped.

[0055] The cooling time was measured as the time from the start of cooling until the average temperature of the multiple slabs constituting the cooling target reached 100°C.

[0056] In addition, a pressure member was installed on the top slab and cooled in the manner shown in Table 1. A room temperature slab was used as the pressure member. The pressure member was installed when the slab was installed in the yard and removed after cooling was completed.

[0057] As shown in Table 1, in Tests 1 to 3, the first cooling process was switched to the second cooling process when the slab temperature reached 400°C. In all Tests 1 to 3, the cooling time was 40 hours or less. In addition, in Tests 1 to 3, the evaluation of warpage was good. In Tests 1 to 3, cooling was performed with the pressure member installed, so particularly good results were obtained in the evaluation of warpage. In addition, in Tests X to Z, where cooling was performed by switching from the first cooling process to the second cooling process, good results were obtained in the evaluation of warpage.

[0058] The evaluation of slab warping was given an "X" if it met either of the following two criteria, and an "O" if it did not meet either criterion. (Criterion 1): A warp that is convex downward when viewed from the side of the slab, known as upward warp, and that exceeds 10 mm per 1000 mm in the longitudinal direction. (Criterion 2): A warp that is convex upward when viewed from the side of the slab, known as downward warp, and that exceeds 50 mm The amount of warping of the slab was determined by measuring the distance from the bottom of the slab placed on the transport platform to the platform surface. Specifically, the distance from the platform surface to the bottom of the slab was measured using a metal tape measure, and the maximum distance was taken as the amount of warping of the slab.

[0059] Test 4, a comparative example, was a case in which cooling was performed only by mist spraying, and although the cooling start temperature was 350°C, the cooling time was 44 hours, which was longer than Tests 1 to 3.

[0060] Tests 5 and 6 were cases where cooling was only performed by water spraying, and although the cooling time was achieved within 12 hours, warping of the slab occurred to a maximum of approximately twice the standard value in Test 5 and approximately 1.5 times the standard value in Test 6.

[0061] (Test Example 2: Cooling Time Comparison Test) [Table 2]

[0062] As shown in Table 2, in the examples where the first and second cooling steps were performed, the temperature after the start of cooling was lower than that of the conventional example where cooling was performed by air cooling at all times. In addition, in the examples, the temperature was below 100°C 40 hours after the start of cooling. [Explanation of symbols]

[0063] 100 Casting equipment 10 Castings 20 Cooling section 21 1st cooling section 22 Second cooling section 40 Cooling target 42 Slabs

Claims

1. A method for producing a cast slab, comprising a cooling step of cooling the cast slab by water cooling, The cooling step a first cooling step of spraying water onto the slab; a second cooling step of discharging running water onto the slab, The method for producing a cast slab, wherein the second cooling step is started after the first cooling step is started.

2. The method for producing a cast slab according to claim 1 , wherein the second cooling step is started after the temperature of the cast slab has reached 450° C. or lower.

3. The cast pieces are stacked in plurality, 2. The method for producing a cast strand according to claim 1, wherein the second cooling step is initiated after the temperature of the side surface of at least one of the plurality of cast strands has reached 450°C or lower.

4. The cast pieces are stacked in plurality, 3. The method for producing a cast strand according to claim 2, wherein the second cooling step is initiated after the temperature of the side surface of at least one of the plurality of cast strands has reached 450°C or lower.

5. 5. The method for producing a slab according to claim 1, wherein pressure is applied from an upper surface of the slab toward a lower surface of the slab in the first cooling step and the second cooling step.

6. A casting manufacturing apparatus including a cooling unit that cools a casting by water cooling, The cooling unit is a first cooling section that sprays water onto the slab; a second cooling section that discharges running water onto the slab; A casting manufacturing apparatus comprising:

7. a water cooling control unit that controls the spraying by the first cooling unit and the discharge by the second cooling unit, The apparatus for manufacturing a cast slab according to claim 6 , wherein the water cooling control unit starts the spraying by the first cooling unit and then starts the discharge by the second cooling unit.

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