JP2006192462A - Billet slab cutting method in continuous casting machine - Google Patents

Abstract

When a steel material is rolled from a billet cast with multiple strands by applying a hot strip continuous rolling process, the billet can be transported to the next process in a predetermined cycle and stably rolled. Provide a billet cutting method that can be used.
When a billet cast by a continuous casting machine having a plurality of strands is transferred to a hot rolling process equipped with welding equipment while being hot, and continuously rolled while welding the billet, a continuous casting machine Then, the billet to be cast is cut for each strand at an interval of the cutting set time T ₀ according to the following equation (1), and the cutting interval of each strand is made equal to the time interval t _i according to the following equation (2). Cut at regular intervals. However, in the formulas (1) and (2), L is the target cutting length (m) of the billet, V _av is the average value (m / min) of the drawing speed of all strands, and n is the number of installed strands. . T ₀ = (L × 60) / V _av (1) t _i = T ₀ / n = (L × 60) / (V _av × n) (2)
[Selection] Figure 2

Description

  The present invention relates to a method for cutting a billet slab in a continuous casting machine, and more particularly to a cutting method for cutting a billet slab cast with multiple strands at a constant cycle.

  In a continuous casting machine, solidification is started with a mold and is drawn while being supported by a slab support roll, and the slab that is completely solidified to the inside is predetermined by a slab cutting machine installed downstream of the slab support roll. Cut to length. This slab is cut into slab slabs, especially slab slabs for thick steel plates, when cutting lengths are set according to customer orders, and mainly in bloom slabs and billet slabs. The following two methods are used: cutting at a fixed length that is the optimum length in the subsequent hot rolling step. However, even when cutting at a certain length, the total length of uncut slabs remaining in the strand at the end of casting is obtained, and if a slab of a predetermined length cannot be obtained, surplus is added to each slab. Dividing and cutting the minutes is performed (see, for example, Patent Document 1).

Thus, conventionally, the method of cutting a slab in a continuous casting machine has been performed based on the length of the slab, in other words, so that the length of the slab is within a predetermined range.
JP 2001-96348 A

  By the way, in recent years, for the purpose of energy saving, billet slabs cast by a continuous casting machine are transported to a hot rolling process equipped with billet welding equipment in a hot state, and billet slabs are welded by billet welding equipment. However, a method of continuously hot rolling a plurality of billet slabs (hereinafter referred to as “hot strip continuous rolling process”) has been performed.

  However, when the hot strip continuous rolling process was performed while cutting the billet slab at a certain length, there were problems in the following two points.

  (1) Normally, in a multi-strand billet continuous casting machine, there is no device for controlling the amount of molten steel injected from the tundish into the mold, and the mold surface is controlled by adjusting the slab drawing speed. Has been done. In such a multi-strand strand billet continuous casting machine, the slab drawing speed is determined by the position of the molten steel surface in the tundish, that is, the head difference, and the inner diameter of the tundish nozzle. However, on the inner wall of the tundish nozzle, metal adhesion may occur due to cooling and solidification of the molten steel when passing through the nozzle, and the substantial inner diameter of the tundish nozzle through which the molten steel can pass is It changes with the strand. In addition, since the molten steel temperature in the tundish is high in the central strand and low in the end strand, it is very difficult to cast all the strands having different molten steel temperatures at a constant speed. If a strand that does not reach a predetermined speed is generated due to variations in the slab drawing speed of each strand, a holding furnace equipped with a heat retaining function for retaining heat of the billet slab in a downstream transport facility is provided. In the equipment that is not installed, the billet slab cannot be transported to the billet welding equipment in a predetermined cycle, and the continuous rolling is interrupted.

  (2) When the slab pulling speed of each strand is in a state of variation and the cutting length is constant, the cutting timing of the billet slabs varies from strand to strand, and in some cases it is cut at a time. As a result, there is a problem that the temperature of the slab is lowered due to the waiting for conveyance, and the billet slab to be conveyed is interrupted at a certain time and the supply of the billet slab to the billet welding equipment is not in time.

  The present invention has been made in view of the above circumstances. The purpose of the present invention is to manufacture a steel material from a billet slab cast by multiple strands by applying a hot strip continuous rolling process. A billet in a continuous casting machine that can carry the billet slab to the next process in a predetermined cycle even if the slab drawing speed is different, and as a result, can stably carry out the hot strip continuous rolling process. It is to provide a method for cutting a slab.

A billet slab cutting method in a continuous casting machine according to a first aspect of the present invention for solving the above-described problem is a billet welding facility in which a billet slab cast by a continuous casting machine having a plurality of strands is kept in a hot state. When continuously rolling a plurality of billet slabs while welding the billet slabs at a billet welding facility, the continuous casting machine uses a billet slab to be cast. In addition, each strand is cut at an interval of the cutting set time T ₀ obtained by the following equation (1), and the cutting interval of each strand is set at an equal interval of time intervals t _i obtained by the following equation (2). It is characterized by cutting. However, in the formulas (1) and (2), T ₀ is the cutting set time (seconds), L is the target cutting length (m) of the billet slab, and V _av is the average slab drawing speed of all strands. The value (m / min), t _i is the time interval (seconds), and n is the number of strands installed.

In the billet slab cutting method in the continuous casting machine according to the second aspect of the invention, in the first aspect of the invention, the casting start time of each strand is a time corresponding to the time interval t _i obtained by the equation (2). It is characterized by starting with staggering.

The billet slab cutting method in the continuous casting machine according to the third invention is the first or second invention, wherein the continuous casting machine is provided with a device for controlling the amount of molten steel injected from the tundish into the mold. In the continuous casting machine, the hot metal surface in the mold is controlled by adjusting the slab drawing speed, and the average value V _av of the slab drawing speed is balanced with the rolling capacity of the hot rolling process. The molten steel surface position in the tundish is adjusted so as to be inside.

  According to the present invention, in the continuous hot strip rolling process, the continuous casting machine cuts the billet cast at predetermined time intervals and at predetermined uniform time intervals at each strand. Due to the fact that the cycle is at regular intervals, it is possible to prevent waiting for billet slabs to be transported and interruption of transport in downstream facilities without installing a buffer facility waiting for billet slabs to be transported. The temperature drop of the slab can also be prevented. In addition, since the cutting is performed at a constant time cycle, the cutting timing is not concentrated at one time or the cutting interval is not short. Therefore, the waiting for conveyance and the interruption of welding due to the variation in the conveyance timing can be suppressed and stable. Continuous welding is possible. Furthermore, since the production capacity of the continuous casting machine can be operated close to the rolling throughput, the amount of surplus billet slabs can be minimized, and the slab drawing speed of each strand can be individually controlled. Instead, since the slab drawing speed of all strands is raised and lowered on average, the rolling throughput and the capacity of the continuous casting machine can be easily matched.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic view of a billet continuous casting machine used in carrying out the present invention.

  As shown in FIG. 1, the billet continuous casting machine 1 is provided with a mold 2 for cooling and solidifying the molten steel 19 to form the outer shell shape of the billet cast 20, and a predetermined position above the mold 2. Is provided with a tundish 3 for relaying and supplying molten steel 19 supplied from a ladle (not shown) to the mold 2. On the other hand, below the mold 2 is a billet cast drawn from the mold 2. A plurality of slab support rolls 5 for guiding downward while supporting the piece 20 and a plurality of pinch rolls 6 for pulling out the billet cast piece 20 are installed, and further, on the downstream side of the pinch roll 6, A plurality of transport rolls 7 for transporting the cast billet slab 20 are installed. At the bottom of the tundish 3, a refractory tundish nozzle 4 for pouring the molten steel 19 into the mold 2 is installed. Between the pinch roll 6 and the transport roll 7, a measure roll 8 for measuring the length of the billet slab 20 passing through is installed. Above the transport roll 7, a billet slab to be cast is provided. A slab cutting machine 9 for cutting 20 into a predetermined length is arranged. As the slab cutting device 9, a conventional cutting machine such as a gas cutting machine or a heat saw cutting machine can be used.

  The mold 2 is provided with a molten metal surface position measuring device 15 for measuring the position of the molten steel surface in the mold 2, and the tundish 3 is a mass for measuring the mass of the molten steel 19 staying in the tundish 3. A measuring device 16 is installed. As the molten metal surface position measuring device 15, an apparatus for determining the molten metal surface position from the transmission intensity of radiation, an apparatus for directly determining the molten metal surface position by an eddy current meter, or the like may be used. The measurement values of the hot water surface position measuring instrument 15 and the mass measuring instrument 16 are input to the control device 10. Further, a thermometer 17 for measuring the surface temperature of the cut billet slab 20 is installed on the downstream side of the slab cutting machine 9, and a measurement value by the thermometer 17 is input to the control device 10. Yes. As the thermometer 17, a thermometer such as a two-color thermometer or an infrared thermometer may be used.

  The pinch roll 6 is driven by a motor 12, and the rotation speed of the motor 12, that is, the rotation speed of the pinch roll 6 is controlled by a motor drive device 11. The motor drive device 11 is pinched by a signal input from the control device 10. The rotation speed of the roll 6 is set. That is, the control device 10 determines the rotation speed of the pinch roll 6, that is, the slab drawing speed so that the mold surface position in the mold becomes a constant position based on the measurement value of the mold surface position in the mold input from the mold surface position measuring device 15. I have control. The rotational speed of the motor 12 is measured by a rotational speed measuring device 13 attached to the motor 12, and the measured rotational speed is input to the motor driving device 11 and the control device 10. The rotational speed of the motor 12 is feedback-controlled by the motor driving apparatus 11 based on the measured value of the rotational speed input to the motor driving apparatus 11. In FIG. 1, only one pinch roll is connected to the motor 12, but all the pinch rolls 6 are connected to the motors 12 and are driven by the respective motors 12.

  The target cutting length (L) of the billet slab 20 is input from the billet length setting device 18 to the control device 10, and the control device 10 receives the input target cutting length (L). And a cutting command for the billet slab 20 is transmitted to the cutting controller 14 based on the rotational speed input from the rotational speed measuring device 13, that is, the slab drawing speed. The cutting controller 14 operates the slab cutting machine 9 based on the transmitted cutting command, and the billet slab 20 is cut. Further, the measurement value of the length of the billet slab 20 by the measure roll 8 is inputted to the control device 10, and the data inputted from the rotational speed measuring device 13 and the data by the measure roll 8 are obtained. Check each other's measurement accuracy.

  The cut billet slab 20A is unloaded from the billet continuous casting machine 1 by the transfer roll 7, and is transferred to the next hot rolling step by an appropriate transfer means such as a transfer carriage. This hot rolling process is equipped with a billet welding facility, and the billet slab 20A carried out in the hot state is continuously hot rolled while being welded by the billet welding facility. Although FIG. 1 shows only one strand of the billet continuous casting machine 1, the billet continuous casting machine 1 has two or more strands having the same structure. However, only one tundish 3, the control device 10, and the billet length setting device 18 are installed in the billet continuous casting machine 1, and the others are installed for each strand. The control device 10 receives information on all strands and can control all strands.

  In the billet continuous casting machine 1 configured as described above, the present invention is carried out as follows.

  First, prior to casting the molten steel 19, a dummy bar (not shown) is inserted between the slab support rolls 5 facing from the outlet side of the pinch roll 6 which is the end of the billet continuous casting machine 1, and the upper end of the dummy bar is inserted. It arrange | positions so that a part may become a predetermined position of the casting_mold | template 2. FIG. The dummy bar is inserted into the continuous casting machine so that the upper end of the dummy bar is located at a predetermined position in the inner wall space of the mold 2 at the start of casting, and prevents leakage of the molten steel 19 injected into the inner wall space of the mold 2 at the start of casting. At the same time, the molten steel 19 is solidified at the upper end of the dummy bar to fit the slab, and the slab is pulled out downstream in the drawing direction.

  With the dummy bar arranged at a predetermined position, a ladle containing molten steel 19 is arranged at a predetermined position above the tundish 3, and the molten steel 19 is poured from the ladle into the tundish 3. The molten steel 19 injected into the tundish 3 is injected into the mold 2 through the tundish nozzle 4. In this case, in order to retain a predetermined amount of molten steel 19 in the tundish 3 or to adjust the casting start timing of each strand, the tundish nozzle 4 is filled with packed sand or the like for a predetermined time. After the elapse of time, casting may be started by removing the packing sand downward for each strand.

  The molten steel 19 injected into the inner wall space of the mold 2 comes into contact with a cast iron or cast steel dummy bar and is cooled to start solidification. In addition, the molten steel 19 comes into contact with the mold 2 and is cooled to form a solidified shell 21 at a site in contact with the mold 2. When a predetermined amount of molten steel 19 is injected into the inner wall space of the mold 2, the pinch roll 6 is driven to start pulling out the dummy bar. As the dummy bar is pulled out, the billet slab 20 having the solidified shell 21 as the surface layer and the unsolidified phase 22 inside is pulled out to the lower side of the mold 2 together with the dummy bar while being supported by the slab support roll 5.

  While controlling the number of rotations of the pinch roll 6 by the control device 10 so that the molten metal surface position measured by the molten metal surface position measuring device 15 becomes a substantially constant position, the dummy bar is continuously pulled out and the molten steel 19 is continuously cast. Is done. The billet slab 20 drawn out below the mold 2 is cooled by cooling water or air mist sprayed from a spray nozzle disposed in the gap of the slab support roll 5, and eventually solidifies to the center.

  In addition, in the continuous casting machine in which the apparatus for adjusting the injection amount of the molten steel 19 from the tundish 3 to the mold 2 is not installed like the billet continuous casting machine 1 shown in FIG. The injection amount of the molten steel 19 is determined by the surface position of the molten steel 19 in the tundish 3 and the inner diameter of the tundish nozzle 4. When the inner diameter of the tundish nozzle 4 is considered to be substantially constant in each strand, the slab drawing speed is determined by the position of the molten steel 19 in the tundish 3. Therefore, it is necessary to control the molten steel surface position in the tundish 3 so that the billet slab 20 falls within the range of the slab drawing speed at which the billet slab 20 is completely solidified inside the billet continuous casting machine 1. This is performed by adjusting the injection amount from the ladle based on the measurement value of the mass measuring device 16.

  When the leading end portion of the dummy bar of each strand is pulled out to a predetermined position of each slab cutting machine 9, the joint between the dummy bar and the billet slab 20 is cut by the slab cutting machine 9. After cutting the seam, the billet slab 20 of each strand to be cast is cut by each slab cutting machine 9 by the following method to obtain a billet slab 20A.

First, the target cutting length (L [unit: m]) of the billet slab 20 </ b> A is input to the billet length setting unit 18. The target cutting length (L) of the billet slab 20A is within the length range that can be conveyed in the billet conveyance line from the billet continuous casting machine 1 to the next hot rolling step, and the time cycle of the billet welding equipment is possible. An arbitrary length is set as the target cutting length (L). Further, the control device 10 calculates the average value of the slab drawing speed according to the following equation (3) from the number of rotations of the pinch roll 6 of each strand, that is, the slab drawing speed of each strand, input from the rotational speed measuring device 13. V _av [unit: m / min]) is calculated. However, (3) V _n in the equation is the n-th strand of slab drawing speed (m / min), n is the number of installed strand billet caster.

Based on the target cutting length (L) input from the billet length setting unit 18 and the average value (V _av ) of the slab drawing speed obtained by calculation, the control device 10 uses the following equation (1): Is used to calculate the cutting set time (T ₀ [unit: second]) and the time interval (t _i [unit: second]) is calculated using the following equation (2).

Then, based on the obtained cutting set time (T ₀ ) and time interval (t _i ), a cutting command is transmitted to the cutting controller 14 of each strand. When the cutting command is input, the cutting controller 14 operates the slab cutting machine 9 to cut the billet slab 20. That is, each strand is cut at an interval of the set cutting time (T ₀ ), and the cutting command is sent to the cutting controller 14 of each strand so that the cutting interval of each strand is equal to the time interval (t _i ). Sent to.

When the cutting interval of each strand is equal to the time interval (t _i ), if the casting start time of each strand is the same time, the length of the billet slab 20A that is cut first in the strand whose cutting order is delayed is It may also occur when the length is too long and exceeds the length range that can be transported in the billet transport line. Therefore, in order to prevent this, it is preferable to delay the casting start timing of each strand by a time corresponding to the time interval (t _i ). However, since the average value V _av of the slab drawing speed cannot be specified before the casting starts, the time interval (t _i ) cannot be obtained from the equation (2). Therefore, the expected slab extraction speed is predicted based on the inner diameter of the tundish nozzle 4 to be used, and the predicted slab extraction speed is substituted into the formula (2) instead of the average value V _av of the slab extraction speed. Then, it is preferable to start casting by shifting the time calculated in this way. By doing in this way, it becomes possible to cut | disconnect the joint of the dummy bar and billet slab 20 in each strand at the space | interval equivalent to time interval (t _i ), and billet slab 20A cut | disconnected first in each strand. Is a length close to the target cutting length (L).

FIG. 2 shows a schematic diagram of cutting when the casting start time is shifted by the time interval (t _i ) in this way. 2, is V _n in slab drawing speed of the n-th strands (m / min), Ln is at the cutting length of the n-th strands, DB is the dummy bar.

Since each strand is cut at an interval of the cutting set time (T ₀ ) as shown in FIG. 2, the cutting length of the billet cast piece 20A becomes a length according to the drawing speed of each strand, and V ₁ to When V _n are all different, L _{1 to} L _n are all different. Therefore, the equipment on the downstream side of the billet continuous casting machine 1 must be planned with equipment that can cope with this variation in length. At the same time, the time cycle of the billet welding equipment must be able to absorb these variations. However, if the target cutting length (L) is set to the above-mentioned median value of the allowable range, it can be sufficiently dealt with. Further, when these time differences are shifted at the time of cutting the joint with the dummy bar, the cutting time is corrected little by little and adjusted so as to cut at a predetermined time cycle.

The temperature of the molten steel 19 staying in the tundish 3 changes in the initial, middle and final stages of casting, and the slab drawing speed changes accordingly. Therefore, it is preferable to calculate the average value (V _av ) of the slab drawing speed at least three times during one heat casting, and to reset the cutting set time (T ₀ ) and the time interval (t _i ). Moreover, since the stable operation will be achieved as the interval becomes shorter, it is preferable to reset the timing at an interval within 10 minutes, preferably within an interval of 1 minute.

Moreover, when the casting capacity of the billet continuous casting machine 1 is not balanced with the rolling capacity of the hot rolling process, which is the next process, adjustment is made by changing the surface height of the molten steel 19 staying in the tundish 3. can do. If the molten metal surface height of the tundish 3 is increased, the average value V _av of the slab drawing speed is increased to increase the casting capacity. Conversely, if the molten metal surface height of the tundish 3 is decreased, the slab drawing speed is increased. The average value V _av decreases and the casting capacity decreases. By adjusting in this way, it is possible to match the rolling capacity very easily compared with the case of adjusting the casting capacity by adjusting the slab drawing speed of each strand.

  Note that the billet casting speed is lowered due to clogging of the tundish nozzle 4 or the like, and the billet casting has a lower limit value of the length range that can be conveyed in the billet conveying line or a lower value value of the length range that satisfies the time cycle of the billet welding equipment. If a strand is generated in which the piece 20A cannot be secured, it is determined that continuous conveyance is not possible, the hot piece continuous rolling process is stopped, and switching to individual rolling is performed.

  In carrying out the hot strip continuous rolling process, the billet slab 20 is cut in this way, so that the unloading time cycle of the cut billet slab 20A becomes a constant interval, and the buffer equipment waiting for the transport of the billet slab 20A Even if it does not install, while waiting for conveyance of billet slab 20A in downstream facilities, and interruption of conveyance can be prevented, the temperature fall of the slab resulting from waiting time can also be prevented. In addition, since the cutting is performed at a constant time cycle, the cutting timing is not concentrated at one time or the cutting interval is not opened, so that waiting for conveyance and interruption of welding due to variations in the conveyance timing are suppressed, and stable continuous Welding becomes possible.

It is the schematic of the billet continuous casting machine used when implementing this invention. It is a figure which shows the cutting | disconnection schematic diagram at the time of cutting a billet cast piece by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Billet continuous casting machine 2 Mold 3 Tundish 4 Tundish nozzle 5 Slab support roll 6 Pinch roll 7 Transport roll 8 Major roll 9 Slab cutting machine 10 Controller 11 Motor drive device 12 Motor 13 Rotational speed measuring instrument 14 Cutting control 15 Hot water surface position measuring device 16 Mass measuring device 17 Thermometer 18 Billet length setting device 19 Molten steel 20 Billet slab 21 Solidified shell 22 Unsolidified phase

Claims (3)

A billet slab cast by a continuous casting machine having a plurality of strands is conveyed in a hot rolling process with a billet welding facility in a hot state, and continuously while welding the billet slab at the billet welding facility. When hot-rolling a plurality of billet slabs, the continuous casting machine cuts the billet slabs to be cast at intervals of a cutting set time T ₀ determined by the following equation (1) for each strand, the cutting interval of each strand, wherein the cutting evenly spaced time intervals t _i obtained by the following expression (2), the cutting method of the billet slab in the continuous casting machine.
T ₀ = (L × 60) / V _av … (1)
t _i = T ₀ / n = (L × 60) / (V _av × n)… (2)
However, in the formulas (1) and (2), T ₀ is the cutting set time (seconds), L is the target cutting length (m) of the billet slab, and V _av is the average slab drawing speed of all strands. The value (m / min), t _i is the time interval (seconds), and n is the number of strands installed. The billet slab in a continuous casting machine according to claim 1, wherein the casting start timing of each strand is shifted by a time corresponding to the time interval t _i obtained by the equation (2). Cutting method. The continuous casting machine is a continuous casting machine in which no device for controlling the amount of molten steel injected from the tundish into the mold is installed, and the molten metal surface in the mold is controlled by adjusting the slab drawing speed. The molten steel surface position in the tundish is adjusted so that the average value V _av of the slab drawing speed is in a range that balances with the rolling ability of the hot rolling process. The cutting method of the billet slab in the continuous casting machine of Claim 2.

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