JP2018196893A - Crater end position detection method and detection device for continuous cast slab - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crater end position detection method and a detection device for continuously cast slabs which can accurately detect a crater end position and are excellent in durability and economy, and contribute to improvement of central segregation. SOLUTION: A plurality of pairs of pinch rolls 5 are arranged in front of a cutting position of a continuously cast slab. One of the pinch rolls 5 is a disc roll 5a that does not contact the edge portion in the width direction of the slab, and the other is a normal roll 5b that contacts the entire width of the slab. And / or the reduction force is measured and the crater end position is specified by the relationship between the measured reduction amount and the reduction force. [Selection diagram] Fig. 2

Description

  The present invention relates to a crater end position detection method and a detection apparatus for a continuous cast slab for detecting a crater end position at which the continuous cast slab is completely solidified.

  In continuous casting, as shown in FIG. 1, the slab solidified by the casting mold is moved downward, and further cooled by spray cooling or the like while passing between a large number of guide rolls and a large number of pinch rolls, After being completely solidified, it is cut into a predetermined length.

  In this continuous casting, defects called center porosity and center segregation occur at the center of the slab thickness that solidifies at the end. Therefore, the defects are suppressed by performing light reduction before complete solidification. In order to perform this light reduction at the optimum position, it is necessary to accurately detect the crater end position at which the continuously cast slab is completely solidified. However, since the crater end position constantly fluctuates due to various factors such as steel composition, casting speed, cooling temperature, and casting temperature, it is not easy to accurately detect the crater end position of a continuously cast slab.

  For this reason, Patent Document 1 describes a technique for detecting a roll load by attaching a strain gauge to a roll chock of a pinch roll and detecting a crater end position based on a change in the roll load before and after complete solidification of a slab. .

  However, in Patent Document 1, since the strain gauge is attached to the roll chock of the work roll that comes into contact with the high-temperature slab, there is a problem that the strain gauge deteriorates within a short period of time and the durability is poor. In addition, since the roll chock is designed to have high rigidity, the amount of distortion is very small and the detection accuracy is not good. Further, since the pair of pinch rolls pressurize the edge portion in the slab width direction where solidification has advanced, there is a problem that the roll load due to the solidified state of the slab center portion cannot be detected with high accuracy.

  Further, in Patent Document 2, an ultrasonic transmitter and an ultrasonic receiver are arranged with a slab interposed therebetween, the central solid fraction is calculated from the intensity of the transverse wave ultrasonic wave transmitted through the slab, and the crater end position is detected. The technology to do is described. However, since the crater end position is constantly changing, a large number of ultrasonic transmitters and ultrasonic receivers must be arranged in the moving direction of the slab, resulting in a high cost. Further, in order to increase the detection accuracy, it is necessary to dispose the ultrasonic transmitter and the ultrasonic receiver close to the surface of the high-temperature slab, which has a problem in durability.

  Patent Document 3 describes a technique for detecting the raising / lowering position and pressure of a roll raising / lowering cylinder in a zone for rolling down a slab and detecting the crater end position from these detection values. However, since the roll reduces the entire width of the slab, the edge of the slab width direction where solidification has progressed will be pressed, and the roll load due to the solidified state of the center part of the slab cannot be detected accurately. There was a problem similar to Document 1.

  Further, Patent Document 4 describes a technique for detecting a crater end position from at least one of relief pressure, pressure fluctuation, stroke displacement amount, and displacement amount fluctuation of a cylinder that lowers a pinch roll. However, this method has the same problem as in Patent Documents 1 and 3.

Japanese Patent Laid-Open No. 9-225611 Japanese Patent Laid-Open No. 11-83814 JP 2000-15409 A JP 2014-18838 A

  Therefore, the object of the present invention is to solve the above-mentioned conventional problems, to detect the crater end position with high accuracy, and to detect the crater end position of a continuous cast slab and to detect it with excellent durability and economy. To contribute to the improvement of central segregation.

  The crater end position detection method of the continuous cast slab of the present invention made to solve the above-mentioned problem is that a plurality of pairs of pinch rolls are arranged before the cutting position of the continuous cast slab, and one of the paired pinch rolls Is a disc roll that does not contact the edge of the slab width direction, and the other is a normal roll that contacts the entire width of the slab, and the amount of reduction and / or reduction force is measured while the center portion of the slab is being reduced by the disc roll. The crater end position is specified by the relationship between the measured amount of reduction and the reduction force.

  As in claim 2, the roll roll length of the roll is preferably set within a predetermined range, and as in claim 3, the amount of reduction of the disk roll is measured by a position sensor provided in a cylinder for rolling down the disk roll. It is preferable to detect and / or detect the rolling force of the disc roll with a cylinder pressure sensor. Further, as in claim 4, a plurality of disc rolls having different roll body lengths are arranged in order from the downstream before the cutting position of the continuous cast slab, and the inside of the plurality of disc rolls according to the width of the cast slab. From the above, it is preferable that the crater end position is specified based on the relationship between the measured reduction amount and the reduction force, and the reduction amount, the reduction force, and the slab according to claim 5. It is preferable to obtain a relationship with the solid phase ratio in advance, obtain the solid fraction at the reduction position from the measured reduction amount and reduction force, and specify the crater end position.

  Further, in the continuous cast slab crater end position detecting device of the present invention made to solve the above problems, a plurality of pairs of pinch rolls capable of reducing the slab are arranged before the continuous cast slab cutting position. One of these pair of pinch rolls is a disk roll that does not contact the edge of the slab width direction, and the other is a normal roll that contacts the entire width of the slab, and the cylinder that squeezes the disk roll is pressed down. A position sensor and / or a pressure sensor for detecting the amount is provided. As in claim 7, the roll roll length of the roll is preferably within a predetermined range, and as in claim 8, a position sensor and / or a pressure sensor is arranged in the cylinder for rolling down the disk roll. It is preferable that Further, as in claim 9, before the cutting position of the continuous cast slab, a plurality of disk rolls having different roll cylinder lengths are arranged in order from the downstream, and one or more of the plurality of disk rolls are cast. It is preferable that the piece can be reduced, and the crater end position can be specified from the measured reduction amount and / or the reduction force, and the reduction amount and the reduction force obtained in advance as in claim 10 The step of storing the relationship with the solid fraction of the slab, the step of obtaining the solid fraction at the reduction position from the reduction amount and the reduction force measured based on the relationship, and the crater end position from the obtained solid fraction It is preferable that the tail is provided with a specifying step.

  According to the method for detecting a crater end position of a continuous cast slab of the present invention, the amount of reduction and the reduction force are measured while the center part of the slab is being squeezed by a disk roll that does not contact the edge part in the slab width direction. Since the crater end position is specified by the relationship between the reduced amount and the reduced force, the solidified state of the center portion of the slab can be accurately detected by removing the influence of the edge portion in the width direction of the solidified slab.

  In addition, since the amount of reduction and / or the reduction force can be measured by a position sensor or pressure sensor provided on the cylinder that lowers the disk roll, there is no deterioration due to radiant heat from a high-temperature slab and a long service life is achieved. Can be made.

It is whole explanatory drawing of a continuous casting installation. It is a longitudinal cross-sectional view of a roll segment. It is a graph which shows the relationship between reduction amount, reduction force, and the solid-phase rate of a slab. It is explanatory drawing which shows the example of several disc roll arrangement | positioning before the cutting position of a continuous casting slab. It is a graph which shows the reduction effect of the segregation index | exponent by this invention.

Embodiments of the present invention will be described below.
FIG. 1 is an overall explanatory view of a continuous casting facility, wherein 1 is a water-cooled casting mold, 2 is a tundish, and 3 is an immersion nozzle. Molten steel is poured into the casting mold 1 from the tundish 2 through the immersion nozzle 3, and solidification starts from the outer portion. The slab is cooled by spray cooling or the like while passing through a number of pairs of guide rolls 4 arranged below the casting mold 1 and solidification proceeds. A roll segment 6 having a plurality of pairs of pinch rolls 5 is disposed before the cutting position of the continuous cast slab, that is, near the completion position of solidification, and light reduction is performed before the slab is completely solidified. Cooling control is performed so that the complete solidification position (crater end position) of the slab is almost constant. However, as described above, the crater end position constantly fluctuates due to various factors. It is desired to detect with high accuracy.

  FIG. 2 is a longitudinal sectional view of a roll segment 6 provided with a pinch roll 5. As shown in FIG. 2, the roll segment 6 includes a plurality of pairs of pinch rolls 5 arranged vertically so as to sandwich the slab. The pinch roll 5 is composed of a pair of a disk roll 5a that does not contact the edge portion in the slab width direction and a normal roll 5b that contacts the entire width of the slab. That is, the length of the large-diameter portion of the disk roll 5a is shorter than the width of the slab and is configured not to contact the edge portion in the slab width direction in which solidification has been completed. For this reason, the rolling force applied to the slab by the disk roll 5a does not act on both ends of the slab, and only the center part is reduced.

  The normal roll 5b is rotatably supported by the lower frame 7, and the upper disk roll 5a is rotatably supported by the upper frame 8. The lower frame 7 includes a pair of left and right cylinders 9, and the upper frame 8 includes a pair of left and right cylinders 10. Both frames lightly reduce the slab by these cylinders 9 and 10. The cylinders 9 and 10 are preferably hydraulic cylinders. The lower frame 7 may be a fixed frame fixed to the base.

  Among these cylinders 9 and 10, at least a cylinder 10 that lowers the disk roll 5 a is provided with a position sensor 11 and / or a pressure sensor 12 that detects the amount of reduction. In this embodiment, the position sensor 11 is called an in-rod sensor, and is a sensor that is detected by a high-frequency coil in which a magnetic body and a non-magnetic body are alternately attached to the cylinder rod at a constant pitch and the movement of the cylinder rod is built-in.

  Since this in-rod sensor can detect the movement of the cylinder rod with high accuracy, it is suitable for detecting the amount of reduction. However, the position sensor 11 for detecting the reduction amount is not limited to this, and other displacement sensors may be used. The position sensor 11 can also be provided on the cylinder 9 of the normal roll 5b. In the embodiment shown in FIG. 2, the upper and lower cylinders 9 and 10 are in-rod sensor built-in types. A commercially available product can be used for the in-rod sensor.

  The pressure sensor 12 detects the reduction force from the pressure of the working fluid in the cylinder 10, and various existing pressure sensors can be used. The pressure sensor 12 does not need to be directly attached to the cylinder 10 but can be attached to the supply path of the working fluid. Since these position sensor 11 and pressure sensor 12 are in a place where they do not receive radiant heat from a high-temperature slab, there is no risk of deterioration due to heat and excellent durability. In addition, the measurement accuracy is higher than that of the ultrasonic sensor and the cost is low.

  The above-described structure is incorporated in each pinch roll 5 arranged in the moving direction of the slab, and the crater end position can be accurately detected from the amount of reduction and the reduction in the rolling pressure in the moving direction of the slab. Details will be described below.

  FIG. 3 is a graph in which the horizontal axis represents the reduction amount (mm) and the vertical axis represents the reduction force (MPa). When the inside of the slab is completely solidified, the reduction amount of the slab becomes small even if the reduction force is increased. Conversely, when the inside of the slab is unsolidified, increasing the reduction force causes internal flow of the slab, so the amount of reduction of the slab also increases. In the graph of FIG. 3, a line indicating the relationship between the reduction amount and the reduction pressure in each case where fs (solid phase ratio) is 1.0, 0.8, and 0.3 is shown.

  Here, the line of fs = 1.0 was specified by the strain gauge type crater end detection method installed in the previous segment. Moreover, the line of fs = 0.8 was specified from the presence or absence of flow generation inside the slab from the structure observation result when the slab was reduced. Moreover, the line of fs = 0.3 was specified by the presence or absence of the occurrence of negative segregation from the result of the structure observation during slab reduction.

  The left side of the line of fs = 1.0 is a complete solid phase region. The region between the fs = 1.0 line and the fs = 0.8 line is a region with a high solid phase ratio. The area between the fs = 0.8 line and the fs = 0.3 line is a low solid phase region, and the right side is an unsolidified region.

  As shown in FIG. 3, if the relationship between the reduction amount and / or the reduction force and the solid fraction of the slab is obtained in advance, the detection position can be determined from the reduction amount and the reduction force measured by the detection device of the present invention. The solid phase ratio can be determined. In addition, since the measurement of the amount of reduction and the reduction force is performed on each of a plurality of pairs of pinch rolls 5 arranged at a constant pitch in the longitudinal direction of the slab, the solids detected at each position in the longitudinal direction of the slab are detected. The crater end position can be accurately identified from the change in the phase ratio. In particular, in the present invention, the pinch roll 5b reduces only the center portion in the width direction of the slab, so that the solidified state of the center portion is not affected by the edge portion in the width direction of the completely solidified slab. It can be detected accurately.

The body length L1 of the disk roll 5a is preferably a length in a range defined by the following formula (1).
W-L1> 0.2 × t (1)
W: width of cast slab (mm), L1: body length of disc roll (mm), t: thickness of cast slab (mm)
The reason for defining the formula (1) is that if it is inside about 10% of the thickness of the slab from both ends of the slab width direction, it is affected by the edge of the slab width direction that has been cooled and hardened first. This is because it becomes difficult. The body length L1 of the disk roll 5a is required to be at least more than 1/3 of the width W of the slab in order to stabilize the conveyance of the slab.

  In addition, the slab cast is not necessarily the same in width, and there are a narrow width, a wide width, and a plurality of widths. For this reason, when the cylinder length of the disk roll 5a is not variable considering only a specific width, if the width of the slab is narrower than that, or conversely wide, proper reduction cannot be performed, and the solidification state is accurately determined. It becomes difficult to detect. Also, if the disk roll is exchanged in accordance with the width of the slab, casting pauses frequently occur, and the productivity may be significantly reduced.

  Furthermore, when only one crater end detection device according to the present invention is installed, the crater end detection device may not necessarily be disposed at an appropriate position for solidification, and the reduction may pass in an incomplete solidification state or the solidified state may be reduced. Again, it becomes difficult to accurately detect the coagulation state.

  For this reason, a plurality of disc rolls having different roll cylinder lengths are arranged in order from the downstream before the cutting position of the continuous cast slab, and one or more of the plurality of disc rolls are selected according to the width of the cast slab. It is preferable to reduce the crater end position based on the relationship between the measured reduction amount and the reduction force.

  FIG. 4 is an example of a plurality of disk roll arrangements before the cutting position of the continuous cast slab. In FIG. 4A, the roll body length of the disk roll 5a is gradually shortened from upstream to downstream. FIG. 4A is preferable because an appropriate disc roll can be selected and used in accordance with the width of a cast slab to be cast.

  Further, as shown in FIG. 4B, in order to gradually shorten the roll body length of the disk roll 5a from the upstream side to the downstream side, if the arrangement thereof is devised without arranging them in order, FIG. ) As well as a disk roll of a certain roll body length and a disk roll of the next short roll body length downstream, and measuring the changes in the rolling force and the amount of rolling in each. Therefore, the crater end can be detected more reliably. Note that the same effect can be achieved by arranging a plurality of groups in which the roll body length of the disk roll is gradually shortened from upstream to downstream.

  Further, as shown in FIG. 4C, when a plurality of disk rolls having the same roll body length are arranged from the upstream to the downstream, and the change in the reduction force and the reduction amount is measured respectively, the same as in FIG. 4B. In addition, the crater end can be detected more reliably.

  Thus, according to the crater end position detection technology of the present invention, the fluctuating crater end position can be specified online, so that the slab is lightly reduced at a position immediately before the slab is completely solidified and the center porosity or Defects called center segregation can be reduced. Therefore, in the continuous casting equipment to which the present invention is applied, as shown in FIG. 5, the segregation index is improved by 15%, which can contribute to the improvement of the center segregation.

DESCRIPTION OF SYMBOLS 1 Mold for casting 2 Tundish 3 Immersion nozzle 4 Guide roll 5 Pinch roll 5a Disc roll 5b Normal roll 6 Roll segment 7 Lower frame 8 Upper frame 9 Cylinder 10 Cylinder 11 Position sensor 12 Pressure sensor

Claims (10)

  Normally, multiple pairs of pinch rolls are placed in front of the cutting position of the continuous cast slab, one of the paired pinch rolls is a disc roll that does not contact the edge of the slab width direction, and the other is in contact with the full width of the slab The roll is measured, and the rolling amount and / or the rolling force is measured while rolling down the center portion of the slab by the disk roll, and the crater end position is specified by the relationship between the measured rolling amount and the rolling force. Crater end position detection method for continuous cast slabs. The crater end position detection method for a continuously cast slab according to claim 1, wherein a disc roll having a range of the following formula (1) is used as the barrel length of the roll.
W-L1> 0.2 × t (1)
Here, W: width of cast slab (mm), L1: body length of disc roll (mm), t: thickness of cast slab (mm), and L1> W / 3   3. The amount of reduction of the disk roll is detected by a position sensor provided in a cylinder for lowering the disk roll, and / or the reduction force of the disk roll is detected by a pressure sensor of the cylinder. Crater end position detection method for continuous cast slabs.   A plurality of disc rolls having different roll body lengths are arranged in order from the downstream before the cutting position of the continuous cast slab, and one or more of the plurality of disc rolls are used according to the width of the cast slab to be cast. 4. The method for detecting a crater end position of a continuous cast slab according to any one of claims 1 to 3, wherein the crater end position is reduced.   The relationship between the reduction amount, the reduction force, and the solid fraction of the slab is obtained in advance, the solid fraction at the reduction position is obtained from the measured reduction amount and the reduction force, and the crater end position is specified. The crater end position detection method of the continuous cast slab according to any one of claims 1 to 4.   A plurality of pairs of pinch rolls capable of rolling down the slab are arranged before the cutting position of the continuous cast slab, and one of these pair of pinch rolls is a disk roll that does not contact the edge in the width direction of the slab. The other is a normal roll that contacts the entire width of the slab, and the cylinder for rolling down the disk roll is provided with a position sensor and / or pressure sensor for detecting the amount of rolling down. A piece of crater end position detector. The crater end position detecting device for a continuous cast slab according to claim 6, wherein a disk roll having a roll body length in the following range is used for the roll.
W-L1> 0.2 × t (1)
W: width of cast slab (mm), L1: body length of disc roll (mm), t: thickness of cast slab (mm)   The crater end position detection device for a continuous cast slab according to claim 6 or 7, wherein a position sensor and / or a pressure sensor is arranged in a cylinder for lowering the disk roll.   Before the cutting position of the continuous cast slab, a plurality of disc rolls having different roll cylinder lengths are arranged in order from the downstream, and the slab can be rolled down by one or more of the plurality of disc rolls and measured. The crater end position detection device for a continuous cast slab according to any one of claims 6 to 8, wherein the crater end position can be specified from a reduction amount and / or a reduction force.   The step of storing the relationship between the reduction amount, the reduction force, and the solid fraction of the slab that has been obtained in advance, and the step of obtaining the solid fraction at the reduction position from the reduction amount and the reduction force measured based on the relationship And a crater end position detection device for a continuous cast slab according to any one of claims 6 to 9, further comprising: a step of specifying a crater end position from the obtained solid phase ratio.