JP2013099760A - Continuous casting apparatus and method for determining state of molten metal of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous casting apparatus which can readily determine a state of a molten metal in a crucible.SOLUTION: The continuous casting apparatus includes: a crucible 10 to which a material 13 to be melted is loaded; a material loading part 63 from which the material 13 to be melted is loaded; an induction heating coil 18 positioned in an outer circumference of the crucible 10 and heating the loaded material 13 to be melted to convert it into the molten metal 14; a melting power supply device 50 for supplying a current to the induction heating coil 18; a bottom plate elevating part L for extracting downwardly an ingot that is formed from the partially solidified molten metal 14; a frequency detection part 52 that is provided to detect a surface position of the molten metal 14 in the crucible 10 and detects a frequency of a supply current to the induction heating coil 18; and a control part 40 for controlling casting based on the detected value of the frequency.

Description

  The present invention relates to a continuous casting apparatus and a method for determining a molten metal state in which a material to be melted such as metal is melted in a crucible and the molten metal is solidified to continuously perform casting.

  The continuous casting method melts while melting a conductive material such as metal into a crucible (melting furnace), and at the same time, a part of the molten metal is gradually cooled in the crucible. This is a casting method in which rod-like or thick plate-like ingots (ingots) having substantially the same cross-sectional shape as that of the crucible are continuously formed. An example of a continuous casting apparatus that performs this continuous casting method is the continuous casting apparatus described in Patent Document 1.

  FIG. 5 is a cross-sectional view showing a crucible portion in the continuous casting apparatus (cold wall induction melting continuous casting apparatus) of the invention according to Patent Document 1. The basic structure of the continuous casting apparatus will be described with reference to FIG.

  The crucible 10 has, for example, an inner peripheral surface with a diameter of about 80 to 500 mm. The crucible 10 has a predetermined interval with respect to a side wall 20 in which a plurality of segments 16 each having a cooling water passage 16 a are divided in a circumferential direction through slits 17 having a predetermined size, and an outer peripheral surface of the side wall 20. And a copper tube induction heating coil 18 having a cooling water passage 18a therein, a water-cooled bottom plate 1 disposed so as to be movable up and down with respect to the side wall 20, and the bottom plate 1 And a drawing shaft 12 that moves up and down.

  The bottom plate 1 includes an upper member 2 and a lower member 3. Each member 2, 3 is formed with a dimension in which the outer diameter in the horizontal cross section is slightly smaller than the diameter of the inner peripheral surface of the side wall 20 so that the molten metal 14 does not leak between the members 2, 3. Yes. The upper member 2 has a bottomed hollow cylindrical shape whose vertical dimension is smaller than the radial dimension. The upper member 2 having a hollow cylindrical shape is inverted, and the bottom portion 2a is disposed above, and the hollow tube portion (cooling water chamber) 2d is disposed below. A concave portion 2b having a non-penetrating and frustum-shaped space is provided at the radial center of the bottom portion 2a disposed above. The side surface 2c that defines the recess 2b is formed in a tapered shape, and the space becomes wider as it goes downward. On the other hand, the lower member 3 is provided with two through holes communicating with the cooling water chamber 2d of the upper member 2, and serves as a cooling water inlet 3a and an outlet 3b. In addition, a drawing shaft 12 is fixed to a central portion in the radial direction at the lower portion of the lower member 3.

  In the illustrated form, the upper member 2 and the lower member 3 of the bottom plate 1 are sealed and integrated from the outer peripheral side. By this seal welding, the hollow cylindrical portion 2d becomes a cooling water chamber 2d communicating with the cooling water inlet 3a and the outlet 3b, and the entire bottom plate 1 is cooled by the cooling water flowing in from the inlet 3a. The molten metal 14 in which the charged material 13 is melted in the crucible 10 flows into the recess 2 b at the beginning of melting and becomes a part of the solidified phase 15 formed in the lower portion of the molten metal 14. When the drawing shaft 12 is lowered in this state, a downward pulling force is transmitted to the solidified phase 15 via the tapered side surface 2c in the recess 2b, and the solidified phase 15 and the molten metal 14 are gradually lowered. And the lower part of the molten metal 14 changes to the solidification phase 15 sequentially with the passage of time, and the length of the ingot (ingot) increases. Then, the ingot is sequentially drawn downward, and finally an ingot having a long rod shape (for example, a length of 300 to 1000 mm) is formed.

  FIG. 6 is a diagram showing a configuration including a control device of a conventional continuous casting apparatus. The extraction shaft 12 is connected to a lifting mechanism composed of a ball screw 31 and a nut 30. A bottom plate elevating part L is constituted by the drawing shaft 12 and the elevating mechanism. The drawing shaft 12 can be moved up and down by rotating the ball screw 31 with the servo motor 33 via the speed reducer 32. The servo motor 33 includes a resolver 34 that detects the rotation angle of the rotation shaft of the servo motor 33.

  The melting power supply device 50 is a device that supplies a high-frequency current for induction heating to the induction heating coil 18 that constitutes an LC resonance circuit together with the melting power supply device 50. 10 is a device for supplying a high-frequency current with an output of about 100 kW and a frequency of about 10-50 kHz. The output of the melting power supply device 50 is controlled by the melting power supply device control unit 51.

  The casting control apparatus 40A includes a drawing control unit 42 and a servo driver 44 including an inverter as main components. The drawing control unit 42 controls the entire casting control apparatus 40 </ b> A as a whole, and controls the lifting / lowering operation of the bottom plate 1 of the crucible 10. When pulling out the ingot downward, the pull-out control unit 42 uses a pull-out preparation completion signal (temperature detection or the like to dissolve the material 13 to be melted in the crucible 10 from the melting power supply device control unit 51. 14 is detected and the bottom plate 1 is lowered by instructing the servo driver 44 and starting the servo motor 33. At this time, the detected value of the rotation angle of the servo motor 33 detected by the resolver 34 is fed back to the servo driver 44.

  In this case, the extraction control unit 42 controls the servo driver 44 so that the bottom plate 1 is lowered from the reference position (the position of the bottom plate 1 shown in FIG. 6) to a predetermined position (for example, 300 to 1000 mm below) at a constant predetermined speed. The rotation (rotation speed and rotation amount) of the servo motor 33 is controlled via In this way, an ingot having a predetermined length can be manufactured by melting the material 13 to be melted in the crucible 10 to form a molten metal 14 and drawing it at a constant speed while solidifying.

JP-A-8-141705 JP 2008-194700 A

  As described above, in the conventional continuous casting apparatus, the molten metal 14 is pulled out in the crucible 10 while the bottom plate 1 is lowered at a constant speed by the casting control apparatus 40A.

  In the invention according to Patent Document 1, the ingot is pulled out at a constant speed. Here, in the middle of drawing, the ingot sometimes cracked or constricted (hereinafter referred to as “crack or the like”). Here, “cracking or the like” means a state in which the upper region and the lower region of the ingot are connected as much as possible, and the case where each region is separated is called “dividing”.

  The cause of cracks and the like in the ingot is that there is a so-called “koji” between the inner peripheral surface of the crucible 10 and the solidified phase 15 (overload caused by the solidified phase 15 being caught on the inner peripheral surface of the crucible 10, etc. ) Occurs, an excessive tensile stress is applied to the ingot, or an influence of a thermal stress difference between a portion close to the molten metal 14 and a portion far from the molten metal 14 in the ingot is mentioned. When cracks or the like are generated in this way, the lower region of the ingot is continuously moved downward with the generated cracks or the like as a boundary, but the upper region of the ingot is the upper portion due to friction with the inner peripheral surface of the crucible 10. When the moving speed of the region is reduced or stagnated, cracks and the like may grow. When cracks and the like grow in this way, in the worst case, the ingot is divided into upper and lower parts, and depending on the state of the division, an accident occurs in which the molten metal 14 flows downward from the bottom of the crucible 10 or overflows from the crucible 10. (Hot water leak) would be very dangerous because it would result in the destruction of the entire device.

  By the way, as described above, when the moving speed of the upper region in the ingot decreases or stagnates, the material 13 to be melted 13 is continuously put into the crucible 10, so that the crucible 10 is reduced by the decrease in the moving speed. The surface (liquid level) of the inner molten metal 14 rises. For this reason, judging the state of the molten metal 14 in the crucible 10 (specifically, the surface of the molten metal 14 rising) is extremely important for predicting the occurrence of the accident. However, conventionally, the state of the molten metal 14 in the crucible 10 has been determined by the operator's visual observation. Moreover, in many cases, the crucible 10 is installed in an airtight container (for example, the state shown in FIG. 2), and the melting and casting of the material 13 to be dissolved can be performed in a vacuum or in an inert gas atmosphere. ing. Therefore, visual observation in this structure is very difficult because an operator has to perform through a small viewing window provided in the airtight container. In addition to this, since it is not known when a crack or the like occurs in the ingot, the visual inspection must be performed clearly during operation of the continuous casting apparatus, which places a heavy burden on the operator.

  By the way, in the invention according to Patent Document 2, since the pulling operation is performed at a constant speed in the invention according to Patent Document 1, there is a “koji” between the inner peripheral surface of the crucible 10 and the solidified phase 15. It is an object to prevent the inner peripheral surface of the crucible 10 from being damaged when it occurs, and to prevent the occurrence of defects such as cracks and irregularities on the surface of the drawn ingot.

  Specifically, the continuous casting apparatus of the invention according to Patent Document 2 includes a torque current detection unit that detects a load torque current of a servo motor when the bottom plate is lowered, and a load torque of the servo motor detected by the torque current detection unit. Extraction overload determination unit for determining that the current exceeds a predetermined value, and melting power in induction heating when the load torque current of the servo motor is determined to exceed a predetermined value by the extraction overload determination unit When the state in which the load torque current of the servo motor is determined to exceed the predetermined value by the induction heating power increase control unit that increases the predetermined amount by the induction heating power increase control unit and the pulling overload determination unit continues for a predetermined time, A pull-out pause system that pauses the servo motor to pause the descent of the bottom plate and restarts the servo motor after a predetermined time to resume the descent of the bottom plate. And a part. When the load torque current exceeds a predetermined value, the induction heating power increase control unit increases the melting power in the crucible to soften or soften the portion where the koji between the crucible side wall and the solidification phase occurs. Eliminates overload by dissolving.

  That is, the invention according to Patent Document 2 is an invention for determining that the extraction load has increased by detecting the load torque current of the servo motor. However, when a crack or the like occurs in the ingot as described above, the drawing load does not always increase. This is because cracks and the like may grow even if the drawing is performed with a constant drawing load. Therefore, the invention according to Patent Document 2 may not be effective when a crack or the like occurs in the ingot. Moreover, judging the state of the molten metal in the crucible as described above is not considered in the invention according to Patent Document 2.

  In view of such problems, the present invention can easily determine the state of the molten metal in the crucible, and thereby a continuous casting apparatus capable of safe and stable continuous casting, and a molten state determination method for the continuous casting apparatus. The issue is to provide.

  The present invention provides a crucible into which a material to be melted is charged, a material charging part for charging the material to be melted into the crucible, and an outer periphery of the crucible, and heats the material to be melted into the crucible. An induction heating coil as a molten metal, a melting power supply device for supplying current to the induction heating coil, and a bottom plate of the crucible can be moved up and down, and a part of the molten metal is solidified in the crucible by lowering the bottom plate. Based on the detected value of the frequency by the frequency detection unit, a frequency detection unit for detecting the frequency of the current supplied from the melting power supply device to the induction heating coil, And a control unit that controls casting.

  According to this, the frequency detection part can detect the surface position of the molten metal in the crucible by detecting the frequency of the current supplied from the melting power supply device to the induction heating coil. For this reason, the state of the molten metal in the crucible can be easily determined.

  As a further aspect of the present invention, the control unit includes at least one of a material charging control unit that controls charging of the material to be melted into the crucible and a pulling control unit that controls the downward pulling of the ingot. Have one.

  According to this, it is determined by the frequency determination part whether the detected value of the frequency is within the vertical range, and the casting is controlled according to this determination. For this reason, casting can be performed while keeping the surface position of the molten metal in the crucible within a predetermined range.

  As a further aspect of the present invention, when the detected value of the frequency by the frequency detector exceeds a set upper limit, the material input control unit has a detected value of the frequency for the material input unit. Stop charging the material to be melted into the crucible until the upper limit is reached.

  According to this, when the detected value of the frequency exceeds the set upper limit, the material charging control unit stops the charging of the material to be melted by the material charging unit into the crucible. For this reason, it can suppress that the molten metal in a crucible continues increasing.

  And as for the present invention, as a further aspect, when the state in which the frequency detection value by the frequency detection unit exceeds a set upper limit continues for a predetermined time, the extraction control unit Stops descending.

  According to this, when the state in which the detected value of the frequency exceeds the set upper limit continues for a predetermined time, the extraction control unit stops the lowering of the bottom plate by the bottom plate elevating unit. For this reason, the ingot is left in a state where it is divided into upper and lower portions to suppress the occurrence of hot water leakage, or even in a state where the ingot does not reach division, the ingot is divided due to growth of cracks and the like. It can be suppressed.

  As a further aspect of the present invention, when the frequency detection value by the frequency detection unit is less than a set lower limit, the extraction control unit has a frequency detection value that is greater than or equal to a set lower limit with respect to the bottom plate elevating unit. Until the bottom plate is lowered.

  According to this, when the detected value of the frequency is less than the set lower limit, the drawing control unit stops the bottom plate from being lowered by the bottom plate elevating unit. For this reason, it can suppress that the molten metal in a crucible continues reducing.

  Further, the present invention provides a crucible into which a material to be melted is charged, a material charging part for charging the material to be melted into the crucible, and an outer periphery of the crucible and melts the material to be melted into the crucible. An induction heating coil to be melted, a melting power supply device for supplying current to the induction heating coil, and a bottom plate of the crucible can be moved up and down, and a part of the molten metal is in the crucible while lowering the bottom plate. A molten metal state determination method in a continuous casting apparatus comprising a bottom plate elevating part for pulling down an ingot formed by solidification, detecting a frequency of a supply current from the melting power supply device to the induction heating coil, It is the molten state judgment method of the continuous casting apparatus which judges the state of the said molten metal based on the detected value of a frequency.

  According to this, the surface position of the molten metal in the crucible can be detected by detecting the frequency of the current supplied from the melting power supply device to the induction heating coil. For this reason, the state of the molten metal in the crucible can be easily determined.

  The present invention can easily determine the state of the molten metal in the crucible. For this reason, safe and stable continuous casting is possible.

It is a block diagram which shows the part regarding melt | dissolution and casting of the continuous casting apparatus which concerns on one Embodiment of this invention. It is a block diagram except a casting control apparatus and a melting power supply apparatus among the whole same continuous casting apparatus. (A) is the graph which showed the change of the detected value of a frequency, (B) is a table | surface which shows the condition of the detected value of a frequency, and the treatment in each condition. It is a flowchart which shows the flow of casting in the continuous casting apparatus. It is sectional drawing which shows the crucible part of a continuous casting apparatus. It is a block diagram which shows an example of the conventional continuous casting apparatus.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing a configuration of a part related to melting and casting of the continuous casting apparatus of the present embodiment. In this continuous casting apparatus, as shown in FIG. 2, the crucible 10 is installed in an airtight container 60, and the melting and casting of the material 13 to be melted such as metal is performed in a vacuum (or in an inert gas atmosphere). Can do.

  The configuration of the continuous casting apparatus shown in FIG. 1 is the same as that of the conventional continuous casting apparatus shown in FIG. That is, it is an apparatus for obtaining an ingot (ingot of metal or the like) by raising and lowering the bottom plate 1 and sequentially pulling out the material to be melted 13 melted in the crucible 10 downward. In addition, a servo motor 33, a speed reducer 32, and a ball screw 31 are used as a drive source for a lifting mechanism that lifts and lowers the bottom plate 1.

  FIG. 2 shows a state where the crucible 10 portion of the continuous casting apparatus shown in FIG. By doing in this way, melt | dissolution and casting can be performed in a vacuum (or in inert gas atmosphere).

  The airtight container 60 is shut off from the outside in an airtight state, has a double wall structure so that the main body 61 of the airtight container 60 can be cooled with water, and has an open / close door 62. The open / close door 62 is provided with a viewing window 62a so that the inside of the airtight container 60 can be viewed by an operator. Further, the opening / closing door 62 is provided with a handle 62b that is gripped by an operator when opening and closing. Further, the main body 61 of the airtight container 60 is also provided with viewing windows 61a and 61b on the upper surface.

  A material charging part 63 is provided at the upper part of the main body 61 of the hermetic container 60, and the material 13 to be melted can be charged into the crucible 10 by this material charging part 63. Further, since the bottom plate 1 of the crucible 10 is configured to be moved up and down by the extraction shaft 12, in order to maintain the airtightness of the extraction shaft 12 and the airtight container 60, the outer peripheral portion 12 a of the extraction shaft 12 is provided with a shaft. A seal 35 is provided.

  The tank body 61 is connected in parallel with a first valve 64a, a second valve 64b, and a third valve. The first valve 64a is connected to the vacuum pump 65, and when in the open state, the air in the airtight container 60 is sucked by the vacuum pump 65 and can be exhausted to the outside. The second valve 64b is connected to a gas cylinder 66 that contains argon gas or the like, and allows the argon gas or the like of the gas cylinder 66 to be supplied into the hermetic container 60 when the gas valve 66 is opened. The third valve 64c is open to the outside, and enables external air to be supplied to the airtight container 60 when the third valve 64c is open.

  With the above configuration, by controlling the opening and closing of the first to third valves 64a to 64c, the material to be dissolved from the material charging unit 63 to the crucible 10 in a state where the inside of the hermetic container 60 is in a vacuum or an inert gas atmosphere. 13, the material to be melted 13 in the crucible 10 is heated and melted by the induction heating coil 18 to form the molten metal 14.

  The configuration of the continuous casting apparatus shown in FIG. 1 is different from the configuration of the conventional continuous casting apparatus shown in FIG. 6 in the configuration of a casting control device 40 and a melting power supply device 50 as control units, and other configurations. Is the same as the configuration shown in FIG. For this reason, the same code | symbol is attached | subjected to the same element on the figure. Hereinafter, the description will focus on the casting control device 40 and the melting power supply device 50, which are different in configuration from the conventional continuous casting device.

  The casting control device 40 includes a frequency determination unit 41, a drawing control unit 42, a material input control unit 43, and a servo driver 44. The melting power supply device 50 includes a melting power supply device control unit 51 and a frequency detection unit 52. However, the frequency detection unit 52 may be provided not in the melting power supply device 50 but in the casting control device 40. In some cases, the frequency detection unit 52 is separated from the continuous casting device and can be attached to and detached from the continuous casting device. It may be said.

  The frequency detection unit 52 is connected to the melting power supply device control unit 51 and detects the frequency of the supply current (high-frequency current) from the melting power supply device 50 to the induction heating coil 18. In this embodiment, the frequency detection unit 52 is provided in the melting power supply device 5 separately from the melting power supply device control unit 51, but may be integrated with the melting power supply device control unit 51. Further, the frequency indicated by the melting power supply device control unit 51 may be detected, or the frequency may be detected by measuring the frequency on the path from the melting power supply device 50 to the induction heating coil 18. That is, the mode of the frequency detection unit 52 is not limited as long as the frequency of the current supplied from the melting power supply device 50 to the induction heating coil 18 can be detected.

  The frequency determination unit 41 receives the frequency detection signal from the frequency detection unit 52, and the detected value of the frequency of the current supplied from the melting power supply device 50 to the induction heating coil 18 has a vertical range with respect to a preset ideal value. It is determined whether it is within the given vertical range (see FIG. 3B).

  The upper and lower limits of the frequency vary depending on the material of the material 13 to be melted, the amount of charge, and the supplied power. As a guideline, the upper limit is the frequency and the lower limit at which the surface position of the molten metal 14 in the crucible 10 becomes the upper end of the crucible 10. Is a frequency at which the molten metal 14 cannot maintain the non-solidified phase (the entire solidification starts). The vertical width of the frequency is several hundred Hz with respect to the frequency of the supply current (about 10 to 50 kHz).

  By determining the frequency, the state of the molten metal 14 in the crucible 10 (specifically, the surface position of the molten metal 14) can be detected. Using this detection result, the state of the molten metal in the crucible 10 can be determined. Next, the principle of the detection will be described. First, when the molten metal 14 in the crucible 10 increases, the material 13 to be melted has conductivity, so that the surface of the molten metal 14 in which the material 13 to be melted having melted has risen, and the LC resonance circuit. The inductance of the induction heating coil 18 that constitutes is reduced.

Where the resonance frequency equation 1 / f = 2π√ (LC)
(F: frequency, L: inductance, C: capacitance)
Thus, the frequency is inversely proportional to the square root of the product of inductance and capacitance. For this reason, when the inductance decreases, the frequency of the supply current increases.

  That is, when the molten metal 14 in the crucible 10 increases (when the surface of the molten metal 14 rises), the frequency increases. On the contrary, when the molten metal 14 in the crucible 10 is reduced (when the surface of the molten metal 14 is lowered), the frequency is lowered. If this relationship is utilized, the state of the molten metal 14 in the crucible 10 can be detected by the change in the detected value of the frequency by the frequency detector 52.

  Next, the drawing control unit 42 controls the raising and lowering of the bottom plate 1 of the crucible 10. When pulling out the ingot, the pull-out control unit 42 receives a pull-out preparation completion signal from the melting power supply device control unit 51 (the melted material 13 is melted in the crucible 10 by the temperature detection or the like to become the molten metal 14. After receiving the detected signal), an instruction is given to the servo driver 44 to activate the servo motor 33 to lower the bottom plate 1 and pull out the ingot.

  In this case, the pull-out control unit 42 controls the servo motor 33 so that the bottom plate 1 is lowered from the reference position (the position of the bottom plate 1 shown in FIG. 1) to a predetermined position (for example, 300 to 1000 mm) at a predetermined speed (constant). Controls rotation (rotation speed and amount).

  For the lowering control of the bottom plate 1 to a predetermined position, for example, a positioning control function (a function of moving the bottom plate 1 to a predetermined position (or a predetermined distance)) is given to the extraction control unit 42, and the bottom plate 1 is predetermined. This is done by lowering to a position.

  The lowering control is performed by, for example, providing a position sensor (not shown) for detecting the lower limit position of the extraction shaft 12 and lowering the extraction shaft 12 by rotating the servo motor 33 at a constant speed. This is performed by stopping the servo motor 33 when the lower limit position is detected by the sensor. In this way, the ingot having a predetermined length can be manufactured by melting the material 13 to be melted in the crucible 10 and pulling it out while solidifying.

  The pull-out control unit 42 instructs the servo driver 44 to end the pull-out operation when the frequency determination unit 41 determines that the detected frequency value exceeds the preset upper limit for a predetermined time. .

  Further, when the frequency determination unit 41 determines that the frequency detection value is less than a preset lower limit, the extraction control unit 42 instructs the servo driver 44 to stop the extraction operation. The stop of the pulling-out operation continues until the frequency determination unit 41 determines that the detected frequency value is equal to or higher than the lower limit.

  The material charging control unit 43 controls the amount of the material 13 to be melted from the material charging unit 63 (described later) to the crucible 10. A predetermined amount of the material to be melted 13 is first charged into the crucible 10 before the ingot is pulled out by the material charging control unit 43. When the ingot is pulled out, the material charging control unit 43 receives the pulling preparation completion signal from the melting power supply device control unit 51 and then gives an instruction to the material charging unit 63 to reduce the ingot by pulling out the ingot. The material to be melted 13 corresponding to the molten metal for 14 minutes is charged (added) into the crucible 10.

  When the frequency determination unit 41 determines that the frequency detection value has exceeded the upper limit, the material charging control unit 43 stops the charging of the material 13 to be melted from the material charging unit 63 into the crucible 10 for a predetermined time. When the detected value of the frequency becomes equal to or lower than the upper limit by the lapse of time, the charging of the material 13 to be dissolved is resumed.

  When the frequency determining unit 41 determines that the frequency detection value has exceeded the upper limit by the drawing control unit 42 and the material charging control unit 43, the charging of the material 13 to be melted into the crucible 10 is stopped. The molten metal 14 in 10 can be prevented from increasing excessively. If the state where the frequency detection value is determined to have exceeded the upper limit as described above continues for a predetermined time, the pulling operation is terminated, and the ingot is left in a state where it is divided into upper and lower portions, and there is a leakage of hot water. Generation | occurrence | production can be suppressed or it can suppress that an ingot will be parted by a crack etc. growing even in the state which does not reach to parting.

  On the other hand, when the frequency determination unit 41 determines that the detected frequency value is less than the lower limit, the drawing operation is stopped, and the surface position of the molten metal 14 in the crucible 10 can be returned to the original position during the stop.

  As described above, in the present embodiment, safe and stable continuous casting is possible.

  Next, the change in the frequency (detected value) of the current supplied to the induction heating coil 18 detected by the frequency detector 52 and the treatment in each case will be described with reference to FIGS. .

As shown in FIG. 3A, examples of changes in the detected frequency value include (a) to (d). Specifically, the following example is shown.

(A) An example in which a crack or the like is generated in the ingot being pulled out, but the crack or the like is repaired (self-repair) while the detected value of the frequency is within a preset vertical range.
(B) An example in which the pulling operation is terminated because cracking or the like has occurred in the ingot being pulled out and the cracking or the like has not been repaired within a predetermined time after stopping the charging of the material 13 to be melted into the crucible 10.
(C) An example in which the amount of material input to the crucible 10 is in an excessive state, and the detection value of the frequency falls within the vertical range after the material 13 to be melted into the crucible 10 is stopped.
(D) An example in which the amount of material input to the crucible 10 is too small, and the frequency detection value is within the vertical range after the drawing is stopped.

Treatments in these cases will be described below (shown in FIG. 3B is a list of treatments). Note that the rate of change (inclination of the graph) at which the detected frequency value changes in FIG. 3A corresponds to the increase or decrease of the molten metal 14 in the crucible 10.

  In FIG. 3A, the detected value of the frequency changes upward, that is, the surface of the molten metal 14 in the crucible 10 rises. One possible cause is that the amount of material input to the crucible 10 is excessive (see frequency change in (c)).

  Another possible cause is a case where a crack or the like occurs in the ingot being pulled out (refer to the frequency changes in (a) and (b)). In this case, the lower part of the ingot continues to move downward as it is pulled out from the crack, but the part where the crack is present is stretched as it is pulled out, and the moving speed of the upper part of the ingot is reduced compared to the lower part. The movement may be stagnant. In this case, the amount of the melted material 13 put into the crucible 10 increases as compared with the amount of decrease in the molten metal 14 in the crucible 10 that accompanies the withdrawal of the ingot, and the molten metal 14 in the crucible 10 increases.

  On the other hand, in FIG. 3A, the frequency detection value changes downward, that is, the surface of the molten metal 14 in the crucible 10 descends. As a cause, it is conceivable that the amount of material input to the crucible 10 is too small (refer to the frequency change in (d)).

  In the case of (a) in FIG. 3A, at the beginning of drawing, the material input amount in the crucible 10 and the drawing of the ingot are balanced, and the detected value of the frequency changes constantly. However, if a crack or the like occurs in the ingot on the way, the surface of the molten metal 14 in the crucible 10 rises even though the drawing is continued. As a result, the frequency detection value increases. In the case of (a), the detected value of the frequency drops midway, because the cracks and the like are naturally repaired within the upper and lower ranges of the frequency. More specifically, the decrease in the detected value of this frequency is caused by the amount of the molten metal in the crucible 10 being in communication with the space generated in the ingot due to cracking or the like, and the molten metal flowing into the space generated in the ingot. It is considered that the detected value of the frequency is lowered by the decrease of. When cracks and the like are naturally repaired in this way and the detected value of the frequency changes within the upper and lower ranges, no particular treatment is performed as the continuous casting apparatus, and the ingot is drawn and the crucible of the material 13 to be melted is removed. 10 (additional) continues.

  In the case of (b), the detected value of the frequency continues to rise and reaches the upper limit of the frequency. As described above, when the upper limit of the frequency is exceeded, the material charging control unit 43 stops the charging of the material 13 to be melted from the material charging unit 63 to the crucible 10. Thereby, the surface of the molten metal 14 in the crucible 10 does not rise. In the case of (b), the ingot is continuously pulled out even after the charging of the material to be melted 13 is stopped. However, since the upper region of the ingot at the boundary of the generated crack or the like is stagnant in the crucible 10, the surface position of the molten metal 14 in the crucible 10 does not change, and the frequency detection value is constant. (Transition on the horizontal line shown).

  Next, if the detected value of the frequency does not fall within the vertical range even after a predetermined time has passed, the cracking of the ingot or the like may have been split up and down without being repaired naturally as described above. Even if it is not divided, it is in a state just before the division. If the drawing is continued as it is, there is a possibility that an accident such as a leak of hot water may occur, so that the drawing control unit 42 ends the drawing of the ingot at this point.

  In (c), since the amount of material input is excessive and the amount of molten metal 14 in the crucible 10 increases compared to the amount of decrease of the molten metal 14 in the crucible 10 corresponding to the drawing of the ingot, the detected value of the frequency increases. When the frequency exceeds the upper limit, as in the case of (b), the material charging control unit 43 stops the charging of the material 13 to be melted from the material charging unit 63 to the crucible 10. In this case, the drawing of the ingot itself continues normally. Therefore, when the charging of the material to be melted 13 is stopped, the surface of the molten metal 14 in the crucible 10 is lowered. For this reason, the detected value of the frequency decreases. When the detected value of the frequency becomes equal to or lower than the upper limit, the charging of the material 13 to be dissolved is resumed (not shown in FIG. 3A). As long as the material input amount is not changed, the frequency detection value is controlled to repeatedly increase and decrease.

  In (d), since the amount of material input is excessive and the amount of molten metal 14 in the crucible 10 decreases compared to the amount of decrease of the molten metal 14 in the crucible 10 corresponding to the drawing of the ingot, the detected value of the frequency decreases. And when it becomes less than the minimum of a frequency, the extraction control part 42 stops extraction of an ingot. Thereby, the surface of the molten metal 14 in the crucible 10 rises. For this reason, the detected value of the frequency increases. When the detected value of the frequency falls below the lower limit, ingot extraction is resumed (not shown in FIG. 3A). As long as the material input amount is not changed, the frequency detection value is controlled to repeatedly decrease and increase.

  Next, FIG. 4 is a flowchart showing a casting flow in the continuous casting apparatus of the present embodiment. Hereinafter, a description will be given with reference to FIG.

  When the material 13 to be melted previously charged in the crucible 10 is melted and the preparation for drawing out the ingot is completed (step S1), the drawing control unit 42 sends an instruction signal to the servo driver 44 to start the servo motor 33. Then, the bottom plate 1 of the crucible 10 is lowered, and at the same time, an instruction signal is sent from the material input control unit 43 to the material input unit 63, and the material 13 to be dissolved is input (added) to the crucible 10 (step S2).

  The frequency determination unit 41 receives a frequency detection signal of the supply current (high-frequency current) supplied to the induction heating coil 18 by the melting power supply device 50 from the frequency detection unit 52 (step S3), and whether the frequency detection value is within the upper limit (that is, Whether or not the introduction of the material 13 to be melted and the withdrawal of the ingot are balanced is determined (step S4). When the frequency determination unit 41 determines that the detected frequency value is equal to or lower than the upper limit (step S4: YES), the process proceeds to step S5.

  In step S5, the frequency determination unit 41 determines whether the frequency detection value by the frequency detection unit 52 is equal to or higher than the lower limit (step S5). When the frequency determination unit 41 determines that the detected frequency value is equal to or higher than the lower limit (step S5: YES), the process proceeds to step S6.

  In step S6, the extraction control unit 42 determines whether the predetermined extraction amount has been reached by determining whether the bottom plate 1 has reached the lower limit (extraction position lower limit), and if it has determined that the predetermined extraction amount has not been reached. (Step S6: NO), the process proceeds to Step S3 in order to continue withdrawing the ingot. When it is determined that the predetermined extraction amount has been reached (step S6: YES), the extraction control unit 42 sends an instruction signal to the servo driver 44 to complete the extraction operation, and at the same time, the material input unit 63 enters the crucible 10 into the crucible 10. The charging of the material to be melted 13 is also finished (step S7). This completes casting (step S8).

  On the other hand, when the frequency determination unit 41 determines that the detected frequency value exceeds the upper limit in step S4 (step S4: NO), the material is excessively charged or the ingot is cracked. Since the molten metal 14 in the crucible 10 is in an increased state, an instruction signal is sent from the material charging control unit 43 to the material charging unit 63, and the charging of the material 13 to be melted is stopped (step S9).

  The material charging control unit 43 continues the charging stop state of the material to be melted 13 for a predetermined time, and proceeds to step S11 after the predetermined time has elapsed (step S10: YES). Step S10 is repeated until the predetermined time has elapsed.

  In step S11, the frequency determination unit 41 determines whether the detected frequency value is within the upper limit. When it is determined that the detected value of the frequency is within the upper limit (step S11: YES), an instruction signal is sent from the material input control unit 43 to the material input unit 63 to start (restart) input of the material 13 to be dissolved (step) S12) The process proceeds to step S3 in order to continue withdrawing the ingot.

  On the other hand, when it is determined that the frequency detection value by the frequency detection unit 52 exceeds the upper limit (step S11: NO), the extraction control unit 42 sends an instruction signal to the servo driver 44 and stops the extraction operation ( Step S13). Specifically, the servo motor 33 is stopped and the lowering of the bottom plate 1 is stopped. Thereby, casting is stopped (step S14).

  In step S5, when the frequency determination unit 41 determines that the detected frequency value is less than the lower limit (step S5: NO), since the molten metal 14 in the crucible 10 has decreased, the withdrawal control unit 42 An instruction signal is sent to the servo driver 44, and the extraction operation is stopped (step S15). Specifically, the servo motor 33 is temporarily stopped to stop the lowering of the bottom plate 1.

  The extraction control unit 42 continues the extraction operation stop state for a predetermined time, and after a predetermined time has elapsed (step S16: YES), the extraction control unit 42 proceeds to step S17. Step S16 is repeated until the predetermined time has elapsed.

  In step S <b> 17, the frequency determination unit 41 determines whether the frequency detection value by the frequency detection unit 52 is equal to or higher than the lower limit. If it is determined that the detected frequency value is equal to or higher than the lower limit (step S17: YES), the extraction control unit 42 sends an instruction signal to the servo driver 44 to start (restart) the extraction operation (step S18), and then to step S6. Transition.

  On the other hand, when the frequency detection value by the frequency detection unit 52 is determined to be less than the lower limit (step S17: NO), the process proceeds to step S16.

  According to this flow, in this embodiment, when the ingot is drawn, the frequency of the supply current (high-frequency current) supplied to the induction heating coil 18 by the melting power supply device 50 is detected, and the drawing control and the material charging control are performed based on the detected frequency. Thereby, even when a crack etc. generate | occur | produce in an ingot, it can avoid reaching serious accidents, such as a hot water leak. For this reason, it is possible to predict the possibility of an accident or to predict that the ingot is being pulled out stably. Therefore, safe and stable continuous casting is possible. In addition, the quality of the ingot can be kept high.

  As mentioned above, although one embodiment was taken up and explained about the present invention, the present invention is not limited to the above-mentioned embodiment, and various changes are possible in the range which does not deviate from the gist of the present invention.

  For example, when the material 13 to be melted into the crucible 10 is excessive (in the case of (c) shown in FIG. 3), or is insufficient (in the case of (d) shown in FIG. 3). As a countermeasure, control may be performed to increase or decrease the amount of material input in accordance with a change in frequency detected by the frequency detection unit 52 to optimize the input of the material 13 to be dissolved.

  In the present embodiment, when the detected frequency value is within the upper and lower ranges, no particular action is taken. However, the material is input with the ideal frequency value (see FIG. 3B) as the target value. You may perform control which adjusts the quantity or the drawing speed of an ingot. Further, based on the change in the change rate of the detected frequency value (the inflection point of the slope of the graph in FIG. 3B), it is detected that a crack or the like has occurred in the ingot. Alternatively, control for adjusting the drawing speed of the ingot may be performed.

  In the present embodiment, the frequency detection value is determined by the frequency determination unit 41 and the drawing control unit 41 and the material input control unit 42 are operated according to the determination result. In addition, the detected value of the frequency may be used to display an alarm, issue an alarm sound, display the status of the molten metal 14 (surface position, etc.), and perform various operations using the detected value of the frequency. Can be made.

DESCRIPTION OF SYMBOLS 10 Crucible 1 Bottom plate 13 Material to be melted 14 Molten metal 18 Induction heating coil 40 Control unit, casting control device 41 Frequency determination unit 42 Extraction control unit 43 Material input control unit 52 Frequency detection unit 50 Melting power supply unit 63 Material input unit L Bottom plate lifting unit

Claims (6)

A crucible into which the material to be melted is charged;
A material charging unit for charging a material to be melted into the crucible;
An induction heating coil located on the outer periphery of the crucible and heating the material to be melted in the crucible to form a molten metal;
A melting power supply for supplying current to the induction heating coil;
A bottom plate lifting and lowering unit that pulls down an ingot formed by solidifying a part of the molten metal in the crucible by lowering the bottom plate by lowering the bottom plate of the crucible;
A frequency detection unit for detecting a frequency of a supply current from the melting power supply device to the induction heating coil;
And a control unit that controls casting based on a detected value of the frequency by the frequency detection unit.   2. The continuous casting according to claim 1, wherein the control unit includes at least one of a material charging control unit that controls charging of the material to be melted into the crucible and a pulling control unit that controls pulling of the ingot downward. apparatus.   When the detected value of the frequency by the frequency detection unit exceeds a set upper limit, the material input control unit, with respect to the material input unit, until the detected value of the frequency falls below a set upper limit, the material to be dissolved The continuous casting apparatus according to claim 2, wherein charging into the crucible is stopped.   4. The pulling control unit according to claim 3, wherein the bottom plate lifting unit stops the descent of the bottom plate when a state in which the frequency detection value by the frequency detection unit exceeds a set upper limit continues for a predetermined time. Continuous casting equipment.   When the frequency detection value by the frequency detection unit is less than a set lower limit, the drawing control unit causes the bottom plate lifting unit to stop the descent of the bottom plate until the frequency detection value is equal to or higher than a set lower limit. Item 4. The continuous casting apparatus according to Item 2 or 3. A crucible into which the material to be melted is charged;
A material charging unit for charging a material to be melted into the crucible;
An induction heating coil that is located on the outer periphery of the crucible and melts the material to be melted in the crucible to form a molten metal;
A melting power supply for supplying current to the induction heating coil;
Molten state in a continuous casting apparatus comprising: a bottom plate elevating unit that can lower and lower a bottom plate provided in the crucible, and lowers the bottom plate while pulling down an ingot formed by solidifying a part of the molten metal in the crucible. A determination method,
A molten state determination method for a continuous casting apparatus that detects a frequency of a current supplied from the melting power supply device to the induction heating coil and determines a state of the molten metal based on a detected value of the frequency.

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