JPH04284955A - Method and device for plasma-heating molten steel in tundish - Google Patents

Abstract

PURPOSE:To execute stable heating to molten steel by ascending a plasma torch so that plasma voltage value between the plasma torch and the molten steel does not become the lower limit setting value or lower. CONSTITUTION:By using the hanging-down ascending/descending type plasma torch 9, the molten steel 4 is plasma-heated. Then, the plasma voltage generated between the plasma torch 9 and the molten steel, is measured by using a plasma voltage detector 31. When the plasma voltage value becomes the lower limit setting value or lower, the plasma torch 9 is ascended with the ascending/ descending mechanism 18 till exceeding the lower limit setting value. In such way, abnormal approach between the plasma torch 9 and the molten steel 4, is prevented. By this method, the distance between these is kept to the suitable condition.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method and apparatus for plasma heating molten steel in a tundish using a suspended lifting type plasma torch, and more particularly, to
The present invention relates to a plasma heating device equipped with an abnormal approach prevention method and an abnormal approach prevention mechanism.

0002

2. Description of the Related Art In continuous casting of steel, operations are performed to heat molten steel and maintain its temperature appropriately. One of the methods of heating molten steel is heating by plasma arc.
This plasma heating technology is based on Utility Model Application No. 61-5305.
There is one shown in Publication No. 2.

In FIG. 4, 1 is a tundish, 2 is a long nozzle connected to a ladle, 3 is a submerged nozzle for injecting molten steel into a mold, and 4 indicates molten steel. The tundish 1 is covered with a cover 5, a part of which is partitioned by a weir 7, and forms a heating chamber 6 covered with a heating chamber cover 8. A plasma torch 9 serving as a cathode is inserted into the heating chamber 6 through a heating chamber cover 8, and an anode 10 is disposed at a position in contact with the molten steel 4 in the tundish. 12 is a power source. And plasma
A plasma arc 11 is generated between the molten steel 4 in contact with the chi 9 and the anode 10, and the molten steel 4 is heated appropriately. Since the heating temperature of this molten steel is determined by the input power, an operation for adjusting the input power is performed while the molten steel 4 is being heated.

0004

[Problems to be Solved by the Invention] The above-mentioned adjustment of the input power is performed by adjusting the distance between the plasma torch 9 and the molten steel surface 13 (hereinafter referred to as the distance between the torch and the molten steel surface), that is, the distance between the plasma torch 9 and the molten steel surface 13. This is done by keeping the plasma at an appropriate distance, keeping the plasma state as stable as possible, and then changing the current value. At this time, the heating chamber 6 is covered with a heating chamber cover 8, and the distance between the torch and the hot water surface cannot be observed.
Check the external height of the tundish and the hot water level in advance, calculate the lowering position of the plasma torch that corresponds to the desired arc length, and adjust the plasma torch according to the calculation results. lowering or raising the tip.

[0005] For this reason, it is difficult to maintain the distance between the torch and the molten metal surface to a predetermined length. The present applicant dealt with such problems and previously filed Japanese Patent Application No. 2-88684 (hereinafter referred to as
As a prior application), we have proposed a plasma heating device that can follow fluctuations in the hot water level 13 and keep the distance between the torch and the hot water level constant.

FIG. 3 is a diagram showing an embodiment of the prior application. In FIG. 3, 1 is a tundish, 6 is a heating chamber, 8 is a heating chamber cover, 9 is a plasma torch, 14 is a torch lifting mechanism, and 4 is molten steel. This device is equipped with a load cell 15 for measuring the total weight of the tundish 1 and the received molten steel 4, a plasma torch insertion position detector 16, and a control mechanism 17. In this figure, H is the height of the molten steel surface 13, Y is the insertion length of the plasma torch 9, and L is the distance between the torch and the molten metal surface.

In this device, the weight of the molten steel 4 in the tundish 1 is determined by the load cell 15 (the weight of the tundish 1 itself is measured in advance), and the molten steel weight and the molten metal level, which have been confirmed in advance, are determined. The height of the molten steel 4 is determined based on the height relationship. In addition, the torch insertion position detector 16
Obtain the torch insertion length obtained by Then, the above-described hot water level height and torch insertion length are input to the control mechanism 17, and the distance between the torch and the hot water level is continuously determined by calculation. Next, the control mechanism 17 operates the torch lifting mechanism 14 so that the distance between the torch and the hot water surface obtained by the calculation matches the distance between the torch and the hot water surface that is separately set from the outside. The plasma torch 9 is raised and lowered.

As mentioned above, the device of the prior application is configured to control the distance between the torch and the molten metal level to a constant set distance even if the molten steel level 13 in the tundish 1 fluctuates. There is.

However, even with the device of the prior application, there are still problems that need to be improved. That is, the load cell 15
The accuracy of the height of the molten steel surface determined based on the weight obtained by the method is not necessarily sufficient.

[0010] On the inside of the tundish, metal may be attached to a part thereof, or there may be defects in the refractory lining. Furthermore, there is a large construction error in the internal dimensions of each tundish. Therefore, the relationship between weight and molten steel level height differs for each tundish and is not exactly constant.

■ Slag, which is lighter than the molten steel, floats on top of the molten steel, and the actual molten metal level shows a low value.

[0012] Therefore, the above-mentioned error in the molten steel level height,
Plasma torch by control mechanism 17 and torch lifting mechanism 14
Depending on the relationship with the position control accuracy of the
There is also a possibility that the tip of the chi 9 may come into contact with the molten steel 4. Plasmato
If contact between the torch 9 and the molten steel 4 occurs, the plasma torch 9 will be damaged, and water may flow out of the water-cooled plasma torch 9, causing a steam explosion.

The present invention solves the problems of the prior art, improves the device of the prior application, and provides a plasma heating method and an abnormal approach prevention mechanism that can prevent the molten steel in the tundish from coming close to the plasma torch. An object of the present invention is to provide a plasma heating device equipped with the following.

[0014]

[Means for Solving the Problems] The present invention provides a plasma heating method that can prevent abnormal approach between molten steel and the plasma torch when a suspended lifting type plasma torch is used, and This relates to a plasma heating device equipped with a mechanism for preventing abnormal access between the plasma and the plasma.

[0015] In order to achieve the above object, in the method of the first invention, the plasma voltage generated between the plasma torch and the molten steel is measured, and if the plasma voltage value becomes below the lower limit set value, , the plasma torch is raised until it exceeds the lower limit set value to prevent abnormal approach between the plasma torch and the molten steel.

In the plasma torch of the second invention,
A torch lifting mechanism that lifts and lowers the plasma torch, a voltage detector that measures the plasma voltage generated between the plasma torch and the molten steel, and a plasma voltage value measured by the voltage detector that is set in advance. a torch approach detector that compares the measured plasma voltage value with the lower limit plasma voltage setting value and generates a torch approach signal if the measured plasma voltage value is smaller than the set voltage value; A torch approach prevention mechanism comprising a torch approach prevention priority circuit that transmits a rise command signal to the torch rise and fall mechanism with priority over other torch rise and fall command signals sent to the torch rise and fall mechanism. There is.

In the plasma torch of the third invention,
A gravimetric level detector that detects the height of the molten steel in the tundish, a torch position detector that detects the insertion length of the plasma torch into the tundish, and a gravimetric level detector that detects the length of the plasma torch inserted into the tundish. A torch that emits a signal to control the distance between the torch and the hot water surface based on the hot water level height detected by the torch position detector and the insertion length of the plasma torch detected by the torch position detector. It is equipped with a torch raising and lowering mechanism consisting of a torch raising and lowering command device, a voltage detector that measures the plasma voltage generated between the plasma torch and the molten steel, and a plasma voltage value measured by this voltage detector and a preset value. A torch proximity detector that compares the measured plasma voltage value with the lower limit plasma voltage setting value and issues a command signal to raise the plasma torch if the measured plasma voltage value is smaller than the lower limit plasma voltage set value; A torch approach prevention mechanism comprising a torch approach prevention priority circuit that receives the signal and transmits the ascending command signal to the torch ascending/descending mechanism with priority over other ascending/descending command signals given to the torch ascending/descending mechanism. We are prepared.

[0018]

[Operation] The plasma voltage generated between the plasma torch, which is an electrode, and the molten steel surface is composed of an electrode voltage drop and a plasma column voltage drop, as shown in the following equation.

Vp = Vn + Vc Vp ; Plasma voltage Vn ; Electrode voltage drop Vc ; Plasma column voltage drop Here, the electrode voltage drop Vn represents the sum of the cathode voltage drop and the anode voltage drop. This electrode voltage drop Vn has no relation to the plasma current or the distance between the torch and the hot metal surface. On the other hand, the plasma column voltage drop Vc has a characteristic of increasing uniformly as the plasma length increases. Therefore, the value of the plasma voltage Vp increases or decreases depending on the distance between the torch and the molten metal surface.

[0020] In this way, if the value of the plasma voltage Vp is kept below a predetermined value (lower limit value), the tip of the plasma torch will not come into contact with the hot water surface.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the structure of an embodiment of the method and apparatus of the present invention. In FIG. 1, the structure of the tundish is the same as that in FIG. 4, so the same reference numerals are given to the same components regarding the tundish, and the explanation thereof will be omitted.

The plasma torch in this embodiment is equipped with a suspended lifting mechanism, and the torch lifting mechanism 18 is a torch that lifts and lowers the plasma torch 9 suspended by a wire. It consists of a torch hoist 19, a torch lifting drive 20 for driving the hoist 19, and a torch position detector 21 for detecting the insertion length Ln of the plasma torch 9 in the tundish 1. 22 is a support frame.

Further, 12 is a plasma power source, and 31 is a plasma voltage detector. 23 is a hot water level detector, which is composed of a weight detector 24 and a hot water level converter 25. Furthermore, 26 is an arc length calculator, 27 is a torch lift/lower command unit, and 28 is an arc length calculator.
32 is a torch approach detector, and 36 is a torch approach prevention priority circuit.

First, the torch raising/lowering mechanism 18 receives a torch raising command signal 43 or a torch lowering command signal 40 given to the torch raising/lowering drive unit 20 from the torch approach prevention priority circuit 36.
According to the regulations, the robot is raising, lowering, or stopping. The torch up command signal 43 and the torch down command signal 40 correspond to the arc length expansion command signal 29 and the arc length reduction command signal 30 issued by the torch up/down command device 27, respectively. Usually, to
The torch lift/lower command unit 27 issues a torch lift/lower command so that the output Lg of the current arc length calculator 26 matches the output Lr of the arc length setter 28, so that the torch/hot water The inter-plane distance Lg is maintained at a constant value determined by the settings.

On the other hand, the plasma voltage signal measured by the plasma voltage detector 31 is sent to the torch approach detector 32. When this measured voltage drops to the lower limit reference value, the torch approach signal 33 is applied to the torch approach prevention priority circuit 36 until this voltage exceeds the reference value and returns. When the torch approach prevention priority circuit 36 receives the torch approach signal 33, it invalidates the command received from the torch lift command device 27 and sends the torch raise command signal 43 to the torch lift mechanism 18.
give.

According to this configuration, the distance between the torch and the molten steel surface 13 can be maintained in an appropriate state without the plasma torch 9 and the molten steel surface 13 coming into abnormal proximity or contacting each other. can do.

FIG. 2 is a diagram showing the structure of the torch access prevention mechanism in FIG. 1. Referring to FIG. 2, details of the torch approach detector 32 and the torch approach prevention priority circuit 36 will be described. The torch approach detector 32 includes a plasma voltage setter 34 for setting the lower limit plasma voltage, a lower limit plasma voltage value B set by the plasma voltage setter 34, and a lower limit plasma voltage value B measured by the voltage detector 31. It consists of a plasma voltage comparator 35 that compares the plasma voltage value A with the plasma voltage value A.

The torch approach detector 32 compares the set lower limit plasma voltage value B with the measured plasma voltage value A, and if the measured plasma voltage value A is smaller than the lower limit plasma voltage value B, Torch access prevention priority circuit 36
The torch approach signal 33 is sent to

In the torch approach prevention priority circuit 36,
When the torch approach signal 33 is received, the lowering prevention contact 38 opens and the arc length reduction command signal 30 from the torch raising/lowering command unit 27 is invalidated. At this time, at the same time, approach/evacuation contact 4
1 is closed, and the torch elevating control relay 42 is activated regardless of the presence or absence of the arc length expansion command signal 29. The torch lift drive machine 2 is activated by the operation of the torch lift control relay 42.
0, a rising command signal 43 is transmitted. The operation of the torch raising control relay 42 continues until the measured plasma voltage A exceeds the lower limit plasma voltage B and the approach/retreat contact 41 returns (opens).

[0030]

Effects of the Invention The present invention provides a plasma heating method in which a plasma voltage generated between a plasma torch and molten steel is measured, and the plasma torch is raised so that the plasma voltage value does not fall below a lower limit set value. The plasma heating apparatus is also equipped with a torch approach prevention mechanism that raises the plasma torch when the plasma voltage value falls below a lower limit set value.

According to the present invention, the distance between the torch and the molten steel surface can be maintained in an appropriate state without the plasma torch and the molten steel surface coming into abnormal proximity or contacting each other. , stable heating of molten steel can be carried out.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the method and apparatus of the present invention.

FIG. 2 is a diagram showing the configuration of the torch access prevention mechanism in FIG. 1;

FIG. 3 is a diagram showing an example of the prior application.

FIG. 4 is a diagram illustrating a conventional plasma heating technique.

[Explanation of symbols]

1 Tundish 4 Molten steel 6 Heating chamber 9 Plasma torch 10 Anode 11 Plasma arc 12 Power supply 13　Hot water surface 18 Torch lifting mechanism 19 Hoisting machine 20 Torch lifting/lowering drive machine 21 Torch position detector 23　Hot water level detector 24 Weight detector 25 Hot water level converter 26 Arc length calculator 27 Torch lift command device 28 Arc length setting device 29 Arc length expansion command signal 30 Arc length reduction command signal 31 Plasma voltage detector 32 Torch proximity detector 33 Torch approach signal 34 Plasma voltage setting device 35 Plasma voltage comparator 36 Torch access prevention priority circuit 38 Lowering prevention contact 39 Torch lowering control relay 40 Lowering command signal 41 Approach/evacuation contact 42 Torch lift control relay 43 Climb command signal

Claims (3)

[Claims] Claim 1: In a plasma heating method for molten steel using a suspended lifting type plasma torch, a plasma voltage generated between the plasma torch and the molten steel is measured, and the plasma voltage value is equal to or lower than a lower limit setting value. , the method for plasma heating molten steel in a tundish is characterized in that the plasma torch is raised until the lower limit setting value is exceeded to prevent abnormal approach between the plasma torch and the molten steel. 2. A molten steel heating apparatus equipped with a suspended, elevating type plasma torch, which includes a torch elevating mechanism for elevating and lowering the plasma torch, and a plasma generated between the plasma torch and the molten steel. A voltage detector that measures voltage compares the plasma voltage value measured by this voltage detector with a preset lower limit plasma voltage setting value, and if the measured plasma voltage value is smaller than the set voltage value, the a torch approach detector that generates a torch approach signal; and a torch approach detector that sends the torch approach signal to the torch lift mechanism with priority over other torch lift command signals sent to the torch lift mechanism. 1. A plasma heating device for molten steel in a tundish, characterized by comprising a torch approach prevention mechanism comprising a torch approach prevention priority circuit for transmitting a command signal. 3. A molten steel heating apparatus equipped with a suspended lifting type plasma torch, comprising: a gravimetric molten steel level detector for detecting the level of the molten steel in the tundish; Torch to detect the insertion length of the torch
The torch and hot water level are determined based on the torch position detector, the hot water level height detected by the gravimetric hot water level detector, and the insertion length of the plasma torch detected by the torch position detector. a torch elevating mechanism comprising a torch elevating and lowering command device that emits a signal for controlling the distance between the plasma torch and the molten steel, and a voltage detector that measures the plasma voltage generated between the plasma torch and the molten steel; The plasma voltage value measured by this voltage detector is compared with a preset lower limit plasma voltage setting value, and if the measured plasma voltage value is smaller than the lower limit plasma voltage setting value, the plasma voltage value is lower than the lower limit plasma voltage setting value.
a torch proximity detector that issues a command signal to raise the torch;
The above-mentioned ascending command signal is received, and this ascending command signal is transmitted to the above-mentioned tow.
A tundish interior comprising a torch approach prevention mechanism comprising a torch approach prevention priority circuit that transmits to the torch lifting mechanism with priority over other lifting command signals given to the torch lifting mechanism. Plasma heating device for molten steel.