JPH04300056A - Plasma torch for heating molten steel in tandish - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma torch for heating molten steel in a tundish, which can maintain the plasma arc length with high accuracy.

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. 9, 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 the plasma arc length (that is, the distance between the plasma torch 9 and the molten steel surface 13, hereinafter simply referred to as the arc length). This is done by keeping the plasma at an appropriate distance, keeping the plasma state as constant as possible, and changing the current value. At this time, the heating chamber 6 is covered with a heating chamber cover 8.
Since the arc length cannot be observed, the plasma torch 9 is raised and lowered using the indicated values of the plasma arc voltage and current as a guide. For this reason, it is difficult to maintain the arc length at a predetermined length.

[0005] In order to deal with such problems, the applicant of the present invention previously published Japanese Patent Application No. 2-88684 (hereinafter referred to as the "prior application") to adjust the arc length by following the fluctuations of the melt level 13. We are proposing a plasma heating device that can be kept constant.

FIG. 8 is a diagram showing an embodiment of the prior application. In FIG. 8, 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 which is a weight detector that measures 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, the height of the molten steel surface 4 is indicated as H, the insertion length of the plasma torch 9 is indicated as Y, and the arc length is indicated as L.

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 from this the height of the molten steel 4 is determined. . Also, the torch insertion length obtained by the torch insertion position detector 16 is obtained. and,
The above-described melt level height and torch insertion length are input to the control mechanism 17, and the arc length is continuously determined by calculation. Next, based on the calculated arc length, the control mechanism 17 operates the torch lifting mechanism 14 to move the plasma torch 9 up and down so that the arc length becomes a constant value.

As described above, the device of the prior application is configured to control the arc length to be constant even if the molten steel level 13 in the tundish 1 fluctuates.

However, even with the device of the prior application, there are still problems that need to be improved. That is, there is a limit to control accuracy, and in order to maintain a constant arc length in a tundish where the molten steel level 13 constantly fluctuates, the operation of the torch lifting mechanism 14 must be performed in very small steps. This will lead to repeated mechanical fatigue.

The present invention solves the problems of the prior art, improves the device of the prior application, and provides a plasma torch for heating molten steel in a tundish, which can reduce the frequency of activation of the torch lifting mechanism. The purpose is to provide the following.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the first invention provides a gravimetric type for detecting the level of molten steel in a tundish in a suspended lifting type plasma torch. A hot water level detector, a torch position detector that detects the insertion length of the plasma torch into the tundish, and an arch
A torch that raises and lowers the plasma torch to control the torch length.
It is equipped with an elevating mechanism consisting of a torch elevating and lowering command device. A deviation calculator that calculates the difference between the arc length and the set arc length, and an arc whose deviation value of the arc length calculated by this deviation calculator is set in advance.
It consists of a deviation comparator that raises or lowers the plasma torch when the upper and lower limits of the control dead zone width of the torch length are exceeded.

[0012] Furthermore, the second invention is characterized in that the torch elevating command device in the first invention is configured to adjust the arc length depending on when the plasma torch is moving up and down and when it is not moving up and down. A control dead band width switcher for changing the control dead band width is connected.

[0013]

[Operation] In plasma arc heating of molten steel in a tundish, the arc length does not necessarily have to be strictly constant, but only needs to be within a certain range. Therefore, the present invention aims to accurately maintain the arc length within an allowable control range.

In the first invention, the elevating mechanism is provided with a torch elevating and lowering command device, and the torch elevating and lowering command device controls the control dead band width (even if the arc length changes, the elevating and lowering operation of the plasma torch is controlled). The plasma torch will not be raised or lowered until the deviation between the set arc length and the actual arc length exceeds the upper or lower limit of the control dead band width. do not have. Therefore, the frequency of activation of raising and lowering the plasma torch can be reduced, and the accuracy of the arc length can be maintained at the level of the control dead zone width.

The second invention is a further improvement of the first invention. In the second invention, a control dead band width switch is connected to the torch lifting/lowering command device. This control dead zone width switch is a device that switches the control dead zone width to different values depending on whether the plasma torch is moving up and down or when it is stopped. For this reason, plasma
When the engine stops moving up and down, it is controlled with a narrow control range, and when it starts after stopping, it is controlled with a wide control range and starts operation. Therefore, the frequency is further reduced and the accuracy of the arc length is further improved.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. In FIG. 1, the structure of the tundish is the same as that in FIG. 9, so the same reference numerals are given to the same components regarding the tundish, and the explanation thereof will be omitted.

This embodiment is a plasma torch equipped with a hanging type elevating mechanism, and the torch elevating mechanism 18 winds up and unwinds the plasma torch 9 suspended by a wire. The torch position detector 21 detects the insertion length Ln of the plasma torch 9 in the tundish 1. 22 is a support frame.

The torch lifting/lowering mechanism 18 is controlled by a torch lifting/lowering command device 27 based on the arc length Lg determined by the hot water level detector 23 and the calculator 26.

[0019] Molten steel level height Lh in the tundish
The hot water level detector 23 is of a gravimetric type, and the weight detector 24 is used to measure the weight of the tundish 1 and the received molten steel 4.
and a molten metal level converter 25 which receives the detection signal of this weight detector 24 and converts it into the molten metal level height Lh of the molten steel 4. or,
Reference numeral 26 denotes a computing unit which receives a signal of the hot water level height Lh obtained by the hot water level converter 25 based on the distance L0 between the bottom surface of the tundish 1 and the heating chamber cover 8, and a torch position detector. The arc length Lg (actual value) is calculated based on the signal of the torch insertion length Ln obtained in step 21. Then, the torch lift command unit 27 controls the torch based on the relationship between the arc length Lg obtained by the calculator 26 and the set arc length Lr set in the arc length setter 28. H. Start or stop the lifting drive machine 20.

FIG. 2 is a diagram showing a control circuit for the torch lifting and lowering mechanism shown in FIG. Referring to FIG. 2, details of the torch elevation command device 27 will be explained. Torch lift command device 27
consists of an arc length deviation calculator 29, an arc length deviation comparator 30, and a changeover switch 31 for sending commands to the torch lifting/lowering drive unit 20 based on the arc length deviation value.

Control of the torch lifting and lowering mechanism is performed as follows. The deviation calculator 29 calculates the deviation ΔL between the set arc length Lr set in the arc length setter (digital switch) 28 and the arc length Lg calculated by the calculator 26. This arc length deviation ΔL is sent to the deviation comparator 30, which sends a command to lower, stop, or raise the plasma torch to the torch lifting/lowering drive unit 20 according to the following criteria.

-D≦ΔL≦+D…
(1) Formula Torch stop
ΔL < -D...Equation (2) Torch lowering ΔL >
+D...Equation (3) Torch rise Here, ΔL (deviation of actual arc length from set arc length) = L
r (set value) - Lg (actual value) D = control dead band width, positive value (upper and lower limits of allowable arc length deviation ΔL)

That is, (1) The plasma torch is not raised or lowered while the deviation ΔL from the set arc length Lr is within the range between the lower limit -D and the upper limit +D of the control dead zone width. ... (1) Equation (2) When the deviation ΔL from the set arc length Lr deviates to the negative side and deviates from the lower limit -D of the control dead band width, a torch lowering command is sent to the torch lifting drive unit 20. Well, plasma
Reduce the distance between the tip of the arc and the molten steel surface, and adjust the actual arc length L.
Shorten g. ...(2) Equation (3) When the deviation ΔL from the set arc length Lr deviates to the positive side and deviates from the lower limit +D of the control dead band width, a torch raising command is sent to the torch raising/lowering drive unit 20. , plasmat
the actual arc length Lg. ...(3)
formula

FIG. 5 is a diagram showing the arc length control process in heating molten steel in the tundish using the plasma torch of FIG. 1. In Fig. 5, curve a is the change in the molten steel level height Lh, and curve b is the sum of the set arc length Lr and the molten metal level height Lh. The curve c shows the transition of the desired height position from the actual arc length Lg.
The curve d shows the change in the height of the plasma torch tip by controlling so that the deviation is within ±D with respect to r, and the curve d is the deviation ΔL of the actual arc length Lg from the set arc length Lr. shows the transition of

As is clear from this figure, even if the molten steel level fluctuates, the actual arc length Lg can be controlled within the reference range (within the control dead band width). Here, for ease of understanding, it is assumed that the rising and falling speed of the plasma torch is much faster than the fluctuation speed of the hot water level height Lh, and the calculation and control results are immediately displayed as the actual position of the plasma torch. It is shown as appearing in

[0026] In the curve d, the points marked with ◯ indicate the point in time when the plasma torch was activated (lowered or raised).

In the curve c, the step-like transition occurs when the hot water level height Lh uniformly decreases (or uniformly increases) near the critical line where the deviation ΔL is −D (or +D). arise. This step-like transition can be explained with reference to FIGS. 7(a) and 7(b). In FIGS. 7(a) and 7(b), Rdn
indicates the downward overtravel length, and Rup indicates the downward overtravel length.

As shown in FIG. 7(a), when the hot water level level falls uniformly, the plasma torch drops every time the deviation ΔL jumps over -D (the black triangle part of the zigzag line of ΔL). It moves, but after a moment it enters the dead zone and the descent command is cut off. Due to the control time delay, the elevator travels over by the downward overshoot length Rdn and stops. After this, if the hot water level falls further, the above-mentioned operation is repeated.

As shown in FIG. 7(b), when the hot water level rises uniformly, the deviation ΔL rises in a stepwise manner, and as shown in FIG.
) is performed (a rising motion).

[0030] The above-mentioned repeated starting and stopping causes the deviation Δ
Since L exceeds the dead band width and remains within the limit range of the dead band even after the correction operation, the deviation ΔL deviates from the dead band width again within a short time, resulting in unexpectedly high frequency inching operation.

FIG. 3 is a diagram showing the configuration of another embodiment of the present invention. In FIG. 3, the same reference numerals are given to the parts already explained in FIG. 1, and the explanation will be omitted.

In this embodiment, the torch lift command device 2
A control dead band width switch 32 is connected to 7. The control dead band width switching device 32 is configured to change the control dead band width of the arc length deviation ΔL depending on whether the torch lifting drive unit 20 is moving up or down or not.

The torch lifting mechanism 18 includes a hot water level detector 23,
The torch is controlled by the torch lift command device 27 based on the arc length Lg determined by the calculator 26. The control dead band width of the arc length, which is the standard, is controlled by the control dead band width switch 32. It is switched each time the lifting drive machine 20 is started or stopped.

FIG. 4 is a diagram showing a control circuit for the torch lifting and lowering mechanism in FIG. 3. In FIG. 4, the same components as those in FIG. 2 are given the same reference numerals, and the explanation thereof will be omitted, and the details of the control dead band width switch 32 and the torch elevation command device 27 will be explained.

In controlling the torch elevating mechanism of this device, the width of the control dead zone is divided into two types, and the width of the dead zone is determined as follows.

[0036] When the torch lifting/lowering drive machine is in operation,
±δs When the torch lifting/lowering drive machine is stopped, ±δmHere, δm>δs, but for example, it is determined as δs = 2/5δm.

Therefore, the commands from the deviation comparator 30 to the torch lifting/lowering drive unit 20 are executed as shown in Table 1.

[0038]

[Table 1]

FIG. 6 is a diagram showing the arc length control situation in heating molten steel in the tundish using the plasma torch of FIG. 3. In FIG. 6, curve a, curve b, curve c, and curve d each indicate the transition of the same items as in the case of FIG. 5. Further, in the curve d, the points marked with ◯ indicate the point in time when the plasma torch was activated (lowered or raised).

As mentioned above, if we look at the transition of each curve in this figure from the start of operation, when ΔL reaches -δm, the torch lifting drive starts operating and the plasma torch rises. , .DELTA.L increases to -.delta.s, the operation of the torch lifting/lowering drive device is stopped. Then, when .DELTA.L becomes -.delta.m again, the torch lifting/lowering drive mechanism is operated to raise the plasma torch. In this way, ΔL is the upper limit +δm
At this point, the torch lift drive is activated to lower the plasma torch.

Next, when comparing the results of FIG. 6 with the results of FIG. 5, the fluctuation of ΔL (curve d) is smaller and more stable in the case of FIG. 6 than in the case of FIG. Here, the number of 〇 marks on curve d, which are the points at which the torch lifting/lowering drive machine starts, is:
There are more cases in FIG. 6 than in FIG. 5. However, in the case of the circle in Figure 5, the number of repeated activations as explained in Figures 7(a) and 7(b) is omitted, and only one activation at the time of the circle is sufficient. . Considering this series of repeated activations, the operating frequency of the torch lifting drive in FIG. 6 is significantly reduced and the mechanical life of the drive is extended.

[0042]

[Effects of the Invention] The first invention has an elevating mechanism for elevating and lowering the plasma torch in order to control the arc length, and this elevating mechanism is equipped with a torch elevating and lowering command device. ,
This torch lift/lower command device has a control circuit that sets a control dead band width and controls the arc length based on the upper and lower limits of the control dead band width. Therefore, the variation in arc length can be kept within the permissible variation range.

In the second aspect of the invention, the torch elevating command device is configured to control the control dead zone width of the arc length depending on whether the plasma torch is in elevating motion or not. A control dead band width switch is connected to change the width. Therefore, the frequency of activation of the torch lifting/lowering drive device is reduced, its service life is lengthened, and the distance accuracy of the arc length is improved.

[Brief explanation of drawings]

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

FIG. 2 is a diagram showing a control circuit of the torch elevating mechanism in FIG. 1;

FIG. 3 is a diagram showing the configuration of another embodiment of the present invention.

FIG. 4 is a diagram showing a control circuit of the torch lifting and lowering mechanism in FIG. 3;

5 is a diagram showing the arc length control process in heating molten steel in a tundish using the plasma torch of FIG. 1; FIG.

6 is a diagram showing the arc length control process in heating molten steel in a tundish using the plasma torch of FIG. 3; FIG.

FIG. 7(a) is a diagram schematically showing the starting/stopping state of the torch lifting/lowering drive machine in a section where the curve c in FIG. 5 is shown stepwise in the descending direction. (b) is a diagram schematically showing the starting and stopping state of the torch lifting/lowering drive machine in the section where the curve c is shown in a stepped manner in the upward direction in FIG.

FIG. 8 is a diagram showing an example of the prior application.

FIG. 9 is a diagram showing an example of a conventional apparatus for plasma heating molten steel in a tundish.

[Explanation of symbols]

1 Tundish 4 Molten steel 6 Heating chamber 9 Plasma torch 10 Anode 11 Plasma arc 18 Lifting mechanism 19 Hoisting machine 20 Torch drive machine 21 Torch position detector 23　Hot water level detector 24 Weight detector 25 Hot water level converter 26 Arithmetic unit 27 Torch lift command device 28 Arc length setting device 29 Deviation Calculator 30 Deviation comparator 32 Control dead band width switcher

Claims (2)

[Claims] Claim 1: In a hanging lift type plasma torch, there is provided a gravimetric level detector for detecting the height of the molten steel level in the tundish, and an insertion length of the plasma torch into the tundish. A torch position detector that detects the
The plasma torch is provided with an elevating mechanism including a torch elevating and lowering command device for elevating and lowering the plasma torch in order to control the torch length.
a deviation calculator that calculates the difference between the arc length determined from the channel insertion length and the hot water level height obtained by the hot water level detector and the set arc length; and the arc length calculated by this deviation calculator. Molten steel in a tundish, comprising a deviation comparator that raises or lowers the plasma torch when the deviation value of the arc length deviates from the upper and lower limits of the control dead zone width of the arc length set in advance. Plasma torch for heating. 2. In the suspended elevating type plasma torch according to claim 1, the torch elevating command device is configured to indicate whether the plasma torch is in elevating motion or not. 1. A plasma torch for heating molten steel in a tundish, characterized in that a control dead band width switcher is connected to change the controlled dead band width of the arc length.