JPS63171838A - Esr melting device - Google Patents

Abstract

PURPOSE:To provide an ESR melting device which has a wide setting rang of melting conditions and can prevent malfunction, by comparing the amplitude amt. and reference value of melting current and making constant value or follow-up control via the increase and decrease in the melting voltage according to the result of said comparison. CONSTITUTION:A difference between the detected value and the set value is positive if the output detected by a current amplitude amt. detector 28 is smaller than the set value of a melting current amplitude program device 26, i.e., if the erosion of an electrode is large as shown in the figure. As a result, the above-mentioned output is amplified by a current amplitude amt. controller 25 and the output voltage of a voltage regulating transformer 32 is gradually increased via a melting voltage controller 18 and a voltage increasing/decreasing driver 14. The melting voltage 20' and melting current 12' are consequently respectively increased successively in the average value and amplitude amt. in parallel. The difference between said output and the set value of the device 26, i.e., the input to the controller 25 is decreased by an increase in the current amplitude amt., i.e., an increase in the output of the detector 28. The input to the controller 18 is decreased by the increase in the voltage 20' simultaneously therewith, by which the output thereof is decreased to substantially zero and the voltage increasing/decreasing driver 14 is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electro-slab remelting (hereinafter referred to as ESR) apparatus, particularly a melting control system.

[Conventional technology]

An outline of the ESR dissolution method will be explained using an example of a conventional ESR device. FIG. 4 is a diagram showing an example of an ESR melting apparatus having a conventional melting control system.

A conductive slag 4 is contained in a crucible 1 in a high temperature molten state, and a consumable electrode (hereinafter referred to as electrode) 3 is placed below the liquid surface of the slag 4.
is immersed at its lower end (hereinafter, the immersion depth will be referred to as electrode immersion amount 40). The electrode 3 is connected to a power source (not shown).
Electricity is applied through the voltage adjustment transformer 32, the melting transformer 31, and the saturable reactor 21, and this current heats the slag 4 with Joule heat, and this heat melts the lower end of the electrode, turning it into droplets and forming the slag. It settles under the refining action of 4, forming a molten metal pool at the bottom. This pool then solidifies sequentially from the bottom to form an ingot 2. In this way, the entire length of the electrode 3 is sequentially melted and refined to be converted into an ingot 2.

In the ESR melting method, melting conditions have a significant impact on the quality of the produced ingot. For example, the electrode immersion amount 40 is the skin slag 3 generated between the ingot 2 and the inner surface of the crucible 1.
0 and the refining effect, and have a significant impact on the surface and internal quality of the ingot. That is, the electrode weight is 40
If it is appropriate and stable, the thickness of the skin slag 30 will be stable, the refining effect will be good, and an ingot with good internal and external quality can be obtained.

In addition, in order to obtain a high-quality ingot, it is desirable that the molten metal pool maintain a constant depth over as wide an area as possible, and in this case, the tip of the electrode is flat and the weight of the electrode is small.

Furthermore, at the start of melting and immediately before the completion of melting, melting becomes unstable and tends to result in an unhealthy ingot, so appropriate melting control is required.

In the ESR device, when performing follow-up control, the electrode weight 4
0 etc. cause periodic fluctuations (hunting) for various reasons,
Along with this, various conditions such as the current value fluctuate. However, by appropriately selecting the variation width (hereinafter referred to as amplitude) and period of this hunting, it is possible to prevent an adverse effect on the ingot.

The conventional control system shown in FIG. 4 (i) controls the average value of the dissolution current 12', and also controls the set value 7' of the dissolution rate program setting device 6 and the electrode weight 8' measured by the load cell 23; The dissolution rate 9' obtained by differential processing is compared with the dissolution rate 9', and based on the comparison result, the dissolution rate control function that controls the voltage raising/lowering drive device 14 of the voltage regulating transformer 32 and (ii) the average value of the dissolution voltage 20' is controlled. At the same time, the amplitude amount due to hunting of the voltage 20' is compared with the setting value of the voltage amplitude amount setting device 16, and the electrode lifting device 22 is driven based on the comparison result, thereby controlling the electrode weight 40. This is a combination of two closed loop control systems (1) and (iii) a saturable reactor 21. Here, the saturable reactor 21 suppresses the excessive current when the current flowing through it is sufficiently large, like a normal glue reactor, and when the current decreases, it magnetically saturates its own magnetic path and increases the inductance. It operates to decrease the current and increase the current.

FIG. 5 shows an equivalent circuit of the conventional ESR device, and FIG. 6 shows the control characteristics of the electrode weight. In FIG. 6, the horizontal axis is the electrode weight 40, and the vertical axis is the slag electrode resistance Rr formed by the slag 4 and the electrode 3 and the melting voltage Vr.

The part of the electrode 3 immersed in the slag 4 has a substantially spherical shape, as shown in FIG. 7, which is a cross-sectional view of the main melting part. The slug electrode resistance Rr with respect to the electrode weight is as shown in FIG. That is, when the weight of the electrode 3 increases from the state where its tip is in contact with the slug 4, the contact area with the slug 4 increases rapidly at the beginning, so the slag electrode resistance R
r decreases rapidly. In this state, the electrode 3 reaches a state where the line 3' formed by its outer diameter cylindrical surface and the spherical surface of the tip (hereinafter referred to as the outer circumference lower end) coincides with the liquid level of the slag 4 (hereinafter referred to as critical). continue. In the electrode weight range above the critical level, the slag electrode resistance Rr is mainly controlled by the thickness of the four slag layers and decreases linearly in proportion to this.

When the electrode 3 continues to hunt around the electrode weight which exceeds the criticality over time, the center of the hunting becomes critical due to melting of the tip.

Since the conventional ESR device described above exhibits substantially constant current characteristics due to the action of the saturable reactor 21, the melting voltage Vr is approximately proportional to the slag electrode resistance Rr. Here, the melting voltage Vr is a downwardly convex monotonically decreasing function, excluding a range where the electrode weight is small. Therefore, in a region above this range, the electrode weight 40 can be determined by measuring the amplitude of the melting voltage Vr caused by a constant amplitude change in the electrode weight 40 due to hunting. The electrode immersion amount control system shown in FIG. 4 utilizes this principle.

[Problem that the invention seeks to solve]

In the conventional ESR melting control system, the melting voltage Vr
As shown in FIG. 6, when the electrode weight is controlled with an accuracy of Δl, when the electrode weight is changed from 11 to 12, the amplitude of the melting voltage Vr changes from ΔVr to ΔVr2. When the electrode weight is small, there is a part where the voltage change is small in the high voltage region (region where the electrode weight is small). This is the melting voltage 20 due to constant current control of the saturable reactor 21.
This is done to avoid an excessive increase in the voltage variation range of ', which would increase equipment costs. However, the existence of this voltage constant range reduces the degree of freedom in setting the melting conditions of the ESR device, and when the electrode weight is reduced in order to obtain a high-quality ingot, the critical point is closer to the origin in Figure 6. Therefore, this electrode weight amplitude range tends to reach this voltage unchanged range, and in extreme cases, the electrode becomes weightless and floating. This is the most inconvenient and malfunctioning phenomenon that makes it impossible to continue dissolving.

An object of the present invention is to provide an ESR melting device that has a wide melting condition setting range and prevents malfunctions.

[Means for solving problems]

The present invention is an ESR melting device characterized in that the amplitude of the melting current is compared with a reference value, and based on the result, the melting voltage is increased or decreased to perform constant value or follow-up control.

[For production]

The present invention detects a melting current that does not cause an invariant range, and controls its amplitude to a constant value or follow-up by increasing and lowering the melting voltage. Therefore, the selection range of the fluctuation range is expanded, and malfunctions due to current interruption can be prevented.

〔Example〕

FIG. 1 shows an example of the dissolution control system of the ESR apparatus of the present invention. The dissolution rate control system' includes a load cell 23 provided as an electrode weight measuring means, a differentiator 9 for differentiating the weight value detected by the load cell 23 to detect the dissolution rate, and a dissolution rate program serving as a dissolution rate setting device. A setting device 6 receives the difference between the output signal 7' of the programming device and the dissolution rate value 9', and a dissolution rate control device 5 amplifies the difference, detects the dissolution current 12' and calculates a temporal average value from this. a dissolution current averaging device 12', an amplifier 10 which receives the difference between the output 11' of the dissolution rate control device 5 and the output of the dissolution current averaging device 12, and an amplifier 10 that uses the output of the amplifier 10 to drive a hydraulic control valve It consists of an electrode lift control device 21 that converts the electrode 3 into a form suitable for use, a power cylinder to which the electrode 3 is suspended, and an electrode lift drive device 22 that sends controlled pressure oil to this cylinder.

The dissolution rate control system differs from the conventional dissolution rate control system shown in FIG. 4 in that the object to be controlled is the voltage generated by the voltage adjustment transformer 32, whereas in the present invention, the control object is the elevation and descent of the electrodes.

Next, the amplitude amount control system 1' includes a current amplitude amount detection device 28 for extracting the amplitude amount of fluctuation from the melting current 12', a melting current amplitude programming device 26, and the programming device 26 and the current amplitude amount detection device 28. a current amplitude control device 25 that receives the difference between the output of the control device 25 and the melting voltage 2° and amplifies it; a melting voltage control device 18 that receives the difference between the output of the control device 25 and the melting voltage 2° and amplifies the power; and the melting voltage control device 1 It consists of a voltage raising/lowering drive device 14 driven by the sun.

The amplitude control system DA' controls the current amplitude of the melting current 12', whereas the conventional system shown in FIG. The difference is that control is performed via a voltage raising/lowering drive device as the main loop.

In the melting apparatus of the present invention, the saturable reactor 21 as in the conventional example shown in FIG. 4 is not necessary.

An equivalent circuit of the melting device of the present invention is shown in FIG. 2, and an electrode elevation control device is shown in FIG. 3. In FIG. 3, when the electrode weight is controlled with an accuracy of ΔE, the electrode weight is changed to 1.
When changing from j2t to j2t, the amplitude of the melting current 1r becomes Δ
Ir, becomes ΔIr.

This occurs when the weight of the electrode is low. The entire region of the Ir curve is an upwardly convex monotonically increasing function, and therefore the current amplitude [A] or the ratio of the current amplitude value (A) to the electrode weight amplitude value [iris] (A / tm
) is valid as a parameter for control,
In other words, it can be seen that there are no unchanged parts shown in FIG. 6, and malfunctions can be completely prevented.

This becomes even more noticeable when the inductance L is large.

Furthermore, even when the inductance L is small, when the slope of the Ir curve changes significantly in an upwardly convex manner before and after the criticality, for example, when the lower end surface of the electrode 3 becomes flat due to low electrode weight dissolution, the electrode weight If a part of the amplitude is below the critical value, the range below the center of the amplitude can be used as the control band. This is very advantageous when operating with a small weight in order to obtain a sound ingot as described above.

Here, if the output detected by the current amplitude detecting device 28 is smaller than the set value of the melting current amplitude programmer 26, that is, if the electrode weight is large as shown in FIG. 3, the difference between the detected value and the set value is ( +). As a result, the current is amplified by the current amplitude control device 25, passes through the melting voltage control device 18 and the voltage raising/lowering drive device 14, and gradually increases the output voltage of the voltage regulating transformer 32. As a result, the average value and amplitude of the melting voltage 20' and the melting current 12' increase in parallel, and in this process, the current amplitude increases, that is, the output of the current amplitude detecting device 28 increases. This results in a decrease in the differential force between this output and the set value of the melting current amplitude programming device 26, that is, the input of the current amplitude control device 25. At the same time, due to the increase in the melting voltage 20', the input to the melting voltage controller 1 decreases, and its output becomes almost O
As a result, the voltage raising/lowering drive device 14 stops.

On the other hand, due to the increase in the average value of the melting current 12', the melting voltage control device' is activated, and the electrode lifting device 22 raises the electrode 3 to reduce the weight of the electrode, so that the melting current 12' increases.
is controlled to a value corresponding to the setting value of the dissolution rate program setting device 6.

In contrast to the above, when the current amplitude is large, the operation is completely opposite to that described above. Other cases can also be easily understood from the above explanation of operation.

This embodiment is characterized in that the power system does not include a reactor and the device is simple. However, in the present invention, a small capacity glue actor may be provided in order to further widen the electrode immersion amount control range.

〔Effect of the invention〕

As described above, the present invention provides stable melting control in the region where the electrode weight is small, which is important in the production of healthy ingots, and completely prevents malfunctions such as melting interruptions.
This greatly improves the functionality of the melting device.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3, and FIGS. 4, 5, and 6 are examples of block diagrams, equivalent circuits, and electrode weights of the melting control system of the present invention and the conventional ESR melting apparatus, respectively. This shows the control characteristics of FIG. 7 is an enlarged view of the dissolved local area. Figure 1

Claims (1)

[Claims] 1. An ESR melting device, characterized in that the amplitude of the melting current is compared with a reference value, and based on the result, constant value or follow-up control is performed by raising and lowering the melting voltage. 2. The ESR melting apparatus according to claim 1, wherein the average value of the melting current is compared with a reference value, and based on the result, constant value or follow-up control is performed by raising and lowering the electrode.