JPS5897288A - Control device for induction furnace - 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] The present invention relates to a control device for an induction furnace.

As an induction furnace for melting or vaporizing metal, for example, as shown in FIG. 1, alumina is While high-frequency power is supplied to an induction coil 5 wound around a closed furnace body 2 made of a refractory material such as As shown by arrow A, a metal material 6 such as zinc is supplied into the furnace body 2 from the material supply port 4 of the furnace body 2 as shown by arrow B while the material is being sampled. It is.

In this type of induction furnace, depending on the amount of molten metal 7 of metal material (metal billet) stored in the furnace body 2
When the in-bee die is in a so-called matching state, which matches the internal impedance of the AC power supply 1, as shown by the solid line in FIG. 2, the voltage applied to the induction coil 5 and the supplied current are as follows. The maximum values Vmax and Imax of the output limit values of the AC power supply device 1 and the potash, the supplied power, that is, the amount of heat for heating the molten metal 7 become maximum.

The amount of shattered molten metal 7 stored in the furnace body 1 decreases by an amount corresponding to the above-mentioned matching state, and the impedance of the induction coil 5 decreases to within the region to the left of 21 shown by the dashed-dotted line. value, the voltage applied to the induction coil 5 becomes Vmax, and the supplied current becomes even smaller than Is, which is smaller than Imax, while the amount of stored molten metal 7 increases more than the above amount WO. When the impedance of the induction coil 5 becomes a value within the region to the right of Z2 indicated by the two-dot chain line, the current supplied to the induction coil 5 becomes I.
max, and the applied voltage is Vs lower than Vmax.
In both of the above cases, the power supplied to the induction coil 5 is considerably lower than in the matched state, and the efficiency of melting or vaporizing the metal is significantly reduced. do.

Therefore, in order to improve the efficiency of melting or vaporization, it is necessary to control the stored amount of the molten metal 7 so that it becomes approximately the above amount W- during operation of the induction furnace.

Conventionally, in order to perform the above-mentioned control, for example, (1) a load cell for gravity-electricity conversion installed at the bottom of the furnace body;
(4) Detect the amount of molten metal 5 stored in the furnace body 2 using an ultrasonic liquid level meter, an X-ray type liquid level meter, etc. This was done using a control device that controlled the temperature so that it almost coincided with -.

However, when using the load cell described in (1) above, the measurement accuracy of the amount of molten metal stored is poor due to its configuration, and the control accuracy is considerably low. When using the measuring device (11), the furnace body The temperature itself is about 1000℃, and due to its installation,
An extra protective device is required, and if a 010 measuring instrument is used, an extra protective device is required (as in the case of iD), and due to the configuration of the induction furnace, fairly powerful X-rays are used. Therefore, the equipment for detecting the amount of accumulation and molten metal stored is complicated and expensive, such as requiring an extra safety device for workers, and the configuration of the entire control device is complicated and its manufacturing cost is high. There was a drawback.

In addition, the conventional control device described above controls the amount of molten metal stored in the furnace body itself to be within a predetermined range, and directly controls the voltage, current, or power supplied to the induction coil. Since it is not a control system, there is also the drawback that the control accuracy for the power supplied to the induction coil is low.

This invention eliminates the various drawbacks mentioned above, detects the output voltage and output lightning current from a power supply, and provides the second method described above.
By effectively utilizing the electrical characteristics of the induction coil as shown in the figure, the detected voltage signal and detected current signal are
By determining whether the voltage is smaller than the reference voltage Vs and the reference current Is, which are appropriately set according to the induction furnace, the AC power supply unit instructs to reduce or increase the amount of metal material supplied into the furnace body. The power supplied to the induction coil is controlled so that it reaches the maximum (rated power), and there is no need for a detector to detect the amount of molten metal stored.The structure is simple and the manufacturing cost is low. The object of the present invention is to provide an inexpensive control device for an induction furnace.

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 3, parts equivalent to those of the induction furnace shown in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

In FIG. 3, 10 supplies AC power of a predetermined frequency with limited output voltage and output current to an induction coil 5 wound around the furnace body 2 of an induction furnace for vaporizing zinc billets, for example. This is an AC power supply device. This AC power supply device 10 has a three-phase commercial AC power supply 11 connected to a bridge rectifier circuit 12 using six thyristors, as shown surrounded by a dashed line in the figure. An inverter circuit 14 using four thyristors is connected to the inverter circuit 14 via a DC reactor 18. The gate of each thyristor of the bridge rectifier circuit 12 and the gate of each thyristor of the inverter circuit 14 are configured to receive firing command signals from output terminals T8 and T4 of the inverter control circuit 15, respectively, by a known method. The inverter circuit 14 is connected to the inverter circuit 14 so that high-frequency AC power is output. Furthermore, this AC power supply device 10 connects the induction coil 5 and a power factor correction capacitor 1 connected in parallel to the induction coil 5 via an autotransformer 16 for impedance matching.
It is connected to 7.

18 is a current Ix output from the AC power supply device 10.
This is a current detector that detects, for example, a known current transformer for measuring instruments. This current detector 18 is connected between the commercial AC power supply 11 and the bridge rectifier circuit 12, and sends an output detected current signal to the inverter control circuit 1.
It is connected so as to be added to the input terminal T1 of No.5.

Reference numeral 19 denotes a voltage detector for detecting the output voltage from the AC power supply device 10, which uses, for example, a known instrument transformer. This voltage detector 19 is connected between the inverter circuit 14 and the autotransformer 16, and is connected so as to apply an output detection voltage signal to the input terminal T2 of the inverter control circuit 15.

Further, in the inverter control circuit 15, the detected current signal received at the input terminal T1 is converted into an appropriate DC voltage signal, and outputted to the output terminal T6.
The detected voltage signal received at the output terminal T6 is converted into an appropriate DC voltage signal and outputted to the output terminal T6. Also,
Based on the signals received at both input terminals T1 and T2 mentioned above,
The high frequency output power from the inverter circuit 14 is controlled by controlling firing command signals to the bridge rectifier circuit 12 and the inverter circuit 14 in a known manner.

20 is a first comparator using, for example, an operational amplifier;
This first comparator 20 receives the output Ix from the output terminal T5 of the inverter control circuit 15 and the potentiometer 21.
It receives the addition signal (Ix-Is) with a signal representing the appropriately set reference current -Is from , and outputs the signal '11 when Ix-Is)Q. The first comparator 20 outputs the signal “01.”
It is connected to an input terminal T1 of a material supply control circuit 22, which will be described in detail later.

23 is a second comparator using, for example, an operational amplifier;
This second comparator 23 receives the output Vx from the output terminal T6 of the inverter control circuit 15 and the potentiometer 24.
After receiving an addition signal (Vx-Vs) with a signal representing an appropriately set reference voltage -Vs from
While outputting signal III when ~'x-Vs(Q
The signal °01 is output when . And the second comparator 2
3 is connected to the input terminal T2 of the supply control circuit 22.

Further, the output terminals of the first comparator 20 and the second comparator 23 are respectively connected to the input terminal of the Nandt gate 26, and the output terminal of the Nandt gate 26 is connected to the supply terminal of the metal billet to the induction furnace. It is connected to a display device 27 that indicates that the item is inappropriate.

Note that the reference current Is and reference voltage Vs set in the two connected potentiometers 21 and 24 are set to the maximum value of the AC power supply 10, depending on the furnace capacity of the induction furnace and the metal to be melted. Output current Imax
, a value appropriately smaller than the maximum output voltage Vmax is selected (see FIG. 2).

The material supply control circuit 22 uses a known motor drive speed control circuit, and the material supply port 4 of the furnace body 2 is
This circuit sends a drive signal to the motor 9 for driving the belt conveyor 8 so that, for example, the zinc billet 6 to be melted or vaporized is carried in at a predetermined supply rate (weight/time). . This material supply control circuit 22
When receiving the signal 111 at both input terminals T+ and T2, a drive signal is sent to drive the motor 9 at a predetermined speed set to a potentiometer (not shown), and a 10" When 101 is received at the input terminal T2, it outputs a command signal to drive the motor 9 at an increased speed, and when 101 is received at the input terminal T2, it outputs a command signal to drive the motor 9 at a reduced speed. There is.

Next, the operation of the above-mentioned control device according to the present invention will be explained.

As shown in FIG. 2, a reference current Is suitably smaller than the maximum output current 1max of the AC power supply 10 is set in the potentiometer 21, and the maximum output voltage Vm of the device 1°
A reference voltage Vs suitably lower than ax is set in the potentiometer 24.

When the power switch (not shown) of the control device is turned on, AC power at a predetermined frequency is supplied from the AC power supply 10 to the induction coil 5 wound around the furnace body 2 in a known manner. Zinc billets 6 to be melted and vaporized are carried into the supply port 3 of the furnace body 2 via a belt conveyor 8 at a predetermined supply rate (weight/hour).

Zn billet (metal material) introduced into the furnace body 2
6 is melted by the induction heating effect of the induction coil 5, and further vaporized, and collected by a known method as shown by arrow A in FIG.

It is now assumed that the amount of molten zinc stored in the furnace body 1 is smaller than the amount corresponding to the state in which the impedance of the induction coil 5 is Zl shown by the dashed-dotted line, as shown in FIG. That is, the impedance of the induction coil 5 that electromagnetically engages with the molten metal has a reactance component larger than the impedance Zo at which the output power of the AC power supply device 10 becomes maximum, and as shown in FIG. The resulting voltage is the output voltage limit value Vmax of the AC power supply 1o, and the current supplied to the induction coil 5 is smaller than the above-mentioned reference current Is. The electric power supplied to the molten metal 7 inside is smaller than the maximum electric power Wmax (=Imax-Vmax).

The current detector 18 detects the current input from the commercial AC power supply 11 to the bridge rectifier circuit 12, in other words, the output current of the AC power supply, and therefore the current supplied to the induction coil 5, and this detected current signal @lx ' is applied to the input terminal T1 of the inverter control circuit 15. In this inverter control circuit 15, the detected current signal Ix' is converted into a DC voltage signal lx representing the detected current by a known method, and this signal lx is added to the signal -Is representing the reference current Is from the potentiometer 21. and is applied to the negative input terminal of the first comparator 20.

In the first comparator 20 described above, (Ix-Is) is determined to be negative, that is, 1x(Is), and the first comparator 20 outputs a low level signal 101.

On the other hand, the voltage detector 19 detects the output voltage of the AC power supply 10, in other words, the voltage that is not applied to the induction coil 5, and this detected voltage signal Vx' is applied to the input terminal T2 of the inverter control circuit 15. be done. In this inverter control circuit 15, the detected voltage signal Vx' is converted into a DC voltage signal Vx representing the detected voltage by a known method, and this signal Vx is converted to a reference voltage Vx from the potentiometer 24.
It is added to the signal -Vs representing s and applied to the negative input terminal of the second comparator 23.

In the second comparator 23 described above, (Vx-Vs)=
(Vmax-Vs) is positive, that is, V x ”:) V
s, and the second comparator 23 outputs a high level signal 11'.

Therefore, 10" is applied to the input terminal T+ of the material supply control circuit 220.
, and "11" is applied to its input terminal T2, and this circuit 22 generates a motor drive signal to increase the drive speed of the motor 9 based on the signal 101 at the input terminal T1 in a known manner. The speed command signal is applied to the motor 9, and the driving speed of the motor 9 is increased, so that the driving speed of the belt conveyor 8 and, therefore, the feeding rate (weight/time) of the zinc billet 6 to the furnace body 2 is increased.

As a result, the amount of zinc stored in the furnace body 2 increases, the impedance-actance component of the induction coil 5 decreases, and the impedance changes to approach lO shown by the solid line in FIG. That is, the impedance changes so as to approach the so-called matching state, which matches the internal impedance of the AC power supply 10. In this case, the voltage applied to the induction coil 5 from the AC power supply 10 is set to Vmax, the current supplied to the induction coil 5 increases, and the electric power supplied to the molten metal 7 in the furnace body 2 increases accordingly. As a result, the amount of heating to the molten metal 7 increases, and the melting of the zinc billet 6 and the vaporization of the molten metal 7 supplied into the furnace body 2 are promoted.

On the other hand, the Nantes gate 26 receives I □ I from the first comparator 20 at one input terminal, and receives °I'' from the second comparator 23 at the other input terminal. A high level signal 111 is output.This signal 11' is applied to the display 27.
is turned on, and an indicator lamp (not shown) lights up in a known manner to notify the operator that the amount of zinc stored in the induction furnace is not appropriate, and also to control the driving speed of the motor 9. This indicates that the feed rate of zinc billets 6 to the furnace body 2 is being increased.

As described above, the amount of molten metal 7 stored in the furnace body 2 increases, and the impedance of the induction coil 5 reaches a region between Zl shown by the dashed-dotted line and Z2 shown by the dashed-two dotted line in FIG. When the value of , as mentioned above, in the first comparator 20
It is determined that the detected current lx from the current detector 18 is larger than the reference current Is from the potentiometer 21, and the output of the first comparator 20 becomes 111. Further, the second comparator 23 determines that the detected voltage Vx from the voltage detector 19 is greater than the reference voltage Vs from the potentiometer 24, and the output of the second comparator 20 becomes 111. Therefore, the input terminals Tl, T of the material supply control circuit 22
2 are both '1'', and the motor 9 is driven at a predetermined speed, that is, at a speed commensurate with the state where the impedance of the induction coil 4 is ZO.

Also, the two input terminals of the Nant gate 26 are @11.
'11, therefore, the output of the Nant gate 26 is I
OI, the indicator 27 is turned off, the indicator lamp (not shown) of the indicator 27 is not lit, and the molten metal 7 in the furnace body 2 is turned off.
Inform the operator that the storage amount is appropriate and that the induction furnace is being operated properly.

Next, the amount of molten zinc 7 stored in the furnace body 2 is determined to be a second amount.
As shown in the figure, it is assumed that the impedance of the induction coil 5 has become larger than the amount corresponding to the state Z2 indicated by the two-dot chain line. That is, contrary to the case described above, the impedance of the induction coil 5 decreases by an amount corresponding to the actance, and the impedance becomes a value in the region to the right of Z2 indicated by the two-dot chain line in FIG. It is assumed that the current supplied to the coil 5 is a limit value Imax, and the voltage applied to the induction coil 5 is lower than the reference voltage Pc.

In this case, the first comparator 20 determines that the detected current I x (=Imax) from the current detector 18 is larger than the reference current Is from the potentiometer 21, and the output of the first comparator 20 becomes Ill. It is said that

On the other hand, in the second comparator 23, the detected voltage Vx from the voltage detector 18 is the reference voltage ~' from the potentiometer 23.
It is determined that the output of the second comparator 23 is smaller than t.
It is considered as ol.

Therefore, based on the signal 10'' received at the input terminal T2, the material supply control circuit 22 controls the drive speed of the motor 9 and, therefore, the supply rate (heavy weight) of the zinc billet 6 to the furnace body 2, contrary to the case described above. A drive control signal is generated which reduces i/time 'r, and this drive control signal is applied to the motor 9.

As a result, the amount of zinc stored in the furnace body 2 decreases, and the impedance of the induction coil 5 changes to approach Zo shown by the solid line in FIG.
0, the amount of heating to the molten metal 7 increases,
Melting of the zinc billet 6 in the furnace body 2 and vaporization of the molten metal 7 are promoted.

In addition, the two input terminals of the Nant gate 26 have 11@1
01 is applied, and the output of this Nant gate 26 is 111
Therefore, as described above, the indicator lamp of the display 27 lights up to notify the operator that the amount of zinc stored in the induction furnace is at an appropriate level, and
It is notified that the feed rate (weight/time) of zinc billet 6 to furnace body 2 is being reduced.

In this manner, in the induction furnace control device having the above configuration, the electrical characteristics of the induction coil 4 are effectively utilized to control the furnace body 1 based on the detection signals of the current supplied to the induction coil 4 and the applied voltage. The storage amount of the metal material to be melted or vaporized in the AC power source can be set to a value within a predetermined range, that is, the electric power supplied from the AC power supply device can be set to approximately the maximum value (rated value). In this way, during the operation of the induction furnace, the AC power supply 10 automatically supplies power to the induction coil 5.
This ensures that the maximum power supply is maintained, and the efficiency of melting or vaporizing the metal billet is increased accordingly.

The display 27 is provided with a digital display circuit (not shown) that indicates the amount of molten metal 7 stored in the furnace body 1 based on the detected current signal Ix from the current detector 18, as described above. The storage amount may be displayed digitally at the same time as the indicator lamp is turned on. In this way, it is possible to specifically inform the operator of the amount by which the material supply rate (""/time'r increases or decreases), thereby increasing the accuracy of the control.

As detailed above, according to the present invention, the output current and output voltage from an AC power supply device whose output voltage and output current are limited are detected, and based on these detected voltage signals and detected current signals, By controlling the amount of metal material supplied into the furnace, the power supplied to the induction coil is directly controlled while the induction furnace is operating, regardless of the detection signal representing the amount of metal material stored in the furnace. Since the control is made to reach almost the maximum (rated power), the accuracy of the control can be increased accordingly, and therefore the efficiency of melting or vaporizing metal materials in the induction furnace can be reliably increased. It can be done.

In addition, since the configuration is configured to perform control based on the detected voltage signal and detected current signal representing the output voltage and output current from the power supply device, without depending on the detected signal of the amount of metal material stored in the furnace, the amount of stored metal material is No detector is required for detection,
Accordingly, the configuration is simple and the manufacturing cost of the entire device can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the configuration of an induction furnace to which the control device of the present invention can be applied, FIG. 2 is a graph showing the impedance characteristics of the induction coil in the induction furnace of FIG. 1, and FIG. FIG. 3 is an electrical circuit diagram of a control device according to the invention. 2...furnace body, 3...metal vapor outlet, 4...metal billet supply port, 5...
・Induction coil, 6... Zinc billet, 7...
... Molten metal, 8... Belt conveyor, 9...
...Motor, 10...AC power supply device, 11.
... Commercial AC power supply, 12 ... Bridge rectifier circuit, 13 ... DC reactor, 14 ...
... Inverter circuit, 15 ... Inverter control circuit, 16 ... Matching autotransformer, 18 ...
...Current detector, 19...Voltage detector, 2
0...First comparator, 21... Potentiometer for setting reference voltage VS, 22... Material supply control circuit, 23... Second comparator, 24 ...
...Potentiometer for setting reference current Is stage, Zo,
Zl, Z2... Impedance of induction coil. Patent applicant: Fuji Electric Seizo Co., Ltd. Agent: Patent attorney: Aoyama, 2 people, 1st prisoner, 2nd figure

Claims (1)

[Claims] (1) While supplying power to the induction coil of the induction furnace by an AC power supply device whose maximum output voltage and maximum output current are limited to predetermined values, a metal material is supplied to the induction furnace and the metal material is melted. In the induction furnace control system, a voltage detector detects the output voltage from the power supply device, a current detector detects the output current from the power supply device, and a voltage detector detects the output current from the power supply device according to the output of the rain detector. A material supply amount that controls the supply amount of metal material to increase or decrease when the output voltage becomes lower than the maximum output voltage or when the current output from the power supply device becomes smaller than the maximum current. A control device for an induction furnace, characterized in that it is equipped with a control means.