JPS6237513B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an operation control device for an induction furnace.

The maximum output voltage and maximum output current are limited to predetermined values, for example, by supplying power to the induction coil of an induction furnace from an AC power supply device such as a high frequency inverter device to melt the metal material introduced into the furnace. Induction furnaces are now being operated.

In this type of induction furnace, depending on the amount of metal material in the furnace, that is, the amount of stored molten metal of the metal material,
The impedance of the induction coil changes as shown in FIG.

In other words, the amount of molten metal stored in the induction furnace is determined by the maximum amount of power supplied from the AC power supply to the induction coil.
When Vmax·Imax, that is, the input impedance of the induction furnace, which is the load of the AC power supply, and the internal impedance of the AC power supply are equal, that is, reduced by an amount equivalent to when they are in a so-called matching state,
As shown by solid lines Z ₂ and Z ₁ in the figure, the input impedance changes, the voltage applied to the induction coil is set to the maximum value Vmax, and the supply current is set to the maximum value
_I2 and _I1 are reduced from Imax, and the power supplied to the induction coil is reduced.

On the other hand, when the amount of metal material stored in the furnace increases more than the amount corresponding to the matching state described above, the impedance of the induction coil changes, as shown by solid lines Z ₄ and Z ₅ in the figure, and the induction coil changes. The current supplied to the coil is the maximum value Imax, and the applied voltage is the maximum value Vmax.
V ₄ and V ₅ decrease, and the power supplied to the induction coil decreases.

As mentioned above, during operation of the induction furnace, if the amount of metal material in the furnace, its temperature, etc. change, the impedance of the induction coil, that is, the load of the AC power supply device changes, and the above-mentioned AC power supply device changes. There was a problem in that the matching between the induction coil and its load was lost, and the power supplied to the induction coil, and therefore the amount of induction heating to the metal material in the furnace, was reduced, resulting in a corresponding decrease in efficiency.

For this reason, conventionally, for example, as shown in FIG. 1, a high frequency inverter device 1 whose maximum output voltage and maximum output current are limited to predetermined values, and an induction coil 3 wound around a furnace body 2 of an induction furnace. A matching single-turn transformer 4 having a plurality of switching taps 4-1, 4-2, . While connecting the switch 6 and the auxiliary capacitor 7 for power factor improvement in parallel, the operator of the induction furnace, while looking at the wattmeter (not shown) for detecting the output power of the inverter device 1, By switching the switching tap, turning the switch 6 on and off, or by setting a margin angle α for the firing angle of the thyristor, etc. of the inverter device 1, and adjusting the firing angle. By this means, the operation of the induction furnace was controlled so that the power supplied to the induction coil 3 was approximately maximized.

However, in the above-mentioned conventional operation control device, the AC power supply device is required to have a considerably larger power capacity than the electric power required depending on the furnace capacity of the induction furnace, and the configuration is accordingly complicated and The drawbacks were that it was large and its manufacturing cost was high.

Furthermore, the switching operation of the above-mentioned changeover tap or switch 6, and the adjustment operation of the margin angle α are performed by the operator according to the indicated value of the above-mentioned wattmeter, and these operations require skill and skill. It also had the drawbacks of being demanding and having poor operability.

This invention was made in order to eliminate the above-mentioned drawbacks, and calculates the impedance of the induction furnace during melting based on the output voltage and output current detection signals of the AC power supply device that supplies power to the induction coil of the induction furnace. By determining whether the calculated impedance is within a predetermined range and lighting the corresponding indicator light, it is easy to determine whether there is too much or too little material being put into the induction furnace. It is an object of the present invention to provide a control device that makes it easy to determine whether or not to input material in order to input maximum power into an induction furnace.

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3.

In FIG. 2, parts equivalent to those of the apparatus shown in FIG. 1 will be described with the same reference numerals.

In FIG. 2, 10 is an AC power supply device that supplies AC power of a predetermined frequency to an induction coil 3 wound around a furnace body 2 of an induction furnace.

The AC power supply device 10 includes a commercial three-phase AC power supply 1
1 is connected to a bridge rectifier circuit 12 using six thyristors, and to this bridge rectifier circuit 12,
An inverter circuit 14 using four thyristors is connected via a DC reactor 13, while the bridge rectifier circuit 12 and the inverter circuit 1
The inverter control circuit 15 is connected to the gate of each of the four thyristors to apply an ignition command signal. The maximum output voltage and maximum output current of this AC power supply 10 are limited to Vmax and Imax, respectively, by the inverter control circuit 15 in a known manner.

Reference numeral 18 denotes a current detector for detecting the output current of the AC power supply 10, which uses, for example, an instrument current transformer. This current detector 18 is connected between the three-phase AC power supply 11 and the bridge rectifier circuit 12. The output of the current detector 18 is applied to a diode rectifier circuit 19, and from the diode rectifier circuit 19, a detection current of a DC voltage representing an input current to the AC power supply 10, or in other words, an output current of the power supply. Signal Ix is output.

Reference numeral 21 denotes a voltage detector for detecting the output voltage of the AC power supply 10, which uses, for example, an instrument transformer. This voltage detector 21 includes the inverter circuit 14 in the AC power supply device 11,
It is connected between the induction coil 3 and the induction coil 3. The output of this voltage detector 21 is applied to a diode rectifier circuit 22, which outputs a detected voltage signal Vx of a DC voltage representing the output voltage of the AC power supply 10.

23 is an arithmetic circuit for impedance calculation, and this arithmetic circuit 23 is connected to the diode rectifier circuit 22.
The detected voltage signal Vx inputted to one input terminal T ₁ from the above is divided by the detected current signal Ix inputted from the diode rectifier circuit 19 to the other input terminal T ₂ to calculate the load of the AC power supply 10. It is connected to calculate the input impedance Zx (=Vx/Ix) of the induction furnace and apply a signal representing this impedance Zx value to the level determination circuit 24.

The level determination circuit 24 includes the arithmetic circuit 23
This circuit determines which of the ranges A ₁ to A ₄ defined by the impedances Z ₁ , Z ₂ , and Z ₄ in FIG. 1 falls within the impedance Zx of the induction furnace calculated in FIG.

The above-mentioned range _A1 is a range in which the impedance of the induction furnace is larger than _Z1 in FIG. 1, and is a range in which the amount of metal material is small and a large amount of metal material needs to be input. Also, in range A ₂ , the impedance of the induction furnace is
This is a range smaller than Z ₁ and larger than Z ₂ and requires a small amount of metal material to be introduced. further range
In A ₃ , the impedance of the induction furnace is between Z ₂ and Z ₄ , and the metal material in the induction furnace is within the appropriate range.

Furthermore, range _A4 is a range where the impedance of the induction furnace is smaller than _Z4 , and is a range where the metal material is excessive.

Impedance calculated by the above calculation circuit 23
When Zx is a value within the first range A ₁ , the output terminal t ₁
Similarly, when the impedance Zx is within the second range _A2 , "1" is output only to the output terminal _t2 . Output terminal
The same applies to t ₃ and t ₄ .

Reference numerals 25-1, 25-2, . Each indicator lamp 25-
1, 25-2, ..., 25-4 are connected to the output terminals t ₁ , t ₂ , ..., t ₄ of the level determiner 24, and when receiving a signal "1" from the corresponding output terminal lights up. In addition, each display lamp 25-1, 2
5-2, . . . are not limited to lamps, and may each be a display device displaying instructions.

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

An appropriate amount of metal material to be melted is put into the furnace body 2 of the induction furnace to be controlled, and the AC power supply 10
When alternating current power is supplied to the induction coil 3, the metal material is heated and melted in accordance with the supplied power.

The current detector 18 detects the current input from the commercial AC power supply 11 to the bridge rectifier circuit 12, that is,
A current Ix corresponding to the output current of the AC power supply 10 is detected, and this detected current signal is converted into a DC voltage signal by a known method by the diode rectifier circuit 19 and applied to the input terminal T ₂ of the arithmetic circuit 23. Ru. In addition, the AC power supply device 1
An output voltage Vx of 0 is detected, and this detected voltage signal is converted into a DC voltage signal by a known method by the diode rectifier circuit 22 and applied to the input terminal T ₁ of the arithmetic circuit 23 .

In the above calculation circuit 23, a value obtained by dividing the detected voltage Vx received at the input terminal _T1 by the current Ix of the signal received at the input terminal _T2 , that is, the input impedance Zx of the induction furnace 3 is calculated. The signal representing this input impedance Zx is sent to the level determination circuit 24.
is applied to

Now, when there is a large shortage of metal material introduced into the induction furnace, the input impedance of the induction furnace is greater than Z ₁ and within the first range A ₁ . In this state, the output terminal t ₁ of the level determiner 24 is set to "1", the display lamp 25-1 lights up, and the other output terminals t ₂ , t ₃ , and t ₄ are all set to "0".
It is said that The signal "1" from the output terminal t1 of the determination circuit ₂₄ is applied to the indicator lamp 25-1, and the indicator lamp 25-1 is turned on and lights up, indicating to the operator that there is a large amount of melt in the furnace body 2. Display the required metal materials to be input.

Further, when the amount of metal material charged into the induction furnace is slightly insufficient compared to the appropriate amount, the input impedance of the induction furnace becomes larger than _Z2 . Therefore, the indicator lamp 25-2 lights up, indicating that a small amount of metal material should be added to the furnace body 2.

Further, when the amount of metal material in the furnace is an appropriate value, the input impedance Zx is a value within the third range A ₃ between the impedances Z ₂ and Z ₄ , and the output terminal t ₃ is set to "1", and the other output terminals t ₁ , t ₂ , and t ₄ are set to "0". Therefore, the indicator lamp 25-3 lights up, indicating that the amount of metal material in the induction furnace is appropriate.

Furthermore, if there is too much metal material in the induction furnace,
The fourth input impedance Zx is smaller than _Z4 .
is a value within the range _A4 , the output terminal _t4 of the determination circuit 24 is set to "1", and the other output terminals _t1 , _t2 , _t3
are both set to "0". Therefore, indicator lamp 2
5-4 lights up to indicate that there is too much metal material in the induction furnace.

In the control device having the above configuration, the display lamp 2
When 5-1 or 25-2 is lit, these indicator lamps go out and indicator lamp 2
By replenishing the metal material into the furnace body 2 until 5-3 lights up, the input impedance of the induction furnace matches that of the AC power supply 10, that is, the output power of the AC power supply 10 is adjusted to the maximum output. It can be maintained by electricity. Therefore, it is possible to more efficiently feed power to the induction coil 3 and melt the metal material. In particular, before the operation of the induction furnace starts, the metal material is charged into the furnace body 2 at a level slightly smaller than the rated capacity of the furnace body 2, and thereafter, according to the commands from the indicators 25-1 and 25-2. Therefore, if the metal material is replenished into the furnace body 2, even if the input impedance of the induction coil 3 changes as the temperature of the metal material (molten metal) in the furnace body 2 increases, By the above-mentioned metal material replenishment operation, the power supplied to the induction furnace can be maintained at approximately the maximum value, and the induction furnace can be operated more efficiently.

As described in detail above, according to the present invention, the load of the AC power supply is controlled based on the detection signal corresponding to the output voltage and output current of the AC power supply that supplies power to the induction coil of the induction furnace to be operated. Since the impedance is automatically calculated and the excess or deficiency of metal material in the induction furnace is displayed based on this impedance signal, the operator can check the amount of metal material stored in the induction furnace just by looking at the above display. It is possible to determine whether the amount of metal material in the furnace is too large, too small, or appropriate, and the induction furnace can always be operated at maximum power by simply replenishing the metal material into the induction furnace. . In other words, it can be operated very efficiently. Further, in the present invention, the impedance can be calculated based on the output voltage and output current of the AC power supply, so the structure is simple and inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the electrical characteristics of a power supply device for an induction furnace to which the present invention can be applied; FIG. 2 is an electric circuit diagram showing the basic configuration of a conventional operation control device;
FIG. 3 is an electrical circuit diagram of an operation control device according to an embodiment of the present invention. 2... Furnace body of induction furnace, 3... Induction coil, 10
...AC power supply, 11...Commercial three-phase AC power supply,
12... Bridge rectifier circuit, 13... DC reactor, 14... Inverter circuit, 18... Current detector, 19... Diode rectifier circuit, 21... Voltage detector, 22... Diode rectifier circuit, 23...
...Input impedance calculation circuit, 24...Level judgment circuit, 25-1, 25-2, ...25-4
...Indicator lamp for material input command.

Claims (1)

[Claims] 1. While supplying power to an induction coil of an 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 In an operation control device for an induction furnace for melting, a voltage detector detects the output voltage of the AC power supply; a current detector detects a value corresponding to the output current of the AC power supply; an arithmetic circuit that divides the output by the output of the current detector to calculate the input impedance of the induction furnace that is the load of the AC power supply; and a state of the impedance of the induction furnace according to the calculation result of the arithmetic circuit. What is claimed is: 1. An operation control device for an induction furnace, comprising: a display device for displaying.