JPH07118384B2 - Arc furnace electrode lifting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to solve the following problems.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lifting device for lifting and lowering an arc electrode in an AC or DC arc furnace.

(Prior Art) Conventionally, in an arc furnace, arc power is supplied to an arc electrode to form an arc at a free end of the electrode. An electrode lifting device using a hydraulic drive device with accumulator having a small stroke is provided in order to make the arc length constant and finely control the electric power.

Also, in order to deal with a case where the charged material collapses in the furnace and a short circuit occurs between the arc electrode and the molten metal in the furnace, the above-mentioned electrode is used for raising and lowering the electrode using an electric motor as a drive source. It is arranged to greatly raise the temperature by switching and using the device (see, for example, Japanese Patent Publication No. 49-20013).

(Problems to be Solved by the Invention) In the structure as described above, a hydraulic drive device with a pressure accumulator for adjusting electric power in response to a change in arc, and an electrode corresponding to the above short circuit Therefore, it is necessary to combine two kinds of devices with an electric drive device for significantly increasing the temperature, which causes a problem that the structure becomes complicated and expensive.

In addition, the electric drive has a drawback that the operation delay occurs due to the inertia of the movable portion from the rotor of the electric motor to the arc electrode, the friction of the drive mechanism, and the like, and the responsiveness is poor in an emergency when the load collapses.

The present invention is provided to solve the problems in the above-described conventional arc furnace. Even with one type of hydraulic drive device having a simple structure, the arc electrode can be finely controlled to move up and down. It has the feature that the arc length can be controlled to a fixed length with extremely high accuracy and the electric power can be controlled.
Responsive to a short-circuit condition when the charge collapses in the furnace, the response is extremely fast, and the arc electrode can be greatly raised in a very short time to prevent a power supply trip and the arc electrode itself. It is an object of the present invention to provide an electrode lifting / lowering device for an arc furnace, which is capable of preventing breakage of the wire and missing of the tip.

(Means for Solving Problems) An electrode lifting device for an arc furnace according to the present invention has an arc electrode that can be lifted and lowered above the furnace, and an arc power supply circuit is connected to the arc electrode. Further, the arc electrode is provided with an elevating mechanism configured to elevate and lower the arc electrode by receiving supply of a liquid, and the arc electrode is supplied by supplying arc power to the arc electrode from the arc power supply circuit. In the arc furnace in which an arc is generated from the charging material in the furnace from the above to melt the charging material in the furnace by the arc and the arc electrode is moved up and down by the lifting mechanism, , A variable displacement constant pressure pump for supplying liquid to the lifting mechanism is connected via a servo valve for controlling the amount of liquid supplied to the lifting mechanism, while The arc current detection circuit and the arc power detection circuit are connected to the peak power supply circuit, and the changes in the arc current detected by the arc current detection circuit and the arc power detection circuit are detected in those circuits. A comparison circuit is connected so as to output a control signal for controlling the servo valve in response to a change in arc power, and the comparison circuit is connected so as to give the control signal to the servo valve.

(Operation) When arc power is supplied to the arc electrode, an arc is generated from the arc electrode to the charge in the furnace. The arc melts the charge.
Changes in the arc length in the furnace are detected as changes in the arc current and arc voltage, and the servo valve is controlled according to the changes. Then, the supply amount of the liquid to the electrode elevating mechanism is controlled by the servo valve, the elevating control of the arc electrode is performed, and as a result, the power control is performed. Also, when the charge collapses in the furnace and a short circuit occurs between the arc electrode and the molten metal in the furnace via the charge collapsed, the servo valve is controlled in the same manner as above, and liquid is fed to the electrode lifting mechanism. A large amount of liquid is supplied to the elevating mechanism from a variable-capacity constant-pressure pump for supplying the arc electrode to a large and sudden rise.

(Embodiment) A drawing showing an embodiment of the present application will be described below. In FIG. 1, 1 is a furnace, 2 is a charge inside the furnace, and most of them are gun iron and scrap in the initial stage of melting. Reference numeral 3 denotes an arc electrode arranged above the furnace, which can be moved up and down freely. Reference numeral 4 indicates an arc power supply circuit connected to the electrode 3, and reference numeral 5 indicates a lifting mechanism for the arc electrode attached to the electrode 3. This elevating mechanism is configured to control the elevating and lowering of the electrode 3 by receiving the supply of liquid (oil or water), as described later in detail. Next, 7 is an arc current detection circuit, which comprises a current transformer 8 attached to the arc power supply circuit 4 and a transformer 9 for stepping down the output thereof. Reference numeral 10 denotes an arc voltage detection circuit, which comprises a connection circuit 11 connected to the supply circuit 4 and the furnace 1 and a transformer 12 for stepping down the voltage obtained at the connection circuit. Reference numeral 14 denotes a comparison circuit, which comprises bridge rectification circuits 15 and 16 connected to the secondary sides of the transformers 9 and 12, respectively. The bridge rectifier circuits 15 and 16 are reversely connected to each other, and the difference between the DC output values of the rectifier circuits is output as a control signal. Reference numeral 17 is a sensitivity adjuster, and 18 is a solenoid in the servo valve.

Next, in FIG. 2 showing the electrode elevating / lowering device 5, 21 is a column in the elevating mechanism 5, which is supported by a plurality of guide rollers 22 so as to be vertically movable. Reference numeral 23 is a supporting arm fixed to the column 21, and the arc electrode 3 is attached to the free end portion thereof. Reference numeral 24 is a cylinder, one end 24a of which is connected to a fixed portion in the arc path, and the other end 24b of which is connected to the column 21. 2
A servo valve 5 is for controlling the amount of liquid supplied to the cylinder 24. In the present specification, the term “supply” is used as a term that indicates both positive supply, that is, liquid feeding into the cylinder 24, and negative supply, that is, liquid discharging from the cylinder 24. Reference numeral 26 is a pump for supplying a liquid to the cylinder 24, which is a variable displacement constant pressure type piston pump. As shown in FIG. 4, this pump 26 instantaneously generates a required flow rate controlled by a servo valve in a state where the discharge pressure is constant and the discharge amount is large and can be instantaneously changed. It has the following characteristics. 27 is a motor for driving the pump 26.

With the above-mentioned configuration, as shown in FIG. 3, for example, when the output value of the comparison circuit 14 becomes large at a positive value, the servo valve 25
When the flow rate of the liquid sent to the cylinder 24 through the cylinder 24 increases, the rising speed of the electrode 3 increases, and the output value of the comparison circuit increases with a negative value, the cylinder 24 increases the servo valve 25.
It is set so that the amount of liquid discharged through the electrode increases and the descending speed of the electrode 3 increases.

In the apparatus as described above, a charging material 2 such as pig iron or scrap is charged into the furnace 1, and arc power is supplied to the arc electrode 3 through the supply circuit 4. Then arc electrode 3
From this, an arc is generated toward the charging material 2, and the charging material is melted by the arc, and it becomes a molten metal in sequence.

In this state, the arc current and the arc voltage are detected by the respective detection circuits 7 and 10, and the comparison circuit 14 outputs the difference value between the two based on the detected values. When the difference value is 0, the servo valve 25 does not operate, and therefore the lifting device 5 does not operate, and the electrode 3 remains in the same state. On the other hand, when the charge 2 melts in the furnace 1 and the distance between it and the electrode 3 increases and the arc length increases, the arc current value detected by the arc current detection circuit 7 decreases and the arc voltage is detected. The arc voltage value detected by the circuit 10 increases. As a result, the output of the comparison circuit 4 becomes negative (see, for example, a in FIG. 3). The magnitude is determined by the magnitude of each of the arc current value and the arc voltage value.
Then, the servo valve 25 operates according to the output of the comparison circuit, the liquid in the cylinder 24 is discharged, and the electrode 3 descends at the speed indicated by a'in FIG. As a result of the lowering, when the arc length becomes a predetermined value, the arc current and the arc voltage respectively become predetermined values, so the output of the comparison circuit 14 becomes 0, and at that point the descending of the arc electrode 3 is stopped. On the other hand, when the distance between the charging material 2 and the electrode 3 is shortened due to the collapse of the charging material in the furnace and the arc length is shortened, the detected arc current increases and the arc voltage decreases. To do. Then, the output of the comparison circuit 14 becomes a positive value (see, for example, FIG. 3b). Then, the servo valve 25 operates in response to such a control signal from the comparison circuit 14, and the liquid from the pump 26 is sent to the cylinder 24 through the servo valve 25. As a result, the electrode 3 rises at a velocity as shown by b'in FIG. When the arc length reaches a predetermined length as a result of the rise, the rise of the electrode 3 is stopped as in the above case.

Since the above-described operation of raising and lowering the electrode 3 is constantly performed sensitively, the arc length between the electrode 3 and the charging material 2 is always kept constant in the furnace 1. In addition, if an example of the responsiveness of the ascending / descending of the electrode 3 and the performance of its ascending / descending speed with respect to the change of the arc length is shown, the responsiveness is
Seconds, ascending / descending speed is, for example, 6 m / min. Further, the above electrode lifting device may be applied to a ladle refining device.

(Results of the Invention) As described above, in the present invention, when the arc power is supplied to the arc electrode 3 to generate the arc from the arc electrode 3 and the charged material in the furnace is heated and melted by the arc, By vertically adjusting the arc electrode 3 by the elevating mechanism, it is possible to stabilize the input of the melting power to the arc furnace, shorten the melting time, and reduce the unit amount of melting power.

Moreover, in the above case, since the changes in the arc current and the arc voltage are detected and the arc electrode 3 is adjusted up and down based on the changes, the arc length between the electrode tip and the charging material, which changes momentarily in the furnace during melting, is adjusted. Then, it can be controlled to a constant length, and there is an effect that melting in the furnace can be performed stably.

Further, in that case, since the servo valve 25 controls the supply amount of the liquid to the elevating mechanism 5, the elevating and lowering of the arc electrode 3 can be finely controlled according to the subtle changes in the arc current and arc voltage, and the arc length can be increased. There is an effect that the electric power control can be performed with high stability by performing the electric power control with extremely high accuracy.

Further, even if it is designed to cope with the subtle changes in the arc current and voltage as described above, the charged material collapsed in the furnace and the space between the arc electrode 3 and the molten metal in the furnace collapsed. When short-circuited via the, the rapid response of the arc current and the sudden drop of the arc voltage are dealt with immediately, and in addition to the quick response of the servo valve 25, the variable-capacity constant-pressure pump 26 quickly and quickly delivers the liquid of the required flow rate The arc electrode 3 can be quickly and greatly raised in response to the cooperative operation of a large amount continuously supplied to the elevating mechanism 5, and the time in the short-circuited state can be made extremely short. It has the effect of quickly normalizing various current values and preventing current trips. At the same time, the increase in the load on the arc electrode 3 due to the increase in the amount of leaning of the furnace interior contents on the arc electrode is quickly eliminated, and the arc electrode Three
There is an effect that it is possible to prevent breakage of the electrode or loss of the electrode tip.

[Brief description of drawings]

The drawings show the embodiments of the present application. FIG. 1 is a schematic view of an arc furnace and an electric system related to the arc furnace, FIG. 2 is an explanatory view of an electrode lifting device, and FIG. 3 is an output of a comparison circuit and lifting of electrodes. FIG. 4 is a graph showing an example of the relationship with the speed, and FIG. 4 is a graph showing the relationship between the discharge pressure and the discharge amount of the pump. 1 ... Furnace, 3 ... Arc electrode, 5 ... Lifting mechanism, 7 ...
Arc current detection circuit, 10 ... Arc voltage detection circuit, 25 ...
… Servo valve, 26… Pump.

Continuation of front page (56) Reference JP-A-55-96598 (JP, A) JP-B-49-20013 (JP, B1) JP-B-52-41893 (JP, B2)

Claims (1)

[Claims] 1. An arc electrode which can be moved up and down is provided above the furnace, an arc power supply circuit is connected to the arc electrode, and a liquid is supplied to the arc electrode. Attaching a lifting mechanism configured to move the arc electrode up and down, and by supplying arc power to the arc electrode from the arc power supply circuit, an arc is generated from the arc electrode to the charging material in the furnace and the arc is generated. In the arc furnace in which the charge in the furnace is melted by means of the above, and the arc electrode is moved up and down by the elevating mechanism, the elevating mechanism is equipped with a variable capacity constant pressure type for supplying liquid to the elevating mechanism. Pump is connected via a servo valve for controlling the amount of liquid supply to the lifting mechanism, while the arc power supply circuit has an arc current detection circuit and an arc voltage. A control for connecting the output circuits and controlling the servo valves in response to changes in the arc current detected by the arc current detection circuit and changes in the arc voltage detected by the arc voltage detection circuit. An electrode lifting device for an arc furnace, comprising a comparison circuit connected to output a signal, and the comparison circuit connected to the servo valve so as to supply the control signal.