JPH1022095A - Torch ignition control device in transfer type plasma heating device - Google Patents

Abstract

(57) Abstract: To provide a highly reliable ignition control device by optimizing the ignition position of a torch and performing preheating of an object to be heated by a pilot arc. SOLUTION: In a transfer type plasma heating apparatus, a nozzle (2) which is a positive pole of a pilot arc circuit and an anode (3) which is a positive pole of a main arc circuit are connected via a switch to reduce the impedance of the pilot arc circuit. based on the detection signal of the pilot arc current shunted to the main arc circuit before signal or main power is applied for determining the impedance determination circuit (14c), torch lifting device (6
A torch ignition control apparatus for a transition type plasma heating apparatus, wherein a) is operated to appropriately control the ignition position of the torch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torch ignition control apparatus in a transition type plasma heating apparatus for heating molten metal in a melting furnace, a refining furnace and a tundish of a continuous casting facility using a transition type plasma torch. It is.

[0002]

2. Description of the Related Art In a melting furnace, a refining furnace, and a tundish in a continuous casting facility, an induction heating apparatus or a plasma heating apparatus is used for melting, heating, and keeping the temperature of a molten metal in a clean atmosphere. .

[0003] Of these heating devices, plasma heating devices can be roughly classified into two types, a transition type plasma type and a non-transition type plasma type, depending on the difference in the position where a plasma arc is generated.

In the transfer type plasma method, an anode is provided on the object to be heated, and the atmosphere between the positive and negative electrodes is ionized by a pilot arc generated between the cathode and the nozzle at the tip of the torch. This is to change the plasma flow from the torch-side cathode to the heating-object-side anode, and is said to be advantageous in terms of heating efficiency because a plasma current flows directly to the heating object.

On the other hand, in the non-transfer type plasma system, the torch itself is provided with both a cathode and an anode, and the plasma generated between them is grown forward by a working gas from the tip of the torch in the form of a jet to act on an object to be heated. And is suitable for thermal spraying and the like.

In the transition type plasma heating apparatus, the control, which is generally called ignition, in which the pilot arc between the cathode and the nozzle is shifted to the main arc between the cathode and the anode, is performed by controlling the entire torch at a predetermined position above a heating target having an anode. After moving the pilot arc generated by applying a high-frequency electric field between the cathode at the tip of the torch and the nozzle from the tip of the torch to the object to be heated by the working gas, the space between the cathode and the anode at the tip of the torch is A method is adopted in which the degree of ionization of the space is sufficiently increased, and a main power is applied between the positive and negative electrodes to shift to a main arc between the positive and negative electrodes. In actual ignition, since the heating target is often a high-temperature molten metal, it is necessary to bring the torch that has generated the pilot arc close to the molten metal, which is the anode, to an appropriate position for the transition of the arc, and hold it for stable ignition. It becomes important. Because if the pilot arc is too far from the anode, the object to be heated, the ionization state between the positive and negative electrodes cannot be obtained sufficiently,
Applying the main power between the positive and negative electrodes will cause an ignition failure in which the arc does not transfer, and conversely, if the torch is too close to the object to be heated at the time of ignition, radiant heat from the high-temperature molten metal,
This is to cause damage to the torch due to splash or the like, or damage to the torch due to immersion of the torch in the molten metal.

Therefore, conventionally, in performing ignition, the torch is once approached to the ignition position above the molten metal surface, which is calculated from the weight of the entire heating vessel, and the ignition operation is attempted, and the ignition is not performed at this position. In that case, the number 1
A method is adopted in which the torch is approached to the molten metal by 0 mm and the ignition operation is repeated.

FIG. 3 is a conceptual diagram showing the configuration of a conventional ignition control device in a transfer type plasma heating apparatus, and FIG. 4 is a time chart showing details of control in the conventional system.

In the ignition procedure, first, the entire torch including the cathode 1 and the nozzle 2 is lowered and set to an appropriate position above the heating object 5 by using the torch elevating device 6a, where the plasma is transferred. Here, the level of the molten metal surface of the heating object 5 is generally determined by using a molten metal level converted from a weight signal of the heating container 4b measured by a load cell or the like in consideration of the shape of the heating container 4b. .

However, since refractory is used on the inner surface of the heating vessel 4b, there is an error in the accuracy of refractory construction and in the level of the molten metal due to wear of the refractory when used repeatedly. In consideration of the error element (1), the vehicle is temporarily stopped by an error from the originally proper torch position.

At this position, the switches 7b and 8b are closed, the pilot arc ignition high frequency power supply 7a and the pilot arc power supply 8a are applied between the cathode and the nozzle, and the pilot arc 10 is ignited between the cathode and the nozzle. After the pilot arc is ignited, the switch 7b is opened, the pilot arc ignition high-frequency power supply 7a is disconnected, and the pilot arc 10 is held by the pilot arc power supply 8a.

Thereafter, the working gas 11 is supplied to grow the pilot arc 10 in a jet-like manner toward the object 5 to be heated, and then the switch 9b is closed to place the cathode 1 and the lower part of the heating vessel 4b. A main arc power supply 9a is applied between the anode 3 and the anode 3 to shift from the cathode 1 to the main arc 12 toward the anode 3.

At this time, if the distance between the position of the torch and the object 5 to be heated is appropriate and the degree of ionization of the space between the tip of the torch and the object to be heated is sufficiently increased by the formation state of the pilot arc 10, A main arc 12 from the cathode 1 to the anode 3 is generated, and the pilot arc 10 formed from the cathode 1 to the nozzle 2 shifts to a main arc toward the anode 3.

However, when the position of the tip of the torch is too far from the object 5 to be heated, or when the ionization degree of the space due to the pilot arc is insufficient, the main arc from the cathode 1 to the anode 3 is not generated. The transition from the pilot arc is not performed.

Therefore, if the transition to the main arc is not performed after a certain period of time from the application of the main arc power supply 9a, the switch 9b is once opened to disconnect the main arc power supply, and then the torch elevating device 6a is again turned on. The position of the torch is further lowered by several tens of mm using
, And trying to shift to the main arc.

[0016]

However, in such a method, an error occurs between the weight of the entire heating vessel and the actual molten metal level due to wear of the refractory used for the heating vessel, Since the appropriate ignition distance between the torch and the molten metal varies depending on the state of the atmospheric gas, the relationship between the ignition position and the success or failure of the ignition is not reproducible, and the reliability of the ignition is lacking.

Further, depending on the atmosphere conditions between the cathode and the cathode, the formation state of the pilot arc, the floating state of impurities on the surface of the object to be heated, etc., even if the torch is brought close to the object to be heated, ignition may fail. However, the approach of the torch and the repetition of ignition may eventually cause the torch to be immersed in the object to be heated, and may cause the torch to be melted.

The present invention provides a highly reliable torch ignition control device in a transfer-type plasma heating apparatus by enabling optimization of the ignition position of the torch and preheating of the object to be heated by the pilot arc. is there.

[0019]

SUMMARY OF THE INVENTION The present invention relates to a plasma heating apparatus using a transfer type torch, wherein a cathode, a pilot arc circuit for generating a pilot arc between nozzles, a cathode, and a contacting object to be heated. In a plasma heating apparatus having a main arc circuit for generating a main arc between anodes, a circuit connecting a nozzle, which is a positive pole of the pilot arc circuit, and an anode, which is a positive pole of the main arc circuit, via a switch. In addition to forming a pilot arc circuit, a detector that detects the voltage and current between the cathode and nozzle is provided, and an impedance determination circuit that determines and determines the change in impedance in the circuit based on the detection signal from the detector The torch lifting / lowering control device is activated based on the result of the judgment by the impedance judgment circuit, and the ignition position of the torch is properly adjusted. Characterized by being configured as Gosuru.

The present invention also relates to a plasma heating apparatus using a transfer type torch, comprising a cathode, a pilot arc circuit for generating a pilot arc between nozzles, a cathode, and an anode in contact with an object to be heated. In a plasma heating apparatus having a main arc circuit for generating a main arc therebetween, a circuit for connecting a nozzle, which is a positive pole of the pilot arc circuit, and an anode, which is a positive pole of the main arc circuit, via a switch, In the main arc circuit, a detector for detecting the current until the transition to the main arc is provided, and the torch elevating control device is operated based on the detection signal of the detector, so that the ignition position of the torch is appropriately controlled. It is characterized by the following.

Conventionally, an ignition method for transferring a pilot arc between a nozzle and a cathode to a main arc between a heating object as an anode and a cathode includes an atmosphere condition in a heating vessel, a surface property of the heating object, and formation of a pilot arc. Due to the fact that the ignition position varies depending on the situation, the ignition position is empirically assumed as a guide. The contact state between the pilot arc and the object to be heated is detected from changes in circuit constants such as the impedance of the electric circuit that generates the pilot arc between the nozzle and cathode, and the torch position appropriate for arc transition is determined. Preliminary heating of the object to be heated is performed by a pilot arc formed at the tip of the torch at the position.

[0022]

FIG. 1 is a conceptual diagram of an ignition control device in a transition type plasma heating device according to the present invention.
Is performed by forming a main arc 12 between the cathode 1 and the anode 3, and in order to form the main arc 12, the cathode 1 is placed in the immediate vicinity of the heating object 5 that is in contact with the anode 3 in advance. And the ionization degree between the two electrodes must be sufficiently increased.

In order to increase the degree of ionization of the space inside the heating vessel, a pilot arc 10 generated between the cathode 1 and the nozzle 2 is applied to the object 5 to be heated. A pilot arc circuit including a cathode 1, a nozzle 2 disposed around the cathode 1 and a pilot power supply 7a for generating a pilot arc therebetween, and a main arc including a main power supply 9a for generating a main arc from the cathode 1 to the anode 3. A circuit and two electric circuits are configured.

Of the two electric circuits, the pilot arc circuit has a negative electrode 1 for the cathode 1 and a positive electrode for the nozzle 2, and has a high-frequency power supply 7a for igniting the pilot arc and a holding electrode for holding the pilot arc after ignition. DC power supplies 8a are connected in parallel via switches 7b and 8b, respectively. When the pilot arc is ignited, both the switch 7b and the switch 8b are turned on, and the cathode 1 is turned on by the high-frequency electric field.
A pilot arc is formed by causing dielectric breakdown in the gap between the nozzle and the nozzle 2. High frequency power supply 7
When a predetermined time elapses until a pilot arc is formed, the switch a is disconnected by opening the switch 7b.
a.

On the other hand, the main arc circuit connects the cathode 1 to-
The pole and the anode 3 are positive poles, and a DC power supply 9a for generating and holding a main arc is connected to both poles via a switch 9b. Since both the negative pole of the pilot arc circuit and the negative pole of the main arc circuit are the cathode 1,
Switches 7b, 8b, 9b as shown in FIG. 1 or FIG.
Are connected as a common line, and the pilot arc circuit and the main arc circuit generally share the cathode 1, but in the present invention, as shown in FIG. 3 is basically different from the conventional method shown in FIG. 3 in that the nozzle 2 and the anode 3 which is the positive pole of the main arc circuit are connected via a switch 8c.

Further, according to the present invention, a voltage detector 14a between the cathode and the nozzle and a current detector 14b are provided in the pilot arc circuit, and a circuit constant such as impedance is determined from these detection signals by an impedance determination circuit 14c. ing. Other configurations such as the point that the cathode 1 and the nozzle 2 are integrally formed as a torch and that the torch can be set at a predetermined position with respect to the object to be heated by the elevating device 6a are the same as those of the conventional method. It is.

Next, the ignition control according to the present invention will be described.

Heating object 5 is heated by heating vessel 4 having anode 3
After that, the torch having the cathode 1 and the nozzle 2 integrally formed together with the upper lid 4a of the heating vessel 4b is placed in the heating object 5
Set above.

Here, in the conventional method, after lowering the torch to a position suitable for the transition of the arc, the pilot arc 10
In the present invention, the torch is positioned at the upper end of the torch elevating device 6a while the pilot arc 10 is ignited. It does not matter which position is lower to some extent, any position may be used as long as it is higher than the position of the torch where the transition from the pilot arc 10 to the main arc 12 is to be performed. The switches 7b and 8b are closed and the pilot arc is connected between the cathode and the nozzle. After applying the ignition high-frequency power supply 7a and the pilot arc power supply 8a to generate the pilot arc 10 between the cathode and the nozzle, the switch 7b is opened and the pilot arc 10 is held by the pilot arc power supply 8a. Thereafter, the working gas 11 is supplied, and the pilot arc 10 is heated.
Grow in a jet to the side.

Next, after the switch 8c is closed, the torch is gradually lowered by using the torch elevating device 6b as shown in FIG. 2A while holding the pilot arc 10 at the tip of the torch. At this time, the pilot arc power supply 8a is connected to the impedance determination circuit 14c between the cathode and the nozzle.
, The impedance formed by the current path flowing through the closed circuit of the switch 8b, the cathode 1, and the nozzle 2 is shown, after which the torch gradually descends and the pilot arc 1
When the tip of the contact 0 comes into contact with the object 5 to be heated, in addition to the above-mentioned closed circuit, a current path newly flowing from the pilot arc power supply 8a to the closed circuit of the switch 8b, the cathode 1, the anode 3, and the switch 8c is connected in parallel. As a result, the impedance shown in the impedance determination circuit 14c appears as a phenomenon as shown in FIG. The decrease in the impedance at this time becomes more remarkable as the contact state of the pilot arc 10 with the heating object 5 becomes denser. Therefore, by monitoring the value of this impedance, the contact state between the pilot arc 10 and the heating object 5 is changed to an electric state. It can be grasped as a general control signal.

Therefore, when the value of the impedance reaches a certain set value Z ₀ , the torch lifting / lowering control device 6b is operated to stop the lowering of the torch as shown in FIG. Is maintained, the positional relationship between the pilot arc 10 and the object to be heated can be controlled to an appropriate position with good reproducibility.

In this manner, by preserving the amount of action of the pilot arc 10 on the object 5 to be heated for a certain period of time, it becomes possible to preheat the object 5 to be heated, and impurities floating on the surface layer of the object to be heated. And at the same time, sufficiently increase the degree of ionization of the main arc path from the cathode 1 to the anode 3 at the bottom of the heating vessel through the heating target portion 5 in performing the transition to the main arc. Can be. During this preheating period, the torch may be held at a fixed position, or the position of the torch may be maintained if the impedance value shown in the impedance determination circuit 14c is kept constant, that is, if the impedance tends to increase. Needless to say, the position of the torch may be controlled by slightly lowering or slightly increasing the position of the torch if the impedance shows a tendency to decrease.

The pilot arc 10 at the tip of the torch
Is in contact with the object to be heated 5 when the current flowing into the path from the anode 3 to the pilot power supply 8a via the switch 8c is applied to the main current detector 1 as shown in FIG.
It is also possible to detect and catch at 3 and use the detection signal of the main current detector 13 in the process of bringing the torch that has generated the pilot arc close to the object 5 to be used, and is suitable for shifting to the main arc. It is possible to configure the control of the torch position detection and the preheating of the heating object 5 described above, and it is also possible to configure the determination logic in combination with the signal of the impedance determination circuit 14c.

What is important is that the provision of the switch 8c constitutes a determination circuit for detecting the flow of the pilot arc current into the anode 3 before the main arc power supply 9a is applied. Before performing the transition, preheating of the heating object 5 and the atmosphere can be performed with the position of the pilot arc properly maintained. After sufficiently increasing the degree of ionization of the space between the tip of the torch and the object 5 to be heated by the pilot arc 10, the switch 8c is opened and the switch 9b is closed at the same time to apply the main arc power supply 9a between the cathode and the anode. Then, the transition to the main arc is performed as shown in (e) of FIG. At the time when the main arc power supply 9a is applied, the atmosphere conditions between the torch and the object to be heated are preheated in a state where the pilot arc is already partially formed between the cathode and the anode, so that the degree of ionization of the atmosphere is sufficient. The transition of the arc when the main arc power supply is applied is easily performed, and stable ignition is possible.

[0035]

【The invention's effect】

(1) Since the contact state between the pilot arc generated between the nozzle and the cathode and the object to be heated, which is the anode, can be detected as the amount of change in the circuit constant of the pilot arc generation circuit, the supply state of the working gas It is possible to set the proper torch position for ignition without being affected by fluctuations in the formation state of the pilot arc due to the fluctuations in the molten metal position due to the formation state of the pilot arc and the wear state of the refractory used in the heating vessel. Ignition can be enabled.

(2) The contact state between the pilot arc generated between the nozzle and the cathode and the object to be heated, which is the anode, is grasped from a change in the circuit constant of the circuit for generating the pilot arc, and the pilot arc is used by using this signal. By controlling the position of the torch so that the contact state between the heating object and the object to be heated is maintained in a certain appropriate state for a predetermined time, it is possible to perform preliminary heating of the surface layer of the object to be heated by a pilot arc, and And the impurities floating on the surface of the object to be heated are melted, and the subsequent transition to the main arc can be ensured.

(3) Using a torch raising / lowering device with a torch raising / lowering device as a reference based on a change in the characteristic value of the pilot arc circuit generated between the nozzle and the cathode, a certain range above and below the pattern is set. By raising and lowering the torch, it is possible to sufficiently increase the degree of ionization under atmospheric conditions when shifting to the main arc.

(4) Conventionally, a method has been performed in which the position of the molten metal surface is calculated from the weight of the entire heating vessel and the like, and the ignition height of the torch is determined from the calculated molten metal surface height. According to this, the contact between the pilot arc and the molten metal surface is detected in the process of approaching the torch having generated the pilot arc to the molten metal surface, so that a weight measuring device for the entire heating vessel can be eliminated.

(5) A change in the circuit constant of the pilot arc circuit generated between the nozzle and the cathode is detected, and the determination level for the detection signal is set to two levels, an appropriate ignition level and an abnormal approach level, thereby igniting. In addition to the control, it is also possible to detect an abnormal approach between the torch and the molten metal and to prevent the torch from being immersed in the molten metal, which has conventionally been a problem.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an ignition control device in a transition type plasma heating apparatus according to the present invention.

FIG. 2 is a time chart showing details of control contents of an ignition control device in the transition type plasma heating apparatus of the present invention.

FIG. 3 is a conceptual diagram of an ignition control device in a conventional transition type plasma heating apparatus.

FIG. 4 is a time chart showing details of control contents of an ignition control device in a conventional transition type plasma heating apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cathode 2 Nozzle 3 Anode 4a Top lid 4b Heating vessel 5 Heating object 6a Torch elevating device 6b Torch elevating control device 7a High frequency power supply for pilot arc ignition 7b Pilot arc ignition switch 8a DC power supply for pilot arc 8b Pilot arc switch 8c circuit Characteristics determination switch 9a Main arc power supply 9b Main arc switch 10 Pilot arc 11 Working gas 12 Main arc 13 Main current detector 14a Pilot arc circuit voltage detector 14b Pilot arc circuit current detector 14c Impedance determination circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location F27B 3/20 F27B 3/20 F27D 11/08 F27D 11/08 E

Claims (2)

[Claims] 1. A plasma heating apparatus using a transfer type torch, wherein a main arc is provided between a cathode, a pilot arc circuit for generating a pilot arc between nozzles, a cathode, and an anode in contact with an object to be heated. In a plasma heating apparatus having a main arc circuit for generating the arc, a circuit for connecting a nozzle, which is a positive pole of the pilot arc circuit, and an anode, which is a positive pole of the main arc circuit, through a switch is formed. A detector for detecting the voltage and current between the cathode and the nozzle is provided, and an impedance determination circuit is formed based on a detection signal from the detector to grasp and determine a change in impedance in the circuit. According to the result, the torch lift control device was operated to control the ignition position of the torch properly. A torch ignition control device in the transition type plasma heating device. 2. A plasma heating apparatus using a transfer type torch, comprising: a cathode, a pilot arc circuit for generating a pilot arc between nozzles, a main arc between the cathode, and an anode in contact with an object to be heated. In a plasma heating apparatus having a main arc circuit for generating a pulse, a circuit for connecting a nozzle, which is a positive electrode of the pilot arc circuit, and an anode, which is a positive electrode of the main arc circuit, through a switch is formed. In addition, a detector for detecting the current until the transition to the main arc is provided, and the torch elevating control device is operated based on the detection signal of the detector to appropriately control the ignition position of the torch. Torch ignition control device in the transfer type plasma heating device.