JPH1022094A - Plasma controller for nonmigrating plasma application device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma controller which optimizes the amount of a plasma working on a subject for heating by controlling the position of a torch. SOLUTION: In a nonmigrating plasma heating device, a load electrode 3 brought into contact with a subject 5 for heating is newly provided, an anode 2 serving as the + pole of an arc circuit is connected to the load electrode 3 via a switch, and a torch lift device 6b is operated in accordance with a signal of an impedance determining circuit 14c which determines the impedance of the arc circuit or with a signal indicating the detection of an arc current which partly flows through the load circuit 3, so as to appropriately control the working position of an arc on the subject for heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma control apparatus in a non-transition type plasma application device such as a plasma heating device or a thermal spraying device using a non-transition type plasma torch.

[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. Among them, the plasma heating apparatus 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 generation position of the plasma arc. In the former, the anode is provided on the object to be heated, and after the atmosphere between the positive and negative electrodes is ionized by the pilot arc generated between the cathode and the nozzle at the tip of the torch, from the cathode on the torch side to the anode on the object to be heated It is said to be advantageous from the viewpoint of heating efficiency since a plasma current flows directly to the object to be heated.

[0003] On the other hand, in the latter, the torch itself is provided with both a cathode and an anode, and the plasma generated between them is grown forward from the tip of the torch in the form of a jet by a working gas to act on the object to be heated. Suitable for etc.

FIG. 3 is a conceptual diagram showing a conventional method of controlling a plasma arc in a non-transfer type plasma heating apparatus. A plasma torch including a cathode 1 and an anode 2 puts an object 5 to be heated into a heating vessel 4b. After that, it is set together with the lid 4a of the heating container. Thereafter, the atmosphere in the heating vessel 4b is increased to a predetermined degree of vacuum, and then the torch elevating device 6
At b, the tip of the torch is lowered from the object 5 to be heated to a predetermined position. At this time, the stop position of the torch is selected empirically based on the atmospheric conditions in the heating vessel 4b, the heating range of the object to be heated, the shape of the plasma flow after ignition, and the like. When the object 5 to be heated is a molten metal or the like, the height may be set at a predetermined distance from the surface of the molten metal using the molten metal height calculated from the weight of the entire heating vessel 4b.

After setting the tip of the torch at an appropriate position based on experience in this way, as shown in the time chart of FIG.
The switches 7b and 8b are closed, and a high-frequency ignition power supply 7a and a plasma DC power supply 8a are applied between the cathode 1 and the anode 2 at the tip of the torch to generate a plasma arc 10 between the positive and negative cathodes. The plasma arc 10 thus generated is heated by the working gas 11 from the tip of the torch 5
, And is made to act on the object 5 to be heated for the purpose of heating or thermal spraying.

[0006]

However, in such a method, in the process of heating or spraying by the plasma arc 10, the position of the torch is moved up and down depending on the reaction state of the object 5 to be heated, and the position of the torch is finely adjusted. However, as shown in the time chart of FIG. 4, there is almost no change in the anode current flowing between the cathode and the anode, and the torch of the torch which has the most influence on the plasma reaction between the plasma arc 10 and the object 5 to be heated. The position control also has to rely on pattern control based on past results, and cannot perform dynamic control of the plasma arc 10, and as a result, it may cause poor heating, insufficient reaction, or excessive input. There was a problem.

When the object 5 to be heated is a molten metal or the like, an error occurs between the weight of the entire heating container and the actual surface of the molten metal due to wear of a refractory used for the heating container 4b. Since the appropriate reaction distance between the torch and the molten metal varies depending on the atmosphere gas conditions between them, reproducibility is not ensured between the torch tip position and the reaction between the plasma flow and the object to be heated, and the heating or spraying process is stable. There were problems such as lack of sex.

The present invention detects the amount of contact of a pilot arc with an object to be heated as a change in an electrical signal such as impedance, and controls the position of the torch using the detected signal as a feedback signal. Provided is a plasma control device in a non-transfer type plasma application device that optimizes the operation amount of plasma to an object.

[0009]

SUMMARY OF THE INVENTION The present invention uses a non-transfer type plasma torch and generates a plasma flow between a cathode and an anode of the torch. In the apparatus, a load electrode is provided so as to be in contact with the object to be processed, and a circuit for connecting the load electrode and the anode of the torch via a switch is formed, and in a circuit for generating a plasma flow,
A detector that detects the voltage and current between the cathode and anode is provided, and an impedance determination circuit is formed based on the signal from the detector to determine the change in impedance in the circuit. The lifting control device is operated to control the torch position properly.

A plasma control apparatus in a non-transfer type plasma application apparatus according to the present invention uses a non-transfer type plasma torch and generates a plasma flow between a cathode and an anode of the torch. In the above, a load electrode is provided so as to be in contact with the object to be processed, and a circuit for connecting the load electrode and the anode of the torch through a switch is formed, and a current flowing from the cathode of the torch to the load electrode side in the circuit. Is provided, and a torch lifting / lowering control device is operated based on a detection signal of the detector to appropriately control a torch position.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Conventionally, control of a plasma arc in a non-transfer type plasma heating apparatus includes controlling a gap between a torch and an object to be heated, controlling an atmosphere in a heating vessel, controlling a blowing amount of a working gas, and the like. In contrast to what has been done based on empirical results in the past, a new load electrode that has contact with the object to be heated is newly provided, and this is connected to the anode to create a current path flowing from the cathode to the object to be heated. When the plasma arc comes into contact with the object to be heated, the plasma current shunted to the current path is captured, and the contact state between the plasma arc and the object to be heated can be grasped.

FIG. 1 shows an embodiment of a plasma control device in a non-transfer type plasma heating device according to the present invention.
The apparatus main body includes a torch in which the cathode 1 and the anode 2 are integrated, and a torch elevating device 6 for setting the position of the torch to the object 5 to be heated.
b, a heating vessel 4b and the like. In the conventional method, as shown in FIG. 3, a high frequency power supply 7a for igniting an arc and a plasma DC power supply 8a for holding an arc are provided to the cathode 1 and the anode 2 via switches 7b and 8b, respectively. Connected in parallel. In the present invention, as shown in FIG. 1, a load electrode 3 having a new contact with the object 5 to be heated is added to the structure of the conventional method, and the load electrode 3 is connected to the anode 2 via a switch 9. It is a different place. In the method of the present invention, the voltage detector 14a between the positive and negative electrodes and the current detector 1 are provided in the arc generating circuit.
4b, and a circuit constant detector 14c such as impedance is provided from these detection signals.

The present invention will be described below in accordance with the operation procedure of the apparatus. After the object 5 to be heated is housed in a heating vessel 4b having a load electrode 3, a torch having a cathode 1 and an anode 2 integrated with each other is placed on the top of the heating vessel. It is set above the object to be heated together with 4a. Here, in the conventional method, after the torch is lowered to a position suitable for heating or spraying, the plasma arc 10 is ignited, and the plasma arc is brought into contact with the object 5 to be heated to perform heating or spraying treatment by plasma reaction. In the method of the present invention, the position of the torch when igniting the plasma arc may be at the upper end of the torch elevating device 6 or at a position somewhat lower than the torch. It suffices that the position is above the position of the torch to act on the object 5 to be heated. The switches 7b and 8b are closed, and the plasma ignition high-frequency power supply 7a and the plasma DC power supply 8a are applied between the positive and negative electrodes. After the plasma arc 10 is generated, the switch 7b is opened to open the plasma arc 10
Is held by the plasma DC power supply 8a, and thereafter, the working gas 11 is supplied to grow the plasma arc 10 in a jet shape on the heating object 5 side.

Next, after the switch 9 is closed, the torch is gradually lowered by using the torch elevating device 6b as shown in FIG. 2A while holding the plasma arc at the tip of the torch. At this time, the impedance formed by the current path flowing from the plasma DC power supply 8a to the closed circuit of the switch 8b, the cathode 1, and the anode 2 is shown in the impedance determination circuit 14c between the positive and negative electrodes. When the tip of the plasma arc 10 gradually comes down and comes into contact with the object 5 to be heated, in addition to the above-described closed circuit, a new closed circuit of the switch 8b, the cathode 1, the load electrode 3, and the switch 9 is newly provided from the plasma DC power supply 8a. Is newly formed, and the branch current 12 flows, so that the impedance shown in the impedance determination circuit 14c decreases as shown in (b) of FIG. Since the decrease in impedance at this time becomes more remarkable as the contact state of the plasma arc 10 with the object 5 to be heated becomes denser,
By monitoring the value of this impedance, the contact state between the plasma arc 10 and the object 5 to be heated can be grasped as an electrical control signal.

Therefore, when the value of the impedance reaches a certain set value Z ₀ , the lowering of the torch is stopped and the position of the torch is maintained as shown in FIG. And the positional relationship between the heating object 5 and the heating target 5 can be controlled to an appropriate position with good reproducibility. Further, during the period of performing the heating or spraying process by the plasma arc, the value of the impedance shown in the impedance determination circuit 14c is kept constant, that is, if the impedance shows a tendency to increase, the position of the torch is slightly lowered or the impedance is lowered. If the tendency is shown, it goes without saying that the position of the torch may be controlled such as slightly raising the position of the torch.

When the plasma arc 10 at the tip of the torch is in contact with the object 5 to be heated, the branch current 12 flowing from the load electrode 3 to the plasma DC power supply 8a via the switch 9 is shown in FIG. (C), it is also possible to detect and catch with the main current detector 13, and the detection signal of the main current detector 13 in the process of approaching the torch having generated the plasma arc to the object to be heated. Can be used to detect the position of the torch suitable for heating or thermal spraying, and to control the amount of action of the plasma to be constant, or to form a determination logic in combination with the signal of the impedance determination circuit 14c. Of course it is possible.

Further, in the plasma processing for thermal spraying or the like, when it is not desirable that the branch current 12 passes through the object 5 to be heated, as shown in the time chart of FIG. It is also possible to adopt a method such as closing the circuit characteristic determination switch 9 only when checking the state.

[0018]

【The invention's effect】

(1) The state in which the plasma arc generated between the cathode and the anode is in contact with the heating object connected to the same potential as the anode depends on the circuit constants such as the impedance of the electric circuit consisting of the positive cathode and the plasma power supply. Since the change is detected as a change, the amount of contact between the plasma arc and the object to be heated can be electrically controlled by configuring dynamic control using the change in the circuit constant as an index.

(2) To set the initial position of the torch in a conventional manner based on empirical judgment from complicated indices such as the atmospheric conditions in the heating vessel, the heating range, and the shape of the plasma arc after ignition. By setting the partial flow rate of the plasma arc to the object to be heated to an appropriate value in advance, the plasma arc can be easily realized with high reproducibility, and stable plasma processing can be performed.

(3) When the object to be heated is a molten metal,
Calculate the position of the molten metal surface from the weight of the entire heating vessel, etc.
Although a method of determining the height of the torch from the calculated level of the molten metal is performed, according to the method of the present invention, the plasma arc is ignited in the process of approaching the torch ignited by the plasma arc to the molten metal surface. Since the contact with the molten metal surface is detected, the weight measuring device for the entire heating container can be omitted.

(4) When detecting changes in circuit constants such as impedance of a circuit for generating a plasma arc generated between a cathode and an anode, two detection levels are provided: an appropriate torch position level and an abnormal approach level. In addition to stabilizing the plasma arc, it is possible to detect an abnormal approach between the torch and the object to be heated and prevent the torch from being immersed in the molten metal, which has been a problem in the past.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a plasma control device in a non-transfer type plasma heating device of the present invention.

FIG. 2 is a time chart showing details of control contents of a plasma control device in the non-transfer type plasma heating device of the present invention.

FIG. 3 is a conceptual diagram of a plasma control device in a conventional non-transfer type plasma heating device.

FIG. 4 is a time chart showing details of control contents of a plasma control device in a conventional non-transfer type plasma heating device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cathode 2 Anode 3 Load electrode 4a Lid 4b Heating container 5 Heating object 6a Torch elevating control device 6b Torch elevating device 7a Plasma ignition high frequency power supply 7b Plasma ignition switch 8a Plasma DC power supply 8b Plasma switch 9 Circuit characteristic judgment switch Reference Signs List 10 plasma arc 11 working gas 12 branch current 13 main current detector 14a plasma generation circuit voltage detector 14b plasma generation circuit current detector 14c impedance determination circuit

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[Procedure amendment]

[Submission date] October 2, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

Next, after the switch 9 is closed, the torch is gradually lowered by using the torch elevating device 6b as shown in FIG. 2A while holding the plasma arc at the tip of the torch. At this time, the impedance formed by the current path flowing from the plasma DC power supply 8a to the closed circuit of the switch 8b, the cathode 1, and the anode 2 is shown in the impedance determination circuit 14c between the positive and negative electrodes. When the tip of the plasma arc 10 gradually comes down and comes into contact with the object 5 to be heated, in addition to the above-described closed circuit, a new closed circuit of the switch 8b, the cathode 1, the load electrode 3, and the switch 9 is newly provided from the plasma DC power supply 8a. Is newly formed, and the branch current 12 flows, so that the impedance shown in the impedance determination circuit 14c decreases as shown in (b) of FIG. Since the decrease in impedance at this time becomes more remarkable as the contact state of the plasma arc 10 with the object 5 to be heated becomes denser,
It is possible to grasp as a electrical control signal to the plasma arc 10 the contact state of the heating object 5 by monitoring the value of the impedance.

Claims (2)

[Claims] In a non-transfer type plasma application device such as a plasma heating device or a plasma spraying device which generates a plasma flow between a cathode and an anode of a torch using a non-transfer type plasma torch, an object to be processed is A detector that provides a load electrode so as to be in contact with it, forms a circuit that connects the load electrode and the anode of the torch via a switch, and detects the voltage and current between the cathode and the anode in the circuit that generates the plasma flow To form an impedance judgment circuit that grasps and determines the change in impedance in the circuit based on the signal from the detector, activates the torch elevating control device based on the judgment result of the impedance judgment circuit, and appropriately controls the torch position A plasma control apparatus in a non-transition type plasma application apparatus, characterized in that: 2. A non-transition type plasma application device such as a plasma heating device or a plasma spraying device using a non-transition type plasma torch to generate a plasma flow between a cathode and an anode of the torch. A load electrode is provided so as to make contact, and a circuit for connecting the load electrode and the anode of the torch via a switch is formed, and a detector for detecting a current flowing from the cathode of the torch to the load electrode side is provided in the circuit. A torch lifting / lowering control device is operated based on a detection signal of a detector, so that a torch position is appropriately controlled.