JP2563832B2 - Electrode breakdown detection method and device in plasma torch and plasma torch - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and an apparatus for detecting electrode breakdown in a plasma torch used for welding or cutting, and a plasma torch.

<Prior Art> Today, a workpiece such as steel or stainless steel is welded or cut by a plasma arc.

The electrode in the plasma torch for generating the plasma arc cannot be used permanently and is consumed depending on the time of use. When the electrode is consumed, a phenomenon called a so-called double arc or a series arc occurs in which an arc is generated from the electrode through the tip, in addition to the main arc generated between the electrode and the workpiece.

If the state of the double arc continues, the electrode and the tip become extremely hot, and these may be melted and, in some cases, the torch itself may be melted and destroyed.

For this reason, it is desirable to detect the consumption of the electrode in advance and replace the electrode. Generally, the usage time of the electrode is empirically determined, and the electrode is replaced by managing the usage time.

Further, a technique for automatically detecting the breakage of electrodes has been proposed (Japanese Patent Laid-Open Nos. 61-269975 and 62-267087).
These techniques constantly detect the plasma arc voltage or the plasma arc current, and detect that the electrode is broken when the detected value fluctuates more than the reference value.

<Problems to be Solved by the Invention> However, in each of the above techniques, the control circuit for detecting the electrode breakage is complicated and expensive.

An object of the present invention is to provide a detection method that can easily detect electrode breakage in a plasma torch, and an inexpensive detection device.

<Means for Solving the Problems> In order to solve the above problems, an electrode breakdown detection method in a plasma torch according to the present invention detects a return pressure of a cooling fluid for cooling an electrode from the inside, and the return pressure is detected. It is characterized by recognizing that the electrode has been destroyed when is lower than the reference pressure.

Further, the detection device includes a plasma torch having a cooling fluid passage for cooling the inside of the electrode and the inside of the torch, detection means for detecting the return pressure of the cooling fluid, and the return pressure is lower than the reference pressure. And a signal generating means for generating a signal from time to time.

Further, the plasma torch is a plasma torch having a cooling fluid passage for cooling the inside of the electrode, and a pressure for detecting the pressure of the cooling fluid flowing through the passage in the cooling fluid passage on the downstream side of the electrode. It is configured by providing a detection hole.

<Operation> In the above detection method, when the return pressure of the cooling fluid flowing inside the electrode for cooling the electrode, that is, the pressure of the cooling fluid on the downstream side of the electrode is detected, the electrode is destroyed. If not, the return pressure is always a constant value if the supply pressure of the cooling fluid is constant. When the electrode is consumed and a double arc is generated to melt and destroy the electrode, the cooling fluid flows out from the melted portion, and the return pressure is reduced.

Therefore, an unbroken electrode was attached to the plasma torch, the return pressure of the cooling fluid at this time was set as the reference pressure, and the return pressure during work was detected, and this detected pressure fell below the reference pressure. It can sometimes be recognized as electrode breakdown.

Further, the detection device, a plasma torch formed with a cooling fluid passage for cooling the inside of the electrode and the inside of the torch,
Detecting means for detecting the return pressure of the cooling fluid,
The return pressure of the cooling fluid for cooling the inside of the electrode and the torch is detected because the return pressure is lower than the reference pressure. When it also drops, a signal is generated, and it is possible to detect that the electrode is destroyed by the signal.

Therefore, if the power supply of the plasma generator is controlled by the signal, for example, the plasma arc can be stopped when the electrode is broken.

Further, in the plasma torch, a pressure detection hole for detecting the pressure of the cooling fluid flowing through the passage is provided in the cooling fluid passage on the downstream side of the electrode cooled by the cooling fluid. The return pressure of the cooling fluid can be detected by connecting with the return pressure detecting means.

<Example> An example of the plasma generator to which the above means is applied will be described below with reference to the drawings.

FIG. 1 is a sectional explanatory view of a plasma torch, FIG. 2 is an explanatory view of electrode breakage detection, and FIG. 3 is a block diagram of a plasma generator.

First, the structure of the plasma torch A will be described with reference to FIG. 1. At a predetermined position on the axis of the plasma torch A, an electrode 1 is detachably attached to an electrode base 2. Inside the electrode 1, a hole 1a for allowing a cooling fluid to flow to cool the electrode 1 is formed.

A conduit 2a is provided at an end of the electrode base 2, and a cooling fluid is supplied from a cooling fluid supply unit 9 provided outside the plasma torch A. Further, inside the electrode base 2, there is provided an internal tube 2b having a protrusion whose tip is approximately equal to the depth of the hole 1a formed in the electrode 1. Two groups 2c and 2d are formed at predetermined positions on the outer circumference of the electrode base 2. The groove 2c is connected to the plasma gas ejection hole 7 formed by the outer peripheral surface of the electrode 1 and the inner peripheral surface of the chip 5 described later by the slit 2e, and the groove 2d is a through hole.
It is connected to the inside of the electrode base 2 by 2f.

An insulating collar 3 is fitted on the outer periphery of the electrode base 2. Through holes 3a, 3b are formed in the insulating collar 3 at positions facing the two grooves 2c, 2d formed on the electrode base 2.

A chip base 4 is fitted on the outer periphery of the insulating collar 3. A tip 5 having a nozzle 5a is detachably attached to the tip of the tip base 4. A cap 6 is detachably attached to the chip base 4.

The chip base 4 has a through hole 4a for plasma gas and a through hole 4b for cooling fluid. The through hole 4a is a conduit 4c
It is connected to the plasma gas supply unit 15 via. The through hole 4b has one end connected to the cooling fluid ejection hole 8 formed by the tip 5 and the cap 6, and the other end connected to the conduit 4d.
It is connected to the return pressure detection unit 10 via.

On the inner peripheral surface of the chip base 4, two grooves 4e and 4f facing the two grooves 2c and 2d formed on the electrode base 2 are formed.
Has been drilled.

In this embodiment, pressurized air is used as the cooling fluid. As the plasma gas, oxygen gas, nitrogen gas, air, or the like is selectively used depending on the type of work material or work content.

In the plasma torch A configured as described above, the cooling air adjusted to a predetermined pressure is supplied to the electrode base 2 via the conduit 2a.
Is supplied to. Then, it is supplied to the electrode 1 through the inner tube 2b to cool the electrode 1. After that, it passes through the inside of the electrode base 2 along the outer circumference of the inner tube 2b, passes from the through hole 2f to the grooves 2d and 4f, and reaches the through hole 4b. Further, the chips 5 and the cap 6 are cooled through the ejection holes 8 formed by the chips 5 and the caps 6 and ejected to the outside of the plasma torch A. At this time, the pressure of the cooling air in the through hole 4b is guided to the return pressure detection unit 10 via the conduit 4d serving as a pressure detection hole and detected.

As mentioned above, the return pressure detected via conduit 4d is
The pressure drop of the cooling air in the electrode base 2, the electrode 1, and the insulating collar 3 from the conduit 2a is detected. Therefore, although the return pressure has individuality due to each plasma torch A, if the supply pressure of the cooling air is constant, a constant pressure corresponding to the supply pressure is detected.

Next, the electrode 1 of the plasma torch A configured as described above
The destruction detection method and device will be described.

It is well known that, in the plasma torch A, when a plasma arc is generated between the electrode 1 and the material to be processed, the electrode 1 is consumed according to the working time (arc time). When the consumed electrode 1 is used, the electrode 1
It is well known that there is a so-called double arc phenomenon in which an arc is generated between the electrode 1 and the material to be processed via the tip 5 in addition to the main arc generated between the material to be processed and the material to be processed.

When the double arc phenomenon occurs, the temperature of the electrode 1 and the tip 5 rapidly rises and melts, and in the worst case, the electrode base 2 and the chip base 4 melt and the plasma torch A becomes unusable. .

The electrode breakage detection method of the present invention pays attention to the fact that, when the electrode 1 is melted and broken, the electrode 1 is formed with a through hole reaching the internal hole 1a at the melted portion.

That is, when the electrode 1 melts, a through hole is formed between the electrode 1 and the hole 1a formed inside the electrode 1, and the cooling air flows out through the through hole, so that the conduit 2a passes through the electrode base. 2, the flow rate in the cooling air passage formed in the electrode 1 and the insulating collar 3 changes, so that the return pressure detected via the conduit 4d drops sharply and significantly.

Therefore, by detecting this return pressure, the electrode 1
It is possible to detect the destruction of the.

FIG. 2 is a schematic explanatory view for detecting electrode breakage by the above method using the plasma torch A.

In the figure, the supply pressure P ₁ of the cooling air supplied to the plasma torch A is adjusted to a predetermined pressure in the cooling air supply unit 9 and supplied. Further, the return pressure P ₂ is supplied to the return pressure detecting unit 10 which serves as a return pressure detecting means and a signal generating means. The return pressure detection unit 10 is composed of a known pressure switch set to a reference pressure described later. Therefore, the return pressure P ₂
Is acting, and an electric signal is generated when the return pressure P ₂ becomes equal to or lower than the reference pressure.

Table 1 shows the measurement results of the return pressure P ₂ corresponding to the supply pressure P ₁ when a new electrode, a slightly broken electrode, and a severely broken electrode were attached to the plasma torch A. Show.

As is clear from Table 1 above, when the supply pressure P ₁ of the cooling air is kept constant, the detected return pressure P ₂ is 0.7 kg / cm ² or more for the unbroken electrode and the destroyed electrode. There is a pressure drop.

Therefore, attach a new electrode to the plasma torch A,
The return pressure P ₂ at this time is detected, and the detected pressure or a pressure slightly lower than the detected pressure in anticipation of a safe value is set as a reference pressure, and the return of the cooling air is continuously performed during the work by the plasma torch A. When the pressure is detected and the pressure drops below the reference pressure, it can be recognized that the electrode has broken.

That is, as described above, the return pressure P ₂ from the plasma torch A is introduced by introducing the return pressure P ₂ into the pressure switch 10 serving as the return pressure detecting means and setting the set pressure of the pressure switch 10 to the reference pressure. ₂ can always be detected, and an electric signal can be generated when the return pressure P ₂ becomes lower than the reference pressure.

Therefore, if the plasma generator is configured to be able to stop the power supply in response to the generation of the electric signal, it is possible to stop the plasma generator at the same time as detecting the electrode breakage, and thus to prevent the plasma torch from being broken. Progress is stopped.

Thus, in the present invention, the return pressure P _{2 of the} cooling fluid is
It is possible to detect the destruction of the electrode by detecting the detected pressure and comparing the detected pressure with the reference pressure, and in order to detect the return pressure P ₂ and compare it with the reference pressure, a known pressure switch is used. Since it can be used, electrode breakage can be easily detected by an inexpensive device as compared with the conventional method of detecting electrode breakage by measuring arc voltage or arc current.

Next, a plasma generator to which the electrode breakage detection device configured as described above is applied will be described with reference to FIG.

In the figure, the DC power supply section 12 driven by the driver circuit 11, the electrode 1, the chip 5, and the workpiece B are electrically connected to each other. The driver circuit 11 is controlled by the control unit 13. An operation start signal is generated by operating the switch 14, and the driver circuit 11, the plasma gas supply unit 15, and the cooling fluid supply unit 9 are respectively controlled by the control unit 13 by this signal so that a predetermined operation can be performed. It is configured.

That is, the electromagnetic valve forming the cooling fluid supply unit 9 is opened by the operation start signal, and the cooling fluid is supplied to the plasma torch A.
And the electromagnetic valve constituting the plasma gas supply unit 15 is opened to supply the plasma gas such as oxygen gas, nitrogen gas, and air to the torch A. Further, the operation power source is supplied to the pressure switch constituting the pressure detecting means 10 to start detecting the return pressure P ₂ of the cooling fluid from the plasma torch A.
Further, the DC power supply unit 12 is driven through the driver circuit 11 and a predetermined voltage is applied to the electrode 1, the chip 5, and the workpiece B to generate a plasma arc. Then, by scanning the plasma torch A on the workpiece B, a predetermined work can be performed.

When the electrode 1 is consumed and the electrode 1 is melted and melted during the predetermined work performed on the workpiece B by the plasma torch A, the return pressure P ₂ is rapidly reduced. The reduced return pressure P ₂ is detected by the pressure switch 10, and when the pressure falls below a preset reference pressure, an electric signal is generated in the pressure switch 10.

As described above, the electric signal is a signal that the destruction of the electrode 1 is detected. This electric signal is transmitted to the control unit 13, and the control unit 13 controls the cooling fluid supply unit 9, the plasma gas supply unit 15, and the driver circuit 11 so as to stop the supply of the cooling fluid and the plasma gas, and the plasma. Stop the arc.

In this way, the return pressure of the cooling fluid for cooling the electrode 1 is detected, the detected pressure is compared with the reference pressure, and the plasma arc is controlled by the signal generated when the detected pressure becomes lower than the reference pressure. If so configured, the electrode 1
It is possible to stop the plasma arc at the time when the breakage of the electrode 1 is detected, and therefore the breakage of the electrode 1 does not proceed.

In addition, in the above-described embodiment, the case where the pressurized air is used as the cooling fluid has been described, but the cooling fluid is not limited to the air, and a cooling liquid such as pressurized water may be used. Is. When pressurized water is used, it is necessary to close the ejection hole 8 formed by the tip 5 and the cap 6 so that the pressurized water can circulate in the plasma torch.

<Effects of the Invention> As described in detail above, according to the electrode breakage detection method of the present invention, by detecting the return pressure of the cooling fluid for cooling the electrode, the breakage of the electrode can be easily detected. You can

Further, the electrode breakage detection device of the present invention is composed of the detection means for detecting the return pressure and the signal generation means for generating a signal when the return pressure is lower than the reference pressure.
The return pressure of the cooling fluid can be detected and compared with a reference pressure, and an electrical signal can be generated when the return pressure falls below the reference pressure. Therefore, when the electric signal is connected to the control unit of the plasma generator, it is possible to stop the plasma generator in response to the generation of the electric signal, and thus the plasma torch is not destroyed. .

Further, the plasma torch of the present invention has a feature that the return pressure of the cooling fluid for cooling the electrode can be guided to the pressure detecting means.

[Brief description of drawings]

FIG. 1 is a sectional explanatory view of a plasma torch, FIG. 2 is an explanatory view of electrode breakage detection, and FIG. 3 is a block diagram of a plasma generator. A is a plasma torch, B is a work material, 1 is an electrode, 2 is an electrode stand, 2a is a conduit, 3 is an insulating collar, 4 is a tip stand, 5 is a tip, 6 is a cap, 9 is a cooling fluid supply part, 10 Is a pressure switch, 11 is a driver circuit, 12 is a DC power supply unit, 13 is a control unit, 14 is a switch, and 15 is a plasma gas supply unit.

Claims (3)

(57) [Claims] 1. A plasma characterized by detecting a return pressure of a cooling fluid for cooling an electrode from the inside, and recognizing that the electrode is broken when the return pressure is lower than a reference pressure. Electrode breakdown detection method in torch. 2. A plasma torch having a cooling fluid passage for cooling the inside of the electrode and the inside of the torch, a detecting means for detecting the return pressure of the cooling fluid, and the return pressure lower than a reference pressure. An electrode breakage detection device in a plasma torch, characterized in that it has a signal generating means for occasionally generating a signal. 3. A plasma torch having a cooling fluid passage for cooling the inside of an electrode, the pressure detection for detecting a pressure of a cooling fluid flowing through the passage in a cooling fluid passage downstream of the electrode. A plasma torch featuring holes.