JPH02217165A - Plasma arc cutting machine - Google Patents

Abstract

PURPOSE:To prevent the breakdown of a chip of the plasma arc cutting machine by comparing the voltage of both ends of a pilot arc limiting resistance with the set voltage by a comparator and controlling the output of a DC power source by the output of the comparator. CONSTITUTION:One end of the pilot arc limiting resistance 2 is connected with the plus side of the DC power source 1 capable of controlling the output. In addition, the other end thereof is connected with the chip C of a cutting torch to constitute a pilot arc circuit. The voltage of both ends of the pilot arc limiting resistance 2 is compared with the set voltage by the comparator 5. The output of the DC power source 1 is controlled by the output of the comparator 5. By this method, when the interval between an electrode and the chip of the cutting torch is short-circuited, the comparator immediately functions and the DC power source is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a plasma arc cutting machine equipped with a pilot arc circuit, and particularly to a short circuit between a torch tip incorporated in the pilot arc circuit and a cutting torch. This article relates to a plasma arc cutting machine that takes measures to prevent damage to cutting torches when this occurs.

[Conventional technology]

・In general, plasma arc cutting machines with a pilot arc circuit perform so-called non-contact cutting, which cuts without making contact between the cutting torch and the base material.
As shown in the figure, the base material (M) is connected to the positive side of a DC power source (1) whose output can be controlled, and the electrode (E) of the cutting torch is connected to the negative side via a smoothing reactor (3). In this circuit, one end of a pilot arc limiting resistor (2) is connected to the positive side of the DC power source (1), and the other end of this resistor (2) is connected to the electrode (E) of the cutting torch.
and the tip of the cutting torch (C) interposed between the base material (M) and the base material (M).
It is constructed by interposing a pilot arc circuit connected to the In this case, first, when starting the arc, a small current is passed between the cutting torch electrode (E) and the cutting torch tip (C) using the DC power supply (1) to generate a pilot arc, and this pilot arc strikes the base metal (M). When touched, a main current flows between the cutting torch electrode (E) and the base 4'A' (M), generating an arc.

[Problem to be solved by the invention]

However, according to the conventional example of structural acid, when the electrode (E) of the cutting torch wears out and the surface peels off, there may be a short circuit between the electrode (E) and the tip (C). If a short circuit were to occur between (E) and (C), the main current that should generate an arc would flow between the electrode (E) and the chip (C), potentially damaging the chip (C).

The present invention was made to solve these conventional problems, and when a short circuit occurs between the electrode and the tip of the cutting torch, the DC power supply is immediately stopped to stop the output between the electrode and the tip. The purpose is to prevent damage to the chip.

[Means to solve the problem]

In order to achieve such an object, the present invention connects one end of a pilot arc limiting resistor to the positive side of a DC power supply whose output can be controlled, and connects the other end to the tip of a cutting torch to form a pilot arc circuit. On the other hand, the present invention is characterized in that a comparator is provided to compare the voltage across the pilot arc limiting resistor with a set voltage, and the output of the DC power source is controlled by the output of this comparator.

[For production]

In the above configuration, the voltage value should be set so that when a short circuit occurs between the electrode of the cutting torch and the tip for generating the pilot arc, the set voltage is higher than the voltage value across the pilot arc limiting resistor. Therefore, when there is a short circuit between the electrode and the tip of the cutting torch, the comparator can immediately operate to stop the DC power supply, thereby reliably preventing damage to the tip.

For example, if the set voltage is set to be equal to the DC power supply voltage, if the electrode of the cutting torch and the tip are short-circuited, the voltage across the pilot arc limiting resistor will become equal to the DC power supply voltage and exceed the set voltage. The comparator operates and stops the DC power supply.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows the overall configuration of a plasma arc cutting machine according to this embodiment. In this figure, (1) is a DC power supply that can control the output, (2) is a pilot arc limiting resistor,
(3) is the smoothing reactor, (E) is the cutting torch electrode, (
M) is the base material, (C) is the electrode of the cutting torch (E) and the base material (
M) is the tip of the cutting torch interposed between them, and the configuration thereof is basically the same as that shown in FIG. A pilot arc circuit is interposed in a circuit in which the electrode (E) of the cutting torch is connected to the negative side via the smoothing reactor (3).

This pilot arc circuit connects one end of a pilot arc limiting resistor (2) to the positive side of a DC power supply (1), and connects the other end of this resistor (2) to the tip of a cutting torch (
When starting the arc, a small current is passed between the cutting torch electrode (E) and the cutting torch tip (C) using the DC power supply (+) to generate a pilot arc. By touching the base material (M), a main current flows between the cutting torch electrode (E) and the base material (M), generating an arc.

In addition, (4) is a power supply for setting the setting voltage VRLF, (5)
is the voltage VR across the pilot arc limiting resistor (2)
and set voltage VREFl! : A comparator that compares
The output of the DC power source (1) is controlled by the output. In Fig. 1, E is the DC power supply voltage, VA is the mold pressure between the cutting torch's electrode (E) and the base material (M), and Vp is the mold pressure between the cutting torch's electrode (E) and the tip (C). be.

In the above configuration, the electrode (E) of the cutting torch and the tip (
C) When a pilot arc is generated between
It becomes p. Here, the set voltage power supply (4) chisel pressure VR
If EF is set to E - Vp < Vr < EF < E, when a pilot arc occurs, the voltage across the pilot arc limiting resistor (2) VR - V HL! ,to
Therefore, the comparator (5) does not operate because it is lower than the set voltage VR1, I7.

Next, when the electrode (E) of the cutting torch and the tip (C) are short-circuited, the mold pressure between the electrode (E) and the tip (C) is V.
Since p=O, pilot arc limit −6=voltage across resistor (2) V b =E, which becomes equal to DC power supply voltage E. Therefore, the voltage across the pilot arc limiting resistor (2) becomes V+<>VREF, which exceeds the set voltage V REF, so the comparator (5) operates to stop the DC power supply (1), and as a result, This prevents the tip (C) of the cutting torch from being damaged.

〔Effect of the invention〕

As explained above, when using the plasma arc cutting machine of the present invention, the - end of the pilot arc limiting resistor is connected to the positive side of the DC power supply whose output can be controlled, and the other end is connected to the tip of the cutting torch. Constructing an arc circuit - On the other hand, a comparator was provided to compare the voltage across the pilot arc limiting resistor with a set voltage, and the output of the DC power supply was controlled by the output of this comparator, so the cutting torch When a short circuit occurs between the electrode of the cutting torch and the tip for generating the pilot arc, by setting the set voltage value to be higher than the voltage value across the pilot arc limiting resistor, the cutting torch When a short circuit occurs between the electrode and the chip, the comparator immediately operates to stop the DC power supply, thereby reliably preventing damage to the chip.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of a plasma arc cutting machine showing an embodiment of the present invention, and FIG. 2 is an overall configuration diagram of a conventional plasma arc cutting machine. (+)...DC power supply, (2)...Pilot arc limiting resistance, (5)...Comparator, (C)...Cutting torch tip, VR...Both ends of pilot arc limiting resistance Voltage, ■ - Setting voltage.

Claims (1)

[Claims] A pilot arc circuit is constructed by connecting one end of a pilot arc limiting resistor to the positive side of a DC power supply whose output can be controlled, and connecting the other end to the tip of a cutting torch.
A plasma arc cutting machine characterized in that a comparator is provided to compare the voltage across the pilot arc limiting resistor with a set voltage, and the output of the DC power source is controlled by the output of the comparator.