JPH064195B2 - Electrode breakdown detection method and detection device in plasma cutting / welding - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and apparatus for automatically detecting breakage of electrodes and nozzles for plasma cutting / welding.

(Prior Art) Electrodes and nozzles in plasma cutting or welding are not permanent and are consumed by arc heat. In order to increase the consumption speed of the electrodes and the like, or to improve the plasma arc concentration, the cooling efficiency of the electrodes of the torch and the like are improved to improve work efficiency.
It is a situation where it is not known when electrode destruction will occur.

Therefore, place a visual supervisor on site to replace the electrode by judging the occurrence of defective work efficiency, or replace it in advance when a certain time has elapsed based on past data, or repeat electrode destruction several times. Then, the electrode was replaced by a series arc generated between the nozzle and the material.

However, if you continue to work without noticing these situations, not only the consumable parts such as the electrodes will be damaged, but also the damage of the torch body will spread and it will cause a big accident. Is worse, the defect rate increases, and it is difficult to automate, so
The establishment of this detection method has been desired.

(Problems to be Solved by the Invention) The present invention provides a detection means for solving these needs, and detects an initial signal of electrode destruction and uses the signal as an abnormality occurrence signal to generate an alarm or an abnormal lamp. The present invention provides an electrode breakdown detection method and a detection device therefor capable of protecting the plasma torch and preventing the occurrence of defective products by performing an emergency stop or the like by issuing a signal or a signal. .

(Means for Solving the Problems) In the present invention, in plasma cutting or plasma welding, either the plasma arc voltage value or the plasma arc current value is constantly detected, and when the detected value fluctuates more than a certain reference value, An electrode breakage detection method and a detection device therefor, characterized in that an automatic control device for judging an electrode breakage notifies an observer by an alarm, a warning light, or the like, or stops the work automatically by the signal.

It is well known that cutting is more prone to electrode breakage than welding, and in order to extend the life of the electrode, in the case of oxygen cutting, zirconium or hafnium is buried in the center of the electrode. I'm using it. However, even under normal conditions, if an arc is generated for about 1 hour, the electrodes will be destroyed. The destruction phenomenon is that the concentration of the cutting arc is deteriorated, the cutting ability is deteriorated, the cutting surface is defective or the cutting becomes impossible, and as a result, the embedded hafnium is consumed and then the electrode is removed. The copper alloy of the main body also starts to wear out and the arc spreads, and along with the wear of the electrode, the wear of the nozzle or the dust of the electrode part adheres to the nozzle to generate a series arc, and not only the nozzle but also the torch It will damage the body.

As a result of investigating how this electrode destruction changes electrically, as shown in the principle of plasma cutting in Fig. 1, a pilot arc is generated between the electrode and the nozzle, and when cutting, the electrode is cut between the electrode and the material. An arc is generated and plasma is generated by the gas flow.
As shown in Fig. I, it was confirmed that the arc voltage (or the same applies to the arc current) drastically changed. A detector that determines this as an electrode breakdown signal based on this change may detect the voltage change between the electrode and the material, but it is also possible to detect the change between other electrodes and the material or between the electrode and the nozzle. It is possible to detect not only the arc current but also the arc current.

Referring to the apparatus shown in FIG. 1, 1 is a material to be cut, 2 is a plasma cutting nozzle, 3 is an electrode,
A cutting power supply 2 is provided between the electrode 3 and the electrode 3, and a pilot power supply 5 is provided between the electrode 3 and the nozzle 2. In the present invention, in such a plasma cutting equipment, the plasma arc voltage during cutting is always detected, and the electrode breakage is detected based on this. That is, a filter circuit 6 that outputs only a predetermined frequency component, a rectification integration circuit 7 that rectifies and integrates the output from the filter circuit 6, and an output value from the integration circuit 7 are preset in the plasma cutting equipment. An electrode breakage detection block composed of a level judgment circuit 8 for judging whether or not the electrode has broken down by comparing it with a predetermined reference value is connected.

Explaining the electrode breakage determination operation, the filter circuit 6 cuts the noise-like waveform from the abrupt voltage fluctuation caused by the electrode breakage occurring in FIG. 2I, and the waveform shown in FIG. II is output. Rectification and integration by circuit 7, Fig. 2
In the level judgment circuit 8 shown in III, a signal having a level larger than a certain level value is outputted as an output signal, and this is outputted as an electrode destruction signal to a relay to give an abnormal light or alarm or automatically stop the cutting work. .

(Example) As an example of the present invention, the description will be made based on the oxygen plasma cutting shown in FIG. 1. The arc voltage in the steady state during cutting is 140V, and the voltage fluctuation due to the anodic behavior is about 10V.
At V, the frequency is approximately 300 Hz and approximately constant. Here, the electrode gradually wears out as the arc time elapses, and there is a moment when the arc time is largely damaged in an instant in about 1 hour. The arc voltage at this time fluctuates greatly, and the frequency is about 70 to 150 V and the frequency is about 30 to 80 Hz. By inputting this fluctuating voltage to the filter circuit 6, only the AC component signal of the fluctuating voltage is output ( Fig. 2 II). This signal is rectified and processed by the integrating circuit 7, and a voltage that is approximately proportional to the duration of the signal is output. This voltage is compared with a preset voltage input in advance by the level judgment circuit 8, and when the preset voltage is exceeded,
By determining that the electrode breakage is abnormal and outputting this signal as an electrode breakage signal to generate an alarm signal, the electrodes can be replaced and the number of defective products can be reduced.

(Effects of the Invention) By carrying out the detection method of the present invention, it is possible to effectively use the electrodes to the maximum, prevent damage to the torch body, and prevent the occurrence of defective products, and it is easy to automate. Is. Further, the apparatus of the present invention can effectively carry out the above method.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining an example of the detection device according to the present invention, and FIGS. 2I to IV are graphs of respective output values corresponding to FIG. 1 ... Material to be cut, 2 ... Plasma cutting nozzle, 3 ... Electrode,
4, 5 ... Power source, 6 ... Filter circuit, 7 ... Rectification product circuit,
8 ... Level determination circuit.

Claims (2)

[Claims] 1. A method for detecting electrode breakage, characterized in that in plasma cutting or welding, either a plasma arc voltage value or a plasma arc current value is constantly detected, and if the fluctuation exceeds a certain reference value, it is judged as electrode breakage. . 2. Plasma cutting or welding equipment,
A filter circuit for inputting either a plasma arc voltage value or a plasma arc current value, a rectifying and integrating circuit for rectifying and integrating a signal passed through the filter circuit, and a reference value preset for the integrated detection value. An electrode breakage detection device characterized in that a level determination circuit that sequentially outputs a fault occurrence signal when compared with a reference value and has a larger variation is provided.