JPH0151040B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a plasma torch having a relatively large current capacity and having a structure in which the outer periphery of a nozzle is mainly cooled with cooling water.

For torches with a large current capacity, it is essential to cool parts that are directly exposed to the arc, such as the electrodes and nozzles, so a direct cooling method is used that circulates cooling water to these parts. In this case, an indirect cooling type torch has a relatively simple structure and can be made smaller and lighter, but a direct cooling type torch has a more complicated structure and a larger torch diameter. In order to increase the current capacity of a torch by reducing its diameter without increasing it, in other words, to make it more compact and have a larger capacity, an important issue is how to efficiently cool the electrode and nozzle, which are easily overheated by arc heat. be.

When a plasma arc is generated from a plasma torch, the electrode side, which is usually made of tungsten material, continues to wear out over time, and the wear increases as the current increases. On the other hand, the inner wall of the nozzle made of copper or copper alloy is exposed to the arc, so when the current increases and reaches a certain limit, the nozzle instantly melts from the overheated nozzle hole. Lose. Furthermore, if double arcing is involved, there is a risk that the nozzle will further be eroded and damaged.

As mentioned above, the electrode wears out relatively slowly, but the nozzle melts away in an instant, and the generation of the plasma arc is interrupted, which has a great effect. Therefore, in order to increase the capacity of the current used and to manufacture the plasma torch, it is necessary to improve the cooling of the torch, with particular emphasis on preventing melting and damage to the nozzle. However, although conventional torches are configured to be cooled with cooling water up to the nozzle tip,
The above objective was not fully achieved due to insufficient circulation of the cooling water.

The prior art will be explained by citing specific examples. FIG. 1a shows a longitudinal sectional view of the tip of a known plasma welding torch with a direct cooling structure. 1
is a tungsten electrode fixed to the electrode holder 2,
3 is an annular nozzle attached to the tip of the inner jacket 12 via an insulator 5; 4 is a nozzle hole provided in the nozzle 3 so as to face the tungsten electrode 1; It is connected to a plasma gas passage 10 formed between them, and a plasma gas 11 flows out. 6 is nozzle 3
O-ring 13a,
Inner jacket 12 and screw 1 via 13b
It is concluded in 3c. Reference numeral 7 denotes a shield cap, in which a shield gas passage 8 is formed through which a shield gas 9 flows so as to surround the welded portions of the welded materials 19a and 19b and the plasma arc 18.
Reference numeral 14 denotes a cooling water passage provided in the inner jacket 12, and as shown in FIG. 1b, it is formed by a cooling water passage consisting of a large number of small holes circumferentially. 15a and 15b are annular cooling water passages connected to the cooling water passage, which are formed between the outer peripheral surface of the nozzle 3 and the nozzle cap 6 surrounding the outer periphery, and the cooling water 16a is connected to these cooling water passages. Passage 1
4, 15a and 15b,
The right half of the vertical section in the figure is the inlet side, and the left half is the outlet side. Further, the cooling water 16a that has flowed around the outer circumference of the nozzle 3 is further circulated within the electrode holder 2 as shown by the arrow, and then drained 16b, so that the tungsten electrode 1 side is also cooled at the same time. Although it is possible to cool the nozzle side and the electrode side with two independent systems of cooling water, in this example, in order to downsize the torch and simplify the cooling water cable, only one system of cooling water is used. . 20 is a tungsten electrode 1 and a material to be welded 19
A plasma arc 18 is generated by the power supply connected to a and 19b. The parts most likely to be overheated by the generation of the plasma arc 18 are the tip of the tungsten electrode 1 and the inner wall of the nozzle hole 4, and the latter must be cooled in particular to prevent the nozzle from melting.

However, because of this configuration, even if the cooling water 16a is supplied from the cooling water passage 14 of the inner jacket 12 to the annular cooling water passages 15a, 15b, most of the amount of cooling water is at the tip of the nozzle 3. The liquid did not reach the passage 15b near the nozzle hole 4, but instead simply short-circuited the passage 15a near the inner jacket 12 and flowed.

In order to investigate how cooling water actually flows through the tip of the torch, which is sealed with metal, a visualization torch was constructed and observed. FIG. 2 is an example showing the observation results of the flow at that time. As can be seen from the figure, the cooling water 16 supplied from the inner jacket 12 to the nozzle 3 does not reach the tip of the nozzle, which is most easily heated by arc heat.
The water flows through the conical surface at the top of the nozzle and causes a short circuit near the cooling water inlet and outlet paths of the inner jacket. Since the cooling water that flows to cool the nozzle tip ends up flowing out without being effectively utilized, the cooling effect of the nozzle cannot be sufficiently increased. In addition, when a plasma arc is generated in the torch and the arc current is increased to increase the load on the nozzle, cooling water locally boils near the nozzle hole at the tip of the nozzle, which is heated by the arc heat. Bubbles caused by boiling repeatedly grow and disappear at fairly rapid intervals. Moreover, in this case, boiling increases in proportion to the load, but the conventional torch described above has a structure that tends to cause short-circuit flow near the cooling water inlet and outlet passages of the inner jacket.
Due to the growth and expansion of bubbles due to boiling, the cooling water flowing through the nozzle increasingly does not reach the nozzle tip and instead flows only to the upper part of the nozzle. As a result, new cold cooling water is not supplied to the tip of the nozzle where air bubbles are generated, resulting in insufficient cooling and melting from the nozzle hole that is overheated to a high temperature.

The present invention was made in view of the problems with the flow of cooling water supplied to the tip of the torch, the boiling phenomenon, and the structure of the torch. The purpose of this project is to provide a plasma torch with improved cooling performance and increased current capacity by improving the cooling structure at the tip.

The plasma torch of the present invention has a structure in which cooling water is passed around the outer periphery of a nozzle that constricts a plasma arc in the nozzle hole, and is directly cooled by water, and includes an electrode, an electrode holder that fixes the electrode, and a An annular nozzle having a nozzle hole on an extended axis of the electrode holder and the electrode and also containing a cooling water passage, and a ring-shaped nozzle attached to the nozzle and having a hole for a cooling water inlet passage and a hole for an outlet passage passing through the annular nozzle. In a plasma torch comprising an inner jacket with both holes opening into the cooling water passage, the cooling water passage inside the nozzle has independent cooling water inlet pipes and cooling water on both sides of the nozzle hole. It consists of an outlet pipe, and an annular connecting pipe that connects the inlet pipe and the outlet pipe at the outer periphery of the nozzle hole, which is the leading edge of the torch, and is configured to flow cooling water to the leading edge of the nozzle. It is characterized by what it did. Furthermore, the inner wall of the passage through which the cooling water flows around the outer periphery of the nozzle is roughened to increase the effective cooling area of the nozzle. Bubbles are generated from the surface processing part due to boiling of cooling water.

Hereinafter, the present invention will be explained with reference to Examples. Third
The figure shows the flow of cooling water at the tip of the plasma torch of the present invention, and the same parts as in FIG. 2 are given the same reference numerals and the explanation will be omitted.

FIG. 4 shows an example of a torch cooling performance test, where line A shows the conventional torch and line B shows the cooling performance results of the torch of the present invention. The boiling start arc current on the vertical axis in the figure means that when a plasma arc is generated in the torch and the arc current is increased,
This shows the arc current value when cooling water starts to boil locally at the tip of the nozzle, which has been overheated by arc heat.
Normally, the plasma arc used in welding, cutting, etc. is generated between the electrode in the torch and the material to be welded or cut (called a transitional arc), but in this case, a high load is applied to the nozzle, so the electrode and nozzle A non-transfer type arc is used that generates an arc directly between the As can be seen from the figure, it was found that the torch of the present invention, which has an improved cooling structure at the tip of the torch, can achieve cooling performance that is more than twice that of the conventional torch.

Figure 5 is a diagram showing an embodiment of the torch tip of the present invention, where figure a is a longitudinal sectional view of the torch, and figure b is an A of figure A.
-A' line is a top sectional view, and Figure c is a lower front view of Figure A, and the same parts as in Figures 1a and 1b are given the same reference numerals, and their explanation will be omitted. The inner jacket 12 is provided with a cooling water inlet passage 14a and a cooling water outlet passage 14b on both sides of the insertion hole 10 through which the plasma gas 11 flows and into which the tungsten electrode 1 fixed to the electrode holder 2 is inserted. Further, a shielding gas passage 8a formed of ten or more small holes is provided around the shielding gas passage 8a. The nozzle 3 is connected to the tip of the inner jacket 12 via O-rings 13a and 13b that prevent plasma gas 11 and cooling water 16 from leaking.
are installed, each cooling water inlet/outlet passage 14
It is fixed with screws 23a and 23b so that a and 14b are aligned. A communication passage 15 connecting the cooling water inlet passage 14a and the cooling water outlet passage 14b is formed around the outer periphery of the nozzle hole 4 at the tip of the nozzle 3, as shown in FIG. The supplied cooling water 16 flows within the cooling water passage.

With such a configuration, the inner jacket 1
The cooling water 16 supplied from the nozzle 2 to the nozzle 3 flows around the outer periphery near the nozzle hole where it is exposed to the plasma arc and is most likely to be heated, so cooling is good and the nozzle can withstand high loads.

When a plasma arc is generated in the torch and the arc current is increased, the cooling water flowing through the torch begins to boil locally at the nozzle tip, which is superheated by the arc heat, and the bubbles due to the boiling become quite large. It repeats growth and extinction in rapid cycles. This phenomenon occurs not only on the nozzle side but also on the electrode side, but compared to a nozzle made of copper, which has excellent thermal conductivity, the cooling position of the electrode side made of tungsten material is also slightly farther from the heating point. , the rate at which boiling of the cooling water occurs is small.

In addition to visualizing the flow, we installed a water pressure detector in the path of the cooling water flowing through the torch and measured changes in water pressure at the inlet and outlet of the cooling water.As a result, we found that the water pressure fluctuated in synchronization with the boiling phenomenon of the cooling water that occurs within the torch. (Vibration also occurs) occurs, and the water pressure fluctuations rise rapidly when the bubbles expand and grow, and when the bubbles disappear, the water pressure drops sharply. From the waveform of water pressure fluctuations, it was found that when the load applied to the torch is constant, the range of water pressure fluctuations due to boiling is small, and the higher the frequency of water pressure fluctuations, the better the cooling performance of the torch.

Figure 6 shows how the torch is loaded using both a transitional arc (an arc is generated between the electrode in the torch and the workpiece) and a non-transitional arc (an arc is generated between the electrode and the nozzle). In addition, this is an example of investigating cooling performance from water pressure fluctuations due to boiling of cooling water, and is the relationship between plasma arc current and water pressure fluctuation characteristics due to boiling. The symbols ○ and ● indicate the conventional torch, and the symbols □ and ■ indicate the improved large-capacity torch of the present invention. When the plasma arc current is increased, the cooling water boils violently, and accordingly, the water pressure fluctuation ΔP (lower diagram) increases and the water pressure fluctuation frequency f (upper diagram) decreases. With conventional torches, boiling tends to occur at low currents, and ΔP
is large and f is small. On the other hand, in the case of the improved large-capacity torch of the present invention, the cooling of the torch is improved, the boiling region of the cooling water moves to the high current side, and the water pressure fluctuation range ΔP due to boiling of the cooling water is small and the water pressure fluctuation frequency f It turns out that is large. In the case of a transition type arc, the boiling region moves further toward the higher current side, but the rate of increase in ΔP is higher than in a non-transition type arc. This is thought to be because the high temperature region of the arc expands as the arc current increases, and the inner wall of the nozzle is likely to be significantly heated, resulting in a high load being applied to the nozzle.

In the case of a transitional arc, when the arc current value exceeded 500A in the conventional torch, melting damage was observed in a part of the nozzle, but with the torch of the present invention, it was possible to maintain the arc even at around 700A. Increasing the nozzle hole diameter eases the load on the nozzle, which reduces boiling of the cooling water, reduces the water pressure fluctuation width ΔP, and allows the nozzle to withstand high current arcs. It was also found that sealing materials such as O-rings used to prevent water leakage were installed away from the tip of the torch, which is likely to be heated by arc heat, so they would not burn out. Boiling of cooling water increases cooling efficiency due to latent heat, but in this case, it is more effective to generate a large number of small bubbles than to expand and grow large bubbles, and furthermore, after generation, these bubbles can be quickly removed. At the same time as draining the water, supplying cold, new cooling water to the affected area improves cooling efficiency.

FIGS. 7a and 7b show an example of the present invention in which this is implemented, and is a nozzle in which a roughening process is previously formed on the inner wall of the passage through which cooling water flows. For example, the above-mentioned surface roughening can easily be done by forming an uneven surface using a machine tool or the like and joining the nozzle to a predetermined shape.

By roughening the area to be cooled, even if the torch generates a high-current plasma arc, many small-diameter bubbles will be generated from the roughened area and the bubbles will disappear. However, since it is quickly discharged, cooling efficiency can be improved.

As explained above, according to the torch of the present invention, the cooling performance is improved by improving the cooling structure of the torch tip without increasing the outer diameter of the torch, and the current capacity of the torch is increased. be able to. In addition, by roughening the inner wall of the passage through which cooling water flows around the outer periphery of the nozzle, a large number of small-diameter bubbles are generated from this roughened surface, improving cooling efficiency. It was written. Additionally, since the nozzle with cooling holes can be made separately from the torch body, assembly is simplified, and essentially no nozzle cap is required. Furthermore, by installing sealing materials such as O-rings used to prevent water leakage away from the leading edge of the torch, which is easily heated by arc heat, they can be burned out even when a high-current plasma arc is generated. Since there is no fear that the arc will be interrupted, there is no need to worry about the interruption of arc generation, and it can also contribute to improving the work efficiency of welding or cutting using plasma arc.

[Brief explanation of drawings]

FIG. 1a is a longitudinal cross-sectional view of a known plasma welding torch, FIG. 1b is a cross-sectional view of the inner jacket shown in FIG. FIG. 3 is a diagram illustrating a plasma torch according to an embodiment of the present invention, and FIG. 3 is a longitudinal cross-sectional view of the torch, and FIGS. A top sectional view and a lower front view along line A', Figure 4 is a diagram showing an example of testing the cooling performance of the torch, and Figure 5 is the cooling water supplied to the nozzle of the torch in Figure 3. Figure 6 is a diagram showing the results of a cooling performance test using a conventional torch and the torch of the present invention, and Figures 7a and b show other embodiments of the present invention. It is a diagram. 1...Tungsten electrode, 3...Nozzle, 4...
... Nozzle hole, 6 ... Nozzle cap, 12 ... Inner jacket, 13a, 13b ... O-ring, 14a ... Cooling water inlet path, 14b ... Cooling water outlet path, 15a, 15b ... Cooling water passage, 16...
...Cooling water, 18...Plasma arc, 19a, 1
9b... Material to be welded, 23... Screw, 23a... Screw hole, 25... Rough surface processing part.

Claims (1)

[Claims] 1. A structure in which cooling water is passed through a nozzle that constricts the plasma arc at the nozzle hole to directly cool the plasma arc,
an electrode, an electrode holder for fixing the electrode; an annular nozzle that covers the electrode and has a nozzle hole on an extension axis of the electrode holder and the electrode; and a cooling water passage attached to the nozzle; In a plasma torch comprising an inner jacket through which a hole for a water inlet passage and a hole for an outlet passage pass through and both holes open to the cooling water passage, the cooling water passage is arranged inside the annular nozzle. The cooling water passage in the annular nozzle has an independent cooling water inlet pipe and a cooling water outlet pipe on both sides of the nozzle hole, and the inlet pipe and the outlet pipe are connected to the tip of the torch. 1. A plasma torch characterized by comprising an annular connecting pipe connected around the outer periphery near a nozzle hole, which is a part of the plasma torch, and configured to flow cooling water to the leading edge of the nozzle. 2. The inner wall of the connecting pipe through which the cooling water flows around the outside of the nozzle is roughened to increase the effective cooling area of the nozzle, and when the nozzle is heated by the plasma arc, 2. The plasma torch according to claim 1, wherein bubbles are generated from the roughened surface by boiling of cooling water.