JPH01306076A - Plasma torch with magnetic field generator - Google Patents

Abstract

PURPOSE:To improve durability of the title plasma torch and to perform plasma machining with high accuracy by providing a magnetic field generator to the plasma torch and providing a magnetic field with maximum magnetic field intensity on the central axis in the vicinity of the cathode surface of the plasma torch. CONSTITUTION:Magnets 5 are permanent magnets having almost box-shaped cross sections and annular external shapes and these are fixed on the periphery of a cathode holder 6 which comes into contact with the periphery of the cathode 1 and holds this cathode. The magnets 5 are fixed so that the ring center and the degree of parallelism thereof are made to almost the same as the axial center 4B of a plasma arc column 4A. By this method, the electrode service life increases and at the same time, plasma machining with high accuracy can be performed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a plasma torch equipped with a magnetic field generator for a plasma processing machine, and in particular to a plasma torch with improved durability and for high-precision plasma processing. Concerning a preferred plasma torch.

(Prior Art) A plasma torch of a conventional plasma processing machine will be described below with reference to a schematic cross-sectional view (FIG. 4) of a typical plasma torch of this type. First, the configuration of the plasma torch will be explained based on FIG. This is broadly divided into an electrode 1 and a nozzle 3. The electrode 1 is connected to the wiring IA from the DC high-frequency circuit, and includes a holder IB made of a copper material such as Cu, which has high thermal conductivity and is a conductor, and hafnium Hf embedded in the center of the tip of the holder IB on the discharge space side.
It is composed of a cathode IC member such as zirconium Z or tungsten W. On the other hand, the nozzle 3 is a structure for circumscribing the electrode 1 through a swirler 6 having an insulating function and holding the electrode 1. , the center line of the orifice 3C at its tip coincides with the center line of the electrode 1. Even with such a configuration, its material or size depends on the material of the workpiece, the processing form, the type of plasma gas, Generally, these are selected and combined as appropriate after taking various conditions such as operating current into consideration.Next, stabilization of plasma discharge 4A will be explained.Conventionally, improvements in the durability of plasma torches and accuracy of plasma processing have been made. The improvement of plasma processing is considered to be an essential task for academic institutions and industries in the field of plasma processing, and stabilization of the arc by swirling airflow is one of the technologies adopted as an effective means to solve the problem of stabilizing plasma discharge. The working gas 2 reaches the swirler 3B through the introduction passage 3A at a predetermined pressure Po.Two swirling speed components are applied here, and a swirling flow 2B is generated up to the orifice 3C, and this swirling flow 2B, the cathode point (hereinafter,
(referred to as a discharge point) is stably held at the center of the electrode l. In other words, if the discharge point is stably held at the center of the electrode 1, the plasma arc column 4A from this discharge point
is also stably maintained. To explain this effect in more detail, as shown in Figure (b), the pressure distribution Pn formed by the swirl flow 2B is such that the pressure at the center of the swirl is lower than the pressure at the outer circumference of the swirl, so the discharge current tries to flow through this low pressure section.

The configuration of conventional plasma torches actively utilizes such properties to stabilize plasma discharge.

(Problems to be Solved by the Invention) However, the conventional plasma torch has the following problems. In conventional technology, the stabilization of the discharge point (that is, the stabilization of the plasma arc column) is performed using the pressure distribution obtained by a hydrodynamic means called swirl flow, so microscopically, the fluctuation of the discharge point ( In other words, fluctuations in the plasma arc column always occur. Furthermore, as shown in Fig. 5, when the cathode IC member wears out due to use ((a) → (b) in the same figure), the cathode surface moves inwards from the initial surface, and the cathode surface follows this. Since the pressure distribution becomes more blunt, fluctuations in the discharge point further increase. 8 loss on the cathode surface further progresses, and when it becomes impossible to maintain the discharge point due to pressure distribution, abnormal discharge occurs, leading to destruction (see figure (a)
)→(C)).

That is, in the conventional configuration, stabilization of the discharge point (ffl, ie, plasma arc column) cannot be achieved to a greater extent than expected due to the fluctuation of the discharge point and the inevitable increase in fluctuation during use. In other words, the fluctuation of the discharge point is considered to be the main cause of the problems of reduced durability of the plasma torch and deterioration of mechanical accuracy.

The present invention focuses on such conventional problems and aims to provide a highly durable plasma torch and a plasma torch that can perform highly accurate plasma processing by suppressing the fluctuation of the discharge point as much as possible. purpose.

(Means for Achieving the Object) In order to achieve the above object, a plasma torch with a magnetic field generator according to the present invention includes a plasma torch equipped with a magnet,
The magnets were arranged so that the magnetic field generated by the magnet had a maximum magnetic field strength on the center line near the cathode surface, on a plane perpendicular to the cathode center line.

The magnet here is a general term for permanent magnets, coils made by electric current, electromagnets, or magnetized things, that is, things with a magnetic field, and the discharge axis of the plasma arc column is almost parallel to the magnetic field lines generated by these 6fJ stones. This is a plasma torch with a magnet, in which the magnet is arranged along the

(Operation) The high-temperature, high-pressure arc column formed within the plasma torch can theoretically be treated as a conductive electromagnetic fluid as a continuum. When an external magnetic field is applied to such a magnetic fluid, it tends to maintain thermodynamic quantities such as density, pressure, and temperature unchanged along the lines of magnetic force. For example, as shown in Fig. 2(a), when an external magnetic field is applied almost parallel to the arc column 4A, if the coordinate axis S is set at any one line of magnetic force 4C, the pressure in the arc column 4A is reduced to P. Then, it can be proven that θP −= 0 −−−·−(1) θS. This is arc pillar 4
This indicates that the pressure of the plasma constituting A does not change along the magnetic field line 4C. If the temperature change T of the arc is unchanged in a minute section on the coordinate axis S taken on the magnetic field lines, then the arc density ρ is also kept unchanged in that minute section. In fact, when an arc strike to which an external magnetic field is applied as shown in Fig. 2 (a) changes its position due to fluctuations such as minute pressure fluctuations, the magnetic field lines are stretched out in order to satisfy equation (1). It fluctuates with However, when the applied magnetic field strength is increased, the force (magnetic pressure) that tries to prevent the arc from fluctuating due to the lines of magnetic force becomes stronger, so the arc column is strongly suppressed from fluctuations and maintained stably along the lines of magnetic force. will be done.

The configuration of the torch described above was made by taking such a phenomenon into consideration, and in the vicinity of the cathode surface, as shown in Fig. 2(b).
As shown in , it has a magnetic field line distribution that is almost parallel to the arc column 4A, and the center line of the cathode (Plasma Arc Co., Ltd. center line 4B
) is attached with a magnetic field generating device such as a permanent magnet 5 so as to generate a magnetic field having the maximum magnetic field strength.

By configuring the plasma torch in this way, it is possible to more stably fix the discharge point to the center of the cathode IC.

(Example) The following is an example of the present invention in drawings (Figures 1 and 3).
Refer to and explain. The first part shows an embodiment of a plasma torch with a magnet according to the present invention, and FIG. 3 shows an experimental graph showing the effects of the first embodiment. The structure of the magnet-equipped plasma torch of the embodiment shown in FIG. 1 is a diagram showing a schematic cross section of an embodiment in which a typical conventional plasma torch outlined in FIG. 4 is equipped with a magnet (prior art). Therefore, in the following description of the configuration, the conventional configuration outlined previously will be omitted, and only the arrangement and configuration of the magnets of the main parts related to the present invention will be mainly described. In the figure, a magnet 5 is a permanent magnet with a ring-shaped cross section and is fixed to the outer periphery of a cathode holder 6 that circumscribes the outer periphery of a cathode l and holds this cathode. . The magnet 5 is fixedly installed so that the center of the ring and the parallel space are at a distance from the axial center line 4B of the plasma arc column 4B. Figure 3 shows the results of this experiment. To explain this, the conventional plasma torch P1 has a cathode that has a cumulative arc time life of about 80 minutes for about 280 starts and stops, and a life span of about 150 times. In contrast, in the plasma torch P2 of this embodiment, the cathode has a life of about 125 minutes of cumulative arc time for about 420 starts and stops, and a life of about 2.
It has a lifespan of about 480 minutes of cumulative arc time when the number of starts and stops is 60 times. Furthermore, when it comes to plasma torch P3, its cathode is turned on and off about 150 times in about 480 times.
We were able to obtain high results with a cumulative arc time life of approximately 740 minutes, and a cumulative arc time life of approximately 740 minutes after approximately 370 starts and stops. Figure 3 shows this on a graph. As can be seen from the drawing, for example, if Pl and P3 are compared based on the same graph, P at the maximum number of starts and stops (the point where the wear curve intersects the vertical axis)
Although there is little difference between I and P3, it can be seen that in a steady operating state (the point where the wear curve intersects the horizontal axis), the durability can be improved several to several tens of times.

Cathode member ()\Funium 11 after use (i.e. after life)
When we compared the depth of 8 strokes in f) with Pl, P2, and P3, we found that P2 and P3 were 1.2 to 1.3 times deeper than Pl (this can also be confirmed by simple calculation). 2
This means an improvement in lifespan of 0-30%.

) Furthermore, regarding the cut surface of the workpiece 7, P2 and P3 are as follows: 1) Compared to 1), it was possible to obtain excellent cutting accuracy with significantly less variation in hevel angle and kerf width. As another embodiment, the magnet material 5 may be changed from the permanent magnet of the first embodiment to a coil made by electric current, an electromagnet, or a magnetized material. Furthermore, the arrangement position, shape, or quantity of the magnets may be changed or combined.

(Effects of the Invention) As explained above, the plasma torch equipped with a magnetic field generator according to the present invention can greatly extend the life of the electrode and at the same time perform plasma processing with higher precision.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of a plasma torch with a magnet according to the present invention, Fig. 2 (a) is a diagram showing the distribution of magnetic flux intensity in a plane perpendicular to the plasma arc axis, and (b) is a diagram showing the plasma arc FIG. 3 is an experimental graph showing the effect of the above embodiment. FIG. 4 is a diagram showing a typical conventional plasma torch, and FIG. 3(a) is a schematic diagram thereof. A diagram showing a cross section, Figure (b) is a diagram showing the pressure distribution created by swirling flow, and Figure 5 is a diagram showing the process in which the cathode member wears out due to use and leads to destruction (Figure (a) → Figure (b) → Figure (C)). 1... Electrode IA... Wiring 1B... Holder tC... Cathode 2... Working gas 2B... Swirling flow 3... Nozzle 3A.
... Gas introduction passage-3B... Swirler-30... Orifice 4A... Plasma arc column 4B... Plasma arc column center line 4C... Line of magnetic force 5... Magnet 6... Insulator ( Swirler) 7...Work material

Claims (1)

[Claims] The plasma torch is equipped with a magnetic field generator such as a magnet, and the magnetic field generated by the magnetic field generator is near the cathode surface of the plasma torch, is axially symmetrical to the central axis of the cathode, and is perpendicular to the central axis. A plasma torch equipped with a magnetic field generator, characterized in that the magnetic field strength is maximum on the central axis on the intersecting planes.