JP2007066677A - Electrode for plasma torch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To extend the life of an electrode of a plasma torch and to stabilize the lifetime. <P>SOLUTION: This electrode A for a plasma torch has a holder 1 formed of copper or a copper alloy and an electrode material 2 formed of a metal selected from a group comprising hafnium, a hafnium alloy, zirconium and a zirconium alloy. A hole 1c is formed at the axial center of the holder 1 to insert and fix the electrode material 2 into/to it; and a depression 5, having a curved-surface-like shape in the depth direction, is formed on a tip surface 2a of the electrode material 2 or a depression 6 of a shape having a top 6a nearly coincident with the axial center 2b of the electrode material 2 in the cross section in the depth direction and having at least one projecting point 6c on a line connecting the top 6a and the tip surface 2a is formed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrode of a plasma torch that can extend the life.

  2. Description of the Related Art Plasma processing methods are widely used in which a plasma arc is jetted toward a workpiece to perform processing such as cutting, welding, or thermal spraying on the workpiece. A plasma torch used for carrying out the plasma processing method includes a conductive electrode configured to be detachable from a conductive electrode base provided on the torch body, and surrounding and insulated from the electrode. An electrically conductive nozzle arranged in a detachable state and configured to be detachable from the torch body, and an insulating cover disposed around the nozzle and configured to be detachable from the torch body. It is configured.

  In the plasma torch, by discharging between the electrode and the nozzle or between the electrode and the workpiece, the gas supplied around the electrode is turned into plasma to form a plasma arc. Since this plasma arc becomes extremely high temperature, the electrode is melted or evaporated by this heat and gradually consumed.

  In particular, in a plasma cutting torch in which a plasma arc in which an oxidizing gas containing oxygen is turned into plasma is jetted toward a material to be cut, the electrode made of copper or tungsten is instantly oxidized and destroyed. For this reason, an electrode used for a plasma cutting torch is generally configured by embedding and fixing an electrode material made of hafnium, zirconium, or an alloy thereof in the center of a holder made of copper or a copper alloy. However, even with an electrode configured in this way, it is inevitable that the electrode material melts and oxidizes every time it is used.

  For this reason, the electrode of the plasma torch always has a problem of how to extend its life, and many proposals have been made to solve this problem.

  For example, the invention described in Patent Document 1 extends the life by preventing the erosion of the electrode material (insertion electrode) from growing and damaging the holder (electrode base). The insertion electrode is closely inserted and fixed in the hole of the electrode base, and is a recess recessed in the axial direction of the insertion electrode, positioned at the center of the tip surface exposed to the outside of the insertion electrode, and perpendicular to the axis. A space having a circular cross section in the direction is formed with a recess having a diameter of 50% to 95% of the diameter of the insertion electrode. In this invention, the base material of 5% to 50% of the diameter, which is the remaining portion of the concave portion formed in the insertion electrode, is disposed along the inner peripheral wall of the electrode base, and even if the insertion electrode grows melted. It is possible to prevent the electrode substrate from being melted, and it is possible to stabilize and extend the life of the electrode.

  On the other hand, since the plasma arc is formed starting from the surface of the electrode material (discharge end face), if the discharge end face is flat, the starting point of the plasma arc at the discharge end face of the electrode material changes, and the quality of the cut surface There is a problem of adversely affecting. For this reason, by forming a conical depression substantially coincident with the axial center of the electrode material (see, for example, paragraph 0004 of Patent Document 1), the starting point of the plasma arc is limited to the depression, thereby improving the quality of the cut surface. Generally, it is configured to improve.

Japanese Patent No. 3179656

  The electrode of the plasma cutting torch always has a problem of extending the life.

  When cutting a workpiece, high-speed cutting can be realized by using a plasma cutting torch, and cutting time can be reduced. Therefore, a plasma cutting torch is expensive like a numerical control (NC) cutting device. Often applied to complex equipment. In such a cutting device, how to achieve continuous operation becomes a problem. For example, if the electrode of the plasma cutting torch is consumed and destroyed during cutting of the material to be cut, the cutting is interrupted at the time of destruction, and much time is required to cope with it. For this reason, the NC cutting device is generally configured to store information that leads to the destruction of the electrode in advance so that the electrode can be replaced immediately before the destruction. However, even with electrodes of the same specification, the degree of progress of consumption of individual electrodes varies, and the problem is not necessarily that they will be destroyed at the same number of times and hours of use, that is, the life is not stable, There is a problem that the reliability of information leading to the destruction of the electrode is low.

  With the technique described in Patent Document 1, it is possible to extend and stabilize the life of the electrode. However, since a recess having a diameter of 50% to 95% of its diameter is formed on the surface of the insertion electrode, the distance between the electrode and the surface of the workpiece is increased by the depth of the recess, and cutting is performed accordingly. There may be a problem of affecting the quality of the surface.

  In addition, in an electrode in which a conical depression is formed on the discharge end face of the electrode material, the starting point of the plasma arc is stable, but there is a problem that the life of the electrode material cannot be extended or stabilized.

  An object of the present invention is to provide an electrode for a plasma torch that can extend the life and can stabilize the life.

  In order to solve the above problems, an electrode for a plasma torch according to the present invention comprises a holder made of copper or a copper alloy, and an electrode material made of a metal selected from the group of hafnium, hafnium alloy, zirconium, and zirconium alloy. An electrode for arc machining using an oxygen-based gas in which a hole is formed in the axial center of the holder and the electrode material is inserted and fixed in the hole, and the discharge end surface of the electrode material has a depth direction A curved depression is formed on the surface.

  An electrode for a second plasma torch according to the present invention has a holder made of copper or a copper alloy, and an electrode material made of a metal selected from the group of hafnium, hafnium alloy, zirconium, and zirconium alloy, An arc machining electrode that uses an oxygen-based gas in which a hole is formed in the axial center of the holder and the electrode material is inserted and fixed in the hole, and a cross-section in the depth direction is formed on the discharge end face of the electrode material Is formed with a recess having a shape having an apex substantially coincident with the axis of the electrode material and having at least one protrusion on a line connecting the apex and the discharge end face.

  In the above plasma torch electrode, a curved recess was formed in the depth direction on the discharge end face of the electrode material fixed to the holder, so that the plasma arc was started from the curved recess starting from the first use of the new electrode. Can be formed. For this reason, it becomes possible to be consumed in a stable state from the initial stage of use, and the life can be extended.

  In the second electrode, the discharge end face of the electrode material has an apex whose cross section in the depth direction substantially coincides with the axis of the electrode material, and at least one line on the line connecting the apex and the discharge end face By forming a depression having a protruding point, the lifetime can be extended and the lifetime can be stabilized as compared with a conventional electrode having a conical depression.

  Hereinafter, preferred embodiments of the electrode according to the present invention will be described. The present invention extends the life of the electrode of the plasma torch and stabilizes the life by reducing the variation in the life of electrodes of the same specification.

  The present inventor has conducted many experiments in order to extend and stabilize the life of the plasma torch electrode. As a result of this, a process for depleting the electrode of the plasma torch when an oxidizing gas containing oxygen is used as the plasma gas will be described. Due to the generation of plasma arc, thermoelectrons are emitted from the tip surface (discharge end surface) of the electrode material, resulting in a high temperature state, the electrode material is oxidized, and the discharge end surface of the electrode material becomes the synergistic effect of the emission of thermoelectrons and the oxidation reaction. It becomes hotter and melts and evaporates and wears out.

  A curved recess (crater) is formed on the discharge end face due to melting and consumption of the electrode material, and the starting point of the plasma arc penetrates from the surface of the holder to heat the holder. Further, the electrode material is oxidized at the moment when the plasma arc is erased, and is oxidized by the influence of the oxidizing gas existing around the electrode, and a part of the electrode material is detached from the crater and the wear progresses. Therefore, every time the plasma arc is formed, a part of the electrode material is consumed, and the consumption progresses as the number of uses increases.

  The holder that constitutes the electrode is internally cooled by cooling water, and forms a stable plasma arc while the balance between the heat supplied by the plasma arc and the heat removed by the cooling water is maintained. Can do. Then, the balance between heat input and cooling to the holder is lost, and when the amount of heat input exceeds the limit, the holder melts at a stretch and leads to destruction.

  The above-described wear is a steady process, and when such a wear process has passed, the electrodes of the same specification have substantially the same life, and can be said to have a stable life. Therefore, it is possible to extend the life by reducing the amount of consumption when the steady consumption process has passed or securing the length of the electrode material that can withstand the consumption.

  However, in the case of an electrode of a plasma torch, unsteady wear may occur in which the electrode material is removed in large quantities so that the electrode material is removed at once when the plasma arc is extinguished. When such wear occurs, the life of the electrode becomes extremely short, and the life of the electrode having the same specification becomes unstable. Therefore, if it is possible to eliminate the consumption that causes the electrode material to be detached in large quantities, it is possible to extend the life and stabilize it.

  Therefore, the present inventor considered a process in which a large amount of electrode material was consumed, and when the plasma arc was formed from the conical surface at the discharge end face of the new electrode, the conical surface was spherical. When moving to the crater, a large amount of electrode material melts at once, and at the time of fire extinguishing, a large amount of electrode material may be detached, and the life of the electrode material is shortened by the removal of this electrode material, The electrodes of the present invention were obtained by conducting trial manufacture and experiment by assuming that the electrodes of the same specification were not released from a large amount of electrode materials all at once, and this would make the life of each electrode unstable. It is.

  Therefore, the electrode of the present invention inserts and fixes an electrode material made of a metal selected from the group of hafnium, hafnium alloy, zirconium, and zirconium alloy to the axial center of a holder made of copper or a copper alloy, and the electrode material In the discharge end face, a curved depression is formed in the depth direction. As described above, the electrode of the present invention can realize a stable molten state from the first use of a new article by forming a curved crater on the discharge end face of the electrode material before use in advance. It is what I did.

  In the present invention, it is important that the dent of the curved surface is a curved surface, and does not limit the radius and depth of the curved surface or the diameter of the surface of the electrode material.

  In the present invention, instead of a curved depression on the discharge end face of the electrode material, the cross section in the depth direction has a vertex that substantially coincides with the axis of the electrode material, and on the line connecting the vertex and the discharge end face A recess having a shape (polygonal recess) having at least one protruding point may be formed. Even if such a polygonal depression is formed, it is possible to realize a relatively stable molten state from the stage of using a new article for the first time.

  Next, the structure of the electrode according to the present embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view illustrating the configuration of an electrode. FIG. 2 is a diagram for explaining the depression formed in the discharge end face of the electrode material. FIG. 3 is a view for explaining a tip portion of a cutter used when forming a polygonal depression.

  As shown in FIG. 1, the electrode A is configured by embedding and fixing a round bar-shaped electrode material 2 in a holder 1 made of copper or a copper alloy. The electrode material 2 may be fixed in direct contact with the holder 1. However, since it is possible to extend the life by providing a metal layer made of silver, gold, or an alloy thereof on the contact surface between the holder 1 and the electrode material 2, in this embodiment, the holder 1 and the electrode A metal layer 3 is formed between the material 2.

  The front end surface 1a serving as the discharge end surface of the holder 1 is a surface in contact with the plasma gas made of an oxidizing gas containing oxygen gas supplied to the surroundings when forming the plasma arc, and the back surface opposite to the front end surface 1a. 1b is a surface which contacts cooling water. A hole 1c for embedding the electrode material 2 along the axis of the holder 1 is formed at the approximate center of the front end surface 1a of the holder 1, and a protrusion is formed on the back surface 1b of the holder 1 to increase the surface area. 4 is formed.

  As described above, in the electrode A in which the protrusion 4 is formed on the back surface 1b of the holder 1, when the electrode A is attached to a plasma torch (not shown), the cooling water flows into contact with the back surface 1b and the protrusion 4 and the electrode A It is comprised so that it can cool efficiently.

  The electrode material 2 can use a metal selected from hafnium, zirconium, or an alloy thereof. In this embodiment, a hafnium round bar is used, and the diameter of the electrode material 2 is slightly smaller than the diameter of the hole 1c formed in the front end surface 1a of the holder 1.

  The metal layer 3 has a function of eliminating a discontinuous portion such as a gap that may be formed between the electrode material 2 and the holder 1 when the electrode material 2 is integrated with the holder 1, and silver, silver alloy, gold, Among the metals selected from gold alloys, a silver alloy is used, and this silver alloy is melted and filled in the gap between the hole 1c and the electrode material 2.

  In the electrode A configured as described above, when the electrode material 2 is embedded in the holder 1, the tip surface 1a of the holder 1 and the tip surface 2a (discharge end surface) of the electrode material 2 are configured as the same surface.

  Further, at the approximate center of the front end surface 2a of the electrode material 2 embedded and fixed in the holder 1, the depth direction of the electrode material 2 (the direction along the axis 2b of the electrode material 2, the axis of the holder 1 is substantially the same). 2), a curved depression 5 as shown in FIG. 2 is formed with a predetermined depth. Further, by forming the curved depression 5 on the tip surface 2a of the electrode material 2, the life of the electrode A can be extended, and the variation in the life of the electrode of the same specification can be reduced and stabilization can be achieved. Is possible.

  The curved recess 5 is preferably the same as or substantially the same as the shape of the crater formed on the electrode material 2, and is preferably formed as a surface obtained by rotating a parabola. Further, the depth of the recess 5 and the diameter at the distal end surface 2a of the electrode material 2 are set in relation to the thickness of the electrode material 2, and are not uniquely set.

  The center of the radius of the hollow 5 made of a spherical surface is set at a position coincident with the front end surface 2a or at a position separated by a predetermined dimension from the front end surface 2a. Therefore, the dent 5 formed around the position coincident with the tip surface 2a becomes a hemispherical dent, and the dent 5 formed around the position separated from the tip surface 2a becomes a bowl-like dent.

  In order to form the spherical recess 5 in the electrode material 2, it is possible to use a blade whose tip is cut into a spherical shape and cut the blade as a cone.

  In this embodiment, the recess 5 has a spherical shape with a radius of 1 mm and a depth from the tip surface 2a of 0.7 mm. Therefore, the diameter of the recess 5 in the tip surface 2a is about 1.99 mm.

  Next, the configuration of the second embodiment of the electrode A will be described. In the present embodiment, a polygonal recess 6 or 7 as shown in FIG. 2 is formed in the electrode A at a predetermined depth. Then, by forming the polygonal depression 6 on the tip surface 2a of the electrode material 2, the life of the electrode A can be extended, and the variation in the life of the electrode of the same specification can be reduced to stabilize. Is possible.

  The polygonal depression is preferably a shape obtained by rotating a line having a large number of inflection points so as to approach the curved surface as much as possible. However, when the deepest position is the apex, the life is extended and stabilized even if the refractive line with at least one second apex is rotated between the apex and the tip surface. Is possible.

  In the present embodiment, as a polygonal depression, the apex coincident with the axis 2b of the electrode material 2, and the shape of the refraction line forming the second apex between the apex and the tip surface 2a is rotated, A plurality of types are configured so that the vertices of the refractive lines have different depths along the axis 2 b of the electrode 2.

  The polygonal recess 6 has a vertex 6a at a position coincident with the axis 2b of the electrode material 2 and a depth of 0.7 mm from the tip surface 2a. A bottom slope 6b having an inclination of 5 degrees is formed, and when a curved surface constituting the bottom slope 6b and the depression 5 is assumed, a second vertex 6c is formed at a position intersecting with the curved surface, and a tip is formed from the second vertex 6c. A second inclined surface 6d of 60 degrees is formed toward the surface 2a. That is, the polygonal depression 6 is configured as a polygon inscribed in the spherical depression 5.

  The polygonal recess 7 is formed by pushing the recess 6 as it is along the axis 2b to a predetermined depth (for example, 0.1 mm). Accordingly, the vertex 7a is formed at a position that coincides with the axis 2b and is 0.1 mm deeper than the vertex 6a of the recess 6, and the second vertex 7c is also 0. 0 than the second vertex 6c of the recess 6. The bottom slope 7b is formed by connecting these vertices 7a and 7c, and the second slope 7d is formed by connecting the second vertex 7c and the tip surface 2a.

  In order to form the polygonal depressions 6 and 7 in the electrode material 2, cutting may be performed using a blade 10 as shown in FIG. 3. The tip portion of the blade 10 has a blade portion H1 constituting a bottom slope having a tip angle of 120 to 150 degrees and a diameter D of 0.9 mm to 1.40 mm, and a tip angle of 30 to 70 degrees and a diameter of 1 A blade portion H composed of a blade portion H2 of .8 mm to 1.9 mm is formed. Therefore, it is possible to form a polygonal depression by cutting the tip surface 2a of the electrode material 2 with the cutter 10 that is aligned with the axis 2b, and adjusting the driving depth of the cutter 10. Thus, the depressions 6 and 7 can be selectively processed.

  Next, as described above, the electrode (Example 1) configured with the curved recess 5 along the axis 2b of the electrode material 2 made of hafnium, and the electrode (Example 2) configured with the polygonal recesses 6 and 7 were formed. The result of the experimental example which measured the lifetime is demonstrated, and the comparison with the conventional electrode is demonstrated collectively. In each example, the number of samples was 5.

  In the experiment, the current was 400 amperes, the plasma gas was oxygen gas, and the flow rate was 35 L / min. The plasma arc was formed by forming a plasma arc for 60 seconds and then stopping once for 30 seconds (an arc time of 1 minute), and this cycle was repeated. The distance between the material to be cut and the plasma torch was 7 mm.

  Each time the number of arcs formed was 30 (arc time 30 minutes), the consumption depth of the electrode material 2 was measured and continued until the electrode broke. Therefore, when the electrode breaks, the number of arc times can be measured, but the consumption depth of the electrode material 2 cannot be measured.

[Example 1]
The electrode which comprised the spherical surface along the axial center 2b of the electrode material 2 and comprised the hollow 5 about 0.7 mm deep was manufactured. Using this electrode, an experiment was conducted to measure the lifetime with the above specifications. The result of this experiment is shown in FIG. As shown in the figure, in the electrode of this example, the consumption of the electrode material 2 progresses as the arc time increases. However, after the arc time of 180 minutes has passed, the progress of the consumption becomes slow, and the arc time of 210 minutes is reduced. Even after the passage of time, it was possible to form a good plasma arc. Then, it was destroyed at an arc time of 217 minutes. Moreover, the standard deviation at the time of destruction was 14.50.

  As a result of the experiment, it can be said that a sufficiently long life can be obtained with an electrode having a spherical depression.

[Example 2]
Next, the electrode which comprised the polygon which consists of polygons along the axial center 2b of the electrode material 2, and the depth from which depth differs about 0.6 mm, about 0.7 mm, 0.75 mm, and 0.8 mm was manufactured. . Using these electrodes, an experiment was conducted to measure the lifetime with the above specifications. As a result of this experiment, the relationship between the arc time of the electrode in which a recess having a depth of about 0.7 mm is formed and the consumption depth of the electrode material 2 is shown by a line 22 in FIG. Further, the relationship between the depth of the depression formed in the electrode and the arc time to break is shown by a line 23 in FIG.

  As shown by the line 22 in FIG. 4, the electrode material 2 is consumed as the arc time increases, and a good plasma arc is formed even when the arc time is consumed to about 1 mm in 180 minutes. Was possible. It was destroyed at an arc time of 185 minutes. Moreover, the standard deviation at the time of destruction was 15.45.

  In addition, as shown in FIG. 5, the arc time of the electrode having a depression depth of about 0.7 mm shows the longest lifetime at 185 minutes, and the electrode having a depth of about 0.75 mm has an arc time of 180 minutes (at the time of destruction). The standard deviation was 15.34). The arc time was 176 minutes (standard deviation at break 14.65) for an electrode having a depth of about 0.8 mm. Furthermore, the electrode having a depth of about 0.6 mm was broken in a short time.

  As a result of the above-mentioned experiment, it can be said that the life of the electrode formed with a recess having a depth of about 0.7 mm is prolonged. In addition, it can be said that the electrode having a depression depth of about 0.75 mm and the electrode of about 0.8 mm have substantially the same performance.

[Comparative example]
The life and stability of the electrode according to the present invention described above were compared with those of a conventionally used electrode (number of samples: 5). The electrode used in this comparative example uses round bar-shaped hafnium as the electrode material. The tip angle of the electrode material is 140 degrees and the diameter at the tip surface of the electrode material is 2. A conical depression that is 1 mm is formed. In this case, the depth of the recess is about 0.4 mm.

  A plasma arc was formed on a conventional electrode under the same conditions as in the above experimental examples, and the consumption depth of hafnium serving as an electrode material was measured. This result is shown in FIG. As shown in the figure, hafnium consumption progresses as the arc increases, and the arc time is about 1.1 mm in 150 minutes, but it is possible to form a good plasma arc. It was destroyed at an arc time of 157 minutes. Moreover, the standard deviation at the time of destruction was 19.69.

  As described above, the average life of the comparative example is 157 minutes and the standard deviation is 19.69, whereas in the case of Example 1 in which the electrode material 2 is formed with the spherical recess 5, the average life is 217 minutes and the standard deviation. 14.50. When both are compared, it can be said that the life of the electrode of Example 2 is clearly extended and the life of the different electrodes is stabilized.

  In the case of the electrode of Example 2, when the depth of the depression is about 0.7 mm, about 0.75 mm, and about 0.8 mm, the average lifetime is 185 minutes, 180 minutes, 176 minutes, and the standard deviation is 15. Since it is 45, 15.34, and 14.65, it can be said that the lifetime is extended and the lifetime is stabilized as compared with the electrode of the comparative example.

  In the case of the electrode of Example 2, it can be said that the depth of the recess is preferably about 0.7 mm and about 0.75 mm.

  In the electrode according to the present invention, the curved surface recess 5 or the polygonal recesses 6 and 7 are formed on the distal end surface 2a of the electrode material 2 along the substantially axial center 2b. It is possible to provide a stable life with little variation even with different electrodes.

It is sectional drawing explaining the structure of an electrode. It is a figure explaining the hollow formed in the discharge end surface of an electrode material. It is a figure explaining the front-end | tip part of the cutter utilized when forming a polygonal hollow. It is a figure which shows the relationship between arc time and the consumption depth of an electrode material. It is a figure which shows the relationship between the depth of the hollow in an electrode, and arc time.

Explanation of symbols

A electrode 1 holder 1a, 2a tip end face 1b back face 1c hole 2 electrode material 2b axis 3 metal layer 4 protrusion 5 curved recess 6,6 polygonal recess 6a, 7a apex 6b, 7b bottom slope 6c, 7c second Vertex 6d, 7d 2nd slope 10 Cutlery 21-24 Lines indicating experimental results

Claims (2)

A holder made of copper or a copper alloy, and an electrode material made of a metal selected from the group of hafnium, hafnium alloy, zirconium, zirconium alloy, and forming a hole in the axis of the holder and An electrode for a plasma torch in which an electrode material is inserted and fixed, wherein a curved depression is formed in a depth direction on a discharge end face of the electrode material. A holder made of copper or a copper alloy, and an electrode material made of a metal selected from the group of hafnium, hafnium alloy, zirconium, zirconium alloy, and forming a hole in the axis of the holder and An electrode for a plasma torch using an oxygen-based gas in which an electrode material is inserted and fixed, the discharge end face of the electrode material having a vertex whose depth section substantially coincides with the axis of the electrode material An electrode for a plasma torch, wherein a recess having a shape having at least one protrusion point is formed on a line connecting the apex and the discharge end face.

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