JP5805409B2 - Electrode for plasma cutting device and plasma torch - Google Patents

Description

  The present invention relates to an electrode for a plasma cutting apparatus used for plasma cutting and a plasma torch including the same.

  The plasma cutting device is a device that thermally cuts a workpiece such as a metal plate by injecting a plasma arc. The plasma cutting device is provided with a plasma torch, and the plasma torch has electrodes and nozzles as consumable parts.

  In such a plasma cutting apparatus, a plasma arc is generated between the electrode of the plasma torch and the workpiece. The plasma arc is narrowed down by a nozzle, thereby generating a high-temperature and high-pressure plasma jet. And a workpiece | work is cut | disconnected by injecting a plasma jet to a workpiece | work. Here, it is known that the plasma arc is generated by the following process.

  First, a small flow rate of plasma gas is supplied between the electrode and the nozzle to generate a plasma gas flow. In this state, when a high voltage is applied to the electrode, dielectric breakdown occurs between the electrode and the inner surface of the nozzle. A pilot arc is generated between the electrode and the nozzle using this dielectric breakdown as a trigger. The pilot arc rides on the plasma gas flow and extends to the workpiece. A plasma arc is generated between the electrode and the workpiece by increasing the flow rate and current of the plasma gas.

  In the plasma cutting apparatus as described above, Patent Document 1 describes that an edge-shaped protrusion is provided on the outer peripheral surface of the electrode so that dielectric breakdown is likely to occur between the electrode and the nozzle.

  Moreover, in FIG. 6 of patent document 2 and patent document 3, in order to make the flow of the plasma gas which goes to a workpiece | work smooth, the electrode in which the groove | channel was formed is shown. That is, in the electrode of Patent Document 2, a recess extending in the circumferential direction is formed on the outer peripheral surface of the electrode, and a groove is formed at the lower end. Further, in the electrode of Patent Document 3, a radial groove toward the center is formed in the tapered portion of the electrode outer peripheral portion. By this radial groove, the plasma gas is guided to the center of the lower end of the electrode.

  Further, Patent Document 4 discloses a plasma torch electrode in which a radial groove is formed in at least one of the electrode body and the tip of the insert.

Japanese Patent Publication No. 5-502189 Japanese Patent Laid-Open No. 11-314162 US Pat. No. 5,451,739 Japanese Utility Model Publication No. 3-47743

  With regard to electrodes and nozzles as consumable parts, there is a demand for longer life in order to reduce costs. However, if the electrode and the nozzle are used for a long time, the inner surface of the nozzle becomes an insulator due to oxidation or the like, and dielectric breakdown hardly occurs. Then, the re-ignition process of the plasma arc is repeatedly executed, the productivity is lowered, and finally the ignition is impossible. In addition, there are other problems related to poor ignition as follows.

  In the initial stage of the plasma cutting process, a part of the electrode material such as hafnium provided on the plasma arc emission surface of the electrode substrate is scattered and adheres to the inner surface of the nozzle. The electrode material adhering to the inner surface of the nozzle can be a starting point for dielectric breakdown, but it can also cause abnormal discharge and degradation of cutting quality.

  Therefore, the inventors of the present invention tried to perform plasma cutting using an electrode material having a recess at the tip. This is because by providing a recess at the tip of the electrode material, the amount of electrode material scattered at the initial stage is reduced, and the electrode material is prevented from adhering to the inner surface of the nozzle. In this case, however, dielectric breakdown may be difficult to occur. In order to solve this problem, as shown in Patent Document 1, it is conceivable to form an edge portion on the outer peripheral surface of the electrode substrate so that dielectric breakdown is likely to occur between the edge portion and the inner surface of the nozzle. .

  However, when an edge portion is formed on the electrode substrate, there is a problem that a plasma arc (pilot arc) generated between the edge portion and the inner surface of the nozzle is constrained by a region formed by the edge portion. That is, a problem arises that the pilot arc stays in the region formed by the edge portion and does not shift to the main arc (so-called “trap”). Since the trace of the arc generated on the inner surface of the nozzle is a trajectory of arc transition, whether or not such a phenomenon has occurred can be determined by observing the arc trace. In the prior art, when a large amount of arc marks are generated on the inner surface of the nozzle, it indicates that the plasma arc is constrained at the edge of the electrode. Such plasma arc restraint causes a torch start error and an increase in unnecessary input power. Further, if the plasma arc is restrained and the nozzle continues to be damaged, it is necessary to replace the nozzle frequently, and the life of the nozzle cannot be extended.

  The problem of the present invention is that the pilot arc generated between the electrode and the nozzle can be smoothly transferred to the main arc to suppress the deterioration of the cutting quality, and the life and productivity of the electrode and nozzle that become consumables are increased. Is to plan.

  An electrode for a plasma cutting device according to the first invention is an electrode used in a plasma cutting device, and includes an electrode base and an electrode material. The electrode base has a discharge surface formed at the tip, a tapered surface formed on the outer peripheral side of the discharge surface, and a plurality of grooves formed from the outer peripheral edge of the discharge surface toward the central portion. . Each of the plurality of grooves has a first side surface and a second side surface that are inclined with respect to the discharge surface. The electrode material is disposed at the center of the discharge surface of the electrode substrate.

  The electrode for the plasma torch is arranged so that the tip portion is located inside the nozzle. For this reason, the outer peripheral edge of the discharge surface is closest to the inner surface of the nozzle. And the some groove | channel is formed toward the center part from the outer periphery of the discharge | release surface, and each groove | channel has a 1st side surface and a 2nd side surface. For this reason, a ridge line is formed on each side surface at the boundary between the discharge surface and the tapered surface. An edge is formed at the intersection of the ridgeline at the boundary between each side surface and the emission surface and the ridgeline at the boundary between each side surface and the tapered surface. For this reason, this edge is the starting point, and dielectric breakdown is likely to occur between the outer peripheral edge of the discharge surface and the inner surface of the nozzle. Further, since the groove is formed from the outer peripheral edge of the emission surface toward the central portion, the plasma arc generated by the dielectric breakdown is likely to move toward the central portion along the edge that is the edge of the groove. Further, plasma gas is supplied from the outer periphery of the electrode base toward the center, and the plasma gas is guided along the side surface of the groove to the center of the emission surface.

  As described above, the plasma arc (pilot arc) generated at the edge formed by the groove on the outer peripheral edge of the emission surface, along with the flow of the plasma gas flowing along the edge which is the edge of the groove or along the groove Towards the center, smoothly moves to the main arc. Therefore, it is difficult to leave an arc mark on the inner surface of the nozzle, and it is possible to suppress a reduction in cutting quality, and thus it is possible to extend the life of the nozzle.

  The electrode for a plasma cutting device according to a second aspect of the invention is the electrode of the first aspect, wherein the first side surface and the second side surface have a first inclination angle and a second side with respect to a virtual surface obtained by extending the emission surface to the groove. There is an inclination angle, and the first inclination angle is larger than the second inclination angle.

  Here, the first side surface has a large first inclination angle with respect to a virtual surface obtained by extending the discharge surface to the groove portion. For this reason, the boundary between the first side surface and the emission surface has a steeper edge than the boundary between the second side surface and the emission surface. For this reason, the edge formed by the boundary between the first side surface, the emission surface, and the tapered surface is likely to be a starting point of dielectric breakdown, and is more likely to cause dielectric breakdown.

  The electrode for a plasma cutting device according to a third aspect of the invention is the electrode of the second aspect, wherein plasma gas is supplied around the electrode base so as to swivel from the outer periphery toward the center of the emission surface. And the 1st side has an edge used as the starting point of a dielectric breakdown in the boundary part with the discharge | release surface, and the 2nd side is arrange | positioned so as to oppose the swirling plasma gas.

  As described above, the edge formed at the boundary portion (intersection of the ridge line) between the discharge surface and the tapered surface of the first side surface is a starting point of dielectric breakdown. On the other hand, the second side surface is disposed so as to face the swirling plasma gas. For this reason, after the plasma gas collides with the second side surface, the plasma gas is guided along the second side surface to the central portion of the emission surface. For this reason, the plasma arc generated at the edge of the first side faces smoothly toward the center of the emission surface along the plasma gas flowing along the second side.

  The electrode for a plasma cutting device according to a fourth aspect of the present invention is the electrode according to any one of the first to third aspects, wherein the tapered surface is formed such that the diameter increases as the distance from the emission surface increases. Is formed of two triangular surfaces as viewed in a direction perpendicular to the emission surface.

  When each groove is formed with a cutting tool having a V-shaped tip, as described above, each groove has two side surfaces. In this case, one side (bottom side) of the two side surfaces is a common side. A ridge line (another side) is formed at the boundary between each side surface and the emission surface, and a ridge line (another side) is also formed at the boundary between each side surface and the tapered surface. . Therefore, when each groove is viewed from a direction orthogonal to the emission surface, that is, in bottom view, when the inclination angle of the two side surfaces with respect to the emission surface is not 90 °, each groove has two triangles with the base as a common side. It is formed with a shape surface.

  Then, a smooth edge is formed at the intersection of the apex of the triangle, that is, the ridge line formed at the boundary between each side surface and the emission surface and the ridge line formed at the boundary between each side surface and the tapered surface. For this reason, the apex of the triangle formed by the side surface of the two side surfaces having a steeper inclination angle with respect to the emission surface is the starting point of dielectric breakdown.

  The electrode for a plasma cutting device according to a fifth aspect of the present invention is the electrode according to any one of the first to third aspects, wherein the tapered surface is formed such that the diameter increases as the distance from the emission surface increases. The first inclination angle is 90 °, and each of the plurality of grooves is formed by one triangular surface as viewed in a direction orthogonal to the radiation surface.

  Similarly to the above, two triangles are formed by the ridgeline of the boundary between each side surface and the discharge surface and the tapered surface. However, when the angle of inclination of the side surface with respect to the emission surface is 90 °, one straight line is obtained in the bottom view, and each groove is formed by one triangular surface in the bottom view. In addition, since each groove | channel is formed by two side surfaces, both the inclination angles with respect to the discharge | release surface of two side surfaces do not become 90 degrees.

  The electrode for a plasma cutting device according to a sixth aspect of the present invention is the electrode according to any one of the first to fifth aspects, wherein the tip emission surface of the electrode material is formed with a concave portion recessed inside.

  As described above, in the initial stage of the plasma cutting process, a part of the electrode material such as hafnium is scattered and adheres to the inner surface of the nozzle, which may cause abnormal discharge and deterioration of cutting quality. Therefore, here, an electrode material having a recess on the tip discharge surface is used. For this reason, the electrode material which scatters in an initial stage decreases, and it can suppress that an electrode material adheres to a nozzle inner surface.

  An electrode for a plasma cutting device according to a seventh aspect includes an electrode base and an electrode material. The electrode base has a discharge surface formed at the tip and a plurality of grooves. The discharge surface has a curved outer periphery. The plurality of grooves are formed from the curved surface of the discharge surface toward the central portion. The electrode material is disposed at the center of the discharge surface of the electrode substrate.

  The electrode for the plasma cutting device is arranged so that the tip portion is located inside the nozzle. For this reason, the outer peripheral edge of the discharge surface is closest to the inner surface of the nozzle, and dielectric breakdown occurs between the outer peripheral edge of the discharge surface and the inner surface of the nozzle, and a plasma arc is generated.

  Here, in the electrode of the present invention, since the outer peripheral edge of the emission surface is not an edge but a curved surface, dielectric breakdown is less likely to occur than in the case of an edge. On the other hand, since a plurality of grooves are formed on the outer peripheral edge, edges are formed on the edges of the grooves. For this reason, dielectric breakdown is likely to occur between the edge formed at the edge of the groove and the inner surface of the nozzle. Since the groove is formed from the outer peripheral edge of the discharge surface toward the central portion, the plasma arc generated at the outer peripheral edge of the discharge surface due to dielectric breakdown moves toward the central portion along the edge of the groove. It becomes easy. For this reason, it becomes difficult for the plasma arc to be trapped at the outer peripheral edge of the emission surface.

  As described above, the pilot arc generated at the outer peripheral edge of the emission surface smoothly transitions to the main arc. Therefore, it is difficult to leave an arc mark on the inner surface of the nozzle, and it is possible to suppress a reduction in cutting quality, and thus it is possible to extend the life of the nozzle.

  An electrode for a plasma cutting device according to an eighth invention is the electrode of the seventh invention, wherein the curved surface of the outer peripheral edge of the emission surface has a radius of 0.05 mm or more and 50% or less of the diameter of the electrode substrate.

  Since the outer peripheral edge of the emission surface is a curved surface having a radius of 0.05 mm or more, dielectric breakdown hardly occurs at the outer peripheral edge, but the arc is not easily trapped. If the radius of the curved surface is too large, the shortest gap between the outer peripheral edge of the discharge surface and the inner surface of the nozzle is difficult to be determined at a single point. For this reason, the location where dielectric breakdown occurs is not specified, and dielectric breakdown is less likely to occur. Therefore, in the eighth invention, the radius of the curved surface is set to 50% or less of the diameter of the electrode substrate.

  An electrode for a plasma cutting device according to a ninth aspect is the electrode according to the eighth aspect, wherein the longitudinal directions of the plurality of grooves are inclined in the same direction with respect to a straight line extending radially from the center of the emission surface.

  A plasma gas flows between the electrode and the nozzle. Generally, the plasma gas flows so as to swirl around the electrode. For this reason, by forming a groove that is inclined along the direction in which the swirling plasma gas flows, the plasma arc moves toward the workpiece and smoothly moves toward the center of the electrode.

  The electrode for a plasma cutting device according to a tenth aspect of the invention is the electrode of the ninth aspect, wherein plasma gas is supplied around the electrode base so as to turn from the outer periphery toward the center of the emission surface. The plurality of grooves are inclined along the swirl direction of the plasma gas.

  Here, as in the ninth aspect, the plasma arc can be smoothly transferred to the workpiece side.

  An electrode for a plasma cutting device according to an eleventh aspect of the invention is the electrode of the seventh aspect, wherein a concave portion recessed inside is formed on the tip emission surface of the electrode material.

  Similarly to the above, since the electrode material having the concave portion on the tip discharge surface is used, the electrode material scattered at the initial stage is reduced, and the electrode material can be prevented from adhering to the inner surface of the nozzle.

  An electrode for a plasma cutting device according to a twelfth aspect of the present invention is the electrode according to any one of the first to eleventh aspects, wherein the electrode material is hafnium.

  A plasma torch according to a thirteenth aspect includes any one of the electrodes according to the first to twelfth aspects and a cylindrical nozzle. The nozzle has an electrode facing portion facing the tip portion of the electrode inside, and an orifice is formed at the tip.

  In the present invention as described above, a pilot arc can be stably generated between the electrode and the nozzle. The generated pilot arc can be smoothly transferred to the main arc. For this reason, damage to the inner surface of the nozzle can be suppressed, deterioration in cutting quality can be suppressed, and the life of the nozzle can be extended.

A sectional view of a plasma torch. The expanded sectional view of the plasma torch front-end | tip part. The expanded sectional view of the electrode of a 1st embodiment. The bottom view of the electrode of 1st Embodiment. The bottom external view of the electrode of a 1st embodiment. The enlarged view of the groove | channel formed in the electrode of 1st Embodiment. The side view of the groove | channel of 1st Embodiment. The figure equivalent to FIG. 3 of 2nd Embodiment. The bottom face partial view of the groove | channel of the electrode of 2nd Embodiment. The enlarged view of the groove | channel of the electrode of 2nd Embodiment. The figure which shows the photograph of the arc trace by the difference in electrode shape.

-First embodiment-
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view in a plane including a central axis (hereinafter simply referred to as “axis”) of the plasma torch 1 according to the first embodiment of the present invention.

[overall structure]
The plasma torch 1 is provided in a plasma cutting device for cutting a metal material such as a steel plate. Although not shown, the plasma cutting device includes an arc power supply circuit and a control device for generating a pilot arc or a plasma arc in the plasma torch 1 and controlling the plasma arc. Further, the plasma cutting device includes devices such as a gas supply system that supplies a plasma gas and an assist gas to the plasma torch 1, and a cooling system that supplies a coolant to the plasma torch 1.

  The plasma torch 1 includes a torch body 2, an electrode 3, a first guide member 4, a second guide member 5, a nozzle 6, a cap portion 7, and the like. The torch body 2, the electrode 3, the first guide member 4, the second guide member 5, the nozzle 6 and the cap portion 7 are arranged coaxially.

[Torch body]
The torch body 2 includes a base part 11, an electrode support part 12, a nozzle support part 13, a cooling pipe 14, a holder 15, a cooling liquid supply pipe 16, a cooling liquid discharge pipe 17, and the like. The base part 11, the electrode support part 12, the nozzle support part 13, and the cooling pipe 14 are arrange | positioned coaxially.

  The base part 11 is formed in a substantially cylindrical shape. A space is formed inside the base portion 11, and the electrode support portion 12, the coolant supply pipe 16, and the coolant discharge pipe 17 are inserted into this internal space. A hole 11 a that communicates with the internal space of the base portion 11 is formed at the tip of the base portion 11.

  The electrode support part 12 is formed in a substantially cylindrical shape and is inserted into the hole 11a of the base part 11, and supports the electrode 3 at the tip part (lower end part in FIG. 1). Between the outer surface of the electrode support part 12 and the inner surface of the base part 11, for example, a seal member S1 such as an O-ring is provided. The electrode support portion 12 is made of metal, and is made of, for example, copper. The electrode support portion 12 is connected to the arc power supply circuit via an electric wiring (not shown). The electrode support portion 12 has a hole 12a penetrating in the axial direction.

  The nozzle support part 13 has a hole 13a that is formed in a substantially conical shape and penetrates in the axial direction, and supports the nozzle 6 at the tip part. The nozzle support portion 13 is attached to the distal end portion of the base portion 11 and covers the outer periphery of the distal end portion of the electrode support portion 12. The inner surface of the nozzle support portion 13 is disposed with a space from the outer surface of the electrode support portion 12. Thereby, a plasma gas passage P <b> 1 through which plasma gas passes is formed between the inner surface of the nozzle support portion 13 and the outer surface of the electrode support portion 12. The plasma gas passage P1 is connected to a gas supply system via a gas supply pipe (not shown). The nozzle support portion 13 is made of metal, and is formed of, for example, copper. Moreover, the nozzle support part 13 is connected to an arc power supply circuit through electric wiring (not shown).

  The cooling pipe 14 guides the cooling liquid from the cooling liquid supply pipe 16 to the electrode 3 to cool the electrode 3, and is arranged in the hole 12 a of the electrode support portion 12. The base end portion (upper end portion in FIG. 1) of the cooling pipe 14 is disposed in the internal space of the base portion 11, and the distal end portion projects from the distal end portion of the electrode support portion 12. A space is formed between the outer surface of the cooling pipe 14 and the inner surface of the electrode support portion 12, and this space communicates with the internal space of the base portion 11. Further, the outer surface of the cooling pipe 14 is arranged with a space from the inner surface of the electrode 3.

  The holder 15 is formed in a substantially cylindrical shape and is fitted to the outer periphery of the base portion 11, and supports the cap portion 7. On the outer peripheral surface of the holder 15, a male screw portion that is screwed with a female screw portion of a nut 18 described later is formed.

  The cooling liquid supply pipe 16 is a pipe for sending the cooling liquid from the cooling system to the cooling pipe 14, and is inserted into the internal space of the base portion 11. The base end portion of the coolant supply pipe 16 is connected to the cooling system, and the tip end portion is connected to the base end portion of the cooling pipe 14 in the internal space of the base portion 11.

  The coolant discharge pipe 17 is a pipe for sending the coolant from the internal space of the base portion 11 to the cooling system, and is inserted into the internal space of the base portion 11. The base end portion of the coolant discharge pipe 17 is connected to the cooling system, and the tip end portion is disposed in the internal space of the base portion 11.

  With the configuration as described above, the coolant supplied from the coolant supply pipe 16 via the cooling pipe 14 is guided to the electrode 3, and thereafter, a space between the outer surface of the cooling pipe 14 and the inner surface of the electrode 3 is formed. Then, it passes through the space between the outer surface of the cooling pipe 14 and the inner surface of the electrode support portion 12 and is sent to the internal space of the base portion 11.

[electrode]
As shown in an enlarged view in FIG. 2, the electrode 3 is formed in a substantially cylindrical shape, has a flange 19 projecting radially outward on the outer peripheral surface, and further has a space formed therein. The inner space is open on the proximal end side and closed on the distal end side. As shown in FIG. 1, the base end portion of the electrode 3 is inserted into the hole 12 a of the electrode support portion 12 and is detachably attached to the electrode support portion 12. In a state where the proximal end portion of the electrode 3 is inserted into the hole 12 a of the electrode support portion 12, the distal end portion of the cooling pipe 14 is disposed in the internal space of the electrode 3. Further, the gap between the electrode 3 and the electrode support portion 12 is sealed by a seal member (not shown). Thereby, the front end side of the hole 12a of the electrode support part 12 is obstruct | occluded. Further, the electrode 3 is electrically connected to the electrode support 12 by contacting the electrode support 12. The structure of the electrode 3 will be described later in detail.

[First guide member]
As shown in FIG. 2, the first guide member 4 is formed in a substantially cylindrical shape, and has a large diameter portion 20 on the proximal end side and a small diameter portion 21 on the distal end side. Moreover, the 1st guide member 4 is formed with the material which has insulation. The first guide member 4 is disposed on the proximal end side inside the nozzle 6. The first guide member 4 has a hole 4a penetrating in the axial direction, and the electrode 3 is inserted into the hole 4a. As described above, the first guide member 4 is disposed between the electrode 3 and the nozzle 6 to electrically insulate the electrode 3 and the nozzle 6 from each other. A seal member S2 is provided between the inner surface of the first guide member 4 and the outer surface of the electrode 3, and a seal member S3 is provided between the outer surface of the first guide member 4 and the inner surface of the nozzle 6. Yes.

  The first guide member 4 is disposed on the tip side of the flange portion 19 of the electrode 3 in the axial direction. The base end portion of the first guide member 4 is in contact with the flange portion 19. A plurality of grooves 4 b extending in the axial direction are formed on the outer peripheral surface of the large-diameter portion 20 of the first guide member 4. The distal ends of the plurality of grooves 4b communicate with the space between the first guide member 4 and the inner surface of the nozzle 6, and the proximal side of the groove 4b is connected to the inner surface of the nozzle support portion 13 and the electrode support portion. It communicates with the plasma gas passage P1 between the 12 outer surfaces.

[Second guide member]
The 2nd guide member 5 is a substantially cyclic | annular member which has the hole 5a penetrated to an axial direction, as shown in FIG. The small diameter portion 21 of the electrode 3 and the first guide member 4 is inserted into the hole 5 a of the second guide member 5. Therefore, the second guide member 5 is disposed between the inner surface of the nozzle 6 and the small diameter portion 21 of the first guide member 4 in the radial direction. The second guide member 5 is disposed between the large diameter portion 20 of the first guide member 4 and the inner surface of the nozzle 6 in the axial direction. A plurality of grooves 5 b communicating with the inside and the outside are provided on the end surface on the front end side of the second guide member 5. Each groove 5b extends obliquely with respect to the radial direction and the circumferential direction. The plasma gas that has passed through the groove 5 b of the second guide member 5 flows so as to swirl around the outer periphery of the electrode 3.

[nozzle]
The nozzle 6 is made of copper and is formed in a substantially cylindrical shape as shown in FIG. The nozzle 6 includes, in order from the base end side, a cylindrical portion 6a having a space inside, and a distal end portion 6b formed on the distal end side of the cylindrical portion 6a.

  Cooling fins 22 are provided in a predetermined region along the axial direction on the outer peripheral surface of the cylindrical portion 6 a of the nozzle 6. In addition, on the outer peripheral surface of the cylindrical portion 6 a, a protruding portion 23 that protrudes in the radial direction is formed on the proximal end side of the cooling fin 22. An electric contact (not shown) is disposed between the upper surface 23 a of the protruding portion 23 and the tip end portion of the nozzle support portion 13. The nozzle 6 is electrically connected to the nozzle support portion 13 through this electric contact.

  A storage portion 24 and an electrode facing portion 25 are formed in the internal space of the cylindrical portion 6a. The storage unit 24 stores the electrode 3, the first guide member 4, and the second guide member 5. The electrode facing portion 25 is a portion facing the tip portion of the electrode 3, and has a first facing surface 25a and a second facing surface 25b. The first facing surface 25a is a surface formed on the proximal end side in the electrode facing portion 25 and parallel to the axial direction. Moreover, the 2nd opposing surface 25b is formed in the front end side following the 1st opposing surface 25a, and is a taper surface where a diameter becomes small toward the front end side. Gaps are formed between the opposing surfaces 25a and 25b of the electrode facing portion 25 and the outer peripheral surface of the electrode 3, and a passage through which plasma gas flows is formed. Further, a curved surface 25c is formed further on the tip side of the second facing surface 25b.

  The tip 6b is formed in a substantially conical shape, and an orifice 26 penetrating in the axial direction is formed in the center. The orifice 26 is continuous with the second facing surface 25b through the curved surface 25c. Further, a flat front end surface 26a orthogonal to the axial direction is formed at the lower end of the front end portion 6b. A chamfered portion 26b is formed between the orifice 26 and the front end surface 26a (boundary portion).

[Cap part]
As shown in FIG. 1, the cap portion 7 is a member that is attached to the tip of the torch body 2 and covers the nozzle 6. The cap unit 7 includes an outer cap 31, an inner cap 32, and a shield cap 33. Each cap 31, 32, 33 is formed in a substantially truncated cone shape, and is arranged coaxially with the electrode 3 and the nozzle 6.

  The outer cap 31 is fixed to the holder 15 by a nut 18 and covers the tip portion of the torch body 2 and the outside of the nozzle support portion 13. Further, a seal member S <b> 4 is provided between the inner surface of the outer cap 31 and the outer surface of the holder 15. A hole 31 a penetrating in the axial direction is formed at the tip of the outer cap 31.

  The inner cap 32 is inserted into the hole 31 a of the outer cap 31. A seal member S <b> 5 is provided between the outer surface of the inner cap 32 and the inner surface of the outer cap 31. A hole 32a penetrating in the axial direction is formed in the inner cap 32, and the tip of the nozzle 6 is inserted into the hole 32a. The tip of the nozzle 6 is held by the inner surface of the inner cap 32. A seal member S <b> 6 is provided between the outer surface of the tip of the nozzle 6 and the inner surface of the inner cap 32.

  The inner surfaces of the outer cap 31 and the inner cap 32 are spaced from the outer surfaces of the nozzle support portion 13 and the nozzle 6. As a result, a coolant passage P2 through which coolant for cooling the nozzle 6 passes is formed. The coolant passage P2 is connected to the cooling system via a coolant supply pipe and a coolant discharge pipe (not shown).

  The shield cap 33 is inserted into the hole 31 a of the outer cap 31 and covers the tip of the nozzle 6. A seal member S <b> 7 is provided between the outer surface of the shield cap 33 and the inner surface of the outer cap 31. The shield cap 33 has a hole 33 a penetrating in the axial direction and formed coaxially with the hole 6 a of the nozzle 6. Further, an assist gas passage P <b> 3 is formed between the inner surface of the shield cap 33 and the outer surface of the nozzle 6. The assist gas passage P3 is blocked by the seal member S4 with respect to the coolant passage P2, and communicates with the assist gas supply passage P4 formed inside the outer cap 31. The assist gas supply passage P4 is connected to a gas supply system via a gas supply pipe (not shown).

[Detailed structure of electrode]
The detailed structure of the electrode 3 is shown in FIG. FIG. 4 shows a view of the electrode 3 viewed from the bottom surface in a direction orthogonal to the emission surface, and FIG. The electrode 3 includes an electrode base 35 and an electrode material 36. The electrode base 35 is a substantially cylindrical member having a distal end closed and a proximal end opened. The electrode base 35 is made of metal and is made of, for example, copper. One surface of the flange 19 of the electrode base 35 is in contact with the tip of the electrode support portion 12, and the other surface is in contact with the first guide member 4.

  As shown in FIG. 3, a tapered surface 38 and a discharge surface 39 are formed at the tip of the electrode base 35. The tapered surface 38 is formed on the outer peripheral side of the emission surface 39 and has a shape whose diameter increases from the emission surface 39 toward the outer peripheral surface of the electrode base 35 on the proximal end side. And the boundary part of the taper surface 38 and the discharge | release surface 39, ie, the ridgeline 40 of the outer periphery of the discharge | release surface 39, is not chamfering etc., Therefore, it is not a curved surface but an edge. The discharge surface 39 is a flat surface orthogonal to the axis, and a concave portion 41 that is recessed inside is formed at the center. On the back side of the discharge surface 39, a convex portion 43 that protrudes toward the base end portion is formed. As shown in FIG. 1, the tip of the cooling pipe 14 is disposed so as to cover the outside of the convex portion 43.

  As shown in FIGS. 4 and 5, a plurality of grooves 46 having a predetermined length are formed on the outer peripheral edge of the discharge surface 39 from the tapered surface 38 to a part of the discharge surface 39. FIG. 6 shows an enlarged appearance of some of the grooves 46. FIG. 7 shows a view of the groove 46 as seen from the side surface of the ridge line 40.

  The plurality of grooves 46 are arranged at equal intervals in the circumferential direction. Each groove 46 is formed by a cutting tool having a V-shaped cross section at the tip, and has a first side surface 51 and a second side surface 52 that are inclined with respect to the discharge surface 39. As shown in FIG. 7, the first side surface 51 has a first inclination angle (90 ° in this example) with respect to a virtual surface obtained by extending the discharge surface 39 to the groove portion, and the second side surface 52 has the same It has the 2nd inclination angle (30 degrees in this example) smaller than the 1st inclination angle to the virtual plane. More specifically, the discharge surface 39 does not exist in the portion where the groove 46 is formed, but when assuming a virtual surface in which the discharge surface 39 is extended to the groove portion, the first side surface 51 is between this virtual surface. The second side surface 52 has a second inclination angle smaller than the first inclination angle with the same virtual surface.

  Each side surface 51, 52 is triangular. More specifically, as shown in FIG. 6, the first side surface 51 has a first side (bottom side) 51a, a second side 51b, and a third side 51c. The second side surface 52 has a first side (bottom side) 52a, a second side 52b, and a third side 52c. The first sides 51a and 52a of the both side surfaces 51 and 52 are formed by the tool tip and are common. The second sides 51 b and 52 b of the side surfaces 51 and 52 are formed by boundaries (ridge lines) between the side surfaces 51 and 52 and the tapered surface 38. Further, the third sides 51 c and 52 c of the side surfaces 51 and 52 are formed by boundaries (ridge lines) between the side surfaces 51 and 52 and the emission surface 39.

  In the groove 51 as described above, the apex T of the first side surface 51, that is, the boundary (ridge line) 40 between the tapered surface 38 and the discharge surface 39, and the second side 51 b and the third side 51 c of the first side surface 51. The intersection T is a sharper edge than the vertex that is the intersection of the second side 52b, the third side 52c, and the ridge line 40 of the second side surface 52. The intersection T serving as the edge is a starting point of dielectric breakdown. Moreover, the 2nd side surface 52 is arrange | positioned so that the flow of the plasma gas to rotate may be opposed so that FIG. 4 may show. In addition, the arrow in FIG. 4 has shown the direction through which plasma gas flows. By this second side surface 52, the swirling plasma gas is smoothly guided to the center of the electrode.

  When the groove 46 of the electrode 3 as described above is viewed from the bottom surface orthogonal to the emission surface 39, only the second side surface 52 can be observed. That is, each groove 46 is formed from one triangular surface in a bottom view. In this embodiment, the inclination angle of the first side surface 51 is 90 °. However, when the inclination angle is smaller than 90 °, the first side surface 51 and the second side surface 52 are obtained when each groove 46 is viewed from the bottom surface. Can be observed. Therefore, in this case, each groove 46 is formed from two triangular surfaces in a bottom view.

  The electrode material 36 is made of hafnium (Hf), which is a thermionic high emission material. The electrode material 36 is inserted into the recess 41 of the electrode base 35 and fixed by brazing. The electrode material 36 is formed in a substantially cylindrical shape, and a recessed portion 36a that is recessed toward the proximal end side is formed at the distal end portion.

[Operation]
In the plasma torch 1, first, a small flow rate of plasma gas is caused to flow between the electrode 3 and the nozzle 6 to generate a plasma gas flow. That is, the plasma gas is supplied from the gas supply system to the plasma gas passage P <b> 1 between the inner surface of the nozzle support portion 13 and the outer surface of the electrode support portion 12. The plasma gas is guided from the plasma gas passage P1 to the first and second guide members 4 and 5, and flows around the electrode 3 while turning. In this state, when a high voltage is applied to the electrode 3, dielectric breakdown occurs between the curved surface 44 formed on the outer peripheral edge of the discharge surface 39 of the electrode base 35 and the inner surface of the nozzle 6.

  More specifically, dielectric breakdown occurs between the apex T of the first side surface 51 and the inner surface of the nozzle 6 among the plurality of grooves 46 formed on the outer peripheral edge of the discharge surface 39. A pilot arc is generated between the electrode 3 and the inner surface of the nozzle 6 using a dielectric breakdown as a trigger. The pilot arc moves to the center of the electrode along the ridgeline of the third side 51c of the first side surface 51 and along the flow of the plasma gas guided by the second side surface 52 formed in the groove 46. Extend to. And the main arc is produced | generated between the electrode 3 and a workpiece | work by increasing the flow volume and electric current of plasma gas.

  The starting point of dielectric breakdown is the apex T formed in a part of the plurality of grooves 46. When the dielectric breakdown operation is repeatedly performed, the wear of the apex T that has been the starting point proceeds, and the edge is not acute. Then, the apex T of another groove among the plurality of grooves 46 becomes a new dielectric breakdown starting point. In this way, stable dielectric breakdown can be generated over a long period of time.

  In this embodiment, when the swirling plasma gas flowing from the side surface of the electrode 3 passes through the ridge line 40, it passes through the second side 52 b and the third side 52 c of the second side surface 52. At this time, the plasma gas flows smoothly along the second side surface 52, and the flow is not hindered. Therefore, the plasma arc is not disturbed.

  In addition, the first side surface 51 that contributes to dielectric breakdown and the second side surface 52 that contributes to rectification of the flow of plasma gas enable stable dielectric breakdown and transfer of a plasma arc without disturbance.

-Second embodiment-
A second embodiment of the present invention is shown in FIG. The second embodiment is different from the first embodiment only in the electrodes, and the other configuration is the same as the configuration of the first embodiment. Accordingly, only the electrodes will be described below.

The electrode 103 of the second embodiment includes an electrode base 135 and an electrode material 136, as in the first embodiment. These basic configurations are the same as those in the first embodiment. That is, a tapered surface 138 and a discharge surface 139 are formed at the tip of the electrode substrate 135. Further, a concave portion 141 is formed in the central portion of the discharge surface 139, and the central surface including the concave portion 141 is a flat surface 142 orthogonal to the axis. Unlike the first embodiment, a convex portion 143 that protrudes toward the base end portion is formed on the back side of the flat surface 142. A curved surface 144 is formed on the outer peripheral edge of the discharge surface 139. The flat surface 142 at the center of 139 is continuously connected to the tapered surface 138 through the curved surface 144. The curved surface 144 preferably has a radius (curvature radius) of 0.05 mm or more and 50% or less of the diameter of the electrode 103. When the radius of the curved surface 144 is smaller than 0.05 mm, the outer peripheral edge of the emission surface 139 has an edge shape. When a plasma arc is generated at the edge portion due to dielectric breakdown, a phenomenon (trap) occurs in which the plasma arc is restrained by the edge portion and does not move to the electrode material 136 at the center of the emission surface. On the contrary, when the radius of the curved surface 144 is too large and exceeds 50% of the diameter of the electrode 103, the shortest gap portion between the inner surface of the nozzle 6 is not fixed at one point. For this reason, the point at which dielectric breakdown occurs is not constant, and the generation of the plasma arc becomes unstable.

  A plurality of grooves 146 having a predetermined length are formed on the outer peripheral edge of the discharge surface 139 from the tapered surface 138 to the curved surface 144 and the flat surface 142. 9A and 9B show a part of the electrode 103 viewed from the bottom surface in the direction orthogonal to the emission surface 139. FIG. FIGS. 10A and 10B show an enlarged appearance of some of the grooves 146.

  The plurality of grooves 146 are arranged at equal intervals in the circumferential direction. As shown in FIG. 9A, each groove is formed to be inclined by an angle α with respect to a straight line N extending radially around the axis. The angle α is preferably 0 ° or more and 60 ° or less, and particularly preferably an angle along the flow of the swirling plasma gas. FIG. 9B shows a groove 146 ′ having an inclination angle of 0 °.

  Here, when the inclination angle (α) exceeds 60 °, when the plasma arc generated in the groove 146 moves, it is easily trapped again in the adjacent groove. As a result, the plasma arc continues to be restrained in the same manner as in the conventional electrode having the outer peripheral edge of the emission surface as an edge.

  As described above, the plasma gas guided by the second guide member 5 is ejected from the orifice 26 of the nozzle 6 while turning around the electrode 103, so that the inclination of the groove 146 is in the direction in which the plasma gas turns. Most preferred is an angle along. The cross section of the groove 146 may be V-shaped, U-shaped, or rectangular. However, it is preferable that an edge is formed at the groove edge 146a (see FIG. 10) of the curved surface 144 and the flat surface 142. . That is, the groove edge 146a is preferably not chamfered after the groove 146 is formed with a cutting tool.

  Further, although the groove 146 is formed from the curved surface 144 to the flat surface 142, the left side of the groove 146 (on the flat surface 142 side) in the sectional view from the side surface direction of the groove 146 in the curved surface 144 shown in FIG. The angle formed by the wall portion with the curved surface 144 is an obtuse angle, and the angle formed by the right wall portion (the curved surface 144 and the tapered surface 138 side) with the curved surface 144 is an acute angle. In such a groove shape, generation of a plasma arc is facilitated at the right edge portion, and the left wall surface is made smoother without impeding the flow of plasma gas.

  In the electrode base 135, the groove 146 as described above is formed on the outer peripheral edge (curved surface 144) of the discharge surface 139 closest to the inner surface of the nozzle 6, whereby the edge portion that is the edge 146 a of each groove 146 and the inner surface of the nozzle 6. Dielectric breakdown is likely to occur between the two. Then, the plasma arc generated by the breakdown breaks toward the center of the electrode 103 along the edge 146a of the groove 146 and the flow of the plasma gas, and the plasma generated at this time travels along the inner wall of the nozzle to the work side.

  As a specific shape of the groove 146, the groove width is preferably 0.05 mm or more in order to reliably generate a plasma arc over a long period of time. Similarly, in order to reliably generate a plasma arc over a long period of time, the groove depth is preferably 0.05 mm or more.

  According to the experiment results of the present inventors, the arc started smoothly 1000 times or more when the groove width or groove depth was 0.05 mm or more. When the groove width or depth was less than 0.05mm, arc ignition failure occurred several hundred times. On the other hand, if the groove depth is too large, the flow of plasma gas is disturbed and the cutting quality is deteriorated. By making the groove depth smaller than the shortest distance between the electrode and the nozzle, the influence on the flow is sufficiently reduced. Specifically, the plasma gas flow is stabilized by setting the groove depth to 0.5 mm or less. The effect on the gas flow is the same for the groove width. In the case of a V-shaped groove, the groove width must be smaller than the groove depth in order to sufficiently exhibit electric field concentration due to the edge. In other words, by making the groove width 0.5 mm or less, the gas flow is stabilized and the dielectric breakdown is smoothed.

  From the above, specifically, the groove width and the groove depth are preferably 0.05 mm or more for ensuring the generation of the plasma arc, and 0.5 mm or less is preferable for stabilizing the plasma gas flow. . Each groove 146 needs to be formed from the curved surface 144 of the outer peripheral edge of the emission surface 139 toward the center, and the groove length is preferably 0.1 mm or more in order to reliably generate a plasma arc. The groove 146 is preferably suppressed to a length that does not reach the electrode material 36. Specifically, 50% or less of the diameter of the electrode 103 (electrode base 135) is preferable. The reason for this is that the groove 146 only creates a trigger for the plasma arc to move toward the electrode material 36, and then the plasma arc is not restrained by the groove 146 and can move freely on the emission surface 139. This is because the arc moves smoothly. In addition, the groove 146 is indispensable for the emission surface 139, but it is more preferable that the groove 146 is not formed on the tapered surface 138 in order to prevent the flow of plasma gas from being hindered. Further, at least 8 grooves are required.

[Operation]
The basic operation is the same as in the first embodiment. In the second embodiment, dielectric breakdown occurs between edges (edge portions) 146 a of the plurality of grooves 146 formed on the curved surface 144 and the inner surface of the nozzle 6. A pilot arc is generated between the electrode 103 and the inner surface of the nozzle 6 using a dielectric breakdown as a trigger. The pilot arc moves to the center along the edge 146a of the groove 146 and the flow of the swirling plasma gas, and further extends to the workpiece. A main arc is generated between the electrode 103 and the workpiece by increasing the flow rate and current of the plasma gas.

[Experimental example]
FIG. 11 shows a state of the nozzle inner surface when a plasma arc is generated by a conventional electrode and when a plasma arc is generated by the second embodiment of the present invention.

  In FIG. 11, the upper photograph shows the electrode observed from the distal end side (lower side in FIG. 1), and the lower photograph shows the nozzle inner surface observed from the proximal end side (upper side in FIG. 1). FIG. 11A shows a conventional electrode in which an edge is formed on the outer peripheral edge of the emission surface. Here, no groove is formed. FIG. 5B shows an electrode in which a curved surface is formed on the outer peripheral edge of the emission surface, and radial grooves are formed on the tapered surface and the flat surface of the emission surface including the curved surface. FIG. 6C shows an electrode in which a curved surface is formed on the outer peripheral edge of the discharge surface, and a groove that includes this curved surface and is inclined along the flowing direction of the swirling gas is formed on the tapered surface and the flat surface of the discharge surface. .

  The arc start conditions are as follows.

Nozzle orifice diameter: 1.35mm
Start current: 25A
Dielectric breakdown voltage: 20kVp-p, 1.5MHz
Start gas: Type = N ₂ (100%), Pressure = 0.1Mpa, Flow rate = 15LPM
From the experimental results shown in FIG. 11, when the conventional electrode is used (FIG. 11A), the trace of the arc restrained at the edge portion which is the outer peripheral edge of the emission surface can be seen. On the other hand, when the outer peripheral edge of the emission surface is curved and a radial groove is formed ((b) in the same figure), traces of the arc are observed, but are significantly less than the conventional electrodes. Further, when the outer peripheral edge of the emission surface is curved and an inclined groove is formed ((c) in the figure), the trace of the arc is hardly seen.

  From the above, by making the edge of the outer periphery of the emission surface formed in the conventional electrode a curved surface and forming a groove from this curved surface to the center part, the trace of the arc formed on the inner surface of the nozzle is remarkably reduced or almost It turns out that it can be lost. Since the trace of the arc generated on the inner surface of the nozzle is a trajectory of the arc transition, the state of the arc transition can be determined by observing the arc trace. A large amount of arc traces on the inner surface of the nozzle indicates that the plasma arc is constrained at the edge of the electrode. Such plasma arc restraint causes a torch start error and an increase in unnecessary input power. On the contrary, when the trace of the arc is small, it indicates that the generation of a smooth plasma arc and the amount of heat input to the nozzle are small. According to the embodiment of the present invention, it is possible to eliminate the restriction of the plasma arc as described above, reduce the nozzle damage, and extend the life of the nozzle.

[Other Embodiments]
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the summary of invention.

  (a) In the second embodiment, all of the plurality of grooves are inclined by the same angle with respect to the axis extending radially from the center. However, the inclination of the grooves is not limited to the above embodiment. For example, two or more types of grooves having different inclination angles may be formed.

  (b) The shape, size, number, and the like of the grooves formed on the outer peripheral edge of the discharge surface are not limited to the above embodiment.

  (c) The electrode material is not limited to hafnium but may be any material that can withstand the high heat of the pilot arc and plasma arc. However, when a plasma gas containing oxygen is used, it is particularly preferable to use an electrode material made of hafnium. This is because, when hafnium becomes an oxide, its melting point rises and exhibits excellent heat resistance. Further, since zirconium has almost the same properties as hafnium, an electrode material made of zirconium may be used.

Further, depending on the type of workpiece (workpiece), N ₂ (non-oxygen) gas may be used as the plasma gas. In this case, tungsten may be used as the electrode material.

DESCRIPTION OF SYMBOLS 1 Plasma torch 3,103 Electrode 6 Nozzle 35,135 Electrode base 36 Electrode material 36a Electrode material recessed part 38,138 Tapered surface 39,139 Ejection surface 41,141 Electrode base recessed part 42,142 Flat surface 51,52 Side surface 144 of groove | channel (Outer edge of discharge surface)
46, 146, 146 'groove 146a groove edge

Claims (7)

An electrode used in a plasma cutting device,
A discharge surface formed at a tip; a tapered surface formed on an outer peripheral side of the discharge surface; and a plurality of grooves formed from an outer peripheral edge of the discharge surface toward a central portion; Each of the grooves has a first side surface and a second side surface inclined with respect to the emission surface;
An electrode material disposed in the center of the discharge surface of the electrode substrate;
Equipped with a,
The first side surface and the second side surface have a first tilt angle and a second tilt angle with respect to a virtual surface obtained by extending the discharge surface to the groove, and the first tilt angle is the second tilt angle. An electrode for a plasma cutting device , having an edge that is larger than the ridge line that is a boundary between the tapered surface and the emission surface and an intersection of the first side surface . A plasma gas is supplied around the electrode base so as to swivel from the outer periphery toward the center of the emission surface,
The first side surface has an edge serving as a starting point of dielectric breakdown at a boundary portion with the emission surface,
The second side surface is disposed so as to face the swirling plasma gas.
The electrode for a plasma cutting device according to claim 1 . The tapered surface is formed such that the diameter increases as the distance from the discharge surface increases.
Wherein the plurality of each of the grooves, in the direction as viewed perpendicular to the emitting surface, and is formed by two triangular faces, a plasma cutting device electrode according to claim 1 or 2. The tapered surface is formed such that the diameter increases as the distance from the discharge surface increases.
The first inclination angle of the first side surface is 90 °, wherein each of the grooves, in the direction as viewed perpendicular to the emitting surface, and is formed in a triangle-shaped surface, according to claim 1 or 2 2. An electrode for a plasma cutting device according to 1. The electrode for a plasma cutting device according to any one of claims 1 to 4 , wherein a concave portion recessed inside is formed on a tip discharge surface of the electrode material. The electrode for a plasma cutting device according to any one of claims 1 to 5 , wherein the electrode material is hafnium. A plasma torch provided in a plasma cutting device,
An electrode according to any one of claims 1 to 6 ;
A cylindrical nozzle having an electrode facing portion facing the tip portion of the electrode inside and having an orifice formed at the tip;
Plasma torch with