JP2007128677A - Plasma torch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma torch of which interval for exchanging a nozzle is prolonged by prolonging a period for well maintaining a function for slenderly narrowing a plasma arc jet. <P>SOLUTION: A front end part (52) of a protection cap (34) surrounding a tip end part (32A) of the nozzle (32) is made of ceramic. A ring-shaped area (60) surrounding a cap orifice (54) at inner face of the protection cap (34) closely contacts an area surrounding a nozzle orifice (44) at outer face of the nozzle (32). The inner diameter of the cap orifice (54) is the same or almost the same with that of the nozzle orifice (44). The cap orifice (54) slenderly narrows the plasma arc in cooperation with the nozzle orifice (44). Assist gas is injected from a plurality of assist gas injection holes (56) outside the circular area (60) of the protection cap (34). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a plasma torch for plasma processing.

  Plasma processing is widely used for cutting and welding mild steel plates and stainless steel plates. The plasma torch includes a cylindrical nozzle having an orifice at a front end portion and an electrode disposed inside the nozzle. A high-pressure main gas (primary gas, plasma gas) is supplied to the space between the nozzle and the electrode, and a high voltage applied between the nozzle and the electrode causes a pilot arc between the nozzle and the electrode near the nozzle orifice. Generated. The main gas around the pilot arc is turned into plasma by the energy of the pilot arc, and it becomes a high-velocity plasma arc jet through the orifice of the nozzle and is ejected toward the workpiece in front. At the same time, the application of a high voltage between the nozzle and the electrode is switched to the application of a high voltage between the workpiece and the electrode, and thereafter a plasma arc jet ejected from the torch to the workpiece is maintained, Processing starts.

  In order to protect the nozzle from the external environment, a plasma torch in which the outer periphery of the tip of the nozzle is covered with a cap (shield) is known (for example, Patent Documents 1 to 3). Further, in order to electrically insulate the cap (shield) and the nozzle, a member made of a heat-resistant electrical insulating material such as ceramics is disposed between the cap and the nozzle (for example, Patent Documents 1 and 3), Alternatively, it is also known that the cap itself is made of ceramics (for example, Patent Document 2). Also, a secondary gas (assist gas, shield gas) is supplied between the cap (shield) and the nozzle, and the secondary gas is ejected around the plasma arc in the exit orifice through which the plasma arc of the cap passes. Is also known (for example, Patent Document 3). Furthermore, the secondary gas flow between the cap and the nozzle is increased by allowing a part of the secondary gas to escape from the discharge hole provided at a location away from the outlet orifice of the cap, thereby cooling the cap with the secondary gas. It is also known to increase the effect (for example, Patent Document 3).

JP 2000-52043 A JP-A-8-294778 Japanese National Patent Publication No. 2-504603

  The shape and inner diameter of the nozzle orifice affect the shape of the plasma arc jet and affect the processing quality. In general, a performance capable of forming a narrowed plasma arc jet is desired. However, as the number of times or time of use of the plasma torch is increased, the plasma arc jet erodes the inner surface of the orifice and the inner diameter of the orifice gradually expands, so that the performance of narrowing the plasma arc jet gradually decreases. Therefore, it is necessary to replace the nozzles at appropriate intervals. In order to extend the life of the nozzle, it has been proposed to embed ceramic pieces with high heat resistance in the nozzle. However, there is a problem that the ceramic piece easily falls out of the nozzle due to a large difference in thermal expansion coefficient between copper, which is the main material of the nozzle, and ceramics.

  Further, in order to improve the so-called plasma torch adhesion, it is desired that the outer diameter of the plasma torch is thinner. And in order to make a plasma torch narrower, it is desired that the space | interval of the space used as the main gas path between a nozzle and an electrode is narrower. In general, the nozzle and the electrode have a shape in which the rear part far from the orifice is thicker than the front part near the orifice. Therefore, it is important to narrow the distance between the nozzle and the rear part of the electrode. However, in the space between the nozzle and electrode, which is the main gas passage, there is only a gas layer between the nozzle and the electrode. Discharge occurs, and a problem arises that a pilot arc is not generated near the orifice.

  Accordingly, an object of the present invention is to lengthen the period during which the performance of finely squeezing the plasma arc jet can be maintained, in other words, to lengthen the interval for replacing the nozzle.

  Another object of the present invention is to make the distance between the nozzle and the electrode narrower so that the outer diameter of the torch can be made thinner.

  A plasma torch according to the present invention comprises an electrode, a nozzle having a nozzle orifice surrounding the electrode and ejecting a plasma arc jet, and a cap orifice surrounding the nozzle and ejecting the plasma arc jet from the nozzle orifice And a cap having. And the annular region surrounding the inlet of the cap orifice on the inner surface of the cap and the annular region surrounding the outlet of the nozzle orifice on the outer surface of the nozzle are in direct contact or in close contact via an intermediate member. .

  According to this plasma torch, the cap orifice acts like an extension of the nozzle orifice and cooperates with the nozzle orifice to serve to narrow the plasma arc jet. Even if the inner diameter of the nozzle orifice is slightly enlarged due to erosion by the plasma arc jet, the cap orifice can make up for this, and the plasma arc jet can be narrowed down finely. The replacement interval can be lengthened.

  In a preferred embodiment, the inner diameter of the cap orifice is the same as or near the inner diameter of the nozzle orifice. Thereby, the cap orifice effectively narrows the plasma arc jet.

  In a preferred embodiment, the plasma torch further includes an assist gas passage provided inside the cap for flowing an assist gas, but prevents the assist gas from the assist gas passage from entering the cap orifice. It has become. An assist gas ejection hole communicating with the assist gas passage for ejecting the assist gas around the cap orifice is provided outside the annular region of the cap. This structure eliminates the need for the cap orifice to have a function of ejecting the assist gas, so that the cap orifice can easily have an inner diameter suitable for narrowing the plasma arc jet.

  In a preferred embodiment, a front portion of the cap where the cap orifice is provided is made of a heat-resistant electric insulating material, for example, ceramic. As a result, the cap orifice is less likely to be eroded, and the above-described advantages are further utilized.

  In a preferred embodiment, the electrode has a metal electrode body having a front part of the main body and a rear part of the main body having a larger outer diameter, and an electric power covering the outer peripheral surface of the electrode rear part integrated with the electrode body. And an insulating film. By using such an electrode, it becomes easy to narrow the distance between the electrode main body and the nozzle and to further reduce the outer diameter of the plasma torch.

  The present invention also provides an electrode and a nozzle incorporated in the plasma torch having the above-described structure.

  ADVANTAGE OF THE INVENTION According to this invention, the period which can maintain the performance which squeezes a plasma arc jet finely can be lengthened, and the interval which should replace a nozzle can be lengthened.

  Further, when the electrode having the above-described structure is adopted, it becomes easy to make the outer diameter of the torch thinner.

  FIG. 1 is a sectional view taken along the center line of a plasma torch according to an embodiment of the present invention.

  As shown in FIG. 1, the plasma torch 10 has a torch body 12 and a front structure 14, and the front structure 14 is a screw that is screwed into the front end of the torch body 12 at the rear end. The ring 16 is detachably attached to the torch body 12. The torch main body 12 has a substantially cylindrical shape as a whole, and includes a cooling water supply pipe 18, an electrode base cylinder 20, an insulator cylinder 22, and a nozzle base cylinder 24, and these components 18 to 24 are composed of the torch main body 12. Are arranged coaxially in the above order from the center to the outer periphery. A plasma gas supply line 26 and an assist gas supply line 28 are formed in the wall of the nozzle pedestal cylinder 24, and the gas outlets 26 </ b> A and 28 </ b> A of these gas supply lines 26 and 28 are connected to the nozzle pedestal cylinder 24. Open on the front of the. Electrical wiring (not shown) for applying a high voltage for pilot ignition and supplying an arc current for maintaining the main arc is connected to the electrode base cylinder 20 and the nozzle base cylinder 24, respectively. The electrode base cylinder 20 and the nozzle base cylinder 24 are electrically insulated by the insulator cylinder 22. Both the electrode base cylinder 20 and the nozzle base cylinder 24 are made of a metal having high electrical conductivity, such as copper.

  The front structure 14 is generally columnar as a whole and tapers forward. The front structure 14 includes an electrode 30, a nozzle 32, and a protective cap 34, and these components 30 to 34 are coaxially arranged in the above order from the center of the front structure 14 toward the outer periphery. .

  Most of the electrode 30 is an electrode body 36, which is pipe-shaped and has a cooling water channel 38 inside thereof. The material of the electrode body 36 is a metal having high electrical conductivity, such as copper. The front portion 36A of the electrode body 36 is tapered forward, the front end portion thereof is closed, and an insert 40 made of a refractory metal such as hafnium, zirconium, tungsten, or an alloy thereof is embedded in the central axis position of the front end portion. . The rear portion 36B of the electrode body 36 has an opening 36C communicating with the cooling water passage 38, the front end portion of the electrode base cylinder 20 described above is inserted into the opening 36C, and the cooling water supply pipe 18 described above is connected to the cooling water passage 38. Inserted inside. The inner peripheral surface and the rear end surface of the rear portion 36B of the electrode main body 36 are in close contact with the outer surface of the front end portion of the electrode pedestal tube 20, and thereby the electrode main body 36 is electrically connected to the electrode pedestal tube 20.

  The outer diameter of the electrode body 36 is larger at the rear portion 36B than at the front portion 36A. The outer peripheral surface of the rear portion 36B having a thick outer diameter is covered with a thin cylindrical insulator film 42 over the entire periphery. The insulator film 42 may be a thin synthetic resin tube such as a heat-shrinkable tube that is externally fitted to the rear portion 36B of the electrode body 36, or may be formed on the outer peripheral surface of the rear portion 36B of the electrode body 36, for example. It may be a thin film of an insulating material such as ceramics formed by a method such as thermal spraying, vapor deposition, or sputtering. In any case, the insulator film 42 is integrated with the electrode body 36 and forms a part of the electrode 30.

  The material of the nozzle 32 is a metal having high electrical conductivity, such as copper. The nozzle 32 has a substantially cylindrical shape and is tapered forward, and a rear end portion thereof forms a flange 32B. The rear surface of the flange 32B is in close contact with the front end surface of the nozzle base tube 24 described above, and the nozzle base tube 24 is electrically connected. Connect. The nozzle 32 surrounds substantially the entire outer periphery of the electrode 30 while being separated from the electrode 30. A nozzle orifice 44 is provided at the central axis position of the front end portion 32 </ b> A of the nozzle 32. A space between the nozzle and the 32 electrode 30 is a plasma gas passage 46 and surrounds almost the entire outer periphery of the electrode 30. The plasma gas passage 46 extends along the inner surface of the nozzle 32 from the rear end to the front end of the nozzle 32, communicates with the plasma gas supply line 26 described above at the rear end, and communicates with the nozzle orifice 44 at the front end. To do. The plasma gas passage 46 extends along the outer surface of the electrode 30 from the rear portion where the insulator film 42 of the electrode 30 is present to the front end portion where the insert 40 is present. The distance between the electrode 30 and the nozzle 32 in the plasma gas passage 46 is minimum at a specific location of the insulator film 42 at the rear portion of the electrode 30 and is second smallest at a location near the insert 40 at the front end portion. However, the presence of the insulator film 42 has the lowest dielectric breakdown voltage in the vicinity of the insert 40 having the second smallest distance, and the pilot arc is most likely to occur there.

  Similar to the nozzle 32, the protective cap 34 has a substantially cylindrical shape and is tapered forward, and at the rear end surface thereof, is closely attached to the front surface of the flange 32 </ b> B of the nozzle 32. The protective cap 34 serves to protect the nozzle 34 from the external environment, and surrounds almost the entire outer periphery of the nozzle 32. The protective cap 34 includes a cylindrical cap body 50 that forms a central portion from the rear portion of the protective cap 34, and a cup-shaped heat-resistant portion 52 that is integrally fixed to the front end of the cap body 50. The material of the cap body 50 is a material having a high rigidity and a lower coefficient of thermal expansion than the material of the nozzle 32 (for example, copper), for example, steel. The material of the heat-resistant portion 52 is an electrically insulating material, such as ceramic, which has higher heat resistance than the material of the nozzle 32 (for example, copper) and also has high resistance to erosion by the plasma jet. The cap body 50 has a flange 50A at its rear end. The claw portion 16A at the front end of the screw ring 16 described above is engaged with the flange 50A, and the screw ring 16 fixes the protective cap 34 and the nozzle 32 on the nozzle base cylinder 24. The heat-resistant portion 52 of the protective cap 34 covers the entire front end portion 32A of the nozzle 32 from the outside. The heat-resistant part 52 includes a front wall part 52 </ b> A and a side wall part 52 </ b> B that rises from the outer peripheral edge of the front wall part 52.

  FIG. 2 is a front view of the front wall portion 52A of the heat-resistant portion 52 as viewed from the front.

  As shown in FIGS. 1 and 2, a cap orifice 54 is provided at the position of the central axis of the front wall portion 52 </ b> A, and the cap orifice 54 communicates with the nozzle orifice 44. An annular region 60 that surrounds the inlet of the cap orifice 54 over the entire circumference on the rear surface (inner surface) of the front wall 52 </ b> A is located around the outlet of the nozzle orifice 44 on the front surface (outer surface) of the front end 32 </ b> A of the nozzle 32. It directly adheres to the annular region that surrounds it. Thereby, the assist gas does not flow into the cap orifice 54, and the cap orifice 54 looks like an extension of the nozzle orifice 44. The inner diameter of the cap orifice 54 is approximately the same as or close to the inner diameter of the outlet of the nozzle orifice 44. A plurality of assist gas ejection holes 56 are provided so as to surround the cap orifice 54 at a position separated from the cap orifice 54 of the front wall portion 52A in the radial direction by the annular region (hereinafter referred to as a close contact region) 60. .

  As a modification, as shown in FIG. 3, an annular region 60 around the inlet of the cap orifice 54 on the inner surface of the front wall 52A, and a corresponding circle around the outlet of the nozzle orifice 44 on the outer surface of the nozzle 32. An annular intermediate member 70 is inserted between the annular region so as to relay the cap orifice 54 and the nozzle orifice 44, and this intermediate member 70 is connected to the annular region 60 around the inlet of the cap orifice 54 and the nozzle orifice 44. The annular region 60 around the inlet of the cap orifice 54 and the annular region around the outlet of the nozzle orifice 44 are in close contact with each other via the intermediate member 70. ) It may be as follows. Thereby, the assist gas does not flow into the cap orifice 54, and the cap orifice 54 looks like an extension of the nozzle orifice 44.

  As shown in FIG. 1, the portion of the protective cap 34 that is present outside the annular region 60 that is in close contact with the front end surface of the nozzle 32 described above, that is, the side wall portion 52 </ b> B of the heat-resistant portion 52 and the cap body 50 are connected to the nozzle 32. The outer periphery of the nozzle 32 is surrounded in a state of being separated from the nozzle 32. A space between the portions 52 </ b> B and 50 of the protective cap 34 and the nozzle 32 is an assist gas passage 58 and surrounds the outer periphery of the nozzle 32. The assist gas passage 48 extends along the inner surface of the protective cap 34 from the rear end to the front end of the protective cap 34, communicates with the plurality of assist gas ejection holes 56 described above at the front end, and caps at the rear end. The main body 50 communicates with an assist gas introduction hole 62 provided in the wall at the rear portion of the flange 50A. Further, an assist gas relay path 64 is formed between the portion of the cap body 50 behind the flange 50A and the screw ring 16, and the assist gas relay path 64 is connected to the assist gas supply pipe 28 and the assist gas introduced above. It communicates with the hole 62.

  The operation of the plasma torch 10 configured as described above will be described below.

  In order to make the outer diameter of the plasma torch 10 as thin as possible, the nozzle 32 is also designed to be as thin as possible. Therefore, as shown in FIG. 1, if the electrode 30 extends from the rear part to the front end part along the outer surface of the electrode 30, the electrode body 30 has a large outer diameter between the rear part 36 </ b> B and the nozzle 32 in the plasma gas passage 46. Is so small that it is comparable to the distance between the front end of the electrode body 36 where the pilot arc is to be generated and the nozzle 32. In particular, the distance between the electrode 30 and the nozzle 32 is minimized at a specific portion of the portion covered with the electrical insulating film 42 at the rear of the electrode 30 (the front edge of the electrical insulating film 42 in this embodiment). The distance is the second smallest in the vicinity of the insert 40 at the front end of the electrode 30. However, due to the action of the insulator film 42 covering the rear portion 36B of the electrode body 30 over the entire circumference, the breakdown voltage at the minimum distance is higher than the breakdown voltage at the front end portion of the electrode 30, and thus the electrode 30 When a high voltage for pilot arc ignition is applied between the nozzle 30 and the nozzle 32, no discharge occurs at the rear portion of the electrode 30, and the pilot arc is reliably generated at a location near the insert 40 at the front end portion of the electrode 30. Can be generated.

  By the way, conventionally, a structure in which an electrode and a nozzle are electrically insulated by interposing an insulating block, which is a component separate from the electrode and the nozzle, between the electrode and the nozzle has been widely adopted. (For example, Patent Documents 1 and 2). In this conventional structure, the thickness of the insulator block is an obstacle to designing the nozzle 32 to be thin. On the other hand, in the plasma torch 10 shown in FIG. 1, the insulating film 42 integrated with the electrode main body 30 can use the electrode main body 30 as a support, so that the flexible film such as soft synthetic resin or rubber can be used. It is possible to form a material much thinner than a conventional insulator block by using a certain material or using a thin film forming technique such as thermal spraying, vapor deposition or sputtering. Therefore, the nozzle 32 can be made thinner and the outer diameter of the plasma torch 10 can be made thinner.

  As shown in FIG. 1 or FIG. 3, the nozzle of the front end portion 32 </ b> A of the nozzle 32 is formed in an annular region 60 where the front wall portion 52 </ b> B of the heat-resistant portion 52 of the protective cap 34 surrounds the inlet of the cap orifice 54. It is in direct contact with the annular region surrounding the outlet of the orifice 44 or in close contact with the intermediate member 70. Therefore, the cap orifice 54 is isolated from the assist gas passage 58, and only the plasma arc jet ejected from the nozzle orifice 44 flows into the cap orifice 54, and the assist gas does not flow. The assist gas is ejected from an assist gas ejection hole 56 different from the nozzle orifice 44 to form an assist gas curtain surrounding the plasma arc jet. The inner diameter of the cap orifice 54 is only about the same size as or the vicinity of the inner diameter of the nozzle orifice 44. In other words, the inner diameter of the cap orifice 54 is not as large as the inner diameter of the nozzle orifice 44 as would be the case if assist gas was allowed to flow through the cap orifice 54. Therefore, the cap orifice 54 functions as an extension of the nozzle orifice 44, that is, functions like a nozzle orifice 44 to narrow the plasma arc jet. As the number of times or hours of use of the plasma torch 10 increases, the nozzle orifice 44 gradually wears and expands due to erosion by the plasma arc jet. However, since the cap orifice 54 is surrounded by a material having higher heat resistance and erosion resistance such as ceramics than the material of the nozzle 32 (for example, copper), it does not expand as easily as the nozzle orifice 44. Therefore, even if the nozzle orifice 44 is somewhat consumed and enlarged, the cap orifice 54 still narrows the plasma arc jet finely, so that the processing quality can be maintained well over a longer period. As a result, the replacement interval of the nozzle 32 also becomes longer.

  Incidentally, according to the prior art, not only the plasma arc jet flows through the cap orifice, but also the assist gas flows so as to surround the plasma arc jet. The inner diameter of the cap orifice must be larger than the inner diameter of the nozzle orifice by the amount necessary to flow the assist gas. Therefore, the cap orifice cannot perform the function of narrowing the plasma arc jet.

  Further, the joint location between the cap body 50 and the heat-resistant portion 52 of the protective cap 34 is not as hot as the nozzle 32. In addition, the material of the cap body 50 has a smaller coefficient of thermal expansion than the material of the nozzle 32. Therefore, unlike a conventional nozzle embedded with ceramic, there is substantially no problem that the heat-resistant portion 52 is detached from the cap body 50.

  As mentioned above, although embodiment of this invention was described, this embodiment is only the illustration for description of this invention, and is not the meaning which limits the scope of the present invention only to this embodiment. The present invention can be implemented in various other modes without departing from the gist thereof.

1 is a cross-sectional view taken along the center line of a plasma torch 10 according to an embodiment of the present invention. The front view of front wall part 52A of the protective cap 52 of the torch 10. Sectional drawing of the nozzle 32 and the protective cap 34 which shows the modification of the torch 10. FIG.

Explanation of symbols

30 Electrode 32 Nozzle 36 Electrode body 36A Electrode body front part 36B Electrode body rear part 34 Protective cap 42 Insulator film 44 Nozzle orifice 46 Plasma gas passage 54 Cap orifice 56 Assist gas ejection hole 58 Assist gas passage 60 Annular region 70 Intermediate member

Claims (10)

An electrode (30);
A nozzle (32) having a nozzle orifice (44) for enclosing the electrode and for emitting a plasma arc jet;
A cap (34) having a cap orifice (54) surrounding the nozzle and ejecting the plasma arc jet from the nozzle orifice (44);
With
An annular region (60) surrounding the inlet of the cap orifice (54) on the inner surface of the cap (34) and an annular region surrounding the outlet of the nozzle orifice (44) on the outer surface of the nozzle (32) are directly A plasma torch (10) that is in close contact with or through an intermediate member. The plasma torch (10) according to claim 1, wherein
A plasma torch (10) wherein the inner diameter of the cap orifice (54) is the same as or near the inner diameter of the nozzle orifice (44). The plasma torch (10) according to claim 1, wherein
An assist gas passage (58) for flowing an assist gas provided inside the cap;
Assist gas from the assist gas passage (58) does not enter the cap orifice (54),
An assist gas ejection hole (56) communicating with the assist gas passage (58) and for ejecting the assist gas around the cap orifice (54) is provided in the annular region (60) of the cap (34). A plasma torch (10) provided outside. The plasma torch (10) according to claim 1, wherein
A plasma torch (10) in which a front portion (52) provided with the cap orifice (54) in the cap (34) is made of a heat-resistant electrical insulating material. The plasma torch (10) according to claim 1, wherein
The electrode (30) is
A metal electrode main body (36) having a main body front portion (36A) and a main body rear portion (36B) having an outer diameter larger than that of the main body front portion (36A);
A plasma torch (10) having an electric insulating film (42) that covers the outer peripheral surface of the rear portion (36B) of the main body integrated with the electrode main body (36). A nozzle (32) for the plasma torch (10) according to claim 1. A nozzle (32) according to claim 1,
The electrode (30) includes a metal electrode main body (36) and an electric insulating film (42) that is integrated with the electrode main body (36) and covers the outer peripheral surface of the main body rear portion (36B). And
The nozzle (32) forms a plasma gas passage (46) between the nozzle (32) and the electrode (30);
The nozzle (32) in which the plasma gas passage (46) extends along the outer surface of the electrode (30) from the portion of the electrode (30) where the electrical insulating film (42) is present to the front end. Electrode (30) for a plasma torch (10) according to claim 1,
A metal electrode body (36);
An electrode (30) provided with an electrical insulating film (42) that covers the outer peripheral surface of the rear portion (36B) of the main body integrated with the electrode main body (36). Electrode (30) according to claim 8,
The electrode main body (36) has a main body front portion (36A) and a main body rear portion (36B) having a larger outer diameter than the main body front portion (36A),
An electrode (30) in which the electrical insulating film (42) covers the outer peripheral surface of the rear portion (36B) of the main body. Electrode (30) according to claim 8,
A plasma gas passage (46) for flowing a plasma gas is formed between the nozzle (32) and the nozzle (32).
The electrode (30) in which the plasma gas passage (46) extends along the outer surface of the electrode (30) from the portion of the electrode (30) where the electrical insulating film (42) is present to the front end.

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