EP0496733B1 - Ajutage perfectionne pour torche a arc de plasma - Google Patents

Ajutage perfectionne pour torche a arc de plasma Download PDF

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Publication number
EP0496733B1
EP0496733B1 EP90911719A EP90911719A EP0496733B1 EP 0496733 B1 EP0496733 B1 EP 0496733B1 EP 90911719 A EP90911719 A EP 90911719A EP 90911719 A EP90911719 A EP 90911719A EP 0496733 B1 EP0496733 B1 EP 0496733B1
Authority
EP
European Patent Office
Prior art keywords
nozzle
electrode
plasma arc
angle
exit port
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP90911719A
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German (de)
English (en)
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EP0496733A1 (fr
EP0496733A4 (fr
Inventor
Nicholas A. Sanders
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hypertherm Inc
Original Assignee
Hypertherm Inc
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Filing date
Publication date
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Publication of EP0496733A4 publication Critical patent/EP0496733A4/fr
Publication of EP0496733A1 publication Critical patent/EP0496733A1/fr
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Publication of EP0496733B1 publication Critical patent/EP0496733B1/fr
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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H05H1/3478—Geometrical details
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/30—Plasma torches using applied electromagnetic fields, e.g. high frequency or microwave energy

Definitions

  • the present invention relates to plasma arc torches, and more particularly to an improved nozzle construction for initiating an arc in such torches utilizing a high voltage, high frequency signal applied to either an electrode or to the nozzle.
  • the oldest, and most widely used method is the high frequency, high voltage spark discharge method.
  • the high voltage, high frequency generates charge carriers which create an electrical current path in the gas in the gap between the cathode and the electrode to establish D.C. flow of current, a pilot arc discharge.
  • the electrode In prior art plasma arc torches the electrode has traditionally had a generally cylindrical configuration, whether a cylindrical disk seated in a solid copper tube as described in the aforementioned U.S. Patent Nos. 3,641,308, 4,203,022 or the electrode-nozzle arrangement shown and described in U.S. Patent Nos. 4,421,970; 4,791,268; and 4,861,962.
  • the lower end of the electrode adjacent the nozzle typically has a cylindrical configuration.
  • the immediately opposite nozzle surface typically mirrors the outer configuration of the electrode, or is smooth, conical and downwardly coverging.
  • the nozzle includes a central exit port where the plasma arc exits the torch and attaches to the workpiece. It is significant that while the transition between the interior nozzle surface and the exit port may be a sharp corner, and while this corner may be closely spaced from the electrode, it is not located in a region where it is closer to the electrode than immediately adjacent portions of the nozzle.
  • US-A-4282418 describes a low power plasma arch torch for micro plasma welding according to the preamble of claim 1 and comprising a nozzle member according to the preamble of claim 9 and having an exit port and a needle point electrode, the exit port being provided with a raised annular edge facing the electrode such that the needle point is closest to the nozzle at the annular edge.
  • Another principal object is to reduce electrode wear as compared to comparable prior art nozzles in comparable torches operated under the same conditions.
  • Yet another principal object of this invention is to reduce the breakdown potential required to initiate an arc discharge in a given plasma arc torch.
  • a further object in the present invention is to provide a nozzle construction which reduces electromagnetic interference during the high frequency, high voltage start up with other electrical and electronic components in the operating area.
  • a still further object of the present invention is to provide a nozzle construction with the foregoing advantages which is simple in construction, has a comparatively low cost of manufacture, and can be used as a replacement part for conventional nozzle of existing plasma arc torches.
  • a plasma arc torch and a nozzle have the features outlined respectively in claims 1 and 9.
  • a plasma arc torch includes an electrode and a nozzle mounted in a mutually spaced relationship at one end of the torch adjacent a workpiece. They are also mounted symmetrically with respect to the torch and each other about a common longitudinal axis. A flow of an ionizable gas passes through the torch and exits a central exit port in the nozzle which is aligned opposite the lower end of the electrode.
  • a DC power supply is attached to the electrode and the nozzle and a high frequency, high voltage coil/generator is electromagnetically coupled to either the negative or positive output of the DC power supply.
  • the nozzle which is typically cup-shaped, receives the electrode within the nozzle with a generally uniform spacing between the electrode in the opposite surfaces of the nozzle.
  • the interior surface of the nozzle facing the electrode has a convex, inwardly projecting, circumferentially extending solid angle or "angle kink" portion.
  • This angle kink is characterized by a minimum radius of curvature (whether a sharp corner, a rounded corner, or even some more complex cross-sectional shape) for a narrow annular region of this surface immediately opposite to the electrode and adjacent the central exit port of the nozzle.
  • This annular region defines the location of preferential initiation of the plasma arc discharge.
  • This kink angle is located at the closest approach between the electrode and the nozzle, and is displaced from the angle formed by the intersection of the central exit port in the nozzle and the interior surface of the nozzle.
  • the angle kink is formed by the intersection of two conical surfaces having different angles of inclination with respect to the longitudinal axis. Comparatively flat angle kinks, e.g. one with an included angle of about 165° are effective.
  • the electrode also has an outwardly projecting angle kink formed by the cylindrical side surface, or a conical transition surface of the lower end of the electrode, and a planar end face oriented perpendicular to the longitudinal axis.
  • the electrode angle kink is also located at the point of closest approach between the electrode and the nozzle and it opposes the angle kink on the nozzle.
  • the electrode and nozzle angle kinks are centered in circumferentially extending annular regions.
  • a plasma arc torch 10 having a nozzle 12 and an electrode 14 is connected to a DC power supply 16. As shown, the positive output of the power supply 16 is connected by lead 18 to the nozzle 12 and the negative side of the power supply 16 is connected by lead 20 to the electrode 14.
  • the plasma arc torch 10 can be any of a wide variety of currently available torch designs in the prior art. Suitable constructions are shown, example, in the aforementioned U.S. Patent Nos. 3,641,308; 4,203,022; 4,791,268; and 4,861,962.
  • a high-frequency coil 22 can be coupled electromagnetically to either the positive lead 18, as shown, or the negative lead 20.
  • the high-frequency coil/generator produces a high-voltage, high-frequency signal which is transmitted over the lead to the nozzle or the electrode.
  • the high-frequency coil generator is of well known, conventional construction, as is the DC power supply.
  • a typical high voltages produced by the coil/generator 22 are in the range typically 5,000 volts at frequencies in the range of 2 to 3 mHz.
  • a flow 24 of an ionizable gas is initiated through an electrode-nozzle chamber 25 exiting the torch through an exit port 44 in the lower face of the nozzle. It assumes a swirling flow path 24a between the lower end of the electrode and the nozzle just before it exits port 44 in the nozzle.
  • a high level oscillating electric field will be generated between the electrode 14 and the nozzle 12.
  • a significant aspect of the present invention is that the interior surface 26 of the nozzle has circumferentially extending (closed loop) projection or peak which is termed herein an angle kink 28. It is significant this angle kink 28 is located at the point of closest spacing between the nozzle 12 and the electrode 14, and represents a line of localized minimum gap separation between the electrode and the nozzle -- as compared, for example, to prior art constructions where the corner associated with the nozzle exit port may have a minimum radius of curvature, but is no closer to the electrode than adjacent portions of the surface. It has been found that this construction reduces the breakdown voltage between a narrow annular region 30 centered on the angle kink 28 and a narrow annular region 32 centered on an electrode angle kink 34.
  • the electrode 14 has a conical tapered end surface 36 and a planar end face 38 oriented perpendicular to a common longitudinal axis 40 of the torch, the nozzle 12, and the electrode 14.
  • the intersection of the surface 36 and the end face 38 defines the angle kink 34.
  • the intersection of conical surface 26a (having an angle A of inclination of about 45° from the axis 40, as shown) and conical surface 26b (having an angle B of inclination of about 60° from the axis 40, as shown) defines the angle kink 28.
  • the angle kink therefore has an included angle of 165° and has a line intersection which is not rounded.
  • angle kinks 28 and 34 and their associated regions 30 and 32 are separated by a gap 42 in an electrode-nozzle chamber 25. While the angle kink 28 and 34 are shown as being directly opposite one another, and this is the preferred embodiment, such a precise opposite alignment is not essential to the operation of this invention.
  • the gap 42 between the angle kinks 28 and 34 is the point of closest spacing between the nozzle and the electrode, at least in the region immediately adjacent the angle kinks.
  • the application of the high frequency to the nozzle 12 over the positive lead 18 concentrates the electric field strength at the nozzle angle kink 28 and provides a reliable breakdown in the zone between the annular regions 30 and 32.
  • the angle kink 28 formed on the interior 36 of the nozzle has a minimum radius of curvature as compared to the radius of curvature of the adjoining portions of the surface so as to create a protrusion which produces the electric field enhancement discussed above.
  • the angle kink 34 on the electrode should have the smallest radius in the immediate region adjoining the point of closest spacing between the electrode and the nozzle at the gap 42.
  • the breakdown voltage can be reduced between the annular regions 32 and 30 with respect to the remainder of the electrode-nozzle chamber 25.
  • an angle kink 34 on the electrode and an angle kink 28 on the nozzle that are each characterized by a minimum radius of curvature, then there will be a strong electric field enhancement that the electrode angle kink 34 which tends to concentrate the electric field strength between the annular regions 30 and 32.
  • This enhanced field strength in turn both assures that breakdown will occur between the zones across the gap 42 and that the breakdown potential will be reduced as compared to the potential required if the nozzle 12 had a simple conical configuration as depicted in Fig. 3.
  • Fig. 4 illustrates alternative embodiment of the present invention where the nozzle has a generally cylindrical interior configuration formed by a cylindrical side wall 12a' and a lower end wall 12b' that includes the exit port 44' (like parts being identified with the same reference number in the different embodiments).
  • the nozzle 12' is spaced symmetrically from the electrode 14'.
  • the nozzle end wall 12b' is spaced closer to the opposite surface of the electrode than the side wall 12a'.
  • An angle kink 28' is formed on the inner surface 26' of the nozzle by the intersection of the generally planar inner surface portion 26a' defining the end wall 12b' and a conical surface 26b' extending between the exit port 44 and the inner surface portion 26a'.
  • the conical surface 16b' is typically inclined at about 10° from the plane of the surface portion 26b'.
  • the angle kink 28' is located at appoint of closest spacing from the electrode 14', and preferably directly opposite an angle kink 34' formed on the lower end of the electrode. As shown, the angle kink 34' is the circumferentially extending solid angle defined by the intersection of a conical surface 36' and an end surface 38'.
  • the electrode 14' has a cylindrical electron emitting insert 48 at the center of its lower end face 38', directly opposite the exit port 44.
  • the angle kinks 28' and 32' are centered in narrow annular regions 30', 32' which define a zone in which the plasma arc discharge will preferentially occur.
  • the gap 42' between the angle kinks 28' and 34' is a point of closest approach.
  • the nozzle construction of the present invention when used with a 200 ampere plasma torch of the type sold by Hypertherm, Inc. under the trade designation MAX 200, reduced the maximum breakdown potential by as much as 10% and reduced electrode wear by as much as 30%. Comparable reductions have been obtained with other torches under standard conditions. Moreover, the pilot arc discharge has been found to occur preferentially and reliably within a zone defined at its end by the annular regions 30 and 32.
  • angle kink on the nozzle has been described as formed by the intersection of combinations of conical and planar surfaces, it may be formed with a rounded cross-section, a rounded cross-section with a circumferentially extending ridge at its "peak", or a variety of other configurations which produce a protrusion with a minimum radius of curvature, in cross section, located at a point of closest spacing to the opposed cathode, or anode, and with this closest spacing being a localised point of minimum spacing.
  • angle kinks have been described and illustrated for the nozzle and electrode as being circumferentially extending, they could be formed to extend in annular displacement over less than 360° about the axis 40.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Geometry (AREA)
  • Plasma Technology (AREA)
  • Arc Welding In General (AREA)

Abstract

Une torche à arc de plasma met en ÷uvre une électrode (14) et un ajutage (12) séparés par un espacement, symétriquement autour d'un axe longitudinal (40) commun, à une extrémité de la torche (10) adjacente à une pièce. La surface intérieure (26) de l'ajutage (12) présente une partie saillante (28) annulaire dirigée vers l'intérieur et située en regard de l'électrode (14) et en un point d'espacement très étroit entre l'électrode (14) et l'ajutage (12). La partie saillante, ou 'coque d'angle' (28), est caractérisée par un rayon de courbure minimal comparé aux rayons de courbure des parties adjacentes de l'ajutage (12) en regard de ladite électrode (14). La surface intérieure (26) est adjacente à un passage de sortie central (44) de l'ajutage (12) et la coque d'angle (28) est espacée de l'intersection de l'orifice de sortie (44) et de l'ajutage intérieur (26). Dans la forme d'exécution préférée, la surface d'ajutage intérieure (26) est formée par deux surfaces coniques ayant chacune des inclinaisons différentes par rapport à l'axe longitudinal (40) de manière à former, au niveau de leur plan d'intersection, la coque d'angle (28) s'étendant circonférentiellement.

Claims (10)

  1. Torche à arc de plasma (10) fonctionnant dans un mode de transfert de l'arc sur une pièce de travail, mais s'amorçant tout d'abord dans un mode d'arc pilote dans lequel une lance (12, 12') agit en coopération avec une électrode (14, 14') montée, avec la lance (12, 12'), dans une relation d'espacement à une extrémité de la torche, de manière à amorcer une décharge d'arc de plasma dans un courant de gaz ionisable passant entre l'électrode et la lance, l'électrode (14, 14') ayant une configuration généralement cylindrique ; la lance (12) comprenant un élément conducteur muni d'un orifice de sortie central (44, 44') opposé à une surface d'extrémité (38) de l'électrode de façon que l'arc de plasma, lorsqu'il s'attache à la pièce de travail, soit fixé par l'électrode ;
       caractérisée en ce que la surface d'extrémité (38, 38') de l'électrode (14, 14') est généralement transversale par rapport à son axe longitudinal (40, 40'), et en ce que l'élément conducteur comprend une surface (26, 26') venant en face de l'électrode au voisinage mais en étant espacée de l'orifice de sortie, cet élément conducteur comportant une pliure d'angle (28, 28') formée dans celui-ci et placée en un point d'espacement minimum entre l'électrode (14, 14') et la lance (12, 12') de manière à produire l'arc pilote préférentiellement et de façon fiable dans la zone de la pliure d'angle (28, 28'), avec un potentiel de claquage réduit lorsqu'on applique un signal à haute tension et haute fréquence aux bornes de l'électrode et de la lance.
  2. Torche à arc de plasma (10) selon la revendication 1, caractérisé en ce que la pliure d'angle (28, 28') : (1) présente un rayon de courbure convexe minimum comparativement au rayon de courbure des parties adjacentes de la surface et (2) est positionnée en un point d'espacement minimum (42) entre l'électrode (14, 14') et la lance (12, 12').
  3. Torche à arc de plasma (10) selon la revendication 1 ou la revendication 2, caractérisée en ce que l'électrode (14, 14') et la lance (12, 12') ont des surfaces extérieure (36, 36') et intérieure (26, 26') venant respectivement en face l'une de l'autre de part et d'autre de l'espacement (42), la surface intérieure (26, 26') de la lance étant placée au voisinage mais en étant espacée de l'orifice de sortie (44, 44'), et les surfaces intérieure et extérieure présentant chacune une pliure d'angle (28, 28' ; 34, 34') formée dans celle-ci.
  4. Torche à arc de plasma (10) selon la revendication 1 ou la revendication 2, caractérisée en ce que la pliure d'angle (28, 28') s'étend de façon continue suivant un chemin en boucle fermée orienté d'une façon générale transversalement par rapport à l'axe longitudinal.
  5. Torche à arc de plasma (10) selon la revendication 1, 2, ou 3, caractérisée en ce que la pliure d'angle (28, 28'; 34, 34') est formée par l'intersection d'une première surface conique (26a, 26a') et d'une seconde surface (26b, 26b').
  6. Torche à arc de plasma (10) selon la revendication 5, caractérisée en ce que la seconde surface (26b, 26b') est également conique mais présente une pente différente de celle de la première surface conique (26a, 26a') par rapport à l'axe longitudinal (40, 40').
  7. Torche à arc de plasma (10) selon la revendication 3, caractérisée en ce que la pliure d'angle (34, 34') formée sur l'électrode (14, 14') est placée dans une partie de cette électrode qui, en fonctionnement normal, est soumise à une faible usure et se trouve adjacente mais en étant espacée latéralement par rapport à la partie de l'électrode (38, 38') située juste au-dessus de l'orifice de sortie (44, 44') de la lance.
  8. Torche à arc de plasma (10) selon la revendication 3 ou la revendication 7, caractérisée en ce que la pliure d'angle (34, 34') de l'électrode et la pliure d'angle (28, 28') de la lance sont dans une relation d'espacement l'une en face de l'autre en un point de séparation minimum entre l'électrode (14, 14') et la lance (12, 12').
  9. Lance (12) pour torche à arc de plasma (10), comportant une première surface intérieure essentiellement cylindrique (26), une partie d'extrémité transversale contenant un orifice de sortie (44) coaxial avec l'axe longitudinal de la surface intérieure (26), et une seconde surface (26a, 26b) s'étendant entre la surface cylindrique intérieure (26) et l'entrée de l'orifice de sortie (44), lance caractérisée en ce que la seconde surface (26a, 26b) est définie par une première partie (26b) partant de la surface cylindrique (26) sous un premier angle d'inclinaison (B) par rapport à l'axe longitudinal, et une seconde partie (26a) partant de l'entrée de l'orifice de sortie (44) sous un second angle d'inclinaison (A) par rapport à l'axe longitudinal, le premier angle d'inclinaison (B) étant supérieur au second angle (A), la jonction de la première partie et de la seconde partie (26b, 26a) de la seconde surface formant un sommet espacé radialement de l'orifice de sortie (44).
  10. Lance (12) selon la revendication 9, destinée à être utilisé dans un chalumeau à arc à plasma (10) selon l'une quelconque des revendications 1 à 8.
EP90911719A 1989-10-20 1990-07-20 Ajutage perfectionne pour torche a arc de plasma Expired - Lifetime EP0496733B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US42467589A 1989-10-20 1989-10-20
US424675 1989-10-20
PCT/US1990/004112 WO1991005629A1 (fr) 1989-10-20 1990-07-20 Ajutage perfectionne pour torche a arc de plasma

Publications (3)

Publication Number Publication Date
EP0496733A4 EP0496733A4 (fr) 1992-06-03
EP0496733A1 EP0496733A1 (fr) 1992-08-05
EP0496733B1 true EP0496733B1 (fr) 1995-08-16

Family

ID=23683469

Family Applications (1)

Application Number Title Priority Date Filing Date
EP90911719A Expired - Lifetime EP0496733B1 (fr) 1989-10-20 1990-07-20 Ajutage perfectionne pour torche a arc de plasma

Country Status (6)

Country Link
EP (1) EP0496733B1 (fr)
JP (1) JPH05502189A (fr)
AU (1) AU628617B2 (fr)
CA (1) CA2065431C (fr)
DE (1) DE69021736T2 (fr)
WO (1) WO1991005629A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH687354A5 (it) * 1992-06-18 1996-11-15 Rodasky Etablissement Elettrodo per torcia per taglio al plasma e torcia atta ad utilizzare detto elettrodo.
US5444209A (en) * 1993-08-11 1995-08-22 Miller Thermal, Inc. Dimensionally stable subsonic plasma arc spray gun with long wearing electrodes

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3914573A (en) * 1971-05-17 1975-10-21 Geotel Inc Coating heat softened particles by projection in a plasma stream of Mach 1 to Mach 3 velocity
JPS5546266A (en) * 1978-09-28 1980-03-31 Daido Steel Co Ltd Plasma torch
US4506136A (en) * 1982-10-12 1985-03-19 Metco, Inc. Plasma spray gun having a gas vortex producing nozzle

Also Published As

Publication number Publication date
CA2065431A1 (fr) 1991-04-21
EP0496733A1 (fr) 1992-08-05
EP0496733A4 (fr) 1992-06-03
WO1991005629A1 (fr) 1991-05-02
JPH05502189A (ja) 1993-04-22
AU6058290A (en) 1991-05-16
CA2065431C (fr) 1995-12-05
DE69021736D1 (de) 1995-09-21
AU628617B2 (en) 1992-09-17
DE69021736T2 (de) 1996-04-25

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