EP0500491A1 - Plasma spray gun for spraying powdered or gaseous materials - Google Patents

Plasma spray gun for spraying powdered or gaseous materials Download PDF

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Publication number
EP0500491A1
EP0500491A1 EP92810094A EP92810094A EP0500491A1 EP 0500491 A1 EP0500491 A1 EP 0500491A1 EP 92810094 A EP92810094 A EP 92810094A EP 92810094 A EP92810094 A EP 92810094A EP 0500491 A1 EP0500491 A1 EP 0500491A1
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EP
European Patent Office
Prior art keywords
plasma
cathode
anode
spraying device
channel
Prior art date
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Granted
Application number
EP92810094A
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German (de)
French (fr)
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EP0500491B1 (en
Inventor
Klaus Dr.-Ing. Landes
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Oerlikon Metco AG
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Sulzer Metco AG
Plasma Tecknik AG
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    • 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
    • H05H1/42—Plasma torches using an arc with provisions for introducing materials into the plasma, e.g. powder, liquid
    • 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
    • H05H1/3484—Convergent-divergent 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
    • H05H1/3436—Hollow cathodes with internal coolant flow
    • 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
    • H05H1/3452—Supplementary electrodes between cathode and anode, e.g. cascade

Definitions

  • plasma sprayers for spraying e.g. powdery material in the molten state are plasma sprayers in use which work with an indirect plasmatron, i.e. a plasma generator with an electrically non-current-carrying plasma jet flowing out of a nozzle.
  • an indirect plasmatron i.e. a plasma generator with an electrically non-current-carrying plasma jet flowing out of a nozzle.
  • the plasma is generated by an arc and passed through a plasma channel to an outflow nozzle, a distinction being made between devices with a short arc and those with a long arc.
  • the plasma which is generated by a powerful arc discharge between a pin-shaped cathode and a hollow cylindrical anode, is melted and axially accelerated, e.g. powder spray material, e.g. Metal or ceramic powder, added laterally in the area of the anode opening.
  • powder spray material e.g. Metal or ceramic powder
  • this type of powder input is unfavorable, since the powder particles, depending on their size and entry speed, are treated differently in the plasma jet. Large powder particles e.g. fly through the plasma jet and are not melted. This leads to poor use of the spray material and to a reduction in the quality of the plasma-sprayed layer.
  • the complex interrelationships between the operating parameters make it difficult to optimize the plasma spraying process. Above all, the disruption of the plasma jet by the carrier gas that flows in from the side and is necessary for the powder transport has a disadvantageous effect.
  • EP 0 249 238 A2 discloses a plasma spraying device in which the spraying material is supplied axially, specifically through a tube which is introduced radially into the nozzle cavity from the side on a nozzle placed in front of the anode and bent into the nozzle axis within the latter is.
  • the arrangement of the feed tube within the plasma jet leads to difficulties because the feed tube and the plasma jet adversely affect one another.
  • the flow of the plasma jet through the feed tube is mechanically hindered, on the other hand, the feed tube in the center of the plasma jet is subjected to extremely high thermal stress.
  • such a device has an elongated plasma channel which extends from the cathode to the anode and is formed by a number of ring-shaped neutrodes which are electrically insulated from one another.
  • the long arc can develop greater thermal energy than a short arc, but is also exposed to more intensive cooling in the longer, relatively narrow plasma channel.
  • DE-GM 1 932 150 shows a plasma spraying device of this type for spraying powdery material, with an indirect plasmatron, which works with a short arc.
  • a hollow cylindrical cathode works together with a likewise hollow cylindrical, nozzle-shaped anode, the cathode protruding into the anode arranged coaxially to this.
  • the hollow cathode also serves as a feed pipe for the spray material, which is introduced axially into the arc space in this way.
  • the plasma gas passes through the annular gap between the cathode and anode into the arc space and then into the anode nozzle, through which the plasma jet is constricted.
  • a disadvantage of this arrangement is the relatively short service life due to the relatively high amperages.
  • the residence time of the spray material emerging from the hollow cathode in the arc space is quite short, so that the powder particles can absorb only relatively little thermal energy in this space, especially since the arc attachment lies at the edge of the cathode and therefore outside the powder jet axis. It may be of advantage that under these circumstances the powder particles have not yet melted until they emerge from the anode nozzle and therefore cannot be deposited on the wall of the anode nozzle. On the other hand, the predominant amount of energy for melting and accelerating the powder particles from the free plasma jet must be applied.
  • the invention relates to a plasma spraying device for spraying solid, powdery or gaseous material, with an indirect plasmatron for generating a long arc, which has at least one cathode, an annular anode distanced from the cathode and one extending from the cathode to the anode stretching plasma channel, which is formed by the anode ring and a number of annular, mutually electrically isolated neutrodes, and with means for an axial supply of the spray material into the plasma jet.
  • the invention aims to improve the efficiency and the service life of such a plasma spraying device and is intended to ensure that the spraying material supplied is processed more uniformly.
  • the invention consists in that the means for supplying the spray material are located at the cathode-side end of the plasma channel and that the plasma channel has a constriction zone in the region near the cathode and widens from this constriction zone towards the anode.
  • the constriction zone compresses the plasma formed in the inlet area of the plasma channel and at the same time narrows the electrical current distribution. This causes an increase in pressure and temperature in terms of gas dynamics and an electrically increased heating in the center of the plasma jet. It is also assumed that the electrical current lines brought together in the constriction zone remain concentrated in the wider area of the plasma channel due to the attraction of parallel current threads and keep the plasma compressed thanks to a so-called plasma dynamic pinch effect. Practical tests with the mentioned constriction zone have shown in any case that an increased energy density and speed of the plasma occurs in the zone of the cathode space near the axis into which the spray material is introduced. The heat transfer to the spray material, e.g. on the powder particles for melting them and the axial acceleration of the powder particles improved. Without the constriction zone, a "cold soul" in the plasma jet is also visually recognizable. However, the constriction zone according to the invention has no anodic function.
  • EP 0 157 407 A2 also shows a plasmatron working with a short arc, in which the plasma channel has an extension following a constriction.
  • the expanded area of the plasma channel is, however, outside the anode nozzle.
  • the plasma is not cooled in this area, but is additionally heated by external action, and no passage of spray material through this channel area is provided.
  • a major advantage of a plasma spraying device working with a long arc and with spray material introduced axially in the cathode compartment is that thermal energy is supplied to the spray material over the entire length of the high-energy arc, so that the spray material emerges from the plasma channel in the molten state.
  • the inventive expansion of the plasma channel from the constriction zone to the anode makes it possible to greatly reduce the heat loss from the bundled plasma jet and to reduce the amount of coolant. It is precisely the shifting of the energy concentration into the arc space that makes it possible to provide an anode with a larger inner diameter instead of an anode nozzle, since at this point it is no longer necessary to influence the free plasma jet by a nozzle effect.
  • the plasma channel at the anode-side end has a diameter at least 1.5 times as large as at the narrowest point of the constriction zone.
  • the expanded part of the plasma channel following the constriction zone can be wholly or partly cylindrical or conical.
  • the cavity of the anode can be flared outwards.
  • the anode can be offset outwards in the channel profile, i.e. the annular anode can have a larger inner diameter than the neutrode adjacent to the anode.
  • the neutrodes forming the plasma channel are usually separated from one another by ring-shaped insulating disks which are generally set back with respect to the channel wall in order to prevent them from being subjected to excessive heat from the plasma jet.
  • the channel wall is through gaps interrupted between the neutrodes, which can lead to undesirable turbulence at the edge of the plasma beam, especially in the inlet area of the plasma channel, in which the plasma is concentrated by the channel wall.
  • a gas-dynamically favorable solution consists in that the neutrode closest to the cathode extends at least to the narrowest point of the constriction zone. This means that there is only a single neutrode in this area, which forms a continuous channel wall.
  • the spray material is preferably introduced into the cathode space through a tube with the aid of a carrier. From here, the particle tracks run essentially within a cone due to the shot effect. With the expansion of the plasma channel mentioned, it can now be achieved that this cone as a whole spreads exclusively within the plasma channel and does not intersect the channel wall, so that no molten particles can deposit on the channel wall. In contrast, an impact of the powder particles on the channel wall in the constriction zone does not lead to deposits, since the powder particles have not yet melted in this area.
  • a central tube can be provided in a manner known per se, which is axially aligned with the plasma channel and projects into the cavity of the neutrode closest to the cathode.
  • this is preferably designed as a hollow cathode, which at the same time forms the tube for supplying the spray material or surrounds a tube insulated from it.
  • rod-shaped cathodes can also be provided, which are arranged distributed in a circle around the central tube.
  • the plasma channel 4 is formed by a number of ring-shaped neutrodes 6 to 12 which are electrically insulated from one another and the ring-shaped anode 3.
  • the cathode rods 1 are anchored in a cathode support 13 made of insulating material.
  • a sleeve-shaped anode carrier 14 made of insulating material, which surrounds the neutrodes 6 to 12 and the anode 3.
  • the whole is held together by three metal sleeves 15, 16 and 17, the first sleeve 15 being screwed to the end on the end face and the second sleeve 16 being screwed to the first circumference, while the third sleeve 17 is loosely anchored on the one hand to the second sleeve 16 and on the other hand is screwed circumferentially to the anode carrier 14.
  • the third sleeve 17 also presses with an inwardly directed flange 18 against the anode ring 3 and thus holds the elements forming the plasma channel 4 together, the neutrode 6 closest to the cathodes being supported on an inner collar 19 of the anode carrier 13.
  • the cathode rods 1 carry at their free ends cathode pins 20 which are made of an electrically and thermally particularly conductive and also high-melting material, e.g. thoriated tungsten.
  • the cathode pins 20 are arranged eccentrically to the respective axis of the cathode rods 1 in such a way that their longitudinal axes are closer to the central longitudinal axis 2 than those of the cathode rods 1.
  • a central insulating body 21 made of high-melting, in particular, is attached to the cathode carrier 13 glass-ceramic material from which the cathode pins 20 protrude into the cavity 22 of the inlet nozzle formed by the first neutrode 6.
  • the exposed part of the outer circumferential surface of the insulating body 21 lies radially opposite a part of the nozzle wall and forms with this wall part an annular channel 23 for the inlet of the plasma gas into the nozzle cavity 22.
  • the supply of the spray material SM, e.g. Metal or ceramic powder into the plasma jet is carried out with the aid of a carrier gas TG at the cathode-side end of the plasma channel 4.
  • a pipe 24 running in the longitudinal axis 2 and held by the insulating body 21 is provided, which also opens into the nozzle cavity 22, whereby the cathode tips 20 extend beyond the mouth 25 of the tube 24.
  • the plasma gas PG is fed through a transverse channel 26 provided in the cathode carrier 13, which transitions into a longitudinal channel 27, from which the plasma gas reaches an annular space 28 and from there into the annular channel 23.
  • a distributor ring 29 with a plurality of through bores 30 is seated on the insulating body 21 provided which connect the annular space 28 with the annular channel 23.
  • the elements forming the plasma channel 4, namely the anode 3 and the neutrodes 6 to 12, are made of insulating material, e.g. Boron nitride, electrically insulated from one another and gas-tightly connected to one another by sealing rings 32.
  • the plasma channel 4 has a constriction zone 33 in the vicinity of the cathode and, following this constriction zone 33, widens towards the anode 3 to a diameter which is at least 1.5 times the channel diameter at the narrowest point of the constriction zone 33 this expansion, the plasma channel 4 runs cylindrical to its anode-side end.
  • neutrodes 6 to 12 e.g. consist of copper
  • the anode 3 is made of an outer ring 34, e.g. made of copper, and an inner ring 35 made of an electrically and thermally particularly conductive and also high-melting material, e.g. thoriated tungsten.
  • the neutrode 6 closest to the cathode rods 1 extends over the entire constriction zone 33, so that the channel wall 52 unites beyond the narrowest point of the constriction zone has a steady course.
  • the parts directly exposed to the arc and plasma heat are largely water-cooled.
  • different cavities for the circulation of the cooling water KW are provided in the cathode holder 13, in the cathode rods 1 and in the anode holder 14.
  • the cathode holder 13 has three annular spaces 36, 37 and 38 which are connected to connecting lines 39, 40 and 41, respectively, and the anode holder 14 has an annular space 42 in the region of the anode 3 and one surrounding all neutrodes in the region of the neutrodes 6 to 12 Cavity 43 on.
  • Cooling water KW is supplied via the connecting lines 39 and 41.
  • the cooling water of the connecting line 39 first passes through a longitudinal channel 44 to the annular space 42 surrounding the most thermally stressed anode 3.
  • the cooling water flows through the cavity 43 of the lateral surface of the neutrodes 6 to 12 back through a longitudinal channel 45 into the annular space 37
  • the cooling water of the connecting line 41 flows into an annular space 38 and out of this into a cavity 46 of the cathode rods 1, which is divided by a cylindrical partition wall 47.
  • the cooling water likewise arrives from the cathode rods 1 into the annular space 37, from which it flows out via the connecting line 40.
  • FIG. 3 shows the approximate course of the arc 48 during operation of the plasma spraying device according to FIGS. 1 and 2, as well as the flow course of the plasma gas PG and the trajectory of the spraying material SM.
  • the effect of the constriction zone 33 and the subsequent expansion of the plasma channel 4 can clearly be seen.
  • the existence of the channel wall 50 relative to the plasma jet is relatively large. Under these circumstances, the channel wall 50 is subjected to less thermal stress in this area, and the cooling capacity can be reduced accordingly.
  • a single cathode 54 is provided, which is designed as a hollow cathode.
  • the neutrode cascade 55 and the anode ring 56, which form the plasma channel 57, are constructed in principle in the same way as the corresponding parts in the embodiment according to FIG. 1, with the difference that the inlet nozzle 58 can run flat here and that the anode ring 56 has a larger inner diameter than the neutrode 59 closest to the anode ring 56.
  • a tube 60 is inserted into the hollow cathode 54 for supplying the spray material, the mouth 61 of which protrudes towards the end of the cathode 54.
  • An insulating tube 62 which projects beyond the mouth 61 of the tube 60 and fixes the tube 60 radially with a spacer ring 63, provides the necessary insulation between the cathode 54 and the tube 60 and protects the latter from excessive heating. Otherwise, the plasma spraying device can be constructed identically or similarly to that according to FIG. 1.
  • FIG. 5 finally shows yet another embodiment of the anode 64, in which the inner wall 65 of the anode ring 66 used is conical to the outside.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Plasma Technology (AREA)
  • Nozzles (AREA)
  • Coating By Spraying Or Casting (AREA)

Abstract

The plasma spray gun has an indirect plasmatron for generating a long arc. Said plasmatron has at least one, for example, three, cathodes (1,20), an annular anode (3) which is at a distance from the cathode, and a plasma channel (4) which extends from the cathode to the anode. The latter is formed by the anode ring (3) and a number of annular neutrodes (5 to 12) which are electrically insulated from one another. The plasma channel (4) has a constriction zone (33) in the region close to the cathode and expands from this constriction zone towards the anode (3). The spray material (SM) is supplied with the aid of a carrier gas (TG) through a central tube (24) which opens in the centre of an inlet nozzle which is formed by the neutrode (5) located closest to the cathode. <??>Using this solution, a higher efficiency and an increased life of the plasma spray gun can be achieved. <IMAGE>

Description

Zum Versprühen von z.B. pulverförmigem Material in schmelzflüssigem Zustand sind Plasmasspritzgeräte im Gebrauch, welche mit einem indirekten Plasmatron arbeiten, d.h. einem Plasmaerzeuger mit einem aus einer Düse ausströmenden, elektrisch nicht stromführenden Plasmastrahl. In der Regel wird das Plasma durch einen Lichtbogen erzeugt und durch einen Plasmakanal zu einer Ausströmdüse geleitet, wobei man zwischen Geräten mit Kurzlichtbogen und solchen mit Langlichtbogen unterscheidet.For spraying e.g. powdery material in the molten state are plasma sprayers in use which work with an indirect plasmatron, i.e. a plasma generator with an electrically non-current-carrying plasma jet flowing out of a nozzle. As a rule, the plasma is generated by an arc and passed through a plasma channel to an outflow nozzle, a distinction being made between devices with a short arc and those with a long arc.

Bei einem grossen Teil der heute technisch eingesetzten Plasmaspritzgeräte wird dem Plasma, das durch eine stromstarke Bogenentladung zwischen einer stiftförmigen Kathode und einer hohlzylinderförmigen Anode erzeugt wird, das aufzuschmelzende und achsial zu beschleunigende, z.B. pulverförmige Spritzmaterial, z.B. Metall- oder Keramikpulver, seitlich im Bereich der Anodenöffnung beigegeben. Diese Art der Pulvereingabe ist jedoch ungünstig, da die Pulverteilchen, abhängig von ihrer Grösse und Eintrittsgeschwindigkeit, eine unterschiedliche Behandlung im Plasmastrahl erfahren. Grosse Pulverteilchen z.B. durchfliegen den Plasmastrahl und werden nicht aufgeschmolzen. Dies führt zu einer schlechten Ausnützung des Spritzmaterials und zu einer Qualitätsminderung der plasmagespritzten Schicht. Ausserdem erschweren die komplexen Zusammenhänge der Betriebsparameter die Optimierung des Plasmaspritzprozesses. Vor allem die Störung des Plasmastrahls durch das seitlich einströmende, für den Pulvertransport nötige Trägergas wirkt sich nachteilig aus.In a large part of the plasma spraying devices used technically today, the plasma, which is generated by a powerful arc discharge between a pin-shaped cathode and a hollow cylindrical anode, is melted and axially accelerated, e.g. powder spray material, e.g. Metal or ceramic powder, added laterally in the area of the anode opening. However, this type of powder input is unfavorable, since the powder particles, depending on their size and entry speed, are treated differently in the plasma jet. Large powder particles e.g. fly through the plasma jet and are not melted. This leads to poor use of the spray material and to a reduction in the quality of the plasma-sprayed layer. In addition, the complex interrelationships between the operating parameters make it difficult to optimize the plasma spraying process. Above all, the disruption of the plasma jet by the carrier gas that flows in from the side and is necessary for the powder transport has a disadvantageous effect.

Aus der EP 0 249 238 A2 ist demgegenüber ein Plasmaspritzgerät bekannt, bei dem die Zufuhr des Spritzmaterials achsial erfolgt, und zwar durch ein Rohr, das an einer der Anode vorgesetzten Düse von der Seite radial in den Düsenhohlraum eingeführt und innerhalb desselben in die Düsenachse umgebogen ist. Die Anordnung des Zuführrohres innerhalb des Plasmastrahls führt jedoch zu Schwierigkeiten, weil das Zuführrohr und der Plasmastrahl sich gegenseitig ungünstig beeinflussen. Einerseits wird die Strömung des Plasmastrahls durch das Zuführrohr mechanisch behindert, andererseits wird das Zuführrohr im Zentrum des Plasmastrahls thermisch ausserordentlich stark beansprucht.In contrast, EP 0 249 238 A2 discloses a plasma spraying device in which the spraying material is supplied axially, specifically through a tube which is introduced radially into the nozzle cavity from the side on a nozzle placed in front of the anode and bent into the nozzle axis within the latter is. However, the arrangement of the feed tube within the plasma jet leads to difficulties because the feed tube and the plasma jet adversely affect one another. On the one hand, the flow of the plasma jet through the feed tube is mechanically hindered, on the other hand, the feed tube in the center of the plasma jet is subjected to extremely high thermal stress.

Energetisch besitzen die heutigen Plasmaspritzgeräte ausserdem einen sehr schlechten Wirkungsgrad. Dies rührt vor allem daher, dass bei anodenseitiger Zufuhr des Spritzmaterials nur der Energieanteil genutzt wird, welcher aus dem Lichtbogen in den freien Plasmastrahl übergeht. Andererseits fliesst ein Grossteil der zugeführten elektrischen Energie innerhalb des Plasmakanals über Wandverluste in das Kühlwasser ab und damit dem Energieinhalt des Plasmastrahls verloren.In terms of energy, today's plasma sprayers also have a very poor efficiency. This is mainly due to the fact that when the spray material is supplied on the anode side, only the energy portion is used which passes from the arc into the free plasma jet. On the other hand, a large part of the electrical energy supplied flows into the cooling water via wall losses in the plasma channel and thus the energy content of the plasma jet is lost.

Dies betrifft insbesondere auch Plasmatrons mit Langlichtbogen. Ein solches Gerät besitzt gemäss der EP 0 249 238 A2 einen von der Kathode zur Anode sich erstreckenden länglichen Plasmakanal, welcher durch eine Anzahl ringförmiger, voneinander elektrisch isolierter Neutroden gebildet ist. Der Langlichtbogen kann zwar eine grössere thermische Energie entwickeln als ein Kurzlichtbogen, ist aber in dem längeren, verhältnismässig engen Plasmakanal auch einer intensiveren Kühlung ausgesetzt.This applies in particular to plasma cartridges with a long arc. According to EP 0 249 238 A2, such a device has an elongated plasma channel which extends from the cathode to the anode and is formed by a number of ring-shaped neutrodes which are electrically insulated from one another. The long arc can develop greater thermal energy than a short arc, but is also exposed to more intensive cooling in the longer, relatively narrow plasma channel.

Es zeigt sich also, dass unter diesen Umständen alle Bemühungen, eine möglichst hohe Energiekonzentration im freien Plasmastrahl zu erhalten, nämlich in dem Bereich, in welchem das Spritzmaterial zugeführt wird, aus den genannten Gründen nicht zu einerwesentlichen Verbesserung des Wirkungsgrades führen können.It turns out that under these circumstances all efforts to obtain the highest possible energy concentration in the free plasma jet, namely in the area in which the spray material is supplied, cannot lead to a substantial improvement in efficiency for the reasons mentioned.

Es sind zwar zahlreiche Vorschläge für Ausführungen von Plasmaspritzgeräten mit besseren Eigenschaften bekannt geworden. Insbesondere wurde vorgeschlagen, die Zufuhr des Spritzmaterials an das kathodenseitige Ende des Plasmakanals zu verlegen.There have been numerous proposals for versions of plasma sprayers with better properties. In particular, it has been proposed to move the supply of the spray material to the cathode-side end of the plasma channel.

Das DE-GM 1 932 150 zeigt ein Plasmaspritzgerät dieser Art zum Versprühen von pulverförmigem Material, mit einem indirekten Plasmatron, das mit einem Kurzlichtbogen arbeitet. Eine hohlzylindrische Kathode arbeitet mit einer ebenfalls hohlzylindrischen, düsenförmig ausgebildeten Anode zusammen, wobei die Kathode in die koachsial zu dieser angeordneten Anode hineinragt. Die Hohlkathode dient zugleich als Zuführrohr für das Spritzmaterial, das auf diese Weise achsial in den Lichtbogenraum eingeführt wird. Das Plasmagas gelangt durch den Ringspalt zwischen Kathode und Anode in den Lichtbogenraum und anschliessend in die Anodendüse, durch welche der Plasmastrahl eingeschnürt wird. Ein Nachteil dieser Anordnung ist die durch die relativ hohen Stromstärken bedingte, relativ geringe Standzeit.DE-GM 1 932 150 shows a plasma spraying device of this type for spraying powdery material, with an indirect plasmatron, which works with a short arc. A hollow cylindrical cathode works together with a likewise hollow cylindrical, nozzle-shaped anode, the cathode protruding into the anode arranged coaxially to this. The hollow cathode also serves as a feed pipe for the spray material, which is introduced axially into the arc space in this way. The plasma gas passes through the annular gap between the cathode and anode into the arc space and then into the anode nozzle, through which the plasma jet is constricted. A disadvantage of this arrangement is the relatively short service life due to the relatively high amperages.

Die Verweilzeit des aus der Hohlkathode austretenden Spritzmaterials im Lichtbogenraum ist ziemlich kurz, so dass die Pulverteilchen in diesem Raum nur verhältnismässig wenig thermische Energie aufnehmen können, zumal der Lichtbogenansatz am Kathodenrand und daher ausserhalb der Pulverstrahlachse liegt. Es mag zwar von Vorteil sein, dass die Pulverteilchen unter diesen Umständen bis zum Austritt aus der Anodendüse noch nicht aufgeschmolzen sind und sich daher nicht an der Wandung der Anodendüse niederschlagen können. Hingegen ist dabei wiederum der überwiegende Energieanteil zum Aufschmelzen und Beschleunigen der Pulverteilchen vom freien Plasmastrahl aufzubringen.The residence time of the spray material emerging from the hollow cathode in the arc space is quite short, so that the powder particles can absorb only relatively little thermal energy in this space, especially since the arc attachment lies at the edge of the cathode and therefore outside the powder jet axis. It may be of advantage that under these circumstances the powder particles have not yet melted until they emerge from the anode nozzle and therefore cannot be deposited on the wall of the anode nozzle. On the other hand, the predominant amount of energy for melting and accelerating the powder particles from the free plasma jet must be applied.

Die Erfindung betrifft ein Plasmaspritzgerät zum Versprühen von festem, pulverförmigem oder gasförmigem Material, mit einem indirekten Plasmatron zur Erzeugung eines Langlichtbogens, welches wenigstens eine Kathode, eine von der Kathode distanzierte ringförmige Anode und einen sich von der Kathode zur Anode erstreckenden Plasmakanal aufweist, welcher durch den Anodenring und eine Anzahl ringförmiger, voneinander elektrisch isolierter Neutroden gebildet ist, und mit Mitteln für eine achsiale Zufuhr des Spritzmaterials in den Plasmastrahl.The invention relates to a plasma spraying device for spraying solid, powdery or gaseous material, with an indirect plasmatron for generating a long arc, which has at least one cathode, an annular anode distanced from the cathode and one extending from the cathode to the anode stretching plasma channel, which is formed by the anode ring and a number of annular, mutually electrically isolated neutrodes, and with means for an axial supply of the spray material into the plasma jet.

Ausgehend von der bekannten Anordnung nach der EP 0 249 238 A2 bzweckt die Erfindung eine Verbesserung hinsichtlich des Wirkungsgrades und der Standzeit eines derartigen Plasmaspritzgerätes und soll sicherstellen, dass das zugeführte Spritzmaterial gleichmässiger aufbereitet wird.Based on the known arrangement according to EP 0 249 238 A2, the invention aims to improve the efficiency and the service life of such a plasma spraying device and is intended to ensure that the spraying material supplied is processed more uniformly.

Die Erfindung besteht darin, dass sich die Mittel für die Zufuhr des Spritzmaterials am kathodenseitigen Ende des Plasmakanals befinden und dass der Plasmakanal im kathodennahen Bereich eine Einschnürungszone aufweist und von dieser Einschnürungszone sich zur Anode hin erweitert.The invention consists in that the means for supplying the spray material are located at the cathode-side end of the plasma channel and that the plasma channel has a constriction zone in the region near the cathode and widens from this constriction zone towards the anode.

Die Einschnürungszone komprimiert das im Einlaufbereich des Plasmakanals gebildete Plasma und engt zugleich die elektrische Stromverteilung ein. Dies bewirkt gasdynamisch eine Erhöhung von Druck und Temperatur und elektrisch eine verstärkte Aufheizung im Zentrum des Plasmastrahls. Es wird ausserdem angenommen, dass die in der Einschnürungszone zusammengeführten elektrischen Stromlinien aufgrund der Anziehung paralleler Stromfäden auch im weiteren Bereich des Plasmakanals konzentriert bleiben und das Plasma dank eines sozusagen plasmadynamischen Pincheffektes komprimiert halten. Praktische Versuche mit der genannten Einschnürungszone haben jedenfalls gezeigt, dass in der achsennahen Zone des Kathodenraumes, in den das Spritzmaterial eingegeben wird, eine erhöhte Energiedichte und Geschwindigkeit des Plasmas entsteht. Damit wird der Wärmeübergang auf das Spritzmaterial, z.B. auf die Pulverteilchen zum Aufschmelzen derselben und die achsiale Beschleunigung der Pulverteilchen verbessert. Ohne die Einschnürungszone ist eine "kalte Seele" im Plasmastrahl auch visuell erkennbar. Die Einschnürungszone nach der Erfindung hat jedoch keine anodische Funktion.The constriction zone compresses the plasma formed in the inlet area of the plasma channel and at the same time narrows the electrical current distribution. This causes an increase in pressure and temperature in terms of gas dynamics and an electrically increased heating in the center of the plasma jet. It is also assumed that the electrical current lines brought together in the constriction zone remain concentrated in the wider area of the plasma channel due to the attraction of parallel current threads and keep the plasma compressed thanks to a so-called plasma dynamic pinch effect. Practical tests with the mentioned constriction zone have shown in any case that an increased energy density and speed of the plasma occurs in the zone of the cathode space near the axis into which the spray material is introduced. The heat transfer to the spray material, e.g. on the powder particles for melting them and the axial acceleration of the powder particles improved. Without the constriction zone, a "cold soul" in the plasma jet is also visually recognizable. However, the constriction zone according to the invention has no anodic function.

Bei den vorbekannten Geräten ist zwar ebenfalls eine Einschnürung vorhanden. Diese befindet sich aber stets im wesentlichen ausserhalb des Lichtbogenbereichs und beeinflusst nur den freien Plasmastrahl, nicht aber den Lichtbogen. Die EP 0 157 407 A2 zeigt ausserdem ein mit Kurzlichtbogen arbeitendes Plasmatron, bei dem der Plasmakanal im Anschluss an eine Einschnürung eine Erweiterung aufweist. Der erweiterte Bereich des Plasmakanals befindet sich jedoch ausserhalb der Anodendüse. Zudem wird das Plasma in diesem Bereich nicht gekühlt, sondern durch äussere Einwirkung zusätzlich erhitzt, und ein Durchlass von Spritzmaterial durch diesen Kanalbereich ist nicht vorgesehen.A constriction is also present in the previously known devices. However, this is always essentially outside the arc area and only influences the free plasma beam, but not the arc. EP 0 157 407 A2 also shows a plasmatron working with a short arc, in which the plasma channel has an extension following a constriction. The expanded area of the plasma channel is, however, outside the anode nozzle. In addition, the plasma is not cooled in this area, but is additionally heated by external action, and no passage of spray material through this channel area is provided.

Bei einem Plasmaspritzgerät nach dem EP 0 249 238 A2 mit einem nach der Einschnürung unveränderten Querschnitt des Plasmakanals hätte eine achsiale Zufuhr des Spritzmaterials im Kathodenbereich, z.B. durch eine Hohlkathode gemäss DE-GM 1 932 150, den Nachteil, dass sich allenfalls bereits innerhalb des Plasmakanals schmelzendes Spritzmaterial an der Wandung desselben niederschlagen und damit zu einer Verschmutzung und einer allmählichen Verengung des Plasmakanals führen könnte.In the case of a plasma spraying device according to EP 0 249 238 A2 with an unchanged cross section of the plasma channel after the constriction, an axial supply of the spray material in the cathode area, e.g. due to a hollow cathode according to DE-GM 1 932 150, the disadvantage that spray material that is already melting inside the plasma channel is deposited on the wall of the same and could thus lead to contamination and a gradual narrowing of the plasma channel.

Ein wesentlicher Vorteil eines mit Langlichtbogen arbeitenden Plasmaspritzgerätes und mit im Kathodenraum achsial eingeführtem Spritzmaterial besteht darin, dass dem Spritzmaterial auf der ganzen Länge des energiereichen Lichtbogens thermische Energie zugeführt wird, so dass das Spritzmaterial bereits im geschmolzenen Zustand aus dem Plasmakanal austritt.A major advantage of a plasma spraying device working with a long arc and with spray material introduced axially in the cathode compartment is that thermal energy is supplied to the spray material over the entire length of the high-energy arc, so that the spray material emerges from the plasma channel in the molten state.

Von dieser Lichtbogenenergie wird bei den bekannten Plasmaspritzgeräten dieser Art nur der aus dem Lichtbogen in den freien Plasmastrahl übergehende Anteil genutzt, wobei jedoch ein erheblicher Teil der Lichtbogenenergie durch Wärmeübergang an die gekühlte Wandung des verhältnismässig engen Plasmakanals verlorengeht.In the known plasma sprayers of this type, only the portion of the arc energy that is transferred from the arc to the free plasma jet is used, but a considerable part of the arc energy is lost through heat transfer to the cooled wall of the relatively narrow plasma channel.

Durch die erfindungsgemässe Ausweitung des Plasmakanals von der Einschnürungszone zur Anode hin lässt sich demgegenüber der Wärmeverlust aus dem gebündelten Plasmastrahl ausserordentlich stark reduzieren und der Kühlmittelaufwand verringern. Dabei ist es gerade die Verlagerung der Energiekonzentration in den Lichtbogenraum, welche es ermöglicht, anstelle einer Anodendüse eine Anode mit grösserem Innendurchmesser vorzusehen, da an dieser Stelle eine weitere Beeinflussung des freien Plasmastrahls durch einen Düseneffekt nicht mehr nötig ist.In contrast, the inventive expansion of the plasma channel from the constriction zone to the anode makes it possible to greatly reduce the heat loss from the bundled plasma jet and to reduce the amount of coolant. It is precisely the shifting of the energy concentration into the arc space that makes it possible to provide an anode with a larger inner diameter instead of an anode nozzle, since at this point it is no longer necessary to influence the free plasma jet by a nozzle effect.

Gemäss einer bevorzugten Ausführungsform der Erfindung hat der Plasmakanal am anodenseitigen Ende einen mindestens 1,5-mal so grossen Durchmesser wie an der engsten Stelle der Einschnürungszone. Dabei kann der auf die Einschnürungszone folgende, erweiterte Teil des Plasmakanals ganz oder teilweise zylindrisch oder konisch verlaufen. Beispielsweise kann der Hohlraum der Anode nach aussen konisch erweitert sein. Andererseits kann die Anode im Kanalprofil nach aussen versetzt sein, d.h. die ringförmige Anode kann einen grösseren Innendurchmesser aufweisen als die der Anode benachbarte Neutrode. Durch diese einzeln oder in Kombination getroffenen Massnahmen lässt sich nicht nur eine Ablagerung des Spritzmaterials an der Anode verhindern, sondern auch deren Wärmebelastung erheblich vermindern.According to a preferred embodiment of the invention, the plasma channel at the anode-side end has a diameter at least 1.5 times as large as at the narrowest point of the constriction zone. The expanded part of the plasma channel following the constriction zone can be wholly or partly cylindrical or conical. For example, the cavity of the anode can be flared outwards. On the other hand, the anode can be offset outwards in the channel profile, i.e. the annular anode can have a larger inner diameter than the neutrode adjacent to the anode. These measures, taken individually or in combination, not only prevent the spray material from depositing on the anode, but also significantly reduce its thermal load.

Die den Plasmakanal bildenden Neutroden sind üblicherweise durch ringförmige Isolierscheiben voneinander getrennt, welche in der Regel gegenüber der Kanalwandung zurückgesetzt sind, um sie einer übermässigen Wärmeeinwirkung des Plasmastrahls zu entziehen. Infolgedessen ist die Kanalwandung durch Spalte zwischen den Neutroden unterbrochen, was zu unerwünschten Turbulenzen am Rande des Plasmastrahls führen kann, und zwar vor allem im Einlaufbereich des Plasmakanals, in welchem das Plasma von der Kanalwandung eingeengt wird. Eine gasdynamisch günstige Lösung besteht darin, dass die der Kathode am nächsten liegende Neutrode sich wenigstens bis zur engsten Stelle der Einschnürungszone erstreckt. D.h. dass in diesem Bereich nur eine einzige Neutrode vorhanden ist, welche eine durchgehende Kanalwandung bildet.The neutrodes forming the plasma channel are usually separated from one another by ring-shaped insulating disks which are generally set back with respect to the channel wall in order to prevent them from being subjected to excessive heat from the plasma jet. As a result, the channel wall is through gaps interrupted between the neutrodes, which can lead to undesirable turbulence at the edge of the plasma beam, especially in the inlet area of the plasma channel, in which the plasma is concentrated by the channel wall. A gas-dynamically favorable solution consists in that the neutrode closest to the cathode extends at least to the narrowest point of the constriction zone. This means that there is only a single neutrode in this area, which forms a continuous channel wall.

Das Spritzmaterial wird vorzugsweise durch ein Rohr mit Hilfe eines Trägers in den Kathodenraum eingebracht. Von hier aus verlaufen die Teilchenbahnen aufgrund des Schroteffektes im wesentlichen innerhalb eines Kegels. Durch die genannte Ausweitung des Plasmakanals lässtsich nun erreichen, dass sich dieser Kegel gesamthaft ausschliesslich innerhalb des Plasmakanals ausbreitet und die Kanalwandung nicht schneidet, damit sich keine geschmolzenen Teilchen an der Kanalwandung ablagern können. Ein Auftreffen der Pulverteilchen auf die Kanalwandung in der Einschnürungszone führt dagegen nicht zu Ablagerungen, da die Pulverteilchen in diesem Bereich noch nicht geschmolzen sind.The spray material is preferably introduced into the cathode space through a tube with the aid of a carrier. From here, the particle tracks run essentially within a cone due to the shot effect. With the expansion of the plasma channel mentioned, it can now be achieved that this cone as a whole spreads exclusively within the plasma channel and does not intersect the channel wall, so that no molten particles can deposit on the channel wall. In contrast, an impact of the powder particles on the channel wall in the constriction zone does not lead to deposits, since the powder particles have not yet melted in this area.

Für die Zufuhr des Spritzmaterials kann in an sich bekannter Weise ein zentrales Rohr vorgesehen sein, das auf den Plasmakanal achsial ausgerichtet ist und in den Hohlraum der der Kathode am nächsten liegenden Neutrode ragt. Im Falle einer einzelnen Kathode ist diese vorzugsweise als Hohlkathode ausgebildet, welche zugleich das Rohr für die Zufuhr des Spritzmaterials bildet oder ein von dieser isoliertes Rohr umschliesst. Es können aber auch mehrere stabförmige Kathoden vorgesehen sein, welche im Kreis um das zentrale Rohr verteilt angeordnet sind.For the supply of the spray material, a central tube can be provided in a manner known per se, which is axially aligned with the plasma channel and projects into the cavity of the neutrode closest to the cathode. In the case of a single cathode, this is preferably designed as a hollow cathode, which at the same time forms the tube for supplying the spray material or surrounds a tube insulated from it. However, a plurality of rod-shaped cathodes can also be provided, which are arranged distributed in a circle around the central tube.

In der Zeichnung sind Ausführungsbeispiele der Erfindung dargestellt, und zwar zeigen:

  • Fig. 1 ein Plasmaspritzgerät nach der Erfindung im Längs schnitt, mit drei Kathoden;
  • Fig. 2 einen auf den Kathodenraum beschränkten Querschnitt nach der Linie 11-11 in Fig. 1 in grösserem Massstab;
  • Fig. 3 eine schematische Schnittansicht des Plasmakanals gemäss der Ausführungsform nach Fig. 1 in grösserem Massstab, mit eingezeichneter Plasma- und Spritzmaterialströmung;
  • Fig. 4 Einzelheiten einer anderen Ausführungsform des Plas maspritzgerätes im Längsschnitt, mit einer Hohlka thode; und
  • Fig. 5 eine andere Ausführungsform des Anodenrings.
Exemplary embodiments of the invention are shown in the drawing, namely:
  • Figure 1 is a plasma spray device according to the invention in longitudinal section, with three cathodes.
  • 2 shows a cross-section, limited to the cathode compartment, along the line 11-11 in FIG. 1 on a larger scale;
  • 3 shows a schematic sectional view of the plasma channel according to the embodiment according to FIG. 1 on a larger scale, with the plasma and spray material flow shown;
  • Fig. 4 details of another embodiment of the plasma spraying device in longitudinal section, with a Hohlka method; and
  • Fig. 5 shows another embodiment of the anode ring.

Das Plasmaspritzgerät nach den Fig. 1 und 2 besitzt drei stabförmige Kathoden 1, welche parallel zueinanderverlaufen und im Kreis um die zentrale Längsachse 2 des Gerätes gleichmässig verteilt angeordnet sind, ferner eine von den Kathoden 1 distanzierte ringförmige Anode 3 und einen von den Kathoden 1 zur Anode 3 sich erstreckenden Plasmakanal 4. Der Plasmakanal 4 ist durch eine Anzahl ringförmiger, voneinander elektrisch isolierter Neutroden 6 bis 12 und die ringförmige Anode 3 gebildet.1 and 2 has three rod-shaped cathodes 1, which run parallel to one another and are evenly distributed in a circle around the central longitudinal axis 2 of the device, furthermore an annular anode 3 distanced from the cathodes 1 and one from the cathodes 1 Anode 3 extending plasma channel 4. The plasma channel 4 is formed by a number of ring-shaped neutrodes 6 to 12 which are electrically insulated from one another and the ring-shaped anode 3.

Die Kathodenstäbe 1 sind in einem Kathodenträger 13 aus Isoliermaterial verankert. An diesen schliesst sich ein hülsenförmiger Anodenträger 14 aus Isoliermaterial an, der die Neutroden 6 bis 12 und die Anode 3 umgibt. Das Ganze wird zusammengehalten durch drei Metallhülsen 15, 16 und 17, wobei die erste Hülse 15 mit dem Kathodenträger 13 stirnseitig und die zweite Hülse 16 mit der ersten umfänglich verschraubt ist, während die dritte Hülse 17 einerseits an der zweiten Hülse 16 lose verankert und andererseits mit dem Anodenträger 14 umfänglich verschraubt ist. Die dritte Hülse 17 drückt ausserdem mit einem nach innen gerichteten Flanschrand 18 gegen den Anodenring 3 und hält damit die den Plasmakanal 4 bildenden Elemente zusammen, wobei sich die den Kathoden am nächsten liegende Neutrode 6 an einem Innenbund 19 des Anodenträgers 13 abstützt.The cathode rods 1 are anchored in a cathode support 13 made of insulating material. This is followed by a sleeve-shaped anode carrier 14 made of insulating material, which surrounds the neutrodes 6 to 12 and the anode 3. The whole is held together by three metal sleeves 15, 16 and 17, the first sleeve 15 being screwed to the end on the end face and the second sleeve 16 being screwed to the first circumference, while the third sleeve 17 is loosely anchored on the one hand to the second sleeve 16 and on the other hand is screwed circumferentially to the anode carrier 14. The third sleeve 17 also presses with an inwardly directed flange 18 against the anode ring 3 and thus holds the elements forming the plasma channel 4 together, the neutrode 6 closest to the cathodes being supported on an inner collar 19 of the anode carrier 13.

Die Kathodenstäbe 1 tragen an ihren freien Enden Kathodenstifte 20, welche aus einem elektrisch und thermisch besonders gut leitenden und zudem hochschmelzenden Material, z.B. thoriertem Wolfram, bestehen. Dabei sind die Kathodenstifte 20 derart exzentrisch zur jeweiligen Achse der Kathodenstäbe 1 angeordnet, dass deren Längsachsen der zentralen Längsachse 2 näher liegen als diejenigen der Kathodenstäbe 1. An den Kathodenträger 13 ist auf der dem Plasmakanal 4 zugewandten Seite ein zentraler Isolierkörper 21 aus hochschmelzendem, insbesondere glaskeramischem Material angesetzt, aus dem die Kathodenstifte 20 heraus in den Hohlraum 22 der durch die erste Neutrode 6 gebildeten Einlaufdüse ragen. Der freiliegende Teil der äusseren Mantelfläche des Isolierkörpers 21 liegt einem Teil der Düsenwandung radial gegenüber und bildet mit diesem Wandungsteil einen Ringkanal 23 für den Einlass des Plasmagases in den Düsenhohlraum 22.The cathode rods 1 carry at their free ends cathode pins 20 which are made of an electrically and thermally particularly conductive and also high-melting material, e.g. thoriated tungsten. The cathode pins 20 are arranged eccentrically to the respective axis of the cathode rods 1 in such a way that their longitudinal axes are closer to the central longitudinal axis 2 than those of the cathode rods 1. On the side facing the plasma channel 4, a central insulating body 21 made of high-melting, in particular, is attached to the cathode carrier 13 glass-ceramic material from which the cathode pins 20 protrude into the cavity 22 of the inlet nozzle formed by the first neutrode 6. The exposed part of the outer circumferential surface of the insulating body 21 lies radially opposite a part of the nozzle wall and forms with this wall part an annular channel 23 for the inlet of the plasma gas into the nozzle cavity 22.

Die Zufuhr des Spritzmaterials SM, z.B. Metall- oder Keramikpulver, in den Plasmastrahl erfolgt mit Hilfe eines Trägergases TG am kathodenseitigen Ende des Plasmakanals 4. Zu diesem Zweck ist ein in der Längsachse 2 verlaufendes und vom Isolierkörper 21 gehaltenes Rohr 24 vorgesehen, das ebenfalls in den Düsenhohlraum 22 mündet, wobei sich die Kathodenspitzen 20 über die Mündung 25 des Rohrs 24 hinaus erstrecken.The supply of the spray material SM, e.g. Metal or ceramic powder into the plasma jet is carried out with the aid of a carrier gas TG at the cathode-side end of the plasma channel 4. For this purpose, a pipe 24 running in the longitudinal axis 2 and held by the insulating body 21 is provided, which also opens into the nozzle cavity 22, whereby the cathode tips 20 extend beyond the mouth 25 of the tube 24.

Das Plasmagas PG wird durch einen im Kathodenträger 13 vorgesehenen Querkanal 26 zugeführt, welcher in einen Längskanal 27 übergeht, aus dem das Plasmagas in einen Ringraum 28 und von da in den Ringkanal 23 gelangt. Zur Erzielung einer möglichst laminaren Einströmung des Plasmagases in den Düsenhohlraum 22 ist ein auf dem Isolierkörper 21 sitzender Verteilerring 29 mit einer Mehrzahl von Durchgangsbohrungen 30 vorgesehen, welche den Ringraum 28 mit dem Ringkanal 23 verbinden.The plasma gas PG is fed through a transverse channel 26 provided in the cathode carrier 13, which transitions into a longitudinal channel 27, from which the plasma gas reaches an annular space 28 and from there into the annular channel 23. In order to achieve a flow of the plasma gas into the nozzle cavity 22 that is as laminar as possible, a distributor ring 29 with a plurality of through bores 30 is seated on the insulating body 21 provided which connect the annular space 28 with the annular channel 23.

Die den Plasmakanal 4 bildenden Elemente, nämlich die Anode 3 und die Neutroden 6 bis 12, sind durch Ringscheiben 31 aus Isoliermaterial, z.B. Bornitrid, gegeneinander elektrisch isoliert und durch Dichtungsringe 32 gasdicht miteinander verbunden. Der Plasmakanal 4 weist im kathodennahen Bereich eine Einschnürungszone 33 auf und erweitert sich im Anschluss an diese Einschnürungszone 33 zur Anode 3 hin auf einen Durchmesser, welcher mindestens 1,5-mal so gross ist wie der Kanaldurchmesser an der engsten Stelle der Einschnürungszone 33. Nach dieser Erweiterung verläuft der Plasmakanal 4 zylindrisch bis an sein anodenseitiges Ende. Während die Neutroden 6 bis 12 z.B. aus Kupfer bestehen, ist die Anode 3 aus einem Aussenring 34, z.B. aus Kupfer, und einem Innenring 35 aus einem elektrisch und thermisch besonders gut leitenden und zudem hochschmelzenden Material, z.B. thoriertem Wolfram, aufgebaut.The elements forming the plasma channel 4, namely the anode 3 and the neutrodes 6 to 12, are made of insulating material, e.g. Boron nitride, electrically insulated from one another and gas-tightly connected to one another by sealing rings 32. The plasma channel 4 has a constriction zone 33 in the vicinity of the cathode and, following this constriction zone 33, widens towards the anode 3 to a diameter which is at least 1.5 times the channel diameter at the narrowest point of the constriction zone 33 this expansion, the plasma channel 4 runs cylindrical to its anode-side end. While neutrodes 6 to 12 e.g. consist of copper, the anode 3 is made of an outer ring 34, e.g. made of copper, and an inner ring 35 made of an electrically and thermally particularly conductive and also high-melting material, e.g. thoriated tungsten.

Um die Plasmaströmung, insbesondere im Düsenbereich, nicht durch Spalte in der Wandung des Plasmakanals 4 zu behindern, erstreckt sich die den Kathodenstäben 1 am nächsten liegende Neutrode 6 über die ganze Einschnürungszone 33, damit die Kanalwandung 52 bis über die engste Stelle der Einschnürungszone hinaus einen stetigen Verlauf aufweist.In order not to impede the plasma flow, in particular in the nozzle area, by gaps in the wall of the plasma channel 4, the neutrode 6 closest to the cathode rods 1 extends over the entire constriction zone 33, so that the channel wall 52 unites beyond the narrowest point of the constriction zone has a steady course.

Die der Lichtbogen- und Plasmawärme unmittelbar ausgesetzten Teile sind weitgehend wassergekühlt. Zu diesem Zweck sind im Kathodenhalter 13, in den Kathodenstäben 1 und im Anodenhalter 14 verschiedene Hohlräume für die Zirkulation des Kühlwassers KW vorgesehen. Der Kathodenhalter 13 weist drei Ringräume 36, 37 und 38 auf, die mit Anschlussleitungen 39, 40 bzw. 41 verbunden sind, und der Anodenhalter 14 weist im Bereich der Anode 3 einen Ringraum 42 und im Bereich der Neutroden 6 bis 12 einen alle Neutroden umgebenden Hohlraum 43 auf. Kühlwasser KW wird über die Anschlussleitungen 39 und 41 zugeführt. Das Kühlwasser der Anschlussleitung 39 gelangt durch einen Längskanal 44 zunächst zu dem die thermisch am stärksten belastete Anode 3 umgebenden Ringraum 42. Von da strömt das Kühlwasser durch den Hohlraum 43 der Mantelfläche der Neutroden 6 bis 12 entlang zurück durch einen Längskanal 45 in den Ringraum 37. Das Kühlwasser der Anschlussleitung 41 fliesst in einen Ringraum 38 und aus diesem in je einen Hohlraum 46 der Kathodenstäbe 1, welcher durch eine zylindrische Trennwand 47 unterteilt ist. Aus den Kathodenstäben 1 gelangt das Kühlwasser schliesslich ebenfalls in den Ringraum 37, aus dem es über die Anschlussleitung 40 abfliesst.The parts directly exposed to the arc and plasma heat are largely water-cooled. For this purpose, different cavities for the circulation of the cooling water KW are provided in the cathode holder 13, in the cathode rods 1 and in the anode holder 14. The cathode holder 13 has three annular spaces 36, 37 and 38 which are connected to connecting lines 39, 40 and 41, respectively, and the anode holder 14 has an annular space 42 in the region of the anode 3 and one surrounding all neutrodes in the region of the neutrodes 6 to 12 Cavity 43 on. Cooling water KW is supplied via the connecting lines 39 and 41. The cooling water of the connecting line 39 first passes through a longitudinal channel 44 to the annular space 42 surrounding the most thermally stressed anode 3. From there, the cooling water flows through the cavity 43 of the lateral surface of the neutrodes 6 to 12 back through a longitudinal channel 45 into the annular space 37 The cooling water of the connecting line 41 flows into an annular space 38 and out of this into a cavity 46 of the cathode rods 1, which is divided by a cylindrical partition wall 47. Finally, the cooling water likewise arrives from the cathode rods 1 into the annular space 37, from which it flows out via the connecting line 40.

Die Fig. 3 zeigt den ungefähren Verlauf des Lichtbogens 48 beim Betrieb des Plasmaspritzgerätes nach den Fig. 1 und 2, sowie den Strömungsverlauf des Plasmagases PG und die Flugbahn des Spritzmaterials SM. Man erkennt deutlich die Wirkung der Einschnürungszone 33 und der anschliessenden Erweiterung des Plasmakanals 4. Die von den einzelnen Kathodenstiften 20 ausgehenden Lichtbogenäste 49 vereinigen sich in unmittelbarer Nähe der Bogenansatzstellen, und zwareinerseits aufgrund des geringen gegenseitigen Abstandes der Kathodenstifte 20 und andererseits wegen der kathodennahen Einschnürungszone 33, welche das Plasma und die Stromlinien derart einengen, dass sich im Zentrum des Plasmakanals 4 bereits an der Stelle der Spritzmaterialzufuhr eine hohe Energiekonzentration ergibt und keine kalte Seele im Plasmastrahl auftritt. Im erweiterten Teil des Plasmakanals 4 ist der bestand der Kanalwandung 50 zum Plasmastrahl verhältnismässig gross. Unter diesen Umständen wird die Kanalwandung 50 in diesem Bereich thermisch weniger beansprucht, und die Kühlleistung lässt sich dementsprechend verringern.3 shows the approximate course of the arc 48 during operation of the plasma spraying device according to FIGS. 1 and 2, as well as the flow course of the plasma gas PG and the trajectory of the spraying material SM. The effect of the constriction zone 33 and the subsequent expansion of the plasma channel 4 can clearly be seen. The arc branches 49 emanating from the individual cathode pins 20 unite in the immediate vicinity of the arc attachment points, on the one hand because of the small mutual distance between the cathode pins 20 and on the other hand because of the constriction zone 33 near the cathode , which narrow the plasma and the streamlines in such a way that a high energy concentration results in the center of the plasma channel 4 already at the point of the spray material supply and no cold soul occurs in the plasma jet. In the expanded part of the plasma channel 4, the existence of the channel wall 50 relative to the plasma jet is relatively large. Under these circumstances, the channel wall 50 is subjected to less thermal stress in this area, and the cooling capacity can be reduced accordingly.

Bei der Ausführungsform nach Fig. 4 ist eine einzelne Kathode 54 vorgesehen, welche als Hohlkathode ausgebildet ist. Die Neutroden-Kaskade 55 und der Anodenring 56, welche den Plasmakanal 57 bilden, sind im Prinzip gleich aufgebaut wie wie die entsprechenden Teile bei der Ausführungsform nach Fig. 1, mit dem Unterschied, dass die Einlaufdüse 58 hier flacher verlaufen kann und dass der Anodenring 56 einen grösseren Innendurchmesser aufweist als die dem Anodering 56 am nächsten liegende Neutrode 59. In die Hohlkathode 54 ist ein Rohr 60 für die Zufuhr des Spritzmaterials eingesetzt, dessen Mündung 61 gegenüber dem Ende der Kathode 54 zurücksteht. Ein Isolierrohr 62, welches die Mündung 61 des Rohres 60 überragt und das Rohr 60 mit einem Distanzring 63 radial fixiert, sorgt für die nötige Isolation zwischen Kathode 54 und Rohr 60 und schützt das letztere vor übermässiger Erwärmung. Im übrigen kann das Plasmaspritzgerät gleich oder ähnlich aufgebaut sein wie dasjenige nach Fig. 1.In the embodiment according to FIG. 4, a single cathode 54 is provided, which is designed as a hollow cathode. The neutrode cascade 55 and the anode ring 56, which form the plasma channel 57, are constructed in principle in the same way as the corresponding parts in the embodiment according to FIG. 1, with the difference that the inlet nozzle 58 can run flat here and that the anode ring 56 has a larger inner diameter than the neutrode 59 closest to the anode ring 56. A tube 60 is inserted into the hollow cathode 54 for supplying the spray material, the mouth 61 of which protrudes towards the end of the cathode 54. An insulating tube 62, which projects beyond the mouth 61 of the tube 60 and fixes the tube 60 radially with a spacer ring 63, provides the necessary insulation between the cathode 54 and the tube 60 and protects the latter from excessive heating. Otherwise, the plasma spraying device can be constructed identically or similarly to that according to FIG. 1.

Die Fig. 5 zeigt schliesslich noch eine andere Ausführungsform der Anode 64, bei welcher die Innenwandung 65 des eingesetzten Anodenrings 66 nach aussen konisch verläuft.5 finally shows yet another embodiment of the anode 64, in which the inner wall 65 of the anode ring 66 used is conical to the outside.

Claims (11)

1. Plasmaspritzgerät zum Versprühen von pulverförmigem oder gasförmigem Material, mit einem indirekten Plasmatron zur Erzeugung eines Langlichtbogens, welches wenigstens eine Kathode (1,20), eine von der Kathode distanzierte, ringförmige Anode (3) und einen sich von der Kathode zur Anode erstreckenden Plasmakanal (4) aufweist, welcher durch den Anodenring (3) und eine Anzahl ringförmiger, voneinander elektrisch isolierter Neutroden (6 bis 12) gebildet ist, und mit Mitteln für eine achsiale Zufuhr des Spritzmaterials in den Plasmastrahl, dadurch gekennzeichnet, dass sich die Mittel (24) für die Zufuhr des Spritzmaterials (SM) am kathodenseitigen Ende des Plasmakanals (4) befinden und dass der Plasmakanal (4) im kathodennahen Bereich der Lichtbogenstrecke eine Einschnürungszone (33) aufweist und sich von dieser Einschnürungszone zur Anode (3) hin erweitert.1. Plasma spraying device for spraying powdery or gaseous material, with an indirect plasmatron for generating a long arc, which has at least one cathode (1, 20), an annular anode (3) distanced from the cathode and one extending from the cathode to the anode Plasma channel (4), which through the anode ring (3) and a number of annular, from each other electrically isolated neutrodes (6 to 12) is formed, and with means for the axial supply of the spray material into the plasma jet, characterized in that the means (24) for the supply of the spray material (SM) at the cathode-side end of the plasma channel (4) are located and that the plasma channel (4) has a constriction zone (33) in the region of the arc path near the cathode and widens from this constriction zone to the anode (3). 2. Plasmaspritzgerät nach Anspruch 1, dadurch gekennzeichnet, dass der auf die Einschnürungszone (33) folgende, erweiterte Teil des Plasmakanals (4) zylindrisch verläuft.2. Plasma spraying device according to claim 1, characterized in that the expanded portion of the plasma channel (4) following the constriction zone (33) is cylindrical. 3. Plasmaspritzgerät nach Anspruch 1, dadurch gekennzeichnet, dass der auf die Einschnürungszone (33) folgende, erweiterte Teil des Plasmakanals (4) konisch verläuft.3. Plasma spraying device according to claim 1, characterized in that the expanded portion of the plasma channel (4) following the constriction zone (33) extends conically. 4. Plasmaspritzgerät nach Anspruch 1, dadurch gekennzeichnet, dass die ringfömige Anode (56) einen grösseren Innendurchmesser aufweist als die der Anode benachbarte Neutrode (59) (Fig. 4).4. Plasma spraying device according to claim 1, characterized in that the ring-shaped anode (56) has a larger inner diameter than that of the anode adjacent neutrode (59) (Fig. 4). 5. Plasmaspritzgerät nach Anspruch 1, dadurch gekennzeichnet, dass die Innenfläche (65) der Anode (64) nach aussen konisch erweitert ist (Fig. 5).5. Plasma spraying device according to claim 1, characterized in that the inner surface (65) of the anode (64) is flared outwards (FIG. 5). 6. Plasmaspritzgerät nach Anspruch 1, dadurch gekennzeichnet, dass der Durchmesser des Plasmakanals (4) am anodenseitigen Ende mindestens 1,5-mal so gross ist wie an der engsten Stelle der Einschnürungszone (33).6. Plasma spraying device according to claim 1, characterized in that the diameter of the plasma channel (4) at the anode-side end is at least 1.5 times as large as at the narrowest point of the constriction zone (33). 7. Plasmaspritzgerät nach Anspruch 1, dadurch gekennzeichnet, dass die der Kathode (1,20) am nächsten liegende Neutrode (6) sich wenigstens bis zur engsten Stelle der Einschnürungszone (33) erstreckt.7. Plasma spraying device according to claim 1, characterized in that the neutrode (6) closest to the cathode (1, 20) extends at least to the narrowest point of the constriction zone (33). 8. Plasmaspritzgerät nach Anspruch 1, dadurch gekennzeichnet, dass für die Zufuhr des Spritzmaterials (SM) ein zentrales Rohr (24) vorgesehen ist, das auf den Plasmakanal (4) achsial ausgerichtet ist und in den Hohlraum (22) der der Kathode (1,20) am nächsten liegenden Neutrode (6) ragt.8. Plasma spraying device according to claim 1, characterized in that a central tube (24) is provided for the supply of the spray material (SM), which is axially aligned with the plasma channel (4) and into the cavity (22) of the cathode (1 , 20) protrudes from the closest neutrode (6). 9. Plasmaspritzgerät nach Anspruch 8, dadurch gekennzeichnet, dass mehrere stabförmige Kathoden (1,20) vorgesehen sind, welche im Kreis um das zentrale Rohr (24) verteilt angeordnet sind.9. Plasma spraying device according to claim 8, characterized in that a plurality of rod-shaped cathodes (1, 20) are provided, which are distributed in a circle around the central tube (24). 10. Plasmaspritzgerät nach Anspruch 9, dadurch gekennzeichnet, dass die Kathoden (1,20) parallel zueinander verlaufen und symmetrisch um das zentrale Rohr (24) verteilt angeordnet sind.10. Plasma spraying device according to claim 9, characterized in that the cathodes (1, 20) run parallel to one another and are arranged symmetrically around the central tube (24). 11. Plasmaspritzgerät nach Anspruch 8, dadurch gekennzeichnet, dass als Kathode eine Hohlkathode (54) vorgesehen ist, welche zugleich das Rohr für die Zufuhr des Spritzmaterials bildet oder ein von dieser isoliertes Rohr (60) umschliesst (Fig. 4).11. Plasma spraying device according to claim 8, characterized in that a hollow cathode (54) is provided as the cathode, which at the same time forms the tube for the supply of the spray material or encloses a tube (60) insulated therefrom (FIG. 4).
EP92810094A 1991-02-21 1992-02-10 Plasma spray gun for spraying powdered or gaseous materials Expired - Lifetime EP0500491B1 (en)

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ATE129378T1 (en) 1995-11-15
JPH0584454A (en) 1993-04-06
CA2061158C (en) 1998-06-30
JP3258694B2 (en) 2002-02-18
US5225652A (en) 1993-07-06
DE4105408C1 (en) 1992-09-17
DE59204023D1 (en) 1995-11-23
EP0500491B1 (en) 1995-10-18
CA2061158A1 (en) 1992-08-22

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