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
  • H05H1/3442—Cathodes with inserted tip

Definitions

• the invention relates to an electrode element for plasma torches and a manufacturing method for such electrode elements.
• Such an electrode element is particularly suitable for plasma cutting, in which oxygen is used as the plasma gas.
• Such electrodes are subject to very high thermal and electrical loads when used in plasma torches, so that they only have a limited lifespan and an expensive replacement of the electrodes is required at more or less long intervals.
• the high thermal stress caused by temperatures up to 50,000 Kelvin require a suitable construction and a suitable selection of the materials used for such an electrode.
• electrodes which consist essentially of hafnium and have a melting temperature in the range of 2220 ° C. have been used for plasma cutting, using oxygen as the plasma gas.
• hafnium has a low work function, making it particularly suitable for use.
• pin-shaped hafnium electrodes with a copper socket are used, taking advantage of the high thermal and electrical conductivity of the copper.
• Gases such as the oxygen already mentioned, are oxidized in copper, so that the thermal conductivity and the electrical contact resistance between copper and hafnium are negatively affected.
• silver or a silver alloy is used according to the prior art.
• Silver also has good thermal and electrical conductivities and a higher work function.
• the formation of oxides in silver is lower than in copper at higher temperatures.
• a corresponding solution is described in EP 0 980 197 A2.
• a copper holder is to be used, into which a silver sleeve, which consists of a selected silver alloy and has a closed bottom pointing into the interior of the copper holder, is pressed into a receptacle designed as a blind hole.
• a pin-shaped electrode made of hafnium is then pressed into this silver sleeve.
• Such a structure has several disadvantages.
• this relates to the complex production, in which the individual elements have to be manufactured separately and in some cases by machining. The three individual parts then have to be put together to form an element, whereby high requirements for joining and handling have to be met due to the relatively small-sized silver sleeve and the Hanfniu pen.
• the mechanical pressing of the silver sleeve and the hafnium pin must be carried out very carefully.
• this object is achieved with an electrode element which has the features of claim 1 and a method for producing it according to claim 13.
• Advantageous refinements and developments of the invention can be achieved with the features specified in the subordinate claims.
• the electrode element according to the invention for the plasma torches in question has at least one core made of a metal or a metal alloy with a smaller work function than a metal or a metal alloy, from which a jacket part enclosing the at least one core is formed, the one or also several core (s) form the actual electrode connected as a cathode.
• the different materials that is to say the core surface and the jacket part, there is a boundary layer formed in a graded form, which is formed from mixed crystals of the respective metals or metal alloys.
• an intermediate layer between the core surface and the cladding part material is made of a further metal or a metal alloy with a larger work function than that of the core material, the interlayer in the direction of the core and the cladding part each having a graded thickness - Transition forms in the form of appropriately trained boundary layers.
• Hafnium or a hafnium alloy can be used as a particularly suitable material for the core, the proportion of alloy components should be kept relatively small.
• tungsten, zirconium or tantalum or alloys of these elements can also be used as core materials.
• a preferred material for the jacket part is copper or a copper alloy.
• the intermediate layer can in turn be formed from silver or a silver alloy.
• boundary layers present according to the invention in an electrode element which each form graded transitions of the different materials not available in the solutions known from the prior art, such as, for example, the one described in EP 0 980 197 A2, since this is not possible in terms of construction and production.
• the electrode elements according to the invention can be produced simply and inexpensively by a shaping and / or joining process using pressure forces (pressing forces), the corresponding ones
• Boundary layers with the graded transitions can be formed without additional technological process steps. Extrusion or hot isostatic pressing are particularly suitable processes.
• Corresponding rod-shaped, wire-shaped or sleeve-shaped elements made of the respective metals or metal alloys can be used as preliminary products for the one or more core (s), the jacket part and / or an intermediate layer
• the respective metal or metal alloy in powder form for these elements.
• the use of powdered, for example silver, is particularly favorable for the formation of the intermediate layer.
• the space between a sleeve-shaped copper part and at least one rod-shaped or wire-like element forming the core can be filled with silver powder and the corresponding intermediate layer with a respective graded transition in the direction of the core surface and in the direction of the shell part as a result of the compressive forces acting during extrusion can train.
• a mixing zone made of the respective two metals or metal alloys, which can be reached by the individual grains of the powder starting material is formed, which is homogeneous over the entire area available.
• the starting powders used can then be produced by means of a pressing process, preferably by cold isostatic pressing, individually or successively one after the other, to produce precursors which ensure sufficient strength for the subsequent extrusion process, and an electrode element according to the invention can subsequently be formed by extrusion.
• rod-shaped elements with a circular cross section can be used as the preliminary product.
• elements with circular cross sections which are hollow on the inside and consequently of sleeve-shaped design.
• This cavity can in turn be filled with a powder of a metal or a metal alloy, which has a higher work function than the core material, before the extrusion.
• elements whose cross sections are star-shaped can also be used to form the cores forming the actual electrodes.
• Such a star-shaped element can then have three or even more webs, each of which are aligned at the same angular spacing from one another, and an enlargement of the respective transition surfaces with the associated low electrical and thermal contact resistances between the core and the jacket part or intermediate layer can thereby be achieved ,
• a core can also be formed from a plurality of wire-shaped elements twisted together, similar to strands frequently used in electrical lines.
• a core formed in this way by twisting wire-shaped elements also increases the
• an electrode element according to the invention it is advantageous to arrange them discretely and equidistantly from one another, each being embedded in the jacket part material, optionally with the interposition of an intermediate layer.
• one should be used prior to extrusion Preheating to a temperature of at least 400 ° C are carried out, in particular to reduce the stress on the extrusion die. Such preheating also has a favorable effect on the formation of mixed crystals or diffusion processes, which can thus take place with great certainty with the relatively high compressive forces acting simultaneously during the extrusion.
• An electrode element according to the invention has low thermal and electrical contact resistances due to the more intimate bond with the graded transitions of the various metals or metal alloys of the individual elements, so that the problem of current corrosion can be counteracted and the service life can be significantly increased. As a result, not only the manufacturing costs for the electrode elements themselves, but also the operating costs of an appropriately equipped plasma torch are significantly reduced for the end user.
• the electrode elements produced by the method according to the invention in which intermediate layers made of silver or silver alloys are used, can also be produced more cost-effectively, since such intermediate layers can be formed with a significantly smaller layer thickness, so that the cost-intensive use of silver can be reduced accordingly.
• a sleeve-shaped copper element can be used to form a jacket part.
• At least one rod-shaped element made of hafnium, for example, can extend over the entire length of the copper sleeve and be inserted into the interior thereof.
• Such a copper sleeve can have an outer diameter of, for example 12 mm and the free cross section inside such a copper sleeve have a diameter of 1.5 mm.
• An electrode element obtained in this way then only has to be inserted into a corresponding plasma torch, such a plasma torch also being able to be designed such that a certain part of such an electrode element arranged in the interior of a plasma torch can be directly flowed around by a cooling medium for dissipating heat.
• hafnium wires preferably twisted together, can also be introduced into such a copper sleeve, the inside diameter of the copper sleeve and the largest dimension of such a core pre-element being dimensioned such that an intermediate space remains which can be filled with a silver powder or a silver powder alloy.
• Such a silver powder forming an intermediate layer should also be used if possible if a core with a non-rotationally symmetrical cross-sectional shape or a sleeve-shaped core are to be formed.
• a rod-shaped element made of hafnium on its outer surface in the direction of the shell part material with a layer essentially formed from silver powder.
• a powder can, for example, be applied in the form of a suspension and for example, solidified on the surface of the rod-shaped hafnium element or subjected to sintering.
• the suspension containing the silver powder can also contain an organic binder which can be expelled thermally during sintering.
• a rod-shaped element provided with such a silver layer can then be reinserted into a sleeve-shaped copper element and an electrode element according to the invention can be produced by extrusion.
• the electrode element according to the invention can also be further developed by being able to connect it to a sleeve-shaped element by forming a corresponding contour, wherein an external thread can preferably be selected.
• a sleeve-shaped element which preferably consists of
• the electrode member is simply herein- or with the formed at 'its outer circumferential surface threaded, as a contour shape in a sleeve-shaped element unscrewed.
• the element according to the invention can also be designed and manufactured in such a way that a cavity which is open on one side has been formed within the jacket part.
• This cavity can be filled with a mabrenners be connected so that the cooling medium, preferably water for heat dissipation can get directly into this cavity.
• Such a cavity can advantageously be formed by backward extrusion. Machining can also be avoided with this method.
• Backward extrusion is a subsequent processing step on an electrode element, the manufacture of which has been described in advance. In this case, an electrode element is produced as a preliminary product, which is kept shorter in length than the finished electrode element with the cavity and is larger than its outer diameter.
• a tool with a mandrel that defines the shape and size of the respective cavity is used and because of the significantly higher flowability, the copper jacket part is almost exclusively deformed.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Arc Welding In General (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Plasma Technology (AREA)
• Polishing Bodies And Polishing Tools (AREA)

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• 2002
  • 2002-03-06 DE DE10210421A patent/DE10210421B4/de not_active Expired - Fee Related
• 2003
  • 2003-03-05 WO PCT/DE2003/000763 patent/WO2003075621A2/fr not_active Application Discontinuation
  • 2003-03-05 AU AU2003240381A patent/AU2003240381A1/en not_active Abandoned
  • 2003-03-05 AT AT03729808T patent/ATE418258T1/de active
  • 2003-03-05 DE DE50310929T patent/DE50310929D1/de not_active Expired - Lifetime
  • 2003-03-05 EP EP03729808A patent/EP1481574B1/fr not_active Expired - Lifetime
  • 2003-03-05 US US10/506,696 patent/US7098422B2/en not_active Expired - Fee Related

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