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
  • 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
  • H05H1/32—Plasma torches using an arc
  • H05H1/34—Details, e.g. electrodes, nozzles
  • H05H1/3425—Melting or consuming electrodes
• • 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 present invention relates to electrodes for a, in particular liquid-cooled, plasma cutting torch and, in particular liquid-cooled, arrangements comprising the same, plasma cutting torches comprising the same and methods for plasma cutting.
• Plasma cutting torches are used for plasma cutting of metals. They typically consist essentially of a torch body, an electrode, a nozzle, and a holder. Modern plasma torches and plasma cutting torches also have a nozzle protection cap mounted over the nozzle. A nozzle is often secured with a nozzle cap.
• the components subject to wear during operation of the plasma cutting torch due to the high thermal stress caused by the arc include, in particular, the electrode, the nozzle, the nozzle cap, the nozzle protection cap, the nozzle protection cap holder, and the plasma gas guide and secondary gas guide components. These components can be easily replaced by an operator and are therefore considered wear parts.
• the plasma cutting torches are connected via cables to a power source and a gas supply that feeds the plasma cutting torch. Furthermore, the plasma cutting torch can be connected to a cooling device for a cooling medium, such as a coolant.
• Plasma cutting torches are subject to high thermal stresses. This is caused by the strong constriction of the plasma jet by the nozzle bore. Small bores are used here to generate high current densities of 50 to 150 A/ mm2 in the nozzle bore, high energy densities of approximately 2x103 W/ cm2 , and high temperatures of up to 30,000 K. Furthermore, higher gas pressures, typically up to 12 bar, are used in plasma cutting torches. The combination of high temperature and high kinetic energy of the plasma gas flowing through the nozzle bore leads to the melting of the workpiece and the expulsion of the molten material. A kerf is created, and the workpiece is severed.
• nitrogen or nitrogen-containing gas mixtures are often used as the plasma gas to cut high-alloy steel, stainless steel, non-ferrous metals, or non-ferrous metal alloys, such as aluminum or an aluminum-magnesium alloy.
• nitrogen or nitrogen-containing gas mixtures are often used as the plasma gas to cut high-alloy steel, stainless steel, non-ferrous metals, or non-ferrous metal alloys, such as aluminum or an aluminum-magnesium alloy.
• a plasma gas flows between the electrode and the nozzle.
• the plasma gas is guided through a gas guide (plasma gas guide).
• plasma gas guide This allows the plasma gas to be directed in a targeted manner. It is often set in rotation around the electrode by a radial and/or axial offset of the openings in the plasma gas guide.
• the plasma gas guide is made of electrically insulating material because the electrode and nozzle must be electrically insulated from each other. This is necessary because the electrode and nozzle have different electrical potentials during operation of the plasma cutting torch.
• an arc is generated between the electrode and the nozzle and/or the workpiece, which ionizes the plasma gas.
• a high voltage can be applied between the electrode and nozzle. This pre-ionizes the path between the electrode and the nozzle and thus forms an arc.
• the arc burning between the electrode and nozzle is also called the pilot arc.
• the pilot arc exits through the nozzle bore and strikes the workpiece, ionizing the path to the workpiece. This allows the arc to form between the electrode and the workpiece. This arc is also called the main arc.
• the pilot arc can be switched off during the main arc. However, it can also continue to operate. In plasma cutting, this is often switched off to avoid placing additional strain on the nozzle.
• the electrode and nozzle are subject to high thermal stress and require cooling. At the same time, they must also conduct the electrical current required to form the arc. Therefore, materials with good thermal and electrical conductivity are used, usually metals such as copper, silver, aluminum, tin, zinc, iron, or alloys containing at least one of these metals.
• the electrode often consists of an electrode holder and an emissive insert made of a material with a high melting temperature (> 3000°C). Tungsten is used as the material for the emissive insert when using non-oxidizing plasma gases such as argon, hydrogen, nitrogen, helium, and mixtures thereof.
• the high-temperature material can be pressed into an electrode holder made of a material with good thermal and electrical conductivity, for example, using positive and/or frictional engagement.
• the electrode and nozzle can be cooled by gas, such as plasma gas or a secondary gas flowing along the outside of the nozzle.
• gas such as plasma gas or a secondary gas flowing along the outside of the nozzle.
• cooling with a liquid such as water, is more effective.
• the electrode and/or nozzle are often cooled directly with the liquid, meaning the liquid is in direct contact with the electrode and/or nozzle.
• a nozzle cap is located around the nozzle. Its inner surface, together with the outer surface of the nozzle, forms a coolant chamber through which the coolant flows.
• Modern plasma cutting torches also have a nozzle protection cap outside the nozzle and/or nozzle cap.
• the inner surface of the nozzle protection cap and the outer surface of the nozzle or nozzle cap form a space through which a secondary or shielding gas flows.
• the secondary or shielding gas exits the bore of the nozzle protection cap and envelops the plasma jet, creating a defined atmosphere around it.
• the secondary gas also protects the nozzle and nozzle protection cap from arcs that can form between the nozzle and the workpiece. These are known as double arcs and can damage the nozzle.
• the nozzle and nozzle protection cap are subjected to significant stress from hot material splashing up.
• the secondary gas whose volume flow during piercing may be higher than that during cutting, keeps the splashing material away from the nozzle and nozzle protection cap, thus protecting them from damage.
• the nozzle protection cap is also subject to high thermal stress and requires cooling. Therefore, materials with good thermal and electrical conductivity are used for it, usually metals such as copper, silver, aluminum, tin, zinc, iron, or alloys containing at least one of these metals.
• the electrode and nozzle can also be cooled indirectly.
• they are in contact with a component made of a material that conducts heat and electricity well, usually a metal such as copper, silver, aluminum, tin, zinc, iron, or alloys containing at least one of these metals.
• This component is cooled directly, meaning it is in direct contact with the usually flowing coolant.
• These components can simultaneously serve as a holder or receptacle for the electrode, nozzle, nozzle cap, or nozzle protection cap, dissipating heat and supplying current.
• the nozzle cap is usually cooled solely by the secondary gas. Arrangements are also known in which the secondary gas cap is cooled directly or indirectly by a cooling liquid.
• Plasma torches, and especially plasma cutting torches, are subject to high levels of wear and tear due to the high energy density and high temperatures involved. This particularly applies to the electrode.
• the lifetime is often too short. Furthermore, there are often large fluctuations in lifetime.
• High cutting quality and cutting speed are achieved when cutting high-alloy steel, stainless steel, non-ferrous metals, or non-ferrous metal alloys by using so-called point electrodes.
• the emissive insert protrudes from the electrode holder and is pointed at the front.
• a long service life and good cutting quality are also achieved for workpiece thicknesses of 6 mm and above.
• the cutting quality can be improved by using nitrogen, argon-nitrogen, nitrogen-hydrogen or argon-hydrogen-nitrogen mixtures.
• the service life of the electrode decreases considerably, even at currents below 100 A, which are relatively small for plasma cutting.
• the emissive insert wears during operation, i.e., when the arc or plasma jet is burning. It gradually burns back, and the portion protruding from the electrode holder shortens. As the burnback increases, the cut quality deteriorates significantly. Especially when cutting high-alloy steel, stainless steel, non-ferrous metals, or non-ferrous metal alloys, this leads to a larger perpendicularity and inclination tolerance of the cutting surface according to DIN ISO 9013, the formation of dross on the underside of the material being cut, and increased roughness of the cutting surface.
• the cut quality is usually no longer acceptable. If it burns back even further, for example, more than 2 mm, the arc transfers from the emissive insert to the electrode holder, causing the entire electrode to suddenly fail. This also destroys the nozzle. It can even destroy the entire torch.
• tungsten electrodes with rare earth oxides to increase their service life and improve the ignitability of the arc.
• rare earth oxides examples include lanthanum, thorium, or cerium oxide. This is known for applications using argon as the gas. If such electrodes are used with nitrogen, their service life decreases rapidly.
• the aim of the invention is to achieve a high cutting speed, a high cutting quality and a long service life of at least the electrode during plasma cutting.
• an electrode for a plasma cutting torch comprising an electrode holder and an emission insert which are connected to one another in a force-fitting, form-fitting and/or material-fitting manner, characterized in that the emission insert consists of an alloy of at least tungsten and at least one of the elements or compounds listed below: zirconium and/or hafnium and/or zirconium oxide and/or hafnium oxide.
• this object is achieved by an electrode for a plasma cutting torch, wherein the electrode has a front end and a rear end, extends along a longitudinal axis and has at least one emission insert at the front end and an electrode holder, in particular wherein at least a part of the emission insert protrudes or projects from the electrode holder in the direction of the front end of the electrode, in particular wherein the emission insert protruding or projecting from the electrode holder has a section that tapers towards the front end, preferably conically.
• this object is achieved by an arrangement comprising an electrode according to one of claims 1 to 23 and a nozzle.
• this object is achieved by a plasma cutting torch comprising an electrode according to one of claims 1 to 23, a nozzle and/or a nozzle protection cap and/or a plasma gas guide part. Furthermore, according to a fifth aspect, this object is achieved by a method for plasma cutting using a plasma cutting torch according to one of claims 27 to 29, wherein the plasma cutting torch (1) is operated with nitrogen or a gas mixture with nitrogen as the plasma gas.
• the proportion of zirconium and/or hafnium and/or zirconium oxide and/or hafnium oxide is at least 0.1%, better at least 0.3% of the volume or mass of the alloy of the emission insert.
• the proportion of zirconium and/or hafnium and/or zirconium oxide and/or hafnium oxide is a maximum of 5%, preferably a maximum of 2% of the volume or mass of the alloy of the emission insert.
• the proportion of tungsten is at least 95%, better at least 98%, and most preferably 99% of the volume or mass of the alloy of the emission insert.
• the electrode has a front end and a rear end, extends along a longitudinal axis L and the emission insert is located at the front end.
• a part of the emission insert may protrude or protrude from the electrode holder towards the front end of the electrode.
• the emission insert protruding or projecting from the electrode holder has a section tapering towards the front end, preferably conically.
• an outer surface of the preferably conically tapered section extending towards the front end along the longitudinal axis L forms an angle ( ⁇ ) of 15° to 30°, preferably of 20° to 25°, between the outer surface and the longitudinal axis L.
• the electrode holder may have a tapered, preferably conical, section towards the front end.
• an outer surface of the preferably conically tapered section extending towards the front end along the longitudinal axis L forms an angle ⁇ of 15° to 30°, preferably of 20° to 25°, between the outer surface and the longitudinal axis L.
• angles ⁇ and ⁇ should have a difference of no more than 10°, better of no more than 5°, and ideally they should be the same size.
• the emission insert at the front end of the electrode has a circular area with a diameter D 3 of maximum 1.5 mm, preferably maximum 1.0 mm, most preferably maximum 0.6 mm.
• the emission insert has a circular area at the front end of the electrode, which has a diameter D3 of at least 0.2 mm, better of at least 0.4 mm.
• the surface at the front end of the electrode can also be other than circular. Regardless of whether it is circular or not, it is advantageous maximum 1.8 mm 2 , better maximum 0.8 mm 2 , ideally maximum 0.3 mm 2 and/or minimum 0.05 mm 2 , better minimum 0.1 mm 2 .
• the emission insert has a largest outer diameter D2 and the electrode holder has a smallest outer diameter D1, the difference between D1 and D2 being between 0.2 mm and 1 mm.
• the plasma cutting torch is operated with nitrogen or a gas mixture with nitrogen or air or a gas mixture with air as secondary gas.
• At least the electrode and/or the nozzle and/or the nozzle protection cap is/are cooled with a liquid medium.
• the workpiece to be cut can be made of a high-alloy steel, a stainless steel or a non-ferrous metal or a non-ferrous metal alloy.
• the non-ferrous metal may consist at least partially of aluminum, copper, titanium, zinc or tin.
• the present invention is based on the surprising finding that the materials used and/or the structural design of the electrode ensure a long service life and high cutting quality even over a long period of time when using a nitrogen-containing plasma gas or mixture in a Plasma torch particularly when cutting high-alloy steel, stainless steel or non-ferrous metal/alloy.
• FIGS. 1 and 2 show sectional views through plasma cutting torch heads according to particular embodiments of the present invention, in which a Electrode according to a particular embodiment of the present invention and an electrode and nozzle arrangement according to a particular embodiment of the present invention have been used.
• FIGS. 3 , 4 and 5 show details of the plasma cutting torch heads of the Figures 1 and 2 contained electrode.
• FIG. 6 shows a sectional view of an electrode according to another particular embodiment of the invention
• Figure 7 shows a sectional view of the Figures 1 , 2 and 3 to 5 electrode shown.
• the plasma cutting torch head 1 shown comprises an electrode 7, a nozzle 4, and a plasma gas supply 3 for plasma gas PG.
• the plasma cutting torch head according to a particular embodiment of the present invention extends along the longitudinal axis L and has a front end 14 and a rear end 15.
• the electrode 7 is screwed into an electrode holder 6 by means of a thread and is cooled from the inside with a cooling medium which is supplied via the interior of a cooling tube 11 as coolant flow WV1 and is returned to a space 13 formed between the exterior of the cooling tube 11 and the electrode holder 6 as coolant return WR1.
• the nozzle 4 is held by a nozzle cap 2. Between the nozzle 4 and the nozzle cap 2, a cooling medium flows in a space 10, which is fed in via the coolant supply line WV2 and returned via the coolant return line WR2.
• a nozzle protection cap 9 encloses the nozzle 4 and the nozzle cap 2.
• secondary gas SG flows through a secondary gas guide 9.1, which simultaneously insulates the nozzle protection cap 9 from the nozzle cap 2 and keeps them at a distance.
• the secondary gas guide 9.1 can, for example, be designed to rotate the secondary gas SG
• the nozzle protection cap 9 is fixed by a nozzle protection cap holder 8, which is attached to the plasma torch head by means of a thread.
• the nozzle 4 has in its interior, as seen from the front end 14, a nozzle channel 4.1 and a conically widening chamber 4.3.
• the inner surface of the chamber 4.2 of the nozzle 4 runs parallel to a conical outer surface 7.1.3 of a section 7.1.1 of the electrode 7. This ensures a good plasma gas flow in the remaining space between the nozzle 4 and the electrode 7.
• the diameter D4 of the nozzle channel 4.1 is 1.2 mm in both figures, for example.
• the front surface 7.2.4 of the emission insert can also be other than circular. Regardless of whether it is circular or not, it is advantageously a maximum of 1.8 mm 2 , preferably a maximum of 0.8 mm 2 , ideally a maximum of 0.3 mm 2 , and/or a minimum of 0.05 mm 2 , preferably a minimum of 0.1 mm 2 .
• “Very close” generally means the following: L1 ⁇ 1.5 mm, better L1 ⁇ 1 mm and/or L1 ⁇ 1.5 *D4, better L1 ⁇ 1.0 * D4, with D4 being the smallest diameter of the nozzle channel.
• a plasma gas guide part 3.1 is mounted between the electrode 7 and the nozzle 4. This guide part isolates the electrode 7 and the nozzle 4 from each other and allows the plasma gas PG to flow into the nozzle interior through openings.
• the plasma gas PG can be set in rotation by radially offsetting the openings relative to the longitudinal axis L or by inclining the openings relative to the longitudinal axis L.
• the electrode 7 consists of an electrode holder 7.1 and an emission insert 7.2. In one embodiment, however, it can also consist of more components.
• the emission insert 7.2 is fastened in the electrode holder 7.1. This can be force-, form-, or by a material bond. This ensures good heat transfer between the emission insert 7.2 and the electrode holder 7.1.
• the electrode holder 7.1 can be water-cooled, and it can have a cavity inside through which the cooling medium flows.
• the electrode holder 7.1 is made of a material with good thermal and electrical conductivity, e.g., copper or silver or an alloy thereof. An alloy as specified in any of claims 1 to 5 can be used for the emission insert 7.2.
• the thermal conductivity is >300W/(m*K), for example, silver 429W/(m*K), copper 398W/(m*K).
• the electrical conductivity is advantageously more than 10 7 S/m (for example, silver 61*10 6 S/m, copper 58*10 6 S/m).
• an alloy of tungsten and zirconium oxide is used.
• the tungsten content is 99.3% and the zirconium oxide content is 0.3% of the alloy's mass.
• the remaining portion to 100% of the mass in this example consists of copper, which accounts for 0.15% of the total mass.
• the plasma cutting torch head 1 shown differs from the one shown in Figure 1 shown plasma cutting torch head in the inner contour of the nozzle.
• the nozzle 4 has in its interior, seen from the front end 14, a cylindrical nozzle channel 4.1, a further essentially cylindrical chamber 4.2 and a conically widening chamber 4.3.
• essentially cylindrical is meant that the cylindrical inner surface of this chamber 4.3 is larger than the inner surface of the smaller conical section shown here directly at the nozzle channel 4.1.
• the inner surface of the chamber 4.3 of the nozzle 4 runs parallel to the outer surface 7.1.3 of section 7.1.1 of the electrode 7. This ensures good plasma gas flow in the remaining space between the nozzle 4 and the electrode 7.
• the front circular surface 7.2.4 of the emission insert 7.2. comes very close to the end of nozzle channel 4.1.
• the length L1 here is, for example, 1.2 mm.
• the diameter D4 of nozzle channel 4.1 is, for example,
• the front surface 7.2.4 of the emission insert may also be other than circular. Regardless of whether it is circular or not, it is advantageously a maximum of 1.8 mm2 , preferably a maximum of 0.8 mm2 , preferably a maximum of 0.3 mm2 , and/or a minimum of 0.05 mm2 , preferably a minimum of 0.1 mm2 .
• the Figures 3 , 4 and 5 show in more detail the structure of the electrode of Figures 1 and 2 .
• the Figures 3 , 4 and 5 show the electrode 7, which extends along a longitudinal axis L and has a front end 7.4 and a rear end 7.3.
• the electrode consists of the electrode holder 7.1 and the emission insert 7.2, which is pressed into the electrode holder 7.1 with its rear section 7.2.1 and is thus connected in a force-locking manner.
• the electrode holder 7.1 has a rear section 7.1.2, which is designed here, for example, with a thread and can be screwed into the electrode holder 6 of the plasma cutting torch head.
• the electrode holder 7.2 has a conically tapered section 7.1.1 with an outer surface 7.1.3 towards the front end 7.4 of the electrode 7. At the front end is a circular surface with a diameter D1.
• An angle ⁇ enclosed by the outer surface 7.1.3 of the conical section 7.1.1 of the electrode holder 7.1 and the longitudinal axis L is, for example, 23° here.
• the emission insert 7.2 has a rear section 7.2.1 projecting into the electrode holder 7.1 and a section projecting from the electrode holder 7.1, which has a cylindrical section 7.2.2 with the diameter D2 and a conically tapered section 7.2.3 with an outer surface 7.2.5.
• the diameter D1 is 2.0 mm, for example.
• the diameter D1 is 2.5 mm, for example.
• the difference between D1 and D2 is 0.25 mm.
• the emission insert 7.2 has a circular area 7.2.4 towards the front end 14, which has a diameter D3 of, for example, 0.4 mm (see Figure 4 ).
• An angle ⁇ enclosed by the outer surface 7.2.5 of the conical section 7.2.3 of the emission insert 7.2 and the longitudinal axis L is, for example, 23°.
• the angles ⁇ and ⁇ of the conically tapered sections of the electrode holder 7.1 and the emission insert 7.2 are of equal size.
• the front surface 7.2.4 of the emission insert may also be other than circular. Regardless of whether it is circular or not, it is advantageously a maximum of 1.8 mm2 , preferably a maximum of 0.8 mm2 , preferably a maximum of 0.3 mm2 , and/or a minimum of 0.05 mm2 , preferably a minimum of 0.1 mm2 .
• the diameter D3 here, for example, is 0.4 mm. This ensures that the electrode's service life is sufficiently long, even during plasma cutting with a nitrogen-containing plasma gas, while remaining sufficiently centered thanks to the relatively small circular area 7.2.4. This ensures a long service life and good cutting quality. Since the diameter D3 in this example is 0.4 mm, the circular area 7.2.4 is 0.125 mm2 .
• the Figure 6 shows an electrode 7, which is different from the one in the Figures 3 to 5 shown embodiments in that the interior is of exemplary solid construction.
• the Figure 7 shows the electrode again Figure 1
• the electrode has a cavity 7.12 inside, which extends from the rear end 7.3 towards the front end.
• cooling is much more effective than with an electrode according to Figure 6 because the coolant passes through, as in Figure 1 and 2
• a cooling tube is placed near the emission insert. This also increases the service life of the electrode, especially that of the emission insert.
• the described electrodes 7 and the described plasma cutting torch 1 are used according to the invention for plasma cutting with a nitrogen-containing plasma gas. This is particularly advantageous for plasma cutting workpieces made of high-alloy steel, stainless steel, or a non-ferrous metal or non-ferrous metal alloy. However, it is also possible to cut structural steel.
• an electrode 7 with an electrode holder 7.1 and an emission insert 7.2 ensures a long service life and good cutting quality.

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

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• 2020
  • 2020-09-25 DE DE102020125073.8A patent/DE102020125073A1/de active Pending
• 2021
  • 2021-07-29 WO PCT/DE2021/100652 patent/WO2022028648A1/fr not_active Ceased
  • 2021-07-29 EP EP21798270.1A patent/EP4193811B1/fr active Active
  • 2021-07-29 EP EP25191433.9A patent/EP4618698A3/fr active Pending
  • 2021-07-29 CN CN202180057632.XA patent/CN116195370A/zh active Pending

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