Device for thermal coating by means of wire arc spraying

Abstract

Arc wire torch (2) and method for thermal coating of surfaces using a wire arc, with a metal wire (3) having a streamlined cross-section.

Description

[0001] In wire arc spraying, an electrically conductive, wire-shaped spray additive is converted from a solid to a liquid state using an electrical discharge process and then applied to a substrate surface.

[0002] The wire arc spraying process is based on the principle that two circular, electrically conductive spray materials, typically in the form of metal wires, are fed towards each other at a constant feed rate by a feeder. Wire arc processes using only one wire are also known. The wires are conductively connected to a power source, which typically carries a voltage of 12 to 50 V. When the two wire ends are sufficiently close, an arc is ignited, which serves as the energy source for melting the wire filler material. A gas stream (compressed air or a technical gas) detaches the molten material from the wire ends and accelerates it as a particle stream onto the component to be coated.

[0003] Conventional wire arc spraying systems achieve melting rates of approximately 5–200 kg / h at particle velocities of approximately 150 m / s. Temperatures exceeding 5000 K are reached in the arc. The layer thicknesses that can be produced with this process range from 50 pm to 20 mm.

[0004] Wire arc spraying is used, among other things, for corrosion protection of steel structures and aluminium tubes for heat exchangers, for wear protection and repair of components, and for the production of solderable layers on capacitors.

[0005] From DE 10 2017 007398 A1, an arc wire burner with at least one electrode made of a trackable wire is already known, wherein the wire has a contour deviating from the cylindrical shape at least between the area of ​​its exit from at least one wire guide element and the arc.

[0006] A major problem in wire arc spraying is vortex shedding of the atomizing gas flow at or behind the wire cross-sections. These vortex regions circulate continuously in the so-called dead zones of the wires and significantly influence the melting behavior (droplet size) and the arc column (plasma-gas interaction), resulting in molten spray particles remaining on the vortex paths near the wire ends. During this time, the material is oxidized by atmospheric oxygen from the ambient or compressed air. The continuous melting of the wire increases the amount of recirculating molten particles, resulting in uneven atomization. The spray jet spreading around the wire ends creates a so-called "Karman vortex street." This causes the particle-laden spray jet to diverge dramatically.Due to the high divergence, some of the particles enter the slower outer regions of the atomizing gas flow. The increased oxidation, the uneven heat content and velocity of the particles in the spray jet lead to reduced particle adhesion to the component being coated. Depending on the wire filler material, the so-called deposition efficiency can be reduced by approximately 50% to 60%, meaning that 50% to 60% of the molten wire material does not adhere to the component being coated and is released into the environment as dust. In addition to the environmental and occupational safety aspects, the economic viability of the process also needs improvement.

[0007] With regard to the spray coating, these effects also lead to a reduction in quality. This manifests itself in the form of reduced adhesion of the spray coating to the substrate, high porosity, high oxide content, and many only partially melted particles in the spray coating.

[0008] Starting from the aforementioned prior art, the object of the present invention is to provide an improved device and an improved method for coating workpieces by means of wire arc spraying, in which the aforementioned disadvantages of the prior art can be reduced.

[0009] According to a first aspect, the present invention relates to a device for thermal coating by means of a wire arc. The device comprises at least one first contact tube, at least one counter electrode with an electrode tip, and an atomizing gas nozzle. The at least one first contact tube has an inner channel for feeding a first streamlined metal wire, preferably according to the second aspect of the present invention, and a contact tube tip with an outlet opening for the first metal wire. A voltage can be applied to the at least one first metal wire fed via the first contact tube and to the at least one counter electrode to form an electric arc for melting the at least one metal wire, wherein an atomizing gas can be expelled from the atomizing gas nozzle for carrying molten metal droplets along a flow axis.The at least one first contact tube and the at least one counter electrode are arranged with their tips converging in the direction of atomization gas discharge. The outer surface of the at least one first contact tube has a streamlined cross-section and / or the cross-sectional areas of the inner channel of the at least one first contact tube are at least partially adapted to the streamlined cross-section of the supplied first metal wire.

[0010] The provision of features such that the cross-sectional areas of the inner channel of the at least one first contact tube are adapted, at least partially, to the streamlined cross-section of the supplied first metal wire makes it possible, in particular, to align the angular position of the cross-sectional area of ​​the first metal wire in the circumferential direction of the wire's longitudinal axis with respect to a flow axis of the atomizing gas flow. The outer surface of the at least one first contact tube can have a streamlined cross-sectional area, at least partially.The streamlined cross-sections of the outer surface of the at least one first contact tube, as well as the streamlined cross-section of the at least one first supplied metal wire, can be positioned in the flow of the atomizing gas such that they exhibit the lowest possible flow resistance with respect to the emitted atomizing gas. This results in significantly less flow resistance to the supplied atomizing gas than is known for round cross-sectional areas of metal wires and outer surfaces of contact tubes from the prior art. Due to the flow-optimized cross-section, the fluid flow of the atomizing gas is affected as little as possible, such that, for example, the formation of vortex streets can be avoided, thereby resulting in an improved discharge pattern of the molten metal droplets along the flow axis.

[0011] In a preferred embodiment, it can be provided that the at least one first contact tube and the at least one counter electrode are arranged in a mirror-symmetrical manner with respect to a plane through a flow medium axis of the atomizing gas flow.

[0012] Furthermore, it can be provided that the at least one counter electrode is designed in the form of a second contact tube, wherein the at least one second contact tube has an inner channel for supplying a second metal wire with a streamlined cross-section, preferably according to the second aspect of the present invention, and a contact tube tip with an outlet opening for the second metal wire. The at least one first and second contact tubes are arranged with tips converging towards each other in the direction of expulsion of the atomizing gas. The outer surface of the at least one second contact tube has a streamlined cross-section at least partially, and / or the cross-sectional area of ​​the inner channel of the at least one first contact tube is adapted at least partially to the streamlined cross-section of the supplied second metal wire.

[0013] According to the invention, at least one first and / or at least one second metal wire is / are continuously fed via a respective contact tube to the area of ​​the contact tube tip. For the continuous feeding, feed devices can be provided according to the invention, which convey the at least one first and / or second metal wire by means of drive elements. The metal wires are typically in continuous form, which are supplied in particular on spools or as ring lay-up in drums. According to the invention, for example, feed rates in the range of 0.5 to 30 meters / minute can be selected, depending on the type of material and wire diameter of the metal wire.The electric arc formed between the at least one first contact tube and the at least one counter electrode or the at least one second contact tube supplies the energy required to melt the supplied at least one first and / or second metal wire. The metal wires are made of the material to be used for coating. The arc serves as the energy source for melting the at least one first and / or second metal wire. The at least one metal wire is melted only in the area of ​​the at least one first and / or second contact tube. The molten at least one first and / or second metal wire is separated into liquid metal droplets by means of an atomizing gas stream and accelerated against the surface to be coated.When the metal droplet hits the surface to be coated, the metal droplets suddenly lose their kinetic energy and release their heat energy, in such a way that the metal droplets are deposited on the surface and form a layer on the surface of the workpiece to be coated made of the material of at least one first and / or second metal wire.

[0014] It may be provided that the at least one first and second contact tube are arranged symmetrically to a plane through a flow axis of the atomizing gas stream.

[0015] By providing the features according to which the cross-sectional areas of the inner channel of the at least one second contact tube and / or the outer surface of the at least one second contact tube have a streamlined cross-section, it is made possible, in particular, to align the angular position of the cross-sectional area of ​​the second metal wire in the circumferential direction of the wire longitudinal axis with respect to the flow medium axis.

[0016] The contact tube tip can preferably be designed as a body with a flow-optimized or streamlined outer shape. The contact tube tip has a longitudinal axis and an internal channel extending along this longitudinal axis for guiding and aligning the supplied metal wire. The supplied metal wire can be fed from the contact tube tip into the atomizer gas stream via the contact tube opening in a defined spatial orientation and, in particular, with a defined orientation in the circumferential direction of the wire's longitudinal axis. The wire's longitudinal axis is positioned at a defined angle relative to the flow axis of the atomizer shaft by means of the contact tube tip.

[0017] According to the invention, the at least one first and / or second contact tube is formed in at least two parts, consisting of the contact tube tip and a subsequent contact tube channel, wherein the contact tube tip is designed to be replaceable.

[0018] In an alternative embodiment not according to the invention, it is also possible to manufacture the entire contact tube, and thus the area of ​​the contact tube tip and the subsequent contact tube channel, in one piece. In particular, additive manufacturing methods can be used to form the one-piece contact tube.

[0019] Furthermore, the non-inventive one-piece embodiment of the contact tube tip and the contact tube channel can be designed such that, to simplify the manufacture of the contact tube along the longitudinal axis, it is formed in multiple parts, for example from a lower and an upper shell, wherein the inner channel for feeding the metal wire is formed proportionally from the upper and lower shell of the contact tube.

[0020] According to the invention, the contact tube tip is further designed to be rotatable relative to the contact tube channel in the circumferential direction of the wire's longitudinal axis, and the angular position of the contact tube tip relative to the contact tube channel is adjustable. This adjustability of the contact tube tip's angular position allows for fine-tuning of the angle in the circumferential direction of the supplied metal wire, thus enabling precise control of the flow around the metal wire and the contact tube tip relative to the atomizing gas. In the aforementioned embodiment, the inner channel is adapted, at least in the region of the contact tube tip, to the streamlined profile of the supplied metal wire.

[0021] Furthermore, it can be provided that the device further comprises at least one feed device for the at least one first and / or second metal wire, wherein the at least one feed device is adapted to the outer cross-section and the outer shape of the supplied metal wire and in particular has streamlined drive elements.

[0022] Additionally, it can be provided that the at least one contact tube is formed at least partially from an electrically conductive material and that the inner tube rests at least section by section on the supplied first or second metal wire to form an electrically conductive connection.

[0023] It may also be provided that at least one first and / or second contact tube is made at least partially from an electrically non-conductive material; in particular, the contact tube tips may be made from a heat-resistant ceramic material.

[0024] To ensure sufficient current supply and output to the supplied metal wire, current transmission elements, such as current guide rails, can preferably be provided in the area of ​​the inner channel of the first and / or second contact tube. The current transmission elements can be arranged to be resilient relative to the inner channel of the first and / or second contact tube, for example, to ensure that the current guide elements are in contact with the supplied metal wire.

[0025] It may also be provided to include a wire guiding device, in particular in the form of a wire guiding tube, wherein the wire guiding device has at least one wire guiding element which includes a guide channel adapted to the outer contour of the supplied metal wire for guiding and aligning the first and / or second metal wire to be supplied.

[0026] The counter electrode can be designed as a stationary electrode, which is particularly preferably designed as a tungsten needle.

[0027] A metal wire for thermal coating comprises a longitudinal axis and a cross-sectional area perpendicular to the longitudinal axis, the cross-sectional area being formed by a streamlined shape. A streamlined shape is defined as one that exhibits low flow resistance.

[0028] The basic shape of the cross-sectional area can be formed by the set of ovals excluding the full circle, whereby the edge of the cross-sectional area can have concave indentations at least section by section.

[0029] The cross-sectional area can preferably include a first axis of symmetry, wherein the dimension of the cross-sectional area along the first axis of symmetry is referred to as length a, and wherein the cross-sectional area preferably includes a second axis of symmetry which is orthogonal to the first axis of symmetry, and wherein the dimension of the cross-sectional area along the second axis of symmetry is referred to as length b.

[0030] The length a can be in the range between 1.0 mm and 8.0 mm, preferably in the range of 2.4 mm to 8.0 mm.

[0031] The length ratio a / b can be in the range of 0.3 to 0.95, preferably in the range of 0.5 to 0.9.

[0032] Thermal coating by wire arc spraying is particularly suitable for producing zinc coatings on surfaces. Zinc can be processed especially well by wire arc spraying. In a preferred embodiment, the metal wire therefore comprises zinc and its alloys as a substantial proportion. Preferably, the metal wire according to the invention consists of zinc and / or its alloys.

[0033] A preferred zinc alloy comprises aluminum, copper, magnesium, and / or titanium, balanced with zinc to 100 wt.%. The alloy may optionally contain impurities in a proportion of 0.1 wt.%, preferably 0.07 wt.%, or less. These impurities are typical impurities originating from the metals used in the alloy.

[0034] In a preferred embodiment, the zinc wire consists of a zinc alloy having an aluminum content of 0.01 to 35 wt.% and / or a copper content of 0.01 to 15 wt.% and / or a magnesium content of 0.01 to 10 wt.% and / or a titanium content of 0.01 to 5 wt.% and balanced with zinc to 100 wt.%, wherein the alloy optionally contains impurities in a proportion of 0.1 wt.% or less.

[0035] The metal wire can thus consist of an alloy containing only aluminum and zinc, or only copper and zinc, or only magnesium and zinc, or only titanium and zinc. However, according to the invention, it is also possible for the alloy to contain, in addition to zinc, two, three, or all four selected from the group consisting of aluminum, copper, magnesium, and titanium.

[0036] A zinc alloy has an aluminium content of 0.01 to 35 wt.%, a copper content of 0.01 to 15 wt.%, a magnesium content of 0.01 to 10 wt.%, and a titanium content of 0.01 to 5 wt.%, balanced with zinc to 100 wt.%, the alloy optionally containing impurities in a proportion of 0.1 wt.% or less.

[0037] The composition of the alloy as a whole corresponds to 100 wt.%. This applies to the alloys described above as well as those described below.

[0038] Preferably the copper content is from 0.01 to 5 wt.%.

[0039] The magnesium content of an alloy according to the invention is preferably from 0.01 to 10 wt.%, in particular from 0.01 to 5 wt.%.

[0040] The titanium content is preferably in the range of 0.01 to 2.5 wt.%, particularly in the range of 0.01 to 1 wt.%.

[0041] Instead of a metal wire made of zinc or its alloys, a metal wire made of aluminum or its alloys can also preferably be used according to the invention. The metal wire consists in particular of aluminum or an aluminum alloy.

[0042] Preferred aluminum alloys contain, in addition to aluminum, at least one, two, or more other metals selected from the group consisting of zinc, magnesium, silicon, titanium, and indium. The proportion of aluminum is at least 50 wt.% based on the total weight of the alloy, which is 100 wt.%.

[0043] A preferred aluminium alloy contains zinc in a proportion of 0.01 to 50 wt.%, supplemented with aluminium to 100 wt.%.

[0044] Another preferred aluminium alloy contains magnesium in a proportion of 0 to 20 wt.%, supplemented with aluminium to 100 wt.%.

[0045] Another preferred aluminum alloy contains silicon in a proportion of 0 to 20 wt.%, supplemented with aluminum to 100 wt.%.

[0046] Another preferred aluminium alloy contains titanium in a proportion of 0 to 5 wt.%, supplemented with aluminium to 100 wt.%.

[0047] Another preferred aluminium alloy contains indium in a proportion of 0 to 5 wt.%, supplemented with aluminium to 100 wt.%.

[0048] The aluminum alloy can also contain two or more metals in the aforementioned areas. Even in this case, the proportion of aluminum is at least 50% by weight of the total weight of the alloy.

[0049] If the metal wire consists of a metal itself, preferably zinc or aluminum, the purity of the metal is preferably 99.9%, in particular 99.94%, more preferably 99.95%, and more preferably 99.99%.

[0050] According to a second aspect, the present invention relates to a method for thermally coating surfaces using a wire arc, comprising the steps of: Feeding at least one first metal wire with a streamlined cross-section, preferably according to the second aspect of the present invention and formed from the coating material via at least one first contact tube, preferably with the features according to the first aspect of the present invention, generating an electric arc between the at least one first metal wire and at least one counter electrode by applying an electrical voltage between the at least one first contact tube and the at least one counter electrode, expelling an atomizing gas to carry metal droplets of the molten at least one first metal wire along a flow medium axis onto a surface of a workpiece to be coated, and aligning the angular position of the cross-sectional area of ​​the at least one first and / or second metal wire in the circumferential direction of the wire longitudinal axis relative to the atomizing gas flow.

[0051] Preferably, the at least one counter electrode is formed by a second contact tube, wherein the method according to the invention preferably comprises the following further steps: Feeding at least one second metal wire with a streamlined cross-section, preferably with the features according to the second aspect of the present invention, formed from the coating material, at least one second contact tube, preferably with the features according to the first aspect of the present invention, and generating an arc between the at least one first and second metal wire by applying an electrical voltage between the at least one first contact tube and the at least one second contact tube.

[0052] Preferably, it can be provided that the at least one contact tube and the wire tips, or only the wire tips, are surrounded concentrically by the atomizing gas.

[0053] Furthermore, the contact tube tips can be arranged at an angle to the flow medium axis.

[0054] It can be provided that the angle between the contact tube tip and the fluid axis is in the range of 5 to 90°.

[0055] Advantageous exemplary embodiments of the present invention are described below with reference to the accompanying figures.

[0056] They show: Fig. 1 a schematic view of a first exemplary embodiment of a device according to the invention for thermal coating by means of a wire arc; Fig. 2 a schematic view of a second exemplary embodiment of a device for thermal coating by means of a wire arc; Fig. 3 a schematic representation of a first exemplary embodiment of a metal wire according to the invention with a streamlined cross-section; Fig. 3 a detailed view of the cross-section of the metal wire according to the invention. Figur 3A ; Figs. 4A - 4B Detail layers of various exemplary cross-sections of a metal wire according to the invention.

[0057] In the Fig. 1 Figure 1 shows a schematic overall view of a first exemplary embodiment of a device according to the invention for thermal coating using a wire arc. The tool device according to the invention comprises a first contact tube 21, a counter electrode 20 with an electrode tip 201, and an atomizing gas nozzle 25. The first contact tube 21 has an inner channel 200 for feeding a first metal wire 41 with a streamlined cross-section 44 and a contact tube tip 210 with an outlet opening 220 for the first metal wire 41. An electrical voltage is applied to the first metal wire 41, which is fed via the first contact tube 21, and to the counter electrode 20 to form an electric arc. The electric arc causes the fed first metal wire 41 to melt in the region of the metal wire tip 43, which emerges from the outlet opening 220 of the first contact tube 21.In the illustrated embodiment, the counter electrode 20 is exemplified as a one-piece tungsten needle. During the use of the device according to the invention for carrying out the process according to the invention, the first metal wire 41 is continuously fed via the first contact tube 21. The electric arc between the tip of the first metal wire 41 and the counter electrode 21 is continuously maintained during the coating process. To compensate for the molten material of the first metal wire 41 that is carried out via the atomizing gas, the wire is continuously fed via the first contact tube 21. At least one feed device can be provided for feeding the first metal wire 41, which in turn includes drive elements for conveying the first metal wire 41. The conveying speed of the first metal wire 41 can be varied and, in particular, adjusted to the selected wire diameter or thickness.The cross-sectional area of ​​the first metal wire 41 is adjusted. Similarly, further first and / or at least one second metal wire are continuously fed in. According to the invention, voltages in the range of 15 to 21 volts can be used for metal wires made of Zn, and voltages of 18 to 19 volts for metal wires made of ZnAl, with the current being selected in the range of 80 A to 1500 A depending on the feed rate and / or the wire cross-section. Generally, voltages in the range of approximately 18 to 40 V can be used according to the invention for forming the arc with metal wires.

[0058] An atomizing gas 30 is emitted from the atomizing gas nozzle 25 to carry molten metal droplets of the first metal wire 41 along the atomizing gas flow 310.

[0059] The first contact tube 21 and the counter electrode 20 are arranged with tips 201, 210 converging in the direction 310 of the atomizing gas 30. In the illustrated embodiment, the outer surface 230 of the first contact tube 21 has a streamlined cross-section, and the cross-sectional area 203 of the inner channel 200 of the first contact tube 21 has a first metal wire 41 sectionally fed to the streamlined cross-section. The liquid metal droplets of the molten first metal wire 41, ejected by means of the atomizing gas flow 310 of the atomizing gas 30, are propelled by the atomizing gas flow 310 against a surface 100 of a material 10 to be coated.

[0060] The Fig. 2 Figure 1 shows a second exemplary embodiment of a device according to the invention for thermal coating using a wire arc. In the illustrated exemplary embodiment of the Fig. 2 The counter electrode 20 was replaced by a second contact tube 22, the second contact tube 22 comprising an inner channel 200 for supplying a second metal wire 42 with a streamlined cross-section and again a contact tube tip 210 with an outlet opening 220 for the second metal wire 42. The first and second contact tubes 21 are arranged with tips 210 converging towards each other in the discharge direction 310 of the atomizing gas 30.

[0061] In the embodiment shown according to Fig. 2 The electrical voltage is applied to the first contact tube 21 and the second contact tube 22 in such a way that the electric current is transferred to the supplied first metal wire 41 and the second metal wire 42, so that as a result the electric arc forms between the two wire tips 43 of the first and second metal wire 41, 42 and the first and second metal wire 41, 42 is locally melted in the area of ​​the two wire tips 43.

[0062] The molten metal droplets of the first and second metal wire 41 and 42 are ejected by expelling an atomizing gas 30 via the atomizing gas nozzle 25 and the resulting atomizing gas stream 310 against a surface 100 of a material 10 to be coated.

[0063] The Fig. 3A Figure 1 shows a schematic view of a section of a metal wire 40 with a streamlined cross-section 44, wherein the metal wire 40 runs along a longitudinal wire axis 45. As shown in Fig. 3A As shown, the metal wire can have 40 turns and bends along the wire's longitudinal axis 45. In the Fig. 3a The circumferential direction 47 of the wire's longitudinal axis 45 is also shown. The metal wire 40 with streamlined cross-section 44 can form the first metal wire 41 or the second metal wire 42, depending on its use. Fig. 3B Figure 1 shows an enlarged detail view of the streamlined cross-sectional area 44 of the metal wire 40 according to the invention, as well as the course of the wire longitudinal axis 45.

[0064] The Figuren 4A bis 4C further exemplary embodiments of a streamlined cross-section 44 of metal wires 40 according to the invention are shown.

Claims

1. A device for thermal coating by means of wire arcs, comprising: - at least one first contact tube (21), - at least one counter electrode (20) comprising an electrode tip (201), and - an atomizing gas nozzle (25), wherein the at least one first contact tube (21) comprises an inner channel (200) for feeding a first metal wire (41) having a streamlined cross-section (44) and a contact tube tip (210) having an outlet opening (220) for the first metal wire (41) respectively, wherein a voltage can be applied to the at least one first metal wire (41) fed via the at least one first contact tube (21) and to the at least one counter electrode (20) in order to form an electric arc for melting the at least one first metal wire (41), wherein an atomizing gas (30) can be ejected from the atomizing nozzle (25) for discharging melted metal droplets along the atomizing gas flow (310), wherein the at least one first contact tube (21) and the at least one counter electrode (20) are arranged with tips (201, 210) converging in the ejection direction (310) of the atomizing gas (30), and wherein the outer surface (230) of the at least one first contact tube (21) has a streamlined cross-section and / or the cross-sectional area (203) of the inner channel (200) of the at least one first contact tube (21) is adapted at least in sections to the streamlined cross-section (44) of the fed first metal wire (41), wherein the at least one first and / or second contact tube (21, 22) is formed in a two-part design from the contact tube tip (210) and an adjoining contact tube channel, wherein the contact tube tip (210) is configured to be interchangeable, characterized in that the contact tube tip (210) comprises a longitudinal axis as well as an inner channel along the longitudinal axis for guiding and for aligning the fed metal wire (41) and is configured to be rotatable relative to the contact tube channel (240) in the circumferential direction (47) of the wire longitudinal axis (45), wherein the angular position is fixable.

2. The device according to claim 1, wherein at least one counter electrode (20) is designed in the form of a second contact tube (22), wherein the at least one second contact tube (22) comprises an inner channel (200) for feeding a second metal wire (42) having a streamlined cross-section (44) and a contact tube tip (210) having an outlet opening (220) for the second metal wire (42) respectively, wherein the at least one first and second contact tube (21, 22) are arranged with tips (201, 210) converging in the ejection direction (310) of the atomizing gas (30), and wherein the outer surface (230) of the at least one second contact tube (22) has at least in sections a streamlined cross-section and / or the cross-sectional area (203) of the inner channel (200) of the at least one second contact tube (22) is adapted at least in sections to the streamlined cross-section (44) of the fed second metal wire (42).

3. The device according to claim 1, wherein the at least one first contact tube (21) and the at least one counter electrode (20) are arranged symmetrically identical to a plane through a central flow axis of the atomizing gas flow (310).

4. The device according to claim 2, wherein the at least one first and second contact tube (21, 22) are arranged symmetrically identical to a plane through a central flow axis of the atomizing gas flow (310).

5. The device according to any one of the preceding claims, wherein the device further comprises at least one feed device for the at least one first and / or second metal wire (41, 42), wherein the at least one feed device comprises in particular streamlined driving elements adapted to the cross-section (44) of the fed metal wire (40).

6. The device according to any one of the preceding claims, further comprising at least one wire guiding device, in particular in the form of a wire guiding hose, wherein the wire guiding device comprises at least one wire passing element having a guiding channel adapted to the cross-section (44) of the fed metal wire (41, 42) for passing through and aligning the metal wire (41, 42) to be fed.

7. The device according to any one of claims 1 to 6, wherein the at least one contact tube (21, 22) is at least partially formed from an electrically conductive material and the inner channel (200) abuts at least in sections on the fed first or second metal wire for forming an electrically conductive connection.

8. The device according to any one of claims 1 to 6, wherein the at least one first and / or second contact tube (21, 22) is at least partially formed from an electrically non-conductive material, wherein the contact tube tips (210) are preferably made of a heat-resistant ceramic material.

9. The device according to any one of the preceding claims, wherein power transmission elements are provided in the area of the inner channel (200) of the first and / or second contact tube (21, 22).

10. A method for thermal coating of surfaces by means of wire arcs, comprising the following steps: - feeding at least one first metal wire (41) having a streamlined cross-section (44), formed from the coating material via at least one first contact tube (21), having the features according to any one of claims 1 to 9; - generating an electric arc between the at least one first metal wire (41) and at least one counter electrode (20) by applying an electric voltage between the at least one first contact tube (21) and the at least one counter electrode (20), - ejecting an atomizing gas (30) for discharging metal drops of the melted at least one metal wire (41) along the ejection direction of the atomizing gas (310) onto a surface of a workpiece (10) to be coated, and - aligning the angular position of the cross-sectional area of the at least one first and / or second metal wire in the circumferential direction of the wire longitudinal axis relative to a center flow axis of the atomizing gas flow.

11. The method according to claim 10, wherein at least one counter electrode (20) is formed by a second contact tube (22), and the method further comprises the following steps: - feeding at least one second metal wire (42) having a streamlined cross-section (44) formed from the coating material via at least one second contact tube (22), having the features according to any one of claims 1 to 10, and - generating an electric arc between the at least one first and second metal wire (41, 42) by applying an electric voltage between the at least one first contact tube (21) and the at least one second contact tube (22).

12. The method according to claim 10 or 11, wherein the at least one contact tube (21, 22) and the wire tips (43) or only the wire tips (43) are surrounded concentrically by atomizing gas (30).

13. Using a device for thermal coating by means of wire arcs, the device comprising: - at least one first contact tube (21), - at least one counter electrode (20) comprising an electrode tip (201), and - an atomizing gas nozzle (25), wherein that at least one first contact tube (21) comprises an inner channel (200) for feeding a first metal wire (41) having a streamlined cross-section (44) and a contact tube tip (210) having an outlet opening (220) for the first metal wire (41) respectively, wherein a voltage can be applied to the at least one first metal wire (41) fed via the at least one first contact tube (21) and to the at least one counter electrode (20) in order to form an electric arc for melting the at least one first metal wire (41), wherein an atomizing gas (30) can be ejected from the atomizing nozzle (25) for discharging melted metal droplets along the atomizing gas flow (310), wherein the at least one first contact tube (21) and the at least one counter electrode (20) are arranged with tips (201, 210) converging in the ejection direction (310) of the atomizing gas (30), and wherein the outer surface (230) of the at least one first contact tube (21) has a streamlined cross-section and / or the cross-sectional area (203) of the inner channel (200) of the at least one first contact tube (21) is adapted at least in sections to the streamlined cross-section (44) of the fed first metal wire (41), wherein the at least one first and / or second contact tube (21, 22) is formed in a two-part design from the contact tube tip (210) and an adjoining contact tube channel, wherein the contact tube tip (210) is configured to be interchangeable, wherein the contact tube tip (210) comprises a longitudinal axis as well as an inner channel along the longitudinal axis for guiding and for aligning the fed metal wire (41) and is configured to be rotatable relative to the contact tube channel (240) in the circumferential direction (47) of the wire longitudinal axis (45), wherein the angular position is fixable to perform a method for thermal coating of surfaces.

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