Plasma torch with fluid cooling, especially for coating the running surfaces of cylinders of reciprocating engines

Abstract

The invention relates to a plasma torch with a plasma channel (30) which penetrates a nozzle plate (14), wherein at least two arc-shaped flow channels are formed in the nozzle plate (14) partially enclosing the plasma channel (30) on both sides, wherein flow-technically separated inlet areas (26a, 26b) are formed in the nozzle plate (14) for the at least two arc-shaped flow channels.

Description

[0001] The invention relates to a plasma torch with fluid cooling according to the preamble of claim 1. In particular, the invention relates to a plasma torch which is suitable in its size and power for coating the running surfaces of cylinders of reciprocating piston engines.

[0002] The engine blocks of modern reciprocating piston internal combustion engines are typically made of cast aluminum, which enables low component weight combined with positive cooling properties. The running surfaces, especially in cast aluminum cylinders, are usually lined (coated) with a thin layer of a wear-resistant, harder material, also to achieve lower friction values ​​between piston and cylinder and the necessary abrasion resistance for long-term operation. Plasma torches subject to the invention use an arc to heat a gas mixture to over 10,000 °C. The material to be applied is sprayed into this hot plasma jet as a fine powder. The powder is melted in the plasma jet, heated to approximately 2,500 °C, and sprayed onto the cylinder surface at a speed of approximately 100 m / s.

[0003] In order to achieve the above-mentioned temperature level, corresponding plasma torches have in particular power outputs of more than 10 kW, preferably power outputs between 12 kW and 20 kW and particularly preferably power outputs of approximately 12 kW to 16 kW.

[0004] The size of such plasma torches is preferably designed so that the plasma torch can be inserted into cylinders with a maximum diameter of 100 mm and still be moved within them, more preferably into cylinders with a maximum diameter of 80 mm or even 75 mm. These are therefore very compact plasma torches that have high heat dissipation requirements.

[0005] For this purpose, the dimensions extending transversely to the insertion direction (longitudinal direction of the plasma torch), height and width, are each preferably a maximum of 50 mm, more preferably a maximum of 40 mm, and particularly preferably a maximum of 35 mm. The invention was specifically designed for a plasma torch with a height and width of 25 mm x 35 mm and a length of approximately 75 mm.

[0006] US Pat. No. 4,506,136 discloses a plasma torch in which the electrode is screwed from the outside of an electrode holding element referred to as the "cathode body." Such an electrode arrangement is unsuitable for the compact plasma torches described above due to the resulting poor heat dissipation. The plasma torch also has a cooling channel with a U-shaped cross-section, the course of which around a plasma channel formed in the plasma torch is not shown or explained in detail.

[0007] DE 10 2017 213 359 A1 discloses a coating lance head, a coating lance, and a masking shield for thermal coating. Furthermore, a coating system and a corresponding method are described. This document does not address fluid cooling. Accordingly, the design and path of a fluid channel are not described or illustrated.

[0008] DE 10 2019 210 524 A1 discloses an electrode assembly for a plasma torch whose dimensions are suitable for coating the running surfaces of cylinders of reciprocating piston engines. However, this document deals with the design of a specific cap section and does not address the cooling issue in detail. Regarding fluid cooling, reference is made to a coolant connection and a coolant line; however, the design and path of a fluid channel are neither described nor illustrated.

[0009] To efficiently dissipate the heat generated in the plasma torch, plasma torches known from practice feature fluid cooling. Specifically, two arcuate flow channels are formed in a nozzle plate of a plasma torch, extending from a central inflow area. These arcuate flow channels enclose a plasma channel penetrating the nozzle plate on both sides. The two arcuate flow channels are rejoined in an outflow area opposite the inflow area.

[0010] The invention is based on the object of improving the geometry of the fluid channels of the plasma torches described above and known from practice with regard to heat dissipation.

[0011] The object is achieved according to the invention with the features of the independent claims. Further practical embodiments and advantages of the invention are described in conjunction with the dependent claims.

[0012] A plasma torch according to the invention comprises a plasma channel penetrating a nozzle plate and in which at least two arcuate flow channels are formed, partially enclosing the plasma channel on both sides. Fluidically separated inflow areas and / or fluidically separated outflow areas are formed in the nozzle plate for the at least two arcuate flow channels.

[0013] Fluidically separated inflow areas are understood, on the one hand, to be inflow areas that are completely separated from one another. Furthermore, inflow areas that are largely fluidically independent of one another are also understood as separate inflow areas. This applies in particular to inflow areas that are connected to one another via a pressure equalization channel, wherein the pressure equalization channel has a maximum of 50% of the cross-sectional area corresponding to the smallest cross-sectional area of ​​the two inflow areas. The cross-sectional area of ​​a pressure equalization channel is preferably a maximum of 30%, more preferably a maximum of 20%, and particularly preferably a maximum of 10% or 5% of the inflow area or of that area of ​​the curved flow channel to which the pressure equalization channel adjoins.Accordingly, the pressure equalization channel can also be arranged downstream of the inflow areas, but it is preferably arranged at least in the first half of the arcuate flow channels.

[0014] The above regarding the inflow areas also applies mutatis mutandis to the outflow areas. In this respect, the invention also encompasses embodiments in which only one inflow area is provided, but two fluidically separated outflow areas are provided. A fluidic separation is considered to exist if the criteria explained above in connection with separate inflow areas are met analogously for the outflow area.

[0015] The invention also encompasses embodiments in which both fluidically separated inflow areas and fluidically separated outflow areas are provided.

[0016] In the case of fluidically separated outflow areas with a pressure equalization channel, the pressure equalization channel can be arranged either directly between the outflow areas themselves or directly upstream of the outflow areas and connect the outflow areas themselves or two sections of the curved flow channels located upstream of the outflow areas. In the latter case, the pressure equalization channel can be arranged at any position between one inflow area or the fluidically separated inflow areas and the outflow areas. Preferably, the pressure equalization channel for two outflow areas is arranged in the second half of the curved flow channels.

[0017] For the sake of completeness, it should be noted that two or more pressure equalization channels may also be formed. Particularly when both fluidically separated inflow areas and fluidically separated outflow areas are provided, it is preferred if two or more pressure equalization channels are formed, in particular one pressure equalization channel in each half of the curved flow channels.

[0018] Furthermore, it is pointed out that obliquely running and / or overlapping pressure equalization channels can also be provided, in particular a pressure equalization channel leading from an inflow region of a first cooling channel to an outflow region of a second cooling channel and / or a pressure equalization channel leading from an inflow region of a second cooling channel to an outflow region of a first cooling channel. Obliquely (forwardly) running pressure equalization channels also means pressure equalization channels which lead from one section of an arcuate flow channel to a comparatively further downstream section of the other arcuate flow channel. Also included are pressure equalization channels which run obliquely (backwards), i.e. which lead from one section of an arcuate flow channel to a comparatively further upstream section of the other arcuate flow channel.With pressure equalization channels running diagonally backwards or diagonally forwards, the amount of fluid flowing through the respective pressure equalization channel can be designed depending on the cross-sectional area of ​​the pressure equalization channel.

[0019] A plasma torch according to the invention has the advantage that very efficient heat dissipation can take place, in particular because the flow-technically separated inflow areas prevent an uneven flow distribution within the flow channels.

[0020] In a further practical embodiment of a plasma torch according to the invention, at least one arcuate flow channel has a change in curvature on the inside before an outflow area, so that a fluid flowing through this flow channel undergoes a change in direction. Preferably, this change in direction is realized using a radius, so that flow losses due to the change in direction are minimized.

[0021] In a further practical embodiment of a plasma torch according to the invention with a common outflow area, the inner walls of the flow channel are designed to taper at an acute angle of <90°. Preferably, the angle is a maximum of 80°, more preferably a maximum of 70°, and particularly preferably a maximum of 60°. In further preferred embodiments, the angle is even selected to be <50°, <45°, or <40°.

[0022] In a further practical embodiment of a plasma torch according to the invention, an at least local flow cross-sectional minimum is formed in the downstream half of at least one arcuate flow channel. Preferably, such a flow cross-sectional minimum is formed in both arcuate flow channels or all arcuate flow channels, each in the downstream half. By forming such a flow cross-sectional minimum in the downstream half, in particular immediately upstream of an outflow region, the cooling fluid can be accelerated in the area of ​​greatest load, thereby further improving heat dissipation and effectively preventing overheating or local vapor lock due to damming or slowing down of the cooling fluid in the area of ​​greatest load.

[0023] Due to the very high temperatures prevailing in a plasma torch according to the invention, it is preferred if the nozzle plate with the at least two arcuate flow channels formed therein is manufactured in one piece. This is particularly achieved as a cast part or by means of an additive manufacturing process, for example, a 3D printing process. This has the further advantage that complicated seals, which are mandatory between two or more components, can be eliminated.

[0024] In particular, molded seals can be used, which enable reliable sealing regardless of the tightening torque of the screws and thus allow for smaller distances between media channels. Furthermore, complex geometries, especially the cross-sections of flow channels described above, can be realized relatively easily through one-piece manufacturing.

[0025] In a further practical embodiment of a plasma torch according to the invention, at least one of the at least two arcuate flow channels has a cross-section which is tapered on the outside. Such a cross-section is preferably provided over the entire flow path, starting from the inflow area to the outflow area. Particularly preferably, the cross-section is composed of at least one arcuate area in which, viewed from the inside to the outside, the h S of the flow channel continuously widens, an adjoining area with approximately constant height h S of the flow channel and an area further outwards in which the h Sthe flow channel is tapered. In this case, the amount of fluid directed through the curved flow channel for heat dissipation can be precisely adjusted to the respective heat dissipation requirements, so that a large amount of cooling water is pumped toward the inside, where the greatest heat is generated and a large amount of heat must be dissipated, while the amount of cooling water is reduced further out.

[0026] In a further practical embodiment of a plasma torch according to the invention, at least one of the at least two arcuate flow channels has a cross-section that is arcuate on the inside and / or has an inner section extending outward from the inside, in which the cross-sectional height is constant or approximately constant. Reference is hereby made once again to the advantages already explained above.

[0027] Since different flow velocities and pressure conditions occur in the two arcuate flow channels, it is further preferred if two inflow regions and / or the at least two arcuate flow channels are connected to one another by means of at least one pressure equalization channel, wherein the cross-sectional area of ​​the pressure equalization channel amounts to a maximum of 50% of the cross-sectional area of ​​the inflow region, the outflow region or the arcuate flow region at the corresponding branching point of the pressure equalization channel, depending on the location of the pressure equalization channel.

[0028] In a further practical embodiment of a plasma torch according to the invention, a radius is formed in at least one flow channel downstream of the inflow area to initially redirect the inflowing fluid outward with minimal turbulence losses. This allows a change of direction for the fluid to be generated with minimal turbulence losses. It is particularly preferred if two changes of direction for the fluid are provided from one inflow area to the outflow area, whereby two radii can also be formed accordingly.

[0029] Further practical embodiments of the invention are described below in conjunction with the drawings. They show: Fig. 1 a longitudinal section through an embodiment of a plasma torch according to the invention, Fig. 2 a sectional view through the Fig. 1 shown plasma torch according to the section line II-II in Fig. 1, Fig. 3 a sectional view through the Fig. 1 and Fig. 2 shown plasma torch according to the section line III-III in Fig. 2, Fig. 4 an enlarged view of the channel cross-section of the Fig. 3 dashed area marked IV, Fig. 5 an isometric representation of a longitudinal section analogous to Fig. 2 in a view from above and Fig. 6 a view of a connection side of the Fig. 1 to 5 shown plasma torch according to arrow VI in Fig. 1.

[0030] Fig. Figure 1 shows a plasma torch 10. The plasma torch 10 is essentially formed by an electrode holding element 12, a nozzle plate 14, a front cover 16, and an insulating plate 18 arranged between the electrode holding element 12 and the nozzle plate 14. The insulating plate 18 is made, in particular, of a temperature-resistant plastic (Peak) and serves as a central component for attaching additional elements. Furthermore, the insulating plate 18 provides electrical insulation between the nozzle plate 14 and the electrode holding element 12.

[0031] A ring element 20 with an electrode 22 arranged therein, which serves as the cathode, is screwed into the electrode holding element 12. An insulating ring 24 is arranged between the ring element 20 and the insulating plate 18.

[0032] In the embodiment shown, the ring element 20 is made of a copper alloy, and the electrode 22 is a tungsten tip cast into the ring element 20. During operation of the plasma torch 10, an arc forms from the electrode 22 as a transition between the electrode 22 and the inside of the plasma channel 30 in the nozzle plate 14, which serves as the anode.

[0033] The tungsten tip is centered over a plasma channel 30.

[0034] The insulating ring 24 protects the insulating plate 18 from the radiant heat of the arc and the high temperatures in the plasma channel 30.

[0035] As from Fig. As can also be seen in Figure 1, an insulating element 28 is arranged on the outside of the electrode holding element 12, which is arranged in the longitudinal direction of the plasma torch 10 between the insulating plate 18 and the front cover 16. In the embodiment shown, the insulating element 28 is made of ceramic. It covers the electrode holding element 12, which serves as the cathode, and prevents unwanted lateral arcing between the electrode holding element 12 and the nozzle plate 14, which serves as the anode.

[0036] In the embodiment shown, the front cover 16 is made of ceramic and prevents sparking at the front between the electrode holding element 12 (cathode) and the nozzle plate 14 (anode).

[0037] An injector holder 64 is attached to the nozzle plate 14. The injector holder 64 serves to hold and secure an injector tube (not shown), through which metal powder is injected into the plasma jet.

[0038] In addition to the elements described and illustrated, there are also various connecting and sealing elements, such as screws, O-rings, etc., which, however, are not essential to the invention in the present case.

[0039] Based on the Fig. 2-6, an embodiment of a plasma torch 10 according to the invention will now be described, wherein identical or at least functionally equivalent elements are given the same reference numerals as in Fig. 1. Unless otherwise stated, these are identically designed elements.

[0040] Fig. 6 shows a view according to the arrow VI in Fig. 1 to the connection side of a plasma torch 10 according to the invention.

[0041] On the top side are two inflow channels 46 for plasma gas, which is injected evenly through channels not shown and through the ring element 20 into the arc formed between the cathode and anode and then guided into the plasma channel 30. The plasma gas, in particular a mixture of argon and hydrogen, is heated in the arc and transfers its kinetic energy to metal powder, which will be discussed below.

[0042] Below are two cooling water return channels 48 and two cooling water supply channels 50. These serve to conduct cooling water through the plasma torch 10 in order to efficiently dissipate heat from the hottest areas of the plasma torch 10, in particular from the electrode holding element 12, the ring element 20, the electrode 22 and the nozzle plate 14.

[0043] Two cooling air ducts 52 are located outside the cooling water return ducts 48. Compressed air is used primarily as cooling air. The cooling air serves to cool the insulation plate 18. Furthermore, the cooling air is used to create an air jacket around the torch to prevent the caking of metal powder.

[0044] In the lowest row of channels on the connection side, two cleaning gas channels 54 and one sheath gas channel 56 are provided.

[0045] Compressed air is primarily used as a cleaning gas to clean the cylinder wall before coating. The cleaning gas is also used to cool freshly coated areas.

[0046] The sheath gas, especially argon, serves to prevent material deposits in the area of ​​the metal powder feed.

[0047] On the underside there is an opening 58 which serves to insert an injector tube (not shown) through which metal powder can be introduced into the plasma torch 10.

[0048] Above the cooling water supply channels 50 there is a power connection 60 for the electrode 22 (cathode).

[0049] Power connections 62 for the nozzle plate (anode) are located to the side of the cooling water supply channels 50. These power connections supply the direct current required for the arc to the nozzle plate 14.

[0050] To cool the plasma torch 10, especially during operation, cooling water is fed, particularly in the area around the plasma channel 30, via the two cooling water supply channels 50 through channels not shown into the nozzle plate 14 and then through the latter. In the embodiment shown, the entry into the nozzle plate takes place in two separate inflow areas 26a, 26b, which are arranged in the Fig. 2 and Fig. 5 are clearly visible.

[0051] Starting from these inflow areas 26a, 26b, the cooling water is guided via an arcuate flow channel 32a, 32b to a common outflow section 34.

[0052] As in the Fig. 2 and Fig. 5, the two inflow areas 26a, 26b are connected to each other by means of a pressure equalization channel 36.

[0053] In the transition area between the inflow areas 26a, 26b and the downstream curved flow channels 32a, 32b, a radius 38a, 38b is formed on the inside to prevent turbulence losses in the fluid flow. The curved flow channels 32a, 32b each have an inside wall 42a, 42b and an outside wall 44a, 44b.

[0054] In the transition region between the respective radius 38a, 38b and the adjoining arcuate flow channel 32a, 32b, there is a change of direction for the fluid, since the fluid is first deflected outwards away from the plasma channel 30 by means of the respective radius 38a, 38b and is then guided around the plasma channel 30 in the arcuate flow channel 32a, 32b at an approximately uniform distance.

[0055] Downstream of the respective curved flow channel 32a, 32b, a further change of direction for the fluid is formed by the respective flow channel 32a, 32b each having a change of curvature 40a, 40b on the inside. As a result, the cooling water is deflected once again from its inward direction immediately before the outflow area 34, so that the resulting tangential angle α (cf. Fig.2) the two inner walls converging from the curved flow channels 32a, 32b are reduced due to the changes in curvature 40a, 40b. This also reduces the angle of the two fluid flows flowing along the curved flow channels 32a, 32b and converging immediately before the outflow area 34, which in turn minimizes flow losses.

[0056] The features of the invention disclosed in the present description, the drawings, and the claims may be essential, both individually and in any combination, for the realization of the invention in its various embodiments. The invention may be varied within the scope of the claims and taking into account the knowledge of the person skilled in the art. List of reference symbols 10 plasma torches 12 Electrode holding element 14 Nozzle plate 16 Front hood 18 Insulation plate 20 ring element 22 Electrode 24 Insulating ring 26a, 26b Inflow area 28 Insulating element 30 plasma channel 32a, 32b arched section 34 Downstream section 36 Pressure equalization channel 38a, 38b Radius 40a, 40b Change of curvature 42a, 42b inside wall 44a, 44b outside wall 46 Inflow channel (for plasma gas) 48 Cooling water return channel 50 Cooling water supply channel 52 Cooling air duct 54 Cleaning gas channel 56 Sheath gas channel 58 Opening (for injector tube) 60 Power connection electrode (cathode) 62 Power connection nozzle plate (anode) 64 injector holders 66a, 66b Tangent α Tangential angle h S Height of the flow channel b SWidth of the flow channel QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 4,506,136

[0006] DE 10 2017 213 359 A1

[0007] DE 10 2019 210 524 A1

[0008]

Claims

[1] Plasma torch with a plasma channel (30) which penetrates a nozzle plate (14), wherein at least two arcuate flow channels are formed in the nozzle plate (14) so as to partially enclose the plasma channel (30) on both sides, characterized by that fluidically separated inflow regions (26a, 26b) and / or fluidically separated outflow regions are formed in the nozzle plate (14) for the at least two arcuate flow channels. [2] Plasma torch according to the preceding claim, characterized by that at least one arcuate flow channel has a change in curvature (40) on the inside in front of an outflow region (34), so that a fluid flowing through this flow channel experiences a change of direction. [3] Plasma torch according to one of the preceding claims, characterized bythat in the case of a common outflow region (34), the inner walls (42a, 42b) of the flow channel are designed to converge at an acute angle of less than 90 degrees. [4] Plasma torch according to the preceding claim, characterized by that the two tangents (66a, 66b) in the direction of the outflow area (34) have an angle of maximum 80 degrees to each other. [5] Plasma torch according to one of the preceding claims, characterized by that in the downstream half of at least one arcuate flow channel an at least local flow cross-sectional minimum is formed. [6] Plasma torch according to one of the preceding claims, characterized by that the nozzle plate (14) is manufactured in one piece with the at least two arcuate flow channels formed therein. [7] Plasma torch according to one of the preceding claims, characterized bythat at least one of the at least two arcuate flow channels has a cross-section which is tapered on the outside. [8] Plasma torch according to one of the preceding claims, characterized by that at least one of the at least two arcuate flow channels has a cross-section which is arcuate on the inside and / or has an inner section extending outwards from the inside, in which the cross-sectional height is constant or approximately constant. [9] Plasma torch according to one of the preceding claims, characterized bythat the two inflow regions (26a, 26b) and / or the at least two arcuate flow channels are connected to one another by means of at least one pressure equalization channel (36), wherein the cross-sectional area of the pressure equalization channel (36) amounts to a maximum of 50 percent of the cross-sectional area of the inflow region (26a, 26b), the outflow region (34) or the arcuate flow region at the corresponding branching point of the pressure equalization channel (36). [10] Plasma torch according to one of the preceding claims, characterized by that a radius is formed in at least one flow channel downstream of the inflow region (26a, 26b) in order to initially redirect the inflowing fluid outwards with low turbulence losses.

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