PLASMABRENNER

Description

[0001] The invention relates to a plasma torch, in particular a plasma cutting torch, and a method for operating a plasma torch.

[0002] Plasma is a highly heated, electrically conductive gas consisting of positive and negative ions, electrons, and excited and neutral atoms and molecules. Various gases are used as plasma gases, such as monatomic argon and / or diatomic gases like hydrogen, nitrogen, oxygen, or air. These gases ionize and dissociate due to the energy of an electric arc. The arc, constricted by a nozzle, is then called a plasma jet. The parameters of the plasma jet can be significantly influenced by the design of the nozzle and electrode. These parameters include, for example, the jet diameter, temperature, energy density, and gas flow velocity.

[0003] In plasma cutting, the plasma is typically constricted by a nozzle, which can be gas- or water-cooled. This allows energy densities of up to 2 x 10⁶ W / cm² to be achieved. Temperatures of up to 30,000 °C are generated in the plasma jet, which, in combination with the high gas flow velocity, enables very high cutting speeds on materials.

[0004] Plasma torches typically consist of a torch head and a torch shaft. An electrode and a nozzle are mounted in the torch head. Plasma gas flows between them, exiting through the nozzle orifice. The plasma gas is usually guided by a gas duct located between the electrode and the nozzle and can be set into rotation.

[0005] Modern plasma torches also feature a feed for a secondary medium, either a gas or a liquid. The nozzle is then surrounded by a nozzle guard. In liquid-cooled plasma torches, the nozzle is secured by a nozzle cap, as described, for example, in DE 10 2004 049 445 A1. The cooling medium then flows between the nozzle cap and the nozzle. The secondary medium flows between the nozzle or nozzle cap and the nozzle guard and exits from the bore of the nozzle guard. It influences the plasma jet formed by the arc and the plasma gas. It can be set into rotation by a gas guide located between the nozzle or nozzle cap and the nozzle guard.

[0006] The nozzle guard protects the nozzle and nozzle cap from heat or molten metal splashing from the workpiece, especially when the plasma jet penetrates the material of the workpiece being cut. It also creates a defined atmosphere around the plasma jet during cutting.

[0007] Nitrogen is frequently used as a secondary gas during plasma cutting of alloy steels to prevent oxygen in the ambient air from coming into contact with the hot cut edges and oxidizing them. Furthermore, the nitrogen reduces the surface tension of the molten metal, allowing it to be more easily expelled from the kerf. This results in burr-free cuts.

[0008] Even when using oxygen as a plasma gas for cutting structural steels, different effects regarding the cutting quality can be achieved through different compositions of the secondary gas, as described in DE 10 2006 018 858 A1, e.g. different nitrogen and oxygen proportions.

[0009] It is also known to change the composition of the secondary gas between individual cutting operations in order to first cut small holes and then large contours. This switching takes place during the period when no cutting is being performed.

[0010] Arrangements are also known in which valves, preferably electromagnetically operated valves, switch or regulate the secondary medium. These are located on a coupling unit between the gas hoses of the plasma torch and the supply hoses for the gas supply.

[0011] Disadvantages of the current state of the art include: It is not possible to quickly switch the secondary medium on and off. It is not possible to quickly switch from one secondary medium to another. It is not possible to react quickly to changes during cutting, e.g., when starting, piercing, or cutting, during the cutting process, when crossing the kerf, or at the end of the cut, by switching the secondary medium. It is not possible to quickly switch between two cutting operations.

[0012] The cause of this is the lines between the valves and the plasma torch. This is particularly critical when switching between different secondary media, for example, an oxidizing (oxygen, air) and a non-oxidizing gas or gas mixture. Switching between a liquid (e.g., water, emulsion, oil, aerosol) and a gas is also critical, because if a common feed, such as a hose, is used, the gas must first flush out all the remaining liquid. This can take several hundred milliseconds.

[0013] Attaching valves to the plasma torch shaft is inconvenient for securing it in the guide system, especially with swivel units this is disruptive.

[0014] Thus, CA 2 917 397 A1 relates to a plasma torch, EP 1 849 550 A2 to a method for plasma cutting and EP 0 790 756 A2 to a method for plasma cutting and a device that uses an oxygen-rich gas shield.

[0015] WO 91 / 02619 A1 discloses a plasma torch which has an improved nozzle.

[0016] It is therefore an object of the invention to specify possibilities for improved conditions during the shutdown, switching or changes in a controlled or regulated operation of a plasma torch during the supply of secondary medium.

[0017] In the plasma torch according to the invention, in particular a plasma cutting torch, at least one secondary medium is guided through a housing of the plasma torch to a nozzle protection cap opening and / or further openings that are present in a nozzle protection cap via at least one feed. At least one valve for opening and closing the feed is provided directly inside the housing of the plasma torch in the at least one feed.

[0018] The supply is divided into at least two parallel feeds through which the secondary medium flows towards the nozzle protection cap opening and / or other openings, and within the housing there are at least two valves for opening and closing the respective divided feed, each of which can be activated individually, so that it is possible for one of the valves alone to open the supply of the secondary medium, for the secondary medium to flow simultaneously through both divided feeds, or for a switch to be made from one divided feed to the other.

[0019] It is possible to insert an orifice, a throttle or an element that changes the free cross-section of the respective feeder compared to the free cross-section of the other divided feeder in at least one of the divided feeders, so that different flow resistances in the divided feeders for a secondary medium as well as different flow velocities and pressures of the secondary medium can be achieved.

[0020] In a further alternative according to the invention, at least two feeds for two different secondary media are guided through the housing of the plasma torch to a nozzle protection cap opening and / or further openings that are present in the nozzle protection cap, and in the feeds for each secondary medium, at least one valve for opening and closing the respective feed is provided within the housing.

[0021] In an alternative version of the invention, the feeds are designed such that the merging of the divided feeds for one secondary medium or the merging of the feeds for different secondary media occurs within the housing of the plasma torch, within the plasma head, in a space formed by the nozzle or nozzle cap and the nozzle protective cap, and the convergence of the secondary media flows from the divided feeds and / or before, during, or after passing through a gas guide of the plasma torch. Accordingly, the convergence should take place within the housing or plasma head.

[0022] The gas flow path should have at least two openings or two groups of openings that guide the respective secondary medium(s). These openings allow for targeted control of the secondary media exiting them. The openings can have different sizes and geometric shapes and / or be oriented in different directions. Openings from different groups can be radially offset from each other. The number of openings in each group can also vary.

[0023] The valves arranged inside the housing can be electrically, pneumatically or hydraulically actuated and are particularly preferably designed as axial valves.

[0024] The valves arranged in the housing should have a maximum outer diameter or a maximum mean surface diagonal of 15 mm, preferably a maximum of 11 mm, and / or a maximum length of 50 mm, preferably a maximum of 40 mm, particularly preferably a maximum of 30 mm, and / or the maximum outer diameter of the housing should be 52 mm, and / or the maximum outer diameter of the valves should be a maximum of %, preferably a maximum of 1 / 5 of the outer diameter or a maximum mean surface diagonal of the housing, and / or require a maximum electrical power consumption of 10 W, preferably 3 W, particularly preferably 2 W for their operation.

[0025] In the case of one or more electrically operated valve(s), the respective secondary medium or plasma gas should flow through the winding of a coil (S) to achieve a cooling effect.

[0026] Advantageously, it can be designed as a quick-change torch with a plasma torch shaft that can be detached from the plasma torch head. This allows for quick and easy access to different processing tasks.

[0027] In addition to the nozzle cap opening or a nozzle cap holder, the nozzle guard should have at least one opening through which at least a portion of one of the secondary media flows. If multiple openings are present, a secondary medium can exit through one or more selected openings toward the workpiece surface. However, it is also possible, as already mentioned, to allow one secondary medium to flow through a group of openings and a different secondary medium to flow through openings belonging to a different group. There can also be at least one opening through which a mixture of two different secondary media can exit.

[0028] Gaseous and / or liquid secondary media can be used. These can be two different gases, for example, selected from oxygen, nitrogen, and a noble gas; two different liquids, for example, selected from water, an emulsion, oil, and an aerosol; or one gaseous and one liquid secondary medium. It is also possible to use two secondary medium mixtures, each composed of the same gases and / or liquids, differing only in the proportions of the secondary media forming the respective mixture. This difference could, for example, be due to a different proportion of oxygen in the secondary media mixture.

[0029] In a further alternative according to the invention for a method of operating a plasma torch, the valve(s) arranged in a secondary medium supply are opened when at least part of the electrical cutting current flows through the workpiece, so that secondary medium can flow out of the plasma torch towards the workpiece surface in this operating state. During the period in which a pilot arc is formed, the valve(s) should be kept closed. This is achieved by a control system, preferably connected to a database.

[0030] During the penetration of the plasma jet into the material of the workpiece, a liquid or a liquid-gas mixture can be used as a secondary medium, and for cutting, a gas or gas mixture can be used as a secondary medium.

[0031] The valve(s) that is / are arranged in a feed for secondary medium should, in the further alternative, be able to be opened at the earliest at the point in time when secondary medium flows from the nozzle protection cap bore at which, when piercing a workpiece, the workpiece has been pierced at least 1 / 3, better half and preferably completely.

[0032] In the alternative configuration, at least one valve located in a secondary medium supply should be able to be switched on and off during the start of cutting, between two cutting sections, when crossing a kerf (F), or at the end of cutting. It is possible to switch two valves located in two different secondary medium supplies during these machining operations. This means that a valve that was previously open can be closed and a valve that was previously closed can be opened.

[0033] When starting a cutting process with a plasma jet, a piercing or incision can occur.

[0034] When cutting a contour, the parameters of the secondary medium (as previously described) can be changed, and at least one other parameter of the plasma cutting process can be modified. This could include, for example, adjusting the electrical parameters, the feed rate, the flow rate, the distance of the plasma torch to the workpiece surface, and / or the composition of the plasma gas. All parameters can be stored in a database and used to enable automated operation with plasma torch control. In addition to the parameters mentioned, the parameters for the specific processing of a workpiece can also be stored and used in the database.

[0035] The invention will now be explained by way of example. The individual features shown and explained in the figures can be combined with one another independently of the respective example or figure.

[0036] This shows: Figure 1 is a schematic sectional view through an example of a plasma torch according to the invention, with a secondary medium supply including one valve and a plasma gas supply; Figure 2 is a schematic sectional view through an example of a plasma torch according to the invention, with a secondary medium supply including two valves and a plasma gas supply; Figure 3 is a schematic sectional view through another example of a plasma torch according to the invention, with a secondary medium supply including two valves and a plasma gas supply; Figure 4 is a schematic sectional view through another example of a plasma torch according to the invention, with a secondary medium supply including two valves and a plasma gas supply; Figure 5a and 6b show a guide for secondary media.Figure 6 is a schematic cross-sectional view through an example of a plasma torch according to the invention, with two secondary medium feeds, each with two valves, and a plasma gas feed; Figure 7 is a schematic cross-sectional view through another example of a plasma torch according to the invention, with two secondary medium feeds, each with two valves, and a plasma gas feed; Figure 8 is a schematic cross-sectional view through another example of a plasma torch according to the invention, with two secondary medium feeds, each with two valves, and a plasma gas feed; Figure 9 is a schematic cross-sectional view through an example of a plasma torch according to the invention, with two secondary medium feeds, each with two valves, and a plasma gas feed with one valve and one vent valve;Figure 10 shows a schematic cross-sectional view through an example of a plasma torch according to the invention, with two secondary medium feeds with two valves and two plasma gas feeds with two valves and a vent valve; Figure 11 shows a cross-sectional view through an axial valve that can be used in the invention; Figure 12 shows a possibility for arranging valves within the housing of a plasma torch; Figure 13 shows another possibility for arranging valves within the housing of a plasma torch; Figure 14 shows another possibility for arranging valves within the housing of a plasma torch; Figure 15a and 16a show a cross-sectional contour with large and small sections (contours); Figure 16a and 17 show a cross-sectional contour with perpendicular and bevel cuts; and Figure 17 shows a plasma torch with its positioning relative to the workpiece.

[0037] Figure 1Figure 1 shows a plasma torch 1 with a plasma torch head 2 comprising a nozzle 21, an electrode 22, a nozzle protective cap 25, a feed 34 for a plasma gas PG1, a feed 61 for the secondary medium SG1, and a plasma torch shaft 3 comprising a housing 30. In the invention, and also in all other examples falling within the scope of the invention, the plasma torch shaft 3 can be formed in one piece and consist solely of a suitably configured housing 30, on which all necessary components can be present and formed.

[0038] The feed 61 can be a gas hose located outside the housing 30, which is connected to a coupling unit 5 for the supply of secondary medium SG1. A further part of the feed 61 and the valve 63, located inside the housing 30, are connected to the gas hose.

[0039] The feed 34 can be a gas hose located outside the housing 30, which is connected to a coupling unit 5 for supplying plasma gas PG1. A solenoid valve 51 for opening and closing the feed 34 is arranged in the coupling unit 5. A further part of the feed 34, located inside the housing 30, connects to the gas hose.

[0040] The electrode 22 and the nozzle 21 are arranged at a distance from each other by the gas guide 23, so that a chamber 24 is formed inside the nozzle 21. The supply 34 of the plasma gas PG1 is connected to the chamber 24.

[0041] The nozzle 21 has a nozzle bore 210, the diameter of which can vary from 0.5 mm for 20 A to 7 mm for 800 A, depending on the electrical cutting current. The gas guide 23 also has openings or bores (not shown) through which the plasma gas PG1 flows. These can also be designed in different sizes or diameters and even numbers.

[0042] The nozzle 21 and the nozzle protective cap 25 are arranged at a distance from each other, such that chambers 26 and 28 are formed within the nozzle protective cap 25. Chamber 26 is located upstream of the guide 27 in the direction of flow of the secondary medium SG1, while chamber 28 is located between the guide 27 and the nozzle protective cap opening 250. The gas guide 27 can be used to symmetry and / or rotate the flow of the secondary medium SG1, for example, a gas, gas mixture, liquid, or gas-liquid mixture. It is also possible to omit the guide 27 if, for example, rotation of the secondary medium SG1 is not desired. The nozzle 21 can also be fixed by a nozzle cap or similar device (not shown). In this case, the nozzle cap and the nozzle protective cap form chambers 26 and 28.

[0043] The secondary gas SG1 is thus fed into chamber 26 via the feed 61 and the valve 63 located in the plasma torch shaft, symmetrical by the guide 27, and set into rotation. The secondary gas SG1 then flows into chamber 28 and exits from the nozzle cap opening 250. It is also possible that one or more further bores 250a are located in the nozzle cap 25 or in a holder for the nozzle cap 25, through which the secondary medium SG1 flows out.

[0044] Valve 63 is a compact axial valve. For example, it has an outer diameter D of 11 mm and a length L of 40 mm. It requires minimal electrical power for operation, in this case approximately 2 W, to reduce heat generation in the housing 30.

[0045] When the arc is ignited and during cutting, the plasma gas PG1 flows through the open valve 51 and the supply 34 into the housing 30 and from there into the space 24 between the electrode 22 and the nozzle 21, ultimately flowing out through the nozzle bore 210 and the nozzle protective cap opening 250. After cutting, the valve 51 is closed again and the supply 34 of the plasma gas PG1 is emptied.

[0046] The secondary medium, in this example a gas (secondary gas SG1), can be switched on and off simultaneously with the valve 51 of the plasma gas PG1 via the valve 63. Due to the arrangement of the valve 63 according to the invention in the plasma torch shaft 3 and close to the plasma torch head 2, the secondary medium SG1 can also be switched on and off at other times.

[0047] In plasma cutting, a pilot arc is first ignited with a low electrical current, for example 10 A to 30 A, which burns between the electrode 22 and the nozzle 21. When the plasma jet 6 generated by the pilot arc touches the workpiece W to be cut, the arc transfers from the nozzle 21 to the workpiece W. The plasma cutting system's control unit detects this via sensors and increases the electrical current to the required value, depending on the workpiece thickness in the processing area, from 30 A to 600 A.

[0048] During the pilot arc, the secondary medium SG1 is not yet required. It actually interferes with and shortens the plasma jet 6 emerging from the nozzle 21, as it flows towards it from the side. Therefore, the plasma torch 1, with its nozzle guard opening 250 and / or openings 250a, must be positioned closer to the workpiece W. This, in turn, poses a risk to the nozzle guard 25 and the nozzle 21 from hot, splashing molten material. This problem can be remedied by switching on the secondary medium SG1 only when at least part of the electrical cutting current is flowing through the workpiece W and the arc has at least partially transferred to the workpiece W. This allows the nozzle guard opening 250 of the plasma torch 1 to be positioned far enough away from the upper surface of the workpiece for piercing, while still enabling the arc to transfer.On the other hand, an arrangement according to the invention, which ensures the rapid supply and flow of the secondary medium SG1 with only a slight time delay after the valve 63 is switched on, protects the nozzle guard 25 and the nozzle 21 from splashing molten hot material from the workpiece W being machined. This is particularly important when cutting thick workpieces with thicknesses of approximately 20 mm or more.

[0049] For thinner workpieces W, however, it is often even better if the secondary medium SG1 only flows through the nozzle guard opening 250 once the workpiece W has been partially or completely pierced by the plasma jet 6. If the secondary gas does not flow during part or all of the piercing time – that is, the time required to completely pierce the workpiece W – smaller piercing holes can be achieved. This results in fewer slag deposits on the workpiece surface, which can interfere with the cutting process.

[0050] Even when cutting at an edge, it is advisable not to let the secondary medium SG1 flow and to keep the valve 63 closed, because here too the pilot arc already passes onto the workpiece W at a greater distance and cuts more reliably.

[0051] During the cutting process itself, the secondary medium SG1 is required to improve the cut quality. This should occur immediately after piercing or initial cutting to ensure good cut quality from the start. Cut quality includes perpendicularity and skew tolerance, roughness, burr attachment, and groove runout (DIN EN ISO 9013).

[0052] A non-flowing secondary medium SG1 can also have a positive effect when traversing cut edges F or when cutting corners or curves. The oscillation or pulsation of the plasma jet 6 can be reduced.

[0053] In Figure 2 is a similar arrangement to that in Figure 1As shown, however, the feed 61 for the secondary medium SG1 in the housing 30 of the plasma torch 1 contains two valves 63 and 64 connected in parallel. The feed 61 for the secondary medium SG1 is thus divided into feeds 61a with valve 64 and 61b with valve 63. This makes it possible to add to the description for Figure 1The system not only allows the flow of the secondary medium SG1 to be switched on and off at the specified times, but also enables the volumetric flow rate to be changed quickly and easily. For example, an orifice 65 is installed in the feed 61a, reducing the volumetric flow rate compared to the feed 61b. This reduction is achieved by the correspondingly smaller free cross-section through which the secondary medium SG1 can flow. The feeds 61a and 61b carrying the partial gas flows of secondary medium SG1a and SG1b are recombined in the plasma torch shaft 3. This means that only one feed 61 to the plasma torch head 2 is required for the secondary medium SG1. This is particularly advantageous for a plasma torch 1 with a quick-change head.

[0054] A reduction in the secondary medium flow has a positive effect at the same times as in the example after Figure 1The described sections are without a flowing secondary medium SG1.

[0055] The ability to quickly switch the secondary medium SG1 flow on and off, along with the additional option of adjusting different volume flows, allows for further improvement of the plasma cutting process, particularly during transition processes such as piercing, scoring, crossing a joint F, cutting a corner or a curve. Furthermore, in contrast to, for example, [the following]... Figure 1 The nozzle 21 is fixed here by a nozzle cap 29. This allows a cooling medium, for example cooling water, to flow in the space between the nozzle 21 and the nozzle cap 22 (not shown).

[0056] Figure 3 shows an example of a similar arrangement as Figure 2However, the feeds 61a and 61b of the secondary media SG1a and SG1b to the secondary medium SG1 are only combined in the plasma torch head 2. In this example, the combination occurs further upstream of the guide 27 of the secondary medium when viewed in the flow direction of the secondary medium SG1.

[0057] Figure 4 Figure 1 also shows an arrangement in which the feeds 61a and 61b of the secondary medium SG1 are only combined in the plasma torch head 2. In this example, the combination takes place after the secondary medium gas guide 27, following the nozzle protective cap 25 and nozzle cap 29 in the flow direction of the secondary medium SG1. The gas guide 27 has two groups of openings, one group for the secondary medium SG1a and the other group for the secondary medium SG1b.

[0058] Advantageously, the openings differ in their design, dimensions, and / or the orientation of their central axes (dash-dot lines), exemplified here by their offset from the radial axis. Openings 271 and 272 of the groups can be arranged in different planes and offset from each other within those planes. This is also shown. Figure 5 . Thus, the secondary medium SG1 can be divided into two differently rotating secondary medium streams SG1a and SG1b as well as SG1 and SG2, which ultimately flow around the plasma jet 6.

[0059] When piercing the workpiece material W, a low or no rotation of the flowing secondary medium SG1 is often advantageous, while a higher rotation is beneficial when cutting. The larger offset g from the radial axis increases the rotation of the exiting secondary medium flow. Additionally, the cut quality can be influenced during cutting by switching between or simultaneously activating the flows of secondary media SG1a and SG1b. This allows for the cutting of long, straight sections with high rotation of the exiting secondary medium SG1 and a high feed rate, and short sections with lower rotation of the exiting secondary medium SG1 and a lower feed rate. A long section typically begins at a length that is at least twice the thickness of the workpiece W to be cut, but is at least 10 mm long.With greater rotation, i.e., a higher angular velocity of the secondary medium SG1 flow, faster cutting is possible; with lower rotation, slower cutting is required. However, a lower feed rate is advantageous for cutting small sections, e.g., small radii that are less than twice the thickness of the workpiece W, saw teeth, or rectangular contours whose edge length is also less than twice the thickness of the workpiece W in the respective processing area. Due to the lower feed rate, the guide system directs the plasma torch 1 more precisely, even when the direction of the movement changes. Furthermore, the plasma jet 6 does not trail, and the groove trail is reduced, which is beneficial for corners on internal contours. Figure 17) and inside corners have a positive effect. For long sections, this is irrelevant; here, cutting can be performed with a higher feed rate and a large rotation of the secondary medium SG1 flow.

[0060] Figures 5a and b The figures show an example guide 27 for the secondary medium, here an example gas, which is referred to here as secondary gas SG1, SG2, SG1a and SG1b.

[0061] The group of bores 271 is for the secondary medium SG1 or SG1a, the bores of group 272 for the secondary medium SG2 or SG1b. The bores of a group are arranged in one plane. For example, the group of bores 271 has an offset of 3 mm to the radial plane, and the group of bores 272 has no offset to the radial plane. When this guide 27 is inserted into the plasma torch 1 after Figure 4When installed, the flow of the secondary medium SG1a, which is supplied through the feeder 61a and the group of bores 271, has a greater rotation with a higher angular velocity than the flow of the secondary medium SG1b, which is supplied through the feeder 61b and the group of bores 272.

[0062] Openings other than bores 271 and 272 are also possible, such as grooves, squares, semicircular or angular shapes. Likewise, the openings can have different free cross-sectional areas through which secondary medium can escape.

[0063] The order according to Figure 6 demonstrates the characteristics of the example. Figure 1The housing 30 has, in addition to the feed 61 for the secondary medium SG1, a feed 62 for a second secondary medium SG2. The feeds 61 and 62 can be hoses located outside the housing 30, which are connected to a coupling unit 5 for supplying the secondary media SG1 and SG2. Each hose is connected to a further section of the feeds 61 and 62 and to valves 63 and 64, which are located inside the housing 30.

[0064] The feeds 61 and 62 for the secondary media SG1 and SG2 are rejoined here in the plasma torch shaft 3. This means that only one feed 66 to the plasma torch head 2 is required for the secondary media SG1 and SG2. This is particularly advantageous for a plasma torch 1 with a quick-change head.

[0065] This arrangement allows not only for rapid switching on and off and rapid changes in the volume flow of the secondary media streams, but also for the composition of the exiting secondary medium to be controlled by switching or simultaneously activating valves 63 and 64. Thus, when cutting a workpiece W made of structural steel, small contours or small sections are cut with a secondary medium mixture that has a higher proportion of oxygen relative to nitrogen, CO₂, air, or argon than when cutting larger sections. The information provided in the explanation applies here. Figure 4 were made. Examples of such contours can also be found in the Figures 15a and 15b The oxygen content is then over 40 vol%. K3 is a small section, while sections K1 and K5 are larger.

[0066] Similarly, it is advantageous to use oxygen as the sole secondary medium when piercing structural steel, as this makes the melt less fluid and speeds up the piercing process. However, during the cutting process itself, an excessively high oxygen content can lead to irregularities on the cut edge or surface. Here, too, a rapid switchover is beneficial.

[0067] Another application is the use of a liquid, such as water, as one of the secondary media. For example, water can be advantageously used as a secondary medium (SG1) for piercing structural steel. This prevents or reduces splashing hot metal, thus protecting the plasma torch (1) and the surrounding area. After piercing the workpiece (W), the water is switched off, and a gas or gas mixture flows as a secondary medium (SG2). The process can also be used for high-alloy steel and non-ferrous metals.

[0068] Furthermore, the secondary medium or secondary medium mixture can also be modified during the transition from vertical cutting to bevel cutting with regard to parameters such as flow velocity, volume flow, rotation, and composition. During bevel cutting, the plasma torch 1 (central axis) is not positioned at a right angle to the workpiece surface, as it is in vertical cutting, but is tilted to create a cut edge with a specific angle. This is advantageous for subsequent processing, usually welding. Since the effective thickness W of the workpiece to be cut changes (increases) during the transition from vertical to bevel cutting, modified parameters are beneficial for achieving higher cut quality. The same principle applies to the transition from bevel to vertical cutting (reduction).

[0069] It is also advantageous if the parameter changes occur in sections that were not on the cutting contour after the workpiece W was cut out, for example at the start of the cut, corners that were bypassed, at the end of the cut, when crossing a kerf or other parts of the "waste piece".

[0070] Figure 7 shows an example of a similar arrangement as Figure 6 However, the feeds 61 and 62 of the secondary media SG1 and SG2 are only combined in the plasma torch head 2. In this example, the combination occurs upstream of the feed guide 27 for the secondary media, viewed in the direction of flow of the secondary media SG1 and SG2.

[0071] Figure 8 Figure 1 also shows an arrangement in which the feeds 61 and 62 of the secondary media SG1 and SG2 are only combined in the plasma torch head 2. Figure 8 demonstrates all the advantages of the example Figure 6 on.

[0072] Further advantages are described below. In this example, the secondary media SG1 and SG2 are combined upstream of the nozzle protection cap 25 and nozzle cap 29 in the flow direction of the secondary media SG1 and SG2, and downstream of the guide 27 for the secondary media. The guide 27 has two sets of openings, one set for secondary medium SG1 and the other for secondary medium SG2.

[0073] Advantageously, openings 271 and 272 differ in their design, exemplified here by their offset from the radial. This is also shown. Figure 5a. Thus, the secondary medium SG1 can form a differently rotating secondary medium flow than the secondary medium SG2, which ultimately flow around the plasma jet 6.

[0074] When piercing the workpiece material, low or no rotation of the secondary media SG1 and SG2 is often advantageous, whereas when cutting, greater rotation with a higher angular velocity is desirable. A larger offset from the radial axis increases the rotation. Additionally, the cut quality can be influenced during a cut by switching or simultaneously activating the flows of the secondary media SG1 and SG2. This allows long, straight sections to be cut with high rotation and velocity, and short sections with lower rotation and velocity. A long section typically begins at a length that is at least twice the thickness W of the workpiece to be cut in the respective machining area, but at least 10 mm.With a higher rotation of the secondary medium(s) flow, faster cutting is possible; with a lower rotation, slower cutting is required. However, a lower feed rate is advantageous for cutting small sections, such as small radii that are less than twice the thickness of the workpiece W in the respective processing area. Examples include sawtooth contours and quadrilateral contours whose edge length is also less than twice the workpiece thickness in the respective processing area. Due to the lower feed rate, the guide system directs the plasma torch 1 more precisely, even when the direction of the feed movement changes. Furthermore, the plasma jet 6 does not trail, reducing groove trailing, which is beneficial for corners on internal contours and inside corners.For long sections this is irrelevant, as rapid cutting is possible with high rotation of the flow of the secondary medium(s).

[0075] In this arrangement, the exiting secondary medium or secondary medium mixture can be changed with regard to parameters such as flow velocity, volume flow, rotation of the flow and composition.

[0076] The Figure 9 Figure 33 shows a valve 31 in the housing 30 of the plasma torch shaft 3, located in the supply 34 of the plasma gas PG1, which switches the plasma gas PG1 on and off. The valve 33 serves to vent the cavity 11, which is particularly necessary at the end of the cut to ensure a rapid outflow of the plasma gas PG1.

[0077] Figure 10 shows in addition to Figure 9The supply 35 of another plasma gas PG2 is provided via a gas hose 35 and a valve 31, analogous to plasma gas PG1. This allows the plasma gases PG1 or PG2 to be switched depending on the process state by opening and closing valves 31 and 32. Valve 33 also serves to vent the cavity 11.

[0078] Figure 11 Figure 1 shows a highly simplified structure of an axial solenoid valve, as used in the invention for secondary media and plasma gas feeds. Inside its body is the coil S with the windings through which the plasma gas can flow from inlet E to outlet A. The opening and closing mechanism is also located inside. The solenoid valve body has a length L and an outer diameter D. The solenoid valve shown here has a length L of 25 mm and a diameter of 10 mm.

[0079] Figure 12Figure 1 shows a possible space-saving arrangement of valves 31, 63, and 64. They are arranged in the housing 30 such that they are positioned in a plane perpendicular to the center line M, each at an angle α1 of 120°. The deviation from this angle should not exceed ± 30°. This arrangement is space-saving and can be positioned in the housing 30 or plasma torch shaft 3. The distances between the central longitudinal axes L1, L2, and L3 of valves 31, 32, and 33 are each ≤ 20 mm. Of valves 31, 32, and 33, at least one valve has its inlet E oriented opposite to the other valves, i.e., opposite to their outlets A. In the example shown, the oppositely oriented valve is valve 33 in cavity 11.

[0080] Figure 13Figure 1 shows an arrangement with four valves 31, 33, 63, and 64. They are arranged inside the housing 30 such that they are positioned in a plane perpendicular to the center line M at angles α1, α2, α3, and α4 of 90° each. The deviation from these angles should not exceed ±30°. This makes the arrangement compact and allows it to be positioned within the housing 30 or the plasma torch shaft 3. The distances between the central longitudinal axes L1, L2, L3, and L4 of the valves 31, 33, 63, and 64 are ≤ 20 mm. Of these valves 31 and 33, at least one valve has its inlet E facing oppositely to the other valves, i.e., oppositely to their outlets A.

[0081] Figure 14Figure 1 shows an arrangement with four valves 31, 33, 63, and 64, as well as a further valve 32. They are arranged inside the housing 30 such that they are positioned in a plane perpendicular to the center line M at angles α1, α2, α3, α4, and α5 of 72° each. The deviation from these angles should not exceed ±15°. This makes the arrangement compact and allows it to be positioned within the housing 30 or the plasma torch shaft 3. The distances between the central longitudinal axes L1, L2, L3, L4, and L5 of the valves are ≤ 20 mm. Of these valves 31 to 33, at least one valve has its inlet E facing oppositely to the other valves, i.e., oppositely to their outlets A.

[0082] Figure 15a A schematic diagram shows the contour guidance of a plasma torch for cutting a contour from a workpiece W, viewed from above. Figure 15bThe resulting workpiece is shown in perspective. Here, a workpiece with two long sections, contours K1 and K5, and several short sections, contour K3, is to be cut. Section K0 is the starting point of the cut; the cutting tool is inserted into the workpiece at this point. Sections with contours K2 and K4 are necessary for the cutting process to achieve a sharp corner and are located in the so-called "waste section"; they are not part of the cut-out workpiece.

[0083] The following options are available during the Piercing: a. At the time of pilot arc operation, the secondary medium is not yet required. It even interferes with and shortens the plasma jet 6 emerging from the nozzle 21, as it flows towards it laterally. Therefore, the plasma torch 1 with its nozzle guard opening 250 must be positioned at a smaller distance to the workpiece surface ( Figure 17, distance d). This, in turn, leads to the nozzle guard 25 and the nozzle 21 being endangered by hot, splashing molten material. This is remedied by switching on the secondary medium only when at least part of the electrical cutting current flows through the workpiece and the arc has at least partially transferred to the workpiece. In this way, the nozzle guard opening 250 of the plasma torch 1 can be positioned at a greater distance d from the workpiece surface for piercing, and the arc still transfers. By flowing the secondary medium SG1 at a higher flow velocity, the nozzle guard 25 and the nozzle 21 are protected from splashing molten material from the workpiece being processed. This is particularly important for workpieces with a thickness of approximately 20 mm or more in the respective processing area. For this purpose, a plasma torch 1 can, for example, be adjusted accordingly. Figures 1 to 10 be used. b. For thinner workpieces, it is more advantageous for the secondary medium to flow through the nozzle guard opening 250 only when the workpiece is partially or completely pierced. If the secondary medium does not flow during part or all of the piercing time – that is, the time required to completely pierce the workpiece – smaller piercing holes will be achieved. This results in fewer slag deposits on the workpiece surface, which can interfere with the cutting process. The secondary medium should flow from the nozzle guard opening 250 no earlier than when the workpiece has been pierced at least 1 / 3, preferably half, and ideally completely. For this purpose, a plasma torch can be used, for example, according to the Figures 1 to 10c. Furthermore, when piercing the workpiece, a low or no rotation of the secondary medium SG1, SG1a, SG1b, SG2 is often advantageous, whereas when cutting, a higher rotation with a higher angular velocity is required. For this purpose, for example, a plasma torch 1 can be used according to the Figures 4 and 8 can be used. Due to the larger offset of the openings 271 and 272 from the radial in the gas guide 27 for the secondary media, the secondary media SG1a and SG1b rotate ( Figure 4 ) as well as SG1 and SG2 ( Figure 8) to varying degrees. The change in rotation of the secondary medium(s) should occur from the nozzle guard opening 250 at the earliest when, during piercing of a workpiece, the workpiece has been penetrated at least 1 / 3, preferably half, and ideally completely. d. It can also be advantageous for piercing into structural steel if water flows as the secondary medium SG1. This prevents or reduces splashing hot metal splashes and thus protects the plasma torch 1 and the surrounding area. After piercing the workpiece, the water is switched off and a gas or gas mixture flows as the secondary medium SG2. The change from water to gas as the secondary medium should occur from the nozzle guard opening 250 at the earliest when, during piercing of a workpiece, the workpiece has been penetrated at least 1 / 3, preferably half, and ideally completely.The process can also be used for high-alloy steel and non-ferrous metals. For this purpose, a plasma torch 1 can be used, for example, according to the specifications. Figure 6 and 10can be used. e. It is also advantageous if, when piercing structural steel, the piercing is performed with oxygen or a higher oxygen content in a secondary medium mixture, because the melt then becomes less fluid and the piercing process is faster. During cutting itself, an excessively high oxygen content can again lead to the formation of irregularities on the cut edge or surface. Changing the secondary medium between piercing and cutting can also be advantageous for cutting high-alloy steel, aluminum, and other metals. The change of the outflowing secondary medium should occur at the earliest when, during piercing into a workpiece, the workpiece has been penetrated at least 1 / 3, preferably half, and ideally completely. For this purpose, a plasma torch 1 can be used, for example, according to the Figure 6 and 10can be used. f. It can be particularly advantageous if the secondary medium and the rotation of the secondary medium flow are changed when piercing the workpiece. This leads to the effects described in points c. and e. The plasma torch 1 can be used as an example, as described in Figure 8 shown will be used.

[0084] In principle, it can be advantageous to change the secondary medium(s) in one or more parameters, such as flow velocity, volume flow, rotation of the flow and composition, during the piercing phase compared to other operating conditions.

[0085] After piercing, the cutting motion is performed with the selected secondary medium. After piercing the workpiece contour K0, the long section K1 is cut, then the cutting motion should move around the corner in section contour K2. A sharp-edged corner is obtained if the plasma cutting torch 1 is guided as in the corner of section contour K2. Here, the plasma cutting torch 1 exits, as in Fig. 15 The plasma torch follows the contour of the part to be cut and is guided over the "waste material" before returning to the contour of the part to be cut. This is also called the "circumscribed corner". Following section contour K2 is section contour K3 with an exemplary sequence of small sections with changes in the feed axis direction. During the time that the plasma torch 1 is guided over the "waste material" in section contour K2, at least one change occurred in the outflowing secondary medium.

[0086] The following possibilities exist when driving over the "waste section" on contour K2: a. It is advantageous to influence the cut quality during cutting by changing the rotation of the secondary medium(s) flow. Long, straight sections are cut with high rotation and high speed, and short sections with lower rotation and lower feed rate. A long section generally begins at a length that is at least twice the workpiece thickness in the respective machining area of ​​the workpiece to be cut, but at least 10 mm. With greater rotation of the secondary medium(s) flow, a higher feed rate can be used; with less rotation, a lower feed rate is necessary. However, a lower feed rate is not recommended for cutting short sections, e.g.,Small radii, for example, less than twice the workpiece thickness in the respective machining area, sawtooth contours, and quadrilateral contours whose edge length is also less than twice the workpiece thickness are advantageous. Due to the lower feed rate, the guide system guides the plasma torch 1 more precisely, even when the direction of the movement changes. Furthermore, the plasma jet 6 does not trail, reducing groove trailing, which is beneficial for corners on internal contours and inside corners. This is irrelevant for long sections, where a higher feed rate can be used with a large rotation of the secondary medium(s) flow. For this purpose, a plasma torch 1 can be used, for example, according to the... Figures 4 and 8can be used. b. It is also advantageous to change the volume flow rate and / or the composition of the secondary medium during cutting. For example, when cutting a workpiece made of structural steel, small contours or small sections are cut with a secondary medium mixture that has a higher oxygen content than when cutting larger sections. The oxygen content is then over 40 vol.%. For this purpose, a plasma torch 1 can be used, for example, according to the Figures 6 to 10 c. It is particularly advantageous to combine the options described in points a. and b. For this purpose, for example, a plasma torch can be used according to the Figure 8d. In this arrangement, the secondary medium or secondary medium mixture can be changed with respect to parameters such as flow velocity, volume flow rate, flow rotation, and composition. e. In principle, it can be advantageous to change the secondary medium or secondary medium mixture with one or more parameters, such as flow velocity, volume flow rate, flow rotation, and composition, during cutting and particularly advantageous when passing over the "waste section".

[0087] If the change of one of the described parameters occurs in the area of ​​the waste part, i.e. not at a cutting edge of the workpiece to be cut out, no transition or difference in the cut quality will be visible on the cutting edge of this workpiece.

[0088] However, it is also possible to change the parameters on a section of the emerging cut edge of the workpiece. For this, in addition to the secondary medium, at least one other parameter of the plasma cutting process must be changed: feed rate, distance plasma torch - workpiece surface (nozzle cap - workpiece surface), electrical cutting current and / or electrical cutting voltage.

[0089] However, it is also possible to implement one of the described changes of the secondary medium when crossing a cutting joint F.

[0090] The cutting process ends in section K10, the end of the cut. Parameters of the outflowing secondary medium or secondary medium mixture can also be changed here.

[0091] After one of the described changes to at least one parameter of the secondary medium(s), the contour K3 is cut with the small sections using the parameter(s) best suited for this purpose.

[0092] The change to the parameters on the section with long contour K5 takes place in the area K4 on the "waste part" analogously to the change in the section contour K2.

[0093] The Figures 16a and 16b They also show a cut component. Here too, a process similar to the one described above is used. Figures 15a and 15b The described form of change of the outflowing secondary medium in sections K2 and K4 between sections K1 and K3, as well as K5, is as follows: The parameters of the outflowing secondary medium for section K3 are changed compared to section K21 because a chamfer at an angle, for example 45°, is cut in section K3. This is also explained in the last paragraph. Figure 6 described.

[0094] Figure 17 Figure 1 shows an example of a plasma torch 1 with its positioning to the workpiece with the distance d between nozzle protection cap 25 and workpiece W. Reference symbol list

[0095] 1 Plasma torch 2 Plasma torch head 3 Plasma torch shaft 5 Coupling unit 6 Plasma jet (pilot or cutting arc) 11 Cavity 21 Nozzle 22 Electrode 23 Gas guide 24 Space (between electrode and nozzle) 25 Nozzle protective cap 26 Space (nozzle and nozzle protective cap) 27 Media guide SG1, SG2, SG1a, SG2a 28 Space (nozzle and nozzle protective cap), towards the nozzle tip 29 Nozzle cap 30 Housing 31 Valve PG1 32 Valve PG2 33 Vent valve 34 Feed PG1 35 Feed PG2 37 Line 51 Valve 61 Feed SG1 61a Feed SG1a 61b Feed SG1b 62 Feed SG2 63 Valve SG1, SG1a 64 Valve SG2, SG1b 65 Aperture 66 Feed 210 Nozzle bore 250 Nozzle protective cap opening 250a Further bore 271 Bores in media guide 27 for secondary medium SG1, SG1a 272 Bores in media guide 27 for secondary medium SG2, SG1b A Outlet D Diameter D Distance plasma torch - workpiece E Inlet F Joint g Offset K Contour of the cut workpiece K0 Cutting start,Piercing K1 Section Contour 1 K2 Section between two sections K3 Section Contour 3 K4 Section between two sections K5 Section Contour K10 Cutting length L Central axis of the plasma torch PG1 Plasma gas 1 PG2 Plasma gas 2 SG1 Secondary medium 1 SG1a Secondary medium 1a SG1b Secondary medium 1b SG2 Secondary medium 2 S Coil L1-L4 Valve spacing V Cutting direction, feed axis direction W Workpiece W1 Cutting area W2 Workpiece thickness α1-α4 Angle,

Claims

1. A plasma torch (1), in particular a plasma cutting torch with a feed line (34) for plasma gas (PG1), in which at least one secondary medium (SG1, SG2) is guided through at least one feed line (61, 62) in a housing (30) of the plasma torch (1) into a nozzle protection cap opening (250) and / or further openings (250a) provided in a nozzle protection cap (25) and in the at least one feed line (61, 62) directly inside the housing (30) of the plasma torch (1), there is at least one valve (63, 64) to open and close the at least one feed line (61, 62) for a secondary medium characterized in that the feed line (61) for a secondary medium is partitioned into at least two parallel feed lines (61a, 61b) through which the secondary medium flows towards the nozzle protection cap opening (250) and / or the further openings (250a) and there are at least two valves (63, 64) in the housing to open and close the respective partitioned feed lines (61a, 61b), which can each be activated individually, and a merging of the partitioned feed lines (61a, 61b) for a secondary medium is arranged within the housing (30) of the plasma torch (1), within a plasma torch head (2) or in a space formed by the nozzle or nozzle cap and the nozzle protection cap or that at least two feed lines (61, 62) for two different secondary media (SG1, SG2) are guided through the housing (30) of the plasma torch (1) to the nozzle protection cap opening (250) and / or any further openings (250a) provided in a nozzle protection cap (25) and, within the housing (30), there is at least one valve (63, 64) in the two feed lines for each secondary medium (SG1, SG2) to open and close the respective feed lines (61, 62) and a merging of the feed lines (61, 62) for a different secondary media (SG1, SG2) within the housing (30) of the plasma torch (1) is arranged within the plasma torch head (2) or in a space formed with the nozzle or nozzle cap and the nozzle protection cap (25).

2. Plasma torch according to claim 1, wherein the secondary media flows from the partitioned feed lines (61a, 61b, and / or 61, 62) or the at least second feed lines (61, 62) for a confluence of secondary medium before, during or after passing through a gas guide (27) of the plasma torch (1).

3. Plasma torch according to claim 1, whereby there is a stop (65), a choke or an element which changes the free cross-section of the respective feed (61a) for a secondary medium relative to the free cross-section relative to the other partitioned feed line (61b) for a secondary medium in at least one of the partitioned feed lines (61a, 61b) for a secondary medium.

4. Plasma torch according to one of the preceding claims, wherein at least two openings (271, 272) or two groups of openings (271, 272) are provided on the gas guide (27) which guide the respective secondary medium(s) (SG1, SG2); wherein preferably the openings (271, 272) have free cross-sections of different sizes and geometric shapes and / or are aligned in different axial directions, or openings (271, 272) of different groups are arranged radially offset from one another, and / or the number of openings (271, 272) in the individual groups is selected differently.

5. Plasma torch according to one of the preceding claims, wherein at least one hollow space (11) connected to the plasma gas supply (34) is provided within the housing (30), the hollow space having an opening at which a valve (33) is provided to open and close the opening, which, when this valve (33) is open, allows the at least one plasma gas to be discharged to from the at least one plasma gas feed line (34) to the nozzle opening (210).

6. Plasma torch according to one of the preceding claims, wherein the valves (33, 63, 64), which are preferably configured as axial valves and arranged inside the housing (30), can be actuated electrically, pneumatically or hydraulically, and particularly preferably have a maximum outer diameter or a maximum average face diagonal of no more than 15 mm, a maximum length of 50 mm and / or the housing's maximum outer diameter is 52 mm and / or the maximum outer diameter of the valves is no more than ½ of the outer diameter or a maximum mean face diagonal of the housing (30) and / or the valve (33) to open and close the opening through which the at least one plasma gas can be discharged from the at least one plasma gas feed line (34) to the nozzle opening (210) when this valve (33) is open, and the valves (63, 64) to open and close the feed line (61, 62) requires a maximum electrical power consumption of 10 W to operate; wherein, preferably in the case of electrically powered valve(s) (33, 63, 64), the respective secondary medium or the plasma gas flows through the winding of a coil (S).

7. Plasma torch according to any one of the preceding claims, wherein the plasma torch (1) is configured as a quick-change torch with a plasma torch body (3) that can be separated from a plasma torch head (2).

8. Plasma torch according to one of the preceding claims, wherein, in addition to the nozzle protection cap opening (250) or a bracket for the nozzle protection cap (25), there is at least one opening (250a) through which at least part of one of the secondary media (SG1, SG2) flows, wherein, if there are several openings (250a), one secondary medium (SG1 or SG2) is discharged through one or more selected opening(s) (250a) towards the workpiece surface.

9. Plasma torch according to one of the preceding claims, wherein gaseous and / or liquid secondary media can be used.

10. Method for operating a plasma torch (1) according to one of the preceding claims, wherein the plasma torch (1) is connected to a control unit which is configured such that the valve(s) (63, 64) to open and close the feed line (61, 62), which is / are arranged in the feed line (61, 62, 61a, 621b) for a secondary medium (SG1, SG2), are open when at least part of the electrical cutting current flows through a workpiece (W), so that secondary medium (SG1, SG2) in this operating condition can flow from the plasma torch (1) towards the workpiece surface and, during a period in which a pilot arc is formed, the valve(s) (63, 64) to open and close the feed line (61, 62) is / are kept closed and / or at least the valve (63, 64) to open and close the feed line (61, 62) for a secondary medium (SG1, SG2), which is switched on and off during the start of cutting (KO), is arranged between two cutting sections (K2), when running over a cut (F) or at the end of cutting (K10).

11. Method according to claim 10, wherein the valve(s) (63, 64) for a secondary medium (SG1, SG2) arranged in a feed line (61, 62, 61a, 61b), are opened at the earliest at a point in time once a workpiece (W) has been pierced halfway and preferably completely.