EP1797747A2 - Plasma torch - Google Patents

Abstract

Disclosed is a plasma torch comprising a torch body, an electrode that is disposed inside the torch body, a nozzle which is provided with a central nozzle port and is positioned so as to cover the electrode separated by a plasma gas duct formed between the same, and a protective nozzle cap. Said protective nozzle cap is equipped with a discharge port that is located at the forward end face thereof and lies opposite the nozzle port as well as an annular secondary gas duct which is arranged within the protective nozzle cap and is connected to the discharge port. The protective nozzle cap is placed so as to be electrically insulated relative to the electrode and the nozzle. The inventive plasma torch further comprises a secondary gas conduit section that is provided with at least one passage. The disclosed plasma torch is characterized in that the secondary gas conduit section is disposed between a secondary gas inlet and the forward end of the secondary gas duct inside the secondary gas duct while the secondary gas duct is embodied in such a way between the secondary gas conduit section and the forward end thereof that the secondary gas duct conveys the secondary gas (SG) at an angle to the longitudinal axis L of the plasma torch in the direction of the forward end of the plasma torch after passing the secondary gas conduit section and a secondary gas duct section which extends substantially parallel to the longitudinal axis L of the plasma torch, and then delivers said secondary gas (SG) to a plasma jet at an essentially right angle to the longitudinal axis L of the plasma torch.

Description

 "Plasma torch"

The present invention relates to a plasma torch according to the preamble of claim 1, which serves both for dry cutting and underwater cutting of various metallic workpieces.

In plasma cutting, an arc (pilot arc) is first ignited between a cathode (electrode) and anode (nozzle) and then transferred directly to a workpiece to produce a cut.

This arc creates a plasma, which is a thermally highly heated, electrically conductive gas consisting of positive and negative ions, electrons, and excited and neutral atoms and molecules.

As plasma gas, gases such as argon, hydrogen, nitrogen, oxygen or air are used. These gases are ionized and dissociated by the energy of the arc. The resulting plasma jet is used to cut the workpiece

A modern plasma torch is made of grand components such as torch body, electrode (cathode), nozzle, one or more protective caps surrounding the nozzle, and the Connections used to supply the burner with electricity, gases and / or liquids.

The nozzle may consist of one or more parts. For direct water-cooled burners, the nozzle is held by a nozzle cap. Cooling water flows between the nozzle and the nozzle cap. The secondary gas flows between the nozzle and protective cap.

For gas-cooled burners and indirect water-cooled burners, the nozzle cap can be omitted. Then the secondary gas flows between the nozzle and protective cap.

The electrode and the nozzle are arranged in a certain spatial relationship to one another and delimit a space - the plasma chamber in which this plasma jet is generated. The plasma jet may be varied in parameters such as e.g. Diameter, temperature, energy density and flow rate of the plasma gas are strongly influenced by the design of the nozzle and electrode.

For the different plasma gases, the electrodes and nozzles are made of different materials and in different shapes.

Nozzles are usually made of copper and water cooled directly or indirectly. Depending on the cutting task and electrical power of the plasma torch, nozzles are used which have different inner contours and openings with different diameters and thus provide the optimum cutting results.

To protect a nozzle from the heat and spewing molten metal of the workpiece during the cutting process, nozzles are enclosed by protective caps. Through the gap between the nozzle and cap flows Secondary gas. This serves to create a defined atmosphere, to constrict the plasma jet and to protect against splashing during piercing.

In the patent application DE 38 32 630 Al the plasma jet is protected underwater cutting by a gas vortex, which rotates at high speed around the plasma jet. On the nozzle cap five to twenty gas guide in the form of a rod are arranged symmetrically. The secondary gas flowing through the conical tangential arrangement of the Gasleitführungen and the burner cap flowing secondary gas flows tangentially around the plasma jet and forms a hyperbolic vortex, which prevents the access of the water to the plasma jet. However, this burner can also be used for dry cutting, wherein the swirling secondary gas protects the burner tip in front of the molten metal of the workpiece, especially during piercing substantially.

In order to prevent the oxidation of the cut surfaces by a reaction with the oxygen in the ambient air, the selection of the secondary gas plays an important role. In the earlier patent application DE 101 44 516 A1 of the present applicant, nitrogen is used as secondary gas. The plasma jet is flowed around with the secondary gas, which is passed between the nozzle cap and protective cap through the resulting passage and exits from the annular opening in the direction of the workpiece. This ensures a substantially non-oxidizing atmosphere on the workpiece. This effect can be enhanced by adding small amounts of hydrogen (eg 1 to 20%).

In the plasma torch according to the patent EP 0 573 653 Bl, the secondary gas passing through an annular secondary gas passage is aligned by an insulator between the nozzle cap and the protective cap. The insulator has small holes which are shaped so that the secondary gas exits along the axial direction of the burner body and surrounds the plasma arc with sufficient quantity and speed. In another Insulator, the secondary current is generated as a circulating current in which the straightening channel formed in the insulator is formed spirally with respect to the central region of the burner.

In patent EP 0 801 882 Bl, a protective cap directs a secondary gas flow along the arcuate surface of a nozzle cap onto the arc. During cutting, the velocity of this flow is reduced so that the arc is not destabilized. This cap contains some vents that divert the excess gas away. The protective cap and secondary gas flow protect the nozzle from molten metal that can splash from a workpiece onto the nozzle and cause damage or parallel arcing.

In the above examples, there is the disadvantage that the plasma jet is unstable by the direct flow of the secondary gas, in particular at a secondary gas flow rate that is greater than the plasma gas flow rate. The instability is especially when driving over technologically related kerfs and direction and speed changes, such. noticeable at corners and at the beginning of cutting. When crossing a kerf, the cutting arc stabilizes only slowly. It comes to swinging the cutting arc. This swinging forms on the resulting cut edge and thus leads to a deterioration in quality.

In US 6,207,923 Bl, a secondary gas flows in a space between a nozzle with an elongated nozzle mouth and a protective cap. The outlet opening of the protective cap is shaped so that the nozzle mouth is partially between the inlet and the outlet of the outlet opening. Such an arrangement produces a substantially columnar flow of secondary gas around the plasma jet without substantially disturbing the plasma jet and is intended to protect the nozzle from spattering metal of the workpiece. Disadvantage of this method is that the nozzle mouth is insufficiently protected against high-spraying metal especially when piercing the plasma jet into the workpiece. Furthermore, the secondary gas can not be targeted in the plasma jet to achieve a good quality cut.

For certain gas combinations, the active participation of the secondary gas in the plasma process is desired. This applies, for example, to the cutting of stainless steels with an ArH ₂ mixture as plasma gas and nitrogen as secondary gas. Here, the secondary gas nitrogen not only acts as a protective gas to protect the interfaces of the oxidizing oxygen in the ambient air, but also actively participates in the plasma process. It reduces the surface tension of the melt, which becomes less viscous and better expelled from the kerf. The result is a beard-free cut. This is not possible with the arrangement described in US Pat. No. 6,207,923 Bl. Even when using oxygen as the plasma gas for cutting structural steels, different effects on the quality of cut can be achieved by different composition of the secondary gas, for example different nitrogen and oxygen fractions.

The invention is therefore based on the object to eliminate the disadvantages of the prior art described. The functions of the secondary gas, such as protection against high-velocity metal, creation of a defined atmosphere around the plasma jet and the active participation of the secondary gas in the plasma process should be ensured without affecting the plasma jet in its stability.

According to the invention this object is achieved in the generic plasma torch by the features according to the characterizing part of claim 1.

The subclaims relate to advantageous developments of the invention. The invention generates a homogeneous secondary gas flow. This homogeneous secondary gas flow leads to a stabilization of the plasma jet. As a result, the oscillation of the cutting arc in difficult to be controlled technologically caused cutting situations, such as driving over the kerf and the corner and cutting start is prevented. This results in a significant improvement in the quality of the cut and a higher cutting speed.

Studies have shown that the disadvantages described can be eliminated by a new form of secondary gas supply. As a result, the advantages of the secondary gas, such as Einschürung the plasma jet, protection of the nozzle against high-metal splash during piercing, Schafrang a defined atmosphere around the plasma jet and the active participation of the secondary gas in the plasma process continue to be used while ensuring the stability of the plasma jet.

In a particular embodiment, the secondary gas is passed through a secondary gas guide part in the secondary gas channel such that the secondary gas flow initially on a nearly cylindrical first surface of the nozzle or nozzle cap, which is directed parallel to the longitudinal axis of the plasma torch hits. Thereafter, the secondary gas is passed through the secondary gas channel part, which is bounded by almost conical mantle or inner surfaces of the nozzle or the nozzle cap and nozzle cap, to the front end of the plasma torch and then fed at an angle of almost 90 ° to the longitudinal axis of the plasma torch a plasma jet. It is assumed that the particularly good homogeneity of the secondary gas, ie the particularly good distribution around a plasma jet, is achieved by initially directing the secondary gas flow onto the jacket surface of the plane extending substantially at right angles to the longitudinal axis of the plasma torch Nozzle or the nozzle cap hits and that is further reset from the front end of the plasma torch and thus the secondary gas has additional time to disperse. It is also advantageous to have the secondary gas rotated by a suitable execution of the secondary gas guide part, for example by displacement of the passages. Then the supply of the secondary gas to the plasma jet is not radial, but tangential. The plasma jet is not unstable in this arrangement due to the great homogeneity of the secondary gas flow, but also retains its stability in transition phases.

This effect is reinforced even if, after passing through the Sekundärgasfuhrungsteils the secondary gas initially not only on the almost cylindrical first lateral surface of the nozzle or the nozzle cap, but at the same time flows into a relaxation room expansion, which allows a greater relaxation of the secondary gas, before the secondary gas then over the conical shell or inner surfaces of the plasma jet is supplied radially or tangentially. In this case, this area of the nozzle cap with expansion chamber extension has a smaller diameter than the beginning of the subsequent conical section.

If a gas-cooled or indirectly water-cooled plasma torch is used, the nozzle cap is often omitted. Then the nozzle takes over the space-limiting task of the nozzle cap. The nozzle is geometrically formed in this case as the nozzle cap. Thus, the advantages of the invention are also guaranteed in this plasma torch variant.

Further features and advantages of the invention will become apparent from the claims and from the following description, are explained in the embodiments with reference to the schematic drawings in detail. Showing:

Figure 1 is a partial sectional view of the front portion of a

Plasma torch according to a particular embodiment of the invention; Figure 1.1 to 1.12 details of Figure 1 with variants of the design of the secondary gas duct.

2.1 shows an embodiment of a secondary gas guide part in plan view from above partially in section; and

Fig. 2.2 shows another embodiment of a secondary gas guide part in

Top view from above partly in section.

Figure 1 shows a plasma torch 1 according to a particular embodiment of the invention. The plasma torch 1 has a torch body 2 with an electrode 3 and a nozzle 4 defining a longitudinal axis L of the plasma torch 1. The electrode 3 and the nozzle

4 are arranged coaxially in the burner body 2, are in a certain spatial relationship and form a plasma chamber 6 through which a plasma gas PG flows, which is supplied via a plasma gas channel 6a. A nozzle cap 5 is arranged coaxially with the longitudinal axis L of the plasma burner 1 and holds the nozzle 4. Between the nozzle 4 and the nozzle cap

5 is a space 11, flows through the cooling water. The cooling water is supplied via a water feed WV and flows through a water return WR.

An annular secondary gas guide member 8 having a plurality of holes in the form of bores, only one of which is denoted by the reference numeral 8a, is in a formed between the nozzle cap 5 and a nozzle cap 7 secondary gas channel 9 between a secondary gas inlet 8b and the front end of the secondary gas channel 9 arranged that the flowing through the passage 8 a secondary gas SG on a nearly cylindrical first lateral surface of the nozzle cap 5, which results in a first cylindrical portion 5 a of the nozzle cap 5 hits. The secondary gas SG is then passed through the secondary gas channel 9, which is bounded by a nearly conical second surface of the nozzle cap 5 in a lower portion 5 b and a corresponding conical inner surface 7 b of the nozzle cap 7, to the front end of the plasma torch 1, then at an angle of nearly 90 ° to the longitudinal axis L of the plasma torch. 1 a plasma jet (not shown) and exits through a Austrittsöfmung 7 a of the nozzle cap 7 from. The rotating secondary gas SG flows around the plasma jet after it leaves a nozzle opening 4a and additionally creates a defined atmosphere around the plasma jet.

The passages 8 a of the Sekundärgasfϊihrungsteils 8 are arranged so that a rotating flow of the secondary gas SG is formed. For example, the passages in the Sekundärgasruhrungsteil 8a, equidistant over the circumference of the secondary gas guide member 8 and radially extending (Figure 2.1) or with an offset to the radial (Figure 2.2), i. be arranged on a respective offset from the actual center of the circle point, arranged.

The inclination of the almost cylindrical first lateral surface of the nozzle cap 5 can amount to ± 15 ° (FIGS. 1.1, 1.2 and 1.3) relative to the longitudinal axis L of the plasma burner 1. With an inclination of W3 = -15 ° (FIG. 1.3), the effect of homogeneity is achieved in a similar way to enlargement of space by cylindrical surfaces and a particularly good homogeneity is achieved.

The transitions between the first and second lateral surfaces of the nozzle cap 5 and corresponding first and second inner surfaces of the nozzle protection cap 7 can be sharp-edged (FIGS. 1.1-1.3), with bevels (FIGS. 1.4-1.6) or radii (FIGS. 1.7-1.9). There is also the possibility of combinations of radii and chamfers at the transitions.

Figures 1.10 -1.12 show embodiments with a relaxation space extension 10 into which the secondary gas SG flows out of the passages 8a of the secondary gas guide part 8 in order to further improve the stability of the plasma jet. This relaxation space extension 10 may have, for example, a round (FIG. 1.10), a rectangular (FIG. 1.11) or a multi-faceted (FIG. 1.12) shape. The features of the invention disclosed in the foregoing description, in the drawings and in the claims may be essential both individually and in any combination for the realization of the invention in its various embodiments.

Claims

claims 1. Plasma torch (1) with: a burner body (2), an electrode (3) arranged in the burner body (2), a nozzle (4) having a central nozzle opening (4a) and arranged so as to cover the electrode (3) separated by a plasma gas channel (6a) formed therebetween, - A nozzle cap (7) having a arranged at its front end, the Düsenöffhung (4a) opposite Austrittsöffhung (7a) and an annular secondary gas channel (9) within the nozzle cap (7), which communicates with the outlet opening (7a) , wherein the nozzle protection cap (7) with respect to the electrode (3) and the nozzle (4) is arranged electrically isolated, and a Sekundärgasfuhrungsteil (8) having at least one passage (8a), characterized in that - The Sekundärgasruhrungsteil (8) in the secondary gas passage (9) between a secondary gas inlet (8b) and the front end of the secondary gas channel (9) is arranged and the secondary gas channel (9) between the Sekundärgasruhrungsteil (8) and its front end is formed such that it the secondary gas SG after passing through the Sekundärgasfuhrungsteils (8) and a longitudinal axis L of the plasma torch (1) substantially parallel Sekundärgaskanalteils (9a) obliquely to the longitudinal axis L of the plasma torch (1) towards the front end of the Plasma torch (1) leads and then at a substantially right angle to the longitudinal axis L of the plasma torch (1) a plasma jet feeds. 2. Plasma torch according to claim 1, characterized in that a nozzle cap (5) is provided which covers the nozzle (3) except at least the Düsenöffhung (4a) and within the nozzle cap (7) and arranged by this on its front end side the secondary gas channel (9) is disconnected. 3. plasma torch according to claim 1 or 2, characterized in that the nozzle cap (5) in the region of the secondary gas guide part (8) has a substantially cylindrical first lateral surface and towards the front end of the plasma torch (1) in the direction of the front End of the plasma torch (1) in the substantially conically tapered second lateral surface of the nozzle (4) or the nozzle cap (5) connects. 4. plasma torch (1) according to claim 3, characterized in that the first lateral surface is inclined at an angle in the range of 0 ± 15 ° to the longitudinal axis L of the plasma torch (1). 5. plasma torch (1) according to claim 3 or 4, characterized in that the transition between the first and second lateral surfaces is rounded, beveled or sharp-edged. 6. Plasma torch (1) according to any one of the preceding claims, characterized in that the nozzle (4) or the nozzle cap (5) in the region of the Sekundärgasfuhrungsteils (8) has a substantially cylindrical outer surface with a recess on which the secondary gas after passing the Sekundärgasfuhrungsteils (8) meets. 7. plasma torch (1) according to claim 6, characterized in that the recess is round or polygonal. 8. plasma torch (1) according to any one of the preceding claims, characterized in that the Sekundärgasruhrungsteil (8) is a ring in which over its circumference at least two passages (8 a) are arranged equidistant. 9. plasma torch (1) according to any one of the preceding claims, characterized in that the / the passage / passages (8 a) extends radially / extend. 10. plasma torch (1) according to any one of claims 1 to 8, characterized in that the passage (8 a) has an offset to the radial. 11. plasma torch (1) according to claim 10, characterized in that the offset is in the range of 0.5 to 4 millimeters. 12. Plasma torch (1) according to any one of the preceding claims, characterized in that the passage (8 a) has a diameter in the range of 0.2 to 1.0 millimeters.