EP1797747B1 - Plasma torch - Google Patents

Description

The present invention relates to a plasma torch which serves both for dry cutting and underwater cutting of various metallic workpieces and to an arrangement of a nozzle cap and a secondary gas guide member for a plasma torch.

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 burner is made of basic 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 A1 In the case of underwater cutting, the plasma jet is protected 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 The present applicant uses nitrogen as a 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 after the Patent EP 0 573 653 B1 For example, 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 the Patent EP 0 801 882 B1 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 Pat. No. 6,207,923 B1 A secondary gas flows in a gap between a nozzle with an extended 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 in particular 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, for cutting 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. With the in US Pat. No. 6,207,923 B1 this arrangement is not possible. 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 US 5 695 662 A discloses a plasma torch having a torch body, an electrode disposed in the torch body, a nozzle having a central nozzle opening and arranged to separately cover the electrode by a plasma gas channel formed therebetween, a nozzle cap, one at its front End face disposed, the nozzle opening opposite the outlet opening and an annular secondary gas channel within the nozzle cap which communicates with the outlet opening, wherein the nozzle cap is electrically isolated with respect to the electrode and the nozzle, a nozzle cap which covers the nozzle except the nozzle opening and disposed within the nozzle cap and is separated from the latter at its front end side by the secondary gas passage, and a secondary gas guide member having at least one passage in the form of bores, wherein the secondary gas guide member in the second is arranged between a secondary gas inlet and the front end of the secondary gas channel and the secondary gas channel between the secondary gas guide part and its front end is formed such that it passes the secondary gas after passing the Sekundärgasführungsteils and a Sekundargaskanalteils obliquely to the longitudinal axis of the plasma torch toward the front end of the plasma torch leads and then at a substantially right angle to the longitudinal axis of the plasma torch a plasma jet supplies.

The US 2001/007320 A1 discloses a nozzle with a nozzle cap and a secondary gas guide part. The secondary gas guide part is formed as a ring.

From the US 5,317,126 A For example, a plasma torch with a nozzle cap and a secondary gas guide member is known.

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 by a plasma torch according to claim 1 and an arrangement according to claim 10.

The respective subclaims relate to respective 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-control technological cutting situations, such. Driving over the kerf and the corner as well as cutting start 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 constriction of the plasma jet, protection of the nozzle against high-metal splash during piercing, creation of 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.

According to the invention, the secondary gas is guided via a secondary gas guide part into the secondary gas channel in such a way that the secondary gas flow initially strikes a virtually cylindrical first lateral surface of the nozzle cap which is directed parallel to the longitudinal axis of the plasma torch. 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 firstly directing the secondary gas flow onto the lateral surface of the secondary gas flow in a plane extending essentially at right angles to the longitudinal axis of the plasma torch Nozzle cap hits and that is further reset from the front end of the plasma torch and thus the secondary gas has more time in addition to spread.

It is also advantageous to separate the secondary gas by a suitable design of the secondary gas guidance part, e.g. to rotate by offsetting 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 enhanced even if, after passing through the secondary gas guide part, the secondary gas initially not only strikes the almost cylindrical first lateral surface of the nozzle cap, but at the same time flows into a relaxation space extension, which allows a greater relaxation of the secondary gas, before the secondary gas then flows over the conical jacket. 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.

Figur 1

eine Teilschnittdarstellung des vorderen Bereiches eines Plasmabrenners gemäß einer besonderen Ausführungsform der Erfindung;

Figur 1.1 bis 1.12

Details von Fig.1 mit Varianten der Gestaltung des Sekundärgaskanals;

Fig. 2.1

eine Ausführungsform eines Sekundärgasführungsteils in Draufsicht von oben teilweise im Schnitt; und

Fig. 2.2

eine weitere Ausführungsform eines Sekundärgasführungsteils in Draufsicht von oben teilweise im Schnitt.

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:

FIG. 1

a partial sectional view of the front portion of a plasma torch according to a particular embodiment of the invention;

FIGS. 1.1 to 1.12

Details of Fig.1 with variants of the design of the secondary gas channel;

Fig. 2.1

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

Fig. 2.2

a further embodiment of a secondary gas guide part in plan view from above partially in section.

FIG. 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 flows a plasma gas PG, which is supplied via a plasma gas channel 6a. A nozzle cap 5 is arranged coaxially to the longitudinal axis L of the plasma torch 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 an outlet opening 7a 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 8a of the secondary gas guide part 8 are arranged so that a rotating flow of the secondary gas SG is formed. For example, the passages in the secondary gas guide part 8a may be equidistant over the circumference of the secondary gas guide part 8 and radially extending (FIG. Figure 2.1 ) or with an offset to the radial ( Figure 2.2 ), ie, aligned with a respective point offset from the actual center of the circle.

The inclination of the almost cylindrical first lateral surface of the nozzle cap 5 can be up to ± 15 ° ( Figures 1.1 . 1.2, and 1.3 ) relative to the longitudinal axis L of the plasma torch 1 amount. At an inclination of W3 = -15 ° ( Figure 1.3 ) the effect of homogeneity is achieved similar to enlargement of space by cylindrical surfaces and achieves a particularly good homogeneity.

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 (FIG. Figures 1.1 - 1.3 ), with bevels ( Figures 1.4 - 1.6 ) or radii ( Figures 1.7 - 1.9 ) be provided. 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, in which the secondary gas SG from the passages 8a of the secondary gas guide 8 flows to further improve the stability of the plasma jet. This relaxation space extension 10 may be, for example, a round ( Figure 1.10 ), a rectangular ( Figure 1.11 ) or a multi-faceted ( Figure 1.12 ) Have shape.

The features of the disclosure disclosed in the foregoing description, and in the drawings, may be material to the realization of the disclosure in its various embodiments both individually and in any combination thereof. The following claims define and limit the present invention.

Claims (13)

1. Plasma torch (1) having:

   - a torch body (2),

   - an electrode (3) arranged in the torch body (2),

   - a nozzle (4) which has a central nozzle opening (4a) and is arranged such that it covers the electrode (3) separately by a plasma gas channel (6a) formed therebetween,

   - a nozzle protection cap (7) which has an outlet opening (7a) that is arranged on its front end side and is opposite the nozzle opening (4a), and has an annular secondary gas channel (9) within the nozzle protection cap (7), which channel is connected to the outlet opening (7a), wherein the nozzle protection cap (7) is arranged electrically insulated from the electrode (3) and the nozzle (4),

   - a nozzle cap (5) which covers the nozzle (4) with the exception of at least the nozzle opening (4a), is arranged inside the nozzle protection cap (7) and is separated from the latter at its front end side by the secondary gas channel (9),

   - a secondary gas guiding part (8) that has at least one opening (8a) in the form of bores, wherein the secondary gas guiding part (8) is arranged in the secondary gas channel (9) between a secondary gas inlet (8b) and the front end of the secondary gas channel (9), and the secondary gas channel (9) is formed between the secondary gas guiding part (8) and its front end such that it guides the secondary gas SG, after passage through the secondary gas guiding part (8) and a secondary gas channel part (9a) that is essentially parallel to the longitudinal axis L of the plasma torch (1), at an angle to the longitudinal axis L of the plasma torch (1) in the direction of the front end of the plasma torch (1) and afterwards essentially at right angles to the longitudinal axis L of the plasma torch (1) to a plasma beam, and the nozzle cap (5), which covers the nozzle (4) with the exception of at least the nozzle opening (4a) and is arranged inside the nozzle protection cap (7) and is separated from the latter at its front end side by the secondary gas channel (9), has in the region of the secondary gas guiding part (8) a first jacket surface, which is inclined at an angle in the range from 0 ± 15° with respect to the longitudinal axis L of the plasma torch (1), and a second jacket surface of the nozzle cap (5), which tapers essentially conically in the direction of the front end of the plasma torch (1), adjoins in the direction of the front end of the plasma torch (1).
2. Plasma torch (1) according to Claim 1, characterized in that the transition between the first and second jacket surfaces is rounded, chamfered or sharp.
3. Plasma torch (1) according to one of the preceding claims, characterized in that the first jacket surface is an essentially cylindrical jacket surface with a depression which receives the secondary gas that has passed through the secondary gas guiding part (8).
4. Plasma torch (1) according to Claim 3, characterized in that the depression is round or polygonal.
5. Plasma torch (1) according to one of the preceding claims, characterized in that the secondary gas guiding part (8) is a ring in which there are arranged, equidistant over its circumference, at least two openings (8a).
6. Plasma torch (1) according to one of the preceding claims, characterized in that the openings (8a) extend radially.
7. Plasma torch (1) according to one of Claims 1 to 5, characterized in that the openings (8a) have an offset with respect to the radial.
8. Plasma torch (1) according to Claim 7, characterized in that the offset is in the range between 0.5 and 4 millimetres.
9. Plasma torch (1) according to one of the preceding claims, characterized in that the openings (8a) have a diameter in the range from 0.2 to 1.0 millimetres.
10. Arrangement of a nozzle cap (5) and a secondary gas guiding part (8) for a plasma torch (1), wherein the nozzle cap (5) has a jacket surface which has, in sequence proceeding from a front end of the nozzle cap (5):

    - a second section (5b) which tapers essentially conically in the direction of the front end of the nozzle cap (5),

    - an essentially cylindrical first section (5a) with an inclination in the range 0 ± 15° with respect to the longitudinal axis of the nozzle cap (5) and

    - a setback which is radial with respect to a longitudinal axis of the nozzle cap (5), wherein the secondary gas guiding part (8) is arranged on the setback, is of annular design and has a multiplicity of openings (8a) in the form of bores which extend radially with respect to the longitudinal axis of the nozzle cap (5) or have an offset with respect to the radial.
11. Arrangement according to Claim 10, characterized in that the transition between the first and second sections of the jacket surfaces is rounded, chamfered or sharp.
12. Arrangement according to Claim 10 or 11, characterized in that the first section of the jacket surface is an essentially cylindrical jacket surface with a depression which receives the secondary gas that has passed through the secondary gas guiding part (8).
13. Arrangement according to Claim 12, characterized in that the depression is round or polygonal.

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