EP0465941B1 - Plasma torch with transferred arc - Google Patents

Abstract

The present plasma torch has a central electrode (10), a nozzle end piece (11) concentric thereto and a concentric torch jacket (73). There is an annular gap (27) for the passage of plasma gas between the electrode (10) and the nozzle end piece (11), and there is an annular channel (75, 76) between the nozzle end piece (11) and the torch jacket (73), the inner wall of which annular channel (75, 76) is partially formed by means of an insulating tube (36, 39) which electrically isolates the two parts (11, 73). <??>In order that this plasma torch can also be operated in particular using alternating current, largely without the risk of forming parasitic arcs, the annular channel (75, 76) is drawn back between the nozzle end piece (11) and the torch jacket (73) at least to the level of the coolant inlet and outlet (61, 62) of the torch jacket (73). At its rearward end, the annular channel (75) is in line connection (55) with a source (56) of a pressurised, gaseous medium. Such a torch is safe in operation even in an atmosphere having electrically conductive particles, such as metallic or foundry dusts and achieves long lives.

Description

The invention relates to a plasma torch for transmitted arc with a central electrode, a concentric nozzle end piece, wherein an annular gap for the passage of plasma gas is present between the electrode and the nozzle end piece, and a concentric burner jacket with outer, middle and inner wall, between the nozzle end piece and an annular channel is present in the burner jacket, the inner wall of which is partially formed by an insulating tube that electrically separates both parts.

A major problem when operating plasma torches, in particular with alternating and three-phase current, is the occurrence of parasitic arcs which burn parallel to the main arc, in particular with the lower edge of the lower nozzle or burner jacket and the outer region of the nozzle or burner end face include in the current flow. Parasitic arches not only significantly impair the stability of the arc column and thus the efficiency and economy of a plasma torch or a system operated with plasma torches, they generally even lead to the complete destruction of plasma torches.

According to DE-PS 33 28 777 it is known to provide the ring channel between the electrode and the nozzle on the inside of the nozzle with an electrically insulating lining to prevent parasitic arcs. However, this measure only provides partial protection because it is parasitic Arcs can find a current path outside the insulating liner.

However, an arrangement aimed at focusing and separating different arcs is used in a combination welding torch according to EP-A-168810. It does not come into consideration for the present problem because of the completely different structural and operational conditions explained there, especially since, for example, an inert gas nozzle is surrounded by a protective gas nozzle which is designed as a full-walled, that is to say not cooled, sleeve and in which the argon-helium supplied -Mixing the task of preventing parasitic arcs at all, which prevents the entry of atmospheric oxygen to the welding point.

Another measure to combat parasitic arches is known from DE-PS 34 35 680. According to this, it is provided that the section of the inner wall part of a water-cooled nozzle which is adjacent to the end wall part is electrically insulated from the section of the end wall part which adjoins the outer wall part by two separate insulating parts penetrating the respective wall part, one of the insulating parts in the end wall part of the Nozzle is arranged. In very hot furnace atmospheres, however, it is very difficult to find a suitable insulating material for the end wall of the nozzle.

In a further development of the last-mentioned concept, it has been provided that the insulation provided in the end face of the nozzle be laid in an end groove. Such a plasma torch has also been carried out. The end groove is formed on the one hand by the outer wall of a nozzle nozzle or end piece and on the other hand by a burner jacket, the burner jacket having on its front side a flange pointing towards the axis of the burner, which offers the insulation piece lying behind a certain heat protection. However, if this burner is in an atmosphere with electrically conductive particles, e.g. B. operated metal or steel dusts, the electrically conductive dusts can precipitate on the cooled insulating piece, so that an electrical bridge from the nozzle neck to the burner jacket form and parasitic arcs can now flow over the outer end edge of the burner jacket.

The invention is based, which Risk of the formation of parasitic arcs, in particular when operating with alternating current, is further restricted, ie with greater success.

This object is achieved in that the annular channel between the nozzle end piece and the burner jacket is withdrawn at least up to the level of the coolant inlet and outlet of the burner jacket and has a line connection at its rear end with a source of a pressurized gaseous medium. Due to its length, the coaxial ring channel already represents a factor that increases operational safety and service life, due to the lack of mechanical connections on which electrically conductive vapors or dusts could be deposited, which could lead to bridges between the nozzle connection piece and the nozzle casing. The line connection to a source of a pressurized gaseous medium is equivalent to blowing a gaseous pressure medium into the ring channel. Blowing the ring channel with gas represents a further step in the direction of increasing operational safety and increasing the service life. The mouth or outlet area of the ring channel is additionally cooled by the gas. Any electrically conductive vapors or dusts that occur are prevented from entering the ring channel. In addition, blowback plasma arc curls are prevented and melt and slag splashes that want to penetrate into the ring channel are rejected and cooled. In addition, oxidation-promoting gases are shielded, which are sucked in from the environment via the plasma arc and have a strong wear-promoting effect on refractory metals that are located outside the plasma gas area. If oxidation-prone burner components do not exist outside the plasma gas range and the process leaves the If oxidizing gases are used in the ring channel, this also converts metallic vapors that reach the effective area of the ring gas jacket to poorly conductive metal oxides. The cooling effect of the additional gas flowing through the ring channel results in a longer service life for coatings or coatings present in the mouth area of the ring channel. Furthermore, the radiation of the plasma arc is reduced by the gas ring jacket flowing out of the ring channel, which is also referred to as enveloping gas, and thus above all the vessel delivery is spared. The length of the ring channel, which extends up to the height of the coolant inlet and outlet of the burner jacket, results in a large homogenization of the gas flow at the outlet from the ring gap up to its mouth.

Since the supply of additional gas into the ring channel can take place independently of the supply of the main plasma gas, the plasma torch is advantageously also suitable for transporting or carrying solid substances in powder or grain form with the additional gas. In contrast to a local supply of solid matter by separate, additionally required lances, the entire plasma arc circumference and a certain distance in the direction of the plasma arc axis can be used for melting or vaporization of the solid matter in the plasma torch according to the invention.

Advantageous developments of the invention are described in the subclaims. Thus, the homogenization of the gas flow through the ring channel can be further improved in that the line connection has a tangential component at the rear end of the ring channel. Instead of a single line connection, several line connections can of course also be used each tangential component can be provided. The at least partially tangential direction of insertion into the ring channel and the leveling that can be achieved with it is particularly important in the case of the conveyance of solids.

Since the electrode and the nozzle end piece require only a low coolant throughput, it is advantageous to assign a separate cooling circuit to the burner jacket, so that the coolant throughput required can be adapted to the respective degree of stress.

Fastening the burner jacket exclusively via its outer wall and the possibility of the middle and inner wall to slide on the housing part serving for fastening makes it possible for the outer tube of the burner jacket exposed to the process temperature and the nozzle jacket attached to it to be exposed without any significant additional stresses to the rest Shell components can stretch.

The nozzle jacket is connected to the jacket tube of the burner jacket via a simple threaded connection, possibly via a connecting part. It is therefore easy to remove and thus enables the electrode and the nozzle or the nozzle end piece to be quickly replaced for other applications, which can also be easily assembled or exchanged by means of threaded connections.

In particular, to the extent that powdery or granular solids are to be transported through the annular gas between the nozzle and the burner jacket through the pressurized gas and fed to the arc, the annular channel is advantageously conically converging in the arc direction in its mouth region.

In order on the one hand to achieve a stable construction of the burner and on the other hand to avoid paragraphs, the insulating tube electrically separating the nozzle end piece and the burner jacket is adjacent to the outside of the nozzle end piece. It is also used to form the conical inner surface in the mouth region of the ring channel.

The surfaces of the conical mouth region of the ring channel can preferably have a coating of insulation material, in particular ceramic, which makes it possible to also convey electrically conductive solids through the ring channel and to feed them to the arc. For this purpose, the insulating tube surrounding the electrode lance is further set back into the ring channel up to the line connection.

In order to give the insulating tube surrounding the electrode lance additional heat protection, the clear diameter of the outer edge of the ring channel at the mouth is preferably smaller than the outer diameter of the inner wall of the ring channel before the conical course begins.

The nozzle end piece is advantageously mechanically connected to the electrode via an annular body made of insulation material and combined with it to form a structural unit. This annular body has passages running parallel to the main axis of the plasma torch, through which the main plasma gas can reach the annular gap between the electrode and the nozzle end piece.

In addition to the mechanical integration of the nozzle end piece with the electrode or the electrode lance, a common coolant circuit is provided for the latter.
In order to influence the gas flow, displacement bodies can be arranged in the ring channel.

Particularly in the case of plasma torches with a very long shaft and strongly inclined installation positions, spacers or supporting bodies are advantageously inserted into the ring channel. These support bodies are shaped as aerodynamically as possible, viewed in the longitudinal axis of the burner, arranged offset from one another and advantageously fastened to the insulating tube assigned to the electrode and the nozzle end piece.
The support body can be designed as a hollow and solid body and run axially parallel or helical and thus contribute to the promotion and management of additives in the
Afford ring channel. Hollow bodies parallel to the axis can preferably be extended as a nozzle-shaped ceramic tube beyond the end face of the nozzle end piece in order, for example, to supply powder locally and in a directed manner to the plasma arc.

Fig. 1

einen Plasmabrenner im Längsschnitt,

Fig. 2

den unteren Teil der aus Elektrode und Düsenendstück gebildeten Elektrodenlanze in einem auszugsweisen Längsschnitt in vergrößerter Darstellung,

Fig. 3

die Befestigung des Brennermantels in einem auszugsweisen Längsschnitt in vergrößerter Darstellung,

Fig. 4

das Verbindungsstück zwischen dem an eine Spannungsquelle angeschlossenen Rohr und der Elektrode im Längsschnitt und

Fig. 5

einen auszugsweisen Querschnitt durch die Elektrodenlanze längs der Linie V-V in Fig. 1.

An embodiment of the invention is shown in the drawing and is explained in more detail below. Show it

Fig. 1

a plasma torch in longitudinal section,

Fig. 2

the lower part of the electrode lance formed from the electrode and nozzle end piece in a partial longitudinal section in an enlarged view,

Fig. 3

the fastening of the burner jacket in a partial longitudinal section in an enlarged view,

Fig. 4

the connector between the tube connected to a voltage source and the electrode in longitudinal section and

Fig. 5

an excerpt cross section through the Electrode lance along the line VV in FIG. 1.

The plasma torch essentially consists of an electrode lance and a torch jacket. The electrode lance again consists essentially of an electrode 10 and a nozzle nozzle or nozzle end piece 11 and the parts holding them. The electrode 10 has a weakly conical end surface and the nozzle nozzle 11 has a weakly conical inner surface and a more conical outer surface.

The electrode 10 is fastened with its outer wall via a substantially sleeve-shaped connecting piece 12 to the current tube 13, a tube connected to the main voltage source, a threaded connection or pairing in each case between the electrode 10 and the connecting element 12 and between this and the current tube 13 consists.

The inner wall of the electrode 10 is slidably guided on an inner tube 14 fastened in the rear end of the plasma torch. Between the flow pipe 13 and the inner pipe 14 there is a plastic center pipe 15 for separating the partial circuits of the coolant for the electrode. In its lower area, the center tube 15 also serves to deflect the coolant flow.

The inner wall of the nozzle end piece 11 is connected via a threaded connection to an annular body 16 made of insulation material, preferably ceramic, and this in turn is connected to the connecting piece 12 via a threaded connection.

The connecting piece 12 (cf. FIGS. 4 and 5) has upper and lower radial passages 17, 18 and parallel to it, distributed uniformly on its circumference Passages 19 extending through the burner axis.

Above the upper radial passages 17, the inner flange of a sleeve 21 made of plastic and between the upper and lower radial passages 17, 18, the inner flange of a central tube 23 is screwed to the connecting piece 12 via a pair of threads.

The ring body 16 screwed to a lower sleeve-shaped projection 25 of the connecting piece 12, to which the nozzle end piece 11 is screwed in turn, has passages 26 which run parallel to the axis of the burner and are in line connection with the passages 19 of the connecting piece 12. The passages 26 point downward into the annular gap 27 between the electrode 10 and the nozzle end piece 11.

Arranged around the flow tube 13 is a plastic tube 28 which has passages 29 running parallel to the axis of the burner, which pass into an annular cavity 31 in the lower region of the tube 28, which creates a connection to the passages 19 of the connecting piece 16. At its upper end, the tube 28 is provided with a flange 32 which has radial passages 33 which are connected to the axially parallel passages 29. To increase the stability, the plastic tube 28 is surrounded by a steel tube 34 with a flange 35. The outside diameter of the steel tube 34 corresponds to the outside diameter of the nozzle end piece 11. An insulation tube 36 is arranged on the outside of the steel tube 34 and has a flange 37 at its upper end. A transition surface 38 is provided between the cylindrical outer surface of the insulation tube 36 and the underside of the flange 37. Another lower ceramic tube 39 lies with its inner surface on the outer surfaces of the steel tube 34 and the nozzle end piece 11 and is detachably connected to the upper insulation tube 36 via a screw or thread connection. At its lower end, the outer surface of the lower ceramic tube 39 is continuously transferred into the conical outer surface of the nozzle end piece 11.

An auxiliary electrode 42 is guided through the inner tube 14 of the electrode lance and is centered in a known manner by spacers. At its upper end, the auxiliary electrode 42 has a current connection 44 for the ignition current. In its upper region, the auxiliary electrode 42 is electrically separated from the inner tube 14 and the other parts of the electrode lance by a plastic disk 45. The plastic disk 45 has one or more radial passages 46 for supplying ignition gas, which can continue to flow through the annular channel formed by the ignition electrode 42 and the inner tube 14.

The electrode 10 and the nozzle end piece 11 are cooled by a common, combined coolant circuit. From the coolant inlet 48, the coolant passes through the annular channel 49 formed by the inner tube 14 and the middle tube 15, is deflected at the bottom of the middle tube 15, flows through the radial passages 18, is deflected by the deflection part 24 and flows through the passages 17 and through the flow tube 13 and the center tube 15 formed ring channel 50 to the coolant outlet 51st

All the parts described so far together form the electrode lance.

Electrically separated from an insulating ring 53 made of plastic, a housing part 54 is centered on the outside of the flange 37 and mechanically firmly connected to the flange 32 of the plastic tube 28.

The housing part 54 has a connection for a tangential feed line 55, which is connected to a compressed gas source 56 for envelope gas. On its inside, the housing part 54 has a downward cylindrical flange 57 (cf. FIG. 3). A so-called pipe connector 58 is fastened under the housing part 54 and has a coolant inlet and outlet 61, 62. An outer jacket tube 63 is in turn attached to the pipe connector 58 via its flange 64. At the lower end of the casing tube 63, a connector 65 is releasably attached. An upper central tube 66, an inner tube 72 and a lower central and separating tube 67 are detachably fastened to an internal thread of the intermediate piece 65 and a nozzle jacket 68 together with the inner wall 69 are detachably fastened to an external thread of the intermediate piece 65. The intermediate piece 65 has passages 71 for the cooling medium of the burner jacket which are aligned parallel to the axis of the burner. The upper middle wall 66 is guided with the upper part of its outer surface in a pressure-tight sliding manner on an inner surface of the pipe connector 58. The inner wall of the nozzle jacket 68 is slidably guided on the inner tube 72. The upper end of the inner tube 72 of the burner jacket 73 is guided in a pressure-tight manner on the cylindrical flange 57 of the housing 54.

All parts described in connection with the electrode lance from the housing 54 to the nozzle jacket 68 together form the burner jacket 73 as a structural unit.

The entire outer surface of the burner jacket 73 is made free of gaps and steps and thus creates good conditions for sealing in the vessel leadthrough, good uniformity of the cooling and also for preventing parasitic arcing.

Between the insulation tube 36, which forms the outer wall of the electrode lance, and the burner jacket 73, an annular channel 75 is formed, which runs for most of its length parallel to the main axis of the burner and has a conical shape 76 in the area in front of the end face of the nozzle end piece 11 . The conical course 76 of the ring channel 75 in the mouth area is formed by the outer surface of the nozzle end piece 11 and a conical inner surface of the nozzle jacket 68. Both conical surfaces have a coating 77 or 78 made of ceramic.

The inside diameter of the nozzle jacket 68 on its end face is smaller than the outer diameter of the nozzle end piece 11, so that the end face of the cooled nozzle jacket 68 for the ceramic tube 39 provides heat protection against the hot atmosphere surrounding the plasma torch or the burner arc.

In particular in the case of large plasma torch lengths and / or inclined installation positions, spacer or support bodies 80 are attached to the insulation tube 36 comprising the electrode lance, which extend as far as the inner tube 72 of the torch jacket.

In addition, displacement body 81 (FIG. 3) can also be attached to the insulation tube 36.

Claims (19)

1. Plasma torch for transferred arc with a centric electrode (10), a concentric nozzle end piece (11), wherein an annular gap (27) is present between the electrode (10) and the nozzle end piece (11) to allow the passage of plasma gas, and with a concentric torch casing (73) with outside, middle and inside wall, wherein an annular duct (75) is present between the nozzle end piece (11) and torch casing (73), the inside wall of said annular duct being partially formed by an insulating tube (36) electrically insulating both parts, and which annular duct extends back between the nozzle end piece (11) and the torch casing (73) at least as far as the level of the coolant inlet and outlet (61, 62) of the torch casing (73), and at its rear end has a pipe connection (55) to a source (56) of a gaseous medium under pressure.
2. Plasma torch according to Claim 1, characterised in that the pipe connection (55) at the rear end of the annular duct (75) has a tangential component.
3. Plasma torch according to Claim 1 or 2, characterised in that the torch casing (73) has its own cooling circuit with outside, middle and inside wall (63, 66, 72).
4. Plasma torch according to Claim 3, characterised in that the outside wall (63) of the torch casing (73) is fastened to a housing portion (58); that the middle wall (66) and the inside wall (72) of the torch casing (73) are connected to the outside wall (63) at a point remote from the coolant inlet point (61), and are guided pressuretight at its rear end to slide in axial direction on the housing portion (58).
5. Plasma torch according to Claim 4, characterised in that the middle wall (66) is connected to the outside wall (63) via a connection part (65) provided with passages and the connection part (65) bears a nozzle casing (68) on its front end.
6. Plasma torch according to Claim 5, characterised in that the nozzle casing (68) is connected to the connection part (65) via a simple threaded connection.
7. Plasma torch according to one of Claims 1 to 6, characterised in that the annular duct (75) has a conical inside face and a conical outside face in its mouth region between the nozzle end piece (11) and the torch casing (73), both faces converging in the direction of the arc.
8. Plasma torch according to Claim 7, characterised in that the insulating tube (36, 39) electrically insulating the nozzle end piece (11) and the torch casing (73) is arranged to abut the nozzle end piece (11) on the outside and also forms the conical inside face of the annular duct (75) in the mouth region.
9. Plasma torch according to Claim 7 or 8, characterised in that the two conical faces of the mouth region are covered by a layer (77, 78) of insulation material, and that the insulating tube (36, 39) extends at its rear end as far as the pipe connection (55).
10. Plasma torch according to one of Claims 7 to 9, characterised in that the inner width of the outside edge of the annular duct (75) on the mouth is preferably smaller than the outside diameter of the inside wall of the annular duct (75) prior to the start of the conical path.
11. Plasma torch according to one of the preceding claims, characterised in that the nozzle end piece (11) is connected mechanically via an annular member (16) made of insulation material to the electrode (10) and combined to form a structural unit, said annular member (16) having passages (26) running parallel to the torch axis from a rear annular duct (29) for the main plasma gas to pass to the annular gap between the electrode (10) and the nozzle end piece (11).
12. Plasma torch according to Claim 11, characterised in that the electrode (10) and the nozzle end piece (11) have a joint coolant circuit.
13. Plasma torch according to one of the preceding claims, characterised in that in the annular duct (75) between the nozzle end piece (11) and the torch casing (73), members taking up a portion of its cross-section area are provided.
14. Plasma torch according to Claim 13, characterised in that the members are displacement members (81).
15. Plasma torch according to Claim 13, characterised in that the members are spacer members (80).
16. Plasma torch according to Claim 15, characterised in that the spacer members (80) are constructed as hollow members.
17. Plasma torch according to Claim 16, characterised in that the hollow members have measurement recorders.
18. Plasma torch according to Claim 16, characterised in that the hollow members extend over the entire length of the annular duct.
19. Plasma torch according to Claim 18, characterised in that the hollow members have an extension to beyond the face of the nozzle end piece.

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