EP0851720A1 - Non-transferred arc plasmatron - Google Patents

Abstract

The generator has an elongated plasma channel (8) formed by a set of neutrodes (1). The electrodes (8,10) required for generating the arc are coaxially with the plasma channel's longitudinal axis (L). The neutrode arrangement contains a number of mutually electrically isolated, plate-shaped neutrodes. The neutrode arrangement has a slot-shaped plasma beam outlet opening (40) which runs parallel to the longitudinal axis of the plasma channel. Each electrode is enclosed by a hollow chamber via which an inert gas is fed. The magnetic field of at least one permanent magnet arrangement (36,37) exerts a force on the arc opposite to the flow of the plasma gas.

Description

The invention relates to an indirect plasmatron for treatment of surfaces according to claim 1.

As indirect plasmatrons, plasma generators are made with one a nozzle flowing, electrically non-current-carrying plasma jet referred to, the arc, as opposed to direct Plasmatrons, is not transferred to the workpiece.

Plasmatrons are used to generate very high temperature plasmas, which are in the range of up to several 10,000 Kelvin can.

Conventional, indirect plasma patrons usually have a nozzle from which a substantially conical plasma jet exit. The one with such a plasmatron on one The surface exposed to the substrate consequently has a circular shape Outline on. However, in many cases this is undesirable, especially when large, rectangular areas with the Plasmatron should be heated or coated.

Another disadvantage that is inherent in the well-known plasmatrons, consists in the fact that the area exposed is relatively small, because the opening of the outlet nozzle has a limited diameter has and a predetermined distance between the nozzle and Substrate must be observed.

From U.S. Patent No. 5,239,161 is a method as well a device for coating substrate surfaces Plasma spraying is known, by means of which the previous mentioned disadvantages can be largely remedied. For this purpose, the device has an elongated plasma chamber, which is limited by a one-piece body. on the one The front of the plasma chamber is the anode and on the other arranged the cathode. The device outlet nozzle or the plasma chamber is slit-shaped and runs parallel to the longitudinal axis of the plasma chamber. Through this Characteristics should be achieved that the emerging plasma jet has a substantially rectangular contour and relative is wide.

Although the basic idea of such a burner is interesting in and of itself has been shown in practice that the device does not allow reliable operation and that in particular serious problems in stabilizing the Arc and the life of the plasma torch occur.

It is therefore the object of the invention to provide an indirect plasmatron to improve in such a way that a stable arc is maintained and that the life of the electrodes, especially the anode, is increased, the plasmatron should be very flexible.

This task is solved by an indirect plasmatron, which the features listed in combination in claim 1 having.

Due to the cascaded structure of the indirect plasmon, its Neutrode arrangement from a plurality of plate-shaped Neutrodes, which are isolated from each other, ensures that the arc made its way through the plasma channel chooses and does not flow successively from neutrode to neutrode. A cascaded structure of the neutrode arrangement enables this addition, the width of the neutrode stack and thus the Width of the outlet opening according to the requirements vary.

By the further feature that each electrode from a chamber is surrounded, via which an inert gas can be supplied, the thermal stress on the electrodes can be reduced by the latter is flushed with an inert gas, for example argon will. On the one hand, this causes an improved cooling of the Electrodes and on the other allows influencing the Arc approach to the electrodes by the area of the arc approach can be changed by the choice of gas. Around to get a diffuse, large base point argon has proven itself very well.

Finally, by using one or more pairs of permanent magnets the shape and position of the arc to be influenced. This is for a plasmatron in which the Plasma jet outlet opening parallel to the longitudinal axis of the plasma channel runs, very important because the arc through the gas flow running transversely to the burner axis into a curved Form is forced. Without the effect of a magnetic field the arc is deflected and curved to the extent that it is subject to strong fluctuations and even tears off. Through the Magnetic arrangements can prevent this by using the magnetic fields exert a force on the arc, which the by the flow of the plasma gas exerted on the arc Counteracts force. By the number, placement and field strength of the magnets used can depend on operating parameters such as for example, gas volume and gas velocity are taken into account and the arc in a predetermined position being held.

By the proposed in a preferred embodiment Form of training of the indirect plasmatron, in which the in individual neutrodes arranged openings to a first gas source can be connected, and those surrounding the electrodes Cavities can be connected to a second gas source Separation between the gas flowing around the electrodes and the actual plasma gas can be reached. For example, this has the advantage of being a reactive gas over those in the neutrodes arranged openings can be fed without this has a negative impact on the life of the electrodes because the electrodes are flushed with an inert gas can be shielded.

Fig. 1

einen Längsschnitt durch das indirekte Plasmatron;

Fig. 1a

eine Frontansicht des indirekten Plasmatrons;

Fig. 2

einen ersten Querschnitt durch das indirekte Plasmatron entlang der Linie A-A in Fig. 1;

Fig. 3

einen zweiten Querschnitt durch das indirekte Plasmatron entlang der Linie B-B in Fig. 1;

Fig. 3a

eine Frontansicht einer Neutrode, und

Fig. 4

einen dritten Querschnitt durch das indirekte Plasmatron entlang der Linie C-C in Fig. 1.

An exemplary embodiment of the invention is to be explained in more detail below with reference to drawings. In these drawings:

Fig. 1

a longitudinal section through the indirect plasmatron;

Fig. 1a

a front view of the indirect plasmatron;

Fig. 2

a first cross section through the indirect plasmatron along the line AA in Fig. 1;

Fig. 3

a second cross section through the indirect plasmatron along the line BB in Fig. 1;

Fig. 3a

a front view of a neutrode, and

Fig. 4

3 shows a third cross section through the indirect plasmatron along the line CC in FIG. 1.

1 shows a schematically represented, indirect plasmatron, based on which the essential in connection with the invention Features to be explained in more detail. The plasmatron consists essentially of a central neutrode arrangement 1, on each side of which there is an electrode body 2, 3, an insulation body 4, 5 and a connecting element 6, 7 connect. The connection elements 6, 7 are used for receiving of electrodes 9, 10, in the present example the left one Electrode 9 the cathode and the right electrode 10 the anode represents.

The neutrode arrangement 1 has a plurality of plate-shaped trained neutrodes la to li, which have a plasma channel 8 limit. The two electrodes 9, 10 are coaxial with Longitudinal axis L of the plasma channel 8 is arranged. To the electrical To increase the longitudinal resistance of the neutrode arrangement 1 are individual neutrodes la to li electrically isolated from each other. Isolation between the neutrodes la to li inserted insulating washers, which favor a clear Representation are not shown.

The neutrode arrangement 1 is on both sides of the electrode body 2, 3 delimited, on the outside of which the insulation body 4, 5 and the connecting element 6, 7.

Both electrode bodies 2, 3 are made of an insulating material.

Both the neutrodes la to li are used to cool the plasmatron as well as the two electrode bodies 2, 3 with cooling water channels 16, 21, 31 provided. The two electrodes 9, 10 are also over cooling water channels 38, 39 attached to one inside externally provided cooling water circuit connected.

Of the nine neutrodes la to li, their five lc to lg are included a plasma gas channel 18 opening centrally into the plasma channel 8 Mistake.

The two electrode bodies 2, 3 each have a central one bore 11, 12 narrowing towards plasma channel 8, into which the respective electrode 9, 10 protrudes in such a way that between the electrode 9, 10 and the bore wall a cavity in Form of an annular channel 19, 20 is formed. These two ring channels 19, 20 are arranged in the insulation bodies 4, 5 Bores 23, 24 each connected to a connection channel 14, 15, through which a gas G can be supplied.

Fig. La shows a front view of the indirect plasmatron. Out this representation it can be seen that the plasma jet outlet opening 40 across the width of five neutrodes lc to 1g extends.

Figure 2 shows a cross section through the plasmatron or Neutrode la along the line A-A in Fig. 1. Using this illustration it can be seen that the neutrode la with a central Cross bore 26 is provided, which is a part of the plasma channel forms and serves to guide the arc. Next are the last neutrodes la, li of the neutrode stack also the two neutrodes 1b adjoining the inside, lh each with a hole that part of the plasma channel 8 (Fig. 1) form and stabilization of the arc to serve. All neutrodes are for cooling with cooling channels 16 provided, which is connected to a cooling water circuit will. The individual neutrodes, with the interposition of insulating plates, connected to each other and be combined to form the neutrode arrangement. On the Representation of the necessary connecting elements as well as if necessary existing sealing elements were deliberately omitted.

The neutrode 1c shown in FIG. 3 is instead of one central transverse bore with a slot-shaped recess 33 provided, which also part of the plasma channel 8th (Fig. 1) forms. The recess 33 leading to the outside forms at the same time part of the plasma jet outlet opening, which in the present example extend over the width of five with such recesses 33 neutrodes lc to lg (Fig. La) extends. The inside of the recess 33 will by a, seen in cross section, semicircular Wall 34 limited. In the center of this semicircular training Wall 34 opens the plasma gas channel 18 into the recess 33.

FIG. 3a shows a front view of the section shown in FIG. 3 Neutrode 1c. From this illustration, both the Recess 33 as well as the mouth of the plasma gas channel 18 can be seen.

The neutrode 1d shown in FIG. 4 largely corresponds that of Figure 3, with two additional permanent magnets 36, 37 are provided, of which one magnet below and the other are arranged above the recess 33. The North-south axes A of the respective magnets 36 and 37 coincide and run at least approximately under a right one Angle to the longitudinal axis L of the plasma channel 8, the magnets 36, 37, seen in the flow direction of the plasma jet, after the longitudinal axis L of the plasma channel 8 are arranged. By this placement will cause the magnetic fields to hit the Arc opposite to the flow of the plasma gas Apply force, causing the arc to be in a predetermined Situation is stabilized. It is understood that each is unequal Poles of the individual magnets 36, 37 lie opposite one another; thus N-S or S-N.

The number of those neutrodes that have a permanent magnet pair can be provided by different operating parameters, such as. Arc current, amount of plasma gas, plasma gas velocity, as well as the geometrical dimensions of the neutrode arrangement etc. are made dependent. As another variation option can use magnets with different field strengths be used. In practice, it has proven useful, about two or three neutrodes with magnets, this number should not be restrictive in any way. Important is also that the neutrodes, in the proposed arrangement the magnet, made of a non-magnetizable material, preferably made of copper or a copper alloy are. The advantage of permanent over electromagnets is u. a. in that no external energy supply is necessary is that the structure can be made more compact and simpler can and that a more targeted influencing of the arc is possible.

Below are some explanations of how a with the plasmatrons provided with the features according to the invention will. Since the basic functioning of generic Plasmatrons is known, however, is only available on the Connection with the invention essential features and operating parameters received:

About the trained in the two connection elements 6, 7 Connection channels 14, 15 become coaxial to the longitudinal axis of the plasma channel 8 an inert gas is supplied, which via the ring channel 19, 20 of the respective electrode body 2, 3 from two sides in flows the plasma channel 8. This gas flows around the two electrodes 9, 10, which has a positive effect on their cooling. In addition this gas shields the electrodes 9, 10 from the actual one Plasma beam, which is particularly important then can if a reactive via the central plasma gas channels 18 Gas is supplied.

By the choice of the gas flowing around the electrodes 9, 10 the base point of the arc which is applied to the electrodes 9, 10, especially that at the anode 10, varies, namely are enlarged, which decreased in a selective manner thermal stress on the electrodes 9, 10 precipitates.

By providing separate gas supply channels 14, 15, 18, new opportunities also open up. For example, as already mentioned above, over the two laterally in the An inert gas is supplied to the channels 14, 15 leading to the plasma channel be while the central plasma gas channels 18 of the A reactive gas can be supplied to neutrodes 1c to 1g, without this having a negative impact on the service life of the Electrodes 9, 10 would have. By supplying a reactive gas an additional performance gain can also be realized.

Another benefit can be gained by using flammable gases, such as butane, can be achieved are supplied through the central plasma gas channels 18. In order to stands in addition to the previously mentioned performance gain chemical energy of the exothermic reaction process is available.

The provision of a plurality of central plasma gas channels 18 provided neutrodes lc to 1g allows the shape of the emerging plasma jet by changing the amount of gas and the gas velocity from plasma gas channel to plasma gas channel 18 is varied.

Due to the specific arrangement of the permanent magnets 36, 37 the arc can be stabilized within the plasma channel 8 will. Among other things, this in a constant operating voltage and therefore a constant burner output, a very quiet operation and increased electrode life noticeable.

Due to the cascaded structure of the neutrode arrangement, the geometric dimension of the plasmatron in the simplest way can be changed by, for example, the number and / or the Training of neutrodes is changed. For example instead of five with a slot-shaped recess Neutrodes whose seven are used, increasing the width of the emerging plasma jet would be changed accordingly. It is also conceivable, for example, that neutrodes are used, whose slot-shaped recess is designed differently, or that neutrodes are used, their for arc stabilization provided holes designed differently are.

Claims (11)

Indirect plasmatron for the treatment of surfaces, characterized by the combination of the following features: an elongated plasma channel (8) is provided, which is formed by a neutrode arrangement (1); the electrodes (9, 10) required to generate the arc are arranged coaxially to the longitudinal axis (L) of the plasma channel (8); the neutrode arrangement (1) comprises a plurality of plate-shaped neutrodes (1a to 1i) which are electrically insulated from one another; the neutrode arrangement (1) is provided with a slot-shaped plasma jet outlet opening (40), the latter running parallel to the longitudinal axis (L) of the plasma channel (8); each electrode (9, 10) is surrounded by a cavity (19, 20) through which an inert gas can be supplied, at least one permanent magnet arrangement (36, 37) is provided, the magnetic field of which exerts a force on the arc counter to the flow of the plasma gas. Indirect plasmatron according to claim 1, characterized in that at least individual neutrodes (1c-1g) with one channel (18) for supplying a gas into the plasma channel (8) are. Indirect plasmatron according to claim 2, characterized in that the longitudinal axis of the channel (18) for supplying a gas at an at least approximately right angle to the longitudinal axis (L) of the plasma channel (8) runs. Indirect plasmatron according to one of the preceding claims, characterized in that the neutrodes (1a-1i) from one non-magnetizable material, preferably made of copper or a copper alloy, and that at least one Neutrode (ld) provided with a permanent magnet pair (36, 37) is. Indirect plasmatron according to claim 4, characterized in that the north-south axes of the respective magnets (36; 37) collapse and at least approximately at a right angle run to the longitudinal axis (L) of the plasma channel (8), wherein the magnets (36, 37) in the direction of flow of the plasma jet seen, arranged along the longitudinal axis (L) of the plasma channel (8) are. Indirect plasmatron according to one of claims 2 to 5, characterized characterized in that at least three neutrodes (1a-1i) are provided and that at least one neutrode (1c-1g) with a channel (18) for supplying a gas into the plasma channel (8) are provided. Indirect plasmatron according to one of claims 2 to 6, characterized characterized in that in individual neutrodes (1c-1g) arranged channels (18) can be connected to a first gas source while the cavities (19, 20) can be connected to a second gas source. Indirect plasmatron according to one of the preceding claims, characterized in that a majority of the neutrodes (1c-1g), to form the plasma channel (8) and the plasma jet outlet opening (40), each with a slot-shaped recess (33) are provided, the channels (18) for supplying a gas open centrally into the respective recess (33). Indirect plasmatron according to one of the preceding claims, characterized in that the neutrode arrangement (1) the plasma jet outlet opening (40) laterally delimiting Neutrodes (1a, 1b, 1h, 1i), which with a bore (26) are provided, which form part of the plasma channel (8) and stabilize the arc in a predetermined position are determined. Indirect plasmatron according to one of the preceding claims, characterized in that the anode (10) is essentially a has flat end surface on which the arc starts. Indirect plasmatron according to one of the preceding claims, characterized in that the cathode (9) is a substantially has a conical tip at which the arc starts.

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