EP1292176A2 - Device for the production of an active gas beam - Google Patents

Abstract

The plasma is generated in a cylindrical discharge chamber (2) with a conically narrowing end (21) that increases the speed of the active gas jet (6). Adjoining the narrowing end is a limiting channel (4) that prevents the spreading out of the discharge zone (22) into free space. The limiting channel is cylindrical, earthed and has a length that is 5 to 10 times greater than its diameter.

Description

The invention relates to a device for generating a chemically active Jet (hereinafter referred to as active gas jet) by means of an electrically generated Plasma in a process gas used. The invention is particularly suitable for the treatment of surfaces, e.g. for pretreatment and cleaning of Surfaces before gluing, coating or painting, for coating, Hydrophilizing, removing electrical charges or sterilizing and for Acceleration of chemical reactions.

Devices are known for the surface pretreatment of workpieces by means of a gas activated in an electrical discharge zone, shown in the publications DE 195 46 930 C1, DE 195 32 412 A1 and EP 03 05 241. In the patent DE 195 46 930 C1 a vortex flow of the to be activated is described Gases passed through an electrical discharge zone, which forms between a conical central electrode and a ring electrode located at the end of a nozzle on the outside.
Another similar method is described in DE 195 32 412 A1, in which the gas to be activated is first introduced and activated in a vortex flow in the region of a discharge zone which arises along the axis of a cylindrical nozzle tube with an internally insulated cylindrical outer electrode and a coaxial central electrode and at the exit of the discharge zone, at which the nozzle tube is narrowed in the form of an annular end face of the cylindrical outer electrode, the gas jet is essentially discharged at the end face of the outer electrode.
A disadvantage of the aforementioned solutions is that the gas jet emerging from the nozzle has a considerable electrical potential, the value of which lies between the potential of the grounded ring electrode and that of the central electrode. With a correspondingly large gas throughput through the outlet opening of the gas flow, discharge tufts additionally bulge out of the nozzle in the direction of the active gas jet. The disadvantage mentioned limits the possible uses of the two aforementioned solutions a) because of the risk of electric shock for the operating personnel and b) because of a possible induced defect formation by electromagnetic fields when treating sensitive materials such as semiconductor substrates, possibly also with doped layers or structures.

According to EP 03 05 241, the gas to be activated is passed directly through an electrical discharge zone. The discharge zone is formed in a tube by means of an electric field, with either electrodes being arranged laterally inside the tube in the direction of flow of the gas, or a discharge chamber made of insulating material without electrodes installed in a waveguide. This solution has the disadvantage already mentioned above that, at a high speed of the activated gas flow, there is a high probability of electromagnetic fields and the electrical discharge zone itself emerging from the discharge chamber in the direction of the active gas jet, since there is no shielding ring electrode at the end of the discharge chamber. The arrangement described in EP 0 305 241 A1 prevents the operator from being endangered by a separate, closed processing chamber in which the surface treatment of the material takes place. The more difficult conditions of material processing are disadvantageous and, if the protective chamber were left out, would lead to an uncontrolled change in the process conditions and endanger the operating personnel.
It is characteristic of all the aforementioned technical solutions that the speed, the temperature and the geometry of the active gas jet are determined by the electrical, thermal and gas dynamic conditions that are necessary for the development or ignition of the electrical discharge zone for gas activation. However, the conditions mentioned for gas activation in an electrical discharge zone do not always prove to be optimal conditions for surface treatment by the active gas jet.
For example, it is very problematic to use an electrical discharge at atmospheric pressure and the resulting temperatures of more than 5000 K for surface treatment, since the majority of the materials to be processed do not withstand such temperatures. Another problem is high process gas speeds - for example supersonic speeds - for the electrical discharge zone, since this can only be maintained with great difficulty under highly dynamic conditions. The mentioned applications of the active gas jet, however, require higher gas throughputs in order to shorten the time within which the active gas jet, starting from the discharge zone, reaches the surface to be processed, because the activity loss of the gas jet is thereby effectively reduced by reducing the recombination processes.

The invention has for its object a new way to Generation of a chemically active jet (active gas jet) by means of a electrical discharge generated plasma in a process gas used find at which at an increased process gas speed the active gas jet on the processing surface develops a high chemical activity and already on Output of the device is electrically neutral, so that it is not a hazard to Operating personnel, environment and processed surface.

According to the invention, the object in a device for generating a chemically active jet (active gas jet) by means of an electrical discharge generated plasma in a process gas used with an essentially cylindrical discharge chamber, through which a process gas flows and in to activate the process gas, plasma generation due to electrical Gas discharge is provided, a gas inlet for the continuous supply of the Process gas into the discharge chamber and an outlet opening for alignment of the active gas jet onto a surface to be processed, characterized in that that the discharge chamber has a tapered end to increase the Has velocity of the active gas jet, the tapered end of the Discharge chamber a limiting channel to prevent the spread of the Discharge zone in the free space for the surface to be processed is arranged downstream, the limiting channel being essentially cylindrical is trained and grounded and its length is greater than the factor 5-10 Cross section is.

An arc discharge is advantageously provided for activating the process gas, the discharge chamber having a central electrode and a hollow electrode which covers the inner wall of the discharge chamber at least in the region of the conically tapered end in a flat and symmetrical manner. The limiting channel preferably adjoins the hollow electrode directly.
The central electrode is expediently rod-shaped and is arranged in the gas inlet region along the axis of symmetry of the discharge chamber.
The central electrode can advantageously be used to increase the power of the active gas jet by means of enlarged electrode areas, which have the shape of a cylinder cap, which includes a cylinder jacket surface of low height and a cover area, and whose opening is aligned coaxially with the axis of the discharge chamber and is arranged above the gas inlet of the discharge chamber.

To improve the stability of the parameters of the active gas jet, it is advantageous to arrange the discharge chamber in an induction field generated at high frequency (radio frequency) in order to activate the process gas.
This can expediently take place in that the discharge chamber (1) is provided with two electrodes which are arranged along the wall of the discharge chamber in the flow direction of the process gas and are operated at radio frequency.
The high-frequency excitation for activating the process gas can also advantageously be achieved by generating an induction field by arranging the discharge chamber in a coil operated at radio frequency.
Another possibility for activating the process gas without contamination of the active gas by electrode material is that the discharge chamber is arranged in a waveguide connected to a microwave source.
For the shaping, selection of the flow type (laminar or turbulent flow) and adjustment of the active gas jet with the desired parameters, in particular speed, temperature, geometric shape and flow type, a beam shaping device is expediently arranged downstream of the limiting channel.
It can be advantageous here that branched nozzles for processing individual partial areas or depressions of the surface to be processed are connected to the outlet of the boundary channel.
The beam-shaping device is expediently adapted to the shape of the surface to be processed by guide plates, the distance between the surface and the beam-shaping device being kept in a defined small area, so that the effectively treated surface comprises a larger area.
For special applications of an active gas jet, jet-shaping devices are provided which incorporate two or more devices according to the invention for generating the active gas jet into a processing channel, wherein several surfaces of a workpiece to be treated simultaneously or surfaces of extruded profiles with any cross section can be processed on all sides in the processing channel with continuous material flow.

When using an active gas jet with special additives (in particular for the coating of surfaces), a feed tube for introducing additives is preferably arranged axially in the discharge chamber, which ends shortly before the discharge chamber exits, an influence of the additives on the discharge characteristic and contamination of the Discharge chamber (1) is avoided by the additives or their reaction products.
To achieve a defined gas flow, it proves to be advantageous if the limiting channel comprises a plurality of individual channels in order to reduce the gas dynamic resistance and the residence time of the active gas in the limiting channel, the individual channels being arranged evenly distributed around a central channel. The supply of additives is particularly favorable if the limiting channel with a plurality of individual channels has a central inlet channel for the additives, the inlet channel being arranged axially in the center of a ring of individual channels through which active gas flows, since there is a premature reaction or disintegration of the additives and contamination of the discharge chamber by the additives can be avoided.
For all of the aforementioned supply variants, the additives in the area of the boundary channel can advantageously be introduced as gases, liquids in the form of aerosols or solids in the form of fine particles.
In a particularly expedient design variant of the invention, the hollow electrode, the limiting channel and the beam-shaping device are manufactured as a uniform rotating body with very good electrical conductivity, the central electrode is surrounded coaxially by an insulator tube and inserted into the discharge chamber formed by the hollow electrode, and the gas inlet into the discharge chamber is initially one cylindrical distribution chamber, wherein tangential flow channels are provided for the process gas from the distribution chamber to the discharge chamber, so that as a result of a spiral gas flow from the distribution chamber into the discharge chamber, arc discharges between the central electrode and the hollow electrode are fixed to an end of the central electrode protruding from the insulator tube. This largely prevents erosion of the insulator tube. Tangential flow channels can advantageously also be guided into a cylindrical annular chamber between the rod-shaped central electrode and the inner surface of the insulator tube, so that the central electrode is cooled directly by a portion of the process gas and exit points of arc discharges are essentially restricted to non-cylindrical surfaces of the central electrode. As a result, the insulator tube is protected even more effectively from the erosion effect of the discharge arc.
The insulator tube is expediently towered over by the central electrode by a length of up to twice the diameter of the central electrode. If the additional process gas supply within the insulator tube is used, the end of the central electrode can be shortened and in extreme cases ends with the end of the insulator tube.
The limiting channel is preferably narrowed conically in the direction of gas flow and has an average ratio of channel diameter to channel length of 1: 8. The limiting channel is advantageously followed by a beam-shaping device with a bell-shaped widened output, so that the working width of the active gas jet is increased.

The basic idea of the invention is based on the fact that, in the known devices of the prior art with plasma-induced active gas jet, either the activity of the gas jet is too low or the active gas jet still has a dangerously high electrical potential when it emerges into the processing space, which leads to a risk to the operating personnel , According to the invention, these mutually influencing problems are eliminated by passing the process gas through three zones in succession. First the process gas (in the discharge space) is activated and accelerated, then the speed-related spreading of the discharge zone out of the discharge space into the active gas jet is intercepted (limited) in a narrow, earthed limiting channel and finally an electrically neutral, chemically active active gas jet by beam-shaping devices according to the desired application (Cleaning, coating, activation, etc.) is formed. The device according to the invention can be combined with all known methods of plasma-induced activation of process gases in which a corona, glow or arc discharge zone (using a direct, alternating or pulse current) or a high-frequency discharge zone generated in an alternating electromagnetic field (with excitation frequencies up to the Microwave range).
The effectiveness of the limiting channel depends essentially on the fact that it has a smaller diameter in relation to the discharge chamber. Therefore, the discharge chamber is tapered in the flow direction of the process gas, so that with a large ratio of the cross section of the discharge chamber to the cross section of the limiting channel, the speed of the active gas jet increases significantly, which means that the time required for the chemically active particles of the active gas jet to travel the distance from the discharge chamber covered to the application site is greatly reduced. As a result of the reduction in time, there are fewer recombinations of active particles (reduced activity loss of the active gas jet) and this leads to an increase in the effectiveness of the active gas jet on the surface to be processed. With very high gas throughput through the discharge zone, discharge tufts bulge out of the discharge zone into the active gas stream flowing out. The electrical conductivity and the associated electrical resistance of the plasma arc with a high current at the same time lead to considerable potential compared to the grounded electrode even at a close distance from the plasma arc of the grounded electrode. In order to prevent the discharge tufts with dangerous electrical potential from escaping into the free space, the active gas jet is guided through a narrow, earthed channel at the exit of the discharge zone. The boundary channel is dimensioned such that a discharge arc entering it has a potential whose size at the entrance to the boundary channel is still too small for a breakthrough to the channel wall. As the path length in the boundary channel increases, the voltage in the discharge arc rises until a breakthrough to the channel wall occurs. The boundary channel must therefore have a minimum length in accordance with the other conditions of plasma generation, which ensures that the aforementioned bulges of the discharge zone into the free space cannot occur. This happens with a ratio of the cross section to the channel length of 1: 5 to 1:10.

The device according to the invention allows the generation of an electrical neutral, chemically active jet, with increased process gas velocity the active gas jet on the surface to be processed has a high chemical Activity unfolds and is electrically neutral at the exit of the device, so that he posed no danger to operating personnel, the environment and Represents surface.

Fig. 1:

eine schematische Darstellung der erfindungsgemäßen Vorrichtung mit elektrischer Entladung, die durch ein beliebiges elektromagnetisches Feld ausgelöst wird;

Fig. 2:

eine Ausgestaltung der Erfindung mit elektrischer Bogenentladung zwischen stabförmiger Zentralelektrode und Hohlelektrode an der Wand der Entladungskammer sowie mit einem aus mehreren Einzelkanälen bestehenden Begrenzungskanal;

Fig. 3:

eine Gestaltung der Erfindung mit Bogenentladung über eine Zentralelektrode in Form einer Zylinderkappe;

Fig. 4:

eine Gestaltungsform mit einem mittels Innenelektroden erzeugten Hochfrequenzfeld;

Fig. 5:

eine Ausführungsform mit Erzeugung der Gasentladung durch Mikrowellen;

Fig. 6:

eine Gestaltungsform mit einem induktiv erzeugten Hochfrequenzfeld;

Fig. 7:

schematische Darstellung der Erfindung zum Aufteilen des Aktivgasstrahls zur gleichzeitigen Bearbeitung einzelner Teilflächen auf Oberflächen mit kompliziertem Relief;

Fig. 8:

schematische Darstellung der erfindungsgemäßen Vorrichtung, wobei die strahlformende Einrichtung einer ebenen Oberfläche angepasst ist;

Fig. 9:

schematische Darstellung wie in Fig. 8, wobei die strahlformende Einrichtung einer sphärischen Oberfläche angepasst ist;

Fig. 10:

eine spezielle Ausgestaltung, bei der mehrere erfindungsgemäße Vorrichtungen mit deren strahlformenden Einrichtungen in einen Bearbeitungskanal mit kontinuierlichem Materialfluss eingebunden sind;
eine Gestaltungsform zum Zuführen von Zusatzstoffen in den Aktivgasstrahl vor dem Begrenzungskanal;

Fig. 11:

eine Gestaltungsform zum Zuführen von Zusatzstoffen vor Beginn des Begrenzungskanals;

Fig. 12:

eine Variante zum Zuführen von Zusatzstoffen am Ende des Begrenzungskanals;

Fig. 13:

eine konstruktive Ausführung der Vorrichtung mit spezieller Gestaltung der Strömungskanäle für das zugeführte Prozessgas bei Aktivierung mittels Bogenentladung.

The invention will be explained in more detail below using exemplary embodiments. The drawings show:

Fig. 1:

is a schematic representation of the device according to the invention with electrical discharge, which is triggered by any electromagnetic field;

Fig. 2:

an embodiment of the invention with electrical arc discharge between rod-shaped central electrode and hollow electrode on the wall of the discharge chamber and with a limiting channel consisting of several individual channels;

Fig. 3:

a design of the invention with arc discharge via a central electrode in the form of a cylinder cap;

Fig. 4:

a design with a high-frequency field generated by means of internal electrodes;

Fig. 5:

an embodiment with generation of the gas discharge by microwaves;

Fig. 6:

a design with an inductively generated radio frequency field;

Fig. 7:

schematic representation of the invention for dividing the active gas jet for simultaneous processing of individual partial surfaces on surfaces with a complicated relief;

Fig. 8:

schematic representation of the device according to the invention, the beam-shaping device being adapted to a flat surface;

Fig. 9:

schematic representation as in FIG. 8, the beam-shaping device being adapted to a spherical surface;

Fig. 10:

a special embodiment in which a plurality of devices according to the invention with their beam-shaping devices are integrated into a processing channel with a continuous material flow;
a design for feeding additives into the active gas jet in front of the limiting channel;

Fig. 11:

a design for adding additives before the start of the limiting channel;

Fig. 12:

a variant for feeding additives at the end of the limiting channel;

Fig. 13:

a constructive design of the device with a special design of the flow channels for the supplied process gas when activated by means of arc discharge.

The basic structure of the device for generating an active gas jet according to FIG. 1 consists of a discharge chamber 2 through which a process gas 1 flows, in which the process gas 1 is activated in the form of an electrical discharge generated by a strong field 3, an essentially cylindrical limiting channel 4 and a beam shaping device 5 for the active gas jet 6 intended for material processing in free space.
The discharge chamber 2 has, in the flow direction of the process gas 1, a conically tapered end 21 (ie a nozzle-like constricted shape) which serves to increase the flow rate of the process gas 1 during its activation in the discharge chamber 2. With this increase in gas velocity, the time required to reach a surface 7 to be machined (only shown in FIGS. 7 to 9) is shortened, and the recombination of active gas particles before reaching the machining location is thus reduced. Simultaneously with the increase in the flow rate, however, there is an increased risk that a discharge zone 22 forming in the discharge chamber 2 due to the action of the field 3 will continue beyond the conically tapered end 21 of the discharge chamber 2. In order to prevent so-called discharge tufts with dangerously high electrical potential as bulges 24 of the discharge zone 22 from the discharge chamber 1 from emerging into the free space as a result of the high gas velocity, the active gas jet 6 accelerated by the tapered end 21 at the exit of the discharge chamber 1 is narrowed , grounded limiting channel 4 out. This effectively prevents the discharge zone 22 from spreading in the direction of the free outlet opening of the active gas jet 6.
The limiting channel 4 is dimensioned such that the part of the discharge zone 22 entering it reaches such a potential, the size of which at the entry into the limiting channel 4 is still too small for a breakthrough to the channel wall, but increases so much with increasing path length in the limiting channel 4, until there is a breakthrough to the earthed wall of the limiting channel 4.
Furthermore, the limiting channel 4 must have a minimum length in accordance with the other conditions of the plasma generation required to activate the process gas 1, which ensures that the aforementioned bulges 24 of the discharge zone 22 cannot occur in the free space. This is usually achieved with a ratio of the channel cross-section to the channel length of 1: 5 to 1:10.
The effectiveness of the active gas jet 6 also depends to a large extent on the fact that the limiting channel 4 has a significantly smaller diameter in relation to the main part of the discharge chamber 2 (in front of its conically tapered end 21), so that with a large ratio (1: 5 to 1: 8 ) of the cross section of the discharge chamber 2 compared to the cross section of the limiting channel 4, the speed of the active gas jet 6 increases significantly, whereby the time required for the chemically active particles of the active gas jet 6 to travel the distance from the discharge chamber 2 to the application site is greatly reduced. As a result of the reduction in time, there are fewer recombinations of active particles (reduced loss of activity of the active gas jet 6) and this leads to an increase in the effectiveness of the active gas jet 6 on the surface 7 to be processed (not shown in FIG. 1). On the other hand, however, due to the small diameter of the delimitation channel 4, the aerodynamic resistance at the tapered end 21 of the discharge chamber 2 will increase and the effectiveness within the discharge zone 22 will be impaired. This can be explained by the fact that the temperature of the plasma increases with increasing pressure. The delimitation channel 4 is therefore essentially cylindrical and has a cross section of 1: 5 to 1: 8 that is adapted to the diameter of the discharge chamber 2.

Process gas 1 is introduced into the discharge chamber 2. The supplied process gas 1 is activated by the interaction with the field 3 in the electrical discharge zone 22, accelerated and largely discharged in the conically tapered part 21 of the discharge chamber 2 and introduced into the limiting channel 4, which spreads the discharge zone 22 outwards into the free zone Processing space prevented. After the limiting channel 4, the active gas jet 6 flows through a jet-shaping device 5, in which it is shaped in accordance with the application in terms of speed, temperature, geometric shape and flow type (laminar or turbulent flow). The discharge zone 22 can arise as desired (depending on the type of field generation used) by direct, alternating or pulse current, electromagnetic induction, microwaves or other types of excitation which trigger an electrical gas discharge when the process gas 1 is used.
FIG. 2 shows the invention in a variant in which the process gas 1 is activated by an arc discharge 34 between two electrodes in the discharge chamber 2. One of the electrodes is a rod-shaped central electrode 31, the other is located on the inner wall of the discharge chamber 2 and forms a so-called hollow electrode 32. The hollow electrode 32 is attached at least to the conically tapered end 21 of the discharge chamber 2. However, it can also form the wall of the discharge chamber 2 itself (as shown, for example, in FIG. 13).
The process gas 1 is introduced tangentially into the discharge chamber 2, in which an electrical arc discharge 34 takes place between the central electrode 31 and the hollow electrode 32 along the inner wall of the discharge chamber 2 by means of a generator 33.
The interaction with the electric arc discharge 34 activates the process gas 1, accelerates it in the conically tapered part 21 of the discharge chamber 1 and largely discharges it on the way to the limiting channel 4. In the subsequent delimitation channel 4, which receives a bulge 23 of the discharge zone 22 that is possible at high gas velocities, a forwarding of the electrical potential of the discharge zone 22 to the outside into the free space of the surface 7 to be processed is prevented. When the gas throughput through the discharge chamber 2 is very high, discharge tufts are blown out into the active gas jet of the delimitation channel 4, ie a bulge 23 of the discharge zone 22 is formed. The electrical conductivity and the associated electrical resistance of the plasma arc (electrical discharge arc in the process gas 1) with a high level Current leads to a considerable potential compared to the grounded hollow electrode 32 even at a close distance from the plasma arc. A considerable electrical potential therefore also occurs outside the discharge chamber 2 when working at a high process gas speed. Under certain circumstances, this potential can still be a few hundred volts at the annular end of the hollow electrode 32. This phenomenon poses a danger to the operating personnel if the processing room is connected at this point. In the event of discharge tufts emerging, electrical defects on sensitive surfaces of objects to be treated - for example semiconductors or semiconductor structures - could also be caused. In order to prevent the bulges 23 (discharge tufts) with dangerous electrical potential due to a high active gas jet velocity from the discharge zone 22 from escaping into the free space, the active gas jet 6 is guided at the outlet of the discharge chamber 2 through the narrow, grounded limiting channel 4, in which a certain aerodynamic congestion, a further discharge of the active gas jet 6 takes place. The limiting channel 4 is dimensioned such that the bulge 23 of the discharge zone 22 entering it has a potential whose size at the entrance to the limiting channel 4 is still too small for a breakthrough to the channel wall. As the path length in the delimitation channel 4 increases, the voltage in the discharge arc rises until a breakthrough to the channel wall occurs. Accordingly, the boundary channel 4 must have a certain minimum length in accordance with the other conditions of the plasma generation, which ensures that the aforementioned bulge 23 of the discharge zone 22 cannot cross the boundary channel 4 and to indicate a ratio between the channel cross section and the channel length of 1/5 to 1/10 is. The active gas jet 6 has a temperature which is comparable to the temperature at the outlet of the discharge chamber 2, but its gas dynamic properties (speed and flow conditions) are essentially determined by the gas throughput and by the dimensions and the structural design of the limiting channel 4.
After the limiting channel 4, the active gas jet 6 flows through the jet-shaping device 5, in which it is shaped in accordance with the application in relation to speed, temperature, geometric shape and flow type (laminar or turbulent flow). Various designs of jet-shaping devices 5 can be used for this, for example nozzles designed in such a way that adiabatic expansion of the active guest jet occurs in order to lower the temperature, or flattened jet-shaping devices 5, as will be described in more detail below, in order to achieve a flat, to form wide active gas jet 6.
The electrical discharge zone 22 can arise for the described device as desired (depending on the type of voltage generator 33 used) by direct, alternating or pulse current.
The active gas jet 6 generated in the discharge chamber 2 unfortunately also loses part of its activity when flowing through the boundary channel 4 as a result of recombination of the active particles and because of the interaction of the active gas jet 6 with the channel wall. In order to reduce the effect of the aforementioned processes, a simultaneous reduction in the cross section of the limiting channel 4 is required if the channel length is shortened. However, this would increase the aerodynamic resistance of the limiting channel 4 and impair the effectiveness within the discharge chamber 2. This can be explained by the fact that the temperature of the plasma increases with increasing pressure. At the same time, a greater thermal load on the central electrode 31 and the hollow electrode 32 is caused, which leads to higher electrode wear. This can be reduced in that the limiting channel 4 consists of two or more grounded individual channels 41 which are arranged parallel to one another in electrically conductive material and which result in a larger effective flow cross section. 2 shows an embodiment in which further individual channels 41 are arranged uniformly distributed around a central single channel 41.
3 shows a generation of an active gas jet 6, in which - in contrast to the example described above - the central electrode 31 has the shape of an electrically conductive cylinder cap instead of the rod shape. This central electrode 31 is arranged coaxially with its opening in the direction of the discharge chamber 2. The process gas 1 is introduced tangentially into a gap between the cylindrical central electrode 31 and the discharge chamber 2. When using such a shape of the central electrode 31, the supporting surface of the arc discharge 34 on the central electrode 31 increases, ie the base points of the arc discharges 34 move on a larger surface when the flow of the process gas 1 is intensely swirled. This prevents overheating in the central electrode 31 and increases the service life and the maximum discharge current.
FIG. 4 shows a variant in which the process gas 1 is activated between two electrodes 35 arranged one after the other in the discharge chamber 2 in the flow direction. By means of a high-frequency generator 36, the discharge zone 22 is generated by a high-frequency discharge in an alternating field 3, the discharge chamber 2 being made of an electrically insulating material (eg quartz).
Since it is well known that the electrical discharge produced when using cold electrodes 35 is unstable under certain pressures, for example at atmospheric pressure, without additional measures, because high electron densities and energy gradients create a space charge layer in front of the electrodes 35 and destabilize the discharge. In high-frequency discharges, this stabilization is carried out by simple measures (as described, for example, by J. Reece Roth in: Industrial Plasma Engineering, Vol. 1: Principles, Inst. Of Physics Publishing, Bristol and Philadelphia, 1995, pp. 382-385, 404-407 , 464f.) Are achieved. Because of the simple maintenance of a stable discharge, an HF discharge for activating the process gas 1 is particularly advantageous.
However, all of the electrodes, as described in the previous design variants for producing the electrical discharge zone 22, are more or less exposed to an erosion process, ie they wear out. This leads to contamination of the discharge chamber 2 and the process gas 1 by electrode material. In order to generate an active gas jet 6 free from contamination by electrode material, the discharge zone 22 is produced without electrodes according to FIG. 5. For this purpose, the discharge chamber 2, which in this example consists of electrically insulating but microwave-transparent material, is introduced into the field 3 of a microwave generator 37, a location of relatively uniform and high field strength being used in a typical microwave conductor 38 which is connected to the microwave generator 37. All other processes which produce the active gas jet 6 from the discharge zone 22 run according to the preceding examples.
A likewise electrodeless activation of the process gas 1 is shown in FIG. 6. Here, a high-frequency generator 36 is used to induce a high-frequency changing field 3 in the discharge chamber 2 with a coil 39. The discharge chamber 2 is arranged within the turns of the coil 39 and forms the desired discharge zone 22 on the inside. The material of the discharge chamber 2 can be selected relatively freely, but is not necessarily ferromagnetic. As already described in the previous examples, the process gas 1 is accelerated in the conically tapered end 21 of the discharge chamber 2 and freed of its dangerous potential in the earthed limiting channel 4, so that an electrically neutral active gas jet 6 is available at the output of the beam-shaping device 5.

For demanding surface treatments, it is often necessary individual parts of surfaces 7 or depressions on workpieces are equivalent to edit. For this purpose, the originally uniform active gas jet 6 for the Processing of individual surface parts 71 and depressions in several beams divided up. Fig. 7 shows a stylized discharge chamber 2, in which the type of Generation of the electrical discharge can be chosen arbitrarily. The generated Active gas is discharged from the discharge chamber 2 through the limiting channel 4 into a jet-shaping device 5, which has branched nozzles 51. The branched nozzles 51 are directed to different partial areas 71 which represent different heights in the surface 7 to be machined and each direct a portion of the active gas jet 6 onto the partial surfaces 71.

In the case of the plasma jet generators known for surface processing, such as, for example, according to DE 195 46 930 C1, DE 195 32 412 A1, the gas jet is broadened after leaving the generator before it reaches the surface to be processed. If this happens too generously, the gas jet loses too much activity on the way to the surface 7 through recombinations and interactions with the gas particles in the surrounding atmosphere. Some additional measures are therefore proposed for the present invention which keep the activity losses on the way from the generation of the active gas jet 6 to the surface 7 to be machined even when the surface 7 is machined at the same time. 8 and 9 show two possibilities for regularly shaped surfaces 7. In FIG. 8, angled, largely flat guide plates 52 are provided as beam-shaping device 5, directly adjoining the delimitation channel 4, and are evenly spaced a short distance above the flat surface 7 must be performed. As a result of this measure, the high gas velocity already generated in the end of the tapered discharge chamber 2 and passed on via the limiting channel 4 is also continued in the beam-shaping device 5 in the form of a beam, which is guided parallel to the surface 7, through a type of boundary layer line. Chemically active particles of the active gas jet 6, which degenerate into an almost laminar flow, thus reach a larger area of the surface 7 to be processed in a very short time before they can recombine. 9 shows the same mode of operation for a spherical surface 7, in which case the guide plates 52 must have a concentric curvature in accordance with the surface curvature in order to achieve the same effect of the laminar flow layer.
Another special design of beam-shaping device is shown in FIG. 10. This example deals with the effective processing of a continuous material flow, in which either an extruded profile 72 or a material flow of identical workpieces are to be processed simultaneously on several surfaces 7 with an active gas jet 6. 10, an extruded profile 72 is guided through a closed processing channel 53, a device according to the invention being attached to at least two opposite sides of this processing channel 53 at an angle to the direction of movement of the extruded profile 72.
All of the arrangements described so far only include the use of a process gas or process gas mixture which is introduced directly into the discharge chamber 1 in a corresponding arrangement. If an additional substance is to be added that is not to be activated in the discharge zone 22, two possible arrangements are possible, either according to FIG. 11 by adding directly in front of the limiting channel 4 or according to FIG. 12 by introducing it directly into the neutral active gas jet 6 can be realized in the beam shaping device 5 after the limiting channel 4.
In the first case (FIG. 11), the additive 8 is supplied via a feed tube 81 which is resistant to high temperatures and which ends a few millimeters before the end of the limiting channel 4 facing the discharge zone 22 and is made of ceramic, quartz or a comparable temperature-resistant material. In order to avoid any interference by this additive 8 in the discharge zone 22, the mass flow of this additive 8 may only make up a fraction of the mass flow of the process gas 1 in the discharge chamber 2. In this embodiment, the discharge chamber 2 is integrated in a housing 9, since an electrodeless activation of the process gas 1 is to be assumed here. In the simplest case, the housing 9 symbolizes a waveguide 38 with a connected microwave source 37 according to FIG. 5, but can also accommodate a coil 39 according to FIG. 7 and an associated cooling.
In the second case (FIG. 12), the activated process gas 1 is guided through a limiting channel 4 with a plurality of parallel individual channels 41, which are arranged in a ring 42. In the center of the boundary channel 4, which is designed as a thick perforated plate, instead of a central individual channel 41 there is a feed channel 82 which is fed in from the outside. The additive 8 is introduced into the center of an active gas jet 6, which approximately represents a gas ring, via this feed channel 82, which is guided from the outside into the center of the ring 42 of the individual channels 41 within the perforated metal plate of the limiting channel 4. Since the active gas jet 6 flows out at a very high speed in the case of the small cross sections of the individual channels 41, the mass flow of the additive 8 can be varied over a wide range via the feed channel 82 and set very precisely.
13 shows the longitudinal and cross-section of the device for generating an electrically neutral active gas jet 6 in a manageable housing 9. The device consists of the discharge chamber 2, the delimitation channel 4 and the beam shaping device 5, which as a unitary body 91 in the form of a non-slip handpiece (pen) made of copper or another very good electrical conductor, a rod-shaped central electrode 31, which is arranged by means of an insulating tube 29 made of quartz, coaxial to the wall of the discharge chamber 2, which also represents the hollow electrode 32. The insulator tube 29 is sealed in a gas-tight manner with respect to the discharge chamber 21 by an elastic sealing ring 92 in the base body 91. The end of the central electrode 31 protrudes from the insulator tube 29 into the discharge chamber 2 by a length of up to twice the diameter of the central electrode 31. The insulator tube 29 itself protrudes into the discharge chamber 2 by at least a length the size of its own outside diameter and thus forms part of the discharge chamber 2 in the form of a hollow cylinder outside its outer surface. The process gas 1 is introduced symmetrically into the discharge chamber 2 into this hollow cylinder near the rear end wall of the discharge chamber 2.
The conically tapered end 21 of the discharge chamber 2 merges smoothly into the narrow delimitation channel 4. The diameter of the boundary channel 4 is in a ratio of 1: 8 to its length and is only shown in a stylized manner in FIG. 13 (not to scale). The beam-shaping device 5 connects to the limiting channel 4. The discharge chamber 2, the delimitation channel 4 and the beam-shaping device 5 are made uniformly from copper and have a common grounded contact 93. The grounded contact 93 is also connected to the negative pole of the voltage generator 33 (not shown in FIG. 13). The positive pole of the voltage generator 33 is connected to the central electrode 31.
The process gas 1 is initially fed via the gas inlet 24 into a cylindrical distribution chamber 25, from which a spiral gas flow is generated in the hollow-cylindrical part of the discharge chamber 2 by way of uniformly distributed tangential flow channels 26. This measure has the effect that the base points of the arc discharge 34 (not shown in FIG. 13) on the central electrode 31 are restricted to its end face and directly adjacent parts of the electrode surface, so that the insulator tube 29 is subjected to less thermal stress and its erosion is reduced.
At the rear end of the base body 91 - more precisely on the rear end wall of the discharge chamber 2, an insulating connection body 94 is fastened (eg screwed), which carries the fastening and the connection of the central electrode 31. The connection body 94 has an additional gas inlet 27, which is connected to the discharge chamber 2 via a narrow annular chamber 28 along the central electrode 31. Through this narrow annular chamber 28, part of the process gas 1 with the function of electrode cooling and direct feeding into the discharge zone 22 is fed between the central electrode 31 and the insulator tube 29. The annular chamber 28 is sealed in the rear in the connecting body 94 by an elastic ring 96 against the central electrode 31, which is guided to the rear to the connecting terminal 95. Tangential flow channels 26 (not shown for annular chamber 28) can also be provided in the annular chamber 28, as between the distribution chamber 25 and the hollow cylindrical part of the discharge chamber 2, in order to generate a spiral gas circulation.
13 now works in the following manner. Part of the process gas 1 is supplied through the additional gas inlet 27 and flows through the annular chamber 28 between the central electrode 31 and the insulator tube 29 into the discharge chamber 2. At the same time, the other (larger) part of the process gas 1 through the gas inlet 24 via the distribution chamber 25 , through the tangential openings 26 of the discharge chamber 2 in its hollow cylindrical part, which is formed by the hollow electrode 32 and the protruding insulator tube 29. This creates a spiral eddy flow in the discharge chamber 2. When the process gas 1 is supplied through the gas inlets 24 and 27 and at the same time a direct voltage is applied between the grounded contact 93 and the connecting terminal 95, an electrical discharge occurs in the discharge chamber 2. The process gas 1 is generated in the discharge zone 22 due to the interactions (analogous to FIG. 2 13, but not shown in FIG. 13), the discharge chamber 2 - accelerated by its conically tapered end 21 - leaves at high speed and flows through the adjoining limiting channel 4 and the beam-shaping device 5 into the (free) processing space. The active gas jet 6 essentially loses its potential in the limiting channel 4, the size of which at the end of the limiting channel 4 is almost zero with respect to ground (earthed). In the subsequent beam-shaping device 5, the active gas jet 6 is then brought to the width and shape desired for the application (as described, for example, in relation to FIGS. 7 to 9). A chemically very effective and electrically neutral active gas jet 6 is thus available for any application.

List of the reference symbols used

1

process gas

2

discharge chamber

21

tapered end

22

discharge zone

23

Bulge of the discharge zone

24

tangential flow channels

25

distribution chamber

26, 27

gas inlet

28

annular chamber

29

Isoiatorrohr

3

field

31

central electrode

32

hollow electrode

33

voltage generator

34

arc

35

RF electrode

36

RF source

37

microwave source

38

microwave guide

39

Kitchen sink

4

limiting channel

41

individual channels

42

Ring (of single channels)

5

beam shaping device

51

branched nozzles

52

baffles

53

machining channel

6

Active gas jet

61

partial beams

7

surface

71

subareas

72

extruded profile

8th

additives

81

supply pipe

82

supply channel

9

casing

91

body

92

elastic sealing ring

93

ground terminal

94

insulating connector body

95

Terminal (of the central electrode)

96

elastic ring

Claims (24)

Device for generating a chemically active jet (active gas jet) by means of a plasma generated by electrical discharge in a process gas used with an essentially cylindrical discharge chamber through which a process gas flows and in which plasma generation as a result of an electrical gas discharge is provided for activating the process gas, a gas inlet for continuously supplying the process gas into the discharge chamber and an outlet opening for aligning the active gas jet on a surface to be processed, characterized in that the discharge chamber (2) has a conically tapered end (21) for increasing the speed of the active gas jet (6) and The tapered end (21) of the discharge chamber (2) is followed by a limiting channel (4) to prevent the discharge zone (22) from spreading into the free space for the surface (7) to be processed, the limiting channel (4) being essentially cylindrical and is earthed and its length is 5 to 10 times greater than its cross-section. Device according to claim 1, characterized in that
An arc discharge (34) is provided for activating the process gas (1), the discharge chamber (2) having a central electrode (31) and a hollow electrode (32) which cover the inner wall of the discharge chamber (2) at least in the region of the conically tapered end (21 ) covered over a large area and symmetrically. Apparatus according to claim 2, characterized in that
the limiting channel (4) is attached directly to the hollow electrode (32). Apparatus according to claim 2, characterized in that
the central electrode (31) is rod-shaped and is arranged along the axis of symmetry of the discharge chamber (2). Apparatus according to claim 2, characterized in that
the central electrode (31) is in the form of a cylinder cap which contains a cylinder jacket surface of low height and a top surface and whose opening is aligned coaxially with the axis of symmetry of the discharge chamber (2) and is arranged above the gas inlet (26) of the discharge chamber (2). Device according to claim 1, characterized in that
to activate the process gas (1), the discharge chamber (2) is mounted in an induction field generated at high frequency (radio frequency). Apparatus according to claim 6, characterized in that
To activate the process gas (1), the discharge chamber (2) is provided with two RF electrodes (35) which are arranged along the wall of the discharge chamber (2) in the flow direction of the process gas (1) and are operated at radio frequency. Apparatus according to claim 6, characterized in that
To activate the process gas (1), the discharge chamber (2) is arranged in a coil (39) operated at high frequency. Device according to claim 1, characterized in that
To activate the process gas (1), the discharge chamber (2) is arranged in a waveguide (38) connected to a microwave source (37). Device according to claim 1, characterized in that
the limiting channel (4) is followed by a beam-shaping device (5) for setting the active gas jet (6) with desired parameters, in particular speed, temperature, geometric shape and type of flow. Apparatus according to claim 10, characterized in that
branched nozzles (51) for machining individual partial surfaces (71) or depressions in the surface (7) to be machined are connected to the outlet of the boundary channel (4). Apparatus according to claim 10, characterized in that
the beam-shaping device (5) is adapted to the shape of the surface (7) to be machined by guide plates (52), the distance between the surface (7) and the guide plates (52) being kept in a defined small area, so that the effectively treated surface (7) covers a larger area. Apparatus according to claim 10, characterized in that
Jet-shaping devices (5) are provided, which incorporate two or more devices according to the invention for generating the active gas jet (6) into a processing channel (53), with multiple surfaces (7) of a workpiece to be treated simultaneously or in the processing channel (53) with continuous material flow Surfaces (7) of extruded profiles (72) with any cross-section can be machined on all sides. Device according to claim 1, characterized in that
A feed tube (81), which is arranged axially in the discharge chamber (2) and ends shortly before the discharge of the discharge chamber (2), is provided for introducing additives (8) into the active gas jet (6), with an influence of the additives (8). on the discharge characteristics and contamination of the discharge chamber (2) by the additives (8) or their reaction products is avoided. Device according to claim 1, characterized in that
the limiting channel (4) comprises a plurality of individual channels (41) in order to reduce the gas dynamic resistance and the residence time of the active gas (6) in the limiting channel (4), the individual channels (41) around a central channel evenly in a ring (42) are distributed. Apparatus according to claim 15, characterized in that
the limiting channel (4) with a plurality of individual channels (41) has a central feed channel (82) for additives (8), the feed channel (82) axially in the center of the ring (42) of individual channels (41) through which activated process gas (6) flows. is arranged. Device according to claim 14 or 16, characterized in that
the additives (8) in the area of the boundary channel (4) can be introduced as gases, liquids in the form of aerosols or solids in the form of fine particles. Apparatus according to claim 4, characterized in that
the hollow electrode (32), the limiting channel (4) and the beam-shaping device (5) are manufactured as a uniform rotating body with very good electrical conductivity, the central electrode (31) as a rod-shaped central electrode (31) coaxially surrounded by an insulator tube (29) Discharge chamber (2), which is formed by the hollow electrode (32), is inserted, and the gas supply for the process gas (1) has tangential flow channels (24) in a cylindrical distribution chamber (15; 16) concentrically surrounding the central electrode (31), wherein, as a result of a spiral gas flow from the distribution chamber (15; 16) into the discharge chamber (2), arc discharges (34) between the central electrode (31) and the hollow electrode (32) have an outlet area concentrated on the end of the central electrode (31). Device according to claim 18, characterized in that
Tangential flow channels (24) in a cylindrical annular part of the discharge chamber (2) between the inner surface of the hollow electrode (32) and the outer surface of the insulator tube (29) are guided so that the process gas (1) the insulator tube (29) from the outside spiral flows around. Device according to claim 18, characterized in that
tangential flow channels (24) are additionally guided into a cylindrical annular chamber (28) between the rod-shaped central electrode (31) and the inner surface of the insulator tube (29), so that the central electrode (31) is cooled directly by a portion of the process gas (1) and exit points arc discharges (34) are essentially limited to non-cylindrical surfaces of the central electrode (31). Apparatus according to claim 19, characterized in that
the end of the rod-shaped central electrode (31) projects beyond the insulator tube (29) by a length of up to twice the diameter of the central electrode (31). Device according to claim 19 or 20, characterized in that
the end of the central electrode (31) ends with the end of the insulator tube (29). Device according to claim 18, characterized in that
the limiting channel (4) is narrowed slightly conically in the direction of gas flow and has an average ratio of channel diameter to channel length of 1: 8. Device according to claim 18, characterized in that
A beam-shaping device (5) with a bell-shaped extended outlet is arranged downstream of the limiting channel (4), so that the working width of the active gas jet (6) is increased.

Images