EP3747241A1

EP3747241A1 - Atmospheric plasma jet having a straight cannula tube

Info

Publication number: EP3747241A1
Application number: EP19701688.4A
Authority: EP
Inventors: Holger Heuermann; Luc Langer
Original assignee: Ionics SA
Current assignee: Ionics SA
Priority date: 2018-02-02
Filing date: 2019-02-01
Publication date: 2020-12-09
Also published as: WO2019149897A1

Abstract

The invention relates to an atmospheric plasma jet operated by means of a high frequency signal in the MHz or GHz range supplied laterally via a coaxial line system (12, 18), comprising a metallic, substantially tubular outer conductor (16) provided with a cannula tube inlet at one end (20), the opposite end (14) thereof being open for plasma generation, and a cannula tube (10, 15, 19) as electrode for plasma generation, wherein the cannula tube passes through the outer conductor in a substantially straight manner from one end to the other. The atmospheric plasma jet according to the invention can be used for cutting or gluing workpieces, or for treating or coating workpiece surfaces. Treatment or coating material can be introduced into the plasma jet by way of the cannula tube.

Description

ATMOSPHERE PLASMAJET WITH STRAIGHT CANNULA TUBE

The present invention relates to a novel construction for the construction of an atmospheric plasma jet operated by a high frequency signal in the MHz or GHz range, as well as the use of novel atmospheric plasma in cutting or gluing processes, as well as in the treatment or coating of workpiece surfaces.

Plasma systems have been in the industry for several decades

Low pressure and atmospheric applications established. For example, in 1970, US Patent 3,534,388, PLASMA JET CUTTING PROCESS, was issued for a jet for cutting. An alternative Plasmajet US 3,567,898, PLASMA ARC CUTTING TORCH was issued in 1971.

In general, these Plasmajets are operated in the DC to the lower MHz range. The plasmas are generated and blown out by arc or spark discharges generated inside. Based on these plasma jets, around 99% of the jets on the market are built.

The first microwave jets in the power class up to 200 W were from the

Company Heuermann HF-Technik GmbH (HHF) launched in 2011 from the market. See http: //www.hhft. com / index.php? page = plasma & subpage = ps_p4. In 2013, HHF also published the first cannula jet on the Internet:

The patent application DE102012004034 was filed on March 2, 2012 and published in 2013. It relates to a high-frequency plasma ignition head with a cannula as electrode and a two-way impedance transformer, which is able to generate a high voltage at a fixed frequency and, as soon as a plasma is formed, to feed energy into it optimally. The design cools the electrodes and, similar to the high energy intensity laser, focuses the plasma jet in a small space. The spotlight can be used as a cutting and welding head.

In general, it is necessary in the generation of plasmas that one for the

Ignition generates a high voltage and provides for the operation of the optimal adjustment for the supply of electrical energy. For this, often two different electrical drive modules (e.g., high voltage generator and power source) are provided. The new microwave jets get by with only one generator whose operating frequency only has to be changed over. An embodiment of a

associated control electronics and control process are z. B. in DE102011055624 described. This control uses a so-called bi-static matching; that is, a high voltage is generated at one frequency (often in the IMS band at 2.45GHz). After plasma ignition is, to maintain the plasma, switched to another frequency (about 20-70MHz away, also in the IMS band). For this switching you need a special measuring and control electronics as well as very broadband

Transistor amplifiers or quite expensive alternatives like klystrons or traveling wave tubes. In this particular art, it is known to those skilled in the art that one works with a mean fixed frequency and a search frequency. The so-called middle one

Operating frequency is between the ignition and the operating frequency. As medium

Operating frequency is targeted in practice the 2.45 GHz frequency.

To ignite a very high voltage is generated, which is often in the two-digit kV range. This is done with the internal impedance transformer.

These jets are constructed as a pin: cylindrical, narrow and with an input on one side and an output on the other side. This design is also ideal for many applications, as it saves so much space and mechanical

Loads can be optimally intercepted.

The above-mentioned HHF Kanülenjet has an S-shaped curved cannula. If only gas is to be passed through the cannula, the S-shape forms no particular disadvantage. However, S-forming already involves many problems in the transportation of powder, so that no reliable operation for all powders is possible. The cannula is not easy to clean. Blockages occur due to the design with the curves and the

Transitions relatively common. Also, for the transport of wires through the cannula, this construction is not ideal, since the wires can be transported only by touching the cannula metal electrode to the plasma. As a result, the wire is contaminated by the electrode material. Furthermore, there is a wear. Due to the different coefficients of friction, a highly continuous process can not be set. Hard wires and fibers (glass fiber, carbon fiber etc.) can not be guided through the cannula jet. An insulation between the high-frequency electrode and the interior material to be performed is practically impossible in the S-shape. Many materials must be protected in particular due to contamination with the cannula metal electrode. Electrically you can put on the wire, which goes through the cannula, no further power source.

The aim of the invention is to provide an improved Plasmajet that does not have the above-mentioned disadvantages. In particular, the plasma jet according to the invention should allow powdery or particulate, fibrous and wire-like materials to pass unhindered through the cannula.

The invention Plasmajet to activate, cleaning, cutting, welding, ignition, for surface treatment, coating, liquid and

Metal evaporation, soldering, melting, air and other gas cleaning be suitable.

The invention now provides an Atmophärenplasmajet available, which can be operated by a high frequency signal in the MHz or GHz range, and a metallic substantially tubular outer conductor which is closed at one end and open at the opposite end to the plasma generation and comprising a cannula tube as a plasma generation electrode, wherein the cannula tube passes through the outer conductor substantially straight, from one end to the other, and the closed end has a cannula tube entrance, and the high frequency signal is supplied laterally via a coaxial conduit system.

Preferably, the plasma jet comprises at least two impedance transformers.

According to an inventive embodiment, the cannula tube is on

electrically connected to the closed end of the outer conductor, and connected behind it with a high-frequency signal source, thereby forming a lamda / 4 transformer (coaxial conductor with a length of approximately 90 degrees); and furthermore, connected between the high-frequency signal source connection and the open outer conductor end by at least one inductance with the outer conductor and thus at least one

Impedanztransformator forms, with another impedance transformer through the

End Capacity between cannula tube end and outer conductor is formed at the opening of the open outer conductor end, since a gap between the cannula tube end and the opening of the open outer conductor end is formed.

Preferably, the cannula tube is further, between the at least one

Inductance and the open outer conductor end connected by at least one further inductance with the outer conductor and thus forms a further impedance transformer.

The plasma jet according to the invention does not have the abovementioned disadvantages. In addition, it has many advantages that are highly relevant in practice.

The plasma jet has, in contrast to the laser beam, only a finite length. Thus omitted, in the applications, the elaborate safeguards typical for

Laser systems. In addition, no electrode removal occurs. The cannula tube construction allows the use of electrodes that are not made of tungsten, up to quite high powers are made. Thus, among other things, oxygen can also be used in the process. This plasma jet does not require a counter electrode and can thus also optimally process plastics and other non-conductors. Due to the microwave excitation, the energy flow of the plasma jet penetrates well oxide layers, which include the processing of eg

Aluminum simplified.

Further, the gas consumption in the implementation with the cannula is significantly lower than standard jets, which leads to an inexpensive use with it.

The fact that the cannula tube is substantially rectilinear, it can be easily cleaned.

This Hochfrequenzplasmajetkonstruktion invention can, in conjunction with the increasingly cheaper semiconductor generators, be made cheaper than the best alternatives (eg., Laser welding equipment) and is otherwise in the same cost frame as the established and used in the mass technique.

The Plasmajet of the invention is particularly suitable for the treatment with powders that can be passed through the cannula tube. In addition, thin wires, as an alternative to powders, may also be used as delivery or treatment material, e.g. for melting, welding or soldering. Care should then be taken to route the wires through the cannula tube at controllable delivery rates.

It has been found that, in particular, also rigid wires and fibers, such as e.g. Glass fibers or carbon fibers, or particles can be passed through the straight cannula tube, which can then be treated by the traversed plasma jet, e.g. ionised, purified, stabilized, carbonized, etc.

Another advantage of the plasma jet according to the invention is that a dielectric material, e.g. Glass or ceramic, preferably shaped as a tube, can be introduced into the cannula tube for insulation between the process material and the metallic cannula tube, which serves as an electrode.

In addition, such tube inserts can produce different jet jet diameter and thus energy densities.

According to a particularly preferred embodiment, additional energy can be supplied to the arc discharge by a suitable current source over the process material in order to noticeably increase the total plasma energy. These and other preferred embodiments will be further described hereinafter with reference to the accompanying drawings.

FIG. 1 is a schematic illustration of a plasma jet according to the invention, in section.

Figure 2 is a corresponding to the Plasmajet of Figure 1 electrical

Equivalent circuit.

The basic principle of the invention is shown in the sectional view in Fig. 1 am

Application example of a TEM coaxial conductor shown.

The housing of the invention Plasmajets is designed as a tubular outer conductor 16 which is closed at one end by an end cap 20 and at the opposite end to the plasma generation is open. The high-frequency energy (short RF energy) is supplied via the coaxial connector 12 with the circular metallic inner conductor 11 and the dielectric 18 located between the inner conductor 11 and the outer conductor 12. This RF connector is i.d.R. on a firm

Characteristic impedance (Zzu) designed.

10 is the circular configured as a cannula metallic inner conductor, which is connected to the coaxial feed line (with the characteristic impedance in the range of Zzu) is shown.

Furthermore, the cannula 10 is guided by the end cap 20 of the otherwise tubular metallic outer conductor 16, and extends to the open end of

Outside conductor, whereby a gap between Kanülenrohrende and opening of the open

Outside conductor end is formed.

Subsequently, in the middle region, the i.d.R. higher resistance inner conductor 15 and complete the i.d.R. Both 15 and 19 are constructed as a cannula and, in combination with the two inductors 13a and 13b, form the impedance transformer of the first two stages.

The transformer shown here has a three-stage impedance transformation. The third stage results from a portion of 19 and the final capacity at point 14 against the outer housing 16.

The length of the end cap up to the contact point between the cannula 10 and the inner conductor 11 is approximately 90 degrees (electrical length at the average operating frequency). As a result, the short circuit in the area of the end cap, which, inter alia, for a mechanical Stability ensures a neutral at the contact point between 10 and 11 transformed and thus has no noticeable effect on the electrical functionality.

The line length of 10 between the contact point between 10 and 11 and the coil terminal of 13a can be almost arbitrary, since the characteristic impedance is also in the range of the supply line Zzu. The inner conductors 15 and 19 have an electrical length of less than 180 °. That is, as long as no plasma has been ignited in the plasma region 14, the electrical input impedance Z to the line 10 via the subsequent

Network of 13a, 15, 13b and 19 transformed into a very high impedance (almost no load) to the point 14.

The structure shown in Fig. 1 thus has behind the coupling of

Microwave energy via the connector (12, 18) a line segment to the coil 13 a on. This is followed by a microwave circuit with a three-stage impedance transformation. The first two stages (13a and 15 as well as 13b and half of 19) are also referred to as autotransformers. The third stage (half of 19 and final capacity) is a gamma transformer.

The entire inner network (from a circuit engineering point of view)

Coupling unit and transformation stages can also be seen from Figure 2 and can be referred to hereinafter as the operating unit of the jet.

Ignition: These three transformers are designed at the ignition frequency so that the impedance of Zzu is transformed in several stages in the high kOhm or even better in the MOhm range. Since the injected power P is very little attenuated in this circuit, remains at the top almost the same power as at the entrance. However, due to the high end impedance Zend, the voltage Uend at the jet tip becomes due to the relationship:

Uend = (P Zend) (1) very high (often in the kV range). This high voltage and the associated very high electric field strengths trigger the ionization of the gas. If a noble gas is passed through the cannula (inter alia), then preferably only this is ionized. In this case, a slender plasma jet with very high energy density results. When air or a similar gas (e.g., pure nitrogen) or no gas is passed through the cannula, there is a relatively broad plasma that forms as a ball when there is no gas flow.

Operation: After the ignition has been made to a different frequency

be switched, which is designed for the operating condition. The plasma has the Footpoint impedance of Zin on. The transformers now need to be designed to transform Zzu's impedance to that of Zin. In this case, the plasma size is maximum and the losses in the SF jet are minimal.

The SF jet is unique in comparison to the previously known cannula jets in that the cannula passes straight through the jet. This construction corresponds to a spare circuit modified from the prior art. It allows u.a. Ceramic or

Introduce glass tubes into the cannula to prevent reaction or friction between the inside material (solid, powder, liquid or gaseous) and the outside (i.d.R.) metallic cannula tube.

For the realization of a radiator, there is a second gas supply line 17, the

mainly for cooling the jet, but also for generating a

Inert gas atmosphere can be used. If you only want to ignite or operate the jet in pulsed mode, then this supply line can be omitted. In this case, the entire interior or only a part may be filled by means of a dielectric, preferably a pressure-tight dielectric in the head region.

The inductors 13a and 13b are realized by thin wires between the inner conductor and the ground (outer case 16).

In the case of the plasma jet according to the invention, the cannula can be cleaned very simply due to the straight design. Blockages can be due to the design without

Rounding and transitions are easily prevented. Remelted cannulas are easy to ream.

As an alternative to the impedance transformers shown here as gamma and autotransformers, impedance transformers can also be used in the HF range

Resonators, various filters, lambda / 4-lines, taped lines as well as concentrated components can be used.

As can be seen from the above description, the Plasmajets invention can be easily used for the surface treatment with powders that can be passed through the cannula tube. In addition, thin wires, as an alternative to powders, may also be used as delivery or treatment material, e.g. for melting, welding or soldering.

In particular, rigid wires and fibers such as glass fibers or carbon fibers, or particles can be passed through the straight cannula tube, which then by the traversed plasma jet can be treated, eg ionised, cleaned, stabilized, carbonized etc.

As a variant, a dielectric material, e.g. Glass or ceramic, preferably formed as a tube, are introduced into the cannula tube, wherein the dielectric is used for insulation between the process material and the metallic cannula tube, which acts as an electrode.

Claims

claims

1. Atmosphärenplasmajet by a high-frequency signal in the MHz or GHz range operable comprehensive

a metallic substantially tubular outer conductor (16) which is closed at one end (20) and open at the opposite end (14) for plasma generation,

a cannula tube (10,15,18) as an electrode for plasma generation, wherein the cannula tube (10,15,18) passes through the outer conductor (16) substantially straight from one end (20) to the other (14) and the closed end (20) has a cannula tube entrance,

a coaxial line system (12, 18) configured to supply a high frequency signal in the Mhz or Ghz range laterally

wherein the cannula tube (10,15,19) at the closed end (20) of the outer conductor (16) is electrically conductively connected thereto

characterized in that

the cannula tube (10, 15, 19) behind it is directly metallically and electrically connected to a high-frequency signal source (12, 18), thereby forming a lambda / 4 transformer (coaxial conductor with a length of approximately 90 degrees), the cannula tube (10 , 15, 19), is connected between the high frequency signal source connection (12, 18) and the open outer conductor end (14) by at least one inductance (13a, 13b) with the outer conductor (16) and thus forms at least one impedance transformer

wherein another impedance transformer through the end capacity between cannula tube end (19) and outer conductor (16) at the opening of the open

Outside conductor end (14) is formed.

2. Atmosphärenplasmajet according to claim 1, characterized in that the

Further, the hypotube (10, 15, 19) is connected between the at least one inductance (13a) and the open outer conductor end (14) by at least one further inductance (13b) with the outer conductor (16) and thus another

Impedanztransformator forms.

3. Atmosphärenplasmajet according to claim 1 or 2, characterized in that the cannula tube (10,15,19) behind the connection of the respective inductance as

Inner conductor of a high-impedance coaxial line is executed.

4. Atmosphärenplasmajet according to one of claims 1 to 3, characterized in that the electrical length of the cannula tube at an average operating frequency in the range of about 20 to 70 MHz between two inductors is approximately 90 degrees.

5. Atmosphärenplasmajet according to one of the preceding claims characterized

in that a dielectric tube, preferably a ceramic or glass tube, is mounted in the cannula tube (10, 15, 19).

6. Atmosphärenplasmajet according to one of the preceding claims characterized

characterized in that the outer conductor (16) has a connecting piece (17) for a gas supply line for cooling the jet or providing a protective gas atmosphere.

7. Atmosphärenplasmajet according to one of claims 1 to 6, characterized in that the interior of the outer conductor is not or at least partially filled with dielectric.

8. Atmosphärenplasmajet according to one of claims 1 to 6, characterized in that the interior of the outer conductor not at all, in whole or in part with

Dielectric, preferably pressure-tight dielectric in the head region (14) is filled.

9. Using a high-frequency Plasmajets with substantially straight

Needle tube as electrode according to one of claims 1 to 8 for cutting or bonding workpieces or treating or coating

Workpiece surfaces.

10. Use according to claim 9, characterized in that treatment or coating material is passed through the cannula tube in the plasma jet.

11. A method for plasma treatment or coating of powder or particle, fiber, wire or tubular objects with a small cross-section, characterized in that said objects by a rectilinear designed as an electrode cannula tube of a Plasmajets according to any one of claims 1 to 8, wherein said objects are passed through the plasma jet and thus treated or coated.