EP3291651B1 - Device and method for creating atmospheric plasma - Google Patents

Description

The invention relates to a device for generating an atmospheric plasma according to the features of claim 1. The invention also relates to a method for generating an atmospheric plasma according to claim 5.

For the treatment of, for example, surfaces made of plastic, metal, ceramics, etc. for the purpose of cleaning, surface activation, polymerisation, germ reduction and the like, it is known to apply an atmospheric plasma to them. By cleaning and/or activating the surface by means of an atmospheric plasma, it can be better wetted with a liquid or an adhesive, for example.

A plasma head with a transformer and a plasma nozzle is used to generate an atmospheric plasma. A process gas in the plasma nozzle is ionized by a discharge due to the high voltage generated by the transformer. The process gas then exits the nozzle as a directed plasma jet or plasma flame.

In order to avoid problems such as cable breaks, breakdowns or power losses, it is known to integrate the transformer and the plasma nozzle in a common plasma head. Due to this compact design of the plasma head, long cables and electronics can be dispensed with, which reduces the risk of cable breaks or breakdowns.

The power loss of the transformer, which accumulates as heat in the housing of the plasma head, has proven to be particularly disadvantageous in this compact design. This heat generation can be so great that the transformer fails or is damaged. The generation of plasma is thus influenced by this heat development.

Known plasma systems, such as in U.S. 2015/0054405 A1 described, have a cooling in which the heat is dissipated by convection from the housing of the plasma head. However, this type of cooling is only sufficient for certain designs or sizes and installation positions of the plasma head. For example, the cooling of the transformer by pure convection proves to be insufficient when the plasma head is used continuously.

The invention is therefore based on the object of creating a device and a method for generating an atmospheric plasma, with which stable and reliable operation is ensured.

A device for solving this problem has the features of claim 1.

Accordingly, it is provided that a plasma head to which a transformer and at least one plasma nozzle is assigned, the transformer and the plasma nozzle forming a spatial unit, having a supply line for a medium flowing through for active temperature control of the plasma head and being in a wall of a housing of the plasma head at least one channel for guiding the medium is arranged. In this case, the channel extends at least in regions over the wall of the plasma head, being connected to at least one inlet. The medium is the process gas. The plasma head can be actively tempered by the flowing medium. Accordingly, depending on the design or the size and the operation of the plasma head, it can be actively temperature-controlled. The flowing medium constantly transports heat away from the plasma head. The plasma head can be kept at a stable temperature during the entire operating time due to the subsequent flow of the medium. A temperature can thus be generated in the plasma head via the medium flowing through, at which a maximum yield of plasma is achieved and at the same time the plasma head works in a particularly stable and reliable manner.

The invention provides that as a medium for temperature control, in particular for cooling, the plasma head, preferably the transformer, an electrode or a Plasma nozzle the process gas itself can be used. the

The use of the process gas as a cooling medium is particularly advantageous since it has to be fed to the plasma head anyway. According to the invention, the process gas first flows through the area around the transformer before it is fed to the plasma nozzle for plasma generation. The temperature of the process gas, which is increased by absorbing the thermal energy, has no effect whatsoever on the efficiency of the plasma formation. For a particularly efficient mode of operation of the plasma head, it can also be advantageous according to the invention if the process gas is mixed with another medium which has proven to be particularly good as a cooling medium. In this way, the heat can be dissipated quickly from the plasma head and a plasma flame can be generated at the same time, without having to install an additional line for the cooling medium on the plasma head.

A particularly advantageous embodiment of the present invention can provide that in a housing, preferably in a wall of the housing, a channel, in particular meandering, for guiding the medium is arranged, which at least partially extends over the wall of the housing and is connected to the at least connected to a supply line. By guiding the channel through the wall of the plasma head, the medium remains in contact with the wall for a particularly long time, which means that the medium can absorb a particularly large amount of thermal energy from the transformer. In particular, a meandering configuration of the channel has proven to be particularly efficient for the transfer of thermal energy to the medium. One end of the channel represents a supply line for the medium, for example for the process gas. The second end of the channel can either be free, so that the gas is fed into the atmosphere, or it can be connected to the supply line for the plasma nozzle, so that the medium is used directly as a process gas for plasma generation. With this design, the compact design of the plasma head can be maintained.

The meandering channel for the medium can be realized by parallel, perpendicular, in particular parallel to a longitudinal axis of the housing, bores in the wall of the housing. The channels can initially be open to the end faces of the hollow-cylindrical housing. These openings can be designed to be closable by a base or cover part of the housing in such a way that alternately two adjacent openings are connected to each other or isolated from each other, so that the meandering channel is formed in the wall. The base or cover part of the housing is, for example, screwed or glued to the housing. A further exemplary embodiment can provide for the channel to be designed as a screw in the wall of the housing. Such a housing with a screw-like channel in the wall can be produced, for example, using an additive process such as a 3D printer.

It can also be provided that the channel is designed as an evaporator for a liquid medium. In this exemplary embodiment, a liquid medium is first fed into the channel in order to then be fed into the plasma nozzle as a gas. Since liquid media generally have a higher heat capacity than gases, the heat transfer between the transformer or the wall and the medium can be increased and at the same time the medium can be used at least partially as a process gas. This also enables layer deposition.

Preferably, the present invention can further provide that at least one heat sink, in particular cooling ribs, along which the medium can be guided, is arranged on an outside of the wall or the housing. As an alternative to the formation of channels in the wall, it can also have cooling bodies on the outside. These heat sinks can then in turn be actively cooled by applying a cooling medium, preferably by a fan.

A method for solving the problem mentioned at the outset has the measures of claim 5 . Accordingly, it is provided that a plasma head, in whose housing a transformer and at least one plasma nozzle is arranged, is actively temperature-controlled by a flowing medium, the medium being guided through a channel in a wall of a housing of the plasma head for the active temperature control of the plasma head , whereby the process gas is used as the medium. With this active temperature control of the plasma head, process heat from the transformer can be actively and efficiently dissipated. Depending on the size and design of the plasma head, a different heat development of the transformer is to be expected. By regulating the flow of the medium, the heat dissipation from the plasma head can be actively controlled so that the plasma head can be operated at an optimal operating temperature. At the optimum operating temperature, the plasma head is particularly reliable and stable.

A further exemplary embodiment of the present invention can provide that for the active temperature control, preferably cooling, of the plasma head, the medium is guided through the housing, preferably through a wall of the housing, of the plasma head, in particular through a channel in the wall of the plasma head and the passage of the medium is controlled by a valve so that the flow depends on the temperature of the plasma head.

Preferably, the present invention can further provide that, for the active temperature control, the medium guided through the wall is preheated and/or is guided through the wall under a predetermined pressure. For this purpose, it can be provided that a temperature sensor is arranged in the plasma head, which measures the temperature and transmits it to a control unit, which accordingly pre-cools or heats the medium. In addition to the temperature of the medium, the pressure can also be varied. For example, when there is a large amount of thermal energy to be dissipated, the pressure of the medium can be increased to control the temperature of the plasma head. By increasing the pressure of the medium, the flow is increased, so that the thermal energy to be absorbed per unit of time is increased. Likewise, the pressure of the medium with which it is guided through the channel can be reduced if only a small amount of thermal energy has to be removed from the plasma head. This pre-temperature control and varying the pressure ensure particularly efficient and therefore reliable and stable operation of the plasma head.

In addition, a further advantageous exemplary embodiment of the present invention can provide that the medium for tempering the plasma head is applied to an outside of the wall. Applying the medium to the outside of the housing or the wall in this way creates a particularly simple way of cooling the plasma head.

Fig. 1

einen Querschnitt durch einen schematisch dargestellten Plasmakopf,

Fig. 2

einen Querschnitt durch eine schematische Darstellung einer Wandung des Plasmakopfes, und

Fig. 3

einen Querschnitt durch ein weiteres Ausführungsbeispiel eines Plasmakopfes.

A preferred embodiment of the present invention is explained in more detail below with reference to the drawings. In this show:

1

a cross section through a plasma head shown schematically,

2

a cross section through a schematic representation of a wall of the plasma head, and

3

a cross section through another embodiment of a plasma head.

An embodiment of a plasma head 10 according to the invention is shown in FIG 1 shown highly schematized in cross section. Essentially, the plasma head 10 consists of a housing 11, inside which a transformer 12 and a plasma nozzle 13 are arranged. The transformer 12 is enclosed by an insulator 14 and connected to a voltage source 15 . The high voltage required to ignite the plasma is generated by the transformer 12 and the voltage source 15 . A wall 23 of the housing 11 of the plasma head 10 is connected to a ground 29 .

The plasma nozzle 13 has an electrode 16 which is coupled to the transformer 12 . The tip of this needle-shaped electrode 16 points in the direction of a ring electrode 17 serving as an outlet for the plasma. Process gas is conducted into the nozzle volume 19 through a process gas inlet 18 . The process gas is shown schematically as arrow 20 here. In reality, the nozzle volume 19 is filled almost homogeneously by a permanent flow of the process gas 18 .

An electrical discharge between the electrode 16 and the ring electrode 17 causes the process gas to be ionized, symbolically represented here as a lightning bolt 21 . The ionized gas leaves the plasma nozzle 13 through the ring electrode 17 as a plasma jet 22 or as a plasma flame.

At least one channel 24 is formed in the wall 23 of the plasma head 10 . In the exemplary embodiment shown here, this channel 24 extends in a meandering manner through the entire wall 23. In 2 a rolled-up wall 23 of the plasma head 10 is shown schematically, so that the meandering course of the channel 24 in the wall 23 becomes clear. The channel 24 has an inlet 25 and an outlet 26 . According to the invention, a medium is let into the inlet 25 via a valve (not shown) or from a storage volume, so that the medium flows at a predetermined pressure through the channel 24 in the direction of the outlet 26 (see arrow 27).

The medium flowing through, which is the process gas, dissipates the heat developed by the transformer 12 . After this process gas has flowed through the channel 24 and has absorbed heat energy from the transformer 12 , it is conducted through the process gas inlet 18 into the nozzle volume 19 by a connecting means 28 shown here in broken lines. The connecting means 18 can be, for example, a hose or a short piece of pipe. This connecting means 18 can also be integrated in the housing 11 or the plasma head 10 . The channel 24 is integrated into the housing 11 or into the wall 23 .

Depending on the size or design or the thermal energy developed by the transformer 12, different media can be used as a coolant. In addition, it is conceivable that, depending on the thermal energy developed, the process gas is pre-cooled or is admitted into the channel 24 at an increased pressure. According to the invention, a control device, not shown, is used for this purpose, which determines the temperature in the plasma head 10 via a temperature sensor, also not shown, in the plasma head 10 and controls the inflow of the process gas in the channel 24 accordingly.

Next to the in the Figures 1 and 2 illustrated embodiment of a channel 24 shows the 3 another embodiment of a channel 30. In the in 3 illustrated channel 30, the medium, as previously at the in 1 described embodiment described, fed to the channel 30 through an inlet, not shown, and fed to the nozzle volume 19 via a connecting means 28 in the manner described above. In the second exemplary embodiment, the channel 30 is arranged in the wall 23 of the plasma head 10 in the manner of a screw. This screw-like arrangement of the channel 30 allows a particularly long contact surface to be produced between the medium and the wall 23, so that the thermal energy is transferred to the medium in a particularly efficient manner.

In addition to the exemplary embodiments shown here, it is also conceivable for the wall 23 to be assigned cooling bodies (not shown), such as cooling fins, on its outer side 31 . The thermal energy of the transformer 12 is also effectively dissipated from the plasma head 10 through these cooling ribs, around which a medium for cooling can also flow, for example.

Claims (7)

1. Apparatus for generating an atmospheric plasma with a plasma head (10) which has a transformer (12) for generating a high voltage and at least one plasma nozzle (13) which can be supplied with a process gas for plasma generation, wherein the transformer (12) and at least one plasma nozzle (13) form a spatial unit and wherein the plasma head (10) has at least one supply line for a medium that is flowing through, the medium being the process gas, for active temperature control of the plasma head (10), characterized in that in a wall (23) of a housing (11) of the plasma head (10) there is arranged at least one channel (24, 30) for guiding the medium, which extends at least in regions over the wall (23) of the plasma head (10) and which is connected to at least one inlet (25).
2. Apparatus for generating an atmospheric plasma according to Claim 1, wherein in the wall (23) of the plasma head (10) there is arranged at least one meandering channel (24, 30) for guiding the medium, which extends at least in regions over the wall (23) of the plasma head (10) and which is connected to at least one inlet (25).
3. Apparatus for generating an atmospheric plasma according to Claim 1 or 2, wherein the channel (24, 30) is in the form of parallel bores, in particular bores arranged parallel to a longitudinal axis of the housing (11), in the wall (23) of the housing (11), wherein the open bores at the face sides of the, in particular hollowcylindrical, housing (11) are connectable or isolatable from one another by way of a base or cover part, so that the meandering channel (24) is formed in the wall (23).
4. Apparatus for generating an atmospheric plasma according to any of the preceding claims, wherein on an outer side (31) of housing (11) there are arranged at least one cooling body, particular cooling fins, along which the medium can be guided.
5. Method for generating an atmospheric plasma with a transformer (12) for generating a high voltage and with at least one plasma nozzle (13) which is supplied with a process gas for generation of the plasma, wherein the transformer (12) and the at least one plasma nozzle (13) form a plasma head (10) and the plasma head (10) is actively temperature-controlled by a flowing medium, wherein the medium used is the process gas, characterized in that for the active temperature control of the plasma head (10) the medium is conducted through a channel (24, 30) in a wall (23) of a housing (11) of the plasma head (10) .
6. Method for generating an atmospheric plasma according to Claim 5, wherein, for the active temperature control, the medium guided through the wall (23) is preadjusted to a temperature and/or guided through the channel (24, 30) under a predetermined pressure.
7. Method for generating an atmospheric plasma according to Claim 5 or 6, wherein an outer side (31) of the housing (11) is exposed to the medium for temperature control of the plasma head (10).

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