Apparatus and method for reducing oxides on the surface of a workpiece

Abstract

The present invention relates to an apparatus (50, 150) for reducing oxides on a workpiece surface, comprising a treatment tunnel (52) extending from an entrance opening (54) to an exit opening (56), a reaction zone (82) disposed within the treatment tunnel (52), a plasma nozzle (2, 84) configured to generate an atmospheric plasma jet (28, 88), a reducing gas supply (74) configured to introduce a reducing gas (23) into the reaction zone (82), and a transport device (58) configured to transport a workpiece (80) through the treatment tunnel (52), the plasma nozzle (2, 84) being arranged and configured in such a way that during operation the atmospheric plasma jet (28, 88) is introduced into the reaction zone (82). The present invention further relates to the use of the apparatus (50, 150) and to a method for reducing oxides on a workpiece surface.

Description

Technical Field

[0006] , , ,

[0001] The present invention relates to an apparatus and a method for reducing oxides on the surface of a workpiece. The present invention further relates to the use of such an apparatus.

Background Art

[0002] It is known from the prior art to reduce oxides on the surface of a metallic workpiece using low-pressure plasma. For example, the oxides on the surface of the workpiece are reduced in order to achieve better wettability of the workpiece surface or to enable the generation of an electrical connection, for example a soldered connection. This is particularly advantageous for subsequent process steps on the workpiece, such as joining or soldering to other workpieces. For example, Patent Document 1 describes a method for removing oxides by low-pressure plasma treatment. However, such low-pressure methods have the disadvantage that, due to the required detachment operations, they can only be integrated into continuous production activities with a great deal of technical effort.

[0003] Attempts have also been made to use atmospheric plasma for the reduction of metal surfaces. However, some of these attempts have not led to the desired results.

[0004] From such a background, the present invention is based on the object of providing an improved apparatus and an improved method for reducing oxides on the surface of a workpiece, which are particularly suitable for in-line use.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Means for Solving the Problems

[0006] According to the present invention, this objective is solved by an apparatus for reducing oxides on the surface of a workpiece, comprising a processing tunnel extending from an inlet opening to an outlet opening, a reaction region located within the processing tunnel, a plasma nozzle configured to generate an atmospheric plasma jet, a reducing gas supply unit configured to introduce a reducing gas into the reaction region, and a transport device configured to transport a workpiece through the processing tunnel, wherein the plasma nozzle is positioned and configured to introduce an atmospheric plasma jet into the reaction region during operation.

[0007] By introducing a plasma jet into the reaction region, the gas volume within the reaction region can be excited or activated, and oxides on the surface of the workpiece being transported through the reaction region are reduced.

[0008] Preferably, the plasma nozzle is also positioned and configured such that the workpiece, which is transported through the processing tunnel by a transport device during operation, is exposed to the atmospheric plasma jet within the reaction region. By directing the atmospheric plasma jet onto the workpiece during operation, the effect of the plasma jet on the workpiece surface can be enhanced, thereby achieving more effective oxide reduction. Furthermore, by exposing the workpiece to the plasma jet, the heat input into the workpiece during reduction can be increased, thereby accelerating the reduction process.

[0009] In in-line operations using plasma for metal surface reduction, one problem is that the workpiece surface being reduced by plasma has a strong tendency to re-oxidize, especially immediately after plasma treatment, reducing the effectiveness of the previous reduction. In particular, experiments have shown that exposing the metal surface to an atmospheric plasma jet to reduce oxides causes the metal surface to heat up significantly, which promotes subsequent re-oxidation in an oxygen-containing atmosphere. Furthermore, the interaction between the atmospheric plasma and the metal surface can alter the metal surface, especially by activating it, which in turn promotes re-oxidation.

[0010] An apparatus for plasma reduction of oxides on a workpiece surface is provided, by arranging a reaction region into which an atmospheric plasma jet is introduced, particularly, a reaction region in which the workpiece surface is exposed to the atmospheric plasma jet to reduce oxides, within a processing tunnel through which the workpiece is transported by a transport device. This apparatus can be easily integrated into a continuously operating in-line process, particularly a manufacturing process. In particular, workpieces to be processed can be transported successively through the reaction region in a controlled manner and subjected to reduction treatment there. On the other hand, the reaction region is isolated from the direct influence of the environment by the processing tunnel. In this way, the environmental conditions acting on the processed workpiece can be better controlled within the reaction region and in a portion of the processing tunnel following the reaction region, and the re-oxidation process can be reduced. In particular, it becomes easier to maintain a low-oxygen or oxygen-free reducing atmosphere within the reaction region and in a portion of the processing tunnel following it, thereby reducing or preventing re-oxidation of the workpiece surface immediately after reduction treatment.

[0011] The apparatus may have a housing, such as a metal housing, that forms a processing tunnel. During operation, the workpiece to be processed enters the processing tunnel through an inlet opening and, after processing in the reaction area, exits the processing tunnel again through an outlet opening. Because there is no need for loading and unloading steps compared to vacuum or low-pressure based processing apparatuses, the apparatus is very suitable for inline operation. The inlet and / or outlet openings may be designed as simple openings through which the workpiece to be processed enters and exits the processing tunnel. Optionally, curtains, such as strip curtains, may be provided at the inlet and / or outlet openings to further separate the atmosphere inside the processing tunnel from the environment.

[0012] In particular, the treatment tunnel is at approximately atmospheric pressure. To reduce or prevent oxygen-containing air from the environment from entering the treatment tunnel, there may be a slight overpressure inside the treatment tunnel compared to the ambient pressure. This overpressure may be created, for example, through a reducing gas supply unit or through individual gas supply units such as a purging gas supply unit.

[0013] Preferably, the processing tunnel has a predetermined minimum length at least between the inlet opening and the reaction region, and / or between the reaction region and the outlet opening. This minimum length may be, for example, 5 cm, preferably 10 cm, and more preferably 20 cm. For example, the distance between the inlet opening and the reaction region, and / or the distance between the reaction region and the outlet opening may be in the range of 5 to 50 cm. In this way, the influence of the ambient atmosphere on the workpiece during or immediately after the reduction treatment is reduced. Preferably, the minimum length is greater than the height of the processing tunnel.

[0014] The processing tunnel may have a width ranging from, for example, a few centimeters, e.g., 10 cm, to a few meters, e.g., 3 m, and / or a height ranging from a few centimeters, e.g., 5 cm, to several tens of centimeters, e.g., 20 cm. In particular, the dimensions of the processing tunnel may be adapted to the dimensions of the workpiece to be processed.

[0015] The processing tunnel preferably has a reduced cross-section between the inlet opening and the reaction region, and / or between the reaction region and the outlet opening, compared to the reaction region. In this way, the influence of the ambient atmosphere on the workpiece during or immediately after the reduction treatment can be further reduced.

[0016] The plasma nozzle is configured to generate an atmospheric plasma jet. For this purpose, the plasma nozzle preferably has a working gas supply unit for supplying working gas to the plasma nozzle and a nozzle opening from which the plasma jet emerges during operation. The atmospheric plasma jet operates within the atmospheric pressure range, particularly at ambient pressure or slightly overpressure. This eliminates the need for a complex negative pressure environment. To apply the atmospheric plasma jet within the reaction region to a workpiece being transported through a processing tunnel by a transport device during operation, the plasma nozzle may preferably be located within or in the reaction region. For example, the housing of the apparatus may have a container in the reaction region into which the plasma nozzle is inserted. Furthermore, the processing tunnel within the reaction region may have a plasma jet inlet opening connected to the nozzle opening of the plasma nozzle, allowing the plasma jet to enter the reaction region during operation. The plasma jet inlet opening and / or the nozzle opening of the plasma nozzle are preferably positioned so that, during operation, the plasma jet is directed toward the area of ​​the transport device from which the workpiece is transported through the reaction region.

[0017] In particular, the conveying device is configured to transport the workpiece to be processed from an inlet opening through a processing tunnel to an outlet opening. For example, the conveying device may be designed as a conveyor belt capable of transporting the workpiece to be processed from an inlet opening through a processing tunnel to an outlet opening. The conveying device may also be part of a larger conveying system in an inline process with several stations. For example, a conveyor belt may be provided through which the workpiece is transported via various processing and / or treatment stations, one of which may be an apparatus for reducing oxides on the surface of the workpiece, as described herein.

[0018] The transport device preferably has a drive with adjustable transport speed. In this way, the processing time of the workpiece within the reaction area can be specifically adjusted. For example, good reduction results on the workpiece surface have been achieved at transport speeds in the range of 0.1 to 10 m / min, particularly in the range of 0.3 to 0.6 m / min. The transport device may be configured to transport the workpiece through the processing tunnel at a constant speed. Alternatively, the transport device may be configured to slow down or stop the transport of the workpiece for a specific time within a specific area of ​​the processing tunnel, for example, within the reaction area. In this way, the reduction process of the workpiece can be affected.

[0019] The reducing gas supply unit is configured to introduce reducing gas into the reaction region. For this purpose, the reducing gas supply unit may have, in particular, a reducing gas source for providing the reducing gas, such as a gas cylinder containing the reducing gas, and a reducing gas line through which the reducing gas is introduced from the reducing gas source into the reaction region. The reducing gas supply unit may be configured to introduce the reducing gas into the reaction region at a predetermined or predetermined gas supply rate. For this purpose, the reducing gas supply unit may have, for example, an adjustable valve. In this way, the gas supply rate may be adjusted in a targeted manner, for example, to suit the material of the workpiece to be processed and / or to suit the speed of the conveying device. A suitable gas supply rate may be, for example, in the range of 5 to 50 l / min, preferably 20 to 40 l / min, and particularly preferably about 35 l / min. As a result, sufficient reducing gas can be utilized for reduction, while simultaneously preventing re-oxidation.

[0020] The reducing gas is preferably a hydrogen-containing gas, such as a mixture of hydrogen and an inert gas like nitrogen or argon.

[0021] When dissociated hydrogen is provided on the oxidized metal surface by a plasma process, it has been found that the reduction of the metal can be carried out at a relatively low temperature. In this way, the surface of a workpiece made of a metal with a low melting point, such as tin with a melting point of about 230 °C, can be effectively reduced.

[0022] For the effective reduction of oxides on the workpiece surface, especially on the surface of a metal workpiece, it has been found to be particularly advantageous that the hydrogen content of the reducing gas is 1 to 10% by volume, preferably 2 to 5% by volume. As further components of the working gas, in particular, nitrogen and argon may also be present. The inert gas is hardly involved in the chemical reaction and is therefore particularly suitable as a carrier gas, for example for hydrogen as the reducing gas, and is thus particularly advantageous as the working gas. For example, forming gas with a hydrogen (H2) content of 5% by volume and a nitrogen (N2) content of 95% by volume may be regarded as the reducing gas.

[0023] The reducing gas is in particular oxygen-free or has an oxygen content of less than 1% by volume, especially less than 0.3% by volume.

[0024] Furthermore, according to the present invention, the above object is solved by using the above-described device or an embodiment thereof for reducing oxides on the workpiece surface, especially on the surface of a metal workpiece.

[0025] The above object is further a method for reducing oxides on the workpiece surface by using the above-described device or an embodiment thereof according to the present invention, wherein one or more workpieces are conveyed through a processing tunnel by a conveying device, an atmospheric plasma jet is generated by a plasma nozzle, a reducing gas is introduced into the reaction region, and the atmospheric plasma jet is introduced into the reaction region.

[0026] Preferably, one or more workpieces conveyed through the processing tunnel are exposed to the atmospheric plasma jet in the reaction region.

[0027] In particular, this apparatus and method serve to reduce oxides on the surface of a workpiece that is at least partially made of metal or a metal alloy, the surface of the workpiece being at least partially metallic. The metal may be, for example, aluminum, copper, silver, iron, nickel, titanium, chromium or tin. More preferably, the apparatus is used within an in-line process where the treated workpiece surface subsequently undergoes a soldering process.

[0028] By reducing oxides on the surface of the workpiece to be soldered using the apparatus or method according to the invention, an improvement in the wetting of the workpiece surface with solder is achieved, so that less flux needs to be used, or it has even been found that it is possible to do without flux altogether. This enables a more environmentally friendly, less harmful to health and more cost-effective soldering process.

[0029] The various embodiments of the apparatus, its use, and the method are described below. Each individual embodiment is applied independently of the others to the apparatus, its use, and the method. Furthermore, the individual embodiments may be combined with each other.

[0030] In one embodiment, the plasma nozzle is configured to generate an atmospheric plasma jet by means of a high-frequency, high-voltage discharge, particularly between at least two electrodes. In particular, the plasma nozzle may be configured to generate a plasma jet by means of a high-frequency arc discharge in an operating gas. The plasma jet generated in this way can be easily adjusted and has been found to be very effective in reducing oxides on metallic surfaces.

[0031] In order to generate an arc-shaped discharge, at least two electrodes and a voltage source for applying a high-frequency high voltage to these electrodes may be provided. The high-frequency high voltage for generating the high-frequency arc-shaped discharge has a voltage intensity in the range of 1 to 100 kV, preferably 1 to 50 kV, more preferably 10 to 50 kV, and a frequency of 1 to 300 kHz, particularly 1 to 100 kHz, preferably 10 to 100 kHz, more preferably 10 to 50 kHz.

[0032] Furthermore, the plasma nozzle may be configured to generate an atmospheric plasma jet by dielectric barrier discharge (DBD). Due to the low temperature of the plasma jet generated by DBD, this discharge method is particularly suitable for processing temperature-sensitive surfaces. To generate a dielectric barrier discharge, at least two electrodes and a dielectric placed between these electrodes may be provided. This dielectric prevents direct discharge between the two electrodes. Preferably, one of the electrodes is grounded. Furthermore, a voltage source is provided to apply a high-frequency high voltage to the electrodes, for example, with a voltage intensity in the range of 5 to 15 kV and a voltage frequency in the range of 7.5 to 25 kHz, particularly in the range of 13 to 14 kHz.

[0033] In a further embodiment of the apparatus, the reducing gas supply unit is configured to supply the reducing gas to the plasma nozzle as a working gas. In a corresponding embodiment of the method, the reducing gas is sent into the plasma nozzle as a working gas. In this way, the reducing gas can be directly introduced into the reaction region through the plasma nozzle, eliminating the need for a separate reducing gas inlet opening from the plasma nozzle into the reaction region. Alternatively, the reducing gas supply unit may have a separate reducing gas inlet opening from the plasma nozzle in order to introduce the reducing gas into the reaction region. By supplying the reducing gas to the plasma nozzle as a working gas, strong excitation of the reducing gas occurs within the plasma nozzle, thereby achieving a strong reducing effect.

[0034] In a further embodiment of the apparatus, the reducing gas supply unit is configured to introduce the reducing gas into the reaction region through a reducing gas inlet opening separate from the plasma nozzle. In a corresponding embodiment of the method, the reducing gas is introduced into the reaction region through a reducing gas inlet opening separate from the plasma nozzle. In this way, the reducing gas flow rate may be adjusted independently of the working gas flow rate of the plasma nozzle. Furthermore, the working gas of the plasma nozzle may be freely selected in this manner. To extend the life of the plasma nozzle, for example, an inert gas may be used as the working gas of the plasma nozzle in this manner. On the other hand, the reducing gas supply unit may also be configured to perform both the supply of the reaction gas as the working gas to the plasma nozzle and the introduction of the reaction gas into the reaction region through a reducing gas inlet opening separate from the plasma nozzle.

[0035] The reducing gas supply unit is preferably configured to introduce the reducing gas into the reaction region under atmospheric pressure or under overpressure. In this way, the reaction region can be effectively filled with the reducing gas so that, in particular, the workpiece being transported through the reaction region during operation is surrounded by the gas and reduced.

[0036] In further embodiments, a purge gas supply unit is provided, configured to introduce a purge gas into the processing tunnel, particularly into the reaction region. Preferably, the purge gas supply unit is configured to introduce a purge gas into the processing tunnel, particularly into the reaction region, under atmospheric pressure or under superpressure. The purge gas may be used to purge the processing tunnel, particularly the reaction region, before, during, and / or after operation in order to reduce the oxygen content in the processing tunnel. For this purpose, an oxygen-free purging gas or a purging gas with an oxygen content of less than 1 volume%, preferably less than 0.3 volume%, is used. Preferably, an inert gas such as argon or nitrogen is used as the purge gas. By introducing a purging gas into the processing tunnel, particularly into the reaction region, the re-oxidation of the reduced workpiece surface can be reduced or even avoided, so that the apparatus can achieve an overall improvement in the reduction of oxides on the workpiece surface.

[0037] An appropriate gas supply rate for purge gas is, for example, within the range of 1 to 30 l / min, preferably 5 to 15 l / min.

[0038] In particular, the purge gas supply unit may have a purge gas source for supplying purge gas, such as a gas cylinder containing purge gas, and a purge gas line through which the purge gas is introduced from the purge gas source into the reaction region.

[0039] It can be particularly advantageous for the purge gas supply unit to be configured to introduce the purge gas into the processing tunnel, especially into the reaction region, before the plasma nozzle is in operation. In this way, the processing tunnel, especially the reaction region, is purged even before the workpiece surface is exposed to the atmospheric plasma jet, and in particular, oxygen is removed, further reducing re-oxidation of the reduced workpiece surface.

[0040] The purge gas supply unit may be configured to introduce the purge gas into the processing tunnel, particularly into the reaction area, through a separate purge gas supply unit. The purge gas supply unit may also be configured to introduce the purge gas into the reaction area through a provided reduction gas inlet opening. In this way, the reduction gas and the purge gas may be introduced into the reaction area simultaneously or continuously through the same reduction gas inlet opening. In particular, the reduction gas supply unit and the purge gas supply unit may be combined with each other, for example, a gas supply unit configured to introduce the reduction gas and / or purge gas into the reaction area may be provided.

[0041] In a further embodiment, the plasma nozzle has a nozzle head from which a plasma jet emerges during operation and which rotates around a rotation axis during operation. During operation, the plasma jet emerges from the nozzle head, particularly at a certain oblique angle with respect to the rotation axis.

[0042] In this way, a larger area can be effectively covered using a plasma jet, allowing for an increase in the gas volume excited by the plasma jet. In particular, the portion of the workpiece surface of the workpiece being transported through the reaction region that is exposed to the plasma jet can be increased. In this way, a larger area of ​​the workpiece surface can undergo reduction treatment in a shorter time.

[0043] In a further embodiment, heating and / or cooling elements are provided, configured to heat and / or cool the workpiece being transported through the processing tunnel.

[0044] In particular, by providing a heating element in the area between the inlet opening and the reaction region of the processing tunnel, the workpiece can be preheated for reduction treatment within the processing chamber, thereby increasing the reduction effect. Furthermore, heating the workpiece can improve the depth effect of the reduction of oxides on the workpiece surface. This is because the depth effect depends, in particular, on the diffusion of atomic hydrogen into the workpiece surface, and diffusion is promoted at higher temperatures.

[0045] In particular, by providing a cooling element in the area between the reaction region and the outlet opening of the processing tunnel, the thermal energy introduced by the plasma treatment can be removed from the workpiece, at least partially. In this way, the workpiece will have a lower temperature when it comes into contact with oxygen again, thereby effectively reducing or even greatly avoiding re-oxidation of the workpiece surface. In particular, a lower temperature on the workpiece surface leads to a lower oxidation rate on the workpiece surface.

[0046] The heating and / or cooling elements may be designed as active or passive elements. Furthermore, temperature control may be provided, and in particular, controlled heating and / or controlled cooling elements may be used. The temperature of the heating element may be set using a control element, depending on the material of the workpiece, so as not to exceed the melting point and thus preventing deterioration of the workpiece. This is particularly advantageous when reducing the surface of metals with low melting points, such as tin.

[0047] In further embodiments, a plasma nozzle or optionally provided individual coating plasma nozzles are configured to provide a protective coating by plasma coating to a workpiece that is transported through a reaction region during operation and exposed to an atmospheric plasma jet within the reaction region. For this purpose, a precursor feed is provided, in particular, configured to introduce a precursor into the plasma jet generated by the plasma nozzle or coating plasma nozzle.

[0048] In this way, to protect the reduced workpiece surface from re-oxidation, a protective layer can be provided to the workpiece after the reduction of oxides on the workpiece surface by plasma coating using a plasma nozzle or optionally an additional coating plasma nozzle.

[0049] The protective layer may be an organic layer, such as a hydrocarbon-containing layer, or particularly a plastic layer. Preferably, the protective layer is an organosilicon protective layer. By covering the workpiece surface with an organic protective layer, oxygen can be isolated from the workpiece surface, and the formation of metal oxides by metal atoms on the workpiece surface is avoided.

[0050] The protective layer may also be an inorganic layer, particularly a silane layer, or a metal or semiconductor oxide layer such as a TiO2 or SiO2 layer. It has been found that oxidation of the metal on the workpiece surface can also be prevented by such a protective layer. In particular, it has been found that oxygen contained as an oxide within the metal or semiconductor oxide layer does not readily bond with the metal on the workpiece surface. Even if the metal or semiconductor oxide layer is very thin, it can still provide good oxidation prevention for the workpiece surface.

[0051] To prevent oxidation of the workpiece surface while a metal or semiconductor oxide layer is deposited as a protective layer, a plasma nozzle or optionally an additional coating plasma nozzle may be configured to generate a plasma jet, which may be generated by the plasma nozzle or coating plasma nozzle using an oxygen-free working gas. In this case, an oxygen-containing precursor may be used to form the metal or semiconductor oxide layer, and the oxygen-containing precursor is introduced, for example, into the plasma jet generated by the plasma nozzle or coating plasma nozzle. It has been found that oxidation of the workpiece surface by oxygen contained in the precursor does not actually occur because the formation of the metal or semiconductor oxide layer from the precursor is very rapid.

[0052] The protective layer may be removed before subsequent processing steps, or alternatively, it may be left on the workpiece surface.

[0053] Plasma coating, particularly the application of layers by plasma polymerization, is generally known and therefore does not need to be described in detail here.

[0054] Preferably, an organic precursor or organosilicon precursor is used to produce an organic protective layer, particularly an organosilicon protective layer.

[0055] Suitable precursors include hexamethyldisiloxane (HMDSO), tetraethyl orthosilicate (TEOS), 3-(trimethoxysilyl)propyl methacrylate (MEMO), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), and generally encompass aminosilanes, triethoxysilanes, organosilanes, organosilanols, siloxanes, polysilazanes, and carbosilanesilanes.

[0056] Other possible precursors include functionalized organosilicon compounds, particularly those comprising epoxy groups such as 3-glycidoxypropyltrimethoxysilane, acrylate groups such as γ-methacryloxypropyltrimethoxysilane, amino groups such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, or [3-(2-aminoethyl)aminopropyl]trimethoxysilane, vinyl groups such as vinyltrimethoxysilane or 1,3-divinyltetramethyldisiloxane, thiol groups such as (3-mercaptopropyl)trimethoxysilane, or sulfan groups such as bis[3-(triethoxysilyl)propyl]tetrasulfide. Furthermore, purely organic precursors, i.e., aliphatic, cyclic, and aromatic precursors such as heptane, 1-hexene, 1-octene, 1-heptine, 1,7-octadiene, 1,5-hexadiene, 1,5-cyclooctadiene, toluene, acetylene, and xylene may also be used.

[0057] Furthermore, a) Organic polar chains, particularly hydroxyl chains, amino chains, carboxylic acid chains, imide chains, anhydride chains, ester chains, or epoxy chains, and / or b) Organically nonpolar chains, especially methyl, ethyl, propyl, vinyl, or butyl chains A Si-based precursor containing a chemical Si-O bond in combination with the other components may also be used.

[0058] Furthermore, metal alkoxides, particularly Si, Ti, Zn, Al, Zr, or Sr alkoxides, may be used as precursors for plasma coatings, especially those using a metal oxide protective layer.

[0059] For example, a protective layer may be provided within the reaction region. For this purpose, for example, a plasma nozzle and a coating plasma nozzle may operate alternately. If the reduction process and coating with the protective layer are performed using a single plasma nozzle, for example, the feeding of the precursor may be switched on and off alternately by a precursor feed. For example, a transport device may be configured to stop the transport of the workpiece within the reaction region so that the reduction process and plasma coating can be performed there in succession.

[0060] Furthermore, a protective layer may be applied within individual coating regions. For this purpose, in a further embodiment, the coating region is positioned between the reaction region and the outlet opening, and the coating plasma nozzle is configured to provide a protective coating by plasma coating to workpieces that are transported through the coating region by a transport device during operation. In this way, continuous reduction processing within the reduction region and continuous plasma coating within the coating region are possible without interference between the two processes.

[0061] By providing a coating plasma nozzle within the coating area, the apparatus may be configured to perform reduction treatment on the workpiece and plasma coating on a workpiece that has already undergone reduction treatment simultaneously and independently.

[0062] In particular, this makes it possible to continuously transport the workpiece through the processing tunnel, preferably at a constant speed, and thus enables simpler in-line installation of the apparatus. Furthermore, this reduces contamination of the reaction area by precursors.

[0063] To further separate the reduction treatment and the plasma coating, preferably the reaction region and the coating region are spaced apart from each other. Preferably, the treatment tunnel in the area between the reaction region and the coating region has a reduced cross-section compared to the reaction region and / or the coating region.

[0064] In further embodiments, the apparatus includes a control device for controlling the apparatus. In particular, the control device may be configured to control the operation of the plasma nozzle and / or any coating plasma nozzle, the operation of the reducing gas supply unit and / or any purging gas supply unit, the transport device and / or any cooling and / or heating elements. In this way, the apparatus and method can be automated, simplifying handling and standardizing the reduction of oxides on the workpiece surface. Furthermore, in this manner, process parameters such as automatic adjustment of the gas supply rate into the processing tunnel, particularly into the reaction region, the transport speed of the workpiece through the reaction region and / or coating region, and / or control of heating and / or cooling elements on workpiece surfaces of different materials, as well as the use of different gas mixtures, can be achieved. Overall, in this way, effective reduction of oxides on workpiece surfaces of different materials can be achieved.

[0065] Further features and advantages of the apparatus, use, and method will become apparent from the following description of exemplary embodiments with reference to the attached drawings. [Brief explanation of the drawing]

[0066] [Figure 1] This shows a plasma nozzle for generating an atmospheric plasma jet, in which the nozzle head rotates around a rotation axis during operation. [Figure 2] A first exemplary embodiment of an apparatus and method for reducing oxides on a workpiece surface is shown. [Figure 3] A second exemplary embodiment of an apparatus and method for reducing oxides on a workpiece surface is shown. [Modes for carrying out the invention]

[0067] Before considering the first exemplary embodiment of the apparatus described herein, we will first explain the general structure and operating principle of a plasma nozzle suitable for the apparatus described herein using the plasma nozzle shown in Figure 1.

[0068] Figure 1 shows a schematic cross-sectional view of a plasma nozzle for generating a plasma jet by high-frequency, high-voltage discharge in the form of an arc discharge.

[0069] The plasma nozzle 2 has a tubular housing 10, which, in the drawing, has an enlarged diameter in its upper section and is rotatably mounted on a fixed support tube 14 with the help of a bearing 12. Inside the housing 10, the upper portion of a nozzle channel 16 is formed, which connects the working gas supply section 25 to the nozzle opening 18.

[0070] An electrically insulating ceramic tube 20 is inserted into the support tube 14. An operating gas 23, such as a reducing gas, is supplied into the nozzle channel 16 through the operating gas supply unit 25, and through the support tube 14 and the ceramic tube 20. The operating gas 23 swirls with the help of a swirl device 22 inserted into the ceramic tube 20 and flows in a spiral manner through the nozzle channel 16 toward the nozzle opening 18, as shown by the spiral arrow 40 in the drawing. The operating gas creates a vortex center within the nozzle channel 16, which runs along axis A of the housing 10.

[0071] A pin-shaped internal electrode 24 is mounted on the swivel device 22, and this internal electrode protrudes coaxially into the upper portion of the nozzle channel 16, to which a high-frequency high voltage is applied with the help of a high-voltage generator 26. The high-frequency high voltage may have a voltage intensity in the range of 1 to 100 kV, preferably 1 to 50 kV, more preferably 1 to 10 kV, and a frequency of 1 to 300 kHz, particularly 1 to 100 kHz, preferably 10 to 100 kHz, more preferably 10 to 50 kHz. The high-frequency high voltage may be a high-frequency AC voltage, a pulsed DC voltage, or a superposition of both voltage forms.

[0072] The metal housing 10 is grounded via the bearing 12 and support tube 14 and acts as a counter electrode, so that a discharge 42 can be generated between the internal electrode 24 and the housing 10.

[0073] Preferably, the internal electrodes 24 located within the housing 10 are aligned parallel to axis A. In particular, axis A may run through the internal electrodes 24.

[0074] The nozzle opening 18 of the nozzle channel is formed by a metal nozzle head 30. This nozzle head is screwed into a threaded hole 32 in the housing 10, and a channel 34 is formed inside the nozzle head. The channel tapers towards the nozzle opening 18, curves, runs diagonally with respect to axis A, and forms the lower portion of the nozzle channel 16 up to the nozzle opening 18. In this way, the plasma jet 28 emerging from the nozzle opening 18 forms a certain angle with respect to axis A of the housing. In the illustrated example, this angle is approximately 45°. This angle may be varied as appropriate by changing the nozzle head 30.

[0075] Therefore, the nozzle head 30 is positioned at the end of the discharge path of the high-frequency arc discharge 42 and is grounded via metallic contact with the housing 10. Thus, the nozzle head 30 guides the outflow gas and plasma jet 28, and the direction of the nozzle opening 18 runs at a predetermined angle with respect to axis A.

[0076] Since the nozzle head 30 is connected to the housing 10 in a rotatable manner, and the housing 10 is rotatably mounted on the support tube 14 via a bearing 12, the nozzle head 30 can rotate relative to axis A. Therefore, in this configuration, the axis of rotation coincides with the housing axis A. A gear 36 is positioned on the extended upper portion of the housing 10, and this gear is connected to a rotary drive 38, such as a motor, via a toothed belt or pinion 37.

[0077] During operation of the plasma nozzle 2 with high frequency and high voltage, an arc discharge 42 is generated between the internal electrode 24 and the housing 10 due to the high frequency of the voltage. The arc of this high frequency arc discharge is carried by the swirling inflowing working gas 23 and directed at the center of the swirling gas flow. The arc 42 then runs almost linearly along axis A from the tip of the internal electrode 24 and finally branches radially onto the housing wall or onto the wall of the nozzle head 30 within the region of the lower end of the housing 10 or within the region of the channel 34. In this way, a plasma jet 28 is generated and emerges through the nozzle opening 18.

[0078] Here, since the discharge occurs in the form of an arc, the terms "arc" and "arc discharge" are used as the phenomenological description of the discharge. The term "arc" is also used elsewhere to refer to a form of discharge in DC discharge where the voltage value is approximately constant. However, in this example, we are dealing with high-frequency discharge in the form of an arc, i.e., high-frequency arc discharge.

[0079] During operation, the housing 10 rotates at high speed around axis A, causing the plasma jet 28 to draw a conical surface that sweeps across the surface of a workpiece (not shown) to be treated. As the workpiece then moves along the plasma nozzle 2, relatively uniform treatment of the workpiece surface is achieved on a strip whose width corresponds to the diameter of the cone drawn on the workpiece surface by the plasma jet 28. The width of the pre-treatment area may be influenced by varying the distance between the nozzle head 30 and the workpiece. The plasma jet 28, by impacting the workpiece surface at a certain angle and being twisted itself, ensures that the plasma has a concentrated effect on the workpiece surface. The direction of rotation of the plasma jet may be the same as or opposite to the rotation direction of the housing 10. The intensity of the plasma treatment by the rotating plasma jet 28 depends on the distance between the nozzle opening 18 and the surface, the angle of incidence of the plasma jet 28 onto the surface to be treated, and the relative velocity between the workpiece and the plasma nozzle 2.

[0080] Figure 2 shows a schematic diagram of a first exemplary embodiment of an apparatus and method for reducing oxides on a workpiece surface.

[0081] The apparatus 50 includes, for example, a metal housing 51 that encloses the processing tunnel 52, which has an inlet opening 54 and an outlet opening 56 for the workpiece 80 to enter or exit. Furthermore, a transport device 58 is provided for transporting the workpiece 80. In this example, the transport device is in the form of a conveyor belt 62 running on drive rollers 60 driven by a motor 61.

[0082] Within the processing tunnel 52, a reaction region 82 is provided at a certain distance from the inlet opening 54 and the outlet opening 56, and the processing tunnel 52 has an enlarged cross-section within this reaction region. Within the reaction region 82, a plasma nozzle 84 is inserted into the housing 51. The plasma nozzle 84 is positioned and configured such that, during operation, an atmospheric plasma jet 88 generated by the plasma nozzle 84 is introduced into the reaction region 82, and in particular, during operation, a workpiece 80 being transported through the reaction region 82 is exposed to the atmospheric plasma jet 88 generated by the plasma nozzle 84. The plasma nozzle 84 may be designed, for example, as plasma nozzle 2 in Figure 1. Alternatively, the plasma nozzle 84 may be designed as a non-rotating plasma nozzle, in which case the plasma jet may emerge, for example, from the nozzle opening in the longitudinal direction of the plasma nozzle. The plasma nozzle 84 has a working gas supply unit 75 (corresponding to the working gas supply unit 25 in Figure 1) for supplying working gas to the plasma nozzle 84.

[0083] The apparatus 50 also includes a reducing gas supply unit 74 configured to introduce a reducing gas, such as a foaming gas, into the reaction region 82. For this purpose, the reducing gas supply unit 74 has a reducing gas source 76, which in this example is designed as a gas cylinder.

[0084] The reducing gas supply unit 74 may be configured to supply reducing gas to the plasma nozzle 84 as working gas. For this purpose, a reducing gas line 77 may be provided to guide the reducing gas from the reducing gas source 76 to the working gas supply unit 75. A controllable valve for controlling the gas supply rate may be integrated into the reducing gas line 77, for example.

[0085] In a possible variant of the exemplary embodiment, the reducing gas supply unit 74 is configured to introduce the reducing gas into the reaction region through a reducing gas inlet opening 92 separate from the plasma nozzle 84. For this purpose, a reducing gas wire 94 may be provided to direct the reducing gas from the reducing gas source 76 to the reducing gas inlet opening 92. A controllable valve for controlling the gas supply rate may be integrated with the reducing gas wire 94, for example. In this variant, a working gas supply unit 75 may also be connected to the reducing gas source 76 to provide a working gas, such as nitrogen or argon, or alternatively, the working gas supply unit 75 may be connected to the working gas source 70 via a working gas wire 72.

[0086] Furthermore, the apparatus 50 may have a purge gas supply unit 96 configured to introduce purge gas into the processing tunnel 52. For this purpose, the purge gas supply unit 96 particularly includes a purge gas source 98 for providing an oxygen-free purge gas, such as nitrogen or argon, and a purge gas line 99 through which the purge gas is delivered from the purge gas source 98 to a purge gas inlet opening 100 in the processing tunnel 52. A controllable valve for controlling the gas supply rate may be integrated into the purge gas line 99, for example.

[0087] If the reducing gas supply unit 74 has individual reducing gas inlet openings 92, as shown in Figure 2, these individual reducing gas inlet openings 92 may also be used as, for example, purge gas inlet openings 100. Alternatively, individual inlet openings are also possible.

[0088] If the reducing gas supply unit 74 does not have a separate reducing gas inlet opening 92, the inlet opening shown in Figure 2 may be used alone as a purge gas inlet opening 100.

[0089] Furthermore, in order to preheat the workpieces being transported by the transport device 58 before they enter the reaction region 82, a heating element 64 is provided between the inlet opening 54 and the reaction region 82 in the transport direction 106 of the transport device 58, and therefore in front of the reaction region 82.

[0090] Furthermore, in order to cool the workpieces transported by the transport device 58 after the reduction treatment in the reaction region 82, a cooling element 104 is positioned between the reaction region 82 and the outlet opening 56 in the transport direction 106, and therefore behind the reaction region 82. In addition, the reaction region 82 itself may also be provided with a heating element and / or a cooling element 102.

[0091] The apparatus 50 further includes a control device 66 for controlling the apparatus, which is connected via communication connections 68 (not all connections are shown for clarity) to the plasma nozzle 84, the gas sources 70, 76, 98, and the valves integrated into the gas lines 72, 77, 94, 99, respectively, as well as to the motor 61 of the transport device 58. The control device 66 is preferably configured to control the gas supply rate in the gas supply units 74, 96, the operation of the plasma nozzle 84, in particular the power used for operation, the speed of the transport device 58, and optionally the temperatures of the heating and cooling elements 64, 102, 104.

[0092] The operation of device 50 is described below.

[0093] Before starting the reduction process using the apparatus 50, a purge gas, such as nitrogen, is first introduced into the processing tunnel 52 via the purge gas supply unit 96, such as the purge gas inlet opening 100, and any oxygen-containing atmosphere present therein is purged out through the inlet opening 54 or outlet opening 56. Alternatively, the processing tunnel 52 may also be purged using a reducing gas that can be introduced into the reaction region 82 via the reducing gas inlet 74.

[0094] Subsequently, the plasma nozzle 84 enters operation, generating an atmospheric plasma jet 88. The atmospheric plasma jet is introduced into the reaction region 82. A reducing gas is introduced into the reaction region 82 by the reducing gas supply unit 74, for example, through the plasma nozzle 84 itself or through an arbitrary reducing gas inlet opening 92. In this way, a reactive reducing atmosphere is created within the reaction region 82.

[0095] The workpiece 80 is transported through the processing tunnel 52 by a transport device 58, optionally preheated by an optional heating element 64, and then transported through the reaction region 82. The reducing gas and plasma jet 88 supplied into the reaction region 82 via the reducing gas supply unit 74 create a reactive atmosphere that acts on the workpiece surface, reducing the oxides on the workpiece surface. Preferably, the plasma nozzle 84 is aligned with the transport device 58 such that the workpiece 80 in the reaction region 82 is exposed to the plasma jet 88, thereby achieving a more concentrated reduction of the oxides on the workpiece surface of the workpiece 80.

[0096] The workpiece 80 may be transported at a constant speed through the reaction region 82 by a transport device 58. Alternatively, the transport device 58 may be configured to interrupt transport during each processing time while the workpiece 80 is inside the reaction region 82.

[0097] The workpiece is further transported through the processing tunnel 52 after the reaction region 82 and optionally cooled there by an optional cooling element 104, thereby reducing or completely preventing re-oxidation of the workpiece surface.

[0098] In any variation of the exemplary embodiment, the plasma nozzle 84 may be configured to provide a protective coating to the workpiece 80. For this purpose, a precursor feed line may be provided, for example, within the area of ​​the nozzle head 86 or in the working gas supply unit 75, through which a precursor can be introduced into the plasma jet 88. The plasma nozzle 84 may also be configured to operate alternately in reduction mode and coating mode so that the workpiece 80, transported through the reaction region 82, first undergoes a reduction treatment in reduction mode, and then a precursor is added in coating mode to provide a protective coating to the workpiece.

[0099] Figure 3 shows a schematic diagram of a second exemplary embodiment of an apparatus and method for reducing oxides on a workpiece surface.

[0100] Apparatus 150 has a similar structure to apparatus 50. The same reference numerals are given to corresponding components. Refer to the above description of Figure 2 for further details.

[0101] Apparatus 150 differs from apparatus 50 in that a coating region 182 is provided between the reaction region 82 and the outlet opening 56, separated from the reaction region 82. Within the coating region 182, a coating plasma nozzle 184 is integrated into the housing 51, and the coating plasma nozzle is configured to provide a protective coating by plasma coating to workpieces 80 that are transported through the coating region 182 by a transport device 58 during operation. For this purpose, a precursor feed 214 is provided that can be used to introduce a precursor into the atmospheric plasma jet 188 generated by the coating plasma nozzle 184 during operation. Furthermore, a purge gas line 212 is provided that allows purge gas to be transmitted from a purge gas source 98 to a purge gas inlet opening 200 in the processing tunnel 52, and particularly into the coating region 182.

[0102] In particular, the coating plasma nozzle 184 may have a structure similar to that of the plasma nozzle 2 in Figure 1, which is referenced herein. Alternatively, the plasma nozzle 84 may be designed as a non-rotating plasma nozzle, in which case the plasma jet may emerge from the nozzle opening, for example, in the longitudinal direction of the plasma nozzle.

[0103] In this example, the precursor feed 214 is configured to introduce the precursor, along with the purge gas provided by the purge gas source 98 via the purge gas line 212, into the region of the nozzle head 186 of the coating plasma nozzle 184 through the purge gas inlet opening 200. Alternatively, a separate precursor feed 215 may be provided, separate from the purge gas inlet opening 200, to directly introduce the precursor, for example, in or into the coating plasma nozzle 184, preferably near the nozzle opening at the nozzle head 186. If a non-rotating coating plasma nozzle is used, this coating plasma nozzle may have a precursor feed that guides the precursor laterally into the nozzle head 186, for example.

[0104] In the exemplary embodiment shown in Figure 3, the plasma nozzle 84 is supplied with a reducing gas as a working gas via the working gas supply unit 75. In the exemplary embodiment shown in Figure 3, the coating plasma nozzle 184 is supplied with a working gas, such as nitrogen and / or argon, provided by the working gas source 192 via the working gas line 194, via the working gas supply unit 190.

[0105] Using the apparatus 50 according to the exemplary embodiment shown in Figure 2, an experiment was conducted to compare the effectiveness of reducing oxides on the surface of a metal workpiece under different process conditions. The working gas used was a reducing gas containing nitrogen and hydrogen, which was supplied as the working gas to the plasma nozzle 84 through the working gas supply unit 75 and thus introduced into the reaction region 82. Nitrogen and argon were used as the purge gas, which was introduced into the reaction region 82 through the purge gas inlet opening 100.

[0106] In the experiment, the proportion of material present in an oxidized state and the proportion present in a metallic state on the surface of a metal workpiece were measured before and after treatment with the apparatus 50. It was found that treatment with the apparatus 50 effectively reduced the proportion of material present in an oxidized state on the surface of the metal workpiece and effectively increased the proportion present in a metallic state on the surface of the metal workpiece. [Explanation of Symbols]

[0107] 2.84 Plasma Nozzle 10 Housing 12 bearings 14 Support tube 16 nozzle channels 18 Nozzle openings 20 ceramic tubes 22 Swivel device 23 Working gas 24 Internal electrode 25, 75, 190 Working gas supply unit 26 High-voltage generator 28, 88, 188 Plasma Jet 30, 86, 186 nozzle heads 32 screw holes 34 channels 36 gears 37 pinion 38 RPM drive 40 Arrows 42 Arc-shaped discharge 50, 150 devices 51 Housing 52 Processing Tunnel 54 Entrance opening 56 Exit opening 58 Conveying devices 60 Drive Roller 61 Motor 62 Conveyor Belts 64 Heating Element 66 Control Devices 68 Communication connection section 70, 192 Working gas source 72, 194 Operating gas wire 74. Reducing Gas Supply Unit 76. Source of reducing gas 77, 94 Reducing gas lines 80 Workpieces 82 Reaction Region 92 Reducing gas inlet opening 96 Purge Gas Supply Unit 98 Purge gas source 99, 212 purge gas lines 100, 200 purge gas inlet opening 102, 104 Cooling elements 106 Conveying direction 182 Coating area 184 Coating Plasma Nozzle 214, 215 Precursor feed

Claims

1. An apparatus (50, 150) for reducing oxides on the surface of a workpiece, - A processing tunnel (52) extending from an inlet opening (54) to an outlet opening (56), wherein during operation, the workpiece (80) enters the processing tunnel (52) through the inlet opening (54) and exits the processing tunnel (52) through the outlet opening (56), - A housing (51) surrounding the processing tunnel (52), - A reaction region (82) located within the processing tunnel (52), - A plasma nozzle (2, 84) configured to generate an atmospheric plasma jet (28, 88), - A reducing gas supply unit (74) configured to introduce a reducing gas (23) into the reaction region (82), - A transport device (58) configured to transport the workpiece (80) through the processing tunnel (52) and It is equipped with, - The plasma nozzles (2, 84) are arranged and configured such that they introduce the atmospheric plasma jets (28, 88) into the reaction region (82) during operation. - Apparatus wherein the processing tunnel (52) has a reduced cross-section between the inlet opening (54) and the reaction region (82), and / or between the reaction region (82) and the outlet opening (56), compared to the reaction region (82).

2. The apparatus according to claim 1, characterized in that the plasma nozzles (2, 84) are arranged such that a workpiece (80) transported through the processing tunnel (52) by the transport device (58) during operation is exposed to the atmospheric plasma jet (28, 88) within the reaction region (82).

3. The apparatus according to claim 1 or 2, characterized in that the reducing gas supply unit (74) is configured to supply the reducing gas to the plasma nozzles (2, 84) as a working gas.

4. The apparatus according to claim 1 or 2, characterized in that the reducing gas supply unit (74) is configured to introduce the reducing gas into the reaction region (82) through a reducing gas inlet opening (92) separate from the plasma nozzles (2, 84).

5. The apparatus according to claim 1, characterized in that a purge gas supply unit (100) configured to introduce purge gas into the processing tunnel (52) is provided.

6. The apparatus according to claim 1, characterized in that the plasma nozzle (2, 84) has a nozzle head (30, 86) from which the plasma jet (28, 88) emerges during operation and which rotates around a rotation axis (A) during operation.

7. The apparatus according to claim 1, characterized in that a heating element (64) and / or cooling elements (102, 104) are provided, configured to heat and / or cool the workpiece (80) that is transported through the processing tunnel (52).

8. The apparatus according to claim 1, characterized in that the plasma nozzles (2, 84) are configured to provide a protective coating by plasma coating to a workpiece (80) that is transported through the processing tunnel (52) during operation and exposed to the atmospheric plasma jet (88, 188) in the reaction region (82).

9. The apparatus according to claim 8, characterized in that a coating region (182) is positioned between the reaction region (82) and the outlet opening (56), and the coating plasma nozzles (2, 184) are configured to provide a protective coating within the coating region (182) by plasma coating to a workpiece (80) that is transported through the processing tunnel (52) by the transport device (58) during operation.

10. Use of the apparatus (50, 150) according to claim 1 for reducing oxides on the surface of a workpiece.

11. A method for reducing oxides on the surface of a workpiece using the apparatus (50, 150) described in claim 1, - One or more workpieces (80) are transported by the transport device (58) through the processing tunnel (52), - An atmospheric plasma jet (28, 88) is generated by the plasma nozzle (2, 84), - A reducing gas is introduced into the reaction region (82), - A method by which the atmospheric plasma jet (28, 88) is introduced into the reaction region (82).

12. The method according to claim 11, characterized in that one or more workpieces (80) transported through the processing tunnel (52) are exposed to the atmospheric plasma jet (28, 88) within the reaction region (82).

13. The method according to claim 11 or 12, characterized in that the reducing gas is introduced into the plasma nozzle (28, 88) as a working gas (23).

14. The method according to claim 11 or 12, characterized in that the reducing gas is introduced into the reaction region (82) through a reducing gas inlet opening (92) separate from the plasma nozzles (2, 84).

15. The apparatus according to claim 5, characterized in that the purge gas supply unit (100) is configured to introduce the purge gas into the reaction region (82).

16. The apparatus according to claim 1, characterized in that individual coating plasma nozzles (2, 184) are provided, and the coating plasma nozzles (2, 184) are configured to provide a protective coating by plasma coating to a workpiece (80) that is transported through the processing tunnel (52) during operation and exposed to the atmospheric plasma jet (88, 188) in the reaction region (82).

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