EP1513625B1 - Method and device for treating the outer surface of a metal wire, particularly for carrying out a coating pretreatment - Google Patents

Abstract

An apparatus for treating the outer surface of a metal wire being moved through the apparatus along a direction of longitudinal extension of the metal wire has two electrodes arranged at a distance in the direction of longitudinal extension of the metal wire, a gas room being arranged between the outer surface of the metal wire to be treated and said electrodes, a dielectric shielding for said electrodes shielding said electrodes towards the metal wire, and an alternating voltage generator generating an alternating high voltage between said two electrodes to provide a dielectric barrier discharge in said gas room above the outer surface of the metal wire. The metal wire serves as an intermediate electrode between said two electrodes.

Description

The invention relates to methods for the treatment of the outer surface of a metal wire with sheath according to the preamble of patent claim 1 and to an apparatus for carrying out such methods with the features of the preamble of claim 8.

Metal wires of defined diameter are made by drawing. In this process, lubricants are used which are found on the surface of the finished metal wires. If a drawn metal wire, for example, to be coated with other metals or plastics, it must first be freed from the lubricant residues. This is done in today's practice in alkaline baths. The renewal and disposal of these alkaline baths is costly. In addition, they represent a considerable expenditure on equipment.

From the EP 0 761 415 B1 For example, there is known a method for increasing the wettability of workpieces with liquids by electrical discharge surface pretreatment. In this method, a concentrated beam of a reactive medium is generated by plasma discharge with the supply of a working gas, and the surface of the workpiece to be treated is swept by this beam. The plasma discharge takes place in a plasma nozzle between a projecting from the rear coaxially into the plasma nozzle pin electrode and a nozzle opening limiting ring electrode, wherein between the pin electrode and the ring electrode a high voltage in the range of 5 to 30 kV and with a frequency in the order of 20 kHz is applied and wherein the focused beam of the reactive medium emerges through the nozzle opening. In the treated with the known method workpieces may be metallic workpieces.

For the treatment of metal wires, the known method and related to its implementation device are less suitable because of their geometry. In order to increase the wettability of the surface of a metal wire having lubricant residues on its surface, these lubricant residues must first be removed. This can not readily be achieved by simply sweeping over the surface of the metal wire with the bundled beam of reactive medium produced in the known method.

From the EP 0 994 637 A2 a method for the plasma treatment of rod or thread-like materials is known in which the respective material passes coaxially through a plasma nozzle. The plasma nozzle has a nozzle tube forming an outer electrode and an inner electrode disposed coaxially in the nozzle tube. By a coaxially formed in the inner electrode channel, the rod or thread-like material is introduced into the interior of the plasma nozzle. In this case, the channel in the inner electrode is lined with a guide tube for the rod or thread-like material made of electrically insulating material. This known method should also be suitable for the plasma treatment of wires. In wires of conductive material, ie in particular in metal wires, but the plasma nozzle would be shorted by the coaxially passing rod or filamentary material between the inner electrode and the outer electrode, so that no more plasma discharge occurred. It should be noted that the applied voltage between the outer electrode and the inner electrode for inducing the plasma discharge is a high-frequency alternating high voltage, in which a local insulation of the rod or filamentary material in the region of the inner electrode through the guide tube is not sufficient to a through To prevent a metal wire impending short circuit between the inner electrode and the outer electrode.

Even with a metal wire, which is already provided with a conductive or non-conductive sheath, so for example an insulating layer, it turns out that to a pretreatment of the sheath before a further coating or a printing of the sheath z. B. with type or manufacturer information by means of a color jet printer can not be waived.

A method for treating the outer surface of a fluorine resin coated metal wire having the features of the preamble of claim 1 and a corresponding apparatus having the features of the preamble of claim 8 are known from JP 11222530 A known. An electrode is wound spirally on a tube of dielectric. Due to the free cross-section of the tube, the metal wire is guided on the tube axis in one direction and an inert atmospheric gas is passed through the tube in the opposite direction. The oxygen concentration of this gas is lowered to 500 ppm or less. At atmospheric pressure, a dielectrically impeded discharge is caused between the metal wire grounded as the counter electrode and as such and the dielectric shielding of the electrode to improve the adhesion properties of the fluororesin coating of the metal wire. With the problem of electrically grounding the fluorine resin coated metal wire, the JP 11222530 A not apart.

From the SU 1362526 A1 a method for treating a metal wire without sheathing with the features of the preamble of claim 1 and a corresponding device with the features of the preamble of claim 8 is known. Here, a plurality of annular electrodes in the direction of the tube axis are arranged one behind the other on a tube of dielectric material, which are connected to different phases of a three-phase high voltage AC generator. The zero phase of this AC high voltage generator is connected to the guided on the tube axis metal wire. The metal wire is not only treated by the discharge between the dielectric shield of the electrodes and its outer surface, but also by the applied AC voltage, which is tuned to its mechanical resonance frequency, intentionally vibrated to shake off coarse contaminants of the metal wire. The suitable frequencies of the alternating high voltages to be applied to the electrodes with the alternating high voltage generator are rather below the usual frequency range for exciting a dielectrically impeded discharge. With problems in the electrical contacting of the metal wire with the zero phase of the AC high voltage generator is the SU 1362526 A1 not apart.

The invention has for its object to provide a method and apparatus for treating the surface of a sheathed metal wire, in which problems in connection with an unreliable electrical contacting of the surface of a sheath or contaminants wholly or partially insulated metal wire are avoided.

This object is achieved by a method having the features of patent claim 1 and a device having the features of patent claim 8. Advantageous embodiments of the method and the device are defined in the dependent claims 2-7 and 9-13.

A dielectrically impeded discharge, i. H. a gas discharge, can be maintained with little technical effort at atmospheric pressure. The dielectrically impeded discharge provides a chemically sufficient environment for the metal wire in the gas space to effectively clean its surface of any lubricant residue within a very short time. In addition, there is a surface activation, which has the consequence that in a subsequent coating of the wire, the applied layer better adheres to the surface of the metal wire or its sheath. In addition, the metal wire or its sheath is heated by the discharge over its surface. This is not a disadvantage; Rather, for example, a wire for a plastic coating usually not only has to be cleaned of lubricant residues and surface-activated, but also heated to a defined temperature in the order of 250 ° C. All this is achieved in a single step with the new process. Dielectric discharge is also advantageous over an unobstructed discharge used in the prior art methods and apparatuses in that the maximum flowing currents are limited and correspondingly relatively simple AC generators may be used.

When treating the surface of a non-electrically conductive metal wire, only the insulating layer around the wire can provide the dielectric shield of the electrode to the conductive metal wire. However, it is preferred that, in this case too, an additional dielectric shield is provided directly in front of the electrode and thus on the other side of the gas space above the outer surface of the sheathing of the metal wire.

As already mentioned, the dielectric discharge can be carried out at atmospheric pressure. However, it is also possible to set a certain overpressure or underpressure in the gas space without any problem. Preference is given to an overpressure of approximately up to 2000 hPa. With With the help of this overpressure, a kind of barrier air system can be realized to prevent the introduction of volatile foreign substances into the gas space. In particular, however, it can be ensured by an overpressure in the gas space that reaction products of the lubricant residues are blown out of the gas space.

Such a blowing out of reaction products of the lubricant residues can also be ensured by flowing through the gas space with air. In a metal wire conveyed in one direction through the gas space, the flow of ambient air should be in the opposite direction in order to keep as far as possible the resulting reaction products from the finished metal wire.

The AC high voltage to cause the dielectrically impeded discharge should be greater than 1 kV and will typically be a few kV. Their frequency is typically in the range of 20 kHz to 3 MHz.

On the wire side, the heating by the discharge in the gas space is often advantageous, as explained above. On the side of the electrode and its dielectric shield, however, it makes sense to dissipate accumulating heat energy in order to avoid overheating. This is preferably done by cooling the dielectric shield of the electrode.

In a specific embodiment of the new method, the gas space in the form of an elongated cylinder, wherein the metal wire is arranged on the cylinder axis. The electrode and its dielectric shield enclose this gas chamber in the shape of a cylinder jacket. The metal wire is continuously conveyed through the gas space.

To ensure sufficient removal of lubricant residue from the surface of the metal wire, the dielectric discharge may be intensified to place multiple gas spaces one behind the other around the metal wire. These parameters also have an influence on the temperature to which the metal wire is heated by the dielectrically impeded discharge. By tuning the parameters, it is possible to heat the metal wire in the gas space to a defined temperature above 200 ° C.

In the new method, the metal wire serves as a counter electrode to the electrode the dielectric shield, so that the discharge between the shield and the surface of the metal wire or its sheath takes place. In this case, the alternating high voltage is generated between two electrodes spaced apart in the longitudinal direction of the metal wire, each with its own dielectric shields. The metal wire connects the regions of the two electrodes with each other, and because of its conductivity, it serves as a counter electrode to both dielectrically shielded electrodes. It can be understood as an intermediate electrode in the middle between the two dielectrically shielded electrodes, on both sides of which gas spaces are formed, in which dielectrically impeded discharges take place.

In the device according to the invention for the treatment of the surface of a metal wire according to the new method, the gas space preferably surrounds the metal wire on all sides.

In order to remove reaction products from the gas space, a compressed air source can be provided, which causes an air flow through the gas space. This air flow preferably has the opposite direction of movement of the metal wire through the treatment space.

The AC generator is designed for an AC voltage greater than 1 kV and a frequency of 20 kHz to 3 MHz.

For the dielectric shielding of the electrode, a cooling device is preferably provided. In order to realize this cooling device, the shield may be in two parts, wherein a free space between the two parts of the shield is connected to a circulation device for a cooling liquid. This circulation device promotes a cooling fluid through the space between the two parts of the shield. The coolant can be water. To reduce the electrical conductivity of the water, it should be distilled water.

The dielectric shield of the electrode may comprise at least one tube. A two-part shield can be formed from two spaced-apart tubes, wherein the distance between the two tubes defines the free space for the coolant. In an arrangement of two tubes into one another, between which a clearance for the cooling liquid is formed, but the electrode can also be arranged directly on the inner tube and thus in the cooling liquid, such that only the inner tube forms the dielectric shield of the electrode. The outer tube then not only defines the clearance for the coolant, but also forms an outer insulation for the electrode.

For the metal wire, a guide device is preferably provided, which guides it on the tube axis. If the metal wire is already aligned in some other defined way, for example by adjacent devices, but no additional guide device is necessary.

In a particularly preferred embodiment of the new device, the gas space through the electrode and its dielectric shield is apparent. In this way it can be visually checked whether the desired dielectrically impeded discharge in the gas space actually takes place. The transparency of the shield can be realized that it is made of glass, such as quartz glass. Also, water as a coolant is sufficiently transparent. The transparency of the electrode can be realized by winding the electrode onto its shield in the form of a wire or ribbon with spaced turns.

Of course, if the gas space does not have to be transparent in the new device, the dielectric shield can of course also be made of a material other than glass. In particular, ceramic materials, such as, for example, aluminum oxide, which in addition to their dielectric properties are distinguished by a high heat resistance, are suitable.

In the new device, there are provided two electrodes with dielectric shields spaced apart in the direction of elongation of the metal wire, the AC generator generating the alternating high voltage between the two electrodes. The metal wire forms the counter electrode to both electrodes and it does not necessarily have to be earthed. In particular, problems with an unreliable grounding of the metal wire partially insulated on its surface by the lubricant residues can be avoided.

Fig. 1

eine erste nicht unter die Patentansprüche fallende Vorrichtung in einer perspektivischen Ansicht,

Fig. 2

die Vorrichtung gemäß Fig. 1 mit einer zusätzlichen Druckluftquelle in einer Seitenansicht,

Fig. 3

eine zweite nicht unter die Patentansprüche fallende Vorrichtung in einer Seitenansicht,

Fig. 4

einen vergrößerten Querschnitt durch die Vorrichtung gemäß Fig. 3,

Fig. 5

eine Ausführungsform der erfindungsgemäßen Vorrichtung in einer Seitenansicht, und

Fig. 6

die Ausführungsform der Vorrichtung gemäß Fig. 5 in einer Seitenansicht bei der Behandlung eines mit einer nicht leitenden Ummantelung versehenen Metalldrahts.

The invention is explained in more detail below with reference to exemplary embodiments and described, in which shows

Fig. 1

a first device not covered by the claims in a perspective view,

Fig. 2

1 with an additional compressed air source in a side view,

Fig. 3

a second device not covered by the claims in a side view,

Fig. 4

an enlarged cross section through the device of FIG. 3,

Fig. 5

an embodiment of the device according to the invention in a side view, and

Fig. 6

the embodiment of the device of FIG. 5 in a side view in the treatment of a non-conductive sheath provided with metal wire.

The device 10 shown in Fig. 1 is used for the treatment of the surface of a metal wire 3. The metal wire 3 is passed through a glass tube 11 and that in the region of the tube axis. Between the surface of the metal wire 3 and the inner surface of the glass tube 11, a gas space 5 containing air remains. The air may be added to reaction or noble gases, but this is not mandatory. On the glass tube 11, an electrode 4 is arranged made of solid copper, wherein no gaps between the electrode 4 and the glass tube 11 are present. Any originally existing gaps are filled with a dielectric paste. The electrode 4 is provided with an opening 12 in order to be able to see the gas space 5 through the glass tube 11 also in the region of the electrode 12. The electrode 4 is connected via a high voltage supply 1 to an AC generator 6 which is grounded to generate a high AC voltage with respect to the ground. This alternating high voltage in the range of a few kV and with a frequency of typically several 100 kHz is applied to the electrode 4 via the high voltage supply line 1. Since the wire 3 is also earthed here, an alternating electric field acts between it and the electrode 4. This alternating field causes a discharge in the gas space 5. This discharge is dielectrically impeded because the glass tube 11 serves as a dielectric shield 2 of the electrode 4. Through the dielectric Disruption of the discharge in the gas space 5 prevents locally larger currents flow through the gas space 5, ie that there is an arc discharge and thus a short circuit of the electrode 4 to earth. As a result, the discharge via the volume of the gas space 5 is stabilized and the AC voltage generator 6 is subject to lower requirements than when occurring arc discharges. Nevertheless, the discharge in the gas space 5 provides a reactive environment around the metal wire 3 to remove lubricant residues and the like attached to the surface of the metal wire 3, ie, to substantially oxidize to CO ₂ and water. In addition, the surface of the metal wire is activated and the metal wire undergoes heating so that it is completely pre-treated for a plastic coating that requires a cleaned and warmed activated surface wire.

Fig. 2 shows a side view of the reproduced in Fig. 1 device 10, wherein in addition a compressed air source 13 is indicated, with the compressed air 14 in the gas space 5 is blown to cause an air flow 15 through the gas space 5 therethrough. The air flow 15 is preferably carried out in the opposite direction to a movement of the metal wire 3 through the gas space 5 in the direction of an arrow 16. With the air flow 15 and any oxidation residues from the oxidation of surface contamination of the metal wire 5 or ablated there inert particles are blown out of the glass tube 11 which could otherwise affect a controlled discharge in the gas space 5.

When testing the device according to FIGS. 1 and 2, the glass tube 11 has an inner diameter of 6 mm. Its length was 400 mm. It stood on both sides by more than 50 mm over the electrode. Using a semiconductor-based AC voltage generator 6 having an efficiency of 90% at a medium-frequency high voltage, the dielectrically impeded discharge at diameters of the metal wire of 0.6 to 1.3 mm could be easily ignited and maintained. The desired cleaning of the surface of the metal wire within a very short time, i. specifically achieved at feed speeds of the metal wire 3 of well over 1 m / s and also up to 5 m / s. The heating was done quickly, which naturally decreased with increasing strength of the metal wire. Subsequent plastic coating of the metal wire so pretreated gave excellent adhesion of the coated plastic.

3 shows a comparison with FIGS. 1 and 2 thereby modified embodiment, a further glass tube 17 is arranged in the glass tube 11 and that coaxial with the glass tube 11 and the metal wire 3. Between the glass tubes 11 and 17 remains a cylinder jacket-shaped space 18. Through the space 18 circulates a circulation device 19, a cooling liquid 20 to to cool the dielectric shield 2 of the electrode 4. While heating of the metal wire 3 is desired and can be adjusted to a certain extent in a conveyed through the device 10 metal wire 3, ie, is a heating of the dielectric shield 2, here practically from the glass tubes 11 and 17 and the cooling liquid 20 in the free space 18 is undesirable beyond a certain extent. Suitable cooling fluids are, in particular, those which have no appreciable electrical conductivity, such as, for example, distilled water.

Fig. 5 shows an embodiment of the device 10 with two electrodes 4 and one dielectric shield 2 for each electrode 4 each of a glass tube 11. Each of the electrode 12 and dielectric shield 2 units may be formed as shown in Figs , That All variants described in these figures can also be realized here. However, the device 10 according to FIG. 5 is not restricted to a series connection of two devices 10, as described in the preceding FIGS. Rather, the AC voltage generator 6 according to FIG. 5 is not grounded, but it brings the alternating high voltage between the two electrodes 4 on. In this way, can be dispensed with a grounding of the metal wire 3. The metal wire 3 acts as an intermediate electrode between the two electrodes 4 and is thus a complete counter electrode for the respective discharge in the respective gas space 5, all conceivable metal wires, the AC conductivity is completely sufficient to the distance between the two electrodes 4 in the longitudinal direction of the metal wire 3 to bridge. In the embodiment of the device 10 according to FIG. 5 as well, the metal wire 3 can, of course, be grounded in order to reliably preclude the build-up of charges thereon. This does not preclude the function of the device 10 according to FIG. 5. However, it avoids all problems with imperfect grounding, for example due to the insulating effect of impurities on the surface of the metal wire 3.

Fig. 6 shows the device according to Fig. 5 in the treatment of a metal wire 3 provided with a sheath 9. This may serve for the outer surface of the metal wire 3, which is actually the surface of the sheath 9, for printing for example, prepare with a color jet printer, not shown here, so that the color on the outside Surface better and more durable clings. The operation of the device 10 in the treatment of the sheathed metal wire 3 according to FIG. 6 is in principle the same as in the treatment of the non-sheathed metal wire 3 according to FIG. 5. The only difference is that a non-electrically conductive sheath 9 the metal wire 3, ie an insulating layer, acts as an additional dielectric shield 11 of the electrodes 4 with respect to the metal wire 3.

All embodiments of the device 10 shown so far advantageously provide an all-round treatment of the outer surface of the metal wire 3 or its sheathing 9.

The gas atmosphere in the gas space 5, in which the dielectrically impeded discharge is caused, may be simple ambient air. To increase the cleaning effect, pure oxygen or other reaction gases can be added. In order to improve the activation of the surface of the metal wire 3 for its subsequent coating, noble gases may also be added.

LIST OF REFERENCE NUMBERS

1 -

High voltage supply

2 -

dielectric shielding

3 -

metal wire

4 -

electrode

5 -

headspace

6 -

AC voltage generator

9 -

jacket

10 -

contraption

11 -

glass tube

12 -

perforation

13 -

Compressed air source

14 -

compressed air

15 -

airflow

16 -

arrow

17 -

glass tube

18 -

free space

19 -

circulation

20 -

coolant

Claims (13)

1. Method of treating the outer surface of a metal wire (3), which is provided with an electrically non-conductive coating (9), a alternating high voltage being applied to an electrode (4), which is provided with a dielectric shielding (2) towards the metal wire (3), to generate a dielectric barrier discharge in a gas room (5) above the outer surface, characterized in that the alternating high voltage is applied between two electrodes (4) with dielectric shieldings (2) arranged at a distance in the longitudinal extension direction of the metal wire (3), the metal wire (3) serving as a counter-electrode for both dielectrically shielded electrodes (4) even without grounding due to its electric conductivity.
2. The method of claim 1, characterized in that the coating is electrically non-conductive and that an additional dielectric shielding (2) is provided in front of the electrodes.
3. The method of any of the claims 1 and 2, characterized in that an overpressure of at least 2000 hPa is set in the gas room (5).
4. The method of any of the claims 1 to 3, characterized in that the alternating high voltage is higher than 1 kV and has a frequency of 20 kHz to 3 MHz.
5. The method of any of the claims 1 to 4, characterized in that the dielectric shielding (2) of the electrodes (4) is cooled.
6. The method of any of the claims 1 to 5, characterized in that the metal wire (3) is heated up in the gas room (5) to a defined temperature of above 200 °C.
7. The method of any of the claims 1 to 6, characterized in that the dielectric shielding (2) of the electrodes (4) arranged at a distance in the longitudinal extension direction of the metal wire (3) are separated.
8. An apparatus for treating the surface of a metal wire provided with an electrically nonconducting coating according to any of the claims 1 to 6, comprising an electrode (4), a dielectric shielding (2) for the electrode (4) adjacent to a gas room (5), the gas room (5) being arranged above the outer surface of the metal wire 3 to be treated, and an alternating voltage generator (6) which applies an alternating high voltage to the electrode (4), characterized in that two electrodes (4) having dielectric shieldings (2) are provided at a distance in the longitudinal extension direction of the metal wire (3), and that the alternating voltage generator (6) generates the alternating high voltage between both electrodes (4), the metal wire (3) serving as a counter-electrode for both dielectrically shielded electrodes (4) even without grounding due to its electric conductivity.
9. The apparatus of claim 8, characterized in that a source for pressurized air (13) is provided which generates an air flow (15) through the gas room (5), the airflow (15) having the opposite direction to a movement of the metal wire (3) through the gas room (5).
10. The apparatus of any of the claims 8 and 9, characterized in that the alternating voltage generator (6) is designed for an alternating high voltage higher than 1 kV and a frequency of 20 kHz to 3 MHz.
11. The apparatus according to any of the claims 8 to 10, characterized in that a cooling device is provided for the dielectric shielding (2) of the electrodes (4), the shielding (2) being two-part, and a free space (18) between both parts of the shielding being connected to a circulating device (19) for a cooling liquid (20).
12. The apparatus of any of the claims 8 to 11, characterized in that the gas room (5) can be viewed through the electrodes (4) and their dielectric shielding (2).
13. The apparatus according to any of the claims 8 to 12, characterized in that the electrodes (4) arranged at a distance in the longitudinal extension direction of the metal wire (3) have separate dielectric shieldings (2).

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