EP0975826B1 - Method for electroplating metallic and non-metallic endless products and device for carrying out said method - Google Patents

Abstract

The present invention is directed to processes and devices for performing the processes comprising electroplating one or more metallic or non-metallic continuous products with metals or metal alloys in a continuous process from aprotic electrolytes free of water and oxygen, wherein the continuous product is passed through a lock system (1) into an encapsulated coating plant under inert gas atmosphere, and the following steps are performed at temperatures <=120° C.:activating the continuous product to be coated;rinsing the continuous product to be coated;contacting the continuous product to be coated;electroplating the continuous product to be coated using a metal or metal alloy;drying the coated continuous product;discharge of the coated continuous product from the plant through a lock system.

Description

The invention relates to a method for electrolytic Coating metallic or non-metallic Continuous products with metals or alloys in a continuous process made of aprotic, water and oxygen-free electrolytes. Another object of the invention is a device to carry out this procedure.

According to the prior art, continuous products such as wire, Strips, long profiles or tubes using aqueous electrolysis processes, by means of melt bath application in a continuous process or by means of galvanic deposition processes are produced.

In a known electrolytic coating process For example, wire with different coatings such as Zinc, nickel or other metals coated. It goes through the wire open cleaning and electrolytic coating baths, which contain aqueous solutions. In these The respective metal is deposited on baths the wire. The thickness of the coating layer depends on it of throughput speed and electric field strength. The deposition rate in this process is related for the time being, however, quite small, and the secluded one Layer is often very porous and hard. This leads to a lack Corrosion resistance, especially with thin layers. Due to the lack of ductility, it can be used in subsequent deformation processes to cracks in the deposited layer come or even peel off the coating. Such Layer completely loses its protective character against corrosion and no longer has a decorative surface.

In the case of electrolytic deposition of a coating metal an aqueous solution will never become one complete cathodic or anodic yield achieved. At the high levels required for continuous coating Current densities generally result in side reactions that lead to Decomposition products in electrolytes and gas evolution cause. Hydrogen evolution occurs in particular on the product leading to embrittlement of the Basic material can lead.

Another disadvantage is that with the electrolytic aqueous Deposition processes and hot-dip processes large quantities Toxic exhaust air and waste water accrue over accordingly complex processes are subjected to cleaning must, whereby toxic hazardous waste remains in any case. So arise, for example, due to the presence of grease residues on the metals to be coated alkaline cleaning in the corresponding solutions, also remains of organic compounds due to the high Temperatures in the zinc kettle, which are around 450 ° C, too extremely toxic organic compounds such as dioxins and Furans can react. Metal sludge continues to fall, Used acids and used alkaline cleaners. In addition to the Exhaust gases mentioned above also continue to drop acid vapors and alkaline vapors.

Other processes for coating continuous products are known. These are based on the application of decorative and corrosion-reducing layers in the molten state. Here is the so-called hot-dip galvanizing and also the hot-dip aluminum known. In the case of hot-dip galvanizing, a previously cleaned and activated continuous product, for example a thin wire, passing through melted high purity zinc. These reactions run at temperatures above 440 ° C, so that in any case also a mechanical The material to be coated is influenced. Certain other base materials to be coated can not be coated at all due to the high temperatures. Another disadvantage is the relative non-uniformity of the applied coating and its very strongly layer-dependent Corrosion resistance. As a result of the stripping process the surface can completely lack the decorative character. A colored design of the surface is not possible.

Shows in all coating processes associated with zinc after a short period of corrosion, the surface blooms through the formation of zinc oxides and zinc carbonates and thus a very negative change of the optics Surface. Uniformity of the coating in these thermal process is therefore not guaranteed.

Another process is the so-called high thermal fire aluminum known. This procedure is the same As with zinc coating a wire through a molten one Pulled aluminum bath and then a stripping process subjected. However, you get layers that Disadvantages similar to those described above Hot-dip galvanizing. The applied by means of fire aluminum Layers have become insufficient due to their Purity, high porosity and inevitable oxide inclusions and thus low corrosion resistance is not proven. Other disadvantages are that the coating is not decorative looks like and one for the fire aluminizing necessary temperatures strong mechanical influences of the material to be coated.

According to the prior art, hot-dip galvanizing can also be carried out with the fire aluminum can be combined. This leads to a somewhat improved corrosion layer through the active cathodic Protective effect of aluminum. It has a disadvantageous effect however, the lack of decorative character. Add to that other disadvantages due to the coating alone high temperatures occur.

Galvanic deposition processes are another state of the art of aluminum known in aprotic water and oxygen-free electrolytes. The separation takes place here of aluminum from baths, the aluminum alkyl complexes from alkali metal halides and aluminum alkyls contain. Aromatic solvents are generally used as solvents or aliphatic hydrocarbons used. such Electrolyte solutions are used, for example, in the EP 0 402 761 A and EP 0 084 816 A.

DE 3023827 C2 describes a system that addresses this Benefits from the process. It consists of a closed off to the outside Tube cell through which to be treated, cathodic Contacted material in the axial direction, preferably continuously is movable along anodes. To both the unwanted Leak of the electrolyte from the tubular cell as well Preventing the entry of air is the A protective gas can be applied to the tube cell. Will continue a tubular connector on both sides of the tube cell connected, the one the longitudinal passage of the electrolyte preventing, vertically deflecting the electrolyte current Has aperture. The T-shaped connectors follow each a lock arrangement consisting of several chambers, in the for the mutual sealing of the individual chambers as Sealant inert gas and / or inert liquid introduced can be.

In the conventional methods of the prior art those before electrolytic coating in aqueous Solutions carried out necessary activation of the continuous product in a separate process step. Since the A-aluminum-organic Components of the electrolyte in moisture decompose, rinsing and drying processes are connected, which remove the remains of the aqueous solutions. The continuous product is only after the rinsing process has been completed in an encapsulated coating system for galvanic metal deposition brought in.

JP 63227797 describes the activation of a metal sheet an electrolytic coating with aluminum also non-aqueous Solvent used.

The technical object of the invention is a method to provide the disadvantages mentioned above the previously known coating processes for continuous products avoids, is inexpensive and for a better coating leads. The process should continue without change of the base material can be carried out, in particular at low temperatures.

• Aktivierung des zu beschichtenden Endlosproduktes
• Spülen des zu beschichtenden Endlosproduktes
• Kontaktierung des zu beschichtenden Endlosproduktes
• elektrolytische Beschichtung des zu beschichtenden Endlosproduktes mit Metall oder einer Metalllegierung
• Trocknung des beschichteten Endlosproduktes
• Austritt des beschichteten Endlosproduktes über ein Schleusensystem aus der Anlage

This technical problem is solved by a process for the electrolytic coating of metallic or non-metallic continuous products with metals or alloys in a continuous process from aprotic water- and oxygen-free electrolytes, the continuous product being passed via a lock system into an encapsulated coating system located under an inert gas atmosphere and the subsequent steps there at temperatures ≤ 120 ° C in this order.

• Activation of the continuous product to be coated
• Rinsing the continuous product to be coated
• Contacting the continuous product to be coated
• electrolytic coating of the continuous product to be coated with metal or a metal alloy
• Drying the coated continuous product
• The coated continuous product emerges from the system via a lock system

Continuous product in the sense of the invention are metallic or understood non-metallic materials that are rolled up in or folded form and are manufactured at the coating is endless in a continuous process be moved through the plant. These include, for example Wires of all thicknesses, strips and long profiles, tubes and similar products.

Non-aqueous electrolytes in the sense of the invention Systems called, the controlled pure separation of the Metal or the metal alloy, in particular aluminum and aluminum alloys via the electrolysis process without Intermediate or carrier layer, allow.

In a preferred embodiment, as continuous products Wire, strips, long profiles or tubes made of metallic or non-metallic materials. It is preferred that these materials with aluminum or aluminum alloys be coated.

Figure 1 shows a process diagram of the inventive method.

FIG. 2 shows an illustration of the lock system, FIG. 3 shows a coating cell.

Figure 4 shows the contacting cell.

FIG. 5 shows a diagram of the overall process.

Figure 1 shows the individual process steps of the invention Process. The continuous product, for example unwound from a reel and initially over a lock sluiced into the coating system. Already when entering the lock system, a cleaning process can be carried out by using the continuous product a gas wiping or spray nozzle is guided (see also figure 2, paragraph 11). Then, as a second process step Activation of the material to be coated. With the Number 3 is a flushing unit in which the material rinsed after activation. Section 4 describes a deflection unit with one or more rollers. This will used to reduce the overall size of the facility and is particularly useful for small diameter continuous products meaningful. The following paragraphs 5 describe individual ones Contacting cells, the numbers 6 the coating cells and the numbers 7 the aftercare. The coated product is then at the end of the process on an appropriate Reel rolled up.

In a preferred embodiment, the electrolytic Coating in the plant a chemical or electrochemical Post-treatment can be carried out. This can also be associated with a simultaneous or subsequent color design within the surface structure. During the after-treatment, mechanical surface compaction takes place, which results in a very shiny surface whereby this is not influenced in the aftertreatment.

In a further preferred embodiment, the entire System designed with closed regeneration cycles, and all liquids used are circulating processed, cleaned and returned. This is particularly the case for the rinsing solutions, the electrolyte solutions and the Activation solution that filters and / or distils as needed can be.

In a further preferred embodiment, the continuous product through the lock system and the flushing system each led to at least three chambers, the middle Chamber B is filled with a barrier liquid and the outer Chamber A contains air and the inner chamber C contains an inert gas contains (see also Figure 2). In a further preferred embodiment the continuous products are not gas and liquid-tight guides into the chambers, so that the liquid in the chambers partially into the Neighboring chambers are running.

These measures, for example, in the lock chamber achieved that no moisture or oxygen the introduction of the continuous product into the system. The barrier liquid located in the middle chamber B. a lock on the air contained in the outer chamber A Due to the design of the guides between the chambers a part of the Barrier liquid from the middle chamber B into the chambers A and C. There is therefore a flushing of the imported continuous product. The collected in chambers A and C. Liquid enters a through a drain system Storage tank and is via a corresponding pump and filtering device returned to the middle chamber B.

The ones designated in FIG. 5 are similar Rinsing chambers constructed, so that here, too, from those in front Do not bath any liquid or gas in the following Can reach chambers.

In a further preferred embodiment, the is the chambers through the overflow or through the guides Liquid cleaned via a circulation system and into the respective Chamber returned. As guides between the chambers bushes or rollers are preferred. The contacting is preferably carried out in a liquid electrolyte filled chamber that contains no anode, being the continuous product via a cathodically connected metal contact to be led. The liquid level of this contacting cell is preferably lower than that of the neighboring coating cell, so that electrolyte solution through the guides get from the coating chamber into the contacting chamber can and so by the purity of the electrolytic solution impurities carried in from the contacting chamber cannot be reduced

In a further preferred embodiment, the electrolytic coating in a coating chamber, which is filled with electrolytic solution, the continuous product is passed through a socket that is insulated.

These measures in the coating cell achieve that the power supply for the continuous product in chambers takes place in which there is no anode, so that it in these contacting cells not for the growth of the deposited Metal, for example on the voltage leading Cathode guides, coming. In the coating chambers themselves there is no current supply, so here the metal deposition only done on the continuous product itself. The order the contacting and coating cells can be in any frequency, depending on the length and size of the Investment.

Introducing the wire into the device according to the invention takes place via particularly expediently designed vacuum or Liquid lock systems, the latter designed similarly are like the contacting cells between the coating cells. This is for both single and multi-wire systems possible. The sealing medium can at the same time Serve cleaning the wire surface. Between the lock systems the processes are always completely inert Atmosphere. In the flushing units, contacting and coating cells the wire guides are targeted like this designed that the wire is evenly spaced from the Coating material serving anodes through the coating cell is moved without electrical contact to neighboring Wires or to get to the anode.

There is a flooding system between the coating cells, in which the electrical Contacting of the wire takes place over the entire length of the system to create even, stable conditions.

The special feature of the invention is that also in this area the wire inside the electrolyte fluid must be located, but the contact outside of the direct Coating areas is. The closure of the environment takes place in addition to the inert atmosphere via flood systems, similar to the lock systems mentioned. The Contacting can be carried out according to the invention via spring-loaded Contact elements are made by grinding or rolling, one flexible diameter adjustment is possible. By the according of the invention designed with respect to the coating field outsourced contact, there is no growing up the contact rollers or contact elements.

According to the invention, the Wire through specially designed deflection systems several times Coating units are guided, so that a low Length limited highly effective facility is possible. Especially appropriate design of the system technology and The method is provided by a storage container Plant shutdown, the continuous product in its original Leave position to unlike classic Procedure to get no start-up losses.

The invention ensures that mechanical or physico-chemical stripping processes not uniformity or homogeneity of the applied surface layer influence. In the method according to the invention, it is possible to the aluminum electrodes in the coating cells without any problems exchange and resume operation immediately.

The auxiliary units, such as filters and storage systems for Lock fluid, cleaning media and electrolytes are designed according to the invention so that a closed environmentally independent operation is possible. waste products are recyclable in a concentrated form. The described method offers the invention described components the possibility of a chemical Passivation of the coating, which is a significant increase which represents corrosion resistance. One according to the invention possible color nuances of the coating itself, not as an order, increases the mechanical resistance of this Coloring significantly compared to paints. The procedure Selection of the coating materials on which the invention is based and electrolytes increased over those shown classical methods of corrosion resistance considerable both in the acidic and in the alkaline range. By an embodiment made in accordance with the invention the exit areas of the wire from the coating and Rinsing tract it becomes possible to dry the wire in dryer or even in thickened form in the desired colors and to receive appropriate coating requirements.

Another object of the invention is a device for electrolytic coating of metallic or non-metallic Continuous products with metals or metal alloys in a continuous process from aprotic water and oxygen free Electrolytes, consisting of a coating system with at least one lock system 1, at least a contacting cell 5, at least one coating cell 6, these assemblies in any number are connected in series and the entire device is encapsulated airtight. The coating system draws are characterized in that they have an activation unit 2 and a Rinsing unit 3 includes in this order and an unwinding unit for the uncoated continuous product outside of encapsulated coating system is arranged. Such Device also serves to carry out the invention Process.

Figure 2 shows a view of the lock system 1. There is preferably from at least three chambers A, B and C, 17, 18, 19, the middle chamber B has a liquid overflow 16 and chambers A and C are designed as overflow chambers are. Chambers A, B and C particularly preferably have one Drain 20, 22 and 23, with the middle chamber in addition has an inlet 21 through which the in the chambers A and C collected barrier liquid into the middle chamber B can be traced back. The number 14 designates one Storage tank, the number 15 a corresponding pump. With the Number 9 denotes the wire guide, number 17 denotes Chamber A, Section 18 Chamber B and Section 19 Chamber C. Numeral 12 denotes the continuous product, that is passed through the chamber and number 11 is preferred used gas wiping or spray nozzle for additional Cleaning the surface of the through the plant led continuous product 12. With the numbers 24 and 25 are designated the inner chamber walls, number 13 a removable plate for sockets. This makes it possible To use continuous products of different diameters, whereby then the corresponding socket can also be used got to. Numeral 10 denotes the liquid level.

Figure 3 shows a coating cell. Figures 3a, 3b and 3d show different views of the one in the cell Carrier 28 for the continuous product 12. Figure 3a shows one Front view, Figure 3b is a side view and Figure 3d a At sight. Figure 3c is a perspective view of the entire coating cell 6. In Figures 3a, 3b and 3d is designated by the number 28 of the carrier made of insulating material. Section 27 shows the ceramic bushing divided into two parts. This is opposite to the direction of the imported continuous product arranged removably from the insulating material and can, for example, against sockets with a modified Diameter can be exchanged.

Figure 3c shows the entire coating cell 6 with the anode plates 26 and the carrier 28 arranged in the middle and the socket 27.

The coating cell 6 preferably has guides for guidance of the continuous product 12, which are designed so that a uniform distance between those in the coating cell arranged anodes 26 and the continuous product to be coated 12 is guaranteed. In a further preferred embodiment the coating cell has an overflow and an inlet for electrolyte.

The guides in the coating cells consist of a Carrier 28 made of insulating material which pierces in the middle is, bushings 27 are arranged in the through bore, which can only be inserted on one side and in a preferred manner Made of ceramic material and for easy interchangeability for continuous products of different diameters are divided.

Figure 4 shows an image of the contacting cell 5. Figure 4a represents an enlargement of the contact area as Side view. Figure 4b shows a perspective view the contacting cell 5. In FIG. 4b, the Section 12 designates the continuous product. This is between a metal roller 29 which is under cathodic voltage and passed through a non-conductive ceramic tension roller 30, with the number 32 the notches in the metal rollers are designated for better guidance of the continuous product 12. With the number 33 are the holding elements for the metal rollers and the ceramic tension rollers. Figure 4a shows one enlarged section of the contact area. The digit 29 shows the metal roller, number 31 a bronze bushing Power supply, section 12 the continuous product and section 30 are the ceramic tensioners. With these the preload set via springs or set screws for the continuous product.

The contacting cell 5 is preferably designed such that that in it a metal roller or a sliding contact is arranged, via which the continuous product is connected cathodically becomes. In addition, one or more ceramic tensioners can be used for setting the preload in the contacting cell be arranged. In a preferred embodiment the metal roller has a notch over which the continuous product is led. In the contacting cell an overflow is preferably arranged so that from the electrolysis cell urgent electrolytes in a collection system can be dissipated.

FIG. 5 shows a view of the coating cell 6 Contacting cell 5 and the rinsing units 3. Figure 5a shows the supervision of these cells and Figure 5b is a side view. It can be seen that the rinsing units 3 in a similar way Are designed like the ones described above Lock systems in Figure 2. They also have one Overflow, as well as neighboring overflow chambers, the middle Chamber is filled with liquid. This can run through the impervious guides into the neighboring chambers and is collected through appropriate processes and in the rinsing chambers returned. With the number 5 are the contacting cells described. These are preferably the coating cells 6 adjacent and filled with electrolyte. The number 6 shows the coating cells with the anodes 26 and the carriers 28 made of insulating material with those therein Ceramic bushings 29 for guiding the continuous products 12 in the coating cells. The coating cells are too filled with electrolyte and have an overflow, one Drain and an inlet through which the respective electrolyte liquids circulated, cleaned and returned can.

The device according to the invention has considerable advantages on previously known devices for metallization of continuous products. So the wire is over non-conductive Pipes and roller guides inside the device, specifically but in the electric field of the coating cell 6, stable positioning. It is through this stable guidance possible, several parallel strands of continuous products, for example several wires, also in a vertical arrangement to lead through the device without causing undesirable electrical contacts and an even distance to the anode is guaranteed. Through the as flood chambers constructed lock systems 1, rinsing units 3 and Contacting cells 5 is an electrical intermediate contact outside the area of effect of the anode material possible, with the continuous product remaining in the electrolyte. The transmission of electrical energy in the contacting cells 5 can both form sliding contacts of flexible contact pins, which are spring-loaded, as well as via resilient contact rollers.

Due to the special storage of the continuous product in the contacting cell 5, as well as through the guides in the coating cell 6, it is possible to have different diameters of endless products. By the preferred Deflection units 4, it is possible to pass through the continuous products to lead several parallel coating cells and thus relatively short systems to enable high throughput speeds.

Even if the system is at a standstill, the continuous product can remain in the chambers without an overreaction on the Surface, such as over-pickling or one-sided over-coating, can take place, while maintaining the inert atmosphere in the system the reaction media in the intermediate containers be stored outside the reaction spaces. Farther it is advantageous that an exchange of the anode material in the Standstill can take place without the material to be coated to remove from the system.

With the inventive method and the inventive It is possible to manufacture continuous products in an industrial device procedure to be carried out and a corresponding Coating device with metals, in particular aluminum. The inventive method and the inventive Device thus replace the previously used Process of hot-dip aluminizing, hot-dip galvanizing and electrolytic Coating in aqueous media.

Claims (28)

1. A process for electroplating metallic or non-metallic continuous products with metals or alloys in a continuous process from aprotic electrolytes free of water and oxygen, wherein the continuous product is passed through a lock system (1) into an encapsulated coating plant under inert gas atmosphere, and the following steps are performed therein at temperatures of ≤120°C in the order below:

   activating the continuous product to be coated;

   rinsing the continuous product to be coated;

   contacting the continuous product to be coated;

   electroplating the continuous product to be coated using a metal or metal alloy;

   drying the coated continuous product;

   discharging the coated continuous product from the plant through a lock system,

   characterized in that the non-coated continuous product is fed from the outside via a lock system (1) into the encapsulated coating plant, and that activating and rinsing of the continuous product to be coated is effected in the encapsulated plant as well.
2. The process according to claim 1, characterized in that wire, tapes, long-profiles or pipes made of metallic or non-metallic materials are employed as continuous products.
3. The process according to claim 1 or 2, characterized in that coating is effected using aluminum or aluminum alloys.
4. The process according to claims 1 to 3, characterized in that during introduction into the lock system (1), a cleaning procedure is performed by passing the continuous product (12) over a gas stripping nozzle or spray nozzle (11).
5. The process according to claims 1 to 4, characterized in that electroplating in the plant is followed by a chemical or electrochemical secondary treatment.
6. The process according to claims 1 to 5, characterized in that the entire plant is of a closed design using regeneration cycles, and that all of the liquids used are treated, purified and recirculated in a circulation process.
7. The process according to claim 6, characterized in that the liquids are rinsing solutions, electrolyte solution and activation solution.
8. The process according to claims 1 to 7, characterized in that the continuous product (12) is passed through deflector units (4) in order to permit high passage rates in short plants.
9. The process according to claims 1 to 8, characterized in that the continuous product (12) is passed through the lock system (1) and the rinsing unit (3), each consisting of at least three chambers (17, 18 and 19), the middle chamber B (18) being filled with a sealing fluid, the outer chamber A (17) containing air, and the inner chamber C (19) containing an inert gas.
10. The process according to claims 1 to 9, characterized in that the continuous products are introduced into the chambers through guides (9) which are not air-tight and liquid-tight, so that part of the liquid in the chambers runs into the adjacent chambers.
11. The process according to claims 1 to 10, characterized in that the liquids discharging from the chambers through the overflow (16) or the guides (9) are purified via a circulation system and re-circulated into the chambers.
12. The process according to claims 1 to 11, characterized in that the guides (9) are bushings or pulleys.
13. The process according to claims 1 to 12, characterized in that contacting is effected in a contacting cell (5) filled with liquid electrolyte, which cell does not include an anode, the continuous product (12) being passed over a metal contact (29) connected as cathode.
14. The process according to claims 1 to 13, characterized in that electroplating is performed in a coating chamber (6) filled with electrolyte solution, the continuous product (12) being passed through a bushing (27) which is insulated.
15. A device for electroplating metallic or non-metallic continuous products (12) with metals or metal alloys in a continuous process from aprotic electrolytes free of water and oxygen, which device is comprised of a coating plant having at least one lock system (1), at least one contacting cell (5), at least one coating cell (6), said assemblies being arranged in series, and the entire device being encapsulated so as to be air-tight, characterized in that the coating plant comprises an activation unit (2) and a rinsing unit (3) in this order, and that a wind-off unit for the non-coated continuous product is arranged outside the encapsulated coating plant.
16. The device according to claim 15, characterized in that the lock system (1) consists of at least three chambers A, B and C (17, 18, 19), the middle chamber B (18) having a liquid overflow, and the chambers A and C (17, 19) being designed as overflow chambers.
17. The device according to claim 15 or 16, characterized in that the chambers A, B and C (17, 18, 19) have outlets (20, 22, 23), the middle chamber B (18) additionally having an inlet (21) through which the sealing fluid collected in chambers A, C (17, 19) can be recirculated into the middle chamber B (18).
18. The device according to claims 15 to 17, characterized in that a gas stripping nozzle or spray nozzle (11) is arranged in chamber C (19).
19. The device according to claims 15 to 18, characterized in that the middle chamber B (18) of the lock system (1) has an overflow (16).
20. The device according to claims 15 to 19, characterized in that the contacting cell (5) has a metal pulley (29) or a wiping contact arranged therein, through which the continuous product (12) is connected as cathode.
21. The device according to claims 14 to 20, characterized in that one or more ceramic tension pulleys (30) are arranged to adjust the bias voltage in the contacting cell (5).
22. The device according to claims 15 to 21, characterized in that the metal pulley (29) has a groove (32) for guiding the continuous product (12).
23. The device according to claims 15 to 22, characterized in that an overflow (16) is arranged in the contacting cell (5), so that electrolyte discharging from the coating cell (6) can be drained off into a collector system.
24. The device according to claims 15 to 23, characterized in that guides (27) to guide the continuous product (12) are arranged in the coating cell (6).
25. The device according to claims 15 to 24, characterized in that anodes (26) are arranged in the coating cell (6).
26. The device according to claims 15 to 25, characterized in that the coating cell (6) has an overflow (16) and an inlet (21).
27. The device according to claims 15 to 26, characterized in that the guides (9) in the coating cell (6) consist of a support (28) made of an insulating material having a through-bore in the center, with bushings (27) being arranged in the through-bore which are penetrable from one side only.
28. The device according to claims 15 to 27, characterized in that the bushings (27) consist of a ceramic material and are split in order to make replacement easier.

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