EP0013874A2 - Apparatus for electrodeposition of aluminium - Google Patents

Abstract

To prevent transport of deleterious oxygen and moisture to liquid electrolyte in an aluminum electroplating vessel, workpieces move towards the vessel through an antechamber containing inert gas under pressure and comprising a plenum chamber opening downwardly into a lock chamber containing aprotic liquid. They move down into the liquid, then up out of it, into and through an inverted-U-shaped passageway containing higher pressure inert gas and which communicates with the lock chamber below the surface of the liquid therein and communicates with the electrolysis vessel above the surface of the electrolyte. At each connection between parts, where atmospheric oxygen might move towards the electrolyte, there are double mechanical seals defining a substantially annular chamber filled with aprotic liquid that forms a gas barrier, and such liquid is, where possible, shielded by inert gas.

Description

The invention relates to an aluminizing cell, consisting of an electroplating tank and locks connected upstream or downstream of this tank for introducing and removing the goods to be electroplated.

• 1. Aluminiumchlorid A1C1₃ und AlBr₃
• 2. Al(III)Hydrid A1H₃ im Gemisch mit A1C1₃
• 3. Al(III)-alkyle, insbesondere Al(C₂H₅)₃,

die mit Alkalimetall-Halogeniden bzw. -Hydriden (bei 2.) elektrisch leitfähige Komplexverbindungen bilden. Alle Bäder sind grundsätzlich vor Feuchtigkeit und Sauerstoff zu schützen, da z.B. (bei 3.) 1 Mol 0₂ die Zerstörung von 2 Mol Elektrolyt bewirkt:

1 Mol H₂0 dürfte 2-3 Mol Elektrolyt unwirksam machen, weil die Aluminiumäthylate nicht mehr imstande sind, Komplexe zu bilden; sie zeigen daher keine elektrische Leitfähigkeit und ihre Bildung ist also ein Verlust an Elektrolyt.Essentially, three aprotic electrolytes are known for the electrodeposition of aluminum as complex salt melts or in organic solvents, the aluminum starting compounds of which are:

• 1.Aluminum chloride A1C1 ₃ and AlBr ₃
• 2.Al (III) hydride A1H ₃ mixed with A1C1 ₃
• 3. Al (III) alkyls, in particular Al (C ₂ H ₅ ) ₃ ,

which form electrically conductive complex compounds with alkali metal halides or hydrides (at 2.). All baths must always be protected against moisture and oxygen, because, for example, (at 3.) 1 mol 0 ₂ causes the destruction of 2 mol electrolyte:

1 mole of H ₂ 0 should render 2-3 moles of electrolyte ineffective because the aluminum ethylates are no longer able to form complexes; therefore they do not show any electrical conductivity and their formation is therefore a loss of electrolyte.

If one considers the inert gas space that must be present above the electrolyte, the electrolyte can be regarded as a getter pump for 0 ₂ and H ₂ 0. This getter pump tries to maintain immeasurably small partial pressures of 0 ₂ and H ₂ 0 in its inert gas space and is used up in the process. A technically usable apparatus for the electrolytic deposition of aluminum must therefore have leak rates as low as a high vacuum system if the service life of the electrolyte is to be sufficient from an economic point of view (about 1 year) and, for mechanical reasons, not too much degradation products of the electrolyte in the gas space on the walls and the controls are to be deposited.

For the introduction and removal of the goods to be electroplated, the electrolyte compartment must have at least one opening which can be closed tightly and which must be designed as a lock in order to move the goods into and out of the electrolyte compartment without oxygen. Due to the large galvanic frames, which have to be used for economic reasons to attach the parts to be galvanized, suitable mechanical vacuum slides are very expensive, their tightness is difficult to test during operation and a repair means the production of the aluminum cell is down.

Liquid locks based on the principle of a U-tube have already been used with great success for the technical solution of similar tasks. The diagram of such a system is shown in FIG. 1. Here, next to the actual electroplating tank G, there is a lock S filled with liquid. A U-shaped space I filled with inert gas is located as a connecting element between the electroplating tank G and the lock chamber S. Arrows indicate the manner in which the goods are conveyed through the lock space S and the inert gas space I into the electroplating tank G. The return transport takes place in the opposite direction of the arrow. A pressure relief valve V connected to the inert gas space I ensures that a slight excess pressure remains constantly in the inert gas space.

As it could be determined, such a system works completely unsatisfactorily as an aluminizing cell. Diethyl ether would be suitable as a lock fluid for the electrolyte system with the aforementioned aluminum starting compound 2 and toluene for aluminum starting compounds 3. Other lock fluids were also considered, but no suitable one for the aluminizing process could be found which was sufficient as oxygen and moisture barrier between atmosphere and electrolyte space acts. In particular, the transport of moisture through the barrier or lock fluid, which for the purpose of filtering, the inward and outward transfer of goods and because of the temperature difference between the outside and the inside, should not be regarded as calm but as moved, is surprisingly high. For example, in a test plant with 160 l of toluene in the lock (0.25 m ² surface) and an electrolyte trough (0.2 m ² surface) with 80 1 electrolyte, corresponding to about 270 mol of Al (C ₂ H ₅ ) ₃ a relative humidity of 40 to 50% about 10 mol H ₂ 0 transported through the lock daily, ie the electrolyte is unusable in a much too short period.

In this system, the transport of oxygen was found to be around 0.2 mol per day. This value is too high for an economical and well-functioning aluminizing cell.

With regard to H ₂ 0, the conditions can be improved by known technical drying processes for toluene with silica gel columns that are regenerated with fresh distilled dry toluene. With this very complex process, toluene can be dried to about 5 to 10 ppm H ₂ O compared to moisture values of 220 to 280 ppm of toluene, which is exposed to an atmosphere of 40 to 50% relative humidity. This drying circuit for the toluene must be very efficient, since the toluene exposed to the atmosphere absorbs moisture very quickly. For example, in experiments carried out, the water content of 200 ml of toluene with a surface area of 16 cm ^{2, which was} agitated by stirring, rose from 5 ppm to 190 ppm in one hour with an air flow of 0.8 l / min (41% relative atmospheric humidity). A suitable drying cycle is therefore an almost intolerable economic burden for an aluminizing process due to its high energy consumption and the technical effort.

The object of the present invention is to provide an improved aluminizing cell with which the above difficulties described are technically, easily and economically resolvable. and which also makes it possible to stay with a liquid lock instead of the complex mechanical lock.

This object is achieved according to the invention in that the liquid lock known per se with an inert gas atmosphere covering the electroplating tank and a lock chamber following in the direction of the lock entrance and filled with an aprotic solvent on the lock entry side is preceded by an additional pre-chamber provided with a loading opening, in which an aprotic solvent is covered Inert gas atmosphere.

A design of the aluminizing cell according to the invention is characterized in that the oxygen transport is reduced to the smallest values that can no longer be measured safely and that the water transport is reduced by a factor of about 10 ² to 10 ³ , so that the durability of the electrolyte is at least one year to calculate.

Further details and features of the invention emerge from the subclaims.

The invention is explained in more detail below using exemplary embodiments with reference to the accompanying drawings.

• Fig. 1 eine schematische Darstellung einer Galvanisierzelle nach dem Stande der Technik,
• Fig. 2 eine schematische Darstellung einer erfindungsgemäßen Aluminierzelle,
• Fig. 3 eine ausführlichere Darstellung einer Aluminierzelle gemäß Fig. 2 in einem schematischen senkrechten Schnitt,
• Fig. 4 eine von links gesehene Seitenansicht der Fig. 3,
• Fig. 5 einen schematischen senkrechten Schnitt gemäß der Schnittlinie V - V der Fig. 3,
• Fig. 6 einen vertikalen Schnitt gemäß der Schnittlinie VI - VI der Fig. 3,
• Fig. 7 eine vergrößerte, teilweise geschnittene Teilansicht der in Fig. 3 mit VII bezeichneten lösbaren Behälterdichtungen und
• Fig. 8 eine geschnittene Seitenansicht der in Fig.6 mit VIII bezeichneten Dichtungen.

The drawings show:

• 1 is a schematic representation of a galvanizing cell according to the prior art,
• 2 shows a schematic representation of an aluminizing cell according to the invention,
• 3 shows a more detailed illustration of an aluminizing cell according to FIG. 2 in a schematic vertical section,
• 4 is a side view of FIG. 3 seen from the left,
• 5 shows a schematic vertical section along the section line V - V of FIG. 3,
• 6 is a vertical section along the section line VI - VI of FIG. 3,
• Fig. 7 is an enlarged, partially sectioned partial view of the releasable container seals in Fig. 3 and VII
• Fig. 8 is a sectional side view of the seals designated VIII in Fig.6.

As FIG. 2 shows, a liquid-filled lock chamber 3 is also arranged parallel to the actual electroplating tank 1 in the aluminizing cell according to the invention. Electroplating tank 1 and lock chamber 3 are connected by a U-shaped inert gas space 2. The main difference between the lock arrangement according to FIG. 1 and the arrangement according to the invention according to FIG. 2 is that the goods to be treated in the electroplating tank 1 are no longer introduced directly into the lock chamber, but first get into a closed pre-chamber 4, which is connected to an inside chamber essential gas-tight door is closed. Below the door 5, the pre-chamber 4 is provided with a calming chamber 14 which is in communication with the lock fluid in the lock chamber 3. The inert gas space 2 contains an inert gas cushion that is as dry and oxygen-free as possible, which is kept under a small excess pressure by means of the pressure relief valve 13 arranged in the prechamber 4. The prechamber 4 is also provided with a pressure relief valve 12, which ensures that the inert gas atmosphere present in the prechamber 4 also remains under a slight excess pressure, which is slightly smaller than the overpressure in the inert gas space 2. The lock chamber 3 is filled with an aprotic solvent.

Due to the fact that a dry and oxygen-free inert gas cushion is located above the entrance of the actual lock chamber 3, the 0 ₂ transport in the ratio of the partial pressures to the smallest values that are no longer reliably measurable and the water transport can be reduced by a factor of about 10 ² to 10 ³ lower. If, for example, 200 ml of moist toluene (300 ppm H ₂ 0) with a surface area of 16 cm ^{2 are introduced} with stirring into an argon atmosphere with 0.073 mbar H ₂ 0 at a flow rate of argon of 0.8 l / min, the toluene dries to 25 ppm in two hours, to 10 ppm in three hours and to 5 ppm of H ₂ in five hours. If the partial pressures are reduced, the exchange processes slow down enormously and the amounts of H ₂ O and 0 _{2 transported} become so low that a shelf life of the electrolyte of at least one year can be expected. This achieves an economically sufficient lifespan for the electrolyte and the galvanic aluminizing cell is inexpensive to manufacture if the electrolyte compartment is sufficiently sealed from the atmosphere.

The partial pressure of 0 ₂ in the atmosphere is approximately 200 mbar. Since the aluminum triethyl in the electrolyte space consumes the oxygen to small values that are no longer measurable, as already mentioned, partial pressure ratios arise, as can be found in high vacuum systems.

It has now been found that the requirements for the lowest leakage rates can be met under the conditions customary in chemical apparatus construction if all the necessary seals are designed to seal the electrolyte space and all the rooms which are on the way of the goods to be introduced and removed. that on a conventional mechanical seal with a sealing ring always a liquid barrier with an aprotic solvent, e.g. Oxygen- and moisture-free paraffin oil follows, which in turn can then be covered with an oxygen- and moisture-free inert gas. Such seals are described in detail below.

Normal paraffin from n-C10 to n-C12 saturated hydrocarbons at a 0 ₂ partial pressure of 0.2 bar takes up about 10 ppm 0 ₂ . This value can be reduced to below 0.1 ppm by flushing with inert gas.

The goods movement in the aluminizing cell according to the invention can be seen from the more detailed representation of FIGS. 3 to 6. The individual goods racks W are introduced via the substantially gas-tight door 5, which, as shown in FIG. 4, is designed as a sliding door. The goods racks W are then attached within the antechamber 4 to the conveyor, which contains two parallel chains or conveyor belts 20. In the direction of the infeed of the goods racks W, the conveyor chains 20 run via a pair of drive rollers 21 in the antechamber 4, a pair of rollers 22 in the lock chamber 3, two pairs of rollers 23 and 24 in the inert gas space 2, a pair of rollers 25 in the head part of the electroplating tank 1, two pairs of rollers 26 and 27 outside and above the pairs of rollers 23 and 24, one pair of rollers 28 above the pair of rollers 22 and two pairs of rollers 29 and 30 in the head part of the prechamber 4. Between the two pairs of rollers 29 and 30 there is a spring-loaded pair of tensioning rollers 31.

• Vorkammer 4, Beruhigungsraum 14, unterhalb des Flüssigkeitsspiegels 32 mit aprotischem Lösungsmittel gefüllte Schleusenkammer 3, oberhalb des Flüssigkeitsspiegels 33 Inertgasraum 2 und unterhalb des Elektrolytflüssigkeitsspiegels 34 Galvanisierkessel 1. Das Ausschleusen erfolgt in umgekehrter Richtung.

The goods racks W suspended in the antechamber 4 then go through the following route during the infeed:

• Pre-chamber 4, calming chamber 14, lock chamber 3 filled with aprotic solvent below the liquid level 32, inert gas chamber 2 above the liquid level 33 and 34 electroplating tank 1 below the electrolytic liquid level. The discharge takes place in the opposite direction.

The actual electroplating tank is designed in the usual way apart from the seals to be described below. Electrodes 41, which are interchangeably suspended, are immersed in the actual container 40 of the electroplating tank provided with a heating jacket. At the top, the container 40 is covered with a dome 48, which is firmly connected to the actual inert gas space 2. Detachable seals designated VII in FIG. 3 enable the container 40 to be separated from the dome. In the container 40 also dip pipes 42, which are used to circulate and filter the electrolyte and open with flanges 42 on the dome 48. Furthermore, of course, the electrodes 41 are provided with power connections, which are also led out in the dome 48 of the electroplating tank. The cathode current supply is carried out in isolation together with the chains 20 from the prechamber 4 to the isolated goods racks W.

As FIG. 6 shows, the goods W introduced there are moved in a manner known per se within the electroplating tank. For this purpose, the electric motor 44 is used, which moves the support rod 47 for the goods racks W back and forth via an eccentric disk 45 and the connecting rod 46. This support rod 47 is mounted on opposite sides of the dome 48 in special seals, which are designated VIII in FIG. 6. These bushings for the support rod 47 are explained in more detail below.

Finally, a level meter 49 is also arranged in the electroplating tank, which is led out upwards via the dome 48 and the inert gas space 2.

As already mentioned in the introduction, all detachable connections between the different parts of the container and at the execution points of pipelines, cables and the like, as far as they lie in the area of the transport route of the goods to be galvanized, are designed in a special way. An example of such a seal is shown in FIG. 7, which is the seal that is labeled VII in FIGS. 3 to 6.

As can be seen in FIG. 7, there is a flange 53 on the upper edge of the electroplating tank container 40, which contains three annular grooves 51, 52, 54 extending over the circumference on its upper side. The troughs 51 and 54 receive sealing rings made of Teflon, Viton or a similar material, while the circumferential trough 52 lying between them forms a liquid space. The counter flange 55 of the dome 48 is ground on its contact surface and then comes to rest against the sealing rings in the grooves 51 and 54, so that the annular space 52 provided for a liquid filling is completely enclosed. The press of the two Flanges 53 and 55 are made with clamping jaws 57 and 58, which are clamped together with a screw bolt 59.

The annular space 52 is connected at opposite points of the annular flange 55 via pipes 56, through which an aprotic solvent, preferably paraffin oil, is passed. This passage takes place via a closed circle, which is indicated schematically in FIG. 3. From a chamber 80 filled with paraffin oil, the paraffin oil is circulated by means of a pump 82 via the pipes 56 and 56 '. The chamber 80 is covered with a further chamber 81, which is filled with an inert gas cushion. This inert gas, preferably N ₂₁ , is also circulated.

In a similar way, the seal on the design of the level meter 49 is also formed on the upper side of the inert gas space 2. Here, too, as can be seen in FIG. 3, the connecting flanges 83 are surrounded by a paraffin oil bath 84, which in turn is covered on its upper side with an inert gas cushion 85. This can be the same inert gas as in chamber 81, that is to say nitrogen, which is in the same circuit is guided, like the nitrogen in the chamber 81 and the nitrogen still present in further seals for inert gas covers. However, a separate chalk can also be provided if, as shown in FIG. 3, there is a further chamber 86 filled with aprotic solvent, preferably paraffin oil, which is covered with an inert gas cushion 87. In the example shown here, the aprotic solvent is circulated via a pump 88, with which the aprotic solvent is also introduced into the seals VII-VII, which are provided on an inspection and assembly cover 89, which closes the inert gas space 2. The seals VII of the cover 89 are designed essentially as the seal described above with reference to FIG.

The seal, generally designated VIII in FIG. 7, of the goods movement rod 47 is shown in more detail in FIG. 8. The goods movement rod 47 is mounted in a recirculating ball bushing with an attached needle bearing 90. This recirculating ball bushing 90 is surrounded by a tubular housing 91, which also forms the outer bearing. The tubular housing 91 is connected at both ends to flanged glands 92 and 93, which are designed in a manner known per se and give the possibility to press the tubular packing together with a union nut and a pressure piece. On the two flange connections on both sides of the tubular housing 91, sealing rings 94 and 95 are provided, which can be made of Teflon, Viton or the like. According to the present invention, pipes 96, 97 open into the tubular housing 91, via which an aprotic solvent can be introduced into the entire interior of the housing 91 and kept in circulation there. This also results in a series connection of a mechanical seal, a liquid seal and a further mechanical seal.

Finally, it should be mentioned that all electrical connection lines for the power supply of the electrodes and the lines of the resistance thermometer 49 and other control devices are melted down in high vacuum bushings.

With regard to the seals, something similar also applies to the filter circuit, for which the necessary taps, the pump and the filters are preferably installed in a boiler which is filled with paraffin oil and covered with inert gas. To change the filter, only the paraffin level needs to be lowered in this boiler. The inert gas stream, which is preferably conducted via a closed circuit, can be passed through a regenerator which reduces the water and oxygen content of the gas.

Claims (10)

1. aluminizing cell, consisting of a galvanizing tank and this boiler upstream or downstream locks for introducing and removing the goods to be galvanized, characterized in that a liquid lock known per se with an inert gas atmosphere (2) covering the galvanizing tank (1) and one In the direction of the lock entrance (5) following lock chamber (3) filled with an aprotic solvent, an additional pre-chamber (4) provided with loading opening (5) is connected upstream of the lock, in which an inert gas atmosphere (2) covering the aprotic solvent is located. 2. aluminizing cell according to claim 1, characterized in that the prechamber (4) below the loading opening (5) contains a calming space (14). 3. aluminizing cell according to claim 1 and 2, characterized in that the inert gas is made oxygen and water-free argon or nitrogen. 4. aluminizing cell according to claim 1 to 3, characterized in that all in the region of the electroplating tank (1) and on the transport path of the goods to be electroplated (W) releasable container seals are designed as double seals (50), in the direction of the outside air of a conventional mechanical Sealing (51) is followed by a sealing space (52) filled with aprotic liquid, preferably paraffin oil. 5. aluminizing cell according to claim 4, characterized in that the aprotic liquid sealant is covered on the outside with an inert gas cushion. 6. aluminizing cell according to claim 4 and 5, characterized in that the inert gas cushion consists of nitrogen or argon. 7. aluminizing cell according to claim 4 to 6, characterized in that the liquid aprotic sealant is put into circulation and in the circulation circuit with an inert gas cushion (81) covered chamber (80) is provided (Fig.3). 8. aluminizing cell according to claim 5 to 7, characterized in that the inert gas, which forms the inert gas cushion for the aprotic liquid sealant, is guided in an open or closed circuit. 9. aluminizing cell according to claim 8, characterized in that the covering inert gas stream is passed through a regenerator which reduces the water and oxygen content. 10. aluminizing cell according to claim 4 to 9, characterized in that the mechanical seals are sealing rings made of fluoropolymer, in particular made of Teflon or Viton.

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