Method and device of conducting a closed cycle of the bath for plating of coatings

Description

[0001] The invention is related to a method and an apparatus for electroplating with a closed electrolyte cycle.

[0002] The known methods and devices for electroplating having a closed electrolyte cycle employ usually an evaporation process. Most often the water used for rinsing is evaporated and a concentrated solution of the components of the electrolyte is obtained. The evaporation process includes usually the application of vacuum for lowering the temperature of the process and increasing the intensity thereof. The known vacuum evaporators have generally an external heating chamber (indirect evaporators, as for example such from the companies Pfaudler, Corning and Cosmos). Known are also vacuum circulating evaporators (Simax Company).

[0003] Another group of evaporators are direct evaporators, in which evaporation takes place at atmospheric pressure (Lancy Company). Therein, the feeded electrolyte is heated in a heat exchanger and supplied from top of a column, wherein it flows down in a counter-current relation to incoming air and evaporates.

[0004] In all present methods and devices for evaporation the solution to be evaporated is heated in the evaporation device, and the heating chamber is an integral part of the evaporator.

[0005] The expense and the costs for hitherto known methods and devices are considerable, especially in the case of chemically aggressive electrolytes, as for example for chromium pfating. The heating elements had to be of special boro-silicate glass or materials of titanium or tantalum. Auxiliary equipment (pumps etc.) must be of special design.

[0006] For example, the costs for an evaporator of Corning Company with a capacity of Q = 67 of evaporated liquid/hr are in the order of US-$ 20,000 (1977).

[0007] Such costs sets back the technique of recycling of wastes despite of obvious effects on environmental protection.

[0008] It is, therefore, the object of the invention to provide a method and an apparatus for electroplating with a closed electrolyte cycle so that evaporation of water from the system is achieved at minimum expense.

[0009] This object is solved according to the invention by providing a method of electroplating in which electrolyte is fed into a circuit from an electroplating bath to an evaporation device, and from the evaporation device after concentration of the electrolyte in the evaporation device back to the electroplating bath, wherein the electroplating bath is heated and the electrolyte fed from the bath into the evaporation device is caused to flow horizontally in a thin film, air being blown, optionally after being heated, upwardly through the horizontally flowing electrolyte film in the whole evaporation device or only a part thereof, wet air having passed through the electrolyte being taken off from the circuit after previous separation of entrained particles, and the concentrated electrolyte from the evaporation device is introduced back to the electroplating bath, the electroplating bath further being made up continuously with washings from a water washer for washing workpieces after treatment in said electroplating bath.

[0010] Preferably, at least 25% of the heat necessary for evaporation in the evaporation device is supplied to the electroplating bath wherein the electrolyte is heated.

[0011] The air taken off from the circuit may be used for mixing after treatment in said electroplating bath.

[0012] The air taken off from the circuit may, after adding water vapour thereto, also be used for washing the workpieces after treatment in said electroplating bath.

[0013] It is also preferable that from the wet air which has passed through the electrolyte and which is taken off from the circuit water is condensed off, and that the condensed water is used as washing water in washers.

[0014] Further, the above object is solved according to the invention by providing an apparatus for electroplating, comprising an electroplating tank and an evaporation device connected with the electroplating tank through means, preferably an air lift pump, for supplying, in use, concentrated electrolyte from the evaporation device to the electroplating tank, wherein the electroplating tank comprises heating means and the evaporation device comprises an evaporating chamber which is horizontally elongated and comprises an upstanding weir whose height establishes the thickness of a horizontal layer of electrolyte flowing, in use, through the chamber, the chamber being provided with an inlet for electrolyte from the electroplating tank at its end remote from the weir, and further comprising a perforated conduit or conduits and/or a conduit or conduits having porous walls, through which, in use, air is fed, optionally after heating, into the chamber, the conduit or conduits extending below the level of the weir, and the chamber being connected at its end adjacent the weir with a separator, an upper part of the separator comprising a drop catcher through which, in use, wet air is taken off, and a lower part of the separator comprising an outlet for taking off the concentrated electrolyte and returning it to the tank, the heating means being connected to a temperature control system for controlling the temperature in the tank.

[0015] Preferably, the evaporation device is of polyvinyl chloride.

[0016] It is also to prefer that the drop catcher is of the labyrinth type and comprises air-flow guide vanes.

[0017] According to the invention, only the electrolyte is evaporated, and the heat necessary therefore is supplied, in principle, to the electrolyte in the electroplating tank or in the vicinity thereof, using the heating element which is a standard equipment of the tank. Optionally, the air introduced into the evaporation device is also heated. When the evaporator used according to the invention is assembled with an already operating electroplating equipment, the heating element already existing in the electroplating tank is used. Thus, doubling the heating elements is avoided. Additionally, the number of devices necessary for control of working parameters of the electrolyte are reduced. If necessary for power reasons, additional heating may be provided, this additional heating being only the complement between the heat power of the already existing equipment and the heat power necessary to achieve evaporation in the required amount.

[0018] According to the invention, evaporation is effected directly by the air passing through the electrolyte to be evaporated which flows in a closed channel and is in the phase of dynamic foam.

[0019] An example of realization of the solution according to the invention is now described with reference to the drawings.

Fig. 1 shows schematically an apparatus for electroplating together with a washer and a feeding tank, and

Fig. 2 shows schematically a single evaporation module.

[0020] In Fig. 1, the evaporation module or device of Fig. 1 is designated with reference numeral 10. With reference to Fig. 2, the feeded electrolyte is supplied by an inlet 1, flows through an evaporation pipe or chamber 2 and over a weir 3 and is finally taken off from a. separator 4 by an outlet 5. In the solution to be evaporated, a conduit 6 for air is immersed parallel to the axis of the pipe 2. The air, passing through the solution, causes mixing by the bubble flow, foam build-up and evaporation of the solution. A drop catcher 7 arrests particles of the solution entrained by the air. For the construction of the evaporation device polyvinyl chloride pipes are usually used.

[0021] Such a solution has a number of advantages in relation to the existing devices.

[0022] The apparatus and the method have a great design simplicity, are easy to realize, simple in operation and failure-free in use. On the basis of the standard module as shown in the example of Fig. 2 it is possible to build multi-module evaporators of a required capacity, usually about 100 I/hr of evaporated liquid. Such evaporators require little space and can be easily combined with already operating electroplating lines.

[0023] For laboratory purposes, the diameter of the pipe or chamber 2 was of D = 70 mm and the length of the evaporation zone 1 = 500 mm (Fig. 2).

[0024] Working on a semi-technical scale, two modules were used in a small electroplating plant for chromium plating. The sizes of a single module were D = 110 mm and 1 = 1200 mm.

[0025] As shown in Fig. 1, washings from washers 8 are directed as a whole by a pipe 20 to an electroplating tank 9. The flow rate of the electrolyte through the evaporation device 10 is controlled by a valve 11. The apparatus has emergency overflow means with an overflow conduit 18. After evaporation, the electrolyte is supplied by a pump 12 to a feeding tank 13 wherefrom it flows to the electroplating tank 9. The temperature in the electroplating tank is controlled by a temperature-control system comprising elements 14, 15, 16 and 17. An air outlet 19 is provided at the evaporation module or device 10.

[0026] Total evaporation from two modules connected in parallel was 10 I/hr. This enables material circulation in the electroplating plant in a closed cycle.

[0027] Fig. 1 does not show ion-exchange columns through which washings flow usually in order to eliminate impurities, for example Cr³⁺ and Fe³⁺ ions.

Claims

1. A method of electroplating in which electrolyte is fed in a circuit from an electroplating bath to an evaporation device, and from the evaporation device after concentration of the electrolyte in the evaporation device back to the electroplating bath, characterized in that the electroplating bath is heated and the electrolyte fed from the bath into the evaporation device is caused to flow horizontally in a thin film, air being blown, optionally after being heated, upwardly through the horizontally flowing electrolyte film in the whole evaporation device or only a part thereof, wet air having passed through the electrolyte being taken off from the circuit after previous separation of entrained particles, and the concentrated electrolyte from the evaporation device is introduced back to the electroplating bath, the electroplating bath further being made up continuously with washings from a water washer for washing workpieces after treatment in said electroplating bath.

2. The method according to claim 1, characterized in that at least 25% of the heat necessary for evaporation in the evaporation device is supplied to the electroplating bath wherein the electrolyte is heated.

3. The method according to claim 1, characterized in that the air taken off from the circuit is used for mixing of washing water in washers for washing the workpieces after treatment in said electroplating bath.

4. The method according to claim 1, characterized in that the air taken off from the circuit is, after adding water vapour thereto, used for washing the workpieces after treatment in said electroplating bath.

5. The method according to claim 1, characterized in that from the wet air which has passed through the electrolyte and which'is taken off from the circuit water is condensed off, and that the condensed water is used as washing water in washers.

6. Apparatus for electroplating, comprising an electroplating tank, and an evaporation device connected with the electroplating tank through means, preferably an air lift pump, for supplying, in use, concentrated electrolyte from the evaporation device to the electroplating tank, characterized in that the electroplating tank (9) comprises heating means (17) and the evaporation device (10) comprises an evaporating chamber (2) which is horizontally elongated and comprises an upstanding weir (3) whose height establishes the thickness of a horizontal layer of electrolyte flowing, in use, through the chamber, the chamber being provided with an inlet (1) for electrolyte from the electroplating tank (9) at its end remote from the weir (3), and further comprising a perforated conduit (6) or conduits and/or a conduit (6) or conduits having porous walls, through which, in use, air is fed, optionally after heating, into the chamber (2), the conduit (6) or conduits extending below the level of the weir (3), and the chamber (2) being connected at its end adjacent the weir with a separator (4), an upper part of the separator comprising a drop catcher (7) through which, in use, wet air is taken off, and a lower part of the separator (4) comprising an outlet (5) for taking off the concentrated electrolyte and returning it to the tank, the heating means (17) being connected to a temperature control system (14, 15, 16) for controlling the temperature in the tank (9).

7. The apparatus according to claim 6, characterized in that the evaporation device (10) is of polyvinyl chloride.

8. The apparatus according to claim 6, characterized in that the drop catcher (7) is of the labyrinth type and comprises air-flow guide vanes.

Ansprüche

1. Elektroplattierverfahren, bei welchem ein Elektrolyt in einen Kreislauf von einem Elektroplattierbad zu einer Verdampfervorrichtung und von der Verdampfervorrichtung nach der Konzentration des Elektrolyten in der Verdampfervorrichtung zurück zum Elektroplattierbad geführt wird, dadurch gekennzeichnet, daß das Elektroplattierbad erwärmt und der von dem Bad in die Verdampfervorrichtung geführte Elektrolyt horizontal in einem dünnen Film strömen gelassen wird, wobei Luft, nachdem sie wahlweise erwärmt worden ist, nach oben durch den horizontal strömenden Elektrolytfilm in der ganzen Verdampfervorrichtung oder nur in einem Teil davon geblasen wird, und feuchte Luft, nachdem sie durch den Elektrolyt hindurchgegangen ist, aus dem Kreislauf nach vorheriger Abtrennung von mitgeführten Teilchen entnommen wird, und daß der konzentrierte Elektrolyt aus der Verdampfervorrichtung zurück in das Elektroplattierbad eingeführt wird, wobei das Elektroplattierbad weiterhin mit Waschungen aus einer Wasserwascheinrichtung zum Waschen von Werkstücken nach der Behandlung in dem Elektroplattierbad kontinuierlich aufbereitet wird.

2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß wenigstens 25 % der für die Verdampfung in der Verdampfungsvorrichtung erforderlichen Wärme dem Elektroplattierbad zugeführt werden, indem der Elektrolyt erhitzt wird.

3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die aus dem Kreislauf abgezogene Luft zum Mischen des Waschwassers in den Wascheinrichtungen für das Waschen der Werkstücke nach der Behandlung in dem Elektroplattierbad verwendet wird.

4. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die aus dem Kreislauf abgezogene Luft nach Zugabe von Wasserdampf zum Waschen der Werkstücke nach der Behandlung in dem Elektroplattierbad verwendet wird.

5. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß aus der feuchten Luft, die durch den Elektrolyten hindurchgegangen ist und die aus dem Kreislauf abgezogen worden ist, Wasser auskondensiert wird und daß das auskondensierte Wasser als Waschwasser in den Wascheinrichtungen benutzt wird.

6. Elektroplattiervorrichtung mit einem Elektroplattierbehälter und einer Verdampfungsvorrichtung, die mit dem Elektroplattierbehälter durch Einrichtungen, vorzugsweise einer Luftheberpumpe verbunden ist, um in Betrieb konzentrierten Elektrolyt aus der Verdampfervorrichtung zum Elektroplattierbehälter zur transportieren, dadurch gekennzeichnet, daß der Elektroplattierbehälter (9) Heizeinrichtungen (17) und die Verdampfervorrichtung (10) eine Verdampferkammer (2) aufweist, die horizontal langgestreckt ist und ein hochstehendes Wehr (3) aufweist, dessen Höhe die Dicke einer horizontalen Elektrolytschicht bestimmt, die in Betrieb durch die Kammer strömt, wobei die Kammer mit einem Einlaß (1) für den Elektrolyten aus dem Elektroplattierbehälter (9) an seinem von dem Wehr (3) entfernt liegenden Ende versehen ist und weiterhin eine perforierte Leitung (6) oder Leitungen und/oder eine Leitung (6) oder Leitungen mit porösen Wänden aufweist, durch welche in Betrieb Luft, wahlweise nachdem sie erwärmt worden ist, in die Kammer (2) geführt wird, die Leitung (6) oder die Leitungen sich unter dem Pegel des Wehrs (3) erstrecken und die Kammer (2) an ihrem dem Wehr benachbarten Ende mit einem Separator (4) verbunden ist, von dem ein oberer Abschnitt einen Tropfenfänger (7), über den im Betrieb feuchte Luft abgezogen wird, un ein unterer Teil einen Auslaß (5) für die Entnahme des konzentrierten Elektrolyten und zur Rückführung zu dem Behälter aufweist, und daß die Heizeinrichtungen (17) mit einem Temperatursteuersystem (14, 15, 16) zum Steuern der Temperatur in dem Behälter (9) verbunden sind.

7. Vorrichtung nach Anspruch 6, dadurch gekennzeichnet, daß die Verdampfervorrichtung (10) aus Polyvinylchlorid besteht.

8. Vorrichtung nach Anspruch 6, dadurch gekennzeichnet, daß der Tropfenfänger (7) in Labyrinthbauweise ausgeführt ist und Luftstromführungsplatten aufweist.

Revendications

1. Procédé de galvanoplastie dans lequel un électrolyte est délivré, en un circuit, d'un bain de galvanoplastie à un dispositif d'évaporation, puis renvoyé au bain de galvanoplastie à partir du dispositif d'évaporation, après concentration de l'électrolyte dans ce dispositif d'évaporation, caractérisé par le fait que le bain de galvanoplastie est chauffé et l'électrode, introduit dans le dispositif d'évaporation à partir du bain, subit une mise en circulation horizontale forcée en un film mince, de l'air étant insufflé, éventuellement après avoir été chauffé, de bas en haut à travers le film d'électrolyte s'écoulant horizontalement dans tout le dispositif d'évaporation ou seulement dans une partie de celui-ci, de l'air humide ayant traverse l'électrolyte étant évacué du circuit après séparation préalable des particules entraînées; et l'électrolyte concentrée provenant du dispositif d'évaporation est réintroduit dans le bain de galvanoplastie, ce bain de galvanoplasti étant par ailleurs continûment renouvelé par des rejets de lavage provenant d'un laveur à l'eau pour laver des pièces à travailler, après traitement dans ledit bain de galvanoplastie.

2. Procédé selon la revendication 1, caractérisé par le fait qu'au moins 25 % de la chaleur nécessaire à l'évaporation, dans le dispositif d'évaporation, est délivrée au bain de galvanoplastie dans lequel l'électrolyte est chauffé.

3. Procédé selon la revendication 1, caractérisé par le fait que l'air évacué du circuit est utilisé pour le mélange d'eau de lavage, dans des laveurs pour laver les pièces à travailler après traitement dans ledit bain de galvanoplastie.

4. Procédé selon la revendication 1, caractérisé par le fait que l'air évacué du circuit est utilisé; après que de la vapeur d'eau y a été ajoutée, pour laver les pièces à travailler après traitement dans ledit bain de galvanoplastie.

5. Procède selon la revendication 1, caractérisé par le fait que de l'eau est condensée à partir de l'air humide qui a traversé l'électrolyte et est évacué du circuit; et par le fait que l'eau condensée est utilisée en tant qu'eau de lavage dans des laveurs.

6. Dispositif de galvanoplastie, comprenant une cuve de galvanoplastie et un dispositif d'évaporation raccordé à cette cuve de galvanoplastie par l'intermédiaire de moyens, de préférence une pompe d'ascension d'air pour délivrer en service, à la cuve de galvanoplastie, un électrolyte concentré provenant du dispositif d'évaporation, caractérisé par le fait que la cuve de galvanoplastie (9) présente des moyens de chauffage (17) et le dispositif d'évaporation (10) comporte une chambre d'évaporation (2) qui est allongée horizontalement et possède une chicane (3) dressée à la verticale, dont la hauteur détermine l'épaisseur d'une couche horizontale d'électrolyte circulant en service à travers la chambre, cette chambre étant munie, à son extrémité éloignée de la chicane (3), d'une admission (1) d'électrolyte provenant de la cuve de galvanoplastie (9), et présentant par ailleurs un ou des conduits perforés (6) et/ou un ou des conduits (6) ayant des parois poreuses à travers lesquelles, en service, de l'air est introduit dans la chambre (2) après chauffage éventuel, le ou les conduits (6) s'étendant au-dessous du niveau de la chicane (3), et la chambre (2) étant reliée à un séparateur (4) à son extrémité adjacente à la chicane, une région supérieure du séparateur présentant un capteur de gouttelettes (7) par l'intermédiaire duquel de l'air humide est évacué en service, et une région inférieure du séparateur (4) présentant une sortie (5) pour évacuer l'électrolyte concentré et pour le renvoyer à la cuve, les moyens de chauffage.(17) étant connectés à un système (14, 15, 16) de commande de la température pour maîtriser la température régnant dans la cuve (9).

7. Dispositif selon la revendication 6, caractérisé par le fait que le dispositif d'évaporation (10) est en polychlorure de vinyle.

8. Dispositif selon la revendication 6, caractérisé par le fait que le capteur de gouttelettes (7) est du type à labyrinthe, et possède des valves de guidage de la circulation d'air.

Drawing