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

Abstract

 The device for conducting a closed cycle of the electroplating bath, especially in the process of electroplating, comprising an electrolytic tank, an evaporation device connected with the electrolytic tank through a device feeding the electroplating bath, is characterized in that in the electrolytic tank or in the vicinity thereof heating devices (17) are comprised and in the evaporation chamber of the evaporation device (10) there are no heating devices, the evaporation chamber (2) of the evaporation device is horizontal and comprises a partition (3), the inlet (1) of the bath to the evaporation chamber is situated on the opposite side in relation to the partition (3), the evaporation chamber (2) comprises a perforated conduit (6) or conduits and/or conduits having porous walls, the evaporation chamber (2) is connected from the side of the partition (3) with a separator (4), the upper part of the separator (4) comprises a drop catcher (7), and the lower part of the separator (4) comprises a conduit (5) taking off the concentrated bath to the electrolytic tank (9), the heating device (17) in the tank being connected to a temperature-control system (14, 15, 16) for control of the temperature of the bath.

Description

[0001] The subject of the invention is a method of conducting a closed cycle of the bath for plating of coatings, especially in the process of electroplating, end devices for conducting a closed cycle of the bath for plating of costings, especially in the process of electroplating.

[0002] The known methods of conducting e closed cycle of the bath in the process of electroplating consist usually in conducting the evaporative process. It is most often aimed at evaporation of water used for rinsing and at obtaining a concentrated solution of the composition corresponding to the composition of electroplating beth, after which rinsing follows.

[0003] The known evaporative processes applied for this purpose are usually conducted at lowered pressure end indirect heating, most often at a raising film of the liquid. The application of vacuum is aimed at lowering the temperature of the process and at increasing the intensity thereof. This increases, however, the degree of difficulty of conducting the process end raises the cost of the process. Those skilled in the art knov. also vacuum processes with forced circulation, of still higher degree of complication and additionally increased costs of conducting the process.

[0004] Another method of conducting the evaporative process is direct evaporation at etmospheric pressure. The feed is he^pted in an external heat exchanger, supplied upward to a column with a packing, wherein it evaporates, flowing down in the counter-current in relation to the flowing air.

[0005] It should be indicated that in all presently applied methods of eveporation the solution - to be evaporated is heated in the ev^pporation zone.

[0006] Known devices for conducting the closed cycle of beth in the process of electroplating comprise usually an evaporator. This is most often aimed at evaporation of water used for rinsing and at obtaining a concentrated solution of the composition corresponding to the composition of electroplating bath, after which rinsing follows.

[0007] The known evaporators are, as a rule, vacuum devices, with an external heating chamber (indirect evaporators). Most often they are the so--called evaporators with a raising film of the liquid (of the comp^pnier Pfaudler, Corning, Cosmos). The application of v^pcuum is aimed at lowering the temperature of the process and at increasing the intensity thereof. This raises, however, the cost of the device. Known also are vacuum circulating evaporators (of the Simex company).

[0008] Another group of the applied evaporators are direct evaporators, in which evaporation proceeds at atmospheric pressure (evaporators of the Lancy company).

[0009] The feed is heated in the external heat exchanger, supplied upward to a column with a packing, wherein while flowing down in the counter--current in relation to the flowing air it evaporates.

[0010] In all presently applied methods of evaporation the heating. chamber is an integral part of the evaporator..

[0011] The cost of hitherto applied methods and devices is considerable, especially in the case of chemically aggressive baths, e.g. the chromium plating bath. In the case of aggressive baths, heating elements of the evaporator should be made of special borosilicate glass (Simax company) or of special materials, e.g. titanium, tantalum. Auxiliary equipment must be of special design (e.g. pumps) etc.

[0012] For example, the cost of the evaporator of Corning company, of the yield of Q=67 1 of evaporated liquid/hr is of the order of US $ 20,000 (1977).

[0013] Such a considerable investment cost, in spite of economic management of the whole enterprise and obvious effects of environmental protection, sets back the progress of the new technique of utilization of wastes.

[0014] The task of the invention is to work out a method end a device for pumping off the bath, comprising an appropriate evaporation device, so that it is possible to achieve the required evaporation of water from the system at the minimum costs.

[0015] The method of conducting a closed cycle of the bath for plating of coatings, especially in the process of electroplating, consists in feeding the bath from the electrolytic machining zone to the evaporation zone, and from the eveporation zone - after concentration of the bath in the evaporation zone - back to the electrolytic machining zone, and according to the essence of the invention it is characterized by that the electroplating bath is heated in the electrolytic machining zone and is introduced to the evaporation zone in which the bath is conducted in a flow in a thin layer horizontally, whereby in the whole evaporation zone or only in a part, thereof through the horizontally Conducted bath air is conducted from below upwards by barbotage, eventually, the conducted air is heated end afterwards wet air conducted through the beth is taken off outside from the circulation after previous separation of entrained particles by the inertia method, end the concentrated solution from the evaporation zone is fed back to the electrolytic machining zone, the electroplating b^pth being made up in a continuous way by washings from a water washer for rinsing of objects after the said electroplating beth.

[0016] According to the invention it is preferable thet the electroplating bath is heated in the electrolytic machining zone, supplying in the s^pid zone at least 25% of heat necessary for evaporation in the evaporation zone. In this case the remaining amount of necessary heat is supplied to air which passes through the bath in the evaporation zone. by barbotege.

[0017] According to the invention it is advisable to introduce to the evaporation zone at least 55% of the volume of the electroplating bath.

[0018] It is preferable, according to the invention, to introduce to the electroplating bath at least 55% of the volume of washings after rinsing of objects treated in the said electroplating bath.

[0019] According to the invention it is advisable that 'the air taken off outside from the circulation is used for mixing the rinsing water in washers for washing the objects after the said electroplating bath.

[0020] It is preferable, according to the invention, that the air taken off outside from the circulation, after adding water vapour thereto, is used for washing the objects after the said electrorla- _ ting bath.

[0021] According to the invention it is advisable tnpt from wet air conducted through the bath, taken off aoutside from the circulation, water is condensed off and said condensed-off water is used as washing water in washers.

[0022] The device for conducting a closed cycle of the beth for plating of coetings, especially in the process of electroplating, comprising an electrolytic tank, en evaporation device connected with the electrolytic tank through a device feeding the electroplating bath, prefer^pbly an air lift pump, according to the essence of the invention is characterized by th^pt in the electrolytic tank heating devices are comprised, end in the evaporation chamber of the evaporation device there are no heating devices, the evaporation chamber of the evaporation device is horizontal and comprises a partition whose height establishes the thickness of the layer of the liquid, the bath inlet to the evaporation chamber is at the opposite side in relation to the partition, the evaporation chamber comprises a perforated conduit or conduits and/or conduits with porous walls, through which air is supplied to the evaporated bath, eventually heated air, the evaporation chamber is from the side of the partition connected with a separator, the upper part of the separ^p- tor comprises a drop catcher through which wet air is taken off, end the lower part of the separator comprises a conduit taking off the concentrated bpth to the electrolytic t^pnk, where by the he^pting device in the tank is connected to the temper^pture-control system to control the temper^ptu- re of the bath.

[0023] It is preferable that the constructional material for building the evaporation device is polyvinyl chloride.

[0024] It is advisable that the drop catcher is of a labyrinth type and comprises air-flow guide vanes.

[0025] According to the invention only the bath is evaporated, and heat necessary to heat the liquid is supplied, in principle, only to the bath in the electrolytic tank or in the vicinity thereof, with the use of the heating element being the standard equipment of the said tank, or only the air introduced to the evaporation zone is heated. When the evaporator is assembled with the already operating electroplating equipment, we use the heating element already existing in the electrolytic machining zone. Due to this, in newly designed lines we avoid doubling the heating elements. The method according to the invention reduces also the number of devices necessary for automatic control of the working parameters of the bath. If necessary for power reasons, additional heating is employed, with the supply of heat power being the complement between the heat power of the already existing equipment and the heat power necessary to conduct evaporation with the reoui- red yield.

[0026] According to the invention, evaporation is effected directly, by letting the air pass through the bath being evaporated flowing in a closed channel, being in the phase of dynamic foam.

[0027] The solution according to the invention is described in the example of realisation by means of the drawing of the exemplary device, which serves for realisation of the method. Fig.l presents a schematic device together with a washer and a feeding tank, and fig.2 presents schematically a single evaporation module applied for realisation according to the invention and marked in fig.1 with number 10. The feed is supplied by a stub pipe 1, it flows by a flow pipe 2, overflows through a partition 3, and from aseparator 4 is taken off by a stub pipe 5- In the evaporated solution, p^p- rellel to the exis of the pipe 2, a supply pipe 6 of air is immereed, said air, passing through the solution, causes barbot^pge and evaporation thereof. The drop catcher 7 arrests particles of the solution entrained by air. As materials for building the device polyvinyl chloride pipes are usually used.

[0028] Such e solution has a number of advantages in relation to the existing devices.

[0029] The device and the method are characterized by big design simplicity, essiness of execution, simple operation and failure-free work during use.

[0030] On the basic of one standard module, such of shown in the example in fig.1, it is possible to build to the device according to the invention malti--module evaporators of the required yield, usually to about 100 1/hr of the evaporated liquid. Such evaporators require little space and c^pn be easily compiled with the already operating electroplating line. In laboratory conditions the operation of one module of the evaporator presented in fig.1, of the length of the pipe 2 of D=70 mm and the length of the evaporation zone 1=025 n.

[0031] In the second experiment two modules of the eveporator were used for closing the materiel circulation after chromium plating in a small elec- tropleting plant working in a semi-technical acale. parameters of a single module: D=110 mm, 1=1200 mm.

[0032] As shown in fig.2, washings from weshere 8 are directed as a whole by a conduit 20 to an electrolytic tank 9. The rate of flow of the bath through the evaporator 10 is controlled by the valve 11: The device has en emergency overflow whose overflow conduit is marked in fig.2 with number 18. After evaporation, the bath is supplied by the pump 12 to the feeding tank 13 wherefrom it flows to the tenk 9. The temperature in the tank is controlled by a temperature-control system consisting of elements 14, 15, 16, 17. The outlet of air from the evaporation module is marked with number 19. Total evaporation from two modules connected parallely was 10 1/hr. It enables closing the materiel circulation of the electroplating plant.

[0033] Fig.2 does not show ion-exchenre columns whrough which washings flow. in order to elimin^p- te impurities, mainly ions Cr³⁺, F^e3+.

Claims

1. A method of conducting a closed cycle of the bath for plating of coatings, especially in the pro- _'ess of electroplating, consisting in feeding the bath from the electrolytic machining zone to the evaporation zone., and from the evoporation zone after concentration of the bath in the evaporation zone back to the electrolytic machining zone, characterized in that the electroplating bath is heated in the electrolytic machining zone end is introduced to the evaporation zone in which the bath in conducted in the flow in a thin film horizontally, whereby in the whole evaporation zone or only in a part thereof through the horizontally conducted bath from below upwards air is conducted by barbotage, eventually, the air being conducted is heated, and afterwards wet air conducted through the bath is taken off outside from the circulation after previous separation of entrained particles by the inertia method, and the concentrated solution from the evaporation zone is introduced back to the electrolytic mp- chining zone, and thereefter the electroplating bath is made up in a continuous way with washings from the water washer for washing the objects after said electroplating bath.

2. / method according to clair 1, Characterized in that the electroplating bath is heated in the electrolytic machining zone, at least 25% of heat necessary for evaporation in tne evaporation zone being supplied in the said zone.

3. A method according to cl^pim 1, characterized in that to the evaporation zone at least 55% of the volume of the electroplating b^pth is fed.

4. A method according to claim 1, ch^practerized in that to the electroplating bath at least 55% of the volume of washings after washing of objects treated in the said electroplating bath is fed.

5. A method according to clpim 1, charaterized in that air teken off outside from the circulation is used for mixing of washing water in washers for washing the objects after the said electroplating bath.

6. A method according to claim 1, characterized in that air teken off outside from the circulation is, after adding water vapour thereto, used for washing the objects after the said electroplating bath.

7. A method according to claim 1, characterized in that from wet air conducted through the beth, taken off outside from the circulation, water is condensed off and said condensed-off water is used as washing water in washers.

8. A device for conducting a closed cycle of the bath for plating of coatings, especially in the process of electroplating, comprising en electrolytic tank, an evaporation device connected with the electrolytic tank through a device feeding the electroplating bath, preferably an air lift pump, characterized in that the electrolytic tank comprises heating devices (17) and in the evaporation chamber of the evaporation device (10) there are no heating devices, the evaporation chamber (2) of the eveporation device is horizontal and comprises a partition (3) whose height establishes the thickness of the horizontal layer of the bath, the inlet (1) of the bath to the evaporation chamber is at the opposite side in relation to the partition (3), the evaporation chamber (2) comprises a perforsted conduit (6) or conduits and/or conduits having porous walls, through which to the evaporated bath air is fed, eventually heated air, the evaporation chamber (2) is connected from the side of the partition with a separator (4), the upper pert of the separator (4). comprises a drop catcher (7) through which wet air is taken off, and the lower part of the separator (4) comprises a conduit (5) taking off the concentrated bath to the tank (9), the heating device (17) being connected to the temperature--control system (14, 15, 16) for controlling the temperature of the bath.

9. A device according to claim 8, characterized in that the constructional material to build the evaporation device is polyvinyl chloride.

10. A device according to claim 8, characterized in that the drop catcher (7) is of the labyrinth type end comprises air-flow guide vanes.

Drawing