EP0132719B1

EP0132719B1 - Method and device of conducting a closed cycle of the bath for plating of coatings

Info

Publication number: EP0132719B1
Application number: EP19840108238
Authority: EP
Inventors: Ryszard Wasiak; Marek Kieszkowski; Dariusz Cichowski; Pawel Ciecko; Maciej Zubr
Original assignee: Instytut Mechaniki Precyzyjnej
Current assignee: Instytut Mechaniki Precyzyjnej
Priority date: 1983-07-30
Filing date: 1984-07-12
Publication date: 1988-03-09
Also published as: DE3469764D1; EP0132719A1

Description

The invention is related to a method and an apparatus for electroplating with a closed electrolyte cycle.
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).
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.
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.
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.
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).
Such costs sets back the technique of recycling of wastes despite of obvious effects on environmental protection.
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.
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.
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.
The air taken off from the circuit may be used for mixing after treatment in said electroplating bath.
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.
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.
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.
Preferably, the evaporation device is of polyvinyl chloride.
It is also to prefer that the drop catcher is of the labyrinth type and comprises air-flow guide vanes.
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.
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.
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.

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.
Such a solution has a number of advantages in relation to the existing devices.
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.
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).
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.
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.
Total evaporation from two modules connected in parallel was 10 I/hr. This enables material circulation in the electroplating plant in a closed cycle.
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.