Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-07-12
2003-10-07
Valentine, Donald R. (Department: 1742)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S275100, C204S263000
Reexamination Certificate
active
06630060
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of carrying out an electro-chemical treatment, especially, for electro-chemically coating conducting parts or parts made to be conducting. The parts are placed in a container which is filled with an electrolyte and includes two electrodes (anode, cathode) connected to a constant voltage source. Electro-chemical coating, i.e. galvanic coating, constitutes the major application of the invention. However, provided the anode and cathode are suitably exchanged, it is also possible to use the method for electro-chemical cleaning or electro-chemical abrasion. Furthermore, anodic/cathodic immersion painting may be included by the invention. In addition, the invention relates to a plant for carrying out an electro-chemical treatment, especially for electro-chemically coating conducting parts or parts made to be conducting. The plant includes a container filled with an electrolyte with two electrodes (anode, cathode) in the container connected to a constant voltage source.
Metallic or plastic parts with surfaces that are pre-treated to render them conductive are galvanically plated for corrosion protection purposes and partly, for decorative purposes. Depending on the size, shape and number of parts or products to be plated, different process techniques are applied.
In the case of continuous processes, endless belts, tubes or wires are pulled through a galvanic bath at a speed of 10 to 300 m/min. Contact of the cathode is established by rollers. The higher the speed, the higher the current density to be applied. In the case of zinc plating, up to 200 A/dm
2
can be achieved. This produces a plating thickness of 15 &mgr;m which takes about 17 seconds.
In the case of a rack method, parts are placed on to the rack, which is electrically connected to the cathode, and suspended in the galvanic bath. For zinc plating, the current density ranges between 2 to 4 A/dm
2
. A plating thickness of 15 &mgr;m builds up in about 20 to 40 minutes. The rack method is suitable for very large parts, for example tubes several meters long and for small parts, for instance valuable turned parts. In general, the parts are placed on the rack manually, since the rack method is not suitable for mass production.
Articles in bulk, especially articles such as bolts, nuts, washers and the like are plated by a drum method. The parts are placed into a perforated drum which is immersed in the galvanic bath. Inside the slowly rotating plastic drum, flexible, isolated cables with non-insulated ends, move over the parts to provide the electric contact with the cathode. In the case of zinc plating, the current density ranges between 0.5 to 1.5 A/dm
2
. This produces a plating thickness of 15 &mgr;m in about 60 to 160 minutes.
Methods and devices for surface coating are known from DE 31 21 397 C1 and DE 32 30 108 C2. Here, electro-chemical surface coating of small parts is shown. The parts are received in a drum which is rotatably drivable in a container. In a first axis position during the coating phase, coats the parts are coated at a low rotational speed. In a second vertically oriented axis position, after the treatment fluid has been drained off, the parts are centrifuged at an increased rotational speed. The means used to carry out the electro-chemical process are not explained in greater detail in these publications.
In continuous operating plants, rack and drum plants, electro-chemical surface treatment takes place in open baths. As a rule, if several such baths are arranged side by side, they form a considerable bath surface. While the processes take place, spray mist and vapors occur which constitute workplace pollution. Accordingly, considerable measures are taken to ensure extraction of the spray mist, vapors and gases which occur during the various process stages. Even in the case of smaller systems, exhaust quantities ranging between 5000 and 10,000 m
3
/h have to be dealt with; in the case of larger systems, exhaust quantities ranging between 100,000 and 200,000 m
3
/h may have to be extracted and treated. The exhaust air enters an air washer and is thereafter released into the open atmosphere. Corresponding quantities of fresh air have to be introduced from the outside, so that considerable ventilator capacities are provided. In the winter, sucked-in cold fresh air has to be heated which requires large amounts of energy, which, in turn, leads to the need for heat exchangers through which hot exhaust air is conducted in a counter flow to cold fresh air.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and device of the above-mentioned type which, while having a simple design, achieves a high coating output.
The objective is achieved by a method where the parts are connected cathodically by a hub of the basket. The electrolyte is pumped through the container in a cycle. The container is sealed to remain gas-proof.
Because the parts are connected cathodically by the hub of the basket, the power supply to the parts is ensured at all times. Circulating the electrolytic solution through the container ensures that the coating is applied to the parts in a uniform and defect-free way. In a preferred embodiment, the parts are re-arranged during the coating operation by rotating the basket around a horizontal axis.
In the container, preferably a flow speed of the electrolytic solution is maintained at least 1 m/min; especially approximately 10 m/min. It is possible to achieve high currency densities which lead to short coating times. The current density is preferably set to approximately 10 A/dm
2
in the case of zinc electrolytes and aluminum electrolytes and to approximately 25 A/dm
2
in the case of acidious copper electrolytes. In particular, an electrolytic solution temperature advantageous for the process is maintained in the container. Optionally, the electrolytic solution has to be heated or cooled within the closed cycle in a suitable place. In the case of non-aqueous electrolyte systems, the term “electrolytic solution” also includes salt melts.
A compensating container in the cycle for the electrolytic solution can ensure permanent freedom from gas in the container.
After a coating phase, the electrolytic solution is pumped out of the container. Remaining electrolyte is centrifuged off the surface of the parts under the effect of a centrifugal force. For this purpose, the basket axis is preferably first set to a vertical position.
This process can be followed by a washing operation in the container itself. Any water adhering to the parts is also centrifuged off the parts under the effect of a centrifugal force. To achieve a uniform coating, it is particularly advantageous if, during the electro-chemical treatment, the parts are continuously re-arranged during the electro-chemical treatment in the stream of electrolytic solution.
To continue to improve the process when using aqueous electrolytes, it is proposed that, a principle-related H
2
-containing partial stream of the electrolytic solution (catholyte) is extracted in the vicinity of the parts, and a principle-related O
2
-containing partial stream of the electrolytic solution (anolyte) is extracted in the vicinity of the anode during the coating phase. Accordingly, through-mixing is avoided and it ensures that in the vicinity of the parts, an electrolyte flow with a sufficiently high percentage of metal ions is added. To carry out the process economically and especially to recover part of the energy used for water decomposition purposes, an inert anode is used. The catholyte stream outside the container, while forming additional H
2
, is fed with metal ions or metal ion complexes. The anolyte stream and the catholyte stream, especially if enriched with metal ions or metal iron complexes, are fed into the cathode chamber or, respectively, the anode chamber of a fuel cell.
For aprotic (proton-free
on-aqueous) electrolytes, and for aqueous electrolytes with very high current requirements, it is advisable to transport the catholyte and anolyte separately. Thi
Bube Dirk
Jansen Rolf
Müller Alois
Väärni Markku
Valentine Donald R.
WMV Apparatebau GmbH & Co. KG
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