DE1089237B - Galvanic bath and process for anodic glazing of objects made of aluminum and aluminum alloys - Google Patents

Description

GERMAN

The invention relates to an electroplating bath and to methods for anodic bathing carried out therewith Shining objects made of aluminum and aluminum alloys. There are different electrolyte compositions has been proposed for such gloss baths, e.g. B. Solutions of glacial acetic acid in water or solutions containing fluoborate. Electrolytes which contain sulfuric acid and chromic acid together are also proposed as brightening baths been. However, these baths have hardly been able to be used in practice because of their composition brings a relatively large amount of material removed from the anode with it, resulting in a rapid Enrichment of aluminum in the bathroom follows. In these baths there is usually a purely chemical attack Objects held by the electrolyte. The chromic acid is developed by the one at the cathode Hydrogen is continuously reduced and loses its effectiveness over the course of the treatment.

Thorough tests have shown that the disadvantages, which hitherto an application of electrolytes with sulfuric acid and chromic acid opposed in practice, by certain dosage of the two Said additives in the bathroom can be largely eliminated, so that excellent results are achieved will.

It has been found that a hot bath containing sulfuric acid and chromic acid in sufficiently high Concentration contains almost all of the oxide layer formation in the anodic treatment of aluminum prevented. Instead of the formation of an oxide layer, there is a strong luster of the material underneath relatively little remaining material removal.

The polishing bath according to the invention is characterized in that the electrolyte 1300 to 1750 g Contains sulfuric acid and 3 to 40 g chromic acid or chromic acid up to the saturation limit per liter. the The best results are obtained with an electrolyte content of 10 to 30 g of chromic acid and 1300 to 1600 g sulfuric acid per liter achieved. However, the bath also gives a good shine effect if the Chromic acid content drops to 3 g / l during operation.

The temperature of the electrolyte should be 50 to 100.degree. C., preferably 80 to 90.degree. High current densities can be used, usually from 25 to 50A7dm ² ; however, the current density can be increased to 80 A / dm ² . The voltage can be 8 to 24 V. It is preferred to work with voltages of 13 to 20 V.

The duration of treatment depends on the nature of the surface of the parts to be polished and the purity of the material. It can be between 5 seconds and 6 minutes, depending on the Galvanic bath

and methods for the anodic brightening of articles made of aluminum

and aluminum alloys

Applicant:
Langbein-Pfanhauser works

Corporation,
Düsseldorf, Hildebrandtstr. 9

Karl Guggenberger, Nuremberg,
has been named as the inventor

Roughness of the surface. Examples of a favorable sulfuric acid and chromic acid content are: 1550 g H ₀ SO ₄ and 12 g chromic acid per liter.

In some cases, a further improvement in the economic operation of the polishing baths can be achieved almost constant effect can be achieved according to the invention in that when carrying out the Polishing process cathodes, preferably made of lead, are used, which are made into a liquid-tight, acid-proof Diaphragm are used. Thereby, one is caused by the cathodically evolved hydrogen prevents strong circulation of the bath, which has a disruptive effect on the polishing effect. Any Osmosis phenomena can be determined by a suitable choice of the electrolyte concentration in the anode and Prevent cathode compartment. The diaphragms can be formed by individual cells, which are the cathodes surround. Instead, one or more diaphragm walls can be inserted in a liquid-tight manner Be used bath tank, which divide this into a number of departments, the largest of which are used Forms anode space serving for the treatment of the goods.

The process can be used for shining purest aluminum with 99.99% Al and commercially available pure aluminum, z. B. from 99.5 to 99.85%> Al with very to be applied with good success. Alloys with a low magnesium content (less than 3%) and those with a low copper and silicon content can also be treated well.

Even with pressed parts with 3.8% Cu, 0.6% Mg, 0.5% Fe, 0.75% Mn and 0.25% Zn, which are chemically

009 607/336

Claims (5)

see the polishing process or the already known electrolytic Methods that could not be treated with success are made according to the method of the invention Perfect gloss achieved, also with wire material with 2.7 «/» Cu and 2.18%. Zn or Al-Mg-Si type alloys with zinc additive. In particular, when carrying out the method, the procedure is that the objects first by a solvent, e.g. B. trichlorethylene, pre-cleaned and electrolytically degreased. To After rinsing, the articles are placed in an electrolytic polishing bath according to the present invention treated. An iron tub with a strong one is expediently used to hold the bath liquid Lead lining. The bath can be heated by inserted bath warmers with a lead jacket or can also be done indirectly using gas, steam or electric radiators. At the edge of the tub is a familiar one Attach a suction device for gases or vapors. The ones for hanging the items serving bars are connected to the positive pole of the power source. The cathodes exist made of lead. The power must be switched on as soon as possible after the objects have been hung in order to to prevent a purely chemical attack. After the treatment is finished, the objects are immersed in running water rinsed off. They can then be sent for further processing, e.g. B. anodic oxidation the surface using one of the electrolytic processes known for this purpose. and chromic acid, characterized in that the electrolyte is 1300 to 1750 g / l sulfuric acid and Contains 3 to 40 g / l chromic acid or chromic acid up to the saturation limit. 2. Galvanic bath according to claim 1, characterized in that the electrolyte 10 to 30 g / l, preferably about 25 g / l chromic acid, and 1300 to 1600 g / l sulfuric acid, preferably 1450 g / l, contains. 3. A method for anodic polishing of objects made of aluminum and aluminum alloys using galvanic baths according to claim 1 or 2, characterized in that the anodic treatment in the electrolyte at temperatures of 50 to 100 ° C and using a current density of 15 to 80 A. / dm ² and a voltage of 8 to 24 V. 4. The method according to claim 3, characterized in that a bath temperature of 80 to 90 ° C, a current density of 25 to 50 A / dm ² at a voltage of 13 to 18 V and a treatment time of 5 seconds to 6 minutes are used. 5. The method according to claim 3 or 4, characterized in that cathodes, preferably from Lead, which are surrounded by liquid-tight, acid-proof diaphragms, which keep the catholyte separate from the rest of the bath liquid. Patent claims: I _n considered publications: 1. Galvanic bath for anodic brightening German patents No. 671 637, 821 898, of objects made of aluminum and aluminum 35 825 937;
alloys containing sulfuric acid, French patent nr. 945 771. © 1 009 607/336 9.60