WERKWIJZE VOOR HET ANODISCH OXYDEREN VAN ALUMINIUM EN ALUMINIUMLEGERINGEN IN EEN CHROOMZUURBAD DOOR ELEKTROLYSE ONDER EEN GELIJKSPANNING VAN MINDER DAN 25V MET EEN KATHODE-OPPERVLAK, DAT VEEL KLEINER IS DAN HET ANODE-OPPERVLAK, EN VOORWERPEN VAN ALUMINIUM OF ALUMINIUMLEGERINGEN, ANODISCH GEOXYDEERD VOLGENS DEZE WERKWIJZE.

摘要

In a process for the surface protection of aluminium and its alloys by anodic oxidation in a bath of chromic acid under a constant voltage with a direct current, the chromic acid concentration is between 15 and 19% by weight, the bath temperature is below 30 DEG C., the electrolysis voltage is below 25 volts, the area of the anodic surface is between 1.7 X B and 2.3 X B dm2, where B is the volume of the bath expressed in litres, and the area of the cathodic surface is below 0.06 X B dm2, the ratio of the number of gram atoms of chromium dissolved in the bath in the hexavalent state to the number of gram atoms in the trivalent state thus remaining constant with a value of above 70. The process is preferably carried out without agitation; using an electrolytic voltage of 21 to 23 volts and with a cathodic surface area of 0.03 B to 0.05 B dm2, and the bath may be subjected to purging over cation exchange material to fix the aluminium salts. The bath may also have added thereto in a proportion of 0.01 - 0.2% by weight of the bath, 9% hydrogen peroxide.