Electropolishing process, in particular for electrolytically brightening metal workpieces

摘要

The invention relates to an electropolishing process and apparatus, in particular for electrolytically brightening workpieces made of aluminium, aluminium alloys or other metals in an electrolyte solution whose basic electrolyte is composed of phosphoric acid or mixtures of phosphoric acid with other mineral acids, such as sulphuric acid, nitric acid or the like, and polyphosphates. The automation of such a brightening plant presents the problem that the relatively long crane lift-over times result in etching phenomena on the workpieces. The invention solves this problem by increasing the dynamic viscosity of the electrolyte solution (3) in the aluminium brightening baths (1) to at least 20 . 10<-3> Ns/m<2>, which is achieved by increasing the polyphosphate content in the electrolyte solution. During lift-over, the electrolyte consequently forms an enveloping, adhesive protective film on the workpieces. To keep the process conditions constant over a long period, the invention provides for the polyphosphates to be formed in the process by controlling the total acid concentration, the operating temperature and the current loading, with the addition of polyphosphates or other additives being avoided. To keep the process conditions constant, if a limiting viscosity value is exceeded, some of the electrolyte solution is pumped into a regeneration reservoir (5), freed of sludge therein, regenerated with fresh acid and fed back to the brightening bath (1). <IMAGE>