A METHOD FOR ELECTROCHEMICALLY PRODUCING COLOURED STAINLESS STEELS INVOLVING THE USE OF A SULPHOCHROMIC SOLUTION WITH LOW CHROME CONTENT

摘要

The present invention proposes an innovation in the process of colouring stainless steels in a sulphochromic solution by a pulsed current, in that the chrome content in the colouring bath is drastically smaller so as to increase the sustainability of the process. In the newly proposed method, the low chrome concentration, of between 4 and 43 g/L of CrO3 in the colouring solution, results in even cleaner technology, providing a more favourable working environment, and also a substantial decrease in production costs. The coloured stainless steels produced using this new method are homogenously coloured and have good resistance to abrasion, being comparable to those obtained using commercial processes, via electrochemistry. Other process parameters must be adjusted in order to compensate for the reduced amount of chrome and ensure product quality. The coloured stainless steel produced by means of the present invention can be used in the building and architecture industries, for covering external and internal walls, ceilings and roofs, sanitary metals, urban furniture, road signs and works of art such as sculptures. This process consists of the following steps: (1) degreasing, (2) washing, (3) electrochemical pre-treatment, (4) washing, (5) colouring in a sulphochromic solution with low chrome content, at a temperature of 25°C to 75°C, applying a current, followed by (6) washing, (7) electrochemical hardening and (8) washing.