Metal treatment – Compositions – Heat treating
Patent
1985-02-28
1986-11-04
Niebling, John F.
Metal treatment
Compositions
Heat treating
148 621, 204 1T, C23C 2224
Patent
active
046208828
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for continuously coloring stainless steel, in which surfaces of the stainless steel are colored by continuously causing a strip of the stainless steel to unidirectionally pass through a coloring solution at a certain velocity. More particularly it relates to a process for continuously coloring a strip of stainless steel by the above-mentioned continuous procedure, which process may achieve uniform coloring, irrespective of inevitable changes with time of the composition and concentration of the coloring solution during the procedure.
BACKGROUND OF THE INVENTION
Well known in the art are chemical processes for coloring stainless steel using a coloring aqueous solution of so-called chromic acid-sulfuric acid series, including, for example, chromic anhydride-sulfuric acid series, sodium bichromate-sulfuric acid series and potassium bichromate-sulfuric acid series. Preferred examples of such coloring solutions are disclosed in UK Patent specifications Nos. 1,122,172 and 1,122,173. When stainless steel is immersed in such a coloring solution colors of various shades may develop on the surfaces of the stainless steel depending upon the time of immersion. This is because, although related to the composition of the steel, depending upon the extent and state of oxide films formed on the surfaces of the steel by particular redox reactions the color shade thereof varies. This variation of the color shade appears continuously. Accordingly, it is possible to develop a color of the predetermined shade by controlling the time of immersion (the processing time). A convenient method for controlling the color shade is disclosed in Japanese Patent Post-examination Publication No. 52-25,817. The principle underlying the disclosed method is such that the difference between the potential of the steel, which is immersed in the coloring solution and on which oxide films are being formed, and the potential of a reference electrode disposed in the coloring solution varies in accordance with the extent of the oxide films being formed on the steel, i.e. in accordance with the color shade, and therefore the color shade may be controlled by measuring and using the above-mentioned potential difference as a measure. Thus, if an article of stainless steel immersed in a coloring solution is taken out of the solution when the above-mentioned potential difference has reached a predetermined value, a colored article having a shade which corresponds to the potential difference value may be obtained. This method in which the potential difference is utilized as a measure for controlling the color shade is very useful when the coloring process is carried out batchwise. In fact when a stainless steel article to be colored is immersed batchwise in a coloring solution, coloring proceeds substantially uniformly over the whole surfaces of the article, and in consequence, if the immersed article is taken out of the coloring solution at the time the potential difference has reached the value corresponding to the desired color shade, it is possible to achieve the substantially same color shade over the whole surfaces of the article.
If uniform coloring can be realized by a continuous procedure, the productivity of the coloring process will be greatly increased. It would be very advantageous if it is possible to develop a certain predetermined color over the whole surfaces of a stainless steel strip, for example, by causing the strip to continuously pass through a coloring solution. More particularly, it is desired to color a stainless steel strip uniformly over the whole length of the strip by providing a vessel containing a coloring solution between a pay-off roll and a wind-up roll and continuously moving the stainless steel strip so that the strip unwound from the pay-off roll may be caused to pass through the vessel and wound up by the wind-up roll while forming colored coatings thereon during its passage through the coloring solution in the vessel.
However, with such a continuous
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Kaito Hideo
Takeuchi Takeshi
Nguyen Nam X.
Niebling John F.
Nisshin Steel Co. Ltd.
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