1989 Volume 75 Issue 6 Pages 918-925
Coloured stainless steel produced by the process of International Nickel Limited is expensive because of low production efficiency. In this paper, a high speed continuous colouring method is described for the cost down of coloured stainless steels.
For the high speed production, high temperature (100°C) colouring solutions and high electric current densities (2A/dm2) were employed. However irregular colouring occurred by using high temperature solutions. For prevention of this trouble, a liquid seal apparatus was developed, which divided the colouring solution to high and low temperature parts without a partition wall. This apparatus was consisted of two boxes with narrow slit nozzles and high and low temperature parts of the colouring solution were gushed against stainless steel hoop in each temperature part. The use of the high temperature colouring solution still caused non-uniform colouring through the top to end of hoop, because of concentration change of the solution by the evaporation of water and loss of the colouring solution taken out with the hoop. For the restoration, a control method was developed, in which were supplied the amounts of the consumed sulfuric acid and chromic acid and water.
With using the above restoration method, uniformly coloured stainless steel hoops whose length was about 150 m can be produced.
