Abstract
Assuming that nC: CrO3 concentration in chromium plating bath, V: Volume loss of the bath by evaporation, etc. in one day operation, v: Dragout in one day operation, and V1: Capacity of rinsings-recovery tank, and supposing that the rinsing effect became worse when the concentration of the tank rinsings was higher than C, the rinsings should be used at concentrations of lower than C. When the operation was conducted so that the concentration of rinsings became just C after one day's work, the volume loss V would be recovered in the plating bath. In the following day's operation, the rinsings remained in the recovery tank was set just at the concentration of C, containing the dragout of CrO3 from the plating bath; and the excess of rinsings was thrown away. In such a process, the CrO3 concentration in chromium plating bath would be nC={V(2V1-v)/2V1v+1}C with no throwing away of recovered rinsings. The ratio of reduction of CrO3 loss between chromium plating bath of low concentration and that of high (m times as high as) concentration was as follows:
R=1/m+2V1V(m-1)/v(2V1-V)≈1/m+V/v(m-1)
Since V<<V1 in general, R will approximately be equal to the right. As the value of V/v is 2-2.5 in practical decorative chromium plating, the loss of CrO3 will largely be reduced when the bath of low CrO3 concentration is used.
