METHOD FOR COATING WITH ZINC PHOSPHATE FERROUS SURFACES

摘要

Metals are given a coating of Zn phosphate by (1) treating the surface with an acidic phosphating soln. contg. Zn, phosphate and alkali metal ions, (2) recharging the soln. as the coating thickness increases by adding (a) a material contg. Zn and phosphate ions and (b) a material contg. alkali metal ions such that (b) has an alkaline reaction w.r.t. (a), and (3) making the compsn. of the phosphating soln. the optimum by adding (a) and (b) in predetermined amts. During the treatment the conductivity of the soln. is maintained constant for a specific temp. by adding (a) or (b). Automatic Zn phosphating is achieved at the same time maintaining the compsns. of the phosphating soln. content. It is possible to use the conductivity of the soln. as an indicator for the addn. of more of the constituents right from the beginning of the process. There is also less waste.