| 摘要 |
PROBLEM TO BE SOLVED: To prevent the change of the color tone in tinning by spraying the face of a steel sheet applied with both Ni plating and tinning after the application of electrotinning with an aq. soln. in which F/whole Sn [molar ratio] in the soln. is controlled to a value equal to or above a specified one. SOLUTION: The face of a steel sheet applied with both Ni plating and tinning is sprayed with an aq. soln. in which the F/whole Sn [molar ratio] in the soln. is controlled to >=7.32. In this way, the sticking of the oxide of tin in the carrying stage of the steel sheet after the plating is prevented, and moreover, the change of the color tone caused by the deposition of Sn(OH)2 and Sn(OH)Cl onto the plated face can be prevented. Moreover, the upper limit of the F/whole Sn [molar ratio] in the spraying soln. is suitably controlled to 12, and, in the case this value exceeds 12, the precipitation of fluorides in accordance with the drop of temp. becomes easy to occur. For controlling this value to the range of 7.32 to 12, a method of feeding NaHF2, or the like into a spraying soln. circulating storage tank, or the like, can be cited.
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