| 摘要 |
A process for producing a bright Sn coating on a metal base, e.g. of low carbon steel, comprises the steps of electrolytically pre-coating the metal base with a preplate of Ni or Ni-Sn alloy from 2 X 10-8 to 65 X 10-8 inch thick, electrolytically plating Sn on to the pre-coated base, and thereafter flow-brightening the plated base by heating to a temperature of from 540 DEG to 850 DEG F. The preplate may be provided by passing current for 5 to 100 milliseconds through a known electro-plating bath using a transistor switching device. Specified baths producing 35% Ni, 65% Sn (by weight) contain SnCl2, NaF, NaHF2, NaCl and NiCl2, 6H2 O and are at a pH of 2.0 to 2.5. Specified Ni baths contain NiCl2, 6H2 O and H3 BO3, one being at a pH of 2.4 and the other, which also contains an unspecified surface active agent, being at a pH of 3.5. The Sn coating may have a thickness corresponding to a weight of 0.25 to 1.5 pounds per base box. The heating of the Sn plated base may be for not longer than 3 seconds after which the plated base is rapidly quenched. Graphs (not shown) illustrate variations in corrosion resistance where different preplating thicknesses of Ni-Sn, different flow-brightening temperatures and different delay times before quenching have been used. |
