GB1000721A - Improvements in or relating to the electrolytic deposition on a workpiece - Google Patents

Abstract

<PICT:1000721/C6-C7/1> <PICT:1000721/C6-C7/2> A process of providing an electrolytic deposit on one face only of the surface of a workpiece comprises disposing the workpiece as cathode in the electrolyte of an electrolytic cell between the anode of the cell and a secondary cathode wth the surface of the workpiece on which the deposit is to be effected directed towards the anode and applying an electric potential across the cell so that the potential difference between the workpiece and the secondary cathode has a value between zero and the voltage of dissolving of the workpiece in the particular electrolyte employed. Fig. 2 shows an anode A and a workpiece B with the cell container serving as a secondary cathode C. A shunt resistance R1 is less than the electrolyte resistance R between the workpieces and secondary cathode. Metal is plated on the workpiece surface facing the anode but the small current which passes through the electrolyte between B and C is sufficient to prevent metal deposition on the workpiece surface remote from the anode. As shown in Fig. 4, the negative pole of a current source is alternately connected to B and C, e.g. to B for 50 seconds and to C for 10 seconds. Fig. 5 (not shown) illustrates an embodiment where the current is periodically reversed for short periods. Several cells may be connected in series. Some examples are of plating Pb and Pb-Sn from fluoborate baths containing the Pb or Pb and Sn fluoborates, free HBF4 and gelatine. Some baths also contain free H3BO3. There are two examples of electroplating Pb-Sn on a Cu-Pb lining to steel, one of electroplating Pb on a bronze (80% Cu, 10% Pb, 10% Sn) lining to steel and one of electroplating Cu on a steel sheet from a bath containing copper cyanide, free NaCN and NaHSO3.