GB940582A - Improvements in or relating to methods of polishing metal surfaces in acid baths - Google Patents

Abstract

<PICT:0940582/C3/1> An aluminium surface is galvanically polished by immerising it in an acid polishing bath at a temperature in the region of 100 DEG C. together with a spaced counter electrode directly connected to it by an electrical conductor. The spacing is such as to avoid gas streaking of the polished surface, e.g. 1 cm. A current of 3 amps may arise. The Figure shows Al plates 1, 2 held in a jig 3 of stainless steel and a stainless steel counter electrode 5 suspended in an acid polishing solution 11 at 98-100 DEG C. such as phosphoric and nitric acids or 77.5% phosphoric, 15.5% sulphuric, 6.0% nitric, 0.5% boric acids and 0.5% copper nitrate. Following the polishing, the jig with the Al plates is removed from the polishing solution, rinsed in hot water, transferred to a 50% solution of HNO3 for 2 minutes and then washed first in cold tap water and then in isopropyl alcohol. The plates are then dried and may be coated with a thin film of ferromagnetic alloy for use as part of a data store in a computer. To polish both sides of an Al plate two counter electrodes may be used or for objects of more complicated shape a number of electrodes may be employed. The jig shown in the Figure comprises a bent rod 3 with turned over ends 4 forming a pair of tongs to hold the plate 1. The counter electrode 5 is welded to one arm of the bent rod and the other Al plate 2 is supported by a pair of jaws one of which 6 is welded to the counter electrode and the other 7 to the free arm of the tongs. The lower end of the counter electrode has a perforated flap 8 forming a stirring paddle when the jig is moved by a rotating crank 1. Brackets 9, 10 on the counter electrode help maintain the Al plates steady.