GB1055001A - - Google Patents

Abstract

<PICT:1055001/C6-C7/1> One surface of aluminium strip 10 is continuously anodized by moving it through an anodizing tank 12 in which the strip isolates two turbulent streams of liquid 14, 15, one liquid stream 14 being an anodizing electrolyte in which is submerged a cathode 26, the average temperature of the liquid streams being at least 50 DEG C. and the current density being at least 100 A.S.F. of strip surface, so as to form an oxide coating of at least 0.1 mil. The other liquid stream 15 may also be an electrolyte of the same composition, in which is submerged an anode 27, or the strip may be moved through a preliminary tank, Fig.3 (not shown), containing electrolyte in which is submerged an anode, or preferably two anodes on both sides of the strip to provide electrolytic cleaning, so providing the passage of current to the strip without requiring contact brushes or rollers. The electrodes may be of lead, or if A.C. is applied, Fig. 4 (not shown), of graphite, being submerged one side only of strip. The electrolyte is preferably 10-40% aqueous sulphuric acid, but may be chromic acid or di- and tri-basic organic acids. As shown (Fig.1), turbulent flow may be maintained against the strip surfaces by means of pumps 32, 42 supplying liquids through pipes 33, 43 to manifolds 35, 44 respectively opening into one end of the tank; the liquid streams 14, 15 leaving through similar manifolds 36, 46 at the opposite end of the tank and passing through pipes 37, 47 to return to the respective pumps. Coolers 38, 48 may be provided for controlling or regulating the electrolyte temperature. The anodized strip 10 may be subsequently drawn through a tank 16 containing aqueous sealant 18, such as acidulated hot water, sodium silicate or nickel acetate solution.