GB1510965A - Etch resistance reduction in vitreous enamelling processe - Google Patents

Abstract

1510965 Electrolytic cleaning, etching of steel; enamelling electrophoretically STEWART & GRAY Ltd 24 July 1975 [24 July 1974] 32782/74 Heading C7B Prior to vitreous enamelling, steel having undesirable etch resistance properties (e.g. high etch resistance, or variation of etching rate across its surface) is treated electrolytically in an acidic electrolyte to reduce the etch-resistance, and is then etched. The electrolytic step may use D.C. of 1À5 to 6 V, pulsed to 12 V at 20 to 30 A/ft<SP>2</SP> for 1¢ to 2 minutes in H 2 SO 4 ; the etching may use 7-9% H 2 SO 4 at 180‹F for 6 minutes. In an example, mild steel sheet fabricated into components is (1) soaked at 90-100‹C in alkali cleaner plus wetting agent (2) cleaned anodically in alkali at 90-100‹C for 2-3 minutes (3) cold water rinsed (4) anodically treated in 8-12% H 2 SO 4 for 1¢ to 2 minutes at room temperature, 1À5 to 6V and 20-30 A/ft<SP>2</SP> (5) cold water rinsed (6) etched as above, (7) hot rinsed then cold rinsed (8) flash nickelled in NiSO 4 .6H 2 O, NaH 2 PO 2 and Na acetate at pH 4À5- 5À5 at 35‹C for 4-6 minutes to give 90-140 mg/ft<SP>2</SP> (9) cold rinsed and neutralised with alkali and (10) borax rinsed; this may be followed by one-step enamelling or two-step enamelling if the Ni flashing is omitted. If enamelling is performed electrophoretically, it may be preceded by electrolytic activation in ZnCl 2 /HCl at 6V.