Patent ID: 6153015
Filing Date: 2000-11-28
Classification: C23G

Abstract:
A process for removing a soap-contaminated conversion layer remaining on a metal workpiece after cold-forming the metal workpiece, wherein said soap-contaminated conversion layer comprises a soap and at least one member selected from the group consisting of phosphates, oxalates and aluminates, said process comprising the steps of:a) providing an aqueous acidic cleaning composition comprising water and at least one acid ingredient selected from the group consisting of nitric acid, phosphoric acid and amidosulphonic acid;b) immersing the metal workpiece with the soap-contaminated conversion layer in the aqueous acidic cleaning composition at a temperature above 60.degree. C. until the soap-contaminated conversion layer is removed from the metal workpiece and until a fatty acid formed from the soap in the conversion layer is dispersed in the aqueous acidic cleaning composition;c) after step b), separating the metal workpiece from the aqueous acidic cleaning composition;d) after step c), cooling the aqueous acidic cleaning composition to a temperature below 55.degree. C. until a fatty acid layer comprising the fatty acid is separated from said aqueous acidic cleaning composition;e) removing said fatty acid layer from said aqueous acidic cleaning composition to form a reusable aqueous acidic cleaning composition; andf) cleaning other metal workpieces with at least a portion of the reusable aqueous acidic cleaning composition.