Process for the demulsifying cleaning of metallic surfaces

A process for demulsifying cleaning of metallic surfaces which are contaminated with a contaminant that is an oil, at least one further non-polar organic compound, a fat, a soap, particulate dirt or at least one anionic organic compound, the process comprising:

• providing an aqueous, alkaline, surfactant-containing bath;
• contacting the metallic surfaces with the aqueous, alkaline, surfactant-containing bath in at least one cleaning zone wherein the bath becomes contaminated with the contaminant;
• wherein the aqueous, alkaline, surfactant-containing bath comprises:
• at least one demulsifying surfactant comprising at least one nonionic surfactant based on ethoxylated alkyl alcohols having an end group cap and ethoxylated-propoxylated alkyl alcohols having an end group cap, and
• at least one cationic organic compound;
• wherein oil droplets having a radius of curvature are formed in the aqueous, alkaline, surfactant-containing bath and the aqueous, alkaline, surfactant-containing bath is kept in a demulsifying state even during increasing contamination with at least one anionic organic compound;
• wherein the content of the at least one demulsifying surfactant in the aqueous, alkaline, surfactant-containing bath ranges from 0.1 to 10 g/l;
• and
• wherein the at least one demulsifying surfactant is selected to adjust the radius of curvature of the oil droplets so that the oil in an agitated bath is partially emulsified and does not accumulate as an oil-containing phase on a surface of the agitated bath, and the oil spontaneously deposits and accumulates as an oil-containing phase on a surface of a quiescent bath.