METHOD FOR ACTIVATING METALLIC SURFACES TO BE PHOSPHATED, PREFERABLY GALVANIZED STEEL SHEET

摘要

A method of activating a metal surface, such as a galvanized steel sheet, before a phosphating process, may involve bringing the metal surface into contact with an activating bath containing activating particles, which may be based on phosphate and/or titanium, dispersed in water. To alleviate or even eliminate the problems of poor adhesion of surface coatings to preferably electrolytically galvanized, phosphated metal strip, an additive that suppresses or at least slows agglomeration of the activating particles may be added to the activating bath. In some examples, polyethylene glycol (PEG) and/or sodium stearate may be added. Further, the particle size distribution of the activating particles present in the activating bath may be determined and the activating bath may be replaced or taken out of operation as a function of the particle size distribution of the activating particles.