Methods for treating a ferrous metal substrate

摘要

Disclosed are methods for treating and coating a ferrous metal substrate, such as cold rolled steel, hot rolled steel, and electrogalvanized steel. These methods include contacting the ferrous metal substrate with an aqueous pretreatment composition comprising: (a) a Group IIIB and/or IVB metal compound; (b) phosphate ions; and (c) water. Also disclosed are off-shift methods of removing iron from the pretreatment bath.

主权项

1. A method for removing iron from a pretreatment bath containing a pretreatment composition comprising a Group IIIB and/or Group IVB metal, comprising:
(a) reducing the pH of the pretreatment bath by at least 0.2; (b) adding phosphate ions to the pretreatment bath in (a); (c) raising the pH of the pretreatment bath in (b) by at least 0.2; and (d) removing an insoluble sludge that forms in the pretreatment bath in (c); wherein the method is performed in the absence of an article to be coated by the pretreatment composition; and wherein the pretreatment bath is substantially free of phosphate ions during operation.