Methods for treating a ferrous metal substrate
AssigneePPG Industries Ohio, Inc.
InventorsRichard M. Vargas, John F. McIntyre
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Abstract
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.
Claims20
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.
A method for removing iron from a pretreatment bath containing a pretreatment composition comprising a Group IIIB and/or Group IVB metal, comprising:
- (a) adding an acid to the pretreatment bath to reduce the pH of the pretreatment composition to below 4.0;
- (b) adding phosphate ions to the pretreatment bath in (a);
- and
- (c) raising the pH of the pretreatment bath in (b) to 4 to 5.5;
- 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.
Dependencies are inferred from the claim text.