Metallgesellschaft Aktiengesellschaft

Dieter Hauffe

Jorg Hieke

Gunter Siemund

Han-yong Oei

Rudolf Vey

Han-Yong Oei

Han Yong Oei

During a method of phosphating a metal surface which includes at least in part iron or steel and is dipped into or flooded with a phosphating solution which contains layer-forming cations and nitrate or equivalent accelerators, the iron content is limited by a precipitation of iron phosphate. A partial volume of the phosphating solution is intermittently withdrawn from the bath tank and in a separate aerator is contacted with oxygen or an oxygen-containing gas. The iron phosphate sludge is removed from the resulting solution, which is then returned to the bath tank. The partial volume of the phosphating solution is supplied from below into and is aerated in an aerator, which is provided with an aspirating aerating agitator and which is tapered at least in its lower portion. When the aerator has been terminated, the phosphating solution which has been depleted of iron(II) is sucked off upwardly and is returned to the bath tank.

Process of phosphating metal surfaces

Disclosed is a process of producing a phosphate coating on a metal having a surface which consists at least in part of iron or steel. The metal is contacted at a temperature in the range from 30.degree. to 50.degree. C. with a phosphatizing solution which contains 5 to 25 g/l zinc, 1 to 10 g/l manganese, 0.1 to 13 g/l iron(II), 5 to 40 g/l phosphate (calculated as P.sub.2 O.sub.5), 5 to 50 g/l nitrate, and which also contains 0.5 to 5 g/l fluoroborate (calculated as BF.sub.4), and 0.05 to 3 g/l tartaric acid and/or citric acid. The solution has been adjusted to weight ratios of Zn:P.sub.2 O.sub.5 =(0.5 to 3):1 and of Mn:Zn=(0.04 to 0.5):1 and to a ratio of free acid to total acid of (0.04 to 0.2):1. It is preferred to add nickel, copper and/or calcium to the phosphatizing solution and to adjust it to a content of Fe(II) not in excess of 10 g/l. The process is particularly suitable for preparing metals for cold working.

Process of producing phosphate coatings on metals

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Bad Vilbel, Germany

Rudolf Vey