Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Patent
1996-07-08
1998-08-18
Kastler, Scott
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
148240, C23C 2207
Patent
active
057954089
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the phosphatising treatment of steel strip or sheet galvanised or alloy galvanised on one side, with the aid of phosphatising solutions which contain zinc, nitrate and nitrite.
The objective of the phosphatising of metals is to produce on the metal surface firmly intergrown metal/phosphate layers, which as such already improve the corrosion resistance and in conjunction with paints and other organic coatings contribute to a considerable increase in the adhesion and in the resistance to corrosion creeping in underneath the coating. In addition, these phosphate layers serve as an insulation against the passing through of electric current and in conjunction with lubricants they facilitate sliding operations.
For the pre-treatment prior to the painting, in particular the low-zinc phosphatising processes are suitable, in which the phosphatising solutions have comparatively low contents of zinc ions of, for example, 0,5 to 1,5 g/l (DE-C-22 32 067, EP-B-39 093). Under these conditions phosphate layers with a high content of phosphophyllite (Zn.sub.2 FE(PO.sub.4).sub.2.4H.sub.2 O) are produced on the steel, which phosphophyllite is considerably more corrosion resistant than the hopeite (Zn.sub.3 (PO.sub.4).sub.2.4H.sub.2 O) precipitated from phosphatising solutions with a higher zinc content. By also adding nickel and/or manganese ions to the low-zinc phosphatising solutions, the protection quality, in conjunction with paints, can be increased further (EP-A-228 151, EP-B-414 296, EP-B.414,301, EP-A-544 650, DE-A-39 18 136). Low-zinc processes with the addition, of, for example, 0,5 to 1.5 g/l manganese ions and, for example, 0,3 to 2,0 g/l nickel ions, are used widely as so-called tri-cation processes for the preparation of metal surfaces for painting, e.g., for the cathodic electrophoretic enamelling of motor vehicle bodies.
Especially for phosphatising electrolytically galvanised or hot-dip galvanised steel strip, processes have been developed which permit the formation of a phosphate layer within short treatment times. Thus, for example, from the DE-A-32 45 411 it is known to provide in particular electrolytically galvanised steel strip with a phosphate layer which has a layer mass of less than 2 g/m.sup.2, wherein solutions are used which contain 1 to 2,5 g/l zinc ions, have a content of free acid of 0,8 to 3 points and an acid ratio of total acid/free acid of 5 to 10. With this the treatment time should be not much more than 5 seconds. With another process for the phosphatising of electrolytically and/or hot-dip galvanised steel strip, for a period of 2 to 30 seconds, in the temperature range of 40.degree. to 70.degree. C., phosphatising solutions are applied, which contain 0,02 to 0,75 g/l zinc ions, 0,2 to 2,0 g/l manganese ions, 0,1 to 2,0 g/l nickel ions, 10 to 20 g/l phosphate ions and 0,5 to 30 g/l nitrate ions. With this the content of free acids must lie in the range of 1,6 to 3,0 points, the content of total acid in the range of 12 to 40 points, and the mass ratio of nickel ions to nitrate ions in the range of 1:10 to 1:60, and the mass ratio of manganese ions to nitrate ions in the range of 1:1 to 1:40 (DE-A-39 27 131).
When the aforementioned phosphatising solutions, which permit a short treatment time, are used on a strip which is galvanised or hot-dip galvanised on both sides, no serious complications occur. However, in recent times use is being made increasingly, in particular in the motor vehicle industry, of steel strip which is galvanised on only one side. When using the aforementioned short-time methods on strip that has been galvanised on only one side, a strong formation of phosphate sludge occurs in the phosphatising solution, which in this quantity is disturbing. In addition, on the steel side an incipient phosphate layer formation occurs, which is undesirable especially when a later phosphatising, e.g, of the motor vehicle body, is planned.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a process for the phosphatising trea
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patent: 5211769 (1993-05-01), Sobata
patent: 5236565 (1993-08-01), Maller
patent: 5244512 (1993-09-01), Kawasaki
Bittner Klaus
Jansen Walter K.M.
Mohr Klaus-Peter
Wendel Thomas
Wietzoreck Hardy
Kastler Scott
Metallgesellschaft Aktiengesellschaft
Striker Michael J.
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