LU86247A1 - AQUEOUS FLOW FOR A HOT GALVANIZATION PROCESS OF A FERROUS PRODUCT - Google Patents

Description

* 4 S.

V

i C 2354/8601.

METALLURGICAL RESEARCH CENTER -CENTRUM V00R RESEARCH IN DE METALLURGIE,

Non-profit association -Vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Aqueous flux intended for a process of hot galvanizing of a ferrous product.

The present invention relates to an aqueous flux based on zinc chloride and to its use for the treatment of a ferrous product before its coating by immersion in a zinc-aluminum bath.

It is known that the coating of a ferrous product requires a prior preparation of the surface of this product, in order to guarantee the adhesion, the continuity and the uniformity of the coating.

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In the case of certain products, in particular steel strips and wires, the surface preparation before immersion in the zinc bath may consist of a heat treatment under a reducing atmosphere. This avoids or removes all traces of oxide on the surface of the product, which can then be immersed directly in the coating bath. However, such a heat treatment requires significant installation, and consequently high investment, which is only justified in the case of large tonnages.

it is also well known that, in coating processes by the so-called dry fluxing process, the preparation of the surface of the product generally comprises a degreasing followed by a rinsing, an acid pickling also followed by a rinsing, fluxing and drying.

The product thus prepared is then immersed in the bath of molten zinc.

In this sequence of operations, fluxing plays, as we know, an important and multiple role. It is used in particular to protect the pickled and rinsed surface against any risk of reoxidation before introducing the product into the zinc bath. It also makes it possible to eliminate the iron salts which may remain on the surface despite the rinsing carried out after pickling, and therefore to avoid their incorporation into the zinc bath. This operation is conventionally carried out by immersing the product in a stream consisting of an aqueous solution of zinc and ammonium chlorides or zinc chlorides and fluorinated compounds.

Such flows are known for example from patents US-A-1,914,269 and US-A-3,806, 356.

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Ges flux Used for many years, play their protective role quite satisfactorily as long as the coating to be deposited later consists of practically pure zinc.

The behavior of these conventional fluxes is however no longer entirely satisfactory when applying the new types of zinc-aluminum coating recently developed.

These new coatings have, depending on their composition, improved ductility and adhesion properties. These properties are very advantageous, for example in the case of parts having to undergo a significant deformation, because this deformation does not cause any cracking or any peeling of the coating. Likewise, the ability of these zinc-aluminum coatings to resist corrosion and to receive a film of paint is better than in the case of conventional zinc coatings.

These improved properties, due to the presence of aluminum in the zinc coating, are particularly marked in the case of a coating alloy recently developed by the present applicant and containing, in addition to zinc, approximately 5% of aluminum and small amounts of misch-metall. Some of these properties are also advantageous when the coating contains more aluminum, for example up to 70% Al.

However, it has been found that with this new type of coating, the use of a conventional flux leads to various defects in the coating. In particular, certain areas of the surface are not covered or do not “t 4.- are insufficiently, or the coating has black spots, or craters or encrustations, which gives rise to a state of unacceptable surface. It appeared that these defects were mainly due to ammonium chloride.

The deposition of new zinc-aluminum coatings therefore poses in this respect a problem which, to the knowledge of the applicant, has not yet been satisfactorily resolved at present.

On the other hand, it has also been found that the use of conventional streams poses ecological problems linked to the elimination of fluorine originating from fluorinated compounds from the streams.

The subject of the present invention is precisely a flux whose composition makes it suitable for use with the zinc baths containing the aforementioned aluminum to form satisfactory coatings from the point of view of their adhesion, their continuity and their uniformity. than that of their ductility, their resistance to corrosion and their ability to receive a film of paint.

The aqueous stream which is the subject of the present invention contains zinc chloride, sodium chloride, potassium chloride and calcium chloride. It may also contain a wetting agent to improve the wettability of the ferrous product by the flow,. · But it does not contain ammonium chloride any more than fluorinated compounds. 1 is intended for use with hot-dip galvanizing baths, continuous or custom, containing zinc, at iy 5.- minus 0.10% by weight of aluminum and possibly mischmetall (lanthanum and cerium), magnesium and / or silicon in contents of less than 1%.

Generally, an aqueous stream in accordance with the present invention contains from 100 to 750 g / l of zinc chloride, from 1 to 100 g / l of sodium chloride, from 1 to 100 g / l of potassium chloride and thence 100 g / l of calcium chloride. If desired, a wetting agent may be added thereto, provided, however, as indicated above, that this wetting agent does not contain ammonium chloride.

The flow according to the invention can be used under the same practical conditions as conventional flows.

In particular, the density of the aqueous stream according to the invention is advantageously between 20 and 40 ° Bé, its pH is between 0.5 and 3, and preferably close to 1, and its temperature is between 70 ° and 90 ° and is preferably greater than 80 ° C. The conditions for drying the product after fluxing must be chosen according to the parameters of the galvanizing line, in particular the speed of the product, and the dimensions of this product.

The following examples illustrate the advantage of the aqueous flux according to the invention used in combination with the coating of ferrous products by means of a zinc-aluminum alloy.

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Example 1.

A steel wire was treated by means of a flux in accordance with the present invention, then galvanized continuously, in an industrial installation practicing a running speed of 25 m / min.

The fluxing and galvanizing conditions were as follows:

Flux bath: temperature: 80 ° C density: 30 ° Be composition: initially ZnCl2 600 g / 1, NaCl 25 g / 1, KCl 5 g / 1, CaCl2 2 then with water until the density indicated. The pH was adjusted to 1 by addition of hydrochloric acid.

Ba.in_de_2a.lv anisat ion:

temperature î 450 ° C

composition: 3.6% Al - Zn residue.

Example 2.

A steel wire, pickled in a bath of hydrochloric acid at 15% and 25 ° C, was treated by means of a flux in accordance with the invention, then galvanized continuously in an industrial installation practicing a running speed 35 m / min.

The fluxing and galvanizing conditions were as follows:

Fluxing bath: temperature: 85 ° C density: 35 ° Be composition: identical to that of Example 1.

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Galvanizing bath:

temperature: 450 ° C

composition; 5.0% Al - Zn residue.

Example 3.

Steel panels were galvanized so, after degreasing with trichlorethylene, pickling with 50% hydrochloric acid, rinsing with water and fluxing by means of a flux in accordance with the invention followed by drying.

The fluxing and galvanizing conditions were as follows: temperature: 85 ° C density: 35 ° Be composition: identical to that of Example 1. Galvanizing bath:

temperature: 450 ° C

composition: 5% Al - 0.04% La - 0.02% Ce -reste Zn.

In the three aforementioned examples, there were obtained coated products absolutely free of the defects mentioned above, namely incrustations in the coating, adhesion defects or irregular thickness.

In combination with a coating process by immersion of the product in a zinc-aluminum bath, the fluxes according to the invention behave much better than conventional fluxes containing ammonium chloride, with or without fluorinated compounds.

Claims (3)

8.- V * 1. > r- 4 Claims. 1. Flux for galvanizing a ferrous product, consisting of an aqueous solution of zinc chloride, characterized in that said aqueous solution contains from 100 to 750 g / 1 of zinc chloride, from 1 to 100 g / 1 sodium chloride, 1 to 100 g / 1 of potassium chloride and 1 to 100 g / 1 of calcium chloride. 2. Flux according to claim 1, characterized in that it contains a wetting agent free of ammonium chloride. 3. Use of a flux according to claim 1 or 2 for the galvanization of a ferrous product by immersion in a zinc bath containing at least 0.10% by weight of aluminum. Drawings: _________ Zl plates _ ^ ... pages of which -, / j cover page ......... description pages ........ A - claims pages ...... A ... repealed descriptive Luxembourg le umm Le manda: aire: Me Alain Rubavina