Metallurgical apparatus – Process
Patent
1991-09-13
1993-06-01
Mastler, Scott
Metallurgical apparatus
Process
266130, 266133, C21D 964, C21D 9573
Patent
active
052157024
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of and an apparatus for guiding at least one steel wire from a furnace into a lead bath, which method is carried out in such a manner that lead drag-out from the lead bath is avoided as much as possible.
2. Discussion of the Related Art
The use of lead tanks or lead baths for heat treatments is sufficiently known in the state of the art. Everywhere where these lead tanks or lead baths are used, one is faced with the problem of lead drag-out. That is, along with the objects to be treated such as steel wires, lead is dragged out of the lead tanks or lead baths in the form of lead drops, whether or not enveloped in a lead-oxide skin. This results in different drawbacks. In the first place, there is the known harmful effect on health and the environment. Further, there is also a qualitative drawback in the sense that the baths located downstream of the lead bath are "poisoned" by the lead particles dragged along. This does not benefit the quality of the treatment connected with these baths downstream. Moreover, wire products for certain applications do not tolerate lead drag-out, for instance those wire products that are electrolytically coated afterwards. Finally, there is the considerable loss of lead itself.
The problem of lead drag-out is a complex problem and presents chemical, physical as well as mechanical aspects.
Therefore, the state of the art presents different solutions to avoid lead drag-out.
Thus, it is sufficiently known from U.S. Pat. No. 3,669,761 to cover the end of the lead bath with a coal bed to avoid the formation of lead oxides (Pb.sub.x O.sub.y). Indeed, lead oxides have the property of being more viscous than lead at the temperatures that prevail at the end of the lead bath, and they are more readily than lead dragged out of the lead bath along with the wires. They also drag pure lead along in the process. A further purpose of the lead bed is to mechanically stop the lead dragged along.
However, despite these well known measures, lead drag-out has remained a major problem wherever lead baths are used.
SUMMARY OF THE INVENTION
It is now an object of the present invention to reduce further the lead drag-out.
According to a first aspect of the present invention, there is provided a method of guiding at least one steel wire from a furnace into a lead bath, whereby the steel wires are kept separated, and, after leaving the furnace, guided over a cooled roller. This roller turns at a peripheral speed that nearly equals the speed of the steel wires. After that, the steel wires disappear into the lead bath and are guided further under an immersed roller. Over the cooled roller and under the immersed roller, the steel wires make an angle that is larger than 150.degree.. The furnace--lead bath transition is sealed by a hood that lets through as little air as possible.
This invention is particularly suitable for a patenting process, which, as is sufficiently known, consists in heating the wire in a furnace to austenitising temperature (about 950.degree. C.) and thereupon cooling the wire at about 500.degree. to 600.degree. C., mostly in a lead bath.
The effect of the above-mentioned features of the invention on the lead drag-out may be explained as follows:
The inventor has discovered that lead drag-out can be reduced further still if the steel wires are covered with a thin oxide skin. Indeed, ferric oxide and lead do not react. All the features of the invention tend to prevent the oxides on the steel wires from flaking.
The steel wires can for instance be kept separated by the teeth of a comb. These teeth must not touch the steel wires. Their only function is to keep the steel wires separated. To prevent deformations of the comb, in view of the very high temperatures at the furnace exit, the comb is preferably cooled with water. If the teeth of the comb touch the steel wires, the oxide scale on the steel wires can flake and lead is dragged out of the lead bath. Preferably, there is a certain distance betw
REFERENCES:
patent: 979931 (1910-12-01), Cowper-Coles
patent: 1052574 (1913-02-01), Davis
patent: 3181977 (1965-05-01), Sturgeon
patent: 3669761 (1970-07-01), Schulze et al.
patent: 3858859 (1975-01-01), Baguet
patent: 4954183 (1990-09-01), DeWitte
Mastler Scott
N.V. Bekaert S.A.
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