Coating processes – Immersion or partial immersion – Molten metal or fused salt bath
Patent
1989-07-31
1992-08-04
Lusignan, Michael
Coating processes
Immersion or partial immersion
Molten metal or fused salt bath
118419, 219421, 219422, 266120, 373144, 427433, 4274342, B05D 118
Patent
active
051357810
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a procedure for operating a hot metallizing furnace for lengths of metal, in particular metal strip, in which the length of metal to be coated is fed from above through the upper area of a smelt of coating material located in a smelt container, and whereby the smelt container is heatable by an induction coil made up of partial coils arranged axially above one another, and in which during hot metallization a bath movement is produced only in the upper area of the smelt by means of switching on the upper partial coil(s) only, while in order to remove deposits, in particular hard zinc deposits, from the smelt container, a bath movement is generated in the lower part of the smelt by switching on the lower partial coil(s).
A hot immersion metallizing furnace is known from DE PS 34 28 999 with a crucible which is surrounded externally by a cylindrical induction coil consisting of several partial coils arranged on top of one another. Here, the depth of the crucible should be equal to or greater than its diameter. During hot metallizing with this known furnace, only the upper partial coils should be switched on. In this way the metal smelt can be heated inductively to a sufficient degree and a stirring effect in the smelt can take place in the upper zone of the container. The movement in the smelt should become progressively weaker towards the bottom of the container, so that deposits of hard zinc or the like settle and remain in the lower part of the crucible and are not entrained up to the top during the metallization process, which would have negative effects on the quality of the strip surface.
The deposits in the lower area of the crucible, which increase in the course of service life, must be removed periodically. For this purpose it is proposed in accordance with DE-PS 34 28 999 to activate the lower partial coil also. As a result of this, the hard zinc or similar deposits are swirled up to the top.
The task of the present invention consists in further improving the operational mode of a hot metallizing furnace with inductive heating, whereby in the upper part of the smelt during the hot metallization procedure only a small stirring effect is produced with a high concentration of power, but for the purpose of removing hard zinc and similar deposits a particularly intensive agitation of the smelt is achieved.
This task is solved in accordance with the invention by a procedure of the kind described at the beginning in that during hot metallizing the upper partial coil(s) is/are connected to a medium frequency source of electricity in a single-phase manner; in that for the removal of the deposits which have collected in the lower area of the smelting vessel, the lower partial coil(s) is/are connected to a mains frequency source of electricity with a three-phase current; and in that the deposits thus agitated are removed from the smelt by means of a collecting tank.
The procedure in accordance with the invention on the one hand ensures that the stirring effect during the heating phase of metallization is relatively small and only present in the upper part of the molten coating metal, so that a distinct separation is achieved between an upper agitated area and a non-agitated lower area of the molten metal.
On the other hand, a particularly intensive stirring effect is produced for the removal of the hard zinc and similar deposits from the bottom area of the smelting vessel. In this way the deposits in the bottom area of the smelting vessel are swirled upwards and distributed roughly evenly throughout the whole depth of the melting bath. When the collecting tank is immersed in the molten metal, the agitated particles can settle in this collecting tank.
The procedure in accordance with the invention can be further developed in an advantageous manner in that for the removal of the deposits, lower and upper partial coils are connected with a mains frequency source of electricity with a three-phase current. In this way the agitation of the deposits is rendered more rapid and more intensive.
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REFERENCES:
patent: 1523647 (1925-01-01), Imhoff
patent: 2669647 (1954-02-01), Segsworth
patent: 3478156 (1969-11-01), Segsworth
Knupfer Peter
Schluckebier Dieter
Lusignan Michael
Otto Junker GmbH
Owens Terry J.
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