Dispensing – Processes of dispensing – Molten metal
Reexamination Certificate
1999-01-12
2001-07-17
Kastler, Scott (Department: 1742)
Dispensing
Processes of dispensing
Molten metal
C164S437000
Reexamination Certificate
active
06260740
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process and a device for influencing the flow propagation of a metallic liquid, which, flows in a guided fashion into a stationary permanent mold from a melt container via a first immersion nozzle part, which has a polygonal, oval or circular cross section, and an intermediate part through a second immersion nozzle part, which has an elongated cross section for production slabs.
DESCRIPTION OF THE PRIOR ART
DE 37 09 188 discloses a casting tube for metallurgical vessels which is subdivided into an upper tubular longitudinal section and a lower rectangular longitudinal section, a conical transition being provided between the two longitudinal sections. The rectangular cross section can in this case have a length/width ratio of 20:1 to 80:1.
Provided at the mouth of the immersion nozzle is a transverse web which guides the liquid steel into the lateral mouth openings. In this case, the steel enters the permanent mold with a relatively high kinetic energy. Moreover, the transverse web is subjected to a high degree of wear.
DE 43 20 723 discloses an immersion nozzle which has a tubular shaped refractory brick shape which is connected via a conical constructional element to a lower rectangular shaped refractory brick dipping into the melt. Longitudinal webs are provided in the flow cross section in the lower shaped refractory brick.
In the region of the inlet of the lower rectangular shaped refractory brick, a transverse web is provided which reflects the flow of the melt in the direction of the widening of the flow shaft. This transverse web configured as a baffle disadvantageously causes strong eddies in the melt.
SUMMARY OF THE INVENTION
It is the object of the invention to avoid the disadvantages of the prior art and to create a process and a device relating to an immersion nozzle for guiding metal melts of which minimizes the turbulence in the immersion nozzle itself and in the permanent mold, and simultaneously the depth of penetration of the fed melt into the liquid crater located in the permanent mold.
The invention achieves this object by a process which includes the steps of reducing a central volumetric flow in a second immersion nozzle part of a metallic liquid received from a first immersion nozzle part; increasing an angle of expansion of the liquid jet so that there is no return flow in a lateral region of the second immersion nozzle part and an intermediate part between the first and second immersion nozzle part, and so that a velocity profile of the metallic liquid at the ouput mouth of the second immersion nozzle part is such that velocity vectors are smaller in the center opening of the mouth than in the regions of the narrow sides. The object is also achieved by an immersion nozzle for performing the process.
According to the invention, in the central case of an immersion nozzle whose mouth part dipping into the melt located in the permanent mold has an elongated cross section, the central volumetric flow is reduced in the inlet region of this immersion nozzle part. This reduction in the volumetric flow is caused by throttling the central, which increase the angle of expansion of the liquid jet, specifically to such an extent that there is essentially no return flow into the lateral region of the immersion nozzle part having a longitudinal cross section.
As a consequence of the throttling and simultaneous spreading of the central volumetric flow, the melt flows from this immersion nozzle part with a velocity profile whose velocity vectors are smaller in the opening mouth than in the regions of the narrow sides.
The quantity fed through the immersion nozzle strikes with this set velocity profile against the liquid crater, which is located in the permanent mold and is withdrawn in accordance with the strand withdrawal rate of 1 to 10 m/min, and penetrates at only slight depths into this liquid crater, in accordance with a mixing length of L=0.2 to 4 m.
Owing to the intensive spreading or expansion of the central volumetric flow, the velocity profile in the region of the narrow sides has at the mouth of the immersion nozzle part having an elongated cross section velocity vectors which have components which permit a return flow on the narrow sides of the permanent mold. As a result, an adequate quantity of fresh melt is fed to the bath level in the permanent mold, with a positive influence on the casting powder applied to the surface. Moreover, this melt flows to the center between the immersion nozzle and permanent mold with only a slight bow wave but in an adequate quantity. The flows of melt combine in the middle of the permanent mold and then flow into the liquid crater in the strand withdrawal direction. There, they fill up the volumetric flow, emerging from the second immersion nozzle part, in the mouth center.
The result of this is a virtually flat and overall only shallow depth penetration into the liquid crater, with the advantage that, for example, in the case of a change in quality of the melt only a short mixing length, and thus a short piece of undesired slab quality is produced.
The throttling of the central volumetric flow is achieved by virtue of the fact that the region upstream of the inlet into the immersion nozzle part having a longitudinal cross section, or the inlet itself is configured in a special way. In any case, the free space is kept adequately open, with the result that a defined quantity always flows in the central region of the second immersion nozzle part.
To throttle the central volumetric flow, the wall of the broad side of the intermediate part arranged in the casting direction upstream of the immersion nozzle part with an elongated cross section has a concave bulge. In an advantageous refinement, this bulge is configured in the shape of a quarter hollow sphere. In a further refinement, it has the shape of a tube segment with a prescribable contour.
The throttling is also achieved by a constriction of the free space for the inlet of the immersion nozzle part. This constriction may be effected by flow bodies which are arranged on the broad side of the immersion nozzle part, or by the inward formation of dents.
In an advantageous way, the constriction has a dimension whose width corresponds approximately to the diameter of the upstream tubular immersion nozzle part, and which corresponds in length to 0.2 to 1.2 times its width.
The leading edges and the trailing edges are of sharp-edged construction and in this case have an angle &bgr; from the leading edge and the inner wall of 90 to 150°. It is possible to combine the shaping of the intermediate part and the constriction. It is proposed in the case of this combination to match the contour of the bulge of the intermediate part to the leading edge of the flow element in the second immersion nozzle part.
REFERENCES:
patent: 37 09 188 (1988-09-01), None
patent: WO 96/29166 (1996-03-01), None
Patent Abstracts of Japan of JP 62 197252 A, Feb. 1988.
Schemeit Hans-Jürgen
Urlau Ulrich
Cohen & Pontani, Lieberman & Pavane
Kastler Scott
Mannesmann AG
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