Dispensing – Molten metal dispensing – Flow controllers or assists
Patent
1996-01-19
1997-12-09
Kastler, Scott
Dispensing
Molten metal dispensing
Flow controllers or assists
266272, B22D 4108, B22D 4118
Patent
active
056956754
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns an arrangement for connection of an elongated rod made of a refractory material for a metallurgical vessel to a lifting device and also encompasses a method for production of the device.
The use of refractory stopper rods to control flow of a metal melt from a kettle or tundish into a mold has long been known. For this purpose the stopper rod is moved in the direction of its longitudinal axis by a lifting device adjacent to it on the exterior of the tundish so that a discharge opening arranged on the bottom of the tundish into which the stopper rod engages and completely enters in the lowered condition is more or less opened. Flow of the metal melt is controllable on this account. This type of control in principle is quite simple, but the extreme conditions prevailing during steelmaking impose special requirements on the materials and technical design of the stopper rod. Thus, the stopper rod must withstand the effect of a metal melt for hours. The stopper rod must also be capable of withstanding the severe temperature fluctuations that act on the stopper rod during a casting process and the lateral forces caused by buoyancy of the metal melt, which exert a severe bending moment on the stopper rod. Rupture of the stopper rod undeniably leads to a situation in which the discharge can no longer be closed, which results in uncontrolled outflow of the melt. It therefore represents a significant safety risk.
In a previous known version (cf. Karl-Ernst Mayer: Stahleisen-Schriften, No. 3 "What the open hearth steel worker must know about his work", 2nd edition, Verlag Stahleisen mbH, Dusseldorf, 1963) the stopper rod consists of a steel rod threaded on one end onto which the actual ceramic stopper that engages in the discharge opening of the tundish during later use is screwed. Several ceramic stopper tubes that fully enclose the steel rod and mesh via keys and slots on their front sides above the stopper are slipped on from the side of the steel rod opposite the stopper so that the part of the stopper rod enclosed with the stopper tubes protrudes over a certain length from the melt when the stopper rod is fully lowered with the tundish filled with steel melt. The stopper rod is supported in the lifting device with the upper end of the steel rod. Since direct contact of the melt with the steel rod would lead to its immediate melting, special attention must be accorded in this stopper rod assembled from several parts (stopper, stopper tubes) to ensure that the joints between the individual parts are tight relative to penetration of steel melt. The connection sites are therefore additionally puttied. The stopper rods prepared beforehand are dried for two days at about 100.degree. C. in a drying furnace before use.
A shortcoming in this previous variant is that preparation of the stopper rods requires relatively high material and labor expense. The steel rods also have a tendency toward warping from the temperature gradients and fluctuations that occur during casting, which can easily lead to rupture of the enclosure and thus destruction of the stopper rod. These shortcomings and the finding that nonmetallic contaminants are transported, on the one hand, by interaction with gas bubbles at the bath surface of the melt by introduction of inert gases (like argon) into the steel melt, and, on the other hand, oxide formation is reduced during the casting process, have led to the development of ceramic stopper rods produced in one piece through which the inert gas can be introduced into the steel melt at the same time. These one-piece stopper rods that are now almost exclusively used in present-day steelmaking have a central longitudinal opening that does not penetrate their lower end and connection openings that communicate from the exterior with the longitudinal opening and serve to introduce the inert gas into the steel melts.
Production of such stopper rods ordinarily occurs by isostatic pressing of a powdered ceramic material to a blank, which is then fired, i.e., s
REFERENCES:
patent: 4946083 (1990-08-01), Fishler et al.
patent: 5303905 (1994-04-01), Pohl et al.
International Search Report, dated 17 Nov. 1994.
International Preliminary Exam Report, dated 02 Aug. 1995.
Karl-Ernst Mayer: Stahleisen-Schriften, No. 3 "What the open hearth steel worker must known about this work", 2nd edition, Verlag Stahleisen MbH, Dusseldorf, Dec. 1963.
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