Metal founding – Process – With measuring – testing – inspecting – or condition determination
Patent
1993-03-18
1994-05-17
Bradley, Paula A.
Metal founding
Process
With measuring, testing, inspecting, or condition determination
1641551, B22C 1904
Patent
active
053119240
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a molten metal level control method and device for continuous casting. More particularly, the present invention relates to a molten metal level control method and device which, through the use of a continuous casting machine equipped with an actuator such as a stopper or a sliding nozzle used to control the input flow of molten metal into the mold, are ideal for use in the continuous production of ingots such as slabs and billets and allow a systematic approach to various types of disturbances such as nozzles clogged with deposits, peeling off of these deposits and irregular bulging. In addition, stable and satisfactory control of molten metal level fluctuations in the mold is provided so that it is possible to deal with play of the actuator.
PRIOR ART
A continuous casting machine, which produces continuous ingots such as slabs and billets from molten metal, may have a configuration similar to that shown in FIG. 21, where molten metal 10 in a ladle 12 passes through a tundish 14 and a nozzle 16 and is then injected into a mold 18. The water-cooled mold 18 causes the surface layers of the molten metal to solidify. The partly solidified steel is then pulled out of the mold using pinch rolls 20. After the steel is further cooled to solidify further, it is cut into pieces of a specified length using a cutter 22 to produce ingots 24 which are then fed to the downstream rolling process.
For continuous casting machines it is very important to secure stability of the level of the molten metal 10 in the mold 18 to ensure good quality ingots. That is, molten metal level fluctuations cause enclosures such as refractory materials and molten slug to be caught up in the molten metal and to be captured in the skin of the solidified ingot 24. This may lead to defects caused by the formation of pinholes and enclosures under the skin and give rise to cracks caused by non-uniform heat relief. Accordingly, for continuous casting the molten metal level is generally controlled to remain constant. This is done by receiving signal from a molten metal level gauge 26 which detects the molten metal level in the mold 18 and by using a stopper 28 or a sliding nozzle to serve as flow control actuator. In recent years, the casting speed has increased so that molten metal level control has gained in importance.
In the past, molten metal level control has generally been carried out by using a molten metal level control system similar to that shown in FIG. 22. The system shown in FIG. 22 comprises a stopper 28 which is an actuator used to control the flow by throttling the flow path from the tundish 14 to the mold 18, a stopper controller 30 which controls the stopper 28 so that it establishes a desired position, a molten metal level gauge 26 which is used to detect the molten metal level in the mold 18, a molten metal level target setting device 32, a comparator 34 which compares the measured value to the target of the molten metal level and outputs the deviation e, and a PID (proportional integral and differential) controller 36 which calculates a stopper position command value u used to eliminate the deviation e by using pre-determined control parameters. For example, Japanese Laid-Open Applications 59-30460 and 63-192545 disclose this kind of molten metal level control.
The operation of such a molten metal level control system is shown in FIG. 23. That is, the molten metal level gauge 26 measures the molten metal level L, comparator 34 computes the deviation e (=Lref-L) of the measured value L from the molten metal level target Lref and, based on this deviation e, the PID controller 36 sends a stopper position command value u to the stopper controller 30. The molten metal level L is then controlled by the stopper controller 30, which causes the stopper 28 to establish a position in accordance with the command value u, and by adjusting the flow q of molten metal, where q is determined by the flow gain Gc which represents the relation between the stopper position x (in the examp
REFERENCES:
patent: 4573128 (1986-02-01), Mazur
patent: 4583717 (1986-04-01), Hasegawa
Arai Kazuo
Asano Kazuya
Ibaraki Michio
Kaji Takayuki
Moriwaki Saburo
Bradley Paula A.
Kawasaki Steel Corporation
Pelto Rex E.
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