Metal founding – Process – With measuring – testing – inspecting – or condition determination
Patent
1997-06-18
1999-06-22
Lin, Kuang Y.
Metal founding
Process
With measuring, testing, inspecting, or condition determination
164454, B22D 1118, B22D 1120
Patent
active
059133570
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for controlling the level of molten metal so as to keep a target level within a mold in the course of casting with a continuous casting machine.
BACKGROUND ART
A casting operation with a continuous casting machine is carried out by the steps of: pouring a molten metal into an upper opening of a cylindrical mold having a water-cooled inner wall and upper and lower openings, cooling the molten metal through the wall in contact with the molten metal to provide a cast slab having an outer solidified shell, continuously withdrawing the cast slab from the lower opening of the mold, further cooling the cast slab, and cutting the solidified slab to a predetermined length after the central portion thereof is solidified to provide a product slab to be used as a starting material for rolling, etc.
In carrying out continuous casting, it is necessary not only to improve productivity by preventing defects such as over-pouring and break-out, occurrence of which is undesirable for stable operation, but also to improve quality of product slabs by achieving uniform cooling and solidifying of molten metal within a mold. One means for achieving these goals is to control the level of molten metal so as to keep a predetermined level within a mold.
The level of molten metal is generally controlled using feedback by detecting the molten metal level within a mold, by calculating PID on the basis of deviation between the determined level and the target level so as to determine an operating position of a pouring means such as a sliding gate and a stopper, which are provided in a pouring nozzle to control pouring into the mold, and supplying a control signal to operate an actuator, e.g., an oil hydraulic cylinder for the pouring means to make the deviation zero.
However, in the operation of a continuous casting machine, deposition and removal of precipitates such as alumina onto or from a contact surface between the molten metal and the pouring means, for example, repeatedly occur, and a gain of pouring rate of the molten metal passing through the pouring means varies, resulting in a fluctuation in the molten metal level. In addition, since the inside of the cast slab when it is pulled downward out of the mold is in an unsolidified state, the cast body repeatedly swells and shrinks between pinch rolls. This phenomena is called bulging. As bulging occurs, molten metal within the cast slab is forced up or down, resulting in a level fluctuation of molten metal within the mold.
Thus, there are many disturbances affecting molten metal level control. On the other hand, nowadays, it is greatly desired to increase the casting rate in a continuous casting operation. It is difficult, therefore, to control the molten metal level with great accuracy and a quick response time even by employing feedback control
In the past, as disclosed in Japan Patent Laid-Open Application No. 5-23811/1993, disturbances were successively estimated by using a control signal applied to a molten metal pouring means or a signal indicating the operating position of the pouring means together with a signal indicating the molten metal level within a mold, and correction was made to the control signal so that estimated disturbances were eliminated. Thus, a method of controlling the molten metal level with high accuracy and a quick response time was employed to give intended effects to a certain extent.
On the other hand, sometimes a withdrawing rate of a cast slab out of a mold must be varied during operation of a continuous casting machine depending on the specifications of the product slabs. In addition, in order to produce product slabs having a good internal structure, sometimes the thickness of cast slabs withdrawn out of a mold must be reduced while the slabs have a liquid core, i.e., a liquid core reduction device. Changes in operating conditions in these cases result in a level fluctuation of molten metal within the mold.
In the past, when changes in operating conditions were expected because the withd
Hanazaki Kazuharu
Oka Masahiko
Lin Kuang Y.
Sumitomo Metal Industries Ltd.
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