Metal founding – Process – With measuring – testing – inspecting – or condition determination
Patent
1993-10-08
1995-09-12
Lin, Kuang Y.
Metal founding
Process
With measuring, testing, inspecting, or condition determination
164484, 164478, B22D 1120
Patent
active
054490340
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a method of dynamically controlling the withdrawal speed in a process for the continuous casting of steel, this method being of the type according to which, on detection of an occurrence of skin sticking in the moulds, the withdrawal speed is subjected to a cyclic variation which comprises a deceleration ramp from the cruising speed to a reduced speed, a healing plateau, and an acceleration ramp from the reduced speed to the cruising speed. .
Occurrences of skin sticking in the moulds of a continuous casting machine are very dangerous, since they can lead to breakouts. Particularly through the system developed by SOLLAC, under the name SAPSOL, the provision of warning of these sticking events is known to be given by an alarm system based on the monitoring of the temperatures of the mould walls by thermocouples inserted at two levels within the thickness of the walls of the vertical mould, below the meniscus. Other alarm systems have also been proposed. In the beginning, after an alarm was detected, the casting operation was stopped for a period of time considered to be long enough for healing to take place. Later, it was proposed that the withdrawal speed should be regulated over a healing cycle such as the one defined above, which avoids bringing the machine to a dead stop. However, this cycle, and more particularly its reduced-speed period, is not without consequences as regards the quality of the product surface and the productivity of the machine.
In horizontal continuous-casting installations, the known art also includes breakout detection methods which utilize stress measurements (EP-A-111 000), and methods which teach that product withdrawal should be stopped only if a sudden fall in temperature in the mould is detected (DE-A-33 07 176).
The object of the invention is to replace the management of this cycle by dynamic control which is adjusted to suit the behaviour of the steel, and which shortens the reduced-speed period to the minimum waiting time required for healing the area where sticking has occurred.
The invention achieves its object by determining the ferritic potential of the steel which is being cast, and by determining at least the gradients of the deceleration and acceleration ramps as functions of this ferritic potential.
The invention is, in effect, based on the discovery--itself based both on scientific considerations and on practical experiments--according to which the ferritic potential, as defined later, can be considered as the decisive factor in the regulation of the withdrawal speed during the healing cycle.
It has also appeared advantageous to determine the length of the healing plateau as a function of the difference between the liquidus and solidus temperatures of the steel which is being cast.
It is advantageous if, in the event of sticking, the reduced speed is of the order of 0.2 to 1 m/minute, so as to allow healing of the area where sticking has occurred.
Other features and advantages of the invention will become evident on reading the detailed description which follows.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of the speeds during the healing cycle,
FIG. 2 comprises three diagrams, displayed one above another: from top to bottom, a graph of healing time (in minutes) as a function of solidification temperature range (in degrees), a graph of deceleration ramp gradient (in m/min.sup.2) as a function of ferritic potential, and a graph of acceleration ramp gradient (in m/min.sup.2) as a function of ferritic potential,
FIG. 3 is a diagram similar to the one displayed in FIG. 1, showing the healing cycles, according to the invention, for three grades of steel, Y, B, D, and the healing cycle for steel of grade Y', analogous to X, according to a conventional method.
DESCRIPTION OF THE INVENTION
The diagram reproduced in FIG. 1 is a graphical representation of withdrawal speed V (in m/min) as a function of time t (in minutes) before, after and during the healing cycle. Before and after this cycle, the withdrawal spe
REFERENCES:
patent: 4911224 (1990-03-01), Keugen et al.
patent: 5305820 (1994-04-01), Tsuru et al.
S. J. Bercovici Light Metals, A. Publication of the Metallurgical Society of AIME 1985 pp. 1285-1299 S. J. Bercovici: `Optimisation of 3C roll caster by automatic control`.
Klein Andre
Wolf Manfred M.
Lin Kuang Y.
Techmetal Promotion
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