JPH03243262A - Controlling method in multi-ply steel continuous casting - Google Patents

Abstract

PURPOSE:To stably cast a high quality cast slab having clear boundary between inner and outer layers by stabilizing a first meniscus level, a second meniscus level and mold metal surface level to the set value. CONSTITUTION:The molten steel surface level and pouring ratio of the molten steel for inner layer to the molten steel for outer layer are decided from target solidified thickness of the outer layer and drawing velocity for the cast slab. The target total pouring rate is decided through a PID control of molten metal surface from deviation between the molten steel surface level in the mold measured with a molten steel surface level gage and the target molten steel surface level. This target total pouring rate is devided into the target pouring rates for the inner layer and the outer layer according to the set pouring ratio of the inner layer to the outer layer as the operation condition. The target pouring rate is calculated through the PID control from deviation between the target pouring rates for the inner layer and the outer layer and the estimated suitable pouring rates for the inner layer and the outer layer, respectively, and stopper opening degree is decided.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention is applied to the continuous casting operation of multi-layer steel, in order to improve the quality of slabs and stabilize the operation, the primary meniscus level, which is the outer layer solidification level, and the inner layer solidification level. The present invention relates to a technique for stabilizing the secondary meniscus level to a set value and further controlling the level of the molten metal in the mold.

BACKGROUND OF THE INVENTION Conventionally, the level control in continuous casting of multi-layered steel has been performed by one person manually opening and closing a stopper.

For this reason, due to fluctuations in the hot water level and injection ratio, the outside! 'The formation of a transition layer due to the mixing of molten steel in the inner and outer layers, the diffusion of casting components in the inner and outer layers, deterioration of slab properties, and nozzle clogging, which occur due to fluctuations in the primary meniscus level (solidification level) and the secondary meniscus level (inner layer solidification level). There were problems with quality control and operational management.

Problems to be Solved by the Invention The purpose of the present invention is to stabilize the interface between the inner and outer layers of molten steel at a level where a DC magnetic field is applied to suppress mixing of the molten steel in the inner and outer layers in continuous casting operations for multilayer steel. The purpose of the present invention is to propose a control method for stably casting high-quality slabs with clear boundaries between the inner and outer layers by controlling the mold level to a set value while maximizing the mixing suppression effect.

Means for Solving the Problems In the method according to the present invention, as a means for solving the above-mentioned problems, a method for controlling the mold level by measuring and controlling the amount of injection into the inner and outer layers is proposed.

In other words, while keeping the injection amount ratio of the inner layer and outer layer constant,
The mold surface level is controlled by the injection amount sum operation.

Alternatively, while controlling the inner layer injection amount to the injection amount determined from the outer layer thickness and drawing speed, the hot water level control is performed by controlling the outer layer injection amount.

In the continuous casting process of multi-layer steel, the primary meniscus level (outer layer solidification level), the secondary meniscus level (inner layer solidification level), and the molding surface height are determined by the injection ratio of the molten steel in the inner and outer layers, the slab withdrawal rate, and the molten steel Determined by solidification rate and DC magnetic field application level.

In this multilayer steel M-type casting operation, the quality of the slab is greatly influenced by the fluctuation of the meniscus level.

In other words, when the interface between the inner and outer layers of molten steel deviates from the level at which a DC magnetic field is applied to suppress mixing, the effect of suppressing molten steel mixing by applying a DC magnetic field is reduced, and the mixing of the components of the molten steel of the inner and outer layers progresses. Casting with the target molten steel composition becomes impossible. In addition, fluctuations in the molten metal level during casting operations are
It is known to have an adverse effect on the properties of slabs.

From the above, stabilizing the primary meniscus level which is the outer layer solidification level, the secondary meniscus level which is the inner layer solidification level, and the mold surface level to the set values is an important issue in terms of quality control.

Therefore, the present inventors assumed feedback control by measuring the first meniscus level, which is the outer layer coagulation level, or the second meniscus level, which is the inner layer coagulation level. As a result of examining the observability of the secondary meniscus level, we obtained the following findings.

The first meniscus level, which is the outer coagulation level, and the second meniscus level, which is the inner coagulation level, are unobservable. Furthermore, with current measurement technology, it is impossible to directly measure the meniscus level below the wet surface of molten steel.

From the above, it is impossible to design a control system based on feedback control of the first meniscus level, which is the outer layer solidification level, or the second meniscus level, which is the inner layer solidification level.

From this, we investigated a method of controlling the level of molten steel by manipulating the amount of molten steel that can be measured and controlled, and we investigated the first meniscus level, which is the outer layer solidification level, and the inner layer solidification level in the mold surface level control using the injection amount sum operation while keeping the injection rate constant. As a result of examining the stability of the secondary meniscus level, which is the outer layer solidification level, by numerical simulation, we found that even when disturbances that fluctuate the hot water surface level are applied, this control method maintains the stability of the primary meniscus level, which is the outer layer solidification level, and It was confirmed that the secondary meniscus level, which is the inner layer coagulation level, converged to the set value.

For this reason, the control method for continuous casting of multi-layer steel is to control the mold level by controlling the sum of injection amounts while keeping the ratio of the amount of molten steel injected into the inner layer and the amount of molten steel injected into the outer layer at a constant value.
Alternatively, if you apply a method of controlling the mold surface level by controlling the outer layer injection amount while keeping the inner layer injection amount at the set value,
The primary meniscus level, which is the solidification level of the outer layer, and the secondary meniscus level, which is the solidification level of the inner layer, can be converged to the set values, making it possible to continuously and stably cast multilayer steel with clearly separated inner and outer layers. becomes possible.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a processing flow in which the control method of the present invention is applied to the control system of a multilayer slab continuous casting facility.

The level of the molten metal and the injection ratio of the molten steel in the inner layer and the molten steel in the outer layer are determined from the target casting ratio of the inner layer and outer layer and the drawing speed of the slab.

Based on the deviation between the mold hot water level measured by the hot water level meter and the target hot water level, the target total injection amount is determined by PID control of the hot water level. This target total injection amount is divided into target injection amounts for the inner layer and the outer layer according to the inner layer and outer layer injection ratios set as operating conditions.

The target injection amount is calculated by PID control from the deviation between the target injection amount for the inner layer and the outer layer and the injection amount adaptively estimated for the inner layer and the outer layer, respectively, and the stopper opening degree is determined.

The flow rate measurement control method is performed by geometrically calculating the area S (■2) through which molten steel is injected into the nozzle based on the stopper opening measured by a 0-operation transformer and the tuyere and stopper shapes.

In addition, from the load cell output attached to the tandate,
The weight of the molten steel in the tundish is measured, and the rad h (ms) of the molten steel is calculated from the molten steel density and the shape inside the tundish.

Regarding the setting of the nozzle flow coefficient C based on the nozzle shape, molten steel viscosity, etc., at the start of operation, values based on past experimental values and operation results are set as initial operating conditions.

At this time, the molten steel flow velocity V (mm/5ee) near the separate outlet is expressed by equation (1) from the molten steel flow rate h in the tundish and the nozzle flow coefficient C.

v=cJ Bako]1...(1) The flow rate Q (mm3/5ee) of molten steel injected from the nozzle can be calculated using the equation (2).

Q=S-V (2) The flow coefficient C is identified by the sequential least squares method based on the flow rate results obtained from the load cell changes at every appropriate sampling time (120 seconds), and the flow rate at the next sampling time is determined by It is incorporated into the control system as a flow rate coefficient in estimated control, and flow rate estimation feedback control is performed.

Effects of the Invention As described above, according to the present invention, in continuous casting of multilayer steel, it is possible to stably produce slabs of excellent quality with clear boundaries between inner and outer layers.

The expected effects of this control method are not only stable operations and rationalization of operating personnel through automation of continuous casting operations for multilayer steel, but also
Considering the effects of improving the quality of slabs and expanding the scope of application of high-quality multilayer steel to the industrial field, we can expect immeasurable effects.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a process flow for continuous casting multi-layer steel melt level control according to the method of the present invention. FIG. 2 is a state diagram of a continuous casting operation for multilayer steel. dr...Target casting ratio for inner and outer layers, m...Target drawing speed (mm/5ee), hr...Target level level (
), qA "* * *Target inner layer molten steel injection amount (mm3/
5ec), q13r-*a Target outer layer molten steel injection amount (mm
3/5ec), qA... Inner layer injection amount (mm3/5
ec), qB... Outer layer injection amount (+sm3/5ec
), qA...Estimated inner layer injection amount (mm3/5ee)
, qB* a mEstimated outer layer injection amount (mm3/5ec
). h--mold hot water level (am), l--shi-dol (inner layer), 2--shi-dol (outer layer), 3--load cell, 4--tandish (inner layer), 5・・・Tandish (outer layer), 6...e mold, 7...electromagnetic brake.

Claims (1)

[Claims] In continuous casting operations for multi-layer steel, while keeping the ratio of the amount of molten steel injected into the inner layer and the amount of molten steel injected into the outer layer at a constant value, the mold surface level can be controlled by the injection amount sum operation, or while the amount of inner layer injection is kept at the set value, By controlling the mold hot water level by controlling the outer layer injection amount, the primary meniscus level, which is the outer layer solidification level, the secondary meniscus level, which is the inner layer solidification level, and the mold hot water level are stabilized at set values. Control method.