JPH0773777B2 - Control method in continuous casting of multi-layer steel - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a primary meniscus level, which is an outer layer solidification level, and an inner layer solidification level, in order to improve slab quality and stabilize operation in continuous casting operation of multi-layer steel. The present invention relates to a technique for stabilizing the secondary meniscus level to a set value and controlling the molten metal level of the mold.

2. Description of the Related Art Conventionally, in the continuous casting operation of multi-layer steel, the molten metal level control has been performed by manually opening and closing a stopper.

Therefore, the transition layer formation due to the mixed molten steel in the inner and outer layers, which occurs due to the fluctuation of 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 due to the fluctuation of the melt surface level and the fluctuation of the injection ratio, There was a problem in quality control and operation control, such as layer casting component diffusion, deterioration of cast slab property, and nozzle clogging.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to stabilize a boundary surface of molten steel in the inner and outer layers at a level to which a DC magnetic field for suppressing the mixing of molten steel in the inner and outer layers is applied in a continuous casting operation of multi-layer steel, Another object of the present invention is to propose a control method for maximizing the mixing suppression effect of No. 1, while controlling the mold molten metal surface level to a set value, and stably casting a high quality slab with clear inner and outer layer boundaries.

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

That is, while always maintaining the injection ratio of the inner layer and the outer layer constant,
The mold level is controlled by the operation of the sum of the injection amounts of the inner layer and the outer layer (total injection amount).

Alternatively, the molten metal level control is performed by controlling the injection amount of the outer layer while controlling the injection amount of the inner layer which is determined by the thickness of the outer layer and the drawing speed.

Action In the continuous casting process of multi-layer steel, the primary meniscus level, which is the outer layer solidification level, the second meniscus level, which is the inner layer solidification level, and the mold level are the molten steel injection ratio of the inner and outer layers, the slab drawing speed, and the solidification of molten steel. Determined by speed and DC magnetic field application level.

In the continuous casting operation of the multi-layer steel, the quality of the slab is greatly influenced by the fluctuation of the meniscus level.

That is, when the boundary surface in contact with the molten steel in the inner and outer layers deviates from the level at which a DC magnetic field is applied to suppress mixing, the effect of suppressing molten steel mixing due to the application of a DC magnetic field is diminished, and the component mixing of the molten steel in the inner and outer layers proceeds, Casting with the target molten steel composition becomes impossible. Also, the fluctuation of the molten metal level during the casting operation is
It is known that the slab properties are adversely affected.

From the above, stability of 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 quality control.

Therefore, the present inventors presuppose feedback control by measuring the primary meniscus level which is the outer layer solidification level or the second meniscus level which is the inner layer solidification level, and the primary meniscus level and the inner layer solidification level which are the outer layer solidification levels, on the premise of feedback control. As a result of examining the observability of the secondary meniscus level, the following knowledge was obtained.

The primary meniscus level, which is the outer layer solidification level, and the second meniscus level, which is the inner layer solidification level, are unobservable. Further, it is impossible to directly measure the meniscus level below the surface of the molten steel with the current measurement technology.

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

Based on this, we investigated a molten metal level control method by measuring molten steel pouring amount operation, and the mold level surface by operating the sum of the pouring amount of the inner layer and the outer layer (total pouring amount) with a constant pouring amount ratio of the inner layer and the outer layer. Outer layer coagulation level in control 1
The stability of the secondary meniscus level and the secondary meniscus level, which is the inner layer solidification level, was examined by simulation by numerical calculation. As a result, even when the fluctuation of the molten metal level was added, the outer layer solidification level was 1 in this control method. Next meniscus level and inner layer solidification level 2
It was confirmed that the next meniscus level converges to the set value.

Therefore, as a control method in the continuous casting of multi-layer steel, the mold level by controlling the sum of the injection amounts of the inner layer and the outer layer (total injection amount) while maintaining the ratio of the inner layer molten steel injection amount and the outer layer molten steel injection amount to a constant value When the level control or the method of controlling the mold surface level by operating the outer layer injection amount while maintaining the inner layer injection amount at the set value, the outer layer solidification level is 1
The secondary meniscus level and the secondary meniscus level, which is the solidification level of the inner layer, can be made to converge to the set values, and it becomes possible to continuously and stably cast the multi-layer steel in which the inner and outer layers are clearly separated.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

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

The level of molten metal, the injection ratio of the molten steel for the inner layer and the molten steel for the outer layer are determined by the target solidified thickness of the outer layer and the drawing speed of the cast slab.

The deviation between the mold level measured by the melt level meter and the target level is used to determine the target total injection amount by PID control. This target total injection amount is divided into the target injection amounts of the inner layer and the outer layer according to the inner layer / outer layer injection ratio set as the operating condition.

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

The flow measurement control method is as follows. The stopper opening measured by the operating transformer and the area S (mm ² ) where molten steel is injected into the nozzle are geometrically calculated from the tuyere and stopper shapes.

Also, from the load cell output attached to the tundish,
The molten steel weight in the tundish is measured, and the molten steel head h (mm) is calculated from the molten steel density and the internal shape of the tundish.

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

At this time, the molten steel flow velocity V (mm / sec) near the tuyere is (1) from the molten steel head h in the tundish and the nozzle flow coefficient C.
It is represented by a formula.

The molten steel flow rate Q (mm ³ / sec) injected from the nozzle is (2)
It can be calculated by a formula.

Q = S · V (2) The flow rate coefficient C is identified by the recursive least squares method based on the flow rate actuality obtained from the mode cell change at every appropriate sampling time (120 sec), and the next sampling time It is taken into the control system as a flow rate coefficient in flow rate estimation 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 multi-layer steel, it is possible to stably produce a slab with clear inner and outer layer boundaries and excellent quality.

The expected effects of this control method are not only operational stability and rationalization of operating personnel by automation of continuous operation of multi-layer steel, but also
Considering the effects of higher quality of slab and expansion of the application range of high-quality double-layer steel in the industrial field, an enormous effect can be expected.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a processing flow of molten steel level control for continuous casting of multi-layer steel according to the method of the present invention. FIG. 2 is a state diagram of a continuous casting operation of multi-layer steel. dr …… Target solidification thickness of inner and outer layers, vr …… Target drawing speed (mm
/ sec), hr …… Target level (mm), qAr …… Target inner layer molten steel injection rate (mm ³ / sec), qBr …… Target outer layer molten steel injection rate (mm ³ / sec), qA …… Inner layer injection Amount (mm ³ / sec), qB …… Outer layer injection amount (mm ³ / sec), h …… Mold level (mm), 1 …… Ladle (inner layer), 2 Ladle (outer layer), 3 …… Load cell, 4 ……
Tundish (inner layer), 5 ... Tundish (outer layer), 6 ... Mold, 7 ... Electromagnetic brake.

Claims (1)

[Claims] 1. In a continuous casting operation of multi-layer steel, while maintaining a constant ratio of the inner layer molten steel injection amount and the outer layer molten steel injection amount,
The level of the mold surface is controlled by operating the sum of the inner layer molten steel injection amount and the outer layer molten steel injection amount (total injection amount), or by controlling the outer layer injection amount while maintaining the inner layer injection amount at a set value. By controlling the level, 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 are stabilized at set values, which is a control method in continuous casting of multilayer steel. .