JPH06304727A - Device for controlling casting velocity - Google Patents

Abstract

PURPOSE:To prevent the surface flaw and to stabilize the casting by increasing the casting velocity in a surface flaw developing range and decreasing the casting velocity in a breakout developing range. CONSTITUTION:Plural heat flux sensors 4 for measuring the conductive heat in a mold 2 in a continuous casting are embedded into a copper plate 3 constituting the mold 2. The heat flux Q obtd. from the heat flux sensors 4 and the casting velocity Vc obtd. from a casting velocity detecting means are obtd. In a signal processing device 6, it is decided whether the heat flux is among the surface flaw developing range/suitable range/breakout developing range, based on the inequality. In this result, in the case of being no suitable range, alarm is sounded with an alarming device 7 and at the same time, the casting velocity is changed through a casting velocity control device 8 and a pinch roll controlling device 9 to obtain the suitable heat flux. By this method, the surface flaw is prevented and the casting can be stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting speed control device in continuous casting, and it is an object of the present invention to control the heat removal in a mold to an appropriate region by increasing or decreasing the casting speed.

[0002]

2. Description of the Related Art Japanese Patent Publication No. 63-539
As disclosed in Japanese Patent Publication No. 03-2003, a thin plate type surface heat flux meter disposed on the outer surface of the mold measures the heat flux according to the heat removal amount of the mold to prevent breakout in continuous casting. The heat flux meter measures the local heat flux of each part of the mold, lowers the casting speed when the wave height of the heat flux waveform representing the temporal change of the heat flux suddenly exceeds a predetermined value, and There is a breakout prevention method in continuous casting, which is characterized by preventing the occurrence of breakout by performing low-speed casting until the wave height returns to the original level.

[0003]

The above technique is a breakout prevention method using a heat flux meter by detecting a change in heat flux, and cannot be used for preventing surface flaws and stabilizing casting. However, the authors paid attention to the relationship between the casting speed and the absolute value of the heat flux, and as a result of repeated research, they found that the breakout occurred when the proper heat flux was not obtained for the casting speed. It was also discovered that by controlling the heat removal in the mold to an appropriate region by increasing or decreasing the casting speed, it can be used for preventing surface defects and stabilizing casting.

[0004]

The present invention focuses on the relationship between the casting speed and the absolute value of the heat flux, and controls the heat removal in the mold to an appropriate region by increasing or decreasing the casting speed. A plurality of heat flux meters capable of measuring heat removal in the mold during casting are embedded in a copper plate, the heat flux obtained from the heat flux meter and the casting speed obtained from the casting speed detecting means are determined, and based on the equation (1) In the method and apparatus for controlling heat removal in a mold, which is to judge which of a surface flaw generation area / appropriate area / breakout occurrence area, and adjust the casting speed to correct the area, Increases casting speed,
It is a casting speed control device that reduces the casting speed in the breakout occurrence region.

0.44Vc ² −0.592Vc + 1.567 ≦ Q ≦ 0.43Vc ² −0.566Vc + 2.029 (1) Q: Heat flux (kal / m ² · hr) Vc: Casting speed (m / min)

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given below with reference to the drawings. FIG. 4 shows the principle of the heat flux sensor, and FIG. 3 shows the outline of the mold assembly and the heat flux sensor embedding position. The heat flux is the amount of heat passing through the mold per unit time and unit area, and corresponds to latent heat / sensible heat released when the molten steel solidifies in the mold. This value greatly changes depending on the continuous casting flux existing between the mold copper plate and the solidified shell that defines the thermal resistance.

Reference numerals 4a and 4b denote thermocouples, which are embedded in a copper plate having a thermal conductivity λ with a distance d.
From the electromotive forces Va and Vb of the thermocouples 4a and 4b, the temperature difference (Ta
It is possible to obtain −Tb) and the heat flux q from the relational expression q = λ / d · (Ta−Tb). As shown in FIG. 3, the heat flux sensor 3c having such a function is embedded in the long side copper plate 3a and the short side copper plate 3b of the mold.

FIG. 1 shows the relationship between the heat flux and the casting speed according to the present invention. The casting speed is the speed at which a slab is drawn out in continuous casting, and the higher the speed, the higher the productivity. Conventionally, a thermocouple has been used to monitor the solidification phenomenon in the mold, but the thermocouple temperature is not a physical quantity that captures the solidification phenomenon itself, but is merely one temperature index. Further, there is a drawback that the value greatly changes due to maintenance such as reworking of the molded copper plate. On the other hand, if the heat flux is used, the heat removal state itself of the slab can be appropriately known.

Explaining this graph concretely, for example, when the casting speed is 1.0 m / min, the appropriate range is 1.4 to 1.85.
It is kcal / cm ² / min. If the heat flux is lower than this, it means that the casting speed is too high, which leads to operational problems such as restraint breakout and bulging due to insufficient shell strength. Further, when the heat flux is high, it means that the heat removal of the surface of the solidified shell is too strong, which increases the thermal strain on the surface of the slab and causes surface defects.

At point A on the graph, heat removal is high relative to the casting speed, and it is desirable to raise the casting speed to A '. At point B on the graph, heat removal is low relative to the casting speed, and it is desirable to lower the casting speed to B '.

FIG. 2 is a block diagram of an apparatus according to the present invention. Molten steel is injected into the mold 2 via the immersion nozzle 1. Reference numeral 4 denotes a heat flux sensor embedded in the mold copper plate, which outputs a voltage and is converted into a heat flux value by the converter 5. Reference numeral 6 is a signal processing device, which determines from casting speed and heat flux whether or not appropriate conditions are met. The casting speed is changed through the control device 9 to obtain an appropriate heat flux.

[0012]

As shown in FIG. 5, the index of surface defect rate is 1 when the casting speed is not controlled, whereas the index of surface defect rate is 0.49 when the casting speed is controlled, which is about half.

Further, as shown in FIG. 6, the breakout occurrence rate index is 1 when the casting speed control is not performed, whereas the breakout occurrence rate index is 0.22 when the casting speed control is performed.
And about 1/4.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a heat flux and a casting speed according to the present invention.

FIG. 2 is a block diagram of an apparatus according to the present invention.

FIG. 3 is a diagram showing an outline of a mold assembly and a heat flux sensor embedding position of the present invention.

FIG. 4 is a diagram showing the principle of a heat flux sensor.

FIG. 5 is a diagram showing a surface flaw occurrence rate index.

FIG. 6 is a diagram showing a breakout incidence index.

[Explanation of symbols]

1: Immersion nozzle for pouring molten steel into a mold,
2: Mold, 3: Copper plate constituting the mold,
4: Heat flux sensor embedded in molded copper plate, 5:
Converter for converting output (voltage) of heat flux sensor into heat flux value, 6: signal processing device, 7: alarm device, 8: casting speed control device, 9: pinch roll control device, 1
0: motor, 11: pinch roll (casting speed detection end), 12: guide roll, 13: mold flux pool, 14: molten steel, 15: solidified shell.

Claims (1)

[Claims] 1. A plurality of heat flux meters capable of measuring heat removal in a mold in continuous casting are embedded in a copper plate, and a heat flux Q obtained from the heat flux meters and a casting speed Vc obtained from a casting speed detecting means are obtained. , Based on the formula (1), the surface flaw generation area / appropriate area /
A casting speed control device that determines which of the breakout occurrence areas, increases the casting speed in the surface flaw occurrence area, and decreases the casting speed in the breakout occurrence area. 0.44Vc ² −0.592Vc + 1.567 ≦ Q ≦ 0.43Vc ² −0.566Vc + 2.029 ………… (1) Q: Heat flux (kcal / m ² · hr) Vc: Casting speed (m / min)