JPH07116781A - Heat insulation method for hot top cast bloom having large cross section - Google Patents

Abstract

PURPOSE:To prevent the development of solidified shell in a meniscus by stopping the drawing-out of a cast bloom at the end period of casting, raising the molten metal surface level at the upper surface of the cast bloom and covering the upper surface of the cast bloom with heat insulating material. CONSTITUTION:The meniscus position is kept to the position of a water-cooling mold 1 during casting and the drawing-out of the cast bloom 8 is stopped at the end period of casting and the meniscus position is raised to the position of a heat insulating frame 6. At the time of using T for the thickness of the cast bloom 8, the meniscus position is adjusted in the range of 0.5-0.7T from the upper end of the water cooling mold 1. After the completion of casting, the exothermic heat insulating agent composed of CaO, SiO2, FeO, etc., is quickly added as the heat insulating material 9, and the upper opening part of the heat insulating frame 6 is covered with a heat insulating cover to start the hot top.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for keeping a slab head warm after casting a large-section slab with a continuous casting machine.

[0002]

2. Description of the Related Art Conventionally, after the completion of casting of a columnar large-section slab with a semi-continuous casting machine, the slab head is delayed for the purpose of delaying the formation of a solid shell at the top of the slab and applying atmospheric pressure to the liquid metal. The part is kept warm. Specifically, after casting,
Immediately install the heat-insulating feeder frame on the mold, push the slab up onto the mold, insert the head of the slab into the heat-insulating feeder frame, and then apply the exothermic heat retaining agent with high calorific value. It is added to keep the slab head warm.

[0003]

However, in the conventional heat retention method, after the completion of casting, in order to perform the so-called hot top, in which the heat is maintained by inserting the slab head into the heat-insulating feeder frame installed on the mold, A certain amount of time elapses from the completion of casting to the start of the hot top. During this period, a solidified shell is generated on the meniscus (the upper surface of the slab) after the completion of casting. When the low temperature casting is performed for the purpose of improving the internal quality, the above-mentioned formation of the solidified shell is particularly remarkable. If the exothermic heat retaining agent is added and heat is maintained in the state where such a solidified shell is generated, the solidified shell of the meniscus is locally redissolved and the edge is cut off from the surroundings, and the separated solidified shell is the exothermic thermal insulation. There is a problem that the agent may be trapped and settled, and may appear as a harmful inclusion defect in the slab.

In consideration of the above-mentioned problems of the conventional method for keeping the temperature of the head of the slab, the present invention provides a method for keeping the head of the large-section slab, which can prevent the solidified shell from being generated in the meniscus. The purpose is to do.

[0005]

Means for Solving the Problems The present invention relates to a method for keeping the temperature of a slab top cast by a continuous casting machine warm, in which a heat insulating and heat insulating frame is previously attached to the upper part of the mold, and the casting surface of the slab is kept hot during casting. Hold the level at the position of the mold, stop the withdrawal of the slab at the end of casting, raise the level of the molten metal on the upper surface of the slab to the position of the heat insulating heat insulation frame, and use the heat insulating heat insulating material on the raised slab upper surface. This is a method for keeping the head of a large-section cast slab covered.

In the present invention, when the thickness of the slab is set to T, the level of the molten metal on the upper surface of the slab at the end of the casting, which is raised to the position of the heat insulating heat insulation frame, is 0.5 to 0.7T from the upper end of the mold. It is preferable to maintain the range. In addition, the heat insulation frame is
A structure having a downward opening taper can be used. Further, it is preferable to add an exothermic heat retaining agent to the heat insulating heat retaining material after the casting is completed.

[0007]

In the present invention, when the slab top cast by the continuous casting machine is kept warm, a heat insulating heat insulating frame is previously attached to the upper part of the mold, and during casting, the level of the molten metal on the upper surface of the slab is set to the position of the mold. In the final stage of casting, stop the withdrawal of the slab, raise the level of the molten metal on the upper surface of the slab to the position of the heat insulating heat insulation frame, and complete the casting, until the temperature of the slab top is maintained. Moreover, it is possible to prevent the formation of a solidified shell on the meniscus.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a vertical type semi-continuous casting apparatus used for carrying out the method of heat-insulating the head of a large-section cast product according to the present invention.

In FIG. 1, a carriage 3 carrying a dummy head 2 is suspended below a water-cooled mold 1 by a wire 4, and the end of the wire 4 is wound around a pulley 5 via a drum (not shown). The dummy head 2 can be raised and lowered in the direction of arrow A by taking or unwinding.

On the upper part of the water-cooled mold 1, a heat-insulating and heat-insulating frame 6 lined with a heat insulating material 6a is fixed in advance.
And this heat insulation heat insulation frame 6 comprises the composite mold. During casting, a ladle 7 is arranged above the heat insulating and heat insulating frame 6, and molten steel is poured into the mold 1 from a dipping nozzle 7a vertically provided from the ladle 7. The lower part of the mold 1 is cooled by spraying, and the wire 4 is loosened at a constant speed according to a predetermined casting speed, whereby the slab 8 is pulled out.
In the figure, 9 is a mold powder as a heat insulating and heat insulating material, which is put in to cover the upper surface of the molten steel.

The head heat retaining method according to this embodiment having the above structure will be described below. During casting, the position of the meniscus (the level of the molten metal on the upper surface of the slab) is adjusted to the water-cooled mold 1.
At the end of casting, the withdrawal of the cast slab 8 is stopped and the position of the meniscus is raised to the position of the heat insulating and heat insulating frame 6. The position of the meniscus is adjusted so as to be in the range of 0.5 to 0.7 T from the upper end of the water-cooled mold 1, where T is the thickness of the cast piece 8.

Explaining the reason why the position of the meniscus is within the above range, if the value is less than 0.5, the heat retaining effect cannot be obtained, so the lower limit is set to 0.5. On the other hand, when it exceeds 0.7, the height of the heat insulating and heat insulating frame 6 becomes too high and the workability is deteriorated, and the economical efficiency is deteriorated.
It was set to 7.

Then, after the casting is completed, as shown in FIG.
Immediately after the heat insulating and heat insulating material 9, CaO, SiO ₂ , FeO,
An exothermic heat insulating agent such as CaSi is added, the upper opening of the heat insulating heat insulating frame 6 is covered with the heat insulating lid 10, and the hot top is started.

Example 1 In producing a slab having a thickness T of 700 mm and a width of 1400 mm, the height from the upper end of the mold to the meniscus portion after completion of casting was 400 mm. Upon completion of casting, an exothermic heat retaining agent was added to the mold powder to maintain it until complete solidification. It was confirmed that the hot top worked effectively without any large shrinkage on the upper surface of the slab after the completion of solidification. Further, as a result of the ultrasonic flaw detection test, no indication was observed, and a slab of good quality was obtained.

Example 2 Casting was carried out in the same manner as above using the heat insulating and heat insulating frame 20 shown in FIG. The heat insulating and heat insulating frame 20 is lined with a heat insulating material 20a and has a downward opening taper. When casting is performed using the heat insulating and heat insulating frame 20 having such a configuration, not only the same effect as described above is obtained, but also as shown in FIG. Since it is smaller than the cubic shape, the yield at the time of cutting off the end on the top side of the slab is improved in the subsequent forging or rolling.

The heat insulating and heat insulating material of the present invention is a mold powder in the above embodiment, but the present invention is not limited to this, and any powder or fibrous material can be used as long as it can prevent heat loss to air. , Any heat insulating material such as granules can be used.

[0017]

As is apparent from the above description, according to the present invention, the hot top can be started immediately after the completion of casting by adding the heat insulating material. Therefore, from the completion of casting to the start of hot top. The time can be shortened, thereby preventing the formation of a solidified shell on the meniscus. In addition, if the heat insulating heat insulating frame is configured to have a downward opening taper, there is an advantage that the yield amount of the cut-off amount of the top end portion at the time of casting or rolling can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a vertical semi-continuous casting apparatus used for a head heat insulating method of the present invention.

FIG. 2 is a cross-sectional view illustrating a heat retaining method at the time of completion of casting according to the present invention.

FIG. 3 is a view corresponding to FIG. 1 showing another configuration of the heat insulating and heat insulating frame.

FIG. 4 is a cross-sectional view for explaining the effect of the configuration of FIG.

[Explanation of symbols]

 1 Water-cooled mold 2 Dummy head 3 Carriage 4 Wire 5 Pulley 6 Insulating heat insulation frame 7 Ladle 8 Cast slab 9 Mold powder 10 Heat insulation lid

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keisuke Tanaka 2-3-1, Niihama, Arai-cho, Takasago-shi, Hyogo Inside the Takasago Plant, Kobe Steel, Ltd. (72) Ichito Minakami 2-3, Niihama, Arai-cho, Takasago-shi, Hyogo No. 1 Inside Takasago Works, Kobe Steel Co., Ltd. (72) Tatsuya Ikoma, Tatsuya Ikoma 2-3-1, Niihama, Arai Town, Takasago City, Hyogo Prefecture (72) Takasago Works, Kobe Steel Co., Ltd. (72) Akira Takeda, Arai Town, Takasago City, Hyogo Prefecture 2-3-1, Niihama Takasago Works, Kobe Steel, Ltd.

Claims (4)

[Claims] 1. A method for heat-retaining a slab top cast by a continuous casting machine, wherein a heat insulating and heat-insulating frame is previously attached to the upper part of the mold, and the level of the molten metal on the upper surface of the slab is held at the position of the mold during casting. Then, at the end of casting, the withdrawal of the slab is stopped to raise the molten metal surface level of the slab to the position of the heat insulating and heat insulating frame, and the raised slab upper surface is covered with a heat insulating and heat insulating material. A method to keep the head of large-scale cast slabs characteristic. 2. When the thickness of the slab is T, the level of the upper surface of the slab at the end of the casting, which is raised to the position of the heat insulation frame, is in the range of 0.5 to 0.7T from the upper end of the mold. The method of claim 1, wherein the head is kept warm. 3. The head heat insulating method according to claim 1, wherein the heat insulating heat insulating frame has a downward opening taper. 4. The head heat insulating method according to claim 1, wherein an exothermic heat insulating agent is added to the heat insulating heat insulating material after the pouring is completed.