JPH02224850A - Method and apparatus for continuously casting cast strip - Google Patents

Abstract

PURPOSE:To produce a cast strip having excellent quality by allowing inert gas of flow toward reverse direction to rotating direction of cooling drum in twin drum type continuous casting and also shutting off the open air accompanied with the rotation. CONSTITUTION:By allowing the inert gas fed from main nozzle 12 arranged into inner part of a protecting cover 10 for covering pouring basin part 4 between the cooling drums 3a, 3b to shield the pouring basin part 4. On the other hand, by allowing the inert gas 14 to flow from nozzles 11a, 11b, toward each reverse direction to the rotating direction of the cooling drums 3a, 3b invasion of the open air developed with the rotation of the cooling drums 3a, 3b into the protecting cover 10, is prevented. By this method, the pouring basin part 4 is perfectly shielded from the open air, and the cast strip having good quality can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a continuous casting method and apparatus for producing thin slabs by cooling and solidifying molten metal by removing heat through a cooling drum.

[Conventional technology]

BACKGROUND ART Recently, a method of directly producing a thin slab having a wall thickness of several fins to several tens of liters close to the final shape from molten metal such as molten steel has been attracting attention. When using this continuous casting method, there is no need for multi-step heat treatment as in conventional methods, and only light rolling is required to obtain the final shape.
The process and equipment will be simplified. Moreover, the thin slab obtained by rapidly cooling and solidifying molten metal in this manner may have a structure and physical properties different from those of slabs manufactured by conventional continuous casting.

As a continuous casting method of this type, a twin drum method is known in which a molten metal pool is formed between a pair of cooling drums, as shown in FIG. Molten metal is supplied from an intermediate container such as a tandy pipe 51 through an immersion nozzle 2 to a sump 4 formed between a pair of cooling drums 3a and 3b. The heat of the molten metal in the sump 4 is removed through the cooling drums 3a, 3b, and solidified shells are formed on the circumferential surfaces of the cooling drums 3a, 3b. And both cooling drums 3a, 3b
The solidified shell formed on the circumferential surface of is integrated at the kissing point 5, and is sent out as a thin slab 6. The thin slab 6 is conveyed to a subsequent process via pinch rolls 7. Note that reference numeral 8 is a cleaning brush for maintaining the surfaces of the cooling drums 3a and 3b in a clean state.

Further, reference numeral 9 is a drum coater that sprays ceramics or the like onto the circumferential surfaces of the cooling drums 3a and 3b in order to generate and grow solidified shells under slow cooling conditions.

In this method, the molten metal rapidly cools and solidifies into a solidified shell at the portions that contact the peripheral surfaces of the cooling drums 3a, 3b. Therefore, when the molten metal poured into the sump 4 is oxidized by oxygen in the atmosphere, the generated oxides are likely to be accompanied by the rotation of the cooling drums 3a, 3b and rolled into the solidified shell. As a result, the cast thin slab 6 has rough skin, cracks, and double skin.

Defects such as water wrinkles are more likely to occur.

Therefore, in Japanese Patent Application Laid-Open No. 62-130749,
It has been proposed to cover the space above the water reservoir formed between the cooling drums with a protective cover and to blow an inert gas into the interior of this closed body.

[Problem to be solved by the invention]

However, the cooling drums 3a, 3b are always rotating toward the sump 4, as shown by the arrows in FIG. Therefore, as the cooling drums 3a, 3b rotate, outside air may pass between the protective cover and the cooling drums 3a, 3b and reach the hot water reservoir 4. Therefore, it is difficult to maintain the space above the water reservoir 4 in a completely non-oxidizing atmosphere.

In order to prevent outside air from entering through the gap between the protective cover and the cooling drums 3a, 3b, a flexible or elastic shoe 5- is attached to the lower end of the protective cover, and this shoe is attached to the cooling drum 3a, 3b. It is conceivable to contact the peripheral surface of 3b. However, in this case, foreign matter adhering to the shoe and small pieces peeled off from the shoe are brought into the water reservoir 4,
May contaminate molten metal.

Further, the intruding outside air is greatly disturbed at the meniscus portion where the cooling drums 3a, 3b first come into contact with the molten metal in the sump 4, making the flow state of the molten metal unstable. The adverse effects of this turbulence in the outside air are noticeable even in casting equipment that is not equipped with the protective cover 10. Moreover, since this is the position where the solidified shell starts to form, the casting conditions become unstable, making it impossible to obtain a thin slab of consistent quality.

Therefore, the present invention prevents the turbulent flow of molten metal and foreign substances near the meniscus by flowing a non-oxidizing gas in the opposite direction to the rotation direction of the cooling drum or by blocking the outside air accompanying the rotation of the cooling drum. The purpose is to prevent contamination and produce thin-walled cast slabs of excellent quality.

[Means to solve the problem]

In order to achieve the purpose of the continuous casting method of the present invention,
When producing thin slabs by rapidly cooling and solidifying molten metal poured into a pool formed between a pair of cooling drums, a non-oxidizing gas is supplied to the cooling drums along both sides of the cooling drums. It is characterized by flowing in the opposite direction to the rotation direction of.

Further, the continuous casting apparatus of the present invention includes a protective cover that covers a pool formed between a pair of cooling drums, a gas supply pipe that supplies non-oxidizing gas into the inside of the protective cover, and a A hood provided along the circumferential surface of the cooling drum, and a nozzle for feeding non-oxidizing gas in a direction opposite to the rotational direction of the cooling drum into a gap between the circumferential surface of the cooling drum and the hood. shall be.

Further, a hood that prevents outside air from reaching the meniscus portion is provided along the circumferential surfaces of the pair of cooling drums forming the pool, and a gap is formed between the hood and the circumferential surfaces of the cooling drums. A brush is rotatably provided at the upstream end of the hood with respect to the rotational direction of the cooling drum, and the brush is brought into contact with the circumferential surface of the cooling drum.

〔Example〕

Hereinafter, the features of the present invention will be specifically explained using examples with reference to the drawings.

FIG. 1 shows an example in which nozzles lla and llb for preventing outside air from entering are attached to a protective cover 10 that covers a water reservoir 4 formed between cooling drums 3a and 3b. A main nozzle 12 is opened inside the protective cover 10, and the space above the water reservoir 4 is maintained in a non-oxidizing atmosphere by an inert gas 13 such as argon or helium sent from the main nozzle 12. . On the other hand, the nozzles lla and llb are arranged to face the gap between the protective cover 10 and the circumferential surface of the cooling drums 3a and 3b. Nozzle lla, l
A part of the inert gas 14 ejected from lb is released to the outside of the protective cover 10 through the gap. Therefore, the flow of outside air along the circumferential surfaces of the cooling drums 3a, 3b caused by the rotation of the cooling drums 3a, 3b is blocked by the inert gas 14 jetting out from the gap, and does not enter the inside of the protective cover 10. .

Note that some types of molten metal are difficult to oxidize, so there is no need to cover the space above the pool 4 with the protective cover IO. In such a case, nozzles lla, ll
so that the inert gas 14 ejected from b flows along the circumferential surfaces of the cooling drums 3a and 3b from near the meniscus.
Set the opening positions of nozzles lla and llb. This prevents the flow of outside air accompanying the rotation of the cooling drums 3a, 3b from causing turbulence in the molten metal near the meniscus.

The intrusion of outside air that would disturb the flow of molten metal in the sump 4 can also be prevented by arranging hoods 15 along the circumferential surfaces of the cooling drums 3a and 3b, as shown in FIG. In this case, a brush 16 or an elastic roll is rotatably attached to the end of the hood 15 on the upstream side with respect to the rotation direction of the cooling drums 3a, 3b. Cooling drum 3a by pressing brush 16 or elastic roll against the circumferential surface of cooling drum 3a, 3b.

The upstream side of the gap 17 formed between the circumferential surface of 3b and the hood 15 is sealed. Therefore, intrusion of outside air is prevented.

The brushes 16 used here are the cooling drums 3a and 3b.
It may be either a driven type that rotates due to the frictional force against it, or a driven type that rotates by being connected to a drive source. When using the drive type brush 16, it is also possible to rotate the brush 16 in the opposite direction to the cooling drums 3a, 3b and provide the function of the cleaning brush 80 explained in FIG. 4. Alternatively, a hood 15 may be attached to the lower end of the protective cover 10 shown in FIG. 1 to maintain the space above the water reservoir 4 in a non-oxidizing atmosphere.

Furthermore, as shown in FIG. 3, an inert gas blowout mechanism can be incorporated into the hood 15. In the case of FIG. 3(a), the plurality of gas jet nozzles 18 are connected to the cooling drums 3a, 3.
b It opens into the gap 17 between the circumferential surface and the hood 15.

Furthermore, the opening direction of the gas jet nozzle 18 is directed toward the brush 16. As a result, the inert gas 14 ejected from the gas ejection nozzle 18 is transferred to the cooling drums 3a, 3b.
flows in the opposite direction to the direction of rotation.

In the case shown in FIGS. 3A and 3B, a ceramic sheet 19 is further attached to the tip of the hood 15 on the side of the water reservoir 4. The lower end of the ceramic sheet 19 is immersed in the hot water pool 4. Therefore, the vicinity of the meniscus where the solidified shell starts forming is the cooling drum 3. i.

The molten metal is cooled and solidified under stable conditions by being shut off from the outside air flow accompanying the rotation of the molten metal 3b and the space above the sump 4.

In this way, by flowing the inert gas in the direction opposite to the direction of rotation of the cooling drums 3a, 3b, or by surrounding the peripheral surface portions of the cooling drums 3a, 3b that reach the water reservoir 4 with the hood 15, the cooling drums 3a, 3b can be cooled. , 3b is prevented from reaching the hot water surface of the hot water pool 4. Therefore, oxidation and turbulence of the molten metal at the initial solidification stage are eliminated, and a solidified shell is generated and grows under stable conditions.

For example, when stainless steel-like casting was carried out with the sump 4 exposed to the outside air, the resulting thin slab had numerous defects such as rough skin, double skin, cracks, and creases. . On the other hand, when casting was carried out using the means shown in FIGS. 1 to 3, the defects occurring in the thin slabs were drastically reduced as shown in Table 19.

Table 1 Protection of the hot water pool and its shadow W [Effects of the invention] As explained above, in the present invention, inert gas is flowed in the direction opposite to the rotational direction of the cooling drum, and the inert gas is poured into the hot water pool. By covering the peripheral surface of the cooling drum upstream of the contact point with a hood, outside air is prevented from reaching the molten metal in the sump due to the rotation of the cooling drum. The outside air that is accompanied by the rotation of the cooling drum and reaches the sump disturbs the flow of molten metal near the meniscus, which is the starting point of solidified shell formation, so by preventing this outside air from entering, the casting conditions can be adjusted. It becomes extremely stable. Furthermore, since oxygen is no longer brought in, oxidation of the hot metal surface is reduced, and the formation of defects in thin slabs due to scum inclusion is also suppressed. In this way, according to the present invention, it is possible to produce thin slabs of excellent quality.

[Brief explanation of the drawing]

Figure 1 shows an example in which the protective cover that covers the space above the water reservoir is equipped with an inert gas ejection mechanism, Figure 2 shows an example in which a part of the circumferential surface of the cooling drum is covered with a hood, and Figure 3 4 shows an example in which an inert gas ejection mechanism is further incorporated into the hood, and FIG. 4 is a schematic diagram showing a twin-drum type continuous casting equipment. 1: Tandice 2: Immersion nozzle 3a, 3b: Cooling drum 4: Water pool 5: Kissing point 6:
Thin piece 7: Pinch roll 8: Cleaning brush 9 Ni drum coater IO: Protective cover ha, jib:
Nozzle 12: Main nozzle 13.14: Inert gas 15
: Hood 16: Brush 17: Gap 18: Gas jet nozzle 19: Ceramic sheet Figure 1 Figure 3 (b) Figure 4

Claims (1)

[Scope of Claims] 1. When manufacturing thin slabs by rapidly cooling and solidifying molten metal poured into a pool formed between a pair of cooling drums, a thin slab is produced along the circumferential surface of the cooling drums. A continuous casting method for thin-walled slabs, characterized in that a non-oxidizing gas is caused to flow in a direction opposite to the rotational direction of the cooling drum. 2. A protective cover that covers a water reservoir formed between a pair of cooling drums, a gas supply pipe that supplies non-oxidizing gas to the inside of the protective cover, and a gas supply pipe provided along the circumferential surface of the cooling drum. Continuous casting of thin-walled slabs, comprising: a hood; and a nozzle for feeding non-oxidizing gas into a gap between the circumferential surface of the cooling drum and the hood in a direction opposite to the rotational direction of the cooling drum. Device. 3. A hood that extends along the circumferential surfaces of a pair of cooling drums forming a pool and forms a gap between the circumferential surfaces of the cooling drums, and a hood that 1. A continuous casting device for thin-walled slabs, comprising a brush rotatably provided at an upstream end.