JPH09141398A - Molten metal flow straighting plate for twin drum type thin sheet continuous casting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cast slab having good surface characteristic without causing any flow mark and surface crack, having the internal structure of the equiaxed crystal and having good internal quality by providing grooves or ruggedness on the surface of a straighting plate opposite to a drum or on the front and rear surfaces of the straighting plate. SOLUTION: The molten metal rising up between the straighting plate 10 and the casting drum 2 through the bottom surface of the straighting plate 10 from the side of a pouring nozzle 9 is stirred by the grooves or the ruggedness on the surface of the straighting plate 10 on the way of rising up and the flow speed is weaked. By this constitution, the waving on the molten metal surface between the straighting plate 10 and the casting drum 2 is restrained and the starting position of solidification is fixed. Further, the tip part of dendritic structure of the solidified shell caused on the surface of the casting drum 2 is melted by stirring the molten metal and distributed in the molten metal to form the new solidified nuclei and in this result, the equiaxed crystal ratio in the cast slab structure can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twin-drum type thin plate continuous casting apparatus for casting thin plate cast pieces.

[0002]

2. Description of the Related Art FIG. 1 is an explanatory view of a twin-drum type continuous casting machine. Place the two horizontal casting drums 2, 2'at the same height,
They are arranged in parallel and close to each other and are rotated in the 6 and 6'directions. Side weirs 3 and 3'are installed in close contact with the side surfaces of the casting drums 2 and 2'in the axial direction. The casting drums 2 and 2'are of the internal water cooling type.

The molten metal 1 is fed to the drums 2 and 2'and the side dams 3,
It is continuously poured into the upper space (melt pool) formed by 3 '. The poured molten metal 1 is cast drums 2 and 2 '.
Cooled by the surface of the solidified shell 4, 2, 2 '
4 'is formed. The solidified shells 4 and 4'are integrated in the minimum gap portion 7 of the drum and taken out as a thin cast piece 5.

According to this twin-drum type continuous casting machine, a thin plate slab having a plate thickness of 5 mm or less and a plate width of 1000 mm or more is produced.
It can be used as a thin plate as it is without performing a complicated post-process, or by performing a light rolling in the post-process.

At this time, preventing wrinkles and surface cracks is a problem in sheet quality. These defects are caused by the fact that the surface of the molten metal is wavy and the solidification start position where the molten metal contacts the casting drum is not uniform in the drum width direction but is non-uniform.

In order to solve this problem, Japanese Patent Laid-Open No. 61-
In Japanese Patent No. 165255, a flow straightening plate (described as a baffle plate in Japanese Patent Laid-Open No. 61-165255) is provided between the injection nozzle and the casting drum, and the flow of discharge from the nozzle collides with the flow straightening plate for discharge. It is said that the flow velocity can be moderated to prevent ripples on the molten metal surface between the straightening vane and the casting drum.

However, with the invention disclosed in Japanese Patent Laid-Open No. 61-165255 alone, the higher the drum rotation speed, the greater the ripples on the molten metal surface at the solidification start position, which cannot be sufficiently prevented.

That is, as the drum rotation speed (casting speed) is increased, the casting amount per unit time is increased, so that the injection amount from the nozzle per unit time is increased. However, since the height of the molten metal surface must be the same on both sides of the straightening vane, the amount of molten metal spouting between the straightening vane and the casting drum per unit time increases from the nozzle side through the bottom of the straightening vane. Therefore, even if the molten metal surface wave caused by the injection flow itself can be prevented, the molten metal surface that flows through the straightening vane causes the molten metal surface ripple to occur between the straightening vane and the casting drum.

Further, as the drum rotation speed is increased and the injection amount from the nozzle per unit time is increased, the force applied to the straightening vane is increased, the holding of the straightening vane becomes difficult, and the dipping depth must be shallow. I don't get.

Further, the invention disclosed in Japanese Patent Laid-Open No. 61-165255 alone does not provide the effect of improving the internal structure of the cast slab, and the internal structure mainly consists of columnar crystals due to quenching. Therefore, the anisotropy of the mechanical properties of the thin plate is large, and in order to realize the isotropic properties, it is desired to form an equiaxed crystal.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a molten metal straightening plate for a twin-drum type thin plate continuous casting apparatus capable of producing a thin plate having excellent surface properties and internal properties of the cast slab.

[0012]

Means of the present invention for solving the above-mentioned problems are as follows. When a molten metal pool is formed between a pair of internal cooling drums that rotate in opposite directions and are arranged parallel to each other and the molten metal in the molten metal pool is continuously cast into a thin plate through a gap between the drum pair, In a molten metal straightening plate for a twin-drum type thin plate continuous casting device, which is immersed between the nozzle for injecting the molten metal in the pool and the casting drum, the molten metal is dipped in parallel with the rotation axis of the casting drum to disperse the molten metal in the width direction of the casting drum. A molten metal straightening plate for a twin-drum type thin plate continuous casting apparatus, characterized in that grooves or irregularities are provided on the surface of the straightening plate facing the casting drum or on the front and back surfaces of the straightening plate.

In the present invention, by providing grooves or irregularities on the surface of the straightening vane facing the casting drum or on the front and back surfaces of the straightening vane, the straightening vane and the casting drum are passed from the nozzle side through the bottom of the straightening vane. The flow velocity of the molten metal that flows up between is weakened by the grooves and irregularities on the surface of the straightening plate, so that the rippling between the straightening plate and the casting drum is suppressed, and the solidification start position is stabilized, so the surface properties of the slab are maintained. And the molten metal agitation between the current plate and the casting drum is promoted, so that the internal structure of the cast piece is also improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In order to realize a good slab surface quality without wrinkles and surface cracks by making the solidification start position constant even during high-speed casting, and further to equiaxed the internal structure of the slab. In the present invention, on the front surface or front and back surfaces of the current plate immersed between the injection nozzle and the casting drum in parallel with the rotation axis of the casting drum,
The feature is that a groove or unevenness is provided.

It is necessary that the groove and the unevenness are formed at least in the molten metal dipping area on the side facing the casting drum, which is below the steady molten metal level.

The molten metal flowing from the nozzle side through the bottom surface of the straightening vane and between the straightening vane and the casting drum is agitated by the grooves and irregularities on the surface of the straightening vane on the way of rising, and the flow velocity is weakened. As a result, the rippling of the molten metal surface between the straightening vane and the casting drum is suppressed, and the solidification start position is made constant. Further, by stirring the molten metal, the tip of the dendrite of the solidified shell formed on the surface of the casting drum is melted and distributed in the molten metal to form new solidified nuclei. As a result, the equiaxed crystal ratio of the slab structure can be increased.

The shape dimensions of the grooves and the irregularities are not particularly specified, but according to the experiments by the present inventors, the depth is preferably 1 mm or more. As for the shape, if the corners of the groove or the bottom of the unevenness are at right angles, the metal may adhere, and it is preferable that the shape is rounded.

The region to be provided with the groove or the unevenness is indispensable below the steady level of the molten metal surface, but it may be provided above the steady molten metal level at a certain point, or even on the entire surface. In that case, in order to prevent erosion of the baffle plate (especially near the surface of the molten metal) due to the molten metal during long-time casting, dip it deeply at the beginning after the start of casting and gradually dip it as the casting progresses. The effect of the present invention can be maintained.

The positional relationship between the immersion depth of the straightening vane and the ejection port of the injection nozzle is not particularly specified, and the bottom of the straightening vane may be deeper or shallower than the ejection port of the nozzle.
In the case of the conventional device, it is effective to make the bottom part of the straightening plate deeper than the nozzle discharge port from the viewpoint of suppressing the surface rippling, but if it is immersed deeply, the force applied to the straightening plate becomes large and it becomes difficult to hold it. Therefore, the dipping depth of the straightening vane was unavoidable. However, when the device of the present invention is used, the effect of suppressing the surface rippling is hardly reduced even when the bottom of the straightening vane is shallower than the nozzle outlet.

Further, the flow velocity of the molten metal after passing through the bottom face of the straightening vane can be naturally reduced by reducing the flow velocity of the molten metal before passing through the bottom face of the straightening vane. It is effective to form grooves or irregularities on the.

Regarding the installation conditions of the straightening vanes, for example, the angle with respect to the horizontal plane and the interval between the casting drum and the casting drum are not specified, but according to the experiments conducted by the present inventors, the angle between the straightening vane and the surface of the molten metal is 30 to 30. It has been found that a change of 90 degrees or a change in the closest distance to the casting drum between 10 and 70 mm is more effective than the conventional straightening plate.

[0022]

EXAMPLE An example of casting using the current plate of the present invention will be shown.
The twin-drum type continuous casting machine used has a diameter of 1200 ×
The width was 1000 mm, the height of the basin was 500 mm, the type of cast steel was stainless steel SUS304, and the casting temperature was a constant superheat of 50 ° C in the tundish. The height variation of the solidification start position in the table was measured by the molten metal surface monitoring video. You.

(Conditions for the current plate) Material: boron nitride (BN) Dimensions: height 500 × width 950 × thickness 30 mm Immersion depth: 100 mm Immersion angle: 45 degrees to the surface of the molten metal. Processing range; whole surface Groove dimensions: width 20 mm, depth 5 mm, pitch 30 mm
(In the case of a lattice, both the vertical groove and the horizontal groove have the above dimensions and are orthogonal to each other.) Shape of groove: 0.5 mm radius of curvature processing is performed on the corner portion of the bottom portion. Distance from casting drum: 30 mm Table 1 shows the results of the examples.

As is clear from the results of Table 1, by using the straightening plate of the present invention, excellent surface properties with less wrinkles and surface cracks, high equiaxed crystal ratio and good internal quality are obtained. A slab can be manufactured.

[0025]

[Table 1]

[0026]

As described above, the present invention has been described in detail. However, by using the straightening plate of the present invention, the solidification start position can be made constant even during high speed casting, and a good slab surface free from wrinkles and surface cracks can be obtained. The properties can be realized, and the internal structure of the slab can be made equiaxed to obtain a slab with good internal quality.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of a twin-drum type continuous casting method.

FIG. 2 is a diagram showing the principle of molten metal agitation when a double-sided straightening plate of the present invention is used.

FIG. 3 is a diagram showing the principle of molten metal agitation when only the drum side surface of the present invention is processed.

[Explanation of symbols]

 1 Molten Metal 2 (2 ') Casting Drum 3 (3') Side Weir 4 (4 ') Solidifying Shell 5 Thin Plate Slab 6 Rotating Direction of Casting Drum 7 Minimum Drum Gap 8 Drum Starting Point 9 Immersion Nozzle 10 Molten metal straightening plate

Claims (1)

[Claims] 1. A basin is formed between a pair of internal cooling drums that rotate in opposite directions and are arranged in parallel to each other,
When continuously casting the molten metal of the molten metal pool portion into a thin plate through the gap of the drum pair, between the nozzle for injecting the molten metal of the molten metal pool portion and the casting drum, it is immersed in parallel to the rotation axis of the casting drum, In a molten metal straightening plate for a twin-drum type thin plate continuous casting device that disperses the molten metal in the width direction of the casting drum, grooves or irregularities are provided on the surface of the straightening plate facing the casting drum or the front and back surfaces of the straightening plate. A molten metal straightening plate for twin-drum type thin plate continuous casting equipment.