JPH07276000A - Dummy sheet for starting strip continuous caster - Google Patents

Abstract

PURPOSE:To provide a dummy sheet, in which the bottommost part of a cast slab can stably be introduced to a carrying device at the rear part at the time of setting to a continuous caster, in the dummy sheet used at the time of starting a twin roll type strip continuous caster. CONSTITUTION:The thickness in the range of 50-500mm length at the upper end part of the dummy sheet 6 is formed so inclination as to thin toward the upper end. The inclination of the upper end part 6-1 is made to be 1/100-1/2500 and the thickness at the most tip part is made to be <=0.2mm. By this method, the cast slab can smoothly be introduced to the carrying device at the rear part without developing the breakage to the bottom part of the cast slab by using this dummy sheet 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dummy sheet for starting a twin-drum type continuous casting machine used for directly producing a thin metal plate.

[0002]

As a casting start method for twin drums,
Conventionally, JP-A-58-218358 and JP-A-59-
As disclosed in Japanese Patent Laid-Open No. 215257, a flying start method without a dummy sheet and JP-A-57-0589
No. 57 and No. 60-121441, there is proposed a method in which a dummy sheet is used, and after a basin of a certain height is formed while the drum is stopped, the basin is started. .

In the flying start system without a dummy sheet, which is represented by Japanese Patent Laid-Open No. 58-218358,
In order to guide the leading portion of the slab, which comes out of the drum immediately after the start, the so-called bottom piece, to the conveying line on the rear surface, a special guide device such as that proposed in JP-A-2-133150 is required. In addition, the initial pouring flow from the tundish to the drum was unstable, and the width of the bottom piece was uneven until the basin was formed, resulting in a so-called "young cloth" slab shape. However, it was difficult to carry it on the rear surface. On the other hand, a dummy sheet as represented by JP-A-57-058957 and JP-A-60-121441 is used, and the drum is stopped, and then a basin of a certain height is formed and then the start is started. In the method, the strength of the slab suddenly changes at the boundary between the part with the dummy sheet and the part without the dummy sheet in the initial stage of casting, and the slab ruptures at this position and smoothly guides the slab to the transportation equipment on the rear surface. Sometimes there was a problem that I could not do it.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a dummy sheet capable of smoothly guiding the bottom (leading) portion of a slab to a conveying device on the rear surface.

[0005]

In order to achieve the above object, the present invention is a dummy sheet used at the time of starting a twin-drum type thin plate continuous casting machine, wherein the dummy sheet is set in the continuous casting machine before the start of casting. At this time, a dummy sheet is used in which the upper end portion of the portion protruding above the kiss portion of the drum has a thickness gradient with respect to the length range of 50 to 500 mm and becomes thinner toward the upper end.

[0006]

[Function] As a result of investigating and researching the boundary between the portion where the dummy sheet exists and the portion where the dummy sheet does not exist, the boundary portion contains more high temperature semi-solidified portion in the inside of the slab than other portions. Since the temperature of the part becomes higher than other parts, the strength of that part decreases and it becomes easier to break,
It has been found that whether or not a semi-solidified portion is formed at the upper end of the dummy sheet is affected by the drum diameter, the thickness of the dummy sheet, or the response of the drum pressure control. In production equipment, it is usual that there is no degree of freedom to change the drum diameter, and the response range of the drum pressure control is limited. Therefore, in any case, it is unavoidable to sandwich the semi-solidified portion. For example, in the case of a dummy sheet thickness of 0.5 mm and a drum diameter of 1200 mm, a wedge-shaped semi-solidified layer having a theoretical thickness of 0.5 mm and a length of 11 mm ( part)
Is sandwiched inside the slab.

Since the latent heat of solidification of the semi-solidified layer passes through the kiss part of the drum, it raises the temperature of the already solidified part of the slab containing the semi-solidified part in a very short time and lowers the strength. When a semi-solidified layer having a uniform thickness is generated, the bottom portion of the cast slab may be broken. On the other hand, like the present invention,
By tapering the tip of the dummy sheet, the thickness of the upper end of the dummy sheet can be made substantially zero, so that it is possible to prevent the semi-solidified layer from being pinched, thereby preventing the bottom portion of the slab from breaking. Since this can be prevented, the obtained slab can be smoothly guided to the transporting device on the rear surface.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a twin-drum type thin plate continuous casting machine. Reference numerals 1 and 1 denote a pair of water cooling drums, and a pair of side dams and these drums (not shown) that rotate synchronously in opposite directions. Molten metal is supplied from a nozzle (not shown) to the space created by and to form a basin. Reference numeral 2 is a molten metal in the pool, which is cooled on the surface of each drum to produce a solidified shell, which moves with the rotation of the drum and moves at the kiss point K of the drum.
At P, the solidified shells formed on the surfaces of both drums are integrated to form the target cast piece 3. A pinch roll 4 conveys the slab to the subsequent process.

When a conventional dummy sheet is used in such a casting machine, as shown in FIG. 2, since the dummy sheet 5 has a constant thickness up to its upper end portion, the upper end portion of the dummy sheet is not covered with the surface of both drums. The bottommost part 3-1 of the formed solidified shell 3 is integrally formed while being cast. Therefore, the uppermost end portion 5-1 of the dummy sheet and the lowermost portion 3 of the cast piece are
At the boundary of -1, semi-solid metal 4 equivalent to the thickness of the dummy sheet
Is discharged downward from the kiss point KP of the drum. There is a semi-solidified metal 4-2 between the solidified shell 3-2 and the molten metal 2 on the drum surface, and a part of the semi-solidified metal 4-2 is taken in by the uppermost end portion 5-1 of the dummy sheet.

FIG. 3 shows that, after some time has elapsed from the state of FIG. 2, the bottommost portion 3-1 of the solidified shell is completely drum kissed.
The state immediately after passing through is shown. When the solidified shell 3 (the slab S) including the semi-solid metal 4-1 passes through the drum kiss point KP in this way, the slab S is no longer cooled by the contact with the drums 1 and 1 and is left in a cooled state. Therefore, the cooling effect on the cast slab S is much smaller than when it was in contact with the drums 1 and 1, and the semi-solidified metal 4-
In the state of containing 1, the reheating phenomenon occurs in which the temperature of the solidified shell 3-1 on both sides of the semi-solidified metal 4-1 rises due to the solidification latent heat.
If the temperature rise due to this recuperation is large, the strength of the slab decreases, the slab cannot withstand the tension during transport and the weight of the slab itself including the dummy sheet, and may break.

FIG. 4 shows a state immediately before the start of casting when casting is performed using the dummy sheet of the present invention. The dummy sheet 6 is set by inserting the main body of the dummy sheet between the drums 1 and 1 so that the upper end of the dummy sheet 6 is located above the drums. The lower end of the dummy sheet (not shown) is sandwiched by pinch rolls. It becomes a state. FIG. 5 shows a casting state immediately after the start when the dummy sheet of the present invention is used.
As shown in FIG. 5, since the tip of the upper end portion 6-1 of the dummy sheet is sufficiently thin, the bottommost portion 3-1 of the slab contains no semi-solidified metal at all, or even if it does, the influence of recuperation due to it is eliminated. Therefore, it is possible to maintain the strength of the slab required for transportation.

Here, the length when the thickness of the upper end portion 6-1 of the dummy sheet is inclined is set to 50 to 500 mm. If the length is less than 50 mm, a semi-solidified portion may be formed at the upper end portion of the dummy sheet. Yes, if it exceeds 500 mm, the sloped part of the upper end of the dummy sheet becomes too long, and it becomes impossible to fit the entire sloped part in the pool above the kiss part of the drum, and the tip projects from the pool. This is because there is a high possibility that they will end up.

The gradient applied to the thickness of the upper end portion 6-1 of the dummy sheet is 1/100 to 1/2500. If it is larger than 1/100, a semi-solidified portion is generated at the upper end portion of the dummy sheet. Possible, 1/2500
If it is less than, the slope of the upper end of the dummy sheet is too gentle, and the entire sloped part cannot be stored in the basin above the kiss part of the drum, and there is a high possibility that the tip of the sloping part protrudes from the basin. This is because.

Further, the reason why the thickness of the tip of the upper end of the dummy sheet is 0.2 mm or less is that if it exceeds 0.2 mm, a semi-solidified portion may be generated at the tip of the dummy sheet.

[0015]

EFFECTS OF THE INVENTION By using the dummy sheet of the present invention, the bottom portion of the cast slab can be smoothly guided to the conveying device on the rear surface without breaking.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a twin-drum type thin plate continuous casting machine.

FIG. 2 is a diagram showing a state immediately after the start of casting when a conventional dummy sheet is used.

FIG. 3 is a diagram showing a state when a little time has passed from the state of FIG.

FIG. 4 is a diagram showing a state immediately before the start of casting in the twin-drum type thin plate continuous casting machine according to the present invention.

FIG. 5 is a diagram showing a state immediately after the start of casting when the dummy sheet of the present invention is used.

[Explanation of symbols]

 1 ... Water-cooling drum 2 ... Molten metal in pool 3 ... Solidified shell 4 ... Semi-solidified metal 5, 6 ... Dummy sheet S ... Cast slab P ... Pinch roll

Claims (3)

[Claims] 1. A dummy sheet used at the time of starting a twin-drum type thin plate continuous casting machine, when the dummy sheet is set in the continuous casting machine prior to the start of casting, the upper end portion of the portion protruding from the kiss portion of the drum is 50 to 500 mm. A dummy sheet for starting a thin sheet continuous casting machine, characterized in that its thickness is made to have a gradient with respect to the length range and becomes thinner toward the upper end. 2. The dummy sheet according to claim 1, wherein
A dummy sheet for starting a thin plate continuous casting machine having a slope of 1/100 to 1/2500 at the upper end. 3. The dummy sheet according to claim 1, wherein
A thin sheet continuous casting machine starting dummy sheet with a thickness of 0.2mm or less at the top end.