JPH07232245A - Dummy sheet for twin roll system continuous casting machine - Google Patents

Abstract

PURPOSE:To prevent a molten steel from flowing out of the surface of a cast billet just after cooling rolls and the joining part of a dummy sheet from breaking. CONSTITUTION:In a continuous casting machine which produces a thin metal strip by supplying a molten metal into a molten well part 3 formed with a pair of cooling rolls 1 which are mutually parallel and rotate in mutually opposite directions, and a pair of side weirs 2 pressed on both end parts of the cooling rolls 1, metal plates 6 set along the circumferential surfaces of the cooling drums 1 are attached on the tip part of a dummy sheet 5 to be inserted into the clearance between the cooling drums 1 and the metal plates 6 are reduced in their thickness toward the top end.

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 smoothly casting in continuous casting of thin metal strips using a twin drum type continuous casting machine.

[0002]

2. Description of the Related Art FIG. 1 shows an outline of a twin-drum type continuous casting machine. This casting machine includes a pair of cooling drums 1, 1 which are parallel to each other and rotate in opposite directions, and a cooling drum 1, 1.
A pair of side weirs 2 and 2 pressed against both end surfaces of 1 forms a pool 3 of molten metal. At the time of casting, after inserting the dummy sheet 4 into the gap between the pair of cooling drums 1 and 1, the molten metal M such as molten steel is supplied to the molten metal pool 3. The molten metal M is solidified and fixed to the dummy sheet 4, and is cooled and solidified on the peripheral surfaces of the cooling drums 1 and 1 to form solidified shells G and G. When the solidified shells G, G have a predetermined thickness, the cooling drums 1, 1 are rotated at a low speed. Solidification shell G, G
Moves in synchronization with the cooling drums 1, 1,
It is integrated at the closest contact point of 1 to form a metal ribbon with a plate thickness of several mm. The metal ribbon is wound on a winder (not shown) together with the dummy sheet. During this period, the molten metal level in the molten metal pool 3 gradually rises, and when it reaches a predetermined level, the cooling drums 1, 1 are rotated while maintaining the molten metal level.

Since the sheet thickness of the metal ribbon manufactured in this manner is close to that of the cold rolled product, the conventional hot rolling step can be omitted and the cold rolling step can be light. Therefore, the process and equipment can be simplified.

[0004]

However, when a relatively high melting point steel such as SUS430, electromagnetic steel, carbon steel, etc. is cast by using this casting machine, the slab immediately after it comes out of the cooling drums 1,1. In some cases, the surface of the steel sheet was broken and molten steel flowed out, or the joint of the dummy sheet broke, and casting had to be interrupted.

The present inventors considered the cause as follows. That is, at the initial stage of casting, the pouring nozzle (immersing nozzle) is in a non-immersed state (open casting) because the molten metal surface level in the pouring bath 3 is low, and the casting speed is low, so the molten metal is discharged from the pouring nozzle. It was considered that the phenomenon of melting of the solidified shell (hereinafter referred to as shell washing) occurs due to the molten steel flow. Therefore, the phenomenon is more likely to occur as the absolute value of the molten steel temperature is higher, that is, as the melting point of the metal is higher.

When the solidified shell is melted, solidification of the molten steel on the dummy sheet becomes insufficient. The portion with insufficient solidification has a low risk of breaking during transportation because of its low strength.

As a method of solving such a problem, for the purpose of quickly increasing the level of the molten metal in the early stage of casting, a metal or an alloy is put into the pool to accelerate the solidification of the molten metal in the pool. The method is, for example, JP-A-63-2.
No. 42450. However, even with such a method, the joining with the dummy sheet was not sufficient, and the breakage of the slab was still unsolved.

In view of the above, the present invention relates to the continuous casting of SUS430, electromagnetic steel, carbon steel, etc., using a twin-drum type continuous casting machine, in which molten steel flows out from the surface of the slab immediately after leaving the cooling drum, and dummy sheet joining is performed. An object is to prevent breakage of a part and smoothly perform casting.

[0009]

A dummy sheet for a twin-drum type continuous casting machine according to the present invention for solving the above-mentioned problems is provided with a pair of cooling drums which are parallel to each other and rotate in opposite directions, and both end faces of the cooling drums. In a continuous casting machine for producing a thin metal strip by supplying molten steel to a molten metal pool formed by a pair of pressed side weirs, a dummy sheet inserted into the gap between the pair of cooling drums at the start of casting. There
A pair of metal plates along the peripheral surfaces of the pair of cooling drums are attached to the leading ends of the dummy sheets, and the thickness of the metal plates is gradually reduced toward the leading ends. . Further, the gradual decrease rate R of the thickness reduction of the metal plate represented by the equation (1) is 0.1 or less. R = Δt / d (1) Formula d; Length of metal plate thickness gradually decreasing area (mm) Δt; Reduction amount of metal plate thickness at d (mm)

[0010]

A dummy sheet for a twin-drum type continuous casting machine according to the present invention comprises a pair of metal members along the peripheral surfaces of a pair of cooling drums at the tip of the portion inserted into the gap between the pair of cooling drums at the start of casting. A plate is attached, and the metal plate gradually decreases in thickness (gradiently) toward the tip.

When the dummy sheet is inserted into the gap between the pair of cooling drums at the start of casting, the peripheral surface of the cooling drum is covered with the metal plate. In this state,
When the molten steel is supplied to the molten metal pool, the molten steel discharged from the discharge hole of the pouring nozzle flows toward the metal plate, then flows along the metal plate, and accumulates in the V-shaped portion formed by the metal plate. Solidify. Further, the molten steel is supplied to the peripheral surface of the cooling drum through the gap between the metal plate and the cooling drum. Cooling of the molten steel supplied to the peripheral surface of the cooling drum is promoted by the metal plate and the cooling drum, so that the formation of the solidified shell is promoted. At this time, since the solidified shell is blocked by the metal plate, melting (shell washing) by molten steel discharged from the discharge hole of the pouring nozzle is suppressed. Therefore, the thickness of the solidified shell uniformly increases in the width direction of the slab, so that molten steel can be prevented from flowing out due to breakage of the solidified shell.

Further, as the thickness of the solidified shell increases uniformly in the width direction of the slab, solidification and fixation of the molten steel to the dummy sheet is promoted, and the strength of the connection portion with the dummy sheet is increased. When the dummy drum connection part is pulled out by rotating the cooling drum in such a state, the thickness of the metal plate attached to the tip of the dummy sheet gradually decreases toward the tip (upper end). The thickness of the slab at the metal plate portion is gradually reduced. As a result, the plate thickness is rapidly reduced, so that the pressure loss of the drum is less likely to occur, and the solidified state of the slab in the dummy sheet joint is made uniform in the casting direction, so that the fracture of the dummy sheet joint can be prevented. .

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a state in which the dummy sheet 5 of this embodiment is mounted on the twin-drum type continuous casting machine described in FIG. The dummy sheet 5 is inserted between the pair of cooling drums 1 and 1, and the thickness and width thereof are substantially the same as the plate thickness of the cast piece to be cast. The material of the dummy sheet 5 is general mild steel. Metal plates 6, 6 are attached to the tip of the dummy sheet 5 along the peripheral surfaces of the pair of cooling drums 1, 1. The material of the metal plates 6 and 6 may be carbon steel when the metal to be cast is carbon steel or electromagnetic steel, and stainless steel is preferable when it is SUS430 stainless steel.

The thickness of the metal plates 6 and 6 gradually decreases toward the tip. As a method for reducing the thickness, in the present embodiment, the metal foil 7 having a plate thickness of 100 μm is shifted in its tip position. After stacking a plurality of sheets, holes are made in the metal foil 7, and the wire 8 is fixed through the holes. As a method of reducing the thickness of the metal plates 6 and 6, grinding or the like may be used instead. Further, for the sake of simplicity of the drawing, an example in which three metal foils 7 are provided on one side is shown, but a plurality of metal foils 7 may be provided if necessary.

As shown in FIG. 3, the rate at which the thickness of the metal plate is reduced is represented by the ratio (Δt / d) between the thickness reduction allowance Δt of the metal plate 6 and the length d at which the thickness is reduced. The gradual decrease rate R is
It is preferably 0.1 or less. R = Δt / d (1) Formula d; Length of metal plate thickness gradual reduction area (mm) Δt; Reduction amount of metal plate thickness at d (mm) When R is larger than 0.1, Alternatively, when R is 0 (conventional method), at the moment when the tip of the metal plate 6 passes through the closest point of the cooling drum, the thickness of the slab sharply decreases, and drum pressure loss occurs, which delays solidification. The strength may decrease and it may be destroyed. The length of the metal plate 6 is about 1/4 of the circumferential length of the cooling drum, and the length d of the gradually decreasing thickness region is a value at which the thickness of the tip of the metal plate is 300 μm or less. The width is almost the same as the plate thickness of the cast slab.

As shown in FIGS. 2 and 4, with the dummy sheet 5 inserted in the gap between the cooling drums 1 and 1, the molten steel M is supplied to the molten metal pool 3 from the discharge holes 10 and 10 of the pouring nozzle 9. . After the molten steel M flows toward the metal plates 6 and 6,
It flows along the metal plates 6, 6 and collects and solidifies in the V-shaped portion formed by the metal plates 6, 6. Further, the molten steel M is supplied to the peripheral surface of the cooling drums 1, 1 through a gap D between the metal plates 6, 6 and the cooling drums 1, 1. Cooling drum 1,1
Cooling of the molten steel M supplied to the peripheral surface of the cooling drums 1 and 1 is promoted by the peripheral surfaces of the cooling drums 1 and 1 and the metal plates 6 and 6 so that the solidified shells G and G are accelerated. At this time, since the solidified shells G, G are covered with the metal plates 6, 6, melting by the molten steel M discharged from the pouring nozzle 9 (shell washing)
Is suppressed. Therefore, the thickness of the solidified shells G, G increases uniformly in the width direction of the slab, and the solidified shells G, G
It is possible to prevent the molten steel M from flowing out due to the breakage of G.

Further, as shown in FIG. 5, solidified shells G, G
With the increase in the uniform thickness in the width direction of the slab, the solidification and fixation of the molten steel M to the dummy sheet 5 is promoted, and the strength of the dummy sheet connecting portion is increased. When the cooling drums 1 and 1 are rotated in this state and the dummy sheet 5 is pulled out, the thickness of the metal plates 6 and 6 gradually decreases toward the tip (upper end), so the cooling drum 1 The sheet thickness of the dummy sheet connecting portion passing between the first and second portions is also gradually reduced. Therefore, since the drum pressure loss due to the rapid decrease in thickness is suppressed, the dummy sheet connecting portion can be prevented from breaking. The metal plates 6 and 6 of the present invention may have a mesh shape in addition to the sheet shape.

[0018]

According to the dummy sheet for a twin-drum type continuous casting machine of the present invention, a metal plate along each peripheral surface of the pair of cooling drums is attached to the tip of the portion inserted into the gap between the pair of cooling drums. The thickness of the metal plate gradually decreases toward the tip.

When the dummy sheet is inserted into the gap between the pair of cooling drums, the peripheral surface of the cooling drum is covered with the metal plate. When molten steel is supplied to the molten metal pool in such a state, the molten steel discharged from the discharge hole of the pouring nozzle flows toward the metal plate and then flows along the metal plate to form V formed by the metal plate. It accumulates in the character part and solidifies. Further, the molten steel is supplied to the peripheral surface of the cooling drum through the gap between the metal plate and the cooling drum. Cooling of the molten steel supplied to the peripheral surface of the cooling drum is promoted by the metal plate and the cooling drum, so that the formation of the solidified shell is promoted. At this time, since the solidified shell is covered with the metal plate, melting by molten steel discharged from the discharge hole of the pouring nozzle is suppressed. Therefore, the thickness of the solidified shell uniformly increases in the width direction of the cast piece, whereby molten steel can be prevented from flowing out due to breakage of the solidified shell, and a cast piece having excellent surface properties can be manufactured.

Further, as the thickness of the solidified shell increases uniformly in the width direction of the slab, solidification of the molten steel into the dummy sheet is promoted, and the strength of the dummy sheet connecting portion is increased. Rotate the cooling drum in this state,
When the dummy sheet connecting part is pulled out, the thickness of the metal plate attached to the tip of the dummy sheet is the tip (upper end).
The slab thickness at the metal plate portion gradually decreases because the slab thickness gradually decreases toward the slab. As a result, since the drum does not release pressure, the solidified state of the slab in the dummy sheet joint is uniform over the casting direction, preventing fracture of the dummy sheet joint and ensuring stable casting without interruption. Can be cast.

[Brief description of drawings]

FIG. 1 is a perspective view showing a twin-drum type continuous casting machine.

FIG. 2 is a perspective view showing a state in which the dummy sheet of the present invention is mounted on a continuous casting machine.

FIG. 3 is a side view for explaining the thickness reduction rate of the dummy sheet of the present invention.

FIG. 4 is a sectional view showing a tip portion of a dummy sheet immediately after casting.

FIG. 5 is a cross-sectional view showing a tip portion of a dummy sheet at an early stage of casting.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cooling drum 2 ... Side dam 3 ... Hot water pool part 4 ... Conventional dummy sheet 5 ... Dummy sheet of this invention 6 ... Metal plate 7 ... Metal foil 8 ... Wire 9 ... Pouring nozzle 10 ... Discharge hole of pouring nozzle G ... Solidified shell D ... Gap between cooling drum and metal plate M ... Molten steel (molten metal)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiromitsu Haga 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Corporation Corporate Technology Development Division

Claims (2)

[Claims] 1. A molten steel is supplied to a molten metal pool formed by a pair of cooling drums that are parallel to each other and rotate in opposite directions, and a pair of side dams that are pressed against both end surfaces of the cooling drum. In a continuous casting machine for producing a ribbon, a dummy sheet inserted into a gap between the pair of cooling drums at the start of casting, and a tip end portion of the dummy sheet has a pair of circumferential surfaces of the pair of cooling drums. A dummy sheet for a twin-drum type continuous casting machine, wherein a metal plate is attached, and the thickness of the metal plate gradually decreases toward the tip. 2. The dummy for a twin-drum type continuous casting machine according to claim 1, wherein a gradual reduction rate R of the thickness reduction of the metal plate represented by the formula (1) is 0.1 or less. Sheet. R = Δt / d (1) Formula d; Length of metal plate thickness gradually decreasing area (mm) Δt; Reduction amount of metal plate thickness at d (mm)