Method for controlling pressure load of chill roll and method for manufacturing thin-walled cast slab

Abstract

To provide a control method for a pressing load of a cooling roll that enables a twin roll-type continuous casting device to make plate thicknesses in a casting direction uniform and to stably cast a thin cast piece, and a manufacturing method for a thin cast piece.SOLUTION: In a control method for a pressing load of a cooling roll in a twin roll-type continuous casting device that supplies molten metal to a molten metal pool part formed of a pair of rotary cooling rolls and a pair of side ingates and forms and grows solidifying shells on peripheral surfaces of the cooling rolls so as to manufacture a thin cast piece, the pair of cooling rolls are fixed so that intervals between the rolls are constant and axes of the rolls are parallel to each other, pressing loads per unit width length of the cooling rolls are set to be 12 N / mm or more, and rotation speeds of the cooling rolls are adjusted so that the pressing loads per unit width length of the cooling rolls are equal to a set value.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for controlling the pressure load of chill rolls in a twin-roll continuous casting machine that produces thin slabs by supplying molten metal to a molten metal pool formed by a pair of rotating chill rolls and a pair of side weirs and forming and growing a solidified shell on the circumferential surface of the chill rolls, and to a method for producing thin slabs. [Background technology]

[0002] As a method for producing thin metal billets, for example, as disclosed in Patent Documents 1 and 2, a twin-roll continuous casting machine is provided, which is equipped with chill rolls having an internal water-cooling structure, and which supplies molten metal from a tundish via an immersion nozzle to a molten metal reservoir formed between a pair of rotating chill rolls, causing solidified shells to form and grow on the circumferential surfaces of the chill rolls, and the solidified shells formed on the respective circumferential surfaces of the pair of chill rolls are joined at a roll kiss point and then reduced to produce thin billets of a predetermined thickness. Such production methods using twin-roll continuous casting machines are applied to various metals.

[0003] In the twin-roll continuous casting machine described above, thin plates (thin billets) with a thickness of, for example, about 1 to 5 mm are produced, so it is not possible to use a large reduction ratio from the billet to the plate, as is the case with ordinary ingot casting and hot rolling lines. As a result, there has been a problem with the uniformity of the finished plate thickness in the casting direction. Therefore, for example, as described in Patent Documents 3 to 8, techniques for controlling the thickness of thin-walled cast slabs have been proposed.

[0004] Patent Document 3 proposes a technique for detecting plate thickness and adjusting roll reaction force. Patent Document 4 proposes a method of controlling the rolling force to be constant in the early stage of casting, and then controlling the roll gap to be constant thereafter. Patent Document 5 proposes a method of controlling the pressure to be constant when the plate thickness is less than a predetermined value, and controlling the roll gap to be constant when the plate thickness is equal to or greater than the predetermined value. Patent Documents 6 and 7 propose a technique for adjusting the thickness by increasing or decreasing the rotation speed of a cooling roll. Patent Document 8 proposes a method in which a predetermined pressure is applied in the early stages of casting, and thereafter the roll reaction force is controlled to be constant and the rolls are parallel to each other. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 07-088602 [Patent Document 2] Japanese Patent Application Publication No. 2019-098342 [Patent Document 3] Japanese Patent Application Publication No. 03-066457 [Patent Document 4] Japanese Patent Application Publication No. 10-211550 [Patent Document 5] Japanese Patent Application Publication No. 59-193740 [Patent Document 6] Japanese Patent Application Publication No. 106650 / 1983 [Patent Document 7] Japanese Patent Application Publication No. 01-154850 [Patent Document 8] Japanese Patent Application Publication No. 2018-176251 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-mentioned conventional plate thickness control method, it has not been possible to stably control the plate thickness in the casting direction. For example, in Patent Documents 3 and 8, the plate thickness is detected and the roll reaction force is adjusted, but this causes fluctuations in the roll gap, which directly affects the plate thickness, and it is not possible to make the plate thickness uniform. On the other hand, in Patent Documents 4 and 5, the roll gap is controlled to be constant. However, if the reaction force suddenly decreases due to fluctuations in the molten metal level in the molten metal pool, the chill rolls cannot be pressed sufficiently, which may result in poor solidification and breakage of the slab. In addition, in Patent Documents 6 and 7, the plate thickness is adjusted by increasing or decreasing the rotation speed of the cooling roll, but this causes fluctuations in the roll gap, which directly affects the plate thickness, and therefore the plate thickness cannot be made uniform.

[0007] The present invention has been made in view of the above-mentioned circumstances, and aims to provide a method for controlling the pressure load of chill rolls in a twin-roll continuous casting machine, which can achieve uniformity in plate thickness in the casting direction and enable stable casting of thin-walled cast strips, and a method for manufacturing thin-walled cast strips. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention provides a method for controlling a pressure load on a chill roll in a twin-roll continuous casting machine that supplies molten metal to a molten metal pool formed by a pair of rotating chill rolls and a pair of side weirs, and produces a thin-walled cast strip by forming and growing a solidified shell on the circumferential surface of the chill rolls, comprising: In a first step from the start of rotation of the cooling roll to the completion of one rotation, the roll gap of the cooling roll is controlled so that the pressing load per unit width length of the cooling roll is constant at 12 N / mm or more; After the first step, The pair of chill rolls are fixed so that the roll gap between them is constant and the roll axes of the pair of chill rolls are parallel, the pressing load per unit width length of the chill roll is set to 12 N / mm or more, and the rotation speed of the chill roll is adjusted so that the pressing load per unit width length of the chill roll is a set value.

[0011] According to the cooling roll pressure load control method having this configuration, In the first step from the start of rotation of the chill roll to the completion of one rotation, the roll spacing of the chill roll is controlled so that the pressure load per unit width length of the chill roll is constant at 12 N / mm or more. This allows the chill roll to be sufficiently pressed to further reliably progress solidification, and prevents breakage of the thin-walled cast slab in the early stages of casting. In the second step following the first step, the pair of chill rolls are fixed so that the roll gap between them is constant and the roll axes of the pair of chill rolls are parallel, the pressing load per unit width length of the chill roll is set to 12 N / mm or more, and the rotational speed of the chill roll is adjusted so that the pressing load per unit width length of the chill roll is a set value. This makes it possible to produce thin-walled cast slabs with a uniform thickness in the casting direction and little thickness variation, and even if the reaction force suddenly decreases due to fluctuations in the molten metal level, the pressing load is ensured, allowing solidification to proceed sufficiently and preventing breakage of the thin-walled cast slab.

[0012] The method for producing a thin cast slab according to the present invention comprises supplying molten metal to a molten metal pool formed by a pair of rotating chill rolls and a pair of side weirs, and forming and growing a solidified shell on the circumferential surface of the chill roll to produce a thin cast slab, and is characterized in that the pressing load per unit width length of the chill roll is controlled by the above-mentioned method for controlling the pressing load of the chill roll.

[0013] According to this method for manufacturing thin-walled cast slabs, the thickness of the thin-walled cast slabs in the casting direction is made uniform, and thin-walled cast slabs with little thickness variation can be produced.In addition, solidification can be allowed to proceed sufficiently, and fracture of the thin-walled cast slabs can be suppressed. Therefore, it is possible to stably produce high-quality thin-walled cast strips with little thickness variation. [Effects of the Invention]

[0014] As described above, the present invention can provide a method for controlling the pressure load of a chill roll in a twin-roll continuous casting machine, which can achieve uniformity in plate thickness in the casting direction and can stably cast thin-walled cast strips, and a method for manufacturing thin-walled cast strips. [Brief explanation of the drawings]

[0015] [Figure 1]1 is an explanatory diagram showing an example of a twin-roll continuous casting apparatus used in a method for controlling a pressure load of a chill roll and a method for producing a thin-walled cast slab according to an embodiment of the present invention.

[0022] FIG. [Figure 2] 2 is an enlarged explanatory top view of the periphery of a chill roll of the twin-roll continuous casting machine shown in FIG. 1. FIG. [Figure 3] FIG. 2 is an explanatory diagram showing a method for controlling a pressure load on a cooling roll according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, a method for controlling the pressure load of a chill roll and a method for producing a thin-walled cast strip according to embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. In this embodiment, molten steel is used as the molten metal, and a thin cast 1 made of steel is produced. In this embodiment, the width of the produced thin cast 1 is within a range of 200 mm to 1800 mm, and the thickness is within a range of 1.0 mm to 2.4 mm.

[0017] First, a twin-roll continuous casting apparatus 10 used in the method for producing a thin-walled cast strip according to this embodiment will be described. The twin-roll continuous casting apparatus 10 shown in FIG. 1 includes a pair of chill rolls 11A, 11B, pinch rolls 12, 13 that support a thin-walled cast strip 1, side weirs 15 disposed at the widthwise ends of the pair of chill rolls 11A, 11B, a tundish 19 that holds molten steel 3 to be supplied to a molten steel pool 16 defined by the pair of chill rolls 11A, 11B and the side weir 15, and an immersion nozzle 18 that supplies molten steel 3 from the tundish 19 to the molten steel pool 16.

[0018] FIG. 2 shows the peripheral structure of the pair of chill rolls 11A, 11B in the twin-roll continuous casting apparatus 10 of this embodiment. In the twin-roll continuous casting apparatus 10 of this embodiment, as shown in Figure 2, hydraulic cylinders 21R, 21L are arranged on the roll shaft of the moving cooling roll 11A, and load cells 22R, 22L are arranged on the roll shaft of the fixed cooling roll 11B.

[0019] The movable cooling roll 11A is configured to move toward or away from the fixed cooling roll 11B by hydraulic cylinders 21R and 21L. The pressure load between the pair of cooling rolls 11A and 11B is measured by load cells 22R and 22L. Furthermore, rotation driving means 23A and 23B for driving the rotation of the cooling rolls 11A and 11B are provided.

[0020] Next, a method for producing the thin-walled cast slab 1 of this embodiment using the above-mentioned twin-roll continuous casting apparatus 10 will be described. Molten steel 3 is supplied from a tundish 19 via an immersion nozzle 18 to a molten steel pool 16 formed by a pair of cooling rolls 11A, 11B and side weirs 15, 15, and the pair of cooling rolls 11A, 11B are rotated in the rotation direction R, i.e., so that the area where the pair of cooling rolls 11A, 11B are adjacent to each other faces the drawing direction of the thin-walled cast 1 (downward in Figure 1).

[0021] As a result, a solidified shell 5 is formed on the peripheral surfaces of the chill rolls 11A and 11B. The solidified shell 5 grows on the peripheral surfaces of the chill rolls 11A and 11B, and the solidified shells 5, 5 formed on the pair of chill rolls 11A and 11B are pressed together at the roll kiss points, thereby casting a thin-walled cast 1 having a predetermined thickness.

[0022] At the start of casting, a dummy sheet (not shown) is placed between the pair of chill rolls 11A, 11B. With the dummy sheet in place, molten steel 3 is poured from a tundish 19 through an immersion nozzle 18 toward the molten steel pool 16. When the surface of the molten steel 3 in the molten steel pool 16 reaches a predetermined position, the chill rolls 11A, 11B begin to rotate. Then, the molten steel 3 moves between the chill rolls 11A, 11B, and solidification of the molten steel 3 progresses, joining the dummy sheet and the thin billet 1. The thin billet 1 is then drawn out following the dummy sheet.

[0023] In the method for controlling the pressure load of the cooling rolls of this embodiment, as shown in FIG. 3, the pressure load per unit width length of the cooling rolls 11A and 11B (hereinafter simply referred to as pressure load) is controlled. 3, in the first step from the start of rotation of the cooling rolls 11A, 11B until they have completed one rotation, the roll gap between the cooling rolls 11A, 11B is controlled so that the pressing load of the cooling rolls 11A, 11B is constant. That is, the hydraulic cylinders 21R, 21L are operated to control the roll gap between the cooling rolls 11A, 11B so that the pressing load measured by the load cells 22R, 22L is constant. In the initial stage of casting, as described above, in order to firmly bond the dummy sheet and the thin billet 1, the pressing load of the chill rolls 11A and 11B is ensured to promote solidification.

[0024] Next, in the second step following the first step, the roll gap between the pair of cooling rolls 11A, 11B is kept constant and the roll axes of the pair of cooling rolls 11A, 11B are fixed so as to be parallel, the pressure load of the cooling rolls 11A, 11B is set to 12 N / mm or more, and the rotation speed of the cooling rolls 11A, 11B is adjusted so that the pressure load of the cooling rolls 11A, 11B becomes the set value. That is, in this embodiment, the roll gap between the pair of cooling rolls 11A and 11B is fixed, and the rotation speed of the cooling rolls 11A and 11B is controlled by the rotation driving means 23A and 23B so that the pressing load measured by the load cells 22R and 22L becomes a set value. During steady-state casting, the roll spacing between the cooling rolls 11A and 11B is fixed to suppress thickness fluctuations in the thin-walled cast slab 1, and solidification is allowed to proceed sufficiently by adjusting the rotation speed of the cooling rolls 11A and 11B so that the pressing load is set to a value of 12 N / mm or more.

[0025] According to the present embodiment of the method for controlling the pressure load of a chill roll and the method for manufacturing a thin-walled cast slab configured as described above, a pair of chill rolls 11A, 11B are fixed so that the roll spacing is constant and the roll axes are parallel to each other, and the rotation speeds of the chill rolls 11A, 11B are adjusted so that the pressure load of the chill rolls 11A, 11B becomes a set value.As a result, the thickness of the thin-walled cast 1 in the casting direction is made uniform, and a thin-walled cast 1 with little thickness variation can be manufactured. Furthermore, the pressing load of the chill rolls 11A, 11B is set to 12 N / mm or more, and the rotational speed of the chill rolls 11A, 11B is adjusted so that the pressing load of the chill rolls 11A, 11B is at a set value. Therefore, even if the reaction force suddenly decreases due to fluctuations in the molten metal level, the pressing load is ensured, solidification can proceed sufficiently, and fracture of the thin-walled cast 1 can be suppressed.

[0026] Furthermore, in this embodiment, in the first step S1 from the start of rotation of the cooling rolls 11A, 11B until they have completed one rotation, the roll spacing between the cooling rolls 11A, 11B is controlled so that the pressing load of the cooling rolls 11A, 11B is constant.This allows the cooling rolls 11A, 11B to be pressed sufficiently to further reliably progress solidification, and prevents breakage of the thin-walled cast 1 in the early stages of casting.

[0027] The above describes in detail the method for producing a thin-walled cast slab according to an embodiment of the present invention, but the present invention is not limited to this and can be modified as appropriate within the scope of the technical concept of the invention. In this embodiment, the twin-roll continuous casting apparatus shown in Figs. 1 and 2 has been described as an example, but the present invention is not limited to this. [Example]

[0028] The results of experiments carried out to confirm the effects of the present invention will be described below. Using the twin-roll continuous casting apparatus shown in Figure 1, thin-walled cast slabs were produced from molten steel containing 0.02 mass% C, 3.5 mass% Si, 0.6 mass% Al, and 0.2 mass% Mn. Here, the diameter of the cooling roll was 600 mm (0.6 m), the width of the cooling drum was 400 mm (0.4 m), and the target thickness of the thin-walled cast slab was 1.4 mm.

[0029] Then, thin billets were cast under the conditions shown in the table. The presence or absence of plate breakage during continuous casting using 500 kg of molten steel and the deviation in thickness of the thin billets in the casting direction were evaluated. The thickness deviation in the casting direction of the thin-walled cast slab was evaluated by sampling four points at 470 mm intervals within a range of a length equivalent to one rotation of the chill roll (1,885 mm), measuring the thickness at the center of the width, and evaluating the maximum difference from the target thickness.

[0030] [Table 1]

[0031] In Comparative Example 1, the pressure load per unit width length of the chill roll was controlled to be constant, but the deviation in the thickness of the cast slab became large, at 15%. In Comparative Example 2, the roll gap between the chill rolls was controlled to be constant, but the thin-walled cast slab broke during the first step from the start of rotation of the chill rolls until they had completed one rotation. In Comparative Example 3, the thickness was measured and the load was feedback controlled, but the deviation in the slab thickness was as large as 10%. In Comparative Example 4, the pressure load per unit width of the chill roll was controlled to be constant in the first step from the start of rotation of the chill roll until it had completed one rotation, and the roll spacing of the chill roll was controlled to be constant in the second step, but the thin-walled cast piece broke during casting.

[0032] In contrast, in Examples 1 to 3 of the present invention, which satisfied the conditions specified in the present invention, no slab fracture occurred during casting, and stable casting was possible. In addition, the deviation in slab thickness was less than 3.0%, and thin slabs with uniform thickness in the casting direction were produced.

[0033] From the above results, it was confirmed that the present invention can provide a method for controlling the pressure load of the chill rolls and a method for manufacturing thin-walled slabs in a twin-roll continuous casting machine, which can achieve uniformity in plate thickness in the casting direction and can stably cast thin-walled slabs. [Explanation of symbols]

[0034] 1 Thin-walled cast billets 3 Molten steel (molten metal) 5 Solidified shell 10 Twin-roll continuous casting machine 11A, 11B Cooling roll 15 Side Weir 16 Molten steel pool section (molten metal pool section) 18 Submerged Entry Nozzle 19 Tundish

Claims

1. 1. A method for controlling a pressure load of a chill roll in a twin-roll continuous casting apparatus for producing a thin-walled cast strip by supplying molten metal to a molten metal pool formed by a pair of rotating chill rolls and a pair of side weirs, and forming and growing a solidified shell on the circumferential surface of the chill rolls, comprising: In a first step from the start of rotation of the chill roll to the completion of one rotation, the roll gap of the chill roll is controlled so that the pressing load per unit width length of the chill roll is constant at 12 N / mm or more; a method for controlling the pressure load of a chill roll, the method comprising the steps of: after the first step, fixing the pair of chill rolls so that the roll gap between them is constant and the roll axes of the pair of chill rolls are parallel; setting the pressure load per unit width of the chill roll to 12 N / mm or more; and adjusting the rotation speed of the chill roll so that the pressure load per unit width of the chill roll reaches a set value.

2. A method for producing a thin cast slab by supplying molten metal to a molten metal pool formed by a pair of rotating chill rolls and a pair of side weirs, and forming and growing a solidified shell on the circumferential surface of the chill rolls, comprising:

2. A method for producing a thin-walled cast strip, comprising controlling the pressing load per unit width length of the chill roll by the method for controlling the pressing load of the chill roll according to claim 1.

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