Method and jig for preventing a slab from falling in a continuous casting machine

Abstract

To provide a method for preventing fall of a cast slab in a continuous casting machine which can prevent fall of a cast slab without adding a large scale cast slab fall prevention device to a pull-out device separately, and to provide a jig.SOLUTION: In a method for preventing fall of a cast slab in a continuous casting machine, a cold charge 1 for solidifying a molten metal 2 in a cast 3 is placed on stand-by at the outside of the cast. The cold charge is supported on the cast, placed into the cast in a supported state in response to abnormal reduction of a pressing force of a pinch roll 6, and continuously supported on the cast.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for preventing a slab from falling and a jig in a continuous casting machine that solidifies a molten metal in a mold and continuously draws it out with a drawing device.

Background Art

[0002] Generally, a continuous casting machine is a facility that continuously draws out a molten metal, such as molten steel, while solidifying it in a mold with a drawing device. The drawing device has a guide roll and a pinch roll in this order, and is configured to guide the slab with the guide roll and support and draw it with the pinch roll. At the initial stage of the operation of the continuous casting machine, a dummy bar is drawn out by the drawing device prior to the slab.

[0003] This pinch roll includes a pressing hydraulic cylinder and a driving motor for supporting and drawing out the slab.

[0004] In addition, there are four types of continuous casting machines: vertical type, curved type, vertical bending type, and horizontal type. Among these, particularly in the case of the vertical type, since most of the weight of the slab is applied to the pinch roll, the role of the pinch roll is very important. However, in this vertical type, there is a high risk that the slab will fall due to a failure of the hydraulic source or hydraulic system of the pressing hydraulic cylinder, or a decrease in the friction coefficient due to the adhesion of oils and fats between the slab and the pinch roll.

[0005] Also, in the curved type or vertical bending type, there is a risk that the slab will fall due to a malfunction in the sequence, a failure of the hydraulic system, or a decrease in the friction coefficient due to the adhesion of oils and fats between the slab and the pinch roll. In any of these cases, if the slab falls, although it may not lead to human disasters, it is inevitable that various mechanical equipment will suffer serious damage.

[0006] Therefore, conventionally, techniques for preventing the above-described slab or dummy bar from falling have been proposed (Patent Documents 1 to 5).

[0007] The technology of Patent Document 1 is to compensate for the hydraulic pressure of the pinch roll reduction hydraulic circuit with an emergency hydraulic circuit when an abnormal increase in the detected value of the slab descent speed or an abnormal decrease in the detected value of the pressure of the hydraulic circuit for pinch roll reduction occurs.

[0008] The technology of Patent Document 2 is to provide a roller that contacts the slab, a pair or a plurality of pairs of cams that sandwich the slab, and a driving means that presses the cams against the slab in the guiding section of the guide roller, and to press the cams against the slab with the driving means when an abnormal increase in the rotational speed of the roller occurs.

[0009] The technology of Patent Document 3 has a reaction member that reacts to a decrease in the slab pressing force of a certain movable roller among a plurality of pairs of fixed rollers and movable rollers that sandwich the slab, and a pressure increasing system that is activated by the reaction member to compensate for the generating force of the pressing device and at the same time increases the slab pressing force of other movable rollers.

[0010] The technology of Patent Document 4 includes an elastic member (coil spring) that biases one of the pinch roll pairs that sandwich the slab, and amplifies the biasing force of the elastic member so that the descent speed returns to normal when an abnormal increase in the descent speed of the slab occurs.

[0011] The technology of Patent Document 5 includes a plurality of fixed-side and pressure-bonding-side roll pairs that hold the slab following the dummy bar, and hydraulic cylinders for applying dummy bar holding pressure to the pressure-bonding-side rolls respectively, and has a bypass mechanism that bypasses the original pressure side pipeline of the hydraulic cylinder in which a decrease in the dummy bar holding pressure is detected to the original pressure side pipeline of the hydraulic cylinder in which a decrease in the dummy bar holding pressure has not been detected.

[0012] Also, separate from the above-described slab fall prevention technology, when ending continuous casting, a technology is known in which a cooling material (also referred to as cooling hardware) is immersed in the mold to forcibly cool the vicinity of the surface (referred to as the top) of the molten steel finally poured into the mold and completely confine the unfrozen molten steel inside the solidified shell (for example, Patent Documents 6 and 7).

[0013] In Patent Document 6, a cooling metalware formed by surrounding a steel material having a projected area that widely covers the surface of molten steel with a ring material is rolled and dropped into a mold.

[0014] In Patent Document 7, in order to more reliably seal the head end of a top slab than in the case of Patent Document 6, a cold material for the head end having a trapezoidal cross-section with a top plate portion at the upper ends of a pair of side wall portions and a protruding portion on the side surface is used, a cavity is formed between the molten steel bath surface and the above top plate, and the lower end side of the above cold material for the head end is immersed in the molten steel.

[0015] Both the cooling metalware of Patent Document 6 and the cold material for cooling the head end of Patent Document 7 described above have no connection with anything other than the slab after being immersed in the molten steel and descend together with the slab, so they are completely ineffective in preventing the slab from falling.

Prior Art Documents

Patent Documents

[0016]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0017] All of the above-mentioned conventional techniques for preventing the casting slab from falling are additions of a casting slab fall prevention mechanism (in Patent Document 1, an emergency hydraulic circuit; in Patent Document 2, a cam for pinching the casting slab; in Patent Document 3, a reaction member and a pressure increasing system; in Patent Document 4, an elastic member for biasing the pinch roll; in Patent Document 5, a hydraulic cylinder for applying a dummy bar holding pressure and a bypass mechanism) that operates when an emergency situation (such as an abnormal increase in the descending speed or an abnormal decrease in the hydraulic pressure for pinch roll reduction) where the casting slab is about to fall occurs, to maintain or reinforce the pressing force on the casting slab (or dummy bar) to the withdrawal device.

[0018] Therefore, there is a problem that equipment costs are incurred for adding the above-mentioned casting slab fall prevention mechanism to the withdrawal device, and there is also a problem that additional inspections are required for maintaining the above-mentioned casting slab fall prevention mechanism, increasing the burden on the workers.

[0019] Accordingly, an object of the present invention is to provide a method and a jig for preventing the fall of a casting slab of a continuous casting machine that can prevent the fall of the casting slab without adding a separate large-scale casting slab fall prevention device to the withdrawal device.

Means for Solving the Problems

[0020] The inventor of the present invention has intensively studied to solve the above-mentioned problems, and as a result, conceived the idea of waiting for a cold material outside the mold, and when the risk of the casting slab falling increases, putting the cold material into the mold while supporting it on the mold to solidify the molten metal in the mold and fix it to the cold material, and thus arrived at the present invention. That is, the present invention is as follows. [1] A method for preventing the fall of a casting slab in a continuous casting machine that guides a casting slab formed by solidifying a molten metal in a mold with guide rolls and applies a pressing force with pinch rolls while withdrawing it, characterized in that a cold material for solidifying the molten metal in the mold is made to wait outside the mold, and in response to an abnormal decrease in the pressing force of the pinch roll, the cold material is put into the mold while being supported on the mold and continuously supported on the mold as it is. [2] The method for preventing the slab from dropping in the continuous casting machine according to [1], characterized by corresponding to at least any one of the abnormal decrease in the pressing force of the pinch roll, the power failure of the drive power supply, the abnormal increase in the slab lowering speed, and the abnormal increase in the drive current of the pinch roll. [3] A slab drop prevention jig used in the method for preventing the slab from dropping in a continuous casting machine, which is a jig for preventing the slab charged into the mold from dropping, A cold material comprising an immersed portion immersed in the molten metal in the mold and a supported portion supported on the mold, and being a slab drop prevention jig. [4] The slab drop prevention jig according to [3], characterized in that the supported portion uses the upper end portion of the mold as a fulcrum. [5] The slab drop prevention jig according to [3] or [4], characterized in that the immersed portion has a vertical member connected to the supported portion and a horizontal member connected to the vertical member. [6] The slab drop prevention jig according to any one of [3] to [5], characterized in that the molten metal is molten steel and the cold material is made of steel. [7] The slab drop prevention jig according to [6], characterized in that the length of the immersion depth portion of the cold material is 26% or more of the length from the molten steel surface to the lower end of the mold. [8] The slab drop prevention jig according to [6] or [7], characterized in that the volume of the immersion depth portion of the cold material is 1% or more of the volume from the molten steel surface to the lower end of the mold.

Effect of the Invention

[0021] According to the present invention, since the supported portion of the cooling material is supported on the mold of the continuous casting machine and the molten metal in the mold can be solidified at the immersed portion of the cooling material and fixed to the cooling material, it is possible to prevent the casting slab from falling without adding a separate casting slab fall prevention device to the drawing device. In particular, due to a power outage or the like, the pressing force of the pinch roll is no longer applied to the casting slab or the dummy bar, or when the pressing force of the pinch roll is no longer applied to the upper casting slab due to the breakage of the portion (joint portion) connecting the upper and lower portions of the casting slab with a partition material or the like, the cooling material can be immediately put into the mold while supporting it at the upper end of the mold, and the molten metal in the mold can be solidified and fixed to the cooling material, so that the fall of the casting slab or the dummy bar can be quickly prevented.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0023] The method for preventing the casting slab from falling according to the present invention is applied to a continuous casting machine that guides a casting slab formed by solidifying and molding molten metal in a mold with guide rolls and applies a pressing force with pinch rolls while pulling it out. Hereinafter, embodiments in the case where the casting target is steel (molten metal is molten steel) will be described, but the present invention is also applicable when the metal is other than steel.

[0024] In continuous casting of steel, depending on the shape and size of the cross-section (the cross-section perpendicular to the length direction which is the drawing direction; the same applies hereinafter), the cast slab is classified into a slab (the cross-section is rectangular, the thickness is 120 - 600 mm, and the width is 700 mm or more), a bloom (the cross-section is approximately square, 160 mm square or more), and a billet (the cross-section is approximately square and less than 160 mm square). However, the present invention is applicable to any of these. Note that as the height (dimension in the casting direction) of the mold 3, 500 - 1300 mm can be mentioned.

[0025] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In a continuous casting machine to which the present invention is applied, for example, as shown in FIG. 4, the molten steel 2 is solidified and formed in a bottomless mold 3 for continuous casting to become a cast slab 4. The cast slab 4 is guided by guide rolls 5 below the mold 3 and then drawn while a pressing force is applied by pinch rolls 6. Generally, in the internally water-cooled mold 3, a solidified shell 7 is formed and grows from the side of the mold wall of the molten steel 2 to form the outer wall of the cast slab 4, but the central part in the thickness direction is not solidified, and the solidification is usually completed up to the central part in the middle of the secondary cooling zone where the cast slab 4 is water-cooled by spray cooling equipment (not shown) provided in the installation area of the guide rolls 5. Note that the molten steel 2 is supplied into the mold 2 through a submerged nozzle 20 immersed from a tundish (not shown) into the molten steel 2 in the mold 3.

[0026] In the method for preventing the fall of the cast slab according to the present invention (hereinafter also referred to as the method of the present invention), for example, it is executed according to the procedure shown in FIG. 1. That is, a cooling material 1 for solidifying the molten steel 2 in the mold 3 is placed outside the mold 3, for example, on the working floor usually provided around the upper end opening of the mold 3, and left on standby (FIGS. 1(a) and (b)). Then, in response to an abnormal decrease in the pressing force of the pinch rolls 6 (see FIG. 3), the cooling material 1 is supported on the mold 3 and then put into the mold 3 (FIGS. 1(c) and (d)), and continuously supported on the mold 3 as it is (FIGS. 1(e) and (f)).

[0027] Here, before the cooling material 1 is put in, the submerged nozzle 20 is closed to cut off the supply of the molten steel 2 into the mold 3.

[0028] As a result, as shown in the schematic diagram of FIG. 3, the molten steel in the mold 3 is promoted to solidify by the cooling material 1, becoming the accelerated solidification part 10, adhering to the cooling material 1, and being supported at the upper end of the mold 3 via the cooling material 1. That is, the accelerated solidification part 10 is held in a suspended state by the cooling material 1, and the drop of the slab 4 connected to the accelerated solidification part 10 can be prevented. In addition, the drop of a dummy bar (not shown) withdrawn at the initial stage of continuous casting can be similarly prevented.

[0029] Further, in the method of the present invention, the abnormal decrease in the pressing force of the pinch roll 6 is regarded as an abnormal situation indicating an increased risk of slab drop, and the cooling material 1 is charged according to this abnormal situation. However, as the abnormal situation, in addition to the abnormal decrease in the pressing force of the pinch roll 6, even when at least one of a power failure of the drive power source of the pinch roll 6, an abnormal increase in the slab lowering speed, and an abnormal increase in the drive current of the pinch roll 6 occurs, it is similarly possible to prevent the drop of the slab (or dummy bar). The method of the present invention is not limited to the above, and can be applied as long as there is a risk of steel slab drop.

[0030] The abnormal increase in the drive current of the pinch roll 6 is caused by the impact when a break occurs at the connecting part, which is a part connecting the upper and lower parts of the slab with a partitioning material or the like. The pressing force of the pinch roll 6 does not reach the slab above the connecting part where this break occurs, and the risk of dropping increases.

[0031] The cooling material 1 used in the method of the present invention is a slab drop prevention jig according to the present invention (hereinafter, also referred to as the present jig). As shown in FIGS. 1 and 2, it preferably comprises an immersed part 12 immersed in the molten steel 2 and a supported part 11 supported on the mold 3. As a support method on the mold 3, for example, a support method using the upper end of the mold 3, specifically, the two opposing edge parts of the upper end opening 30 of the mold 3 as fulcrums can be mentioned. A suitable supported part 11 for this support method is a rod-shaped body, and its length should be made larger than the distance between the two opposing edge parts of the upper end opening of the mold 3, and both ends of the rod-shaped body of the supported part 11 should be made supportable with the two edge parts as fulcrums.

[0032] Further, the immersed part 12 preferably has a vertical member 13 connected to the supported part 11 and a horizontal member 14 connected to the vertical member 13. Here, the vertical member 13 is a member whose longitudinal direction is the vertical direction (the direction of gravity) when the supported part 11 is supported with the upper end of the mold 3 as a fulcrum (see Fig. 1(f)), and the horizontal member 14 is a member whose longitudinal direction is the horizontal direction. In Figs. 1 and 2, an example is shown in which one horizontal member 14 is provided for each vertical member 13, but two or more horizontal members 14 may be provided for each vertical member 13.

[0033] By connecting the horizontal member 14 to the vertical member 13, the force for the cooling material 1 to hold the rapid solidification part 10 in a suspended state can be strengthened.

[0034] Also, in the present cooling tool which is a cooling material, as shown in Fig. 2, it is preferable that two or more vertical members 13 of the cooling material 1 are provided and are shaped so as not to contact the outer diameter of the immersion nozzle 20 when immersed in the molten steel 2, and are provided in parallel. Further, the horizontal member 14 may have any shape as long as it can hold the rapid solidification part 10 in a suspended state without contacting the immersion nozzle 20, but it is preferably provided so as not to face the immersion nozzle 20. Thereby, as shown in Fig. 1, even when the immersion nozzle 20 is immersed in the molten steel 2, the immersed part 12 of the cooling material 1 can be put into the molten steel 2 without interference with the immersion nozzle 20.

[0035] In this case, when the cooling material 1 is charged, as shown in Fig. 1, the tip side of the immersed part 12 of the cooling material 1 is directed toward the upper end opening 30 of the mold 3 at the standby position (Figs. 1(a) and (b)), and an operator appropriately pushes the supported part 11 toward the tip side with a pusher (not shown) (Fig. 1(c)). As a result, the tip side becomes heavier than the rear end side (the supported part 11 side) from the contact position between the cooling material 1 and the edge of the upper end opening 30 of the mold 3, the cooling material 1 tilts around the contact position, and the immersed part 12 is dropped into the molten steel 2 (Fig. 1(d)). Further, by pushing the supported part 11 to the vicinity of the immersion nozzle 20, while supporting the supported part 11 with the edge of the upper end opening 30 of the mold 3 as a fulcrum, the immersed part 12 connected thereto can be held in the molten steel 2 (Figs. 1(e) and (f)).

[0036] As the dimensions of the bar-shaped material that serves as the supported portion 11 of the chill 1 with both ends in the width direction (lateral mold) of the upper end opening of the mold 3 as fulcrums, from the perspective of achieving a stable support state, the length is 1.4 to 2.0 times the distance between the fulcrums, and the diameter varies depending on the material, but the condition is to ensure a cross-sectional area that can support the load in the vertical direction of the in-machine slab. In the example of Fig. 2, the cross-sectional shape of the supported portion 11 is circular, but it may also be polygonal. In the case of a polygonal cross-section, the diameter is the diameter of a circle having the same area as that polygon.

[0037] Also, as the dimensions of the immersed portion 12 of the chill 1 having the shape shown in Fig. 2, when the dimensions of the molten steel injection portion of the mold are, for example, length = 400 mm, width = 310 mm, and height = 810 mm, from the perspective of ease of loading operation, the length of the vertical member 13 (along the height direction of the mold during immersion) = 265 mm, width (along the lateral direction of the mold during immersion) = 90 mm, thickness (along the lateral direction of the mold during immersion) = 25 mm can be cited, and the length of the horizontal member 14 (along the height direction of the mold during immersion) = 45 mm, width (along the lateral direction of the mold during immersion) = 90 mm, thickness (along the lateral direction of the mold during immersion) = 25 mm can be cited. When the dimensions of the molten steel injection portion of the mold are scaled up or down from the above case, the dimensions (length, width, thickness) of the vertical member and the horizontal member can be scaled up or down at the same scaling rate.

[0038] The present invention assumes application to the steel industry where the molten metal is molten steel. In that case, the chill 1 is preferably made of a material having a strength capable of holding the steel slab in a suspended state and a melting point equal to or higher than that of steel, and among these, it is preferably made of steel which is advantageous in terms of production cost.

[0039] When a steel-made chill 1 is introduced into the molten steel 2, the length L1 of the immersion depth portion 16 (see Fig. 5) of the chill 1 is preferably 26% or more of the length L2 of the portion from the molten steel surface of the molten steel 2 to the lower end of the mold 3 (also referred to as the molten steel portion 18 in the mold). If L1 is less than 26% of L2, the amount of the promoted solidification portion 10 generated may be insufficient, and it may be difficult to prevent the slab from falling. From the perspective of equipment constraints of the chill 1, L1 is a length not exceeding the width of the mold in the input direction. If L1 is larger than the mold width, when tilting with the indicating portion as the starting point during input, it interferes with the mold, and the immersed portion 12 is prevented from being dropped into the molten steel 2.

[0040] Also, similar to the above, when charging the steel cold material 1 into the molten steel 2, the volume V1 of the immersion depth portion 16 (see FIG. 5) of the cold material 1 is preferably 1% or more of the volume V2 of the molten steel portion 18 in the mold. . When V1 is less than 1% of V2, the amount of the promoted solidification portion 10 generated is insufficient, and it may be difficult to prevent the casting slab from falling. .

Example

[0041] [Example 1] Among the implementations of the method of the present invention in the embodiment shown in FIG. 1, in Example 1, a curved continuous casting machine was used. The temperature of the molten steel when injecting into the mold was 1520 °C. The dimensions of the molten steel injection portion of the mold 3 were 400 mm in length × 310 mm in width × 810 mm in height. The drawing speed was 0.7 m / min. The cold material 1 which is the tool of the present invention was made of mild steel and manufactured in the shape shown in FIG. 2 (a shape having a supported portion 11 and an immersed portion 12).

[0042] The supported portion 11 was a round bar with a diameter of 600 mm and a length of 40 mm. The immersed portion 12 was plate-shaped, the length of the vertical member 13 (along the height direction of the mold during immersion) = 265 mm, the width (along the transverse direction of the mold during immersion) = 45 mm, the thickness (along the transverse direction of the mold during immersion) = 25 mm, and the length of the horizontal member 14 (along the height direction of the mold during immersion) = 45 mm, the width (along the transverse direction of the mold during immersion) = 90 mm, the thickness (along the transverse direction of the mold during immersion) = 25 mm.

[0043] The distance between the two vertical members 13 of the immersed portion 12 was 1.13 times the outer diameter (106 mm) of the immersion nozzle 20.

[0044] The length L1 of the immersion depth portion 16 of the cold material 1 was 26% of the length L2 of the molten steel portion 18 in the mold, and the volume V1 of the immersion depth portion 16 of the cold material 1 was 1% of the volume V2 of the molten steel portion 18 in the mold.

[0045] Before the continuous casting operation, the cold material 1 was placed on standby on the working floor around the mold 3 (Figs. 1(a) and (b)). Then, in response to an abnormal decrease in the pressing force of the pinch roll 6 during the operation, the immersion nozzle 20 was closed (closing the stopper at the upper end), and the cold material 1 was supported on the mold 3 and then introduced into the mold 3 (Figs. 1(c) and (d)), and then continuously supported on the mold 3 as it was (Figs. 1(e) and (f)). When introducing the cold material 1, an operator pushed the supported part 11 with a dedicated pusher (not shown) to drop the immersed part 12 into the mold 3.

[0046] As a result, the accelerated solidification part 10 was formed about 10 minutes after the introduction of the cold material 1, and it was supported at the upper end of the mold through the immersed part 12 and the supported part 11, thereby preventing the casting slab 4 from falling (see Fig. 3). [Example 2] In Example 1, the introduction of the cold material 1 was carried out during the continuous casting operation in response to an abnormal increase in the drive current of the pinch roll 6 reflecting that the casting slab broke at the joint part. Otherwise, it was the same as in Example 1.

[0047] As a result, the accelerated solidification part 10 was formed about 10 minutes after the introduction of the cold material 1, and it was supported at the upper end of the mold through the immersed part 12 and the supported part 11, thereby preventing the upper part of the broken joint part of the casting slab 4 from falling (see Fig. 6).

Explanation of reference numerals

[0048] 1 Cold material 2 Molten steel (molten metal) 3 Mold 4 Casting slab 5 Guide roll 6 Pinch roll 7 Solidified shell 10 Accelerated solidification part by cold material 11 Supported part (cold material) 12 Immersed part (cold material) 13 Vertical member (cold material) 14 Horizontal member (cold material) 16 Immersion depth part 20 Immersion nozzle Upper opening of the mold 30

Claims

1. A method for preventing the drop of a slab in a continuous casting machine, in which a slab formed by solidifying molten metal in a mold is guided by guide rolls and pulled out while applying a pressing force with pinch rolls, comprising: A steel cooling material for solidifying the molten metal in the mold is standby outside the mold, and in response to an abnormal decrease in the pressing force of the pinch rolls, the steel cooling material is put into the mold while being supported on the mold and continuously supported on the mold as it is. A method for preventing the drop of a slab in a continuous casting machine.

2. The method for preventing the drop of a slab in a continuous casting machine according to claim 1, characterized in that it corresponds to at least any one of an abnormal decrease in the pressing force of the pinch rolls, a power failure of the drive power source, an abnormal increase in the slab lowering speed, and an abnormal increase in the drive current of the pinch rolls.

3. A slab drop prevention jig used in the method for preventing the drop of a slab in a continuous casting machine, which is put into the mold, comprising: A slab drop prevention jig, which is a steel cooling material composed of an immersed part immersed in the molten metal in the mold and a supported part supported on the mold.

4. The slab drop prevention jig according to claim 3, characterized in that the supported part is pivoted on the upper end part of the mold.

5. The slab drop prevention jig according to claim 3 or 4, characterized in that the immersed part has a vertical member connected to the supported part and a horizontal member connected to the vertical member.

Images