JP7704079B2 - Method and tool for preventing falling of cast pieces in a continuous casting machine - Google Patents

Description

The present invention relates to a method and a jig for preventing the falling of a cast piece in a continuous casting machine in which molten metal is solidified and molded in a mold and then continuously drawn out by a drawing device.

In general, a continuous casting machine is a facility in which molten metal, such as molten steel, is solidified and molded in a mold while being continuously drawn out by a drawing device. The drawing device has a guide roll and a pinch roll in that order, and is configured so that the slab is guided by the guide rolls while being supported and drawn by the pinch rolls. At the beginning of the operation of the continuous casting machine, a dummy bar is drawn out by the drawing device prior to the slab.

The pinch roll is equipped with a hydraulic cylinder for pressing and a motor for driving it to support and pull out the slab.

There are four types of continuous casting machines: vertical, curved, vertical bending, and horizontal. In the case of the vertical type, most of the weight of the slab is placed on the pinch rolls, so the pinch rolls play a very important role. However, with this vertical type, there is a high risk of the slab falling due to a breakdown in the hydraulic source or hydraulic system of the pressing hydraulic cylinder, or a decrease in the coefficient of friction due to the adhesion of oils and grease between the slab and the pinch rolls.

In addition, even with curved or vertical bending dies, there is a risk of the slab falling due to sequence malfunctions, hydraulic system failure, or a decrease in the coefficient of friction caused by the adhesion of oil and grease between the slab and the pinch rolls. In any of these cases, if the slab falls, it is inevitable that serious damage will be caused to various machinery and equipment, even if it does not result in a personal injury.

Therefore, technologies have been proposed to prevent the above-mentioned cast pieces or dummy bars from falling (Patent Documents 1 to 5).

The technology in Patent Document 1 involves compensating for the hydraulic pressure in 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 in the pinch roll reduction hydraulic circuit occurs.

The technology in Patent Document 2 involves providing, in the guide section of the guide rolls, rollers that come into contact with the slab, one or more pairs of cams that sandwich the slab, and a drive means for pressing the cams against the slab, and when there is an abnormal increase in the rotational speed of the rollers, the drive means presses the cams against the slab.

The technology in Patent Document 3 has a reaction member that reacts to a decrease in the casting pressure of one of the multiple pairs of fixed and movable rollers that sandwich the casting, and a pressure increase system that is activated by the reaction member to compensate for the force generated by the pressing device and at the same time increase the casting pressure of the other movable rollers.

The technology in Patent Document 4 involves the use of an elastic member (coil spring) that biases one of a pair of pinch rolls that sandwich the slab, and amplifies the biasing force of the elastic member when the descent speed of the slab increases abnormally so that the descent speed returns to normal.

The technology of Patent Document 5 is to provide a hydraulic cylinder for applying dummy bar holding pressure to each of the rolls on the pressing side among a plurality of fixed side and pressing side roll pairs that hold the cast piece next to the dummy bar, and to provide a bypass mechanism that diverts the main pressure side line of the hydraulic cylinder in which a drop in dummy bar holding pressure has been detected to the main pressure side line of the hydraulic cylinder in which a drop in dummy bar holding pressure has not been detected.

In addition to the above-mentioned technology for preventing the slab from falling, a technology is also known in which, when completing continuous casting, a cooling material (also called cooling metal) is immersed in the mold to forcibly cool the area near the surface (called the top) of the molten steel finally poured into the mold, thereby completely sealing the unsolidified molten steel inside the solidified shell (for example, Patent Documents 6 and 7).

In Patent Document 6, a cooling metal piece made of a steel material with a projected area covering a wide area of the surface of the molten steel and surrounded by a ring material is rolled down into the mold.

In Patent Document 7, in order to seal the head end of the top cast piece more reliably than in Patent Document 6, a head end cold material with a trapezoidal cross section having a top plate portion at the upper end of a pair of side walls and a protrusion on the side is used, a cavity is formed between the bath surface of the molten steel and the top plate, and the lower end side of the head end cold material is immersed in the molten steel.

The cooling hardware in Patent Document 6 and the cooling material for cooling the head end in Patent Document 7 both have no connection to anything other than the slab after being immersed in the molten steel and descend together with the slab, making them completely ineffective in preventing the slab from falling.

Japanese Unexamined Patent Publication No. 52-109431 Japanese Unexamined Patent Publication No. 53-011126 Japanese Unexamined Patent Publication No. 54-015423 Japanese Unexamined Patent Publication No. 61-253154 JP 2012-125820 A JP 2002-263804 A JP 2017-080773 A

All of the above-mentioned conventional technologies for preventing the slab from falling are achieved by adding a mechanism for preventing the slab from falling to the drawing device, which operates in the event of an emergency in which the slab is about to fall (such as an abnormal increase in the falling speed or an abnormal decrease in the hydraulic pressure for pinch roll compression) to maintain or reinforce the pressing force on the slab (or dummy bar) (patent document 1: an emergency hydraulic circuit; patent document 2: a cam for clamping the slab; patent document 3: a reaction member and a pressure increase system; patent document 4: an elastic member for biasing the pinch roll; and patent document 5: a hydraulic cylinder and a bypass mechanism for applying pressure to hold the dummy bar).

This poses the problem of incurring equipment costs to add the above-mentioned slab drop prevention mechanism to the drawing device, and also poses the problem of increased burden on workers as additional inspections are required to maintain the above-mentioned slab drop prevention mechanism.

The present invention aims to provide a method and tool for preventing the slab from falling in a continuous casting machine, which makes it possible to prevent the slab from falling without adding a large-scale slab fall prevention device to the drawing device.

The inventors of the present invention have conducted intensive research to solve the above problems, and as a result, have come up with the idea of storing a cold material outside the mold, and when the risk of the slab dropping increases, supporting the cold material above the mold while pouring it into the mold, so that the molten metal in the mold solidifies and adheres to the cold material, thereby completing the present invention.
[1] A method for preventing a slab from falling in a continuous casting machine in which a slab formed by solidifying molten metal in a mold is guided by a guide roll and drawn out while applying a pressing force with a pinch roll, comprising the steps of:
A method for preventing a slab from falling in a continuous casting machine, characterized in that a cold material for solidifying the molten metal in the mold is kept waiting outside the mold, and in response to an abnormal decrease in the pressing force of the pinch rolls, the cold material is poured into the mold while supported on the mold, and continues to be supported on the mold.
[2] A method for preventing a slab from falling in a continuous casting machine as described in [1], characterized in that the method responds to at least one of an abnormal decrease in the pressing force of the pinch rolls, a power outage of the driving power source, an abnormal increase in the descent speed of the slab, and an abnormal increase in the driving current of the pinch rolls.
[3] A jig for preventing a slab from falling into a mold, which is used in a method for preventing a slab from falling in a continuous casting machine, comprising:
A jig for preventing a cast piece from falling, which is a cold material consisting of an immersed part that is immersed in the molten metal in the mold and a supported part that is supported on the mold.
[4] The jig for preventing a cast piece from falling as described in [3], characterized in that the supported portion has an upper end portion of the mold as a fulcrum.
[5] The jig for preventing a cast piece from falling as described in [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 jig for preventing a cast piece from falling as described in 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 jig for preventing a cast piece from falling as described in [6], characterized in that the length of the immersion depth of the cold material is 26% or more of the length from the surface of the molten steel to the bottom end of the mold.
[8] A jig for preventing a cast piece from falling, as described in [6] or [7], characterized in that the volume of the immersion depth of the cold material is 1% or more of the volume from the surface of the molten steel to the bottom of the mold.

According to the present invention, the supported portion of the cold material is supported on the mold of the continuous casting machine, and the molten metal in the mold can be solidified by the immersed portion of the cold material to adhere to the cold material, so that it is possible to prevent the slab from falling without adding a separate device to prevent the slab from falling to the drawing device. In particular, if a power outage or other reason causes the pinch rolls to no longer press against the slab or dummy bar, or if the pinch rolls no longer press against the upper slab due to a break in the part (connecting part) that connects the upper and lower parts of the slab with a partition or other material, the cold material can be immediately poured into the mold while being supported by the upper end of the mold, and the molten metal in the mold can be solidified and adhered to the cold material, quickly preventing the slab or dummy bar from falling.

FIG. 2 is a schematic diagram showing a procedure for introducing a cooling material in an embodiment of the present invention. FIG. 2 is a three-dimensional diagram showing a schematic example of a cooling material according to the present invention. FIG. 5 is a schematic diagram showing a state in which a cold material is charged into the continuous casting machine of FIG. 4 to form an accelerated solidification portion. 1 is a schematic diagram showing an example of a continuous casting machine to which the method of the present invention is applied. FIG. 2 is a diagram for explaining preferred conditions for the dimensions and volume of the cooling material according to the present invention. FIG. 2 is a diagram showing an embodiment of the method of the present invention in response to a break at a joint of a slab.

The method for preventing the fall of a cast piece according to the present invention is applied to a continuous casting machine in which a cast piece, which is formed by solidifying molten metal in a mold, is guided by a guide roll and drawn out while applying a pressing force with a pinch roll. Below, an embodiment in which the casting object is steel (molten metal is molten steel) is described, but the present invention can also be applied to cases in which the casting object is a metal other than steel.

In continuous casting of steel, the cast piece is broadly classified into slabs (rectangular cross section, 120-600 mm thick, 700 mm wide or more), blooms (approximately square cross section, 160 mm square or more), and billets (approximately square cross section, less than 160 mm square) depending on the shape and size of their cross sections (meaning a cross section perpendicular to the length direction, which is the drawing direction; the same applies below), and the present invention can be applied to any of these. The height of the mold 3 (dimension in the casting direction) can be 500-1300 mm.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In a continuous casting machine to which the present invention is applied, as shown in FIG. 4, for example, molten steel 2 is solidified and molded in a bottomless mold 3 for continuous casting to become a slab 4. The slab 4 is guided by a guide roll 5 below the mold 3, and then drawn out while being pressed by a pinch roll 6. In a mold 3 that is generally internally water-cooled, a solidified shell 7 is formed and grows from the mold wall side of the molten steel 2 to form the outer wall of the slab 4, but the center in the thickness direction is not solidified, and solidification to the center is usually completed in the middle of the secondary cooling zone, where the slab 4 is water-cooled by a spray cooling device (not shown) installed in the installation area of the guide roll 5. The molten steel 2 is supplied into the mold 2 from a tundish (not shown) through an immersion nozzle 20 immersed in the molten steel 2 in the mold 3.

The method for preventing the falling of a cast piece according to the present invention (hereinafter also referred to as the method of the present invention) is carried out, for example, according to the procedure shown in Figure 1. That is, the cold material 1 for solidifying the molten steel 2 in the mold 3 is kept waiting outside the mold 3, for example on a work floor that is usually provided around the upper opening of the mold 3 (Figures 1(a) and (b)). Then, in response to an abnormal decrease in the pressing force of the pinch roll 6 (see Figure 3), the cold material 1 is poured into the mold 3 while being supported on the mold 3 (Figures 1(c) and (d)), and is continued to be supported on the mold 3 (Figures 1(e) and (f)).

Here, before the cold material 1 is added, the submerged nozzle 20 is closed to cut off the supply of molten steel 2 into the mold 3.

As a result, as shown in the schematic diagram of Figure 3, the solidification of the molten steel in the mold 3 is accelerated by the cold material 1, becoming the accelerated solidification section 10, which adheres to the cold material 1 and is supported at the upper end of the mold 3 via the cold material 1. In other words, the accelerated solidification section 10 is held in a suspended state by the cold material 1, preventing the cast piece 4 connected to the accelerated solidification section 10 from falling. The dummy bar (not shown), which is withdrawn at the beginning of continuous casting, can also be prevented from falling in a similar manner.

In addition, in the method of the present invention, an abnormal decrease in the pressing force of the pinch rolls 6 is regarded as an abnormal situation indicating an increased risk of the slab falling, and cold material 1 is introduced in response to this abnormal situation. However, even if the abnormal situation includes at least one of the following, in addition to an abnormal decrease in the pressing force of the pinch rolls 6, a power outage in the driving power source of the pinch rolls 6, an abnormal increase in the descent speed of the slab, and an abnormal increase in the driving current of the pinch rolls 6, the falling of the slab (or dummy bar) can be similarly prevented. Note that the method of the present invention is not limited to the above and can be applied whenever there is a risk of the slab falling.

The abnormal increase in the driving current of the pinch roll 6 is caused by the impact when a break occurs at the joint, which is the part that connects the upper and lower parts of the slab with a partition or the like. The pressing force of the pinch roll 6 is no longer able to reach the slab above the joint where the break occurred, increasing the risk of it falling.

The cold material 1 used in the method of the present invention is a jig for preventing the casting from falling according to the present invention (hereinafter, also referred to as the jig of the present invention), and as shown in Figures 1 and 2, is preferably composed of an immersed part 12 that is immersed in the molten steel 2 and a supported part 11 that is supported on the mold 3. As a method of supporting on the mold 3, for example, a supporting method using the upper end of the mold 3, more specifically, the two opposing edges of the upper end opening 30 of the mold 3, as a fulcrum is exemplified. The supported part 11 suitable for this supporting method is a rod-shaped body, the length of which is greater than the distance between the two opposing edges of the upper end opening of the mold 3, and both ends of the rod-shaped body of the supported part 11 can be supported with the two edges as fulcrums.

The immersed portion 12 preferably has a vertical member 13 connected to the supported portion 11 and a horizontal member 14 connected to the vertical member 13. Here, the vertical member 13 refers to a member whose longitudinal direction is the vertical direction (vertical direction) when the supported portion 11 is supported with the upper end of the mold 3 as a fulcrum (see FIG. 1(f)), and the horizontal member 14 refers to a member whose longitudinal direction is the horizontal direction (horizontal direction). Note that, although an example in which one horizontal member 14 is provided for each vertical member 13 is shown in FIG. 1 and FIG. 2, two or more horizontal members 14 may be provided for each vertical member 13.

By connecting the horizontal member 14 to the vertical member 13, the force with which the cold material 1 holds the accelerated solidification portion 10 in a suspended state can be strengthened.

In addition, in the present invention jig, which is a cold material, as shown in FIG. 2, two or more vertical members 13 of the cold material 1 are provided, and it is preferable that they are provided parallel to each other and have a shape that does not contact the outer diameter of the submerged nozzle 20 when immersed in the molten steel 2. Furthermore, the horizontal member 14 may have any shape as long as it can hold the accelerated solidification portion 10 in a suspended state without contacting the submerged nozzle 20, but it is preferable that it is provided so as not to face the submerged nozzle 20. This allows the immersed portion 12 of the cold material 1 to be introduced into the molten steel 2 without interference from the submerged nozzle 20, even when the submerged nozzle 20 is immersed in the molten steel 2, as shown in FIG. 1.

In this case, when the cold material 1 is poured, as shown in FIG. 1, the tip side of the immersed part 12 of the cold material 1 is directed toward the upper end opening 30 of the mold 3 in the waiting position (FIGS. 1(a) and (b)), and the worker pushes the supported part 11 toward the tip side with an appropriate pusher (not shown) (FIG. 1(c)). From the contact position between the cold material 1 and the edge of the upper end opening 30 of the mold 3, the tip side becomes heavier than the rear end side (supported part 11 side), and the cold material 1 tilts around the contact position, and the immersed part 12 is dropped into the molten steel 2 (FIG. 1(d)). Furthermore, by pushing the supported part 11 to the vicinity of the submerged nozzle 20, the supported part 11 is supported with the edge of the upper end opening 30 of the mold 3 as a fulcrum, while the immersed part 12 connected to it can be held in the molten steel 2 (FIGS. 1(e) and (f)).

The dimensions of the rod-shaped material that serves as the supported part 11 of the cold material 1, with both ends of the width direction (horizontal mold) of the upper end opening of the mold 3 as supports, are as follows: length = 1.4 to 2.0 times the distance between supports, and the diameter, which varies depending on the material, must ensure a cross-sectional area that can support the vertical load of the cast slab inside the machine. In the example of Figure 2, the cross-sectional shape of the supported part 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 the polygon.

In addition, the dimensions of the immersed portion 12 of the cooling material 1 in the shape of FIG. 2, when the dimensions of the molten steel pouring portion of the mold are, for example, length = 400 mm, width = 310 mm, and height = 810 mm, from the viewpoint of ease of pouring work, can be length (along the mold height direction when immersed) = 265 mm, width (along the mold lateral direction when immersed) = 90 mm, and thickness (along the mold lateral direction when immersed) = 25 mm for the vertical member 13, and length (along the mold height direction when immersed) = 45 mm, width (along the mold lateral direction when immersed) = 90 mm, and thickness (along the mold lateral direction when immersed) = 25 mm for the horizontal member 14. If the dimensions of the molten steel pouring portion of the mold are enlarged or reduced from the above case, the dimensions (length, width, thickness) of the vertical member and horizontal member can be enlarged or reduced by the same enlargement or reduction ratio.

The present invention is intended to be applied to the steel industry, where molten metal is turned into molten steel. In this case, the cold material 1 is made of a material that has the strength to hold the steel slab in a suspended state and has a melting point equal to or higher than that of steel, and is preferably made of steel, which is advantageous in terms of manufacturing costs.

When pouring steel cold material 1 into molten steel 2, it is preferable that the length L1 of the immersion depth portion 16 (see FIG. 5) of the cold material 1 is 26% or more of the length L2 of the portion from the surface of the molten steel 2 to the bottom end of the mold 3 (also called the molten steel portion 18 in the mold). If L1 is less than 26% of L2, the amount of accelerated solidification portion 10 produced will be insufficient, and it may be difficult to prevent the slab from falling. From the viewpoint of equipment constraints for the cold material 1, L1 is a length equal to or less than the mold width in the pouring direction. If L1 is greater than the mold width, it will interfere with the mold when tilted from the indicator portion during pouring, preventing the immersed portion 12 from dropping into the molten steel 2.

Similarly to the above, when the steel cold material 1 is poured into the molten steel 2, the volume V1 of the immersion depth 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. If V1 is less than 1% of V2, the amount of accelerated solidification portion 10 produced will be insufficient, and it may be difficult to prevent the slab from falling.

[Example 1]
Among the embodiments shown in Fig. 1, a curved type continuous casting machine was used in Example 1. The molten steel temperature when poured into the mold was 1520°C. The dimensions of the molten steel pouring portion of the mold 3 were 400 mm length x 310 mm width x 810 mm height. The withdrawal speed was 0.7 m/min. The cold material 1, which is the jig of the present invention, was made of mild steel and manufactured into the shape shown in Fig. 2 (a shape having a supported portion 11 and a immersed portion 12).

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, with the vertical member 13 having a length (along the mold height direction when immersed) of 265 mm, a width (along the mold width direction when immersed) of 45 mm, and a thickness (along the mold width direction when immersed) of 25 mm, and the horizontal member 14 having a length (along the mold height direction when immersed) of 45 mm, a width (along the mold width direction when immersed) of 90 mm, and a thickness (along the mold width direction when immersed) of 25 mm.

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

The length L1 of the immersion depth portion 16 of the cold material 1 was set to 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 set to 1% of the volume V2 of the molten steel portion 18 in the mold.

Before the start of the continuous casting operation, the cold material 1 was left waiting on the work 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 operation, the submerged nozzle 20 was closed (the stopper at the upper end was closed), and the cold material 1 was poured into the mold 3 while being supported on the mold 3 (Figs. 1(c) and (d)), and was then supported continuously on the mold 3 (Figs. 1(e) and (f)). When pouring the cold material 1, the worker pushed the supported part 11 with a specially prepared pusher (not shown) to drop the immersed part 12 into the mold 3.

As a result, an accelerated solidification portion 10 was formed about 10 minutes after the cold material 1 was added, and was supported at the upper end of the mold via the immersed portion 12 and the supported portion 11, thereby preventing the slab 4 from falling (see Figure 3).
[Example 2]
In Example 1, the cold material 1 was added in response to an abnormal increase in the driving current of the pinch rolls 6, which reflected the breakage of the slab at the joint during the continuous casting operation. Other than this, the present embodiment was the same as Example 1.

As a result, the accelerated solidification portion 10 was formed about 10 minutes after the cold material 1 was added, and was supported at the upper end of the mold via the immersed portion 12 and the supported portion 11, which prevented the upper portion of the slab 4 above the broken joint from falling (see Figure 6).

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

Claims (5)

A method for preventing a slab from falling in a continuous casting machine in which a slab formed by solidifying molten metal in a mold is guided by a guide roll and drawn while applying a pressing force with a pinch roll, comprising the steps of:
A method for preventing a cast piece from falling in a continuous casting machine, characterized in that a steel chill material for solidifying the molten metal in the mold is kept waiting outside the mold, and in response to an abnormal decrease in the pressing force of the pinch rolls, the steel chill material is poured into the mold while being supported on the mold, and continues to be supported on the mold. The method for preventing slab drop in a continuous casting machine according to claim 1, characterized in that it responds to at least one of the following: an abnormal decrease in the pressing force of the pinch rolls, a power outage of the driving power source, an abnormal increase in the descent speed of the slab, and an abnormal increase in the driving current of the pinch rolls. A jig for preventing a slab from falling into a mold, which is used in a method for preventing a slab from falling in a continuous casting machine, comprising:
A jig for preventing a cast piece from falling, which is a steel cooling material consisting of an immersed part that is immersed in the molten metal in the mold and a supported part that is supported on the mold. The jig for preventing the casting from falling, as described in claim 3, characterized in that the supported part has the upper end of the mold as a fulcrum. The jig for preventing the casting from falling, as described in 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.

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