JPH0555216B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a mold that cools and solidifies supplied molten metal in order to continuously cast metal such as steel. This invention relates to a continuous casting mold that can control the degree of cooling by limiting the amount of heat transferred.

(Prior art) The mold used for continuous casting is formed into a cylindrical body, and its outer peripheral wall is cooled (generally water-cooled) to solidify the molten metal supplied to the hollow shaft and form a slab. It is a device that does this. In the mold, the mold has a hollow shaft part according to the shape and dimensions of the desired slab cross section, and a cooling water jacket is installed on the outside of the mold so that cooling water flows along the outer peripheral wall of the mold. has been done. Therefore, the heat of the molten metal is absorbed by the cooling water flowing through the mold, and the molten metal is cooled and solidified to become a slab. Continuous casting is
Molten metal stored in a hot water tank is supplied to these molds, where it is cooled to form a slab solidified at least on the outer periphery, and then continuously drawn using a drawing device installed downstream of the mold. This is done by pulling it out. In addition,
The casting direction (the axial direction of the mold) in continuous casting is not limited to vertical (downward), but may be horizontal or inclined, and the hollow shaft of the mold is not necessarily straight, but may also be curved.

Classifying according to the form of the cylindrical body (mold), there are the following two types of molds.

(a) Mold that integrally forms a cylindrical body: In a mold for obtaining a small cross-section slab, the mold is an integral cylinder or square cylinder, and in a mold for a large cross-section rectangular slab (slab or bloom), A cylindrical body is often assembled by closely adhering a plurality of mold elements divided in the circumferential direction. The former is called a tubular mold, and the latter is an assembled mold, but in both cases, the mold is integrally formed, and the hollow shaft part (in the direction perpendicular to the shaft) has a continuous inner circumferential wall, giving it a so-called closed cross section. There is.

As the slab solidifies and cools, it contracts and its cross-sectional size becomes smaller. Therefore, in order to maintain contact between the mold and the slab, the hollow part of the mold is pre-filled so that the downstream side has a smaller dimension. It has a taper.

(b) A mold in which a cylindrical body is formed by a plurality of mold elements that are separated and independent from each other: In order to obtain a slab with a relatively large cross section, following the mold of (a) above, a mold that is separated and independent from each other is used. A mold may be provided in which a plurality of mold elements arranged in a cylindrical shape are independently movable in a direction perpendicular to the peripheral wall surface of the mold. In this mold, the inner circumferential walls of each mold element are not brought into close contact with each other as in (a) above, but are arranged with a gap between them, and each is pressed against the surface of the slab by the biasing force of a spring or cylinder.
For example, when the slab has a rectangular cross section, mold elements are often placed only on the long sides, resulting in an incomplete cylindrical body. This applies not only to rectangular slabs but also to circular cross-section slabs, but since there are gaps between mold elements, the part after a solidified layer has been formed on the surface of the molten metal, that is, the downstream side of the mold in (a) above. established in

As mentioned above, the slab contracts as it solidifies and cools, but according to the mold of (b), each divided mold element is reliably pressed against the surface of the slab, so there is no gap between them. Therefore, the slab can be cooled reliably and uniformly. That is, this type of mold is provided instead of providing the above-mentioned taper in the hollow part of the mold, and is called a self-tapered mold, an adjustable mold, a cooling plate, or the like.

By the way, in conventional molds, regardless of whether the shape of the cylindrical body (mold) is (a) or (b), the mold is made only of copper or copper alloy, which has high thermal conductivity, or It was formed by attaching a liner made of graphite or the like, which also has high thermal conductivity, in close contact with the inner circumferential wall. This is because unless a material with high thermal conductivity is placed in a state where heat transfers easily, the heat of the molten metal will be difficult to transfer to the cooling water, and the mold (especially the inner peripheral wall) will become hot and melt. Because there is. The mold in (a) above is described in "12. Continuous casting method" of the "Steel Handbook" and in Japanese Patent Publication No. 1983-26812, while the mold in (b) is described in "World
It is described in "Steel &Metalworking" Vol. 4, 1982, p. 160, etc.

(Problems to be Solved by the Invention) When performing continuous casting using a conventional mold, the following problem occurs. In other words, when forming a cylindrical body (mold) as in (a) above, cooling of the slab progresses unevenly, which tends to cause deformation and cracks in the slab. If you try to solve this problem by replacing it with the mold in b), you will sacrifice safety in case the slab surface breaks. This will be explained in detail below.

Generally, in the mold (a) in which the mold is integrally formed, the taper provided in the hollow part of the mold is set in advance for each metal to be cast based on careful calculations and experiments. This means that if the taper amount (reduction rate of cross-sectional dimension) of the mold is greater than the degree of shrinkage of the slab, it will not be possible to pull out the slab smoothly, and conversely, if the taper amount is small, the slab and mold will This is because a gap is formed between the two, impeding heat transfer, and preventing the cooling (solidification) of the slab from proceeding. The thermal conductivity of air is several thousandths of that of copper, so when a gap is formed, heat transfer is extremely reduced.

However, when continuous casting is actually performed, it is extremely rare for the slab to shrink along the taper of the mold. In other words, the degree of shrinkage of a slab also changes depending on the casting (drawing) speed and the temperature of the molten metal, so even if the type (components) of the cast metal is the same, the degree of shrinkage will change each time it is cast or over time during casting. It will change as time passes. Additionally, as the mold solidifies and cools, it rarely shrinks in a manner similar to the original cross-section; in most cases, a circular cross-section deforms into an ellipse, or a rectangular cross-section becomes nearly diamond-shaped. .

As mentioned above, while the thermal conductivity of the mold is extremely high, if a gap forms between the surface of the slab and the mold, heat transfer is extremely hindered. If there is contact with the gap, there will be a large difference in the cooling intensity between the contact area and the gap area. This distribution of cooling intensity causes the slab to shrink so as to promote the above-mentioned deformation, so that partial cooling and deformation progress further by the time the slab leaves the mold. As a result, a non-uniform or asymmetric solidified structure is formed inside the slab, and cracks occur.

The mold in (b), which presses the mold elements onto the surface of the slab, is connected downstream of the mold in (a) by shortening it to prevent uneven cooling and deformation of the slab. Since there are gaps between the elements, it cannot be expected to have the ability to repair breaks on the slab surface. In other words, if the surface of the slab (solidified layer) in the mold breaks for some reason during casting, in the case of mold (a), by temporarily stopping drawing (or reducing its speed), The slab is repaired and the molten metal inside does not break out, but in (b) the molten metal leaks out from the gap between the mold elements.
A breakout is extremely dangerous as the hot molten metal can damage molds and other equipment and cause personal injury.

To prevent breakouts, for example, there is a method of constantly measuring the temperature of the mold to detect breaks on the surface of the slab within the mold, but if the mold in (a) is short, this method is not suitable. There are also problems. In other words, it is necessary to repair the broken part before it comes out of the mold (a), so in this case,
It is necessary to increase the sensitivity of fracture detection and to stop pulling out within a short time. For example, (a)
When the length of the mold is 200 mm and the casting (pulling) speed is 2 m/min, it is necessary to detect the breakage and stop the drawing within 6 seconds at the latest. Generally, in continuous casting, the slab is pulled out while oscillating the slab mold, so the temperature of the mold does not maintain a steady value even while the casting is being performed normally. Nevertheless, raising the detection sensitivity and immediately stopping the drawing will stop the drawing even though the slab has not broken. In other words, there will be more opportunities for erroneous operations, which will worsen operational efficiency.

To summarize the above, conventional molds have problems regardless of the form of the cylindrical body (mold).
It has been difficult to prevent breakout and to prevent uneven cooling from proceeding.

(Objective of the Invention) This invention was made to solve the above-mentioned problems. It has a function to repair fractures on the surface of the slab, prevents breakouts, and also prevents uneven cooling of the slab. The object is to provide a continuous casting mold that can minimize deformation and cracking.

(Means for Solving the Problems) The gist of the present invention to achieve the above object is to integrally form a cylindrical mold, give its hollow shaft a circular or polygonal cross section, In a continuous casting mold in which the outer peripheral wall of the mold is cooled with water or the like, the molten metal supplied to the hollow shaft is continuously cooled and solidified to form a slab.
An interior material made of a heat-resistant material is attached to a portion of the inner circumferential wall of the mold in the axial direction, and a hollow portion is provided at a suitable location at the contact area between the interior material and the mold.

(Function) According to the continuous casting mold of the present invention, in the appropriate place in the mold, that is, in the place where the interior material is attached and the cavity is provided in the contact area between this and the mold, the cavity has a heat insulating effect. Since the heat transfer from the slab to the cooling water is restricted by As a result, the progress of uneven cooling and deformation is suppressed. Furthermore, since the cylindrical mold is integrally formed, even if the surface of the slab inside the mold breaks for some reason during casting, it can be repaired and breakout can be prevented.

(Example) Hereinafter, an example of the present invention will be described based on the drawings. 1 and 2 are a longitudinal sectional view and a cross sectional view of essential parts of a mold for horizontal continuous casting of steel according to the first embodiment.

As shown in FIG. 1, in horizontal continuous casting, a mold A is connected to a tundish E for storing molten steel M, and a drawing roll F is disposed downstream of the mold A. Therefore, the molten steel M is supplied to the tundish E and is temporarily stored there, and then flows into the mold A where it is cooled, becomes a slab C, and is continuously drawn out by the rolls F. At this time, molten steel M
is the refractory connected to the nozzle Ea of the tundish E.
It flows into the mold A through Eb, and from the time it comes into contact with the inner peripheral wall of the mold A, a solidified layer Ca is formed sequentially from the contact surface, that is, from the outer periphery, and a slab C is formed.

Since the equipment shown in the figure is for obtaining slabs with a circular cross section, mold 1 of mold A has a diameter on its inner periphery that takes into account shrinkage of the slab during cooling, and a diameter that takes into account shrinkage in the casting direction. It is formed into a cylindrical shape with a taper. Since the mold 1 is a so-called tubular mold formed from a single piece of copper alloy,
This hollow shaft portion is a closed circle. The mold A is equipped with a cooling water jacket 3 and a partition pipe 3a on the outside of the mold 1, so that the supplied cooling water flows along the outer peripheral wall of the mold 1. Further, a thermocouple 4 is inserted into the upstream portion of the mold 1 to measure the temperature of the mold 1 during casting, so that abnormalities such as breakage of the slab can be detected.

In this embodiment, a part of the inner circumferential wall of the mold 1 on the downstream side is expanded in diameter, and a shallow recess 2a is formed in the outer circumferential wall.
A graphite liner 2 with a graphite liner 2
has heat resistance and self-lubricating properties, so that the slab C can be drawn out smoothly. The inner diameter of the liner 2 is determined to match that of the mold 1, and the liner 2 is defined as the part of the mold 1 where the liner 2 is not attached.
The connection was made so that there were no steps or gaps on the inner peripheral wall. On the other hand, a recess 2a provided in the outer peripheral wall of the liner 2
was provided on the downstream side of the liner 2, as shown in FIG. 2, around almost the entire circumference except for four equally spaced protrusions.
Since the liner 2 was attached to the enlarged diameter part of the mold 1 by shrink-fitting the mold 1, the four convex parts are in close contact with the mold 1, but the remaining recesses 2a are in contact with the mold 1 and the liner 2. There is an empty space 2a in between.

When continuous casting is performed using mold A of this embodiment, cooling of the slab proceeds as follows. Molten steel M flowing into mold A from tandate E
first comes into contact with the mold 1, which has high thermal conductivity, in the part where the liner 2 is not attached, and is strongly cooled, forming a solidified layer Ca on the outer periphery. As the slab C is pulled out by the rolls F, the solidified layer Ca moves to the downstream side, but as mentioned above, in many cases, the slab C reaches the part where the liner 2 is installed.
(The solidified layer Ca) is slightly deformed, and a gap G is generated in a part of the contact portion with the inner circumferential wall of the mold 1 (or liner 2), resulting in a uniform contact state. This solidified layer Ca soon reaches the part where the hollow part 2a is provided between the mold 1 and the liner 2, but here, the heat transfer is restricted by the heat insulating effect of the hollow part 2a. Therefore, even if the slab and the liner 2 come into uniform contact, there will be no extreme deviation in the cooling strength. Therefore, deformation and partial cooling hardly progress beyond this point, and therefore a high-quality slab with a nearly perfect circular cross section, an almost axially symmetric solidified structure inside, and no cracks can be obtained.

From the above point, in the mold A, the empty part 2a
It is preferable that the part without the hollow part 2a be short, but since heat movement is restricted in the part provided with the hollow part 2a, it is desirable to make it somewhat longer in the axial direction in order to obtain the necessary thickness of the coagulated layer Ca. . However, since the deviation in cooling strength is small in the part with the hollow part 2a, even if this is made longer to extend the total length of the mold A, deformation and uneven cooling will not proceed; on the contrary, the surface of the slab C ( coagulation layer
This has the advantage of making it easier to deal with the breakage of Ca). In other words, even when the thermocouple 4 detects an abnormality in the temperature of the slab 1, the broken part is connected to the mold A.
Since the breakage can be repaired by stopping the withdrawal (or reducing its speed) before it comes out, breakout can be reliably prevented without any erroneous operation. Further, since the cooling of the slab C proceeds gradually, it is suitable for casting high carbon steel or high alloy steel, which are prone to cracking by rapid cooling.

Here, mold 1 (thickness 10 mm) and liner 2 (thickness 10 mm)
Let us quantitatively consider the transfer of heat in the part where the air space 2a (0.3 mm) is provided between the 2 mm and 2 mm), based on Fig. 2. FIG. 2 is a cross-sectional view of a portion of the mold A having the hollow portion 2a, excluding the cooling water jacket 3 and the partition pipe 3a. In this figure, the thickness of the solidified layer Ca is 10 mm, and it is assumed that the solidified layer Ca is deformed into a slightly oval shape in the vertical direction. The mold C and liner 2 are in contact in the vertical direction S1, but the liner 2 is in contact with the liner 2 in the horizontal direction S2, with a thickness of 0.2 mm.
A gap G occurs.

The heat of the molten steel M passes through the solidified layer Ca, the gap G (for S2), the liner 2, the hollow part 2a, and the mold 1.
It is transmitted to the cooling water on the outer peripheral wall. The heat transfer coefficient between the molten steel M and the solidified layer Ca is α _M , the heat transfer coefficient between the mold 1 and the cooling water is α _W , the solidified layer Ca, the gap (air),
G, the thermal conductivity λ and the thickness t of the liner (graphite) 2, the cavity 2a, and the mold (copper alloy) 1 are as follows: [λ _C , t _C ] = [25 (kcal/mh°C), 0.01 (m)] [λ _G , t _G ] = [0.05 (〃), 0.0002 (〃)] [λ _L , t _L ] = [100 (〃), 0.01 (〃)] [λ _A , t _A ] = [0.05 (〃), 0.0003 (〃)] [λ _n , t _n ] = [200 (〃), 0.01 (〃)] (The thermal conductivity λ of each part varies somewhat depending on the temperature, but , the above is a typical value at the approximate temperature during casting), and assuming that the cylindrical wall is a flat plate, the total heat transfer resistance R from the molten steel M to the cooling water is R = R _M + R _C + R _G + R _L + R It is expressed as _A + R _n + R _W. However, the heat transfer resistance of each part is R _M =1/α _M , R _C =t _c /λ _c , R _G =t _G /λ _G , R _L =t _L /λ _L , R _A =t _A /λ _A , R _n = t _n /λ _n , R _W = 1/α _W In general, an amount of heat proportional to the reciprocal of this resistance R moves from the molten steel M toward the cooling water.

Here, when entering numerical values into α, λ, and t, R _M + R _W = 0.00105 (m ² h℃/kcal) R _C = t _c / λ _c = 0.0004 (〃) R _G = t _G / λ _G = 0.0004 (〃)...For S2 R _L = t _L / λ _L = 0.0001 (〃) R _A = t _A / λ _A = 0.006 (〃) R _n = t _n / λ _n = 0.00005 (〃). From this, the total heat transfer resistance R toward S2 is R=0.0116 (m ² h℃/kcal), while the R toward S1 where R _G =0 is R=0.0076 (m ² h℃/kcal). The ratio of the amount of heat transfer in the portion where piece C and liner 2 are in contact (toward S1) to that in the portion where gap G exists between them (toward S2) is small, 0.0116/0.0076=1.53.

If the empty part 2a is not provided in mold A,
The total heat transfer resistance R, excluding R _A from the above values, is: S2 direction: R = 0.0056 (m ² h℃/kcal) S1 direction: R = 0.0016 (〃), and the above ratio is 0.0056/ The value is as large as 0.0016=3.5, which results in a significant deviation in the cooling strength.

In mold A of this example, heat transfer is restricted by the heat insulating effect of the cavity 2a, but the liner 2 is easily overheated and melted (burned out) due to this, as follows. can be dealt with.
(b) The liner 2 directly directs the molten steel M without passing through the solidified Ca.
The liner 2 is likely to overheat if it comes into contact with the liner 2, so if the slab breaks, stop drawing as soon as possible to avoid erroneous operation and repair it. (b) When casting with a high drawing speed, the hollow part 2a
Install a different liner with a smaller area or thickness (depth). (c) If the drawing speed is further increased or if the liner 2 and the hollow part 2a are provided closer to the upstream side of the mold A, ceramic materials such as boron nitride or ultraviolet materials such as Hastelloy, which have higher heat resistance than graphite, may be used. A liner (interior material) is formed from an alloy material and installed.

Next, a second embodiment of the present invention will be described based on FIGS. 3 to 5.

FIG. 3 relates to a mold for horizontal continuous casting of steel for obtaining slabs with a rectangular cross section. 1st
Similar to the figure, the left side of the figure is connected to a tundish (not shown), and the slab D is passed through in the right direction to construct the structure. The fourth cormorant is a sectional view taken along the line (-) in FIG. 3 (excluding the cooling water jacket 13 and the partition pipe 13a), and FIG.

Mold B1 shown in FIG. 3 is a so-called assembled mold, in which four mold elements 11a corresponding to four sides and the same number of mold elements 11b are brought into close contact with each other.
By integrally fastening them, a closed cylindrical mold 11 with a rectangular cross section is formed. A cooling structure consisting of a cooling water jacket 13 and a partition pipe 13a is provided on the outside of the mold 11, and a thermocouple 4 for detecting mold abnormality is inserted into the upstream portion of the mold element 11a.

Downstream of the mold B1, the above-mentioned adjustable mold, that is, the four mold elements 21 that are separated and independent from each other as shown in FIG. Mold B2 pressed against the four sides of the mold B2, and
A mold B3 having the same configuration is connected. In addition,
In both molds B2 and B3, the mold elements 21 and 31 are equipped with graphite liners 22 and 32 on their inner circumferential walls, respectively, and cooling water jackets 23 and 32 on their outer circumferential walls.
33 and partition pipes 23a, 33a are provided. With these molds B2 and B3, the slab D
Even if the liners 22 and 32 contract, the liners 22 and 32 are always in contact with them, so that coagulation can proceed uniformly and reliably. Moreover, compared to cooling by water spray, there is also the effect of preventing bulging (swelling due to internal pressure) of the mold D.

The feature of the mold B1 of this embodiment is that a shallow groove-shaped recess 11c along the casting direction is provided in the downstream inner circumferential wall of the downstream mold element 11b of the mold 11, and the mold element 11b is fitted with a graphite liner 12 extending over the entire length of the liner 11b. The liner 12 has an upstream convex portion connected to the mold elements 11a, 11.
Since it is clamped at b, the mounting position will not shift. Further, the inner circumferential wall was designed to have no step or gap between it and the inner circumferential wall of the mold 11a.

FIG. 4 is a cross-sectional view of this part, and as shown in the figure, the liner 12 is also installed so that the four elements are assembled in close contact with each other, like the mold 11.
Further, the recesses 11c of the mold element 11b are concentrated near the four corners of the rectangular hollow portion and near the lower surface, and a hollow portion 11c is formed between the mold element 11b and the liner 12. This is because the corners of the rectangular slab D are cooled from two orthogonal sides, so if heat transfer is not restricted, the slab D will be cooled too quickly, deforming it into a diamond shape, or causing cracks in the solidified structure. This takes into consideration the fact that in horizontal continuous casting, only the lower surface of the slab D often comes into contact with the liner 12 due to the influence of gravity.

In the mold B1 of this embodiment, as in the case of the previous embodiment, heat transfer in the portion provided with the hollow portion 11c is restricted, so that the slab D is not deformed before it is pulled out and leaves the mold B1. Partial cooling does not occur. That is, even if a part of the slab D undergoes some diamond-shaped deformation in the upstream part of the mold B1 and reaches the liner 12 and comes into contact with the inner circumferential wall unevenly, the part that tends to come into contact (the corner Since a hollow part 11c having a heat insulating effect is provided in the area (near the upper surface and the lower surface), uneven cooling will not occur, and therefore deformation will not proceed.

When the slab D is further pulled out and reaches the molds B2 and B3, each surface of the slab D except for the four corners is uniformed by the effect of the liners 22 and 32 pressed by the spring 34. As a result, it is possible to obtain a high-quality slab whose cross section maintains an extremely accurate rectangular shape and whose internal solidified structure is symmetrical and free of cracks.

In the mold B1, the hollow part of the closed cross section can be lengthened without causing deformation and partial cooling of the slab, so that even when the surface of the slab D breaks, the thermocouple 4 is connected to the mold 11a. By detecting temperature abnormalities, breakouts can be reliably prevented without erroneous operation.

In this embodiment as well, the hollow portion 11c can have a different size or be provided at a different location, and the liner 12 can also be made of an interior material made of ceramics or heat-resistant metals other than graphite. Also, mold B following mold B1
2 and B3 may be arranged in series at an appropriate distance in the axial direction.

Although the above two embodiments have been shown regarding horizontal continuous casting molds for steel, the continuous casting mold of the present invention can be of a vertical type (vertically oriented) or an inclined type, and can also be used for continuous casting of metals other than steel. can be used. Further, it is also easy to form the hollow shaft portion as a curved mold. Furthermore, since the cooling strength at appropriate locations can be adjusted according to the shape of the cross-section of the slab, it is suitable for obtaining slabs with special cross-sectional shapes, not just circular and rectangular shapes.

(Effects of the Invention) The continuous casting mold of the present invention described above provides the following effects.

(1) Since uneven cooling of the slab does not proceed, deformation and cracking can be minimized, and high-quality slabs with a symmetrically formed solidification structure can be obtained.

(2) Since the cylindrical mold is formed unilaterally, it has the function of repairing breaks on the surface of the slab, making it possible to reliably prevent breakouts.

(3) Since the cooling intensity can be freely adjusted by restricting heat transfer, it can also be used for casting metals with high crack susceptibility or slabs with special cross-sectional shapes.

(4) It can be easily adapted to changes in the casting material and casting speed by simply changing the dimensions and arrangement of the cavity.

[Brief explanation of the drawing]

The drawings all show a mold for horizontal continuous casting of steel, and FIG. 1 is a vertical sectional view of the mold relating to the first embodiment, FIG. 2 is a sectional view of the main part at the - part of FIG. The figure is a longitudinal cross-sectional view of a mold related to the second embodiment, FIG. 4 is a cross-sectional view of a main part at the - section in FIG. 3, and FIG. 5 is a view taken in the direction of the - section in FIG. 3. A, B1, B2, B3...Mold, C, D...
...Slab, E... Tundish, G... Gap, M... Molten steel, 1,11... Slab, 2,12,
22, 32...Liner, 2a, 11c...Empty part (recess), 11a, 11b, 21, 31...Mold element.

Claims (1)

[Claims] 1. By integrally forming a cylindrical mold, giving its hollow shaft a circular or polygonal cross section, and cooling the outer peripheral wall of the mold with water, the hollow shaft can be In continuous casting molds, in which molten metal supplied to the mold is continuously cooled and solidified to form slabs, an interior material made of a heat-resistant material is attached to a portion of the inner peripheral wall of the mold in the axial direction. , a mold for continuous casting that has a cavity at a suitable location in the contact area between the interior material and the mold. 2. The continuous casting mold according to claim 1, further comprising a coaxially disposed subsequent mold portion in which a cylindrical mold is formed by a plurality of mold elements that are pressed against the surface of the slab separately and independently from each other. . 3. The continuous casting mold according to claim 1 or 2, wherein the hollow portion is provided near a corner of the hollow shaft portion. 4. The continuous casting mold according to claim 1, wherein the hollow groove is provided near the lower surface of the hollow shaft portion.