JPH0647153B2 - Mold for continuous casting and continuous casting method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a continuous casting mold for cooling and solidifying molten metal such as molten steel to form a slab, and a continuous casting method using the same.

[Prior Art] A mold used for continuous casting has a cylindrical mold integrally formed (or combined and integrated), and molten metal (molten metal) supplied to the hollow shaft (cavity) of the mold. ) Is a device for cooling and solidifying to form cast pieces. In order to cool the molten metal in the hollow shaft portion, a cooling water jacket is provided on the outside of the mold so that the cooling water flows along the outer peripheral wall of the mold. In continuous casting, molten metal once stored in a tundish (molten metal pan) is supplied to such a mold, where a cast piece with at least the outer peripheral portion solidified is formed, and this is continuously drawn out to the downstream side of the mold. Done by Such continuous casting method is more widely used in the metal manufacturing industry because it has better quality uniformity and product yield than the ingot casting method.
In particular, Japan's continuous casting rate for steel has reached over 90%. Hereinafter, steel will be described as an example.

Continuous casting of steel in Japan has developed industrially since the 1950s, but most of the methods have been vertical (vertical or curved), and cast slabs with a rectangular cross section from the beginning. It was The vertical continuous casting method is a casting method in which the mold (hollow shaft) is arranged substantially vertically, and molten steel is poured into the upper tundish to draw the slab downward.
Meniscus (free surface) for molten steel poured into the mold
Is formed, the outer peripheral portion of the molten steel is solidified starting from here,
It becomes a slab. Such a vertical continuous casting method has been popular especially for casting a slab having a rectangular cross section, since a slab having a circular cross section with sufficient quality could not be obtained before the fine casting technique was completed.

On the other hand, the horizontal continuous casting method, which has been developed in the fields of cast iron and non-ferrous metals, has been reviewed and put into practical use in the field of steel in recent years. In this method, the mold is made horizontal and one end (upstream end) of the mold is tightly connected to the tundish, and the slab is pulled out in the horizontal direction. A ring-shaped refractory called a break ring is placed at the connection between the tundish and the mold to prevent molten steel from flowing out, and instead of the meniscus, the tip of the break ring (to be exact, the tip and the mold) Coagulation starts from the contact point with the inner surface. The molten steel supplied to the mold does not oxidize due to contact with air, so clean slabs can be obtained, and because the molten steel pressure in the mold is high (the pressure in the tundish acts), the solidified shell adheres to the mold. However, there are many features such as uniform and stable solidification progressing, and therefore, even a slab with a circular cross section can be easily cast. Therefore, the method of densely connecting the tundish and the mold via the break ring is beginning to be adopted not only in the horizontal type but also in the vertical continuous casting method.

In this continuous casting method, the break ring plays an important role as described above, but since it is used in contact with high temperature molten steel without being cooled and cannot be exchanged during casting, it has a thermal effect. Chemically and mechanically, very strict quality characteristics are required. In order to satisfy this, as the break ring, a special ceramic material such as boron nitride (BN) or sialon having high strength at high temperature, high resistance to thermal damage and high thermal shock resistance is used.

The break ring is first attached to the upstream end of the mold,
In this state, it is usual to connect the mold and the tundish so that the back surface (the end surface on the upstream side) is overlapped with the tap hole of the tundish. There are forms. One is to press the flat portion of the tip of the break ring against the upstream end surface (flange surface) of the mold to bring it into close contact, and the other is to insert the tip end into the upstream end of the mold hollow shaft portion. However, in the former case, when the flat surface wears, molten steel enters the upstream end surface of the mold and smooth casting cannot be performed, that is, the life of the break ring is short, so the latter form is widely adopted. .

In order to continuously cast a slab with a specified cross section, a mold is used in which a hollow shaft part with a cross section that substantially matches the shape and dimensions of the cross section is formed uniformly in the axial direction of the mold. It This is a technology that has been followed since ancient times with or without break rings. A taper (gradual contraction of the hollow shaft) is provided on the inner surface of the mold according to the contraction of the slab as it cools, or a part of the mold is expanded outward to prevent deformation of the mold (for example, Japanese Patent Publication No. 46-21094). However, the cross-sectional shape of the hollow shaft portion is almost equal to the cross-sectional shape of the final (cooled) cast piece anywhere in the mold.

Even in molds that use break rings,
Since the cross section of the mold hollow shaft is almost equal to the final cross section of the slab, the outer shape of the break ring mounted on the mold, particularly the break ring fitted at the upstream end of the hollow shaft as described above, is: After all, it was almost the same as the final cross section of the slab. In other words, when casting a slab with a circular cross section, use a break ring with a circular outer shape when viewed from the front,
A rectangular break ring was used to obtain a rectangular slab. For example, the break ring shown in Japanese Utility Model Publication No. 61-30761 also has a rectangular outer shape and opening shape in order to obtain a rectangular slab (however, a part of it is small so that no gap is created between it and the inner peripheral surface of the mold). It is curved outwards) and then inserted into the mold.

[Problems to be Solved by the Invention] As described above, the break ring formed of a special ceramic material is a consumable item and is usually used at every casting (every time all molten steel in the tundish is cast). It needs to be replaced, but it is a fairly expensive part. This is because the material is special, and the molten steel must be in close contact with the inner peripheral surface of the mold so that molten steel will not be inserted between the mold and the inner peripheral surface of the mold, so highly accurate processing is essential. Therefore, in the continuous casting method using the break ring, it is said that the cost reduction is the deciding factor of the casting cost reduction.

Above all, a break ring, which has a contour equal to the cross section of the cast piece and is inserted into a mold to obtain a cast piece having a rectangular cross section other than a circular shape, is particularly expensive. For example, when obtaining a slab with a rectangular cross section, the break ring has vertical and horizontal dimensional accuracy, and if there is a curved surface (roundness) at the corner of the slab, this curved surface part is also accurately processed, Must be along the inner surface of the mold. In addition, compared with a circular shape, the wall thickness is increased to prevent bending on each side, resulting in higher material costs and processing costs.

In the continuous casting method in which the tundish and the mold are closely connected using such a break ring, it is easy to obtain a slab having a circular cross section, but the circular slab is not desirable in handling after being cast. There are many. That is, as described above, since continuous casting of steel has been developed to obtain rectangular slabs, in general steel mills, slab handling equipment that follows casting equipment, that is, transportation, cooling, heating and rolling before rolling, etc. This is because all of the above facilities are already configured and configured for rectangular slabs. In order to replace these with new equipment for circular slabs, enormous capital investment is required. Even if such a slab handling facility is newly installed, it is necessary to consider the unstable rolling in the lateral direction of the circular slab, so the equipment is more important than the slab with a polygonal cross section such as a rectangular slab. It is disadvantageous in terms of cost.

[Object of the Invention] The present invention has been made to solve the above problems, and reduces the manufacturing cost of the break ring,
It is intended to provide a continuous casting mold and a continuous casting method that can obtain a good quality slab at a low cost by reducing the facility load for handling the slab.

[Means for Solving the Problems] In order to achieve the above object, the continuous casting mold according to claim 1 of the present invention has a mold having a hollow shaft portion, and the outer peripheral wall thereof is water-cooled. A break ring is attached to the upstream end, the molten metal supplied to the hollow shaft portion from the upstream end is solidified, and in a continuous casting mold that forms a cast piece that is pulled out from the downstream end, the hollow shaft portion of the mold is A) The cross-sectional shape at the upstream end is a perfect circle, b) The cross-sectional shape is gradually changed from upstream to downstream while keeping the circumference constant, and c) The cross-sectional shape is 4 at the downstream end. It is a polygon that is more than a polygon.

In the continuous casting method according to claim 2 of the present invention, a break ring having a perfect circular outer shape is inserted into the upstream end of the mold in the continuous casting mold according to claim 1, and the break ring is inserted. Then, the mold is tightly connected to the tap hole of the tundish, the molten metal is poured into the tundish, and the molten metal is supplied to the hollow shaft portion to solidify the outer peripheral portion of the molten metal. A slab having a polygonal cross section of quadrilateral or more is obtained by drawing by a drawing means arranged downstream of the mold.

[Operation] In the continuous casting mold of the present invention, since the cross-sectional shape of the hollow shaft portion of the water-cooled mold gradually changes from upstream to downstream, the downstream end has a quadrilateral or more polygonal shape,
While forming a solidified shell on the outer peripheral portion of the molten metal supplied to the hollow shaft portion from the upstream end and along the inner surface of the mold, the solidified shell shape is changed according to the cross-sectional shape of the hollow shaft portion, and at the downstream end A slab that has a solidified shell with a polygonal cross section and is drawn out of the mold is formed.

Moreover, since the cross-sectional shape of the upstream end of the mold hollow shaft portion is a perfect circle, a break ring having a perfect circular outer shape can be attached to the upstream end. The break ring, which has a perfect circular outer shape, disperses stress and has high strength, so the wall thickness can be reduced and it can be easily processed by a lathe.
It can be manufactured at a relatively low cost.

In the above mold, the cross-sectional shape of the hollow shaft portion is gradually changed, but its peripheral length is kept substantially constant.
For example, it is easily formed by casting a cylindrical mold material.

Further, according to the continuous casting method of the present invention, the molten metal supplied from the tundish flows into the hollow shaft portion of the mold while receiving the molten metal pressure in the tundish and being shielded from the outside air, and break ring A solidified shell is generated from the tip end surface of the mold to the outer peripheral portion, and the solidified shell moves toward the downstream side of the mold hollow shaft portion by being pulled out by the drawing means, and the solidified shell of the hollow shaft portion adheres to the inner peripheral surface of the mold. The shape changes according to the change in the cross-sectional shape, and the polygonal cross-section exits the mold at the downstream end of the mold. The slab in this state has a molten metal inside, but after leaving the mold, it solidifies to the inside by natural heat dissipation or forced cooling, and has the same polygonal cross section.
It becomes a complete cast piece.

Since the obtained slab has a polygonal cross-section and does not roll unstable in the lateral direction, handle the slab with existing rectangular slab handling equipment or similar equipment that can be newly installed at low cost. You can

Further, as the break ring, the one having a perfect circular outer shape is fitted and used at the upstream end of the mold, so that the manufacturing cost of the break ring is low as described above and the fitting portion is not worn away. It is possible to cast for a long time.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows, as a first embodiment, a vertical cross-sectional view of a horizontal continuous casting mold and a main casting facility for obtaining a steel slab having a four-piece cross section. Also, Fig. 2 (a), (b), (c)
Are cross-sectional views of (a)-(a), (b)-(b), and (c)-(c) of FIG. 1, respectively (however, the figures (b) and (e) are only the main parts). Is shown).

The main equipment for horizontal continuous casting shown here is:
As shown in FIG. 1, a mold A is connected to a tundish E that stores molten steel J, and a drawing roll G is arranged downstream thereof. Mold A is a water-cooled cylindrical mold 1
Thus, a cavity (hollow shaft portion) Aa is formed inside thereof, and its upstream end is closely connected to a nozzle Ea which is a tap hole of the tundish E via a break ring C. Therefore, the molten steel J poured into the tundish E is directly supplied into the cavity Aa, where it is cooled to be a cast slab L. Since the cast slab L is continuously drawn out by the roll G, the molten steel J constantly flows into the cavity Aa and is continuously cast. La refers to a solidified shell forming the outer peripheral portion of the slab L, and is a portion where the molten steel J contacts the inner wall of the mold 1 and is cooled and solidified.

Since the steel has a high melting point and therefore the temperatures of the molten steel J and the solidified shell La are also high, the inner wall of the mold 1 is prevented from being burnt out or sticking to the solidified shell La, and the solidified shell La is prevented.
In order to help the continuous production of the slab, the slab L is vibrated several tens to several hundreds of times per minute by the drawing roll G. That is, the roll G pulls out the slab L in the direction of the arrow in the figure while repeating forward rotation, stopping, and slight reverse rotation.

The mold A is equipped with a cooling water jacket 2 and a rectifying pipe 2'as shown in FIG. 1 on the outside of an integral mold 1 made of a copper alloy so that the cooling water flows.

The characteristic of this mold A is that the cross-sectional shape of the internal cavity Aa is changed from upstream to downstream of the mold 1. That is, the cross-sectional shape of the cavity Aa is a perfect circle 1a (diameter as shown in FIG. 2A) from the upstream end of the mold 1 (position (a)-(a) in FIG. 1) to the middle of the mold 1. Is also constant), but downstream from that in Fig. 2 (b) and Fig.
As shown in (c), two adjacent sides 1b having four sides 1b.
It has a four-sided shape with a circular arc 1c (the center of which is coaxial with the perfect circle 1a) between. This side 1b appears from the position (x)-(x) in FIG.
Since the length is gradually increased toward the downstream side, the cross-sectional shape of the cavity Aa gradually changes. And even though the cross-sectional shape changes, the cavity
The perimeter of Aa, that is, the sum of the lengths of the four sides 1b and the four arcs 1c is set to be substantially unchanged with respect to the perimeter of the perfect circle 1a.

In this embodiment, the diameter of the perfect circle 1a is 151 mm (radius 75.5 mm)
Then, from the position (x)-(x) in FIG. 1 to the downstream of the mold 1, the side 1b is gradually lengthened to be closer to the inner side and the arc 1c.
Gradually increase the radius of the lower end ((c)-
At (c) position, side 1b has a length of 100 mm, and the distance between opposing sides is 142.
It is a quadrilateral with 8 mm and an arc 1c radius of 87.1 mm with rounded corners (see Fig. 2 (c)). Since the circumference of the perfect circle 1a is 474.4 mm and the circumference of the quadrangle at the downstream end is 521.5 mm, the amount of change in circumference at the downstream end with respect to the upstream end is +47.1 mm, that is, + 10%.

In the general continuous casting mold, to the downstream, so as to maintain the contact between the slab that is cooled and shrinks and the mold inner surface,
It is usual to reduce the size of the cavity in the mold (and therefore the perimeter), but the reason for slightly increasing the perimeter as described above in this mold A is as follows. One is that the mold 1 differs from other molds (in general molds) in that the cross-sectional shape of the cavity Aa changes from upstream to downstream, and the side 1b gradually protrudes inward.
On the four surfaces corresponding to the side 1b, the surface of the slab L and the inner surface of the mold 1 must be kept in contact with each other. Another reason is
The cross-section of the slab L gradually approaches a rectangular shape, but the corners of such a cross-section are strongly cooled by the two sides that sandwich it, so when casting a steel type with high susceptibility to cracking. Rather, avoiding contact between this portion and the inner surface of the mold 1 is to prevent cracks (corner cracks) due to local cooling.

The break ring C connecting the nozzle Ea of the tundish E and the mold A is made of boron nitride (BN), and is a perfect circular ring having two side surfaces as shown in FIGS. 1 and 2 (a). Formed. Then, the small diameter portion Ca is fitted and mounted on the upstream end of the mold 1, and the rear surface (end surface near the upstream side) on the large diameter portion Cb side is brought into close contact with the tip end surface of the nozzle Ea. The outer diameter of the small diameter portion Ca is the upstream end of the mold 1 (true circle 1a)
Since the inner surface of the nozzle Ea is equal to the inner diameter of the nozzle Ea, and the back surface is finished flat together with the tip surface of the nozzle Ea, the molten steel J does not flow out from these connecting portions during casting. In this respect, the break ring C requires particularly high precision in processing the outer circumference of the small diameter portion Ca that is the connection portion with the mold 1, but since the small diameter portion Ca is a perfect circle, it can be processed with almost no difficulty. . The large-diameter portion Cb does not need to be circular in terms of function, but is circular in consideration of easy processing and minimizing the material cost (usage amount) of BN. The break ring C also has a shape without the small diameter portion Ca and functions even if the tip surface is flattened and brought into close contact with the end surface of the mold 1. However, since the tip surface is worn during casting, as described above. Small diameter Ca
The life is extended by forming and inserting into the mold 1.

With the casting equipment configured as described above, a slab L having a quadrilateral cross section is cast as follows.

When the molten steel J is supplied from the tundish E into the cavity Aa of the mold A through the nozzle Ea and the break ring C, the tip surface of the break ring C and the inner peripheral surface of the mold 1 are brought into contact with each other as described above. As a starting point, the molten steel J in the mold 1
A solidified shell La is formed on the entire circumference of, and the solidified shell La grows as a slab L and continues, whereby continuous casting is performed. Slab L
Moves in the mold 1 while being vibrated by the drawing roll G, so that it can be smoothly cast without breaking the solidified shell La or sticking to the inner peripheral surface of the mold 1. Since the solidified shell La is formed along the shape of the cavity Aa, for example, in the vicinity of the upstream end of the mold 1, it has the same cross-sectional shape as the perfect circle 1a in FIG. 2 (a).

However, from the middle of the mold 1 (position (x)-(x) in Fig. 1) to the downstream, the cross-sectional shape of the cavity Aa changes,
Since 1b gradually protrudes inward, the cross-sectional shape of the solidified shell La changes as it is pulled out by this side 1b. In the cast slab L until it leaves the mold 1,
Moreover, since the solidified shell La is thin (the molten steel J inside) and is easily deformed at high temperature, the cross-sectional shape changes smoothly as described above. Moreover, as described above, the cast slab L (solidified shell L
Since a) is pulled out while maintaining contact with the mold 1 on the four surfaces corresponding to the side 1b, each part in the cross section is uniformly cooled to form a good quality solidified structure without cracks. Thus, the slab L exits the mold A in a quadrilateral cross section that is equal to the cross section (see FIG. 2 (c)) of the cavity Aa at the downstream end of the mold 1. This slab L further solidifies to the inside by natural heat dissipation, but since the final shape is the above-mentioned quadrilateral, it can be used as a conventional slab handling facility (not shown) including the drawing roll G and a conventional slab. The same equipment for rectangular slabs can be used.

In this embodiment, the side 1b is formed from the middle of the mold 1 to change the cross-sectional shape of the cavity Aa. However, the degree of change (for example, the side length in the final cross-sectional shape of the cast slab L), and Depending on the deformability of the solidified shell La (in other words, the size of the cross section of the cast steel or the slab L, or the casting speed),
It is better to move this position appropriately. Further, the cavity Aa near the upstream end of the mold 1 may be provided with a taper (that is, the diameter of the perfect circle 1a is gradually reduced toward the downstream) in accordance with the contraction of the cast slab L accompanying cooling.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a diagram of a horizontal continuous casting mold of steel for obtaining a slab having a quadrilateral cross section. Similar to FIG. 1, a slab M is cast in the right direction of the drawing. 4 (a), (b) and (c) are respectively (a)-of FIG.
It is a cross-sectional view in (a), (b)-(b), (c)-(c) (only a main part is shown).

The mold B shown in FIG. 3 is a cylindrical mold 11 also made of copper alloy, and a cooling water jacket 13 and a rectifying pipe 1 on the outside thereof.
Although having 3 ', a graphite liner 12 is mounted inside in the downstream side portion, and the inner peripheral surface of the mold 11 and the inner peripheral surface of the liner 12 are connected without a step to form a cavity Ba. . The liner 12 reduces the drawing resistance of the slab M in the mold B by utilizing the self-lubricating property of graphite. Then, the upstream end of the mold 11 is closely connected to the nozzle Fa of the tundish F via the break ring D, as in the above embodiment. The upstream end of the mold 11 is formed in a flange shape, and the thermocouple 14 is inserted from the outside as shown in the figure.

Also in this mold B, the cross-sectional shape of the internal cavity Ba is changed from upstream to downstream of the mold 11 (including the graphite liner 12). The cross-sectional shape of the cavity Ba is a perfect circle 11a as shown in FIG. 4 (a) at the upstream end of the mold 11 (position (a)-(a) in FIG. 3), but from that position to the downstream. As a closed curve as shown in Fig. 4 (b), it gradually approaches the quadrangle, and the downstream end of the mold 11 and its vicinity (Fig. 3).
(portion downstream from position (c)-(c)) has sides 11b on four sides and 4
4-sided shape with smooth arc 11c at the corner (see Fig. 4 (C))
I chose The above closed curve changing from the perfect circle 11a (Fig. 4 (b)
(Refer to), the radius of curvature of the part that is deviated by 90 ° from the center point is gradually increased, and the radius of curvature of the part between them is gradually decreased. It has an infinite radius and forms side 11b. Since the cross-sectional shape of the slab M is largely changed between the upstream end and the downstream end of the mold 11, in this embodiment, the solidified shell Ma is most likely to be deformed from the most upstream position, and the radius of curvature is as described above. Cavity Ba
The cross-sectional shape of was changed gently.

And again, the perimeter across the cavity Ba is
Was set to be almost constant over the entire length of. In this embodiment, the diameter of the perfect circle 11a at the position (a)-(a) in FIG. 3 is 256.5 mm, and the cavities Ba at the downstream end (after the position (c)-(c) in FIG. 3) face each other. Distance between pieces 11b 200mm, 4
The corner 11c has a quadrangle with a radius of 20 mm. The circumference of the perfect circle 11a is 805.8 mm, and the circumference of the quadrangle at the downstream end is
Since it is 765.7 mm, the circumference of the downstream end with respect to the upstream end is -4
This is a slight decrease of 0.1 mm, or -5%.

This change in the circumferential length provided in the cavity Ba takes into account the contraction of the cast slab M (solidified shell Ma) due to cooling in the mold 11. The solidified shell Ma is located at the upstream end of the mold 11 (see FIG. 3).
(a)-(a) position) That is, it is formed on the outer peripheral portion of the molten steel K from the position of the tip surface of the break ring D described later, but the temperature drops and contracts before it is withdrawn from the mold 11 and exits from the downstream end. . Meanwhile, the amount of contraction of the circumference of the solidified shell Ma is the product of α and the temperature drop width ΔT to the peripheral length and the downstream end at the upstream end of the solidified shell Ma, where α is the thermal expansion coefficient of the solidified shell Ma. That is, × ΔT × α. When casting low carbon steel in this example, the circumference of the solidified shell Ma contracted by about 40 mm based on the above equation, so the cavity Ba had a circumference change corresponding to this. Therefore solidified shell Ma
Is kept in contact with the inner peripheral surfaces of the mold 11 and the graphite liner 12 and is drawn out to the downstream side while being surely cooled.

As shown in FIG. 3, the upstream end of the mold 11 forms a taper portion having a circular cross section and a diameter enlarged toward the tundish F up to the positions (a)-(a), and the outer circumference is formed at this portion. A true circular break ring D having the same taper on the surface is inserted. The break ring D is made of ceramic containing boron nitride (BN) as a main component, and the tip surface of the break ring D when fitted in the mold 11 coincides with the positions (a)-(a), and the back surface of the break ring D is closer to the mold 11. It has a protruding size. Since the outer peripheral surface is easily provided with a taper by lathe processing or the like, it can be manufactured at a low cost as in the first embodiment, and the joint with the mold 11 and the tundish F can be sealed. In particular, the break ring D is designed such that the taper portion is pushed into the mold 11 and fitted therein.
There is an advantage that the joint with the mold 11 is more reliable and the compressive stress generated inside prevents the crack.

Even with the mold B of this embodiment, a slab M having a quadrilateral cross section equal to the cavity Ba of FIG. 4 (c) is cast in the same manner as in the first embodiment described above. In particular, in the cavity Ba of the mold B, the cross-sectional shape changes gradually, and the inner peripheral surface of the cavity Ba is in contact with the surface of the solidified shell Ma so as to cool it. It is also suitable for casting at drawing speed. Graphite liner 12
Has a lower thermal conductivity than the mold 11 (copper alloy), the cooling strength can be adjusted by adjusting the length and the thickness, and therefore, even a steel type having high crack susceptibility can be cast.

Further, the thermocouple 14 inserted into the mold 11 can detect the break ring D and the generation state of the solidified shell near the upstream end of the mold 11. For example, the solidified shell is a mold 11
If it is not pulled out normally due to breakage or sticking inside, the thermocouple 14 informs the temperature drop of the mold 11. By receiving such information from the thermocouple 14 and changing the drawing speed and the vibration pattern applied to the slab M, continuous casting can be performed more smoothly.

In the mold B, the cross-sectional shape and size of the cavity Ba were made constant in the portion downstream of the position (c)-(c) in FIG. 3, but the vertical and horizontal portions of this portion were adjusted in accordance with the contraction of the slab M. The dimensions may be tapered. For the graphite liner 12 installed here, replace it with another material having heat resistance and lubricity (for example, BN, ZrO ₂ or special metals).
It can also be fitted with a liner or coated with. If such a material has sufficient heat resistance, it can be installed over the entire length from the upstream end of the mold 11, and if it has sufficient lubricity, it may not be necessary to withdraw the slab M while vibrating it as described above. is there.

Although the present invention has been described above with reference to the two embodiments, the present invention can be carried out as follows.

a) For example, in accordance with the first embodiment, the hollow shaft portion (cavity) at the downstream end has an octagonal cross-sectional shape, and a cast piece having an octagonal cross-section is cast using this mold. In many cases, the octagonal slab can be used as a slab handling facility subsequent to the casting facility, for either a rectangular slab or a circular slab. Not limited to an octagon, a slab having a polygonal cross-sectional shape of quadrilateral or more (not limited to one having the same length on each side) can be easily implemented by the present invention. Further, how to change the shape of the hollow shaft portion up to the downstream end is not limited to that shown in the embodiment.

b) A pinch roll having a strong pressing force may be provided near the outlet of the mold, and the cast piece deformed by being pulled out of the mold may be supplemented with the roll.

c) Not only steel but also non-ferrous metal slabs such as copper and aluminum can be cast.

d) The present invention is not limited to horizontal continuous casting, but vertical continuous casting or diagonally standing upright and closely connected to the tap hole at the bottom of the tundish can be performed as vertical continuous casting.

e) When applied to vertical continuous casting, a seal tube or the like for preventing molten metal oxidation may be attached to the upstream end of the mold instead of the break ring. In the vertical continuous casting method, the solidification starts from the meniscus described above, so the break ring is often unnecessary, but the molten metal is oxidized when it comes into contact with air in the meniscus, so in order to prevent this, from the tap hole of the tundish. The upstream end of the mold is covered with a seal tube, and an inert gas is sealed inside. Also in this case, if the upstream end of the mold is a perfect circle, the cost of the consumable seal tube is significantly reduced.

[Effects of the Invention] According to the continuous casting mold of the present invention described above, 1) although a slab having a polygonal cross section is obtained, the cross-sectional shape at the upstream end of the mold hollow shaft is true. Since it is circular, it is possible to use a break ring (or a ring or tube-shaped attachment such as a seal tube) having a perfect circular outer shape at its upstream end. When the outer shape is a perfect circle, they are manufactured at a relatively low cost and have high strength, so that the manufacturing cost of the slab is reduced. Also, when casting various slabs with different cross-sectional shapes, one kind of break ring (same for other attachments) can be used if the cross-section at the upstream end of the mold hollow shaft part has the same perfect circle. However, in this case, the production cost is further reduced by mass-producing one type.

2) From upstream to downstream, the cross-sectional shape of the mold hollow shaft gradually changes from a true circle to a polygon while the peripheral length remains almost constant. Therefore, the inner peripheral surface of the mold is pulled out at least at each side. Make sure to contact the slab to be cooled and cool it. That is, since the cooling strength is not biased, a preferable solidified structure is formed inside the slab.

Further, according to the continuous casting method of the present invention, 1) since the cross section of the obtained cast piece is a polygon, the equipment for handling the cast piece should be an existing one for rectangular cast pieces, or As compared with the case of the circular cast slab, a new one having a simpler structure may be newly installed, so that the overall equipment cost of the continuous casting equipment including this can be reduced.

2) Since a break ring having a perfect circular outer shape is particularly inserted and used at the upstream end of the mold of the above mold, continuous molding (mass production of slabs) can be performed for a long time with the break ring manufactured at low cost. . From the above points, the manufacturing cost of the slab becomes considerably low.

3) The original advantage of the continuous casting method in which the tundish and the mold are closely connected is utilized as it is.

[Brief description of drawings]

The drawings all show a horizontal continuous casting mold for steel and main casting equipment, and FIG. 1 is a longitudinal sectional view thereof in relation to the first embodiment, FIG. 2 (a), (b), (c) is a cross-sectional view taken along lines (a)-(a), (b)-(b), and (c)-(c) of FIG. 1, respectively. Further, FIG. 3 is a longitudinal sectional view of the vicinity of the mold according to the second embodiment, and FIGS. 4 (a), (b) and (c) are (a)-(a) and (b) of FIG. 3, respectively. -(b), (c)-(c) is a cross-sectional view. A, B …… Mold, Aa, Ba …… Cavity, C, D …… Break ring, E, F …… Tundish, G …… Drawing roll, J, K …… Molten steel, L, M …… Slab , La, Ma ... solidified shell,
1,11 …… Mold, 1a, 11a …… True circle, 11b, 11b …… Side,
2, 13 ... Cooling water jacket, 12 ... Graphite liner.

Claims (2)

[Claims] 1. A mold having a hollow shaft portion, the outer peripheral wall of which is water-cooled and a break ring is attached to an upstream end of the mold to solidify molten metal supplied from the upstream end to the hollow shaft portion. In a continuous casting mold that is a cast piece that is drawn out from the downstream end, the hollow shaft portion of the mold has a) the cross-sectional shape at the upstream end is a true circle, and b) the perimeter is substantially constant from upstream to downstream. The continuous casting mold is characterized in that the cross-sectional shape is gradually changed while maintaining it, and c) at the downstream end, the cross-sectional shape is a polygon with four or more sides. 2. A continuous casting mold according to claim 1, wherein a break ring having a perfect circular outer shape is fitted at the upstream end of the mold, and the mold is opened through the break ring. , The molten metal is poured into the tundish, and the molten metal is supplied to the hollow shaft of the mold to solidify the outer periphery of the molten metal, which is then pulled out from the mold. A continuous casting method, characterized in that a slab having a polygonal cross-section of quadrilateral or more is obtained by pulling out by a means.