JPH0275445A - Mold and method for continuous casting - Google Patents

Abstract

PURPOSE:To reduce load to the equipment and to obtain an ingot having good quality at low cost by gradually varying cross sectional shape of a hollow shaft part in a mold from upstream side toward downstream side and making it the polygon of more than square shape at downstream end. CONSTITUTION:The cross sectional shape of the cavity Aa is varied from middle part toward downstream side in the mold 1 and the side 1b is gradually protrud ed toward inner side. the ingot L till discharging from the mold 1 has still thin solidified shell, and as it is easily deformed at high temp., the cross sec tional shape is smoothly varied. As the ingot L is drawn while holding contact with the mold 1 at four sides corresponding to the side 1b, each part in the cross section surface is uniformly cooled, to form the good quality solidified structure without any crack. By this method, the ingot L becomes four side shape cross section surface as the same section as the cavity Aa in the down stream end of the mold 1 to discharge from the mold A.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a continuous casting mold for cooling, solidifying and solidifying molten metal such as molten steel into slabs, and a continuous casting method using the same. be.

[Prior art] A mold used for continuous casting has a cylindrical mold that is integrally formed (or combined into one), and molten metal is supplied into the hollow shaft (cavity) of the mold. This is a device that cools and solidifies (molten metal) to form slabs. In order to cool the molten metal within the hollow shaft, a cooling water jacket is provided on the outside of the mold, and the cooling water is configured to flow along the outer peripheral wall of the mold. Continuous casting involves supplying molten metal stored in a tundish (molten metal pot) to such a mold, forming a slab with at least the outer periphery solidified, and continuously drawing this to the downstream side of the mold. It will be done.

This continuous casting method is already widely used in the metal manufacturing industry because it has superior quality uniformity and product yield compared to the ingot method, and the continuous casting rate in Japan for sea bream in particular is over 90%. It has reached the point of surpassing it.

Below, steel will be explained as an example.

Continuous steel casting in Japan has developed industrially since the 1950s, but from the beginning, most of the methods were vertical (vertical or curved) and cast slabs with a rectangular cross section. Ta. The vertical continuous casting method is a casting method in which a mold (the hollow shaft of the mold) is arranged almost vertically, molten steel is poured into the mold from an upper tundish, and the slab is drawn downward. A meniscus (free surface) is formed in the molten steel poured into the mold, and the outer periphery of the molten steel solidifies from this point to become a slab. Before detailed casting techniques were developed, slabs with a circular cross section of sufficient quality could not be obtained, so this vertical continuous casting method became particularly popular for casting slabs with a rectangular cross section.

In contrast, the horizontal continuous casting method, which has traditionally been developed in the fields of cast iron and non-ferrous metals, has recently been reconsidered and put into practical use in the field of steel.

In this method, the mold is held horizontally, one end (upstream end) of the mold is tightly connected to a tundish, and the slab is pulled out in the horizontal direction. A ring-shaped refractory called a break ring is inserted at the connection between the tundish and the mold to prevent molten steel from flowing out. Solidification starts from the point of contact with the surrounding surface. The molten steel supplied to the mold does not come into contact with air and oxidize, so a clean slab can be obtained.The molten steel pressure inside the mold is high (pressure inside the tundish acts), so the solidified shell adheres closely to the mold. It has many advantages, such as uniform and stable solidification, and because of this, even slabs with a circular cross section can be easily cast. For this reason, the method of closely connecting the dungeon shell and the mold via a break ring is beginning to be adopted not only in horizontal casting methods but also in vertical continuous casting methods.

In this type of continuous casting method, the break ring plays an important role as mentioned above, but because it is used without being cooled in contact with high-temperature molten steel and cannot be replaced during casting, it is , which requires very strict chemical and mechanical quality characteristics. To meet this requirement, special ceramic materials such as boron nitride (BN) and sialon, which have high high-temperature strength, corrosion resistance, and thermal shock resistance, are used as break rings.

First, attach the break ring to the upstream end of the mold.
In this state, it is normal to connect the mold and tundish by placing the back side (end surface closer to the upstream side) on the tap hole of the tundish, but there are two ways to attach the break ring to the mold. be. One is to attach the flat part of the tip of the break ring to the upstream end surface of the mold (
The other type is to fit the tip into the upstream end of the hollow shaft of the mold. However, in the former case, when the flat part wears out, molten steel enters the upstream end face of the mold, making it impossible to cast smoothly. In other words, the life of the break ring is short, so the latter form is widely adopted. .

In order to continuously cast slabs with a predetermined cross section, a mold is used in which a hollow shaft portion with a cross section that approximately matches the shape and dimensions of the cross section is uniformly formed in the axial direction of the mold. Ru. This is a technique that has been followed for a long time, regardless of whether a brake ring is used or not. The inner surface of the mold is tapered (gradual contraction of the hollow shaft part) to accommodate the shrinkage of the slab as it cools, or a part of the mold is expanded outward to prevent mold deformation (for example, Japanese Patent Publication No. 46-21094
However, the dimensional change is very small, and the cross-sectional shape of the hollow shaft is almost the same as the final (cooled) slab no matter where it is in the mold.

Conventionally, even in molds that use break rings,
Since the cross section of the hollow shaft of the mold is uniform and approximately equal to the final cross section of the slab, the external shape of the break ring attached to the mold, especially the break ring inserted into the upstream end of the hollow shaft as described above, is as follows: As expected, it almost corresponded to the final cross section of the slab. In other words, when casting slabs with a circular cross section, use a break ring with a circular external shape when viewed from the front.
Rectangular break rings were used to obtain rectangular slabs. For example, the break ring shown in Utility Model Publication No. 61-30761 is also formed with a rectangular outer shape and opening shape in order to obtain a rectangular slab (however, a part of the break ring is formed into a rectangular shape to prevent a gap from forming between the mold and the inner peripheral surface of the mold. (curved outward) and inserted into the mold.

[Problem to be solved by the invention] As mentioned above, the break ring made of a special ceramic material is a consumable item, and the brake ring is used every time it is cast (every time all of the molten steel in the tundish has been cast). It needs to be replaced, but it is a fairly expensive part. This is because the material is special and the mold must be in close contact with the mold to prevent molten steel from getting between it and the inner peripheral surface of the mold, so highly accurate machining is essential. Therefore, in the continuous casting method using a break ring, it is said that the cost reduction is the decisive factor in reducing the casting cost.

In order to obtain a cast piece having a cross section other than a round shape, such as a rectangular one, a break ring having an outer diameter equal to the cross section of the cast piece and inserted into a mold is particularly expensive. For example, when obtaining a slab with a rectangular cross section, the break ring must be machined not only to ensure vertical and horizontal dimensional accuracy, but also to accurately machine the curved corners (rounded corners) of the slab. It must be aligned with the inner circumferential surface of the mold. Also, compared to a circular shape, the wall thickness is increased to prevent bending on each side, resulting in higher material 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 slabs with a circular cross section. many. In other words, as mentioned above, continuous casting of steel developed to obtain rectangular slabs, so in general steelworks, the slab handling equipment that follows the casting equipment, such as conveyance, cooling, heating before rolling, and rolling, etc. This is because all of the equipment is already configured for rectangular slabs. In order to replace these with new equipment for circular slabs, a huge amount of capital investment would be required. Furthermore, even if such slab handling equipment were to be newly installed, the unstable rolling of circular slabs in the lateral direction must be taken into account, so the equipment would be more expensive than square slabs or other slabs with polygonal cross sections. This would be disadvantageous in terms of cost.

[Purpose of the Invention] This invention was made to solve the above-mentioned problems, and by reducing the production cost of break rings and the equipment burden related to handling slabs,
The object of the present invention is to provide a continuous casting mold and a continuous casting method that can produce high-quality slabs at low cost.

[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 six hollow shaft parts, and the outer peripheral wall of the mold is water-cooled. In the continuous casting mold, a break ring is attached to the upstream end of the continuous casting mold, and the molten metal supplied from the upstream end to the hollow shaft part is solidified to form a slab that is pulled out from the downstream end. a) The cross-sectional shape at the upstream end is a perfect circle; (a) The cross-sectional shape gradually changes from upstream to downstream while keeping the circumference approximately constant; c) At the downstream end, the cross-sectional shape is a perfect circle. is made into a polygon with more than four sides.

Further, 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 continuous casting mold according to claim 1, and the break ring is inserted through the break ring. Then, the mold is tightly connected to the tapping hole of the tundish, and the molten metal is poured into the tundish and supplied to the hollow shaft portion, thereby solidifying the outer circumferential portion of the molten metal. A polygonal cast piece having a cross section of four sides or more is obtained by drawing it out by a drawing means arranged downstream.

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

Further, since the cross-sectional shape at 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. Break rings with a perfectly circular outer shape disperse stress and have high strength, allowing for reduced wall thickness, and can be easily machined using lathes, etc.
Can be manufactured at relatively low cost.

In addition, in the above mold, the cross-sectional shape of the hollow shaft portion is gradually changed, but its circumference remains almost constant.
For example, it can be easily formed by forging a cylindrical mold material.

Further, according to the continuous casting method of the present invention, the molten metal supplied from the tundish is subjected to the molten metal pressure in the tundish and is shielded from the outside air, and flows into the hollow shaft part of the mold, and flows into the tip of the break ring. A solidified shell is generated from the surface to the outer periphery, and the solidified shell is pulled out by the pulling means and moves downstream of the hollow shaft of the mold, and while closely contacting the inner peripheral surface of the mold, the solidified shell forms a cross section of the hollow shaft. It changes shape as the shape changes, and exits the mold with a polygonal cross section at the downstream end of the mold. The slab in this state has molten metal inside, but after leaving the mold, it solidifies to the inside due to natural heat radiation or forced cooling, and the slab has the same polygonal cross section.
It becomes a complete slab.

The obtained slab has a polygonal cross section and does not roll unstablely in the horizontal direction, so it can be handled using existing equipment for handling rectangular slabs or similar equipment that can be newly installed at low cost. can.

In addition, the break ring has a perfectly circular outer shape and is used by fitting it into the upstream end of the mold.As mentioned above, the manufacturing cost of the break ring is low, and the fitting part does not wear out. It is possible to cast for a long time.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 shows, as a first embodiment, a vertical sectional view of a horizontal continuous casting mold and main casting equipment for obtaining a steel slab with a rectangular cross section. Also, Fig. 2 (a), (b)
) and (c) are respectively (a) - (a) and (
b) A cross-sectional view taken along lines (b) and (c) and (c) (however, (b) and (c) only show the main parts).

The main equipment for horizontal continuous casting shown here is:
As shown in FIG. 1, a mold A is connected to a tundish E for storing molten steel J, and a drawing roll G is disposed downstream thereof. Mold A is a water-cooled cylindrical mold l.
This forms a cavity (hollow shaft part) Aa inside thereof, and its upstream end is tightly connected to the nozzle Ea, which is the 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 and becomes slab. Since the slab is continuously pulled out by the roll G, the molten $1iJ constantly flows into the cavity Aa, and continuous casting is performed. La refers to the solidified shell forming the outer periphery of the slab, and is the part where the molten QJ contacts the inner wall of the mold I and is cooled and solidified.

Sea bream has a high melting point, and therefore the temperature of the molten steel J and the solidified shell La are also high, so the inner wall of the mold L may be burned out or the solidified shell La may be damaged.
In order to prevent sticking and to help the continuous generation of solidified shells La, the slab is vibrated several tens to hundreds of times per minute by a drawing roll G. That is, the roll G pulls out the slab in the direction of the arrow in the figure while repeating normal rotation, stopping, and slight reverse rotation.

Mold A has a cooling water jacket 2 and a rectifier pipe 2 on the outside of an integral mold l made of copper alloy, as shown in Fig. 1.
It is configured to be equipped with ° to circulate cooling water.

A feature of this mold A is that the cross-sectional shape of the internal cavity ^a changes from upstream to downstream of the mold l. In other words, the cross-sectional shape of the cavity ^a is a perfect circle 1a from the upstream end of the mold I (position (a)-(a) in Figure 1) to the inside of the mold 1 as shown in Figure 2 (a). (the diameter is constant), but as shown in Figures 2(b) and 2(c), downstream there are sides 1b on four sides and an arc 1c (its diameter is constant) between two adjacent sides tb. It was made into a four-sided shape with the center coaxial with the perfect circle 1a). This side 1b appears from the (X)-(X) position in FIG. 1 and gradually increases in length toward the downstream, so that the cross-sectional shape of the cavity Aa gradually changes. Even though the cross-sectional shape changes, the circumference across the cavity Aa, that is, the sum of the lengths of the four sides 1b and the four arcs 1c, does not generally change with respect to the circumference of the perfect circle 1a. I made it.

In this example, the diameter of the perfect circle 1a is 151 mm (radius 75.5vn), and the side 1b is gradually lengthened and moved inward from the (X)-(X) position in Fig. 1 to the downstream of the mold l. At the same time, the radius of the arc 1c is gradually increased, and at the downstream end (position (c)-(c) in Figure 1), the length of side ib is 100III11, and the distance between opposing sides is 142.8.
nu++, the radius of the arc 1c is 87.1 mm, and the four corners are rounded (see Fig. 2(c)). Since the circumference of the perfect circle 1a is 474.4 mm and the circumference of the quadrilateral 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. lmm5 or +10%.

In general continuous casting molds, downstream of the continuous casting mold, contact is maintained between the slab, which shrinks as it cools, and the inner surface of the mold.
It is normal to reduce the dimensions (and therefore the circumference) of the cavity in the mold, but in this mold A, the circumference was slightly increased as mentioned above (for the reasons listed above). Unlike the mold (in a general mold), the cross-sectional shape of the cavity ^a changes from upstream to downstream, and the side 1b gradually protrudes inward, so that the four sides corresponding to the side !b are free of slabs. The surface of the slab and the inner surface of the mold 1 must maintain contact with each other.Another reason is that the cross section of the slab gradually approaches a rectangular shape, and the corners of this cross section are Since the two sandwiched sides are strongly cooled, when casting a steel type that is highly susceptible to cracking, it is better to avoid contact between these parts and the inner surface of the mold l to prevent cracking due to localized cooling (corner cracking). .

The break ring C that connects the nozzle Ea of the tanditshu E and the mold A is made of boron nitride (B N ) and is a perfect circular ring with two-stage side surfaces as shown in Figures 1 and 2 (a). Formed as. The small diameter portion Ca is fitted into the upstream end of the mold t, and the back surface on the large diameter portion Cb side (the end surface closer to the upstream side) is brought into close contact with the tip surface of the nozzle Ea. The outer diameter of the small diameter portion Ca is equal to the inner diameter of the upstream end (perfect circle 1a) of the mold l, and the back surface is formed by the nozzle E.
Since the tip surface of a is finished flat, the melt 11J will not flow out from these connections during casting. In this regard, the break ring C requires particularly high accuracy in machining the outer periphery of the small diameter part Ca, which is the connection part with the mold l, but since the small diameter part Ca is a perfect circle, it is difficult to do so. It can be processed without any problem. Although the large diameter portion cb does not need to be circular from a functional point of view, it is important that it is easy to process and B.
The shape is circular in consideration of minimizing the material cost (M used) of H. In addition, this break ring C has a small diameter portion Ca.
A mold with a flat tip and a shape that does not have any cracks! It will function even if it is placed in close contact with the end face of the mold, but the end face will be worn out during casting, so the small diameter part Ca is formed as described above. The lifespan will be longer if you insert it into the

Using the casting equipment configured as described above, a slab having a quadrilateral cross section is cast in the following manner.

When 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 starting point is the point of contact between the tip surface of the break ring C and the inner peripheral surface of the mold l, as described above. As a result, a solidified shell La is formed around the entire circumference of the molten steel J in the mold 1, and this continues to grow as slabs, thereby achieving continuous casting.

Since the slab moves within the mold l while being vibrated by the drawing roll G, it may cause breakage of the solidified shell La or mold l.
It can be cast smoothly without any sticking with the inner peripheral surface of the mold. Since the solidified shell La is formed along the shape of the cavity Aa, it has the same cross-sectional shape as the perfect circle 1a in FIG. 2(a), for example, near the upstream end of the mold 1.

However, what is inside the mold 1 ((x)-(x) position in Figure 1)?
From downstream, the cross-sectional shape of the cavity Aa changes and the side 1b gradually protrudes inward, so that as the solidified shell La is pulled out, the cross-sectional shape changes as it is pressed by the side 1b. In the slab until it leaves the mold, the solidified shell La is still thin (the inside is molten).
ilJ), the cross-sectional shape changes smoothly as described above because it is easily deformed due to the high temperature. Moreover, as mentioned above, since the slab L (solidified shell La) is pulled out while maintaining contact with the mold l on the four sides corresponding to side 1b, each part in the cross section is cooled evenly, resulting in a high quality product without cracks. Forms a coagulated tissue. The slab thus leaves the mold A with a quadrilateral cross section equal to the cross section of the cavity Aa at the downstream end of the mold 1 (see FIG. 2(C)). This slab further solidifies to the inside due to natural heat dissipation, but since the final shape is the above-mentioned quadrilateral, the following slab handling equipment (not shown), including the drawing roll G, cannot be used conventionally. The same equipment for rectangular slabs can be used.

In this example, the side lb is formed from inside the mold I to change the cross-sectional shape of the cavity Aa.
Depending on the degree of change (for example, the side length of the final cross-sectional shape of the slab) and the deformability of the solidified shell La (in other words, the casting steel type, cross-sectional size of the slab, or casting speed), It is better to move this position. Also, mold 1
The cavity Aa near the upstream end of ゛ is provided with a taper (that is, a perfect circle of 1
It is also good to gradually decrease the diameter of a toward the downstream.

Next, a second embodiment of the present invention will be described based on FIGS. 3 and 4. FIG. 3 is a diagram of a horizontal continuous casting mold for steel, also for obtaining slabs with a quadrilateral cross section. As in FIG. 1, a slab M is cast toward the right side of the figure. Figures 4(a), (b), and (c) are the third
Figures (a)-(a), (b)-(b), (c)-(c)
FIG.

Mold B shown in Fig. 3 has a cylindrical mold 11 made of prepared alloy, a cooling water jacket 13 and a rectifier pipe 13° on the outside, but a graphite liner is placed inside the downstream part. 12 is installed, and the inner circumferential surface of the mold 11 and the inner circumferential surface of the liner 12 are connected without any step, forming the cavity B.
It forms a. The liner 12 reduces the pulling resistance of the slab M in the mold B by utilizing the self-lubricating property of graphite. The upstream end of the mold 11 is tightly connected to the nozzle Pa of the tundish F via the break ring D, as in the previous embodiment. In addition, mold 1
The upstream end portion of 1 is formed into a flange shape, and a thermocouple 14 is inserted from the outside as shown in the figure.

In this mold B as well, the mold 11 (graphite container 12
) from the upstream to the downstream of the internal cavity B
The cross-sectional shape of a is varied. Cavity Ba
The cross-sectional shape of the upstream end of the mold 11 ((a) in FIG.
At position (a), it is a perfect circle 11a as shown in Fig. 4(a), but from that position downstream it gradually approaches a quadrilateral as a closed curve as shown in Fig. 4(b). At the downstream end and its vicinity (the part downstream from the position (c)-(c) in Fig. 3), there is a four-sided shape with sides ub on four sides and smooth arcs llc at the four corners (Fig. 4 (c)). ).

The above-mentioned closed curve (see Fig. 4(b)) that changes from the perfect circle 11a gradually increases the radius of curvature of the part shifted by 90 degrees from the center point, and gradually increases the radius of curvature of the part between them. The radius of curvature of the curved portion is made infinite near the downstream end to form the side 11b.

Since the cross-sectional shape of the slab M must be changed significantly between the upstream and downstream ends of the mold 11, in this embodiment, the solidified shell Ma
The cross-sectional shape of the cavity Ba is gradually changed by gradually changing the radius of curvature starting from the most upstream position where Ba is most likely to deform.

Again, the circumferential length across the cavity Ba was set to be approximately constant over the entire length of the mold 11.

In this embodiment, the diameter of the perfect circle 11a at the position (a)-(a) in FIG. 3 is 256.5 mm, and the cavity Ba at the downstream end (after the position (c)-(c) in the figure) Distance between sides 11b is 200 mm, arc L at four corners
It was made to be a quadrilateral with a radius of lc of 20 mm. Perfect circle 1
The circumference of 1a is 805.8 mm, and the circumference of the quadrilateral at the downstream end is 765.7 mm, so the circumference of the downstream end relative to the upstream end is -40.1 mm, which is a slight decrease of -5%. It means that you let it happen.

This circumferential length change provided in the cavity Ba takes into consideration the shrinkage of the slab M (solidified shell Ma) due to cooling within the mold ll. The solidified shell Ma is located at the upstream end of the mold 11 (
It is formed on the outer periphery of the melt 11 from the tip surface of the break ring D (positions (a) to (a) in FIG. descend and contract. Meanwhile, the amount of shrinkage of the circumference of the solidified shell Ma is the product of α, the circumferential length σ at the upstream end of the solidified shell Ma, and the temperature drop width ΔT to the downstream end, where α is the coefficient of thermal expansion of the solidified shell Ma. , that is, ρ×ΔTXα. When casting low carbon steel in this example, solidified shell M
Since the circumferential length of a shrinks by about 40 mm based on the above formula, the cavity Ba was given a corresponding change in circumferential length. Therefore, the solidified shell Ma maintains its entire outer circumferential surface in contact with the mold 11 and the inner circumferential surface of the graphite liner 12, and is pulled out downstream while being reliably cooled.

As shown in FIG. 3, the upstream end of the mold 11 is
Up to the a) position, a tapered part with a circular cross section and an enlarged diameter toward the tongue plate F is formed, and a perfectly circular break ring D having the same taper on the outer peripheral surface is fitted into this part. The break ring D is made of ceramic whose main component is boron nitride (BN), and when it is inserted into the mold 11, its tip surface corresponds to the position (a)-(a), and its back surface corresponds to the position (a)-(a). The size was made to stand out more. Since the outer circumferential surface can be easily tapered by lathe machining or the like, it can be manufactured at low cost as in the first embodiment, and the joints with the mold 11 and the tundish F can be sealed. In particular, this break ring D has the advantage that the tapered portion is pushed into the mold 11 and fitted, so that it is more securely joined to the mold 11, and the compressive stress generated inside prevents it from cracking.

Even if the mold B of this embodiment is used, a slab M having a quadrilateral cross section equal to the cavity Ba in FIG. 4(c) is cast in the same manner as in the first embodiment described above. In particular, the cross-sectional shape of the cavity Ba of this mold B changes slowly, and the inner circumferential surface contacts the surface of the solidified shell Ma all the way around to cool it, so it can be cooled at a fairly high speed (high It is also suitable for casting at high drawing speeds. Note that the graphite liner 12 has a lower thermal conductivity than the mold 11 (copper alloy), so the cooling strength can be adjusted by adjusting the length and thickness, so even steel types with high crack susceptibility can be cast. can.

Further, the state of formation of a solidified shell near the break ring D and the upstream end of the mold 11 can be detected by the thermocouple 14 inserted into the mold 11.

For example, if the solidified shell is not drawn out properly due to breakage or sticking within the mold 11, the thermocouple 14 notifies the temperature drop of the mold 11. By receiving such information from the thermal lightning pair 14 and changing the drawing speed and the vibration pattern applied to the slab M, continuous casting can be carried out more smoothly.

In mold B, the cross-sectional shape and dimensions of the cavity Ba were kept constant in the part downstream from the position (C)-(C) in Fig. 3, but the length and width of this part changed as the slab M contracted. Dimensions may be tapered. In addition, the graphite liner 12 installed here may be replaced with a liner made of other heat-resistant and lubricating materials (for example, BN or Zr (IS or special metals)) or coated. If such a material has sufficient heat resistance, it can be inserted throughout the entire length of the mold 11 from the upstream end, and if it has sufficient lubricity, it is not necessary to pull out the slab M while vibrating it as described above. Sometimes there isn't.

Although this invention has been described above with reference to two embodiments, it is also possible to implement it as shown below based on the invention.

a) For example, following the first embodiment, the cross-sectional shape of the hollow shaft portion (cavity) at the downstream end is made octagonal, and this mold is used to cast a slab having an octagonal cross-section. Octagonal slabs can often be used as slab handling equipment subsequent to casting equipment, whether for rectangular slabs or circular slabs. The present invention can easily be applied to slabs which are not limited to octagonal shapes but whose cross-sectional shapes are polygonal shapes of four or more sides (the lengths of each side are not limited to equal lengths). Furthermore, the manner in which the shape of the hollow shaft portion is changed up to the downstream end is not limited to that shown in the embodiment.

b) Pinch rolls with strong reduction blades may be provided near the exit of the mold, and this roll may be used to additionally deform the slab that has been deformed by being pulled out of the mold.

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

d) It is not limited to horizontal continuous casting; if the mold is erected vertically or diagonally and closely connected to the tapping hole at the bottom of the tundish, it can be carried out as vertical continuous casting.

e) When applied to vertical continuous casting, a seal tube or the like for preventing oxidation of molten metal may be installed at the upstream end of the mold in place of the break ring. In the vertical continuous casting method, solidification starts from the meniscus as mentioned above, so break rings are often unnecessary.However, if the molten metal comes into contact with air at the meniscus, it will oxidize, so to prevent this, the mold is The upstream end of the tube is covered with a seal tube, and an inert gas is sealed inside. Again, if the upstream end of the mold is perfectly circular, the cost of the seal tube, which is a consumable item, is considerably reduced.

[Effects of the Invention] According to the continuous casting mold of the present invention described above, 1) Although a cast slab with a polygonal cross section can be obtained, the cross-sectional shape at the upstream end of the hollow shaft of the mold is Since it is perfectly circular, a break ring (or a ring or tube-shaped attachment such as a seal tube) with a perfectly circular outer shape can be used at its upstream end. When these have an external shape or a perfect circle, they can be manufactured at relatively low cost and have high strength, so the manufacturing cost of the slab is reduced. In addition, even when casting slabs with different cross-sectional shapes, if the cross-section at the -L flow end of the mold hollow shaft is made into the same perfect circle, one type of break ring (other fittings are the same) can be used. Can it be used? In this case, 1
Manufacturing costs are further reduced by mass producing different types of products.

2) From upstream to downstream, the cross-sectional shape of the hollow shaft of the mold gradually changes from a perfect circle to a polygon while the circumference remains almost constant. This method cools the cast slab by making sure that it comes into contact with the cast slab. In other words, since the cooling strength is not biased, a favorable solidification structure is formed inside the slab.

Furthermore, according to the continuous casting method of the present invention, ■) Since the cross section of the obtained slab is polygonal, existing equipment for handling rectangular slabs must be used, or As compared to the case of circular slabs, it is only necessary to newly install one with a simpler structure, so the overall equipment cost for continuous casting equipment including this will be reduced.

2) Since a break ring with a perfect circular outer shape is inserted into the upstream end of the above mold, long-term continuous casting (mass production of slabs) is possible with a break ring manufactured at low cost. .

From the above points, the manufacturing cost of slabs is considerably low.

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

[Brief explanation of the drawing]

The drawings show a mold for horizontal continuous casting of steel and the main casting equipment, and Fig. 1 is a vertical cross-sectional view of them in the first embodiment, Fig. 2 (a), (b),
(c) are (al(a), (b)-(
b), (c) - (c) is a cross-sectional view. Moreover, FIG. 3 is a vertical cross-sectional view of the vicinity of the mold related to the second embodiment, and FIGS. 4(a), (b), and (c) are respectively
Figures (a)-(a), (b)-(b), (c)-(c)
FIG. A, B...Mold, ^a, Ba...Cavity,
C, D...Break ring, E, F...Tandish, G...Drawing roll, J, K... Molten steel, L, M...
・Slab, La, Ma-solidified shell, 1.11...mold, I
a, 1la - perfect circle, lb, llb...side, 2.13.
...Cooling water jacket, 12...Graphite liner. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. The mold has a hollow shaft, the outer peripheral wall of which is water-cooled, and a break ring is attached to the upstream end, and the molten metal supplied from the upstream end to the hollow shaft is solidified. Let me,
In a continuous casting mold made with a slab drawn from the downstream end, the hollow shaft of the mold has: a) a perfect circular cross-sectional shape at the upstream end, and b) a substantially constant circumference from upstream to downstream. c) At the downstream end, the cross-sectional shape is made into a polygon of four sides or more. 2. In the continuous casting mold according to claim 1, a break ring having a perfect circular outer shape is inserted into the upstream end of the mold, and the mold is tightly inserted into the tap hole of the tundish through the break ring. By connecting and pouring molten metal into a tundish and supplying the molten metal to the hollow shaft portion of the mold, the outer circumference of the molten metal is solidified, and this is pulled out by a pulling means disposed downstream of the mold. A continuous casting method characterized by obtaining a polygonal slab having a cross section of four sides or more.