KR102179557B1 - Mold and casting method - Google Patents

Abstract

The present invention, a metal body having an inner space, and a mold formed to surround the inner surface of the metal body, spaced downward from a predetermined height of the metal surface, and comprising a coating layer formed on the lower area of the inner surface, and casting using the same As a method, a mold and casting method capable of improving the quality of cast pieces by preventing solidification of the mold flux are proposed.

Description

Mold and casting method {MOLD AND CASTING METHOD}

The present invention relates to a mold and a casting method, and more particularly, to a mold and a casting method capable of improving the quality of the cast by preventing the solidification of the mold flux.

The continuous casting facility is a facility that continuously injects molten steel into a mold, solidifies it into a cast iron, and continuously draws it from the mold.

The mold is made of copper with good heat transfer, and the coolant is circulated inside. The molten steel injected into the mold is cooled by the mold and can be solidified into a cast iron. Specifically, the mold is a pair of long sides, each extending in one direction, facing each other, and a pair of long sides, each extending in a direction crossing a pair of long sides, facing each other and connecting a pair of long sides. Includes short side plate. The molten steel passes through the space formed by a pair of long and short sides and is solidified and cast into cast iron. At this time, a solidification shell is formed from the hot water surface of the molten steel, and the solidification shell grows and becomes thicker as it goes downward.

During casting of the cast steel, mold flux is injected into the molten steel surface. The mold flux flows between the inner surface of the mold and the solidification shell of the cast, and is used for lubrication and heat transfer rate control between them.

Meanwhile, the mold flux may be supercooled inside the mold to solidify from a liquid phase to a solid phase. In this case, the solidified mold flux may form irregularly shaped crystals on the inner surface of the mold. Accordingly, the solidification of the cast slab is delayed from the top to the bottom of the mold due to the solid mold flux, and the cast slab may shrink unevenly. Accordingly, the duty-free crack may occur in the cast iron, and the crack may be deepened due to the duty-free duty, thereby causing the cast iron to burst.

The technology that serves as the background of the present invention is published in the following patent documents.

KR 10-0347605 B1 KR 10-1766856 B1

The present invention provides a mold and a casting method capable of improving the quality of the cast by preventing the solidification of the molten mold flux between the inner surface of the mold and the solidification shell of the cast.

A mold according to an embodiment of the present invention is a mold for solidifying molten steel, comprising: a metal body having an inner space; And a coating layer formed to surround the inner surface of the metal body, wherein the coating layer is spaced downward from a predetermined height of the hot water surface, and is formed in a lower region of the inner surface.

The coating layer may have different thicknesses at the bottom and the top in the vertical direction.

The thickness of the coating layer may be thicker than the thickness of the top.

The thickness of the coating layer may gradually decrease from the bottom to the top.

The thickness of the lower end of the coating layer may be greater than 0 and less than or equal to 3 mm.

The difference between the height of the hot water surface and the height of the top of the coating layer may be greater than 0 and within 200 mm.

The coating layer may include an insulating material.

The insulating material may include yttria stabilized zirconia.

The coating layer may include an alloy.

The alloy may include a nickel chromium alloy.

The coating layer may include 5 to 100% by weight of an insulating material and 0 to 95% by weight of an alloy based on the total weight of the coating layer.

The coating layer may have a lower thermal conductivity than the metal body.

A casting method according to an embodiment of the present invention includes the steps of injecting molten steel into a mold and supplying a mold flux to the molten steel surface; Solidifying the molten steel to cast a cast steel; Introducing a molten mold flux between the cast and the mold; And a process of contacting the molten mold flux with the coating layer formed on the lower area of the inner surface of the mold, spaced downward from the height of the molten steel surface.

The process of contacting the molten mold flux may include controlling heat transfer between the mold and the molten mold flux using the coating layer; It may include; a process of preventing solidification of the molten mold flux.

In the process of controlling the heat transfer, the amount of heat transfer from the molten mold flux to the inner surface of the mold is reduced from the top to the bottom of the coating layer, and the coating layer is made of 5 to 5 insulating materials for the total weight of the coating layer. It includes 100% by weight, and may include 0 to 95% by weight of the alloy.

According to an embodiment of the present invention, the amount of heat transfer between the molten mold flux and the inner surface of the mold can be adjusted by using a coating layer formed on the lower region of the inner surface of the mold between the inner surface of the mold and the solidification shell of the cast steel. . At this time, the amount of heat transfer from the solidification shell to the inner surface of the mold may be reduced from the top to the bottom of the coating layer. Accordingly, it is possible to prevent the molten mold flux from being supercooled to solidify from a liquid phase to a solid phase. That is, it is possible to prevent the solid mold flux from being formed in an uneven thickness in the lower region of the inner surface of the cast steel. From this, it is possible to stably grow the solidification shell, smoothly lubricate between the solidification shell and the mold, and prevent the solidification shell from being pressed against the solid mold flux. Accordingly, it is possible to suppress or prevent the generation of cracks and cracks on the surface of the cast steel, such as by duty free.

According to an embodiment of the present invention, it is possible to reduce the thickness of the coating layer from the bottom to the top of the coating layer. That is, the lower end of the coating layer can be thickened and the upper end can be made thin. Accordingly, shrinkage of the cast slab from the upper region to the lower region of the mold may be compensated for with a change in the thickness of the coating layer. That is, it is possible to stably maintain contact between the coating layer of the mold and the solidification shell of the cast steel.

1 is a schematic diagram of a casting facility according to an embodiment of the present invention.
2 is a schematic diagram of a mold according to an embodiment of the present invention.
3 is a cross-sectional view of a mold according to an embodiment of the present invention.
4 is a diagram illustrating an internal state of a mold when casting a cast piece by a casting method according to an embodiment of the present invention.
5 is a view for explaining a heat transfer path between a mold and a cast steel when casting a cast steel.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and will be implemented in various different forms. Only the embodiments of the present invention are provided to complete the disclosure of the present invention and to completely inform the scope of the invention to those of ordinary skill in the relevant field. In order to describe the embodiments of the present invention, the drawings may be exaggerated, and the same reference numerals in the drawings refer to the same elements.

Hereinafter, an embodiment of the present invention will be described based on a casting process of casting various molten steels into cast pieces. However, the mold according to the embodiment of the present invention can be applied in various ways to various treatment processes of casting various melts in various ways.

1 is a schematic diagram of a casting facility according to an embodiment of the present invention.

Referring to Figure 1, a casting equipment according to an embodiment of the present invention will be described.

The casting facility, as shown in FIG. 1, is formed in a tundish 10 that receives and temporarily stores molten steel, and is formed in a rectangular cylindrical shape with open upper and lower portions, and receives molten steel stored in the tundish 10. An immersion nozzle for solidifying a mold 20, connected to the lower part of the tundish 10, inserted into the upper part of the mold 20, and injecting molten steel temporarily stored in the tundish 10 into the mold 20 30, and a cooling table 40 arranged in the casting direction under the mold 20, guiding the cast pieces S drawn from the mold 20 in the casting direction, and cooling and molding the cast pieces S Includes.

The molten steel may be a variety of molten steel for manufacturing cast pieces of various steel types, including, for example, carbon steel and stainless steel.

Hereinafter, for convenience of explanation, the molten steel accommodated in the tundish 10 is separately divided into tundish molten steel, and the molten steel injected into the mold 20 and cast into a cast steel is referred to as molten steel (M). And the unsolidified molten steel (M) in the solidified shell (C) and the solidified shell (C) to be described later is collectively referred to as cast steel (C, M).

The molten steel may be solidified while passing through the inner space of the mold 20 to be cast into a cast iron. A solidification shell (C) may be formed from the hot water surface of the molten steel (M) inside the mold (20). The solidified shell (C) grows and thickens as it goes downward.

During casting of the cast steel, the mold flux (F) is injected into the molten steel (M). The mold flux flows between the inner surface of the mold 20 and the solidification shell C of the cast steel, and is used for lubrication and heat transfer rate control therebetween. Meanwhile, during casting, the molten steel M may be controlled so that the molten steel M is positioned at a predetermined height within the mold 20 at a predetermined height. For example, while measuring the height of the metal surface of the molten steel (M) using an eddy current level meter, the immersion nozzle 30 adjusts or cools the amount of the molten steel (M) in the immersion nozzle 30 so that the measured height of the metal surface is maintained at a predetermined level. It is possible to adjust the drawing speed of the cast iron in the base 40.

2 is a schematic diagram of a mold according to an embodiment of the present invention. 3 is a cross-sectional view of a mold according to an embodiment of the present invention. In this case, FIG. 3 is a cross-sectional view showing a cross-sectional shape of the mold by cutting the mold along line A-A' of FIG. 2.

With reference to FIGS. 2 and 3, a mold 20 according to an embodiment of the present invention will be described in detail.

The mold (20: 21, 22, 23, 24) according to an embodiment of the present invention is a mold 20 that solidifies molten steel (M), a metal body (21, 22) having an inner space, and a metal body (21). , It includes a coating layer 24 formed to surround the inner surface of 22). The coating layer 24 is spaced downward from a predetermined height H ₀ , and is formed in a lower region of the inner surfaces of the metal bodies 21 and 22.

In this case, the mold 20 may further include a cooling member 23. In addition, the coating layer 24 may include an insulating material and may have a lower thermal conductivity than the metal bodies 21 and 22. The coating layer 24 may be formed by a thermal spray coating method. When forming the coating layer 24, a heat insulating material may be used alone. Alternatively, when forming the coating layer 24, a heat insulating material and an alloy may be mixed and used.

The height of the metal surface (H ₀ ) means a predetermined height at which the meniscus of the molten steel M is located during the casting process using the mold 20. The metal surface height H ₀ may be predetermined by casting conditions including, for example, steel type, casting speed and molten steel temperature.

On the basis of the bath surface height (H _0), separate the inner surface of the mold 20, set a higher region than the bath surface height (H ₀₎ to the upper region of the mold 20, a lower area than the bath surface height (H ₀₎ It is set as the lower area of the mold 20. The height of the bath surface (H ₀ ) is determined as the interface between the upper region and the lower region of the mold 20.

The metal bodies 21 and 22 may solidify the molten steel M injected into the inner space. The metal bodies 21 and 22 may include a pair of short side plates 21 and a pair of long side plates 22. At this time, each of the pair of short side plates 21 may extend in one direction, for example, in the thickness direction of the cast pieces C and M, face each other, and may be spaced apart from each other in one direction.

A pair of long side plates 22 extend in the other direction, such as the width direction of the cast pieces (C, M), which is a direction intersecting with the pair of short side plates 21, face each other, and are spaced apart from each other in the other direction. It may be installed to connect the short side plate (21).

The inner space of the metal bodies 21 and 22 may be defined by a pair of short side plates 21 and a pair of long side plates 22. Molten steel (M) passes through the inner space of the metal body (21, 22) and can be cast into cast pieces (C, M).

Meanwhile, the inner space of the metal bodies 21 and 22 is referred to as the inner space of the mold 20. Likewise, the inner surfaces of the metal bodies 21 and 22 are referred to as the inner surfaces of the mold 20.

The structures of the metal bodies 21 and 22 may have various structures in addition to the structures described above.

The cooling member 23 may be mounted on the outer surface of the pair of long side plates 22. The cooling member 23 has a flow path therein, and may receive cooling water from the flow path. For example, the metal bodies 21 and 22 made of copper may be cooled by cooling water flowing through the flow path. The molten steel M passing through the inner spaces of the metal bodies 21 and 22 may be cooled by exchanging heat with the metal bodies 21 and 22.

A solidification shell (C) may be formed along the inner surfaces of the metal bodies (21, 22) from the hot water surface of the molten steel (M). The solidification shell (C) may grow and thicken as it goes downward. At this time, the mold flux (F) may be injected into the molten steel (M).

The mold flux F may be introduced between the inner surfaces of the metal bodies 21 and 22 and the solidification shell C of the cast pieces C and M. The mold flux (F) can be used for lubrication and heat transfer rate control between the inner surfaces of the metal bodies 21 and 22 and the solidification shell C of the cast pieces C and M.

The coating layer 24 may be formed to surround the inner surfaces of the metal bodies 21 and 22. Here, the coating layer 24 may be formed by a thermal spray coating method using a laser or flame. Specifically, the coating layer 24 may be formed by a thermal spray coating method using a thermal insulation material such as ceramic powder as a coating material, or may be formed by a thermal spray coating method using a powder mixture of ceramic powder and alloy powder as a coating material.

The coating layer 24 may be spaced downward from the height H ₀ of the hot water surface to be formed in a lower region of the inner surfaces of the metal bodies 21 and 22. The coating layer 24 may control heat transfer between the inner surfaces of the metal bodies 21 and 22 and the mold flux F. Specifically, the coating layer 24 may reduce heat transfer from the mold flux F to the metal bodies 21 and 22. Here, reducing heat transfer means reducing a heat transfer rate or heat transfer amount.

As the coating layer 24 is spaced downward from the height of the hot water surface (H ₀ ), the initial generation of the solidification shell C may be smooth. That is, when separated from the top of the coating layer 24 downward in the bath surface height (H _0), bath surface has a height (H _0), the inner surface and the mold flux (F) of the metal body (21, 22) in the can in contact. Accordingly, cooling of the mold flux (F) may be smooth, and from this, the molten steel (M) may be smoothly solidified.

That is, at the height of the hot water surface (H ₀ ), the inner surfaces of the metal bodies 21 and 22 and the hot water surface of the molten steel M can smoothly exchange heat through the mold flux (F), and the initial formation of the solidification shell (C) is It can be smooth.

From the top height to the bottom height of the coating layer 24, the inner surfaces of the metal bodies 21 and 22 and the mold flux F may contact through the coating layer 24. The coating layer 24 has a lower thermal conductivity than that of the metal bodies 21 and 22.

When the coating layer 24 contains 100% by weight of ceramic with respect to the total weight of the coating layer 24, the thermal conductivity of the coating layer 24 is about 1 W/mK. And when the material of the metal bodies 21 and 22 is copper, the metal bodies 21 and 22 have a thermal conductivity of about 400 W/mK. The lower the thermal conductivity, the more difficult the heat transfer. The greater the thermal conductivity, the easier the heat transfer.

Thus, from the top height to the bottom height of the coating layer 24, the coating layer 24 can reduce heat transfer from the mold flux F to the metal bodies 21, 22, that is, the cooling of the mold flux F. Can slow it down.

As described above, in the lower region of the inner surfaces of the metal bodies 21 and 22, the coating layer 24 may control heat transfer from the mold flux F to the metal bodies 21 and 22 while contacting the mold flux F. More specifically, the coating layer 24 may reduce heat transfer from the mold flux F to the metal bodies 21 and 22.

Heat transfer can be controlled by adjusting the thickness of the coating layer 24. To this end, the coating layer 24 may have different thicknesses at the bottom and the top in the vertical direction. For example, as the thickness of the coating layer 24 is thicker, the heat transfer rate may be slower and the heat transfer amount may be smaller. On the other hand, as the thickness of the coating layer 24 is thinner, the heat transfer speed may be faster and the heat transfer amount may be greater. Accordingly, by differently adjusting the thickness of the coating layer 24 in the vertical direction, for example, in the longitudinal direction of the cast pieces C and M, heat transfer can be controlled according to the height in the lower regions of the inner surfaces of the metal bodies 21 and 22.

Heat transfer from the mold flux F to the metal bodies 21 and 22 is referred to as heat transfer of the mold flux F. The heat transfer amount from the mold flux F to the metal bodies 21 and 22 is referred to as the heat transfer amount of the mold flux F.

The coating layer 24 may have a lower thickness thicker than an upper thickness. Accordingly, the coating layer 24 may further reduce heat transfer of the mold flux F at the lower end than at the upper end. The thickness of the coating layer 24 may gradually increase from the top to the bottom. Accordingly, the coating layer 24 may gradually and significantly lower the heat transfer of the mold flux F from the top to the bottom. That is, the heat transfer of the mold flux F may be relatively large at the top of the coating layer 24 and may be relatively small at the bottom of the coating layer 24.

The coating layer 24 may form an inclined surface with the inner surfaces of the metal bodies 21 and 22 at a predetermined angle. The cross-sectional shape of the coating layer 24 may be a right triangle or an obtuse triangle.

According to the above-described shape, the shrinkage of the cast pieces C and M from the upper region to the lower region of the mold 20 may be compensated for with a change in the thickness of the coating layer 24. Thus, it is possible to stably maintain contact between the coating layer 24 and the solidification shell (C).

That is, the coating layer 24 may have a function of controlling the heat transfer of the mold flux F and a function of compensating for the shrinkage of the cast pieces C and M in combination.

During casting of the cast pieces C and M, the temperature of the inner surfaces of the metal bodies 21 and 22 gradually decreases toward the lower side. The temperature of the mold flux F also decreases as it goes downward along the inner surfaces of the metal bodies 21 and 22. Therefore, if the thickness of the coating layer 24 is gradually increased from the top to the bottom of the coating layer 24, a decrease in the temperature of the mold flux F can be suppressed. Accordingly, it is possible to prevent the mold flux F from being supercooled in the lower regions of the inner surfaces of the metal bodies 21 and 22. Accordingly, it is possible to prevent the mold flux F from solidifying and crystallizing from a liquid phase to a solid phase.

The thickness D _b of the lower end of the coating layer 24 may be greater than 0 and less than or equal to 3 mm. The thickness of the top of the coating layer 24 may be greater than zero. More specifically, the thickness of the upper end of the coating layer 24 may be a predetermined thickness value approaching zero.

The closer the thickness (D _b ) of the lower end of the coating layer 24 is to 3 mm, the better the effect. That is, as the thickness D _b of the lower end of the coating layer 24 is thicker, cooling of the mold flux F can be suppressed, and the occurrence of defects in the cast pieces C and M can be reduced.

If the thickness (D _b ) of the lower end of the coating layer 24 exceeds 3 mm, there is a problem in that the cast pieces (C, M) cannot be cooled to the desired temperature in the inner space of the metal bodies 21 and 22, and 3 Due to the thickness of the coating layer 24 exceeding mm, there is a problem in that a pressing defect occurs in the cast pieces C and M.

The upper end of the coating layer 24 may be located at a height spaced downward from the height of the bath surface (H ₀ ). That is, the upper end of the coating layer 24 may be located between the height of the hot water surface (H ₀ ) and the lower ends of the metal bodies 21 and 22. The lower end of the coating layer 24 may be positioned at the same height as the lower end of the inner surfaces of the metal bodies 21 and 22.

The height difference H between the height of the bath surface H ₀ and the top of the coating layer 24 may be greater than 0 and within 200 mm.

If the top height of the coating layer 24 is the height of the bath surface (H ₀ ) or higher than the height of the bath surface (H ₀ ), there is a problem that the solidification shell (C) is not formed smoothly.

Preferably, the height of the top of the coating layer 24 may be 100 or less and 200 mm or less downward from the height of the hot water surface (H ₀ ). The closer the top height of the coating layer 24 is to a height spaced 200 mm downward from the height H ₀ of the hot water surface, the better the effect of the coating layer 24. That is, defects of the cast pieces C and M can be effectively reduced.

When the height of the top of the coating layer 24 deviates from 200 mm downward from the height of the hot water surface (H ₀ ), it is difficult to delay heat transfer of the mold flux F, and it is difficult to suppress the solidification of the mold flux F.

The coating layer 24 may include an insulating material. In this case, the insulating material may include ceramic. The ceramic may include Yttria-stabilized zirconia (YSZ). The yttria stabilized zirconia may contain 8% by weight of Y ₂ O ₃ and 92% by weight of ZrO _{2 based} on the total weight of the yttria stabilized zirconia. Of course, the above-described content may vary. Ceramic plays a role of controlling the heat transfer of the mold flux F while preventing the metal bodies 21 and 22 from directly contacting the mold flux F. Specifically, ceramic plays a role of lowering the heat transfer of the mold flux (F).

The coating layer 24 may include an alloy. In this case, the alloy may include a nickel chromium alloy. The nickel chromium alloy serves to protect the inner surfaces of the metal bodies 21 and 22. When the nickel chromium alloy is mixed with the heat insulating material, the nickel chromium alloy serves to adjust the ceramic content in the coating layer 24. Meanwhile, the thermal conductivity of the nickel cropped alloy may be closer to that of yttria stabilized zirconia than that of copper. Accordingly, the nickel chromium alloy in the coating layer 24 may assist the yttria-stabilized zirconia to reduce heat transfer of the mold flux (F). In addition to the nickel crop alloy, stainless steel may be used as the alloy. The insulating material and the alloy may be uniformly mixed in the coating layer 24.

The ceramic content of the coating layer 24 can be adjusted using an alloy. For example, if the alloy of the coating layer 24 is 0% by weight, the ceramic content is 100% by weight. If the alloy of the coating layer 24 is 100% by weight, the ceramic content is 0% by weight. At this time, more preferably, the coating layer 24 may include 5 to 100% by weight of ceramic and 0 to 95% by weight of an alloy based on the total weight of the coating layer 24.

If the ceramic content of the coating layer 24 is less than 5% by weight, the effect of the coating layer 24 may be somewhat small. For example, it may be difficult for the coating layer 24 to prevent the mold flux F from solidifying into a solid state in the lower regions of the inner surfaces of the metal bodies 21 and 22. As the content of ceramic in the coating layer 24 increases, the effect of the coating layer 24 increases and the heat transfer of the mold flux F decreases to prevent solidification of the mold flux F, and defects in the cast steels (C, M) occur. Can be reduced.

When the content of ceramic, that is, yttria-stabilized zirconia is 100% by weight of the total weight of the coating layer 24, the effect of the coating layer 24 for lowering the heat transfer of the mold flux F is best. The higher the ceramic content, the better the thermal insulation effect of the coating layer 24. As the ceramic content increases until the ceramic content reaches 5% by weight of the total weight of the coating layer 24, the effect of the coating layer 24 rapidly increases. Can increase.

Since the thermal conductivity of yttria-stabilized zirconia is about 1 W/mK, and the thermal conductivity of the nickel chromium alloy is about 11.6 W/mK, the thermal conductivity of yttria-stabilized zirconia is smaller.As the content of yttria-stabilized zirconia increases, the coating layer ( 24) cooling delay effect can be increased.

Meanwhile, after the ceramic content reaches 5% by weight of the total weight of the coating layer 24, the increase in the effect of the coating layer 24 may be relatively slowed as the ceramic content increases.

According to the above, the mold 20 according to the embodiment of the present invention suppresses the cooling of the mold flux F inside the mold 20 by using the coating layer 24, so that the mold flux F is liquid. It is possible to prevent the formation of an amorphous solid material on the inner surface of the mold 20 while being solidified in the solid state. Accordingly, in the casting process using the mold 20, heat transfer control and lubrication between the cast steel and the mold 20 are smoothly prevented from forming a crack on the cast steel by duty free.

4 is a diagram illustrating an internal state of a mold when casting a cast piece by a casting method according to an embodiment of the present invention. 5 is a view for explaining a heat transfer path between the mold and the cast steel when casting the cast steel by the casting method according to an embodiment of the present invention.

Hereinafter, a casting method according to an embodiment of the present invention will be described with reference to FIGS. 4 and 5.

Casting method according to an embodiment of the present invention is a casting method using the above-described casting equipment and mold 20, injecting molten steel (M) into the mold 20, and mold flux (F: The process of supplying F1, F2, F3), the process of solidifying molten steel (M) to cast the cast steel (C, M), the molten mold flux (F3) between the cast steel (C, M) and the mold (20) The inflow process and the process of contacting the molten mold flux (F3) with the coating layer 24 formed in the lower area of the inner surface of the mold 20 by being spaced downward from the height of the hot water surface (H ₀ ) of the molten steel (M). Include.

Here, the coating layer 24 may include ceramics and alloys. Specifically, the coating layer 24 may include 5 to 100% by weight of ceramic and 0 to 95% by weight of an alloy based on the total weight of the coating layer 24. Ceramics may have less thermal conductivity than alloys. In the case of an alloy such as a nickel chromium alloy, the thermal conductivity is about 11.6 W/mK. On the other hand, in the case of ceramics such as yttria stabilized zirconia, the thermal conductivity is about 1 W/mK. The alloy may have a lower thermal conductivity than the metal bodies 21 and 22 of the mold 20. The thickness d of the coating layer 24 may have different thicknesses at the top and bottom in the vertical direction. At this time, the lower end of the coating layer 24 may be thicker than the upper end. As the mold flux (F), a mold flux (F) having a melting point of 1100°C or less may be used. The mold flux (F) may not contain fluorine.

Inject molten steel (M) into the mold (20). Here, the hot water surface of the molten steel M may be controlled to maintain a predetermined hot water surface height H ₀ . The molten steel (M) is cooled by the mold (20) and begins to solidify, and a solidification shell (C) is generated downward along the inner surface of the mold (20) at the height of the hot water surface (H ₀ ). The solidified shell (C) may grow and thicken in the thickness direction of the cast pieces (C, M) while being drawn downward along the inner surface of the mold (20). At this time, the molten steel (C, M) may be in a state in which the mold flux (F) is applied to the hot water surface.

Referring to FIG. 4, the mold flux F may form three layers. Among them, the upper layer is a powdery mold flux (F1) layer, the middle layer is a sintered mold flux (F2) layer, and the lower layer is a molten mold flux (F3) layer. A slag bear may be formed on the inner surface of the mold 20 near the height H _{0 of the} hot water surface.

The molten steel (M) is solidified in the inside of the mold (20) to cast the cast steel (C, M), and the cast steel is continuously drawn downward. Along with this, the molten mold flux (F3) is introduced between the solidification shell (C) and the mold (20).

Thereafter, the molten mold flux F3 is brought into contact with the coating layer 24 formed in the lower region of the inner surface of the mold 20 by being spaced downward from the height H ₀ of the hot water surface. At this time, a process of controlling heat transfer between the mold 20 and the molten mold flux F3 using the coating layer 24 and a process of preventing solidification of the molten mold flux F3 are performed.

When the conventional mold flux solidifies, the thermal resistance index may decrease by about twice or more compared to the molten mold flux. That is, the thermal resistance index varies greatly. In addition, it is difficult to predict the amount of solidification of the mold flux and the position of the solidified mold flux during casting. For this reason, when the molten mold flux is solidified, it is difficult to control heat transfer within the mold 20. Accordingly, cracks may occur in the cast pieces (C, M) due to duty free.

On the other hand, in the embodiment of the present invention, in the process of controlling heat transfer, from the top to the bottom of the coating layer 24, the amount of heat transfer from the molten mold flux F3 to the mold 20 is reduced, and the heat transfer rate is reduced. I can make it. Thereby, it is possible to prevent the mold flux F3 melted in the mold 20 from solidifying into a solid state during casting.

5 is a view for explaining a heat transfer path between a mold and a cast steel when casting a cast steel.

5A shows a heat transfer path from molten steel to the mold when there is no coating layer inside the mold as in the prior art. In the absence of a coating layer, since the flux and the mold are in direct contact, a part of the flux may solidify into a solid state. At this time, the thickness and position of the solidified flux F4 in the mold is irregular, and it is difficult to accurately predict this. Accordingly, it is difficult to control heat transfer in the mold by the solidified flux F4.

5B shows a heat transfer path inside a mold according to an embodiment of the present invention. Since the coating layer is present on the inner surface of the mold, cooling of the flux is alleviated, and the flux can maintain a liquid phase. That is, no solid flux is generated on the inner surface of the mold. Since the thickness and thermal conductivity of the coating layer are determined and do not change, heat transfer control inside the mold can be smoothly performed by the coating layer. That is, cooling of the solidification shell (C) can be smooth, and thus, it is possible to prevent the generation of defects in the cast steel.

Experimental example

A casting process is performed using a mold according to an embodiment of the present invention. In this case, stainless steel 304 was used as the molten steel. The thickness and formation position of the coating layer in the mold were different as shown in Table 1 below. And after the casting process was finished, the surface defect of a cast steel was measured.

Top height
(mm) Top thickness
(mm) Bottom thickness
(mm) Ceramic content
(weight%) Alloy content
(weight%) Defect reduction effect Experimental Example 1 200 0.1 1.0 0 100 Small effect Experimental Example 2 200 0.1 1.0 2 98 Small effect Experimental Example 3 200 0.1 1.0 5 95 50% reduction Experimental Example 4 200 0.1 1.0 50 50 50% reduction Experimental Example 5 200 0.1 1.0 100 0 60% reduction Experimental Example 6 100 ~ 0 1.0 25 75 50% reduction Experimental Example 7 200 ~ 0 1.0 25 75 90% reduction Experimental Example 8 200 ~ 0 2.0 25 75 100% reduction Experimental Example 9 200 ~ 0 3.0 25 75 100% reduction Experimental Example 10 200 ~ 0 4.0 25 75 Small effect Experimental Example 11 300 ~ 0 1.0 25 75 Small effect

Here,'~ 0'means that the approximate value of the top thickness is 0. That is, in Experimental Examples 6 to 11, the top thickness may be close to approximately 0. The ceramic content is the content of yttria stabilized zirconia based on the total weight of the coating layer. The alloy content is the content of the nickel chromium alloy relative to the total weight of the coating layer. The defect reduction effect means the effect of reducing defects in the cast steel by the coating layer. The effect of reducing defects was quantified by cutting the cast into a predetermined unit length and checking the number of cracks with duty free of the cut cast steel.

Experimental Examples 1 to 5 show the change in the effect of reducing defects of cast steel by the coating layer when the top height, top thickness, and bottom thickness of the coating layer are the same and the ceramic content and alloy content are different.

Referring to Table 1, Experimental Example 1 is a case where the coating layer does not contain ceramics such as yttria stabilized zirconia, and at this time, it was confirmed that the effect of reducing defects of the cast steel by the coating layer was small. Comparing Experimental Example 2 and Experimental Example 3, it can be seen that when the coating layer contains 5% by weight or more of ceramic, the effect of reducing defects of the cast steel by the coating layer increases rapidly. In Experimental Examples 3 to 5, it can be seen that the effect of reducing defects of the cast steel by the coating layer is slowed after the ceramic content of the coating layer exceeds 5% by weight. Through Experimental Examples 1 to 5, it is possible to know the optimum content of the ceramic content and the alloy content of the coating layer according to the embodiment of the present invention. That is, the coating layer is most effective when it contains 100% by weight of ceramic.

Experimental Examples 6 to 11 show a change in the effect of reducing defects of cast steel by the coating layer when the ceramic content and alloy content of the coating layer are the same, and the top height and the bottom thickness of the coating layer are different. Through this, it is possible to know the optimum values of the top height and the bottom thickness of the coating layer.

In Experimental Examples 6 and 7, it can be seen that when the upper height of the coating layer is 200 mm lower than the height of the hot water surface, the effect of reducing defects of the cast steel by the coating layer is greatly increased than when the upper height of the coating layer is 100 mm lower than the height of the hot water surface. have. That is, it is more preferable that the coating layer is located somewhat lower than the height of the hot water surface. At this time, looking at Experimental Examples 7 and 11, it can be seen that when the upper height of the coating layer is lower than 200mm from the height of the hot water surface, the effect of reducing defects of the cast steel by the coating layer is rather small.

In addition, in Experimental Examples 7 to 10, it can be seen that as the thickness of the lower end of the coating layer increases, the effect of reducing defects of the cast steel by the coating layer increases significantly. At this time, looking at Experimental Examples 10 and 11, it can be seen that when the thickness of the lower end of the coating layer exceeds 3 mm, the effect of reducing defects of the cast steel by the coating layer is rather small.

In other words, the coating layer should be spaced downward from the height of the metal surface so that the solidification shell can be formed smoothly at the height of the metal surface, and cool the cast steel to an appropriate level when the cast steel exits the mold. do.

The optimum conditions for the coating layer for this are, referring to the above-described experimental examples, the top of the coating layer is located at a height 200mm apart from the height of the hot water surface, the bottom of the coating layer is located at the same height as the bottom of the mold, and the thickness of the bottom of the coating layer Is 1 to 3 mm, and the coating layer may contain 100% by weight of ceramic.

The above embodiments of the present invention are for the purpose of explanation of the present invention and are not intended to limit the present invention. It should be noted that the configurations and methods disclosed in the above embodiments of the present invention will be modified in various forms by combining or intersecting with each other, and such modified examples can also be viewed as the scope of the present invention. That is, the present invention will be implemented in a variety of different forms within the scope of the claims and the technical idea equivalent thereto, and a person in the technical field to which the present invention corresponds can various embodiments within the scope of the technical idea of the present invention. You will be able to understand.

20: mold 21: a pair of short sides
22: a pair of long side plates 24: coating layer
H ₀ : Height of the hot water surface C: Coagulation shell
F3: molten mold flux

Claims (15)

As a mold to solidify molten steel,
A metal body having an inner space; And
Including; a coating layer formed to surround the inner surface of the metal body,
The coating layer is spaced downward from the height of the metal body so as to contact the inner surface of the metal body with the mold flux inside the metal body at a predetermined height of the metal body, and is formed in a lower region of the inner surface,
The mold having a height difference between the height of the bath surface and the top of the coating layer is greater than 0 and within 200 mm. The method according to claim 1,
The coating layer is a mold having different thicknesses at the bottom and the top in the vertical direction. The method according to claim 2,
The coating layer is a mold whose thickness at the bottom is thicker than the thickness at the top. The method according to claim 2,
The coating layer is a mold whose thickness gradually decreases from the bottom to the top. The method according to claim 3 or 4,
The thickness of the lower end of the coating layer is more than 0 and 3 mm or less. delete The method according to claim 1,
The coating layer is a mold comprising an insulating material. The method of claim 7,
The heat insulating material is a mold containing yttria stabilized zirconia. The method according to claim 1 or 7,
The coating layer is a mold containing an alloy. The method of claim 9,
The alloy is a mold comprising a nickel chromium alloy. The method according to claim 1,
The coating layer is a mold containing 5 to 100% by weight of an insulating material and 0 to 95% by weight of an alloy based on the total weight of the coating layer. The method according to claim 1,
The coating layer is a mold having a lower thermal conductivity than the metal body. As a casting method,
Injecting molten steel into a mold and supplying a mold flux to the molten steel surface;
Solidifying the molten steel to cast a cast steel;
Introducing a molten mold flux between the cast and the mold;
Including; a process of contacting the molten mold flux with the coating layer formed on the lower region of the inner surface of the mold, spaced downward from the height of the molten steel,
The molten mold flux is brought into contact with the metal body of the mold at the height of the metal surface to cool the molten mold flux, thereby creating a solidification shell of the cast steel,
Casting method for reducing heat transfer from the molten mold flux to the metal body by using the coating layer from the top height to the bottom height of the coating layer. The method of claim 13,
The process of contacting the molten mold flux,
Casting method comprising; the process of preventing the solidification of the molten mold flux. The method of claim 14,
In the process of controlling the heat transfer, the amount of heat transfer from the molten mold flux to the inner surface of the mold is reduced from the top to the bottom of the coating layer,
The coating layer is a casting method comprising 5 to 100% by weight of an insulating material and 0 to 95% by weight of an alloy based on the total weight of the coating layer.

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