KR20230083055A - Method of mold and mold - Google Patents

Abstract

A method for manufacturing a mold according to an embodiment of the present invention includes a process of solidifying molten steel in a first mold, a process of detecting a solidification shrinkage (SD) generated during solidification of molten steel in the first mold for each height of the first mold, The process of preparing the design width by height for the second mold to be manufactured using the detected amount of solidification shrinkage (SD) by height, the width (W) by height of the inner wall of the second mold, the design width by height A process of preparing a second mold may be included.
Therefore, according to the embodiments of the present invention, it is possible to improve the compensation rate for the solidification shell shrinkage. That is, by manufacturing a mold by designing a width for each mold height according to different amounts of solidification shrinkage for each height, the compensation rate for the solidification shrinkage for each height is improved. Therefore, it is possible to suppress or prevent the occurrence of defects on the surface of the cast steel due to shrinkage of the solidification shell.

Description

Mold manufacturing method and mold {Method of mold and mold}

The present invention relates to a method for manufacturing a mold and a mold, and more particularly, to a method for manufacturing a mold and a mold capable of suppressing or preventing the occurrence of defects in a cast steel.

A mold for cast slab includes a pair of long side walls and a pair of short side walls. Then, molten steel is injected into the inner space partitioned by a pair of long side walls and a pair of short side walls, and the molten steel is solidified in the mold to manufacture a cast steel.

When molten steel is supplied into the mold, the solidification shell of the molten steel in the mold starts to form from the molten surface, and the thickness of the solidification shell increases downward. Then, when the molten steel is solidified inside the mold to form a solidification shell, solidification contraction occurs in the solidification shell. In particular, when the liquid molten steel is transformed into a solid phase in the upper part of the mold, a large contraction of the solidification shell occurs. In addition, the solidification shrinkage of the solidification shell is different for each height of the mold. If the mold cannot compensate for this shrinkage of the solidification shell, an air layer or gap is created between the mold and the solidification shell. When a gap is created, the heat transfer ability between the mold and the solidification shell or molten steel is reduced, resulting in a delayed solidification phenomenon, resulting in break out and defects in the cast steel.

In order to solve the problem of such solidification and shrinkage, the width of the inner wall surface of the mold is prepared to decrease toward the bottom. At this time, the amount or rate of decrease of the width of the inner wall of the mold toward the bottom is kept constant. However, even in this case, the shrinkage of the solidification shell cannot be sufficiently compensated for, and a gap is still created between the mold and the solidification shell. This is because the solidification shrinkage decreases from the top to the bottom of the mold, but the solidification shrinkage does not decrease at a constant rate. That is, as the width of the inner wall surface decreases toward the bottom at a constant rate of decrease, the different solidification shrinkage amount for each height cannot be sufficiently compensated.

Korea Patent Registration 10-1060114

The present invention provides a method for manufacturing a mold and a mold capable of effectively compensating for the solidification shrinkage of a solidification shell by height.

The present invention provides a mold manufacturing method and mold capable of improving the compensation rate for shrinkage of the solidification shell.

A method for manufacturing a mold according to an embodiment of the present invention includes the steps of solidifying molten steel in a first mold; detecting a solidification shrinkage (SD) generated during solidification of the molten steel in the first mold for each height of the first mold; preparing a design width for each height of a second mold to be manufactured using the detected amount of solidification shrinkage (SD) for each height; A process of preparing a second mold such that the width W of the inner wall of the second mold by height corresponds to the design width by height.

The process of detecting the solidification shrinkage (SD) for each height of the first mold is a plurality of design points (DP) having different heights below the molten steel molten steel surface height (P _M ) on the inner wall surface of the first mold the process of setting up; Detecting a solidification width (SW) by detecting a length between both ends in the width direction of the solidification shell formed by solidification of molten steel at each of the plurality of design points (DP) set in the first mold; And the plurality of designs by subtracting the solidification width (SW) detected at each of the plurality of design points (DP) from the width (W _M ) at the molten surface height (P _M ) on the inner wall surface of the first mold. A process of calculating the solidification shrinkage (SD) at each point (DP); may include.

In setting the plurality of design points DP in the first mold, the distance between the plurality of design points DP may be set to increase downwardly.

In setting the plurality of design points DP in the first mold, the distance between the plurality of design points DP may be set to increase to a constant value.

The plurality of design points (DP) set in the first mold include first to fourth design points (DP ₁ to DP ₄ ), which are points sequentially away from the lower side of the molten surface height (P _M ), The distance (G ₁ ) between the bath surface height (P _M ) and the first design point (DP ₁ ), the distance (G 2 ) _between the first design point (DP ₁ ) and the second design point (DP ₂ ), The distance ₍ G 3 ) between the second design point (DP ₂ ) and the third design point (DP ₃ ), and the distance (G ₄ ) between the third design point (DP ₃ ) and the fourth design point (DP ₄ ). ), it is preferable to adjust so as to increase at a constant rate from the first interval (G ₁ ) to the fourth interval (G ₄ ).

The process of preparing the design width for each height may include setting a plurality of points (P) at the same position as the plurality of design points (DP) set in the first mold on an inner wall surface of the second mold; Process of subtracting (W M - SD) the solidification shrinkage (SD) for each of the plurality _of design points (DP) from the width (W _M ) of the inner wall surface at the molten surface height (P _M ) in the first mold ; Determining the subtraction value (W _M - SD) at each of the plurality of design points (DP) as the width (W) at each of the plurality of points (P) set on the inner wall surface of the second mold; can include

In preparing the second mold, the height of the second mold, the width of the top end, and the width at the preset height of the molten steel bath surface may be designed to be the same as the height of the first mold, the width of the top end, and the height of the molten steel bath surface. .

A step of preparing the first mold, wherein the step of preparing the first mold is such that the width of the inner wall surface decreases downward and the rate of decrease of the width of the inner wall surface is uniform in the height direction. can include

The process of detecting the solidification shrinkage (SD) at each of the plurality of design points (DP) is to supply and solidify the first molten steel to the first mold, and the first molten steel at the plurality of design points (DP) Detecting the amount of coagulation shrinkage (1SD) of; supplying and solidifying the second molten steel to the first mold, and detecting a solidification shrinkage (2SD) of the second molten steel at the plurality of design points (DP); Calculating an average solidification shrinkage (AS) of the solidification shrinkage (1SD) of the first molten steel and the solidification shrinkage (SSD) of the second molten steel for each of the plurality of design points (DP); In subtracting the solidification shrinkage (SD) for each of the plurality of design points (DP) from the width (W _M ) of the inner wall surface at the molten surface height (P _M ) of (W _M - SD), the plurality of design points The solidification shrinkage (SD) for each (DP) may be the average solidification shrinkage (AS) for each of the plurality of design points (DP).

The process of selecting the first and second molten steels may include a process of supplying and solidifying a plurality of types of molten steel to the first mold; detecting the amount of solidification shrinkage generated during solidification of each of the plural types of molten steel; and selecting the molten steel having the largest amount of solidification shrinkage among the detected amounts of solidification shrinkage as the first molten steel and selecting the molten steel having the smallest amount of solidification shrinkage as the second molten steel.

The process of detecting the amount of solidification shrinkage generated during solidification of each of the plurality of types of molten steel may include a process of detecting the amount of solidification shrinkage at the molten steel surface height (P _M ) of the first mold.

Embodiments of the present invention are a mold having an inner space into which molten steel can be injected, including a body having the inner space, a plurality of points having different heights are set on an inner wall surface of the body, The width at each of the plurality of points on the inner wall surface decreases toward the bottom, and a rate of decrease of the width may be changed at a plurality of points in the height direction.

Intervals in the height direction between the plurality of points may be different from each other.

Intervals in a height direction between the plurality of points may increase downward.

Intervals in a height direction between the plurality of points may increase to a constant value.

The plurality of points include first to fourth points, which are points that sequentially move away from the lower side of the molten steel molten steel surface height supplied into the body, and the distance between the molten steel surface height and the first point (G ₁ ), the first In the interval between the first and second points (G ₂ ), the interval between the second and third points (G ₃ ), and the interval between the third and fourth points (G ₄ ), the first It is preferable that it increases at a constant rate from the interval G ₁ to the fourth interval G ₄ .

The inner wall surface of the body is provided with an inclined surface that moves away from the outer wall surface opposite to the inner wall surface toward the bottom, and the inclination slope of the inner wall surface of the body may be changed using the plurality of points as inflection points.

An inclination of the inclination of the inner wall surface of the body may decrease toward the bottom.

The width at each of the plurality of points may be designed by solidifying molten steel using a designing parent mold for designing the mold, and using the obtained solidification shrinkage by height.

According to the embodiments of the present invention, it is possible to improve the compensation rate for the solidification shell shrinkage. That is, by manufacturing a mold by designing a width for each mold height according to different amounts of solidification shrinkage for each height, the compensation rate for the solidification shrinkage for each height is improved. Therefore, it is possible to suppress or prevent the occurrence of defects on the surface of the cast steel due to shrinkage of the solidification shell.

And, in manufacturing the mold, a plurality of types of molten steel were solidified to detect the solidification shrinkage rate, and the average value of the solidification shrinkage rate was reflected to design the width by height of the inner wall surface of the mold. Therefore, it is possible to manufacture a cast steel in which the solidification shrinkage rate is suppressed or prevented for a plurality of types of steel.

1 is a view showing a casting apparatus including a mold according to an embodiment of the present invention.
2 is a three-dimensional view showing a mold according to an embodiment of the present invention.
3 is an exploded perspective view of a mold according to an embodiment of the present invention.
Figure 4 (a) is a front view of the mold according to an embodiment of the present invention, as seen from the 'A' side of Figure 2, in order to explain the width by height of the inner wall surface of the first wall.
Figure 4 (b) is a front view as seen from the 'B' side of Figure 2 in order to explain the inclination by height with respect to the inner wall surface of the first wall in the mold according to an embodiment of the present invention, a pair of It is a drawing showing only one of the walls.
Figure 5 (a) is a front view of the mold according to an embodiment of the present invention, as seen from the 'B' side of Figure 2, in order to explain the width by height of the inner wall surface of the second wall.
Figure 5 (b) is a front view as seen from the 'A' side of Figure 2, in order to explain the inclination by height with respect to the inner wall surface of the second wall in the mold according to an embodiment of the present invention, a pair of This is a drawing showing only one of the two walls.
6 is an exploded perspective view showing a part of a parent mold used to manufacture a mold according to an embodiment of the present invention.
7 is a view for explaining the amount of shrinkage of the solidification shell for each height during solidification of molten steel in the mother mold.
8 is a flow chart showing a method for manufacturing a mold according to an embodiment of the present invention.
9 is a graph showing solidification shrinkage and average shrinkage in the first direction for each height of the mother mold when the first molten steel and the second molten steel are charged into the mother mold and solidified.
10 (a), (c), (e), (g), (i) are photographs of the surface of the billet according to the first to fifth experimental examples.
10 (b), (d), (f), (h), and (j) are graphs showing the roughness (mm) of the surface of the billet, that is, the height (mm) of the surface in the first to fifth experimental examples. .

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, only these embodiments will complete the disclosure of the present invention, and will fully cover the scope of the invention to those skilled in the art. It is provided to inform you. In order to explain the embodiments of the present invention, the drawings may be exaggerated, and the same reference numerals in the drawings refer to the same components.

1 is a view showing a casting apparatus including a mold according to an embodiment of the present invention.

Referring to FIG. 1, the casting apparatus includes a tundish 20 that receives and stores molten steel from a ladle 10, a mold 3000 that receives molten steel from the tundish 20 and initially solidifies it into a predetermined shape, A nozzle 22 for supplying molten steel from the tundish 20 to the mold 3000 is included.

In addition, the casting apparatus is installed on the lower side of the mold 3000, and includes a cooling unit 40 for completely solidifying by spraying cooling water to the unsolidified slab 1 drawn from the mold 3000. Here, the cooling unit 40 includes a plurality of segments 41 . In addition, each of the plurality of segments 41 may be a means having a plurality of rolls rotatable by the force of moving the cast steel 1 and a nozzle positioned between the plurality of rolls to spray cooling water to the cast steel 1. .

Hereinafter, with reference to Figs. 2 to 5, the mold in the embodiment of the present invention will be described. The mold according to the embodiment may be for casting a billet slab. Also, the mold may be for casting a billet of low carbon steel, medium carbon steel, or high carbon steel.

Of course, the mold 3000 may be for manufacturing cast steel of various types of steel other than the above-described low carbon steel, medium carbon steel, and high carbon steel. In addition, it may be a mold for manufacturing various cast pieces, such as slabs and blooms, in addition to billets.

2 is a three-dimensional view showing a mold according to an embodiment of the present invention. 3 is an exploded perspective view of a mold according to an embodiment of the present invention. Figure 4 (a) is a front view of the mold according to an embodiment of the present invention, as seen from the 'A' side of Figure 2, in order to explain the width by height of the inner wall surface of the first wall. Figure 4 (b) is a front view as seen from the 'B' side of Figure 2 in order to explain the inclination by height with respect to the inner wall surface of the first wall in the mold according to an embodiment of the present invention, a pair of It is a drawing showing only one of the walls. Figure 5 (a) is a front view of the mold according to an embodiment of the present invention, as seen from the 'B' side of Figure 2, in order to explain the width by height of the inner wall surface of the second wall. Figure 5 (b) is a front view as seen from the 'A' side of Figure 2, in order to explain the inclination by height with respect to the inner wall surface of the second wall in the mold according to an embodiment of the present invention, a pair of This is a drawing showing only one of the two walls.

Referring to FIG. 2 , a mold 3000 includes a body 3100 having an inner space IS. In addition, the mold 3000 may include a cooling water passage (not shown) installed buried inside the body 3100 so that the cooling water circulates.

Referring to FIG. 3, the body 3100 is an inner wall surface (IF: IF _L , IF _S ) facing the inner space (IS) and a surface opposite to the inner wall surface (IF: IF _L , IF _S ) and is exposed to the outside. It includes an outer wall surface (OF: OF _L , OF _S ), which is a surface.

As shown in FIG. 3 , the body 3100 is provided so that the widths (W: W _L , W _S ) of the inner wall surfaces (IF: IF _L , IF _S ) decrease toward the bottom. At this time, four or more points of different heights are set on the upper surface of the molten steel supplied to the inside of the body 3100, that is, below the molten metal height P _M , and the widths at each of the plurality of points are different. do.

Here, the width (W: W _L , W _S ) of the inner wall surface (IF: IF _L , IF _S ) may mean the length in the horizontal direction. More specifically, the widths (W: W _L , W _S ) of the inner wall surfaces (IF: IF _L , IF _S ) mean the length in the first direction (X-axis direction) and the length in the second direction (Y-axis direction). can do.

Hereinafter, in describing the mold 3000 according to the embodiment, a plurality of points set to four will be described as an example. In addition, it is assumed that the first point (P ₁ ), the second point (P ₂ ), the third point (P ₃ ), and the fourth point (P ₄ ) are set below the molten surface height (P _M ) in this order.

In setting the first to fourth points P ₁ to P ₄ , the distance between the first to fourth points P ₁ to P ₄ is set to decrease toward the upper side and increase toward the lower side. . That is, in setting the first to fourth points (P ₁ to P ₄ ), the distance between them and the point located immediately above is reduced toward the top. In other words, the distance from the point located right above increases downward. That is, the distance (G ₁ ) between the molten surface height (P _M ) and the first point (P ₁ ) is the shortest, and the distance (G 4 ) between _the fourth point (P ₄ ) and the third point (P ₃ ) is the longest In other words, the distance from the point immediately above is 'the distance between the first point (P ₁ ) and the height of the water surface (P _M ) (G ₁ ) < the distance between the second point (P ₂ ) and the first point (P ₁ ) (G ₂ ) < Distance between point 3 (P ₃ ) and point 2 (P ₂ ) (G ₃ ) < Distance between point 4 (P ₄ ) and point 3 (P ₃ ) (G ₄ ) ' It is in order.

The width of the inner wall surface IF of the body 3100 decreases toward the bottom. At this time _, the width ₍ W: W _L , W _S ) is provided to have a designed width by a method according to an embodiment described later.

When the widths (W: W _L , W _S ) of the inner wall surfaces (IF: IF _L , IF _S ) decrease downward, the decreasing rate of the width decreases at a plurality of points (P ₁ to P ₄ ) in the height direction. prepared to change That is, the widths (W: W _L , W _S ) of the inner wall surfaces (IF: IF _L , IF _S ) decrease toward the lower side, and the widths (W: W _L , W _S ) of the inner wall surfaces (IF: IF L , IF _S ) W _S ) is provided so that the decreasing rate is not uniform and different in the height direction. At this time, the width decreasing rate in the area from the upper end _PU to the first point P ₁ is constant, and the width decreasing rate in the area from the first point P ₁ to the second point P ₂ is constant, , the width reduction rate is constant in the region from the second point (P ₂ ) to the third point (P ₃ ), and the width reduction rate in the region from the third point (P ₃ ) to the fourth point (P ₄ ) is constant. can

And, as the widths (W: W _L , W _S ) of the inner wall surfaces (IF: IF _L , IF _S ) decrease toward the bottom, the width of the upper end (P _U ) and the width of the first point (P ₁ ) ( W _L1 , W _S1 ) are provided so that the difference in width is the largest. At this time, as described above, since the width reduction rate in the region from the upper end _PU to the first point P ₁ is constant, the point of the bath surface height P _M , the first to fourth points P ₁ to P ₄ ), the difference between the width (W _LM, W _SM ) of the molten surface height (P _M ) and the width (W _L1 , W _S1 ) of the first point (P ₁ ) is the largest. That is, the difference between the widths W _L1 and W _S1 of the first point P ₁ and the widths W _L2 and W _S2 of the second point P ₂ , the width W _L2 of the second point P ₂ , W _S2 ) and the difference between the widths (W _L3 , W _S3 ) of the third point (P ₃ ), the width (W _L3 , W _S3 ) of the third point (P ₃ ) and the width of the fourth point (P ₄ ) Compared to the difference between (W _L4 , W _S4 ), the difference between the width (W _LM, W _SM ) of the bath surface height (P _M ) and the width (W _L1 , W _S1 ) of the first point (P ₁ ) is prepared to be large do.

Accordingly, in the following section of the molten surface height (P _M ), the section where the most rapid change in width occurs is the section between the molten surface height (P _M ) and the first point (P ₁ ). As such, _the distance (G 1 ) between the first point (P ₁ ) and the molten metal surface height (P _M ) immediately above the first point (P ₁ ) is the shortest, and the width (W _{LM ,} Since the difference between W _SM ) and the width (W _L1 , W _S1 ) of the first point (P ₁ ) is the largest, when the width changes from the bath surface height (P _M ) to the first point (P ₁ ), the most abrupt It changes.

In this way, the difference between the widths (W _LM, W _SM ) at the molten surface height (P _M ) and the widths (W _L1 , W _S1 ) at the first point (P ₁ ) is the largest, inside the body 3100 This is because the closer the solidification shell is to the molten surface, the greater the shrinkage of the solidification shell. That is, by rapidly changing the widths (W _LM, W _SM ) at the height of the molten metal surface (P _M ) and the widths (W _L1 , W _S1 ) at the first point (P ₁ ), the upper region close to the molten surface inside the body It is possible to improve the coagulation shrinkage compensation rate in

In addition, as described above, the rate at which the widths (W: W _L , W _S ) of the inner wall surfaces (IF: IF _L , IF _S ) decrease is not uniform but different in the height direction. That is, the difference between the width (W _M : W _LM , W _SM ) at the bath surface height (P M ) and the width (W _L1 , W _S1 ) at the first point ( _{P 1} ), the width of the first point (P ₁ ) The difference between (W _L1 , W _S1 ) and the width (W _L2 , W _S2 ) of the second point (P ₂ ), the width (W _L2 , W _S2 ) of the second point (P ₂ ) and the third point (P ₃ ), the difference between the widths (W _L3 , W _S3 ) of the third point (P ₃ ) and the difference between the widths (W _L3 , W _S3 ) of the fourth point (P ₄ ) (W _L4 , W _S4 ) may be arranged differently. This is because the amount of shrinkage of the solidification shell may vary depending on the height of the mold 3000 when the solidification shell shrinks as the molten steel solidifies.

As such, since the amount of shrinkage of the solidified shell is different depending on the position of the height of the mold 3000, in the embodiment, the width of the inner wall surface (IF: IF _L , IF _S ) of the body 3100 is used by using the amount of shrinkage of the solidified shell according to the height of the mold. (W: W _L , W _S ) is designed to manufacture a mold. That is, after separately preparing a mold for design (hereinafter, a mother mold), a plurality of points of at least four or more are set below the molten metal surface height (P _M ) of the mother mold. And, after detecting the amount of solidification shrinkage at each of a plurality of points, the mold 3000 is manufactured by designing the width at each point according to the amount of solidification shrinkage at each point.

Designing or determining the width (W: W L , W _{S ) of the inner wall surface (IF: IF L , IF S ) of the} mold 3000 to be manufactured, that is, the body 3100, according to the amount of solidification shrinkage by height in the parent mold The method will be described in detail with reference to FIGS. 6 and 7 hereinafter.

Hereinafter, the body 3100 as described above will be described as being composed of a plurality of walls.

The body 3100 includes a plurality of walls 3110 and 3120. That is, referring to FIG. 2 , the body 3100 includes a pair of first walls 3110 each extending in a first direction (X-axis direction) and spaced apart in a second direction (Y-axis direction). It extends in a second direction (Y-axis direction) intersecting with the extension direction of the first wall 3110 and includes a pair of second walls 3120 spaced apart in the first direction (X-axis direction). can

Also, the pair of first walls 3110 and the pair of second walls 3120 are interconnected. For example, one end of the pair of first walls 3110 is connected to one end and the other end of the pair of second walls 3120, and one end and the other end of the other second wall 3120 are connected. The other end of the first wall 3110 is connected. Accordingly, an inner space IS surrounded by a pair of first walls 3110 and a pair of second walls 3120 is provided.

Therefore, the inner wall surface IF of the body 3100 described above is the inner wall surface of the pair of first walls 3110 (hereinafter, the first inner wall surface IF _L ) and the pair of second walls 3120. It can be described as including an inner wall surface (hereinafter, a second inner wall surface IF _S ) of. In addition, the outer wall surfaces OF of the body 3100 are the outer wall surfaces of the pair of first walls 3110 (hereinafter, the first outer wall surfaces OF _L ) and the outer wall surfaces of the pair of second walls 3120. (Hereinafter, it can be described as including the second outer wall surface (OF _S )).

Therefore, as shown in (a) of FIGS. 3 and 4 , the length in the first direction (X-axis direction) of the first inner wall surface IF _L of the first wall 3110 is the length of the first inner wall surface IF _L . It is defined by the width (W _L : W _LM , W _L1 , W _L2 , W _L3 , W _L4 ). In addition, as shown in (a) of FIGS. 3 and 5, the length in the second direction (Y-axis direction) of the second inner wall surface IF _S of the second wall 3120 is the length of the second inner wall surface IF _S It is defined as width (W _S : W _SM , W _S1 , W _S2 , W _S3 , W _S4 ).

Further, in the horizontal direction of each of the first wall 3110 and the second wall 3120, a length crossing the width direction is defined as 'thickness'. Accordingly, the thickness (T _L : T _LM , T _{L1 ,} T _L2 , T _L3 , T _L4 ) of the first wall 3110 is the length in the second direction (Y-axis direction) (see FIG. 4(b)) , the thickness of the second wall 3120 ( _TS : T _SM , T _{S1 ,} T _S2 , T _S3 , T _S4 ) is the length in the first direction (X-axis direction) (see (b) of FIG. 5).

In this way, although the body 3100 has been described as being composed of a pair of first walls 3110 and a pair of second walls 3120, a pair of first walls 3110 and a pair of second walls (3120) may be provided integrally. That is, the pair of first walls 3110 and the pair of second walls 3120 may not be coupled using a separate coupling means, but may be integrally manufactured by a method such as compression molding. A mold including such a body 3100 is called a 'tube type mold'.

Of course, the body 3100 may be provided by coupling the first wall 3110 and the second wall 3120 through separate coupling means.

As shown in FIG. 3, the body 3100 is provided so that the width is different for each position or height in the height direction (Z-axis direction), and the width (W: W _L , W _S ) decreases toward the bottom. arranged to do Hereinafter, the first inner wall surface IF _L of the first wall 3110 and the second inner wall surface IF _S of the second wall 3120 will be described in more detail.

As shown in (a) of FIGS. 3 and 4 , the first inner wall surface IF _L of the first wall 3110 is provided so that its width decreases toward the bottom. At this time, the first inner wall surface (IF _L ) is provided to have different widths at different positions in the height direction, and is provided to have different widths at at least four different points below the bath surface height (P _M ). For example, the widths (W _L1 , W L2 ) at the first to fourth points (P ₁ to P _{4 )} , which are four positions of different heights, on the lower side of the bath surface height (P _M ) of the first inner wall surface (IF _{L )} , W _L3 , W _L4 ) are provided to be different. At this time, the widths (W _L1 to W _L4 ) at the first to fourth points (P ₁ to P ₄ ) are compared to the width (P _LM ) at the molten surface height (P _M ) at the first inner wall surface (IF _L ) small.

Also, the second inner wall surface IF _S of the second wall 3110 is provided in the same shape as the first inner wall surface IF _L described above. That is, the second inner wall surface IF _S of the second wall 3110 is provided such that its width decreases toward the lower side, and the same position on the first inner wall surface IF _L , that is, the first to fourth points ( P ₁ to The widths (W _S1 , W _S2 , W _S3 , and W _S4 ) at P ₄ are provided to be different. At this time, the widths (W _S1 to W _S4 ) at the first to fourth points (P ₁ to P ₄ ) are compared to the width (P _SM ) at the molten surface height (P _M ) at the second inner wall surface (IF _S ) small.

The first to fourth points P 1 to ₄ on the first inner wall surface IF _{L .} P ₄ ) and the first to fourth points P 1 to ₄ on the second inner wall surface IF _S . P ₄ ) is a point of equal height. And the first to fourth points P 1 to ₄ on the first and second inner wall surfaces IF _L and IF _S , respectively. P ₄ ) is determined based on the height (P _m ) of the molten steel molten steel surface charged into the body 3100 .

The height (P _M ) of the molten steel molten steel surface may be the height of a point spaced apart by a predetermined distance downward from the upper end (P _U ) of the body 3100 . For example, when the molten steel is charged so that the molten steel molten steel is located at a point 100 mm away from the upper end _PU of the body 3100 downward, from the lower end P _B of the body 3100 to the molten steel molten steel surface is the height of the bath surface. At this time, when the position of the top (P _U ) of the body 3100 is Omm and the height (P _M ) of the tungsten surface is described based on the top (P _U ) of the body 3100, the height (P _M ) of the tungsten surface is at the 100mm point becomes

And, the first point (P ₁ ) of the first and second walls 3110 and 3120 is a point spaced downward from the upper end (P _U ) by a first distance (S ₁ ), and the second point (P ₂ ) is It is a point spaced from the upper end (P _U ) to the lower side by a second distance (S ₂ ) greater than the first distance (S ₁ ). In addition, the third point (P ₃ ) is a point spaced from the upper end (P _U ) to the lower side by a larger third distance (S ₃ ) than the second distance (S ₂ ), and the fourth point (P ₃ ) is It is a point spaced from the upper end (P _U ) to the lower side by a fourth distance (S ₄ ) greater than the third distance (S ₃ ).

The section from the molten surface height (P _M ) to the lower end (P _B ) is divided into a plurality of sections in the height direction. At this time, in the upper and lower molten metal surface height (P _M ) and the first to fourth points (P ₁ to P ₄ ), the distance between points disposed adjacent to each other increases downward. That is, the first interval (G ₁ ) between the bath surface height (P _M ) and the first point (P ₁ ), the second interval (G 2 ) between the first point (P ₁ ) and the second point (P ₁₂ ), the _second In the third interval (G 3 ) between the second point (P ₂ ) and the third point (P ₃ ) and the fourth interval (G 4 ) between the third _point (P ₃ ) and the fourth point (P _{4 )} , The first interval (G ₁ ) is the smallest and the fourth interval (G ₄ ) is the largest. At this time, the distance (G ₁ ) between the molten surface height (P _M ) and the first point (P ₁ ), and the distance (G ₂ to G 4 ) between the first to fourth points (P ₁ to P _{4 )} are constant values can be increased to Preferably, the ratio of the first to fourth intervals (G ₁ to G ₄ ) is 1: 2: 3: 4 (G ₁ : G ₂ : G ₃ : G ₄ = 1 : 2 : 3 : 4), The first to fourth points (P ₁ to P ₄ ) are set.

For example, if the height (P _M ) of the bath surface is a point 100 mm apart from the top (P _U ) downward, the length from the height (P _M ) (100 mm point) to the bottom (P _B ) is divided However, the ratio of the first to fourth intervals (G ₁ to G ₄ ) is 1: 2: 3: 4 (G ₁ : G ₂ : G ₃ : G ₄ = 1 : 2 : 3 : 4). .

At this time, since the first point (P ₁ ) is a point spaced downward from the molten surface height (P _m ) by the first interval (G ₁ ), the position of the first point (P ₁ ) is limited to the molten surface height (P _m ) It can be described as the sum of 1 interval (G ₁ ). In addition, since the second point P ₂ is a point spaced downward from the first point P ₁ by the second distance G ₂ , the position of the second point P ₂ is equal to the first point P ₁ . It can be described as a value obtained by adding the second interval G ₂ to . Similarly, the position of the third point (P ₃ ) is the value obtained by adding the third interval (G ₃ ) to the second point (P ₂ ), and the position of the fourth point (P ₄ ) is at the third point (P ₃ ). It can be described as a value obtained by summing the fourth interval G ₄ . In this case, the position of the fourth point P ₄ may be the lower end P _B of the body.

By setting the positions of the first to fourth points (P ₁ to P ₄ ) in this way, the distance between them and the immediately upper point is shorter toward the top. That is, the order is 'first interval G1 < second interval G2 < third interval G3 < fourth interval G4'.

In each of the first and second inner wall surfaces IF _L and IF _S , the width at the first to fourth points P ₁ to P ₄ , that is, the first to fourth widths W _L1 to W _L4 ( W _S1 to W _S4 ) are different. At this time, the width decreases from the first point P ₁ to the fourth point P ₄ . That is, the second widths W _L2 and W _S2 are smaller than the first widths W _L1 and W _S1 , and the third widths W _L3 and W _S3 are smaller than the second widths W _L2 and W _S2 . and the fourth widths W _L4 and W _S4 are smaller than the third widths W _L3 and W _S3 .

As such, each of the first and second inner wall surfaces IF _L and IF _S is provided so that the width decreases toward the bottom, thereby causing contraction in the first direction (X-axis direction) and contraction in the second direction (Y-axis direction) of the solidification shell. Shrinkage can be compensated for. That is, by providing the widths (W _L1 , W _L2 , W _L3 , W _L4 ) of the first inner wall surface (IF _L ) decrease toward the bottom, shrinkage of the solidification shell in the first direction (X-axis direction) can be compensated for. can In addition, the widths (W _S1 , W _S2 , W _S3 , W _S4 ) of the second inner wall surface (IF _S ) are provided so as to decrease toward the bottom, thereby compensating for shrinkage of the solidification shell in the second direction (Y-axis direction). can

In addition, when the widths of the first and second inner wall surfaces IF _L and IF _S decrease downward, the rate of decrease in the width of the inner wall surfaces IF _L and IF _S is not uniform or constant in the height direction. arranged to be different. At this time, the rate at which the width decreases is provided to be changed at first to fourth points P ₁ to P ₄ in the height direction.

Here, the reduction rate of the width can be calculated using the width difference at each of the two adjacent points and the interval between the adjacent points (see Equation 1).

[Formula 1]

A more specific example of the reduction rate will be described. At this time, the rate of decrease in width between the molten surface height P _M and the first point P ₁ will be described as an example. For this purpose, the following assumptions are made. The total height of the body 3100 or the first wall 3110 is 1000 mm, the distance (G ₁ ) between the first point (P ₁ ) and the molten surface height (P _M ) is 210 mm, and the width of the molten surface height (P _M ) It is assumed that the width W _L1 of this 200 mm and the first point P ₁ is 199 mm. In this case, the width decrease rate between the molten metal surface height P _M and the first point P ₁ may be calculated as in Equation 1 below.

[Calculation 1]

And, the width reduction rate between the first point (P ₁ ) and the second point (P ₂ ), the width reduction rate between the second point (P ₂ ) and the third point (P _{3 ), the third point (P 3} ) and the fourth point (P ₃ ). A width reduction rate between points P ₄ may also be calculated in the same way as the above-described method.

Also, the rate of decrease in width of the second inner wall surface IF _S of the second wall 3120 is calculated in the same manner as the rate of decrease in width of the first inner wall surface IF _S described above. Therefore, a detailed description thereof will be omitted.

As such, when the widths of the first and second inner wall surfaces IF _L and IF _S decrease downward, the rate at which the widths of the inner wall surfaces IF _L and IF _S decrease is not uniform or constant in the height direction. arranged to be different.

In addition, in the difference in width from the point immediately above, the difference between the width (W _LM, W _SM ) of the bath surface height (P _M ) and the width (W _L1 , W _S1 ) of the first point (P ₁ ) is the largest, , the difference between the widths W _L3 and W _S3 of the third point P ₃ and the widths W _L4 and W _S4 of the fourth point P ₄ is minimized. Accordingly, the width change is most steep in the section between the molten surface height (P _M ) and the first point (P ₁ ), and the width change is the most rapid in the section between the third point (P ₃ ) and the fourth point (P ₁₄ ). the most gentle

In this way, the change in width in the section between the molten surface height (P _M ) and the first point (P ₁ ) is made more rapid than in other sections, thereby solidifying at the upper part of the body 3100 where the solidification shell contracts the most. Shrinkage can be effectively compensated. More specifically, the solidification shell shrinks the most at the height adjacent to the molten surface at the upper part of the body 3100, and the solidification shrinkage in this section can be effectively compensated.

The widths (W _L1 to W _L4 ) (W _S1 to W _S4 ) at each of the first to fourth points (P ₁ to P ₄ ) are designed according to the amount of solidification shrinkage of the solidification shell at the first to fourth points of the parent mold. is the width In other words, the first width (W _L1 , W _S1 ) at the first point (P ₁ ), the second width (W _L2 , W _S2 ) at the second point (P ₁ ), the third point ( The third width (W _L3 , W _S3 ) at the P ₁ ) and the fourth width (W _L4 , W _S4 ) at the fourth point (P ₁ ), respectively, are at each of the first to fourth points of the parent mold. It is designed using the amount of solidification shrinkage.

In this way, the shrinkage of the solidified shell according to the height can be effectively compensated by the widths W _L1 to W _L4 (W _S1 to W _S4 ) adjusted according to the heights of the inner wall surfaces IF _L and IF _S . That is, in the case of the conventional mold, although the width of each of the first and second inner wall surfaces is provided to decrease toward the bottom, the rate of decrease in width is constant or the same. In other words, the width is reduced at a constant rate regardless of the amount of shrinkage for each position in the height direction. In this case, the tendency for the solidification shrinkage to decrease toward the bottom can be compensated in response, but since the tendency to decrease the solidification shrinkage toward the bottom does not decrease at a uniform rate, compensation for different solidification shrinkage for each height is not necessary. It was lacking. Accordingly, a large amount of surface defects due to solidification shrinkage are generated on the surface of a cast steel, for example, a billet.

However, in the case of the embodiment, since the widths (W _L1 to W _L4 ) (W _S1 to W _S4 ) for each height of the inner wall surface (IF _L , IF _S ) were adjusted according to the different amount of solidification shrinkage for each height, the shrinkage of the coagulation shell was reduced. can be effectively compensated. In addition, since the widths (W _L1 to W _L4 ) (W _S1 to W _S4 ) of the inner wall surfaces (IF _L , IF _S ) are designed by reflecting the actual amount of solidification shrinkage by height, the solidification shrinkage by height can be more effectively compensated. there is. Accordingly, it is possible to minimize or prevent the occurrence of defects due to solidification shrinkage on the surface of the cast steel.

In addition, each of the first and second inner wall surfaces IF _L and IF _S of the body 3100 are provided as inclined surfaces so as to be farther away from the outer wall surfaces OF _L and OF _S toward the bottom. In other words, the body 3100 is provided such that its thickness increases toward the bottom. More specifically, each of the first and second inner wall surfaces IF _L and IF _S may be provided with an inclination of 4 steps or more, as shown in FIGS. 4(b) and 5(b) . . That is, each of the first and second inner wall surfaces IF _L and IF _S inclines downwardly away from the outer wall surfaces OF _L and OF _S , and at this time, the inclination may be changed four or more times.

More specifically, each of the first and second inner wall surfaces IF _L and IF _S has at least the first to third points P ₁ to P ₃ as inflection points, and the first to fourth inclined surfaces change in inclination. (F _L1 to F _L4 ) (F _S1 to F _S4 ). That is, the first and second inner wall surfaces IF _L and IF _S are gradually moving from the upper end _PU to the first point P ₁ , as shown in FIG. 4(b) and FIG. 5(b) . The outer wall surfaces (OF _L , OF _S ) and the first inclined surfaces (F _L1 , F _S1 ) moving away from each other with the first slope, and the outer wall surfaces (OF _L , OF from the first point P ₁ to the second point P ₂ ) _S ) and the second slope (F _L2 , F _S2 ), which move away from the second slope, and the outer wall surface (OF _L , OF _S ) and the third slope from the second point (P ₂ ) to the third point (P ₃ ). The third slope (F _L3 , F _S3 ), the fourth slope (F _L4 ), _which moves away from the outer wall surface (OF _L , OF _S ) with a fourth slope from the third point (P 3 ) to the fourth point (P ₄ ) , F _S4 ).

Also, the first to fourth inclined surfaces F _L1 to F _L4 ( F _S1 to F _S4 ) are provided to have different inclinations. That is, the first to fourth slopes are different from each other, and the relationship between the sizes is in the order of 'first slope > second slope > third slope > fourth slope.

In this way, by providing the first inner wall surface IF _L as an inclined surface so as to be away from the first outer wall surface OF _L toward the bottom, the extension direction (X-axis direction) of the first inner wall surface IF _L intersects. direction, that is, it is possible to compensate for the shrinkage of the solidification shell in the second direction (Y-axis direction). In addition, by providing the second inner wall surface (IF _S ) as an inclined surface so as to be farther away from the second outer wall surface (OF _S ) toward the bottom, the extension direction (Y-axis direction) of the second inner wall surface (IF _S ) intersects. direction, that is, it is possible to compensate for the shrinkage of the solidification shell in the first direction (X-axis direction).

Hereinafter, a method for manufacturing a mold according to an embodiment of the present invention will be described with reference to FIGS. 6 and 7 .

6 is an exploded perspective view showing a part of a parent mold used to manufacture a mold according to an embodiment of the present invention. 7 is a view for explaining the amount of shrinkage of the solidification shell for each height during solidification of molten steel in the mother mold.

Here, (a) of FIG. 7 is the molten metal surface height (P _M ) of the mother mold, (b) of FIG. 7 is the first design point (DP ₁ ) of the mother mold, and (c) of FIG. 7 is the second design point of the mother mold. The design point (DP ₂ ), Figure 7 (d) is the third design point (DP ₃ ) of the mother mold, Figure 7 (e) is the solidification shell at each of the fourth design point (DP ₄ ) of the mother mold It is a plan view to explain the width (solidification width) and the width of the inner space.

Hereinafter, with reference to FIG. 6, the mother mold will first be described. At this time, for convenience of explanation, reference numerals such as the first and second inner wall surfaces (IF _L , IF _S ), the height of the molten surface (P _M ), and the width (W _LM , W _SM ) of the molten surface height of the parent mold are used in the embodiment It is explained in the same way as the mold according to.

And, four points below the molten surface height (P _M ) are set in the mother mold, and are named as first to fourth design points (DP ₁ to DP ₄ ) in order to distinguish them from the mold according to the embodiment.

The parent mold 4000 may include a body having an inner space IS and a cooling water passage (not shown) installed buried inside the body to circulate cooling water. At this time, the body of the parent mold 4000 has a shape provided so that the widths (W _L , W _S ) of the inner wall surfaces (IF: IF _L , IF _S ) toward the inner space (IS) decrease toward the bottom. At this time, as the widths W _L and W _S decrease toward the bottom of the inner wall surface IF: IF _L , IF _S , the width decreasing rate is constant.

More specifically, the body 4100 of the mother mold 4000 includes a pair of first walls 4110 extending in a first direction (X-axis direction) and spaced apart in a second direction (Y-axis direction), Each of them extends in a second direction (Y-axis direction) and includes a pair of second walls 4120 spaced apart from each other in a first direction (X-axis direction). Further, the width (W _{L ) of the first inner wall surface (IF L )} of the first wall 4110 and the width (W S ) of the second inner wall surface (IF _S ) of the second wall ₄₁₂₀ each decrease toward the bottom. do.

However, in the case of the mother mold 4000, when the widths W _L and W _S of the first and second inner wall surfaces IF _L and IF _S decrease toward the bottom, the decrease slope or decrease rate is constant. In addition, each of the first and second inner wall surfaces IF _L and IF _S are inclined to be farther away from the first and second outer wall surfaces OF _L and OF _S toward the bottom, and as shown in FIG. 6, the upper end From (P _U ) to the lower end (P _B ) is inclined to have a constant slope.

The parent mold 4000 may be a mold that has been previously used. More specifically, it may be a mold that causes surface defects due to solidification and shrinkage, and causes problems in the quality of the slab due to the surface defects. Of course, the mother mold 4000 may be separately prepared to have the shape and structure as described above.

Also, the mother mold 4000 may be referred to as a first mold, and a new mold manufactured by designing a width according to the solidification shrinkage rate of the mother mold 4000 may be referred to as a second mold 3000.

Hereinafter, a method of detecting the amount of solidification shrinkage by height in the mother mold 4000 as described above will be described.

When the mother mold 4000 is prepared, molten steel is charged into the mother mold 4000. At this time, the molten steel is charged so that the molten steel surface has a preset height. For example, molten steel is charged so that the molten steel surface is positioned at a point 100 mm apart from the uppermost end (P _U ) of the mother mold 4000 downward.

The molten steel charged into the mother mold 4000 is cooled by cooling water circulating inside the mother mold 4000, and in this process, a solidification shell C is formed as shown in FIG. 7 . At this time, the solidification shell starts to form from the height of the molten surface, and the thickness of the solidification shell (C) may increase downward.

Then, when the molten steel is solidified to form the solidification shell (C), solidification shrinkage occurs in the solidification shell (C). At this time, the amount of shrinkage of the solidification shell (C) may be different in the height direction, and a greater shrinkage occurs in the upper part than in the lower part.

In the embodiment, the amount of shrinkage of the solidified shell (C) for each height is detected, and the mold 3000 of the present invention is manufactured using this. To this end, a plurality of design points at different heights to detect the amount of solidification shrinkage are first set. At this time, it is preferable to detect the amount of solidification shrinkage by setting four or more design points. In the embodiment, the detection of solidification shrinkage at four different height design points (DP ₁ to DP ₄ ) will be described as an example.

That is, in each of the first and second inner wall surfaces IF _L and IF _S , the first design point DP ₁ spaced downward by the first distance G ₁ from the bath surface height P _m , the first A second design point (DP ₂ ) spaced apart by a second distance (G ₂ ) from the design point (DP ₁ ), and a third design point (spaced apart by a third distance (G ₃ ) from the second design point (DP ₂ ). The amount of solidification shrinkage is detected at each _of the fourth design points (DP ₄ ) spaced apart from the third design point (DP ₃ ) by the fourth interval (G ₄ ).

At this time, in the first to fourth intervals G ₁ to G ₄ , the first to fourth design points DP ₁ to DP ₄ are set such that the interval increases toward the bottom. At this time, the ratio of the first interval (G ₁ ): the second interval (G ₂ ): the third interval (G ₃ ): the fourth interval (G ₄ ) is 1 : 2 : 3 : 4 (G ₁ : G ₂ : It is preferable to set the first to fourth design points (DP ₁ to DP ₄ ) by G ₃ : G ₄ = 1 : 2 : 3 : 4. At this time, when the height of the tungsten surface (P _M ) is a point 100 mm apart from the upper end (P _U ) downward, the length from the height (P _M ) (100 mm point) to the lower end (P _B ) is divided, The ratio of the first to fourth intervals (G ₁ to G ₄ ) is 1: 2: 3: 4 (G ₁ : G ₂ : G ₃ : G ₄ = 1 : 2 : 3 : 4).

And, the position of the first point (P ₁ ) is set to the position of the value obtained by adding the first interval (G ₁ ) to the molten surface height (P _m ), and the position of the second point (P ₂ ) is the first point ( It is set to the position of the value obtained by adding the second interval (G ₂ ) to P ₁ ). Similarly, the position of the third point (P ₃ ) is the value obtained by adding the third interval (G ₃ ) to the second point (P ₂ ), and the position of the fourth point (P ₄ ) is at the third point (P ₃ ). It may be set to a position of a value obtained by summing the fourth interval G ₄ .

The solidification shrinkage by height (SD: SD _L , SD _S ) is the length between the ends of the solidification shell (C) at the first to fourth points (P ₁ to P ₄ ) and the molten surface height (P _M ) It is detected using the difference between the widths (W _LM , W _SM ) of the inner space (IS). Here, the length between both ends of the solidification shell (C) refers to the length between both ends of the solidification shell (C) in the first direction (X-axis direction) and solidification in the second direction (Y-axis direction). It may mean the length between both ends of the shell (C).

Hereinafter, for convenience of explanation, the length between both ends of the solidification shell (C) is abbreviated as 'solidification width (SW: SW _L , SW _S )'. In addition, according to this, the solidification width (SW _L : SW _L1 to SW _L4 ) in the first direction (X-axis direction) is the length between both ends of the first inner wall surface (IF _L ) in the extension direction in the solidification shell (C) can be explained as In addition, the solidification width (SW _S : SW _S1 to SW _S4 ) in the second direction (Y-axis direction) is the length between both ends of the second inner wall surface (IF _S ) in the extension direction in the solidification shell (C) can be explained

Reflecting this definition, the method for _{calculating the amount} of solidification shrinkage for each _height will be described again. DP ₄ ) can be calculated as the difference between the solidification widths (SW _L1 to SW _L4 ) (SW _S1 to SW _S4 ) in each.

That is, the solidification widths (SW _L1 to SW _L4 ) in the first direction at the first to fourth design points (DP ₁ to DP ₄ ) and the first direction width (IS) of the interior space (IS) at the bath surface height ( _PM ) By calculating the difference between W _LM ), it is possible to calculate the solidification shrinkage (SD _L1 to SD _L4 ) at each of the first to fourth design points (DP _L1 to DP _L4 ) in the first direction. In addition, the difference between the solidification widths (SW _S1 to SW _S4 ) in the second direction at the first to fourth design points (DP ₁ to DP ₄ ) and the second direction width (W _SM ) in the bath surface height (P _M ) Through the calculation, it is possible to calculate the solidification shrinkage (SD _S1 to SD _S4 ) at each of the first to fourth design points (DP _S1 to DP _S4 ) in the second direction.

Referring to FIG. 7, a method for calculating the amount of solidification shrinkage for each height in the first direction will be described in more detail below. _The solidification shrinkage (SD _L1 ) at the first design point (DP ₁ ) is, as shown in _FIG . It is calculated by calculating the difference between the solidification widths (SW _L1 ) at 1 design point (P ₁ ) (SD _L1 = W _LM -SW _L1 ). In addition, the solidification shrinkage (SD _L2 ) at the second design point (DP ₂ ) is the width (W _LM ) of the interior space (IS) in the first direction at the bath surface height (P _M ) and , It is calculated by calculating the difference between the solidification widths (SW _L2 ) at the second design point (P ₂ ) (SD _L2 = W _LM -SW _L2 ). In addition, the solidification shrinkage (SD _L3 ) at the third design point (P ₃ ) and the solidification shrinkage (SD _L4 ) at the fourth design point (P ₄ ) are calculated in the same manner as described above (SD _L3 = W _LM -SW _L3 , SD _L4 = W _LM - SW _L4 ).

The method for calculating the amount of solidification shrinkage by height in the second direction is the same as the method in the first direction described above. That is, the solidification shrinkage (SD _S1 ) at the first design point (DP ₁ ) is the width (W _SM ) of the interior space (IS) in the second direction at the bath surface height (P _M ) as shown in FIG. 7 (b) and , It is calculated by calculating the difference between the solidification widths (SW _S1 ) at the first design point (DP ₁ ) (SD _S1 = W _SM -SW _S1 ). In addition, the solidification shrinkage (SD _S2 ) at the second design point (DP ₂ ) is the width (W _SM ) of the interior space (IS) in the second direction at the bath surface height (P _M ) as shown in (c) of FIG. , It is calculated by calculating the difference between the solidification widths (SW _S2 ) at the second design point (DP ₂ ) (SD _S2 = W _SM -SW _S2 ). In addition, the solidification shrinkage (SD _S3 ) at the third design point (P ₃ ) and the solidification shrinkage (SD _S4 ) at the fourth design point (P ₄ ) are calculated in the same way as the method described above (SD _S3 =W _SM -SW _S3 , SD _S4 = W _SM - SW _S4 ).

In this way, molten steel is charged and solidified into the mother mold 4000, and at the first to fourth design points (DP ₁ to DP ₄ ) in the first direction (X-axis direction) and the second direction (Y-axis direction), respectively. Detecting the amount of solidification shrinkage (SD _L1 to SD _L4 ) (SD _S1 to SD _S4 ) can be performed for multiple types of molten steel.

More specifically, among the plural types of molten steel, molten steel of the first steel type (first molten steel) having the largest solidification shrinkage amount and molten steel of the second steel type (second molten steel) having the smallest solidification shrinkage amount are used. At this time, each of a plurality of types of molten steel is supplied to the mother mold 4000 to detect the solidification shrinkage, and then the solidification shrinkage at the same height is compared, and the molten steel having the largest solidification shrinkage is the first molten steel and the molten steel having the smallest solidification shrinkage. is selected as the second molten steel.

Here, the plural types of molten steel may be those manufactured as billet cast steel. In addition, the contents of the main components in the first and second molten steels may be as shown in Table 1, for example.

C (wt%) Si (wt%) Mn (wt%) 1st molten steel 0.10 0.20 0.451 2nd molten steel 0.82 0.20 0.449

Hereinafter, a method of manufacturing a mold according to an embodiment of the present invention using the first molten steel and the second molten steel will be described with reference to FIGS. 8 and 9 .

8 is a flow chart showing a method for manufacturing a mold according to an embodiment of the present invention. 9 is a graph showing solidification shrinkage and average shrinkage in the first direction for each height of the mother mold when the first molten steel and the second molten steel are charged into the mother mold and solidified.

When the first and second molten steels are prepared, they are charged into the mother mold 4000 and solidified (S110 and S120). At this time, any one of the first and second molten steel, for example, the first molten steel is first charged into the mother mold and solidified (S110). When the solidification of the first molten steel starts, the solidification shrinkage (1SD _L1 to 1SD _L4 ) at each of the first to fourth design points (DP ₁ to DP ₄ ) in the first direction (X-axis direction), and the The amount of solidification shrinkage (1SD _S1 to 1SD _S4 ) at each of the first to fourth design points (DP ₁ to DP ₄ ) is detected (S211 and S212).

When the solidification using the first molten steel is completed, the solidified material obtained by solidifying the first molten steel is carried out from the mother mold 4000 . Then, the second molten steel is charged into the mother mold 4000 and solidified (S120). When the solidification of the second molten steel starts, the solidification shrinkage (2SD _L1 to 2SD _L4 ) at each of the first to fourth design points (DP ₁ to DP ₄ ) in the first direction (X-axis direction), and the The amount of solidification shrinkage (2SD _{S1 to 2SD S4 ) at each of the first to fourth design points (DP 1 to DP 4} ) is detected ( S221 and S222 ).

Next, solidification shrinkage in the first direction (1SD _L1 to 1SD _L4 ) detected at each of the first to fourth design points (DP ₁ to DP ₄ ) when the first molten steel is solidified and the first molten steel when the second molten steel is solidified are determined. The average shrinkage _{(AS L1 ,} AS _L2 , AS _L3 , AS _L4 ) between the first direction solidification shrinkage (2SD _L1 to 2SD _L4 ) detected at each of the first to fourth design points (DP 1 to DP ₄ ) is calculated (S310). . That is, the first to fourth average shrinkage amounts (AS _L1 to AS _L4 ) in the first direction are the first to fourth solidification shrinkage amounts (1SD _L1 to 1SD _L4 ) in the first direction detected using the first molten steel and It can be obtained by calculating the average of the first to fourth solidification shrinkages (2SD _L1 to 2SD _L4 ) in the first direction detected using the second molten steel.

A more detailed description of this is as follows. The first solidification shrinkage (1SD _L1 ) at the first design point (DP ₁ ) during solidification of the first molten steel and the first solidification shrinkage (2SD _L1 ) at the first design point (DP ₁ ) during solidification of the second molten steel. ), the first average shrinkage amount AS _L1 is calculated by calculating the average of . In addition, the second solidification shrinkage (1S _L2 ) at the second design point (DP ₂ ) during solidification of the first molten steel and the second solidification shrinkage (DP 2 ) at the second design point (DP ₂ ) during solidification of the second molten steel ( By calculating the average of 2S _L2 ), the second average shrinkage amount AS _L2 is calculated. Then, the third average shrinkage amount (AS _L3 ) and the fourth average shrinkage amount (AS _L4 ) are calculated in the same manner.

9 and Table 2, in the first direction, the first average shrinkage amount (AS _L1 ) is 0.4 mm, the second average shrinkage amount (AS _L2 ) is 0.74 mm, the third average shrinkage amount (AS _L3 ) is 1.09 mm, The fourth average shrinkage amount (AS _L4 ) may be 1.36 mm.

First average shrinkage (AS _L1 ) Second average shrinkage (AS _L2 ) Third average shrinkage (AS _L3 ) 4th average shrinkage (AS _L13 ) 0.4mm 0.74mm 1.08mm 1.36mm

In addition, solidification shrinkage in the second direction (1SD _S1 to 1SD _S4 ) detected at each of the first to fourth design points (DP ₁ to DP ₄ ) at the time of solidification of the first molten steel and the first to fourth design points at the time of solidification of the second molten steel are measured. The average shrinkage (AS _S1 , _{AS S2} , AS _S3 , AS _S4 ) of the second direction solidification shrinkage (2SD _S1 to _{2SD S4} ) detected at each of the fourth design points (DP 1 to DP ₄ ) is calculated (S320). Since this is the same as the method for calculating the average shrinkage in the first direction described above, specific descriptions and specific values are omitted.

The first to fourth average shrinkage amounts (AS _L1 , AS _L2 , AS _L3 , and AS _L4 ) in the first direction obtained in this way and the first to fourth average shrinkage amounts (AS _S1 , AS S2 , AS _L4 ) in the second direction obtained in this way. AS _S3 , AS _S4 ) to prepare the mold. That is, the first to fourth widths W L1 to W with respect to the first inner wall _surface IF _L of the mold to be manufactured using the first to fourth average shrinkages AS _L1 to AS _L4 in the first direction. _L4 ) is designed (S410). In addition, the first to fourth widths W S1 to W _{S4 of} the second inner wall surface IF _S are designed using the first to fourth average shrinkages AS _S1 to AS _S4 in the second direction (S420). ).

First, a method (S410) of designing the first to fourth widths W _L1 to W _L4 in the first inner wall surface IF _L will be described in more detail as follows. The width at the first to fourth points P ₁ to P ₄ on the first inner wall surface IF _L is the first to fourth average shrinkage amounts AS _L1 to AS _L4 in the first direction and the molten surface height ( It is designed using the width (W _LM ) of the first direction in P _M ). That is, the first width (W _L1 ) at the first point (P ₁ ) on the first inner wall surface (IF _L ) is the first average from the width (W _LM ) in the first direction at the height of the bath surface ( _PM ). It is designed by subtracting the amount of shrinkage (AS _L1 ) (W _L1 =W _LM - AS _L1 ). In addition, the second width (W _L2 ) at the second point (P ₂ ) is a value obtained by subtracting the second average shrinkage (AS _L2 ) from the width (W _LM ) in the first direction at the molten surface height (P _M ) is designed (W _L2 =W _LM - AS _L2 ). In the same way, the third width (W _L3 ) and the fourth width (W _L4 ), respectively, are the third average shrinkage amount ( _{AS L3} ) and the third average shrinkage amount (AS _L3 ) It is designed by subtracting each of the 4 average shrinkages (AS _L4 ) (W _L3 =W _LM - AS _L3 , W _L4 =W _LM - AS _L4 ).

To explain more specifically, it will be described as an example that the width (W _LM ) at the molten surface height (P _M ) of the first inner wall surface (IF _L ) is 200 mm. The first width (W _L1 ) of the first point (P ₁ ) on the first inner wall surface (IF _L ) is the first average shrinkage amount (AS _L1 ) from the width (W _LM ) (200 mm) at the bath surface height (P _M ) ) (0.4mm), the first width W _L1 is designed to be 199.6mm (200mm-0.4mm). In addition, by subtracting the second to fourth average shrinkage amounts (AS _L2 to AS _L4 ) from the width (W _LM ) at the molten surface height (P _M ) in the same way, the second to fourth widths (W _L2 to W _L4 ) can design

The first to fourth widths W _S1 , W _S2 , W _S3 , and W _S4 of the second inner wall surface IF _S are designed in the same way as the first inner wall surface IF _L (S420). That is, the first width (W _S1 ) of the first point (P ₁ ) on the second inner wall surface (IF _S ) is the first average shrinkage amount (AS _S1 ) from the width (W _LM ) at the bath surface height (P _M ) It is designed as a value minus (mm). In addition, the remaining second to fourth widths (W _S2 to W _S4 ) are each designed as a value obtained by subtracting the first, second, and third average shrinkages (AS _S2 , AS _S3 , and AS _S4 ) from the width (W _LM ) at the bath surface height (P _M ).

At this time, the widths (W _L4 , W _S4 ) of the fourth point (P ₄ ) on the first and second inner wall surfaces (IF _L , IF _S ), respectively, are calculated from the width (W _LM ) at the bath surface height (P _M ) It may be designed as a value obtained by further subtracting 0.1 mm from the value obtained by subtracting the fourth average shrinkage (AS _L4 , AS _S4 ). This is to further extend the life of the mold by reducing friction between the first and second inner wall surfaces (IF _L , IF _S ) and the cast steel at the bottom of the mold.

In this way, the design (S410) of the first to fourth widths W _L1 to W _L4 of the first inner wall surface IF _L , and the first to fourth widths W of the second inner wall surface IF _S When the design (S420) of _S1 to W _S4 is completed, a mold is manufactured using this (S500). That is, the width at each of the first to fourth points P ₁ to P ₄ of the first inner wall surface IF _L is set to the designed first to fourth widths W _L1 to W _L4 , and The body 3100 of the mold 3000 is formed such that the width at each of the first to fourth points P ₁ to P ₄ of the wall surface IF _S becomes the designed first to fourth widths W _S1 to W _S4 . manufacture

10 (a), (c), (e), (g), (i) are photographs of the surface of the billet according to the first to fifth experimental examples. 10 (b), (d), (f), (h), and (j) are graphs showing the roughness (mm) of the surface of the billet, that is, the height (mm) of the surface in the first to fifth experimental examples. .

In measuring the roughness, the tip of the roughness meter was brought into contact with the surface of the billet, and the surface height was measured while moving the tip in the width direction of the billet. In addition, in measuring the surface height while moving the tip in the width direction of the billet, it was measured at a plurality of positions in a direction crossing the width direction, that is, in the longitudinal direction. In addition, the average heights measured at a plurality of locations are shown in (b), (d), (f), (h), and (j) of FIG. 10 .

Here, the billet according to Experimental Example 1 is manufactured with a mother mold. In addition, the billets according to the second to fifth experimental examples are manufactured by the mold according to the embodiment. In addition, the billets according to the second to fifth experimental examples are cast using molten steel of different types of steel having at least carbon (C) and manganese (Mn) contents.

Carbon (C) wt% Manganese (Mn) wt% Example 1 0.0981 0.451 Second Experimental Example 0.0929 0.46 Example 3 0.0935 0.447 Example 4 0.0863 0.449 Example 5 0.0897 0.425

Referring to (b) of FIG. 10 , in the case of the billet manufactured by the mother mold, a large defect was generated that was about 1.89 mm inward from the surface. It can be confirmed through (a) and (b) of FIG. 10 that this occurs at a point about 120 mm away from one end (0 mm) in the billet width direction.

On the other hand, referring to (d), (f), (h) and (j) of FIG. 10, in the case of the billets according to the second to fifth experimental examples, all the sizes of the most deeply sunken defects were less than 1 mm, and the first It is significantly smaller than the experimental example. That is, 0.25 mm in the second experimental example, 0.71 mm in the third experimental example, 0.94 mm in the fourth experimental example, and 0.25 mm in the fifth experimental example are the deepest defects, all of which are smaller than those of the first experimental example.

From this, it can be seen that surface defects can be reduced when a cast steel is manufactured using the mold according to the embodiment. This is because, in the case of the mold according to the embodiment, the widths (W _L1 to W _L4 ) (W _S1 to W _S4 ) for each height of the inner wall surface (IF _L , IF _S ) are designed and provided by reflecting the different solidification shrinkage for each height. Accordingly, it is possible to effectively compensate for the solidification shrinkage by height. In addition, by making the width change more rapid in the section between the molten surface height (P _M ) and the first point (P ₁ ) than in other sections, solidification in the upper part of the body 3100 where the solidification shell contracts the most Shrinkage can be effectively compensated.

And, in manufacturing the mold, a plurality of types of steel, that is, molten steel are solidified to detect the solidification shrinkage rate, and the average value of the solidification shrinkage rate is reflected to design the width by height of the inner wall surface. Therefore, in the case of the mold according to the embodiment, it is possible to manufacture a cast steel in which the solidification shrinkage rate is suppressed or prevented for a plurality of steel types.

3100: body 3110: first wall
3120: second wall IF: inner wall surface
IF _L : 1st inner wall surface IF _S : 2nd inner wall surface
P _M : Water level

Claims (19)

A process of solidifying molten steel in a first mold;
detecting a solidification shrinkage (SD) generated during solidification of the molten steel in the first mold for each height of the first mold;
preparing a design width for each height of a second mold to be manufactured using the detected amount of solidification shrinkage (SD) for each height;
Preparing a second mold such that the width (W) of the inner wall surface of the second mold is the design width by height. The method of claim 1,
The process of detecting the solidification shrinkage (SD) by height of the first mold,
setting a plurality of design points (DP) having different heights below the molten steel molten steel surface height (P _M ) on the inner wall surface of the first mold;
Detecting a solidification width (SW) by detecting a length between both ends in the width direction of the solidification shell formed by solidification of molten steel at each of the plurality of design points (DP) set in the first mold; and
By subtracting the solidification width (SW) detected at each of the plurality of design points (DP) from the width (W _M ) at the molten surface height (P _M ) on the inner wall surface of the first mold, the plurality of design points (DP) process of calculating the amount of solidification shrinkage (SD) in each; Method for manufacturing a mold comprising a. The method of claim 2,
In setting the plurality of design points (DP) in the first mold, the manufacturing method of the mold is set so that the distance between the plurality of design points (DP) increases downward. The method of claim 3,
In setting the plurality of design points (DP) in the first mold, the manufacturing method of the mold is set so that the distance between the plurality of design points (DP) increases to a constant value. The method of claim 4,
The plurality of design points (DP) set in the first mold include first to fourth design points (DP ₁ to DP ₄ ), which are points that sequentially move away from the lower side of the molten surface height (P _M ),
A distance ₍ G 1 ) between the molten surface height (P _M ) and the first design point (DP ₁ ), and a distance (G ₂ ) between the first design point (DP ₁ ) and the second design point (DP ₂ ) , the distance (G 3 ) between the second design point (DP ₂ ) and the third design point (DP ₃ ), the distance (G ₃ ) between the third design point (DP ₃ ) and the fourth design point (DP ₄ ) ₄ ), in the first interval (G ₁ ) to the fourth interval (G ₄ ), the manufacturing method of the mold is adjusted to increase at a constant rate. The method of claim 2,
The process of preparing the design width for each height,
setting a plurality of points (P) on the inner wall surface of the second mold at the same positions as the plurality of design points (DP) set in the first mold;
Process of subtracting (W M - SD) the solidification shrinkage (SD) for each of the plurality _of design points (DP) from the width (W _M ) of the inner wall surface at the molten surface height (P _M ) in the first mold ;
Determining the subtraction value (W _M - SD) at each of the plurality of design points (DP) as the width (W) at each of the plurality of points (P) set on the inner wall surface of the second mold; A method for manufacturing a mold comprising The method of claim 6,
In preparing the second mold,
The mold manufacturing method of designing such that the height of the second mold, the width of the uppermost end, and the width at the preset molten steel molten steel surface height are the same as the height of the first mold, the width of the uppermost end, and the height of the molten steel molten steel surface. The method of claim 1,
Including the process of preparing the first mold,
The process of preparing the first mold, the manufacturing method of the mold including the process of preparing such that the width of the inner wall surface decreases downward, and the rate of decrease of the width of the inner wall surface is uniform in the height direction. The method according to any one of claims 6 to 8,
The process of detecting the solidification shrinkage (SD) at each of the plurality of design points (DP),
supplying and solidifying the first molten steel to the first mold, and detecting a solidification shrinkage (1SD) of the first molten steel at the plurality of design points (DP);
supplying and solidifying the second molten steel to the first mold, and detecting a solidification shrinkage (2SD) of the second molten steel at the plurality of design points (DP);
Calculating an average solidification shrinkage (AS) of the solidification shrinkage (1SD) of the first molten steel and the solidification shrinkage (SSD) of the second molten steel for each of the plurality of design points (DP);
In subtracting the solidification shrinkage (SD) for each of the plurality of design points (DP) from the width (W _M ) of the inner wall surface at the height (P _M ) of the first mold (W _M - SD),
Wherein the solidification shrinkage (SD) for each of the plurality of design points (DP) is the average solidification shrinkage (AS) for each of the plurality of design points (DP). The method of claim 9,
Including the process of selecting the first and second molten steel,
The process of selecting the first and second molten steel,
supplying each of a plurality of types of molten steel to the first mold to solidify it;
detecting the amount of solidification shrinkage generated during solidification of each of the plural types of molten steel; and
Among the detected amounts of solidification shrinkage, selecting the molten steel that generated the largest amount of solidification shrinkage as the first molten steel and selecting the molten steel that generated the smallest amount of solidification shrinkage as the second molten steel. The method of claim 10,
The process of detecting the amount of solidification shrinkage generated at the time of solidification of each of the plurality of types of molten steel,
A method of manufacturing a mold comprising the step of detecting the amount of solidification shrinkage at the molten surface height (P _M ) of the first mold. A mold having an inner space into which molten steel can be injected,
Including a body having the inner space,
A plurality of points having different heights are set on the inner wall surface of the body,
The width at each of the plurality of points on the inner wall surface of the body decreases toward the bottom,
A mold in which the rate of decrease of the width is changed at a plurality of points in the height direction. The method of claim 12,
A mold having different distances in a height direction between the plurality of points. The method of claim 13,
The distance between the plurality of points in the height direction increases downward. The method of claim 14,
A mold in which intervals in the height direction between the plurality of points increase at a constant value. The method of claim 15
The plurality of points include first to fourth points that are sequentially distant from the lower side of the height of the molten steel molten steel surface supplied into the body,
The distance between the basal surface height and the first point (G ₁ ), the distance between the first and second points (G ₂ ), the distance between the second and third points (G ₃ ), the third In the interval (G ₄ ) between the third point and the fourth point, the mold increases at a constant rate from the first interval (G ₁ ) to the fourth interval (G ₄ ). The method according to any one of claims 12 to 16,
The inner wall surface of the body is provided with an inclined surface that moves away from the outer wall surface opposite to the inner wall surface toward the bottom,
The mold in which the inclination of the inner wall surface of the body is changed using the plurality of points as inflection points. The method of claim 17
A mold in which the slope of the inner wall of the body decreases toward the bottom. The method according to any one of claims 12 to 16,
The width at each of the plurality of points is a mold designed using a solidification shrinkage by height obtained by solidifying molten steel using a design mother mold for designing the mold.

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