Method for manufacturing a mold and mold

Abstract

A method for manufacturing a mold and a mold capable of effectively compensating for solidification shrinkage of a solidified shell for each height are provided. [Solution] The method includes the steps of solidifying molten steel in a first mold, detecting the amount of solidification shrinkage SD that occurs when the molten steel in the first mold solidifies for each height of the first mold, setting a design width for each height for a second mold to be manufactured using the detected amount of solidification shrinkage SD for each height, and setting the second mold so that the width W for each height of the inner wall surface of the second mold is the design width for each height.

Description

[Technical Field]

[0001] The present invention relates to a mold manufacturing method and a mold, and more particularly to a mold manufacturing method and a mold that can suppress or prevent the occurrence of defects in cast pieces. [Background technology]

[0002] A mold for casting a slab includes a pair of long side walls and a pair of short side walls, and molten steel is poured into an internal space defined by the pair of long side walls and the pair of short side walls, and the molten steel is solidified in the mold to produce a slab. When molten steel is supplied into the mold, a solidified shell begins to form from the molten steel surface, but the thickness of the solidified shell increases as it moves downward. When the molten steel solidifies inside the mold and forms a solidified shell, solidification shrinkage occurs in the solidified shell. In particular, when the liquid molten steel transforms into a solid phase at the upper part of the mold, significant shrinkage of the solidified shell occurs. Furthermore, the amount of solidification shrinkage of the solidified shell varies depending on the height of the mold. If the mold cannot compensate for this shrinkage of the solidified shell, an air layer or gap occurs between the mold and the solidified shell. The creation of a gap reduces the heat transfer ability between the mold and the solidified shell or molten steel, causing delayed solidification, which can lead to breakouts and defects in the cast slab.

[0003] To solve the problems associated with solidification shrinkage, the width of the inner wall of the mold is made to decrease downward. In this case, the amount or rate of decrease of the width of the inner wall of the mold as it progresses downward is made constant. However, even in this case, a gap still occurs between the mold and the solidified shell because the shrinkage of the solidified shell cannot be sufficiently compensated for. This is because the amount of solidification shrinkage decreases from the top to the bottom of the mold, but the amount of solidification shrinkage does not decrease at a constant rate. In other words, since the width of the inner wall decreases downward at a constant rate, it is not possible to sufficiently compensate for the amount of solidification shrinkage that varies depending on the height. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent Registration No. 10-1060114 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a mold manufacturing method and a mold that can effectively compensate for solidification shrinkage of a solidified shell at each height. Another object of the present invention is to provide a mold manufacturing method and a mold that can improve the compensation rate for shrinkage of the solidified shell. [Means for solving the problem]

[0006] The method for manufacturing a mold of the present invention is characterized by including the steps of solidifying molten steel in a first mold, detecting the amount of solidification shrinkage SD that occurs when the molten steel solidifies in the first mold for each height of the first mold, setting a design width for each height of a second mold to be manufactured using the detected amount of solidification shrinkage SD for each height, and setting up the second mold so that the width W for each height of the inner wall surface of the second mold is the design width for each height.

[0007] The process of detecting the amount of solidification shrinkage SD for each height of the first mold is performed by measuring the height P of the molten steel surface on the inner wall surface of the first mold. M a step of setting a plurality of design points DP having different heights below the first mold, a step of detecting a length between both ends in the width direction of a solidified shell formed by solidification of molten steel at each of the plurality of design points DP set in the first mold to detect a solidification width SW, and a step of detecting a height P of the molten steel surface on the inner wall surface of the first mold. M Width W at M and calculating the amount of solidification shrinkage SD at each of the plurality of design points DP by subtracting the solidification width SW detected at each of the plurality of design points DP from the calculated amount of solidification shrinkage SD. When setting the plurality of design points DP in the first mold, it is preferable to set the plurality of design points DP so that the intervals between the plurality of design points DP increase as they move downward.

[0008] When setting a plurality of design points DP in the first mold, the plurality of design points DP can be set so that the intervals between the plurality of design points DP increase by a constant value. The plurality of design points DP set in the first mold are located at the height P M The height of the molten metal surface P Mand the first design point DP1, the interval G2 between the first design point DP1 and the second design point DP2, the interval G3 between the second design point DP2 and the third design point DP3, and the interval G4 between the third design point DP3 and the fourth design point DP4 are preferably adjusted so that they increase at a constant rate from the first interval G1 to the fourth interval G4.

[0009] The process of setting the design width for each height includes a process of 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, and a process of setting the height P of the molten metal surface in the first mold. M Width of the inner wall at W M Subtract the solidification shrinkage amount SD for each of the plurality of design points DP from (W M -SD) process and the deduction (W M -SD) as the width W at each of the plurality of points P set on the inner wall surface of the second mold. When providing the second mold, it is preferable to design the second mold so that its height, width at its uppermost end, and width at a preset height of the molten steel surface are the same as those of the first mold.

[0010] The method for manufacturing the mold includes a step of providing the first mold, and the step of providing the first mold preferably includes a step of providing the first mold so that the width of the inner wall surface decreases as it progresses downward, and the rate of decrease in the width of the inner wall surface is uniform in the height direction. The step of detecting the amount of solidification shrinkage SD at each of the plurality of design points DP includes a step of supplying and solidifying a first molten steel into the first mold and detecting an amount of solidification shrinkage 1SD of the first molten steel at the plurality of design points DP, a step of supplying and solidifying a second molten steel into the first mold and detecting an amount of solidification shrinkage 2SD of the second molten steel at the plurality of design points DP, and a step of calculating an average amount of solidification shrinkage AS of the amount of solidification shrinkage 1SD of the first molten steel and the amount of solidification shrinkage 2SD of the second molten steel for each of the plurality of design points DP, and M Width of the inner wall at W M Subtract the solidification shrinkage amount SD for each of the plurality of design points DP from (W M -SD), the amount of solidification shrinkage SD for each of the plurality of design points DP can be an average amount of solidification shrinkage AS for each of the plurality of design points DP. It is preferable that the method for manufacturing a mold includes a step of selecting the first and second molten steels, and the step of selecting the first and second molten steels includes a step of supplying each of a plurality of types of molten steel to the first mold and solidifying it, a step of detecting the amount of solidification shrinkage that occurs when each of the plurality of types of molten steels solidifies, and a step of selecting the molten steel that has caused the largest amount of solidification shrinkage among the detected amounts of solidification shrinkage as the first molten steel and selecting the molten steel that has caused the smallest amount of solidification shrinkage as the second molten steel.

[0011] The mold of the present invention is a mold having an internal space into which molten steel can be poured, and includes a body having the internal space, wherein a plurality of points at different heights are set on an inner wall surface of the body, the width of each of the plurality of points on the inner wall surface of the body decreases as it progresses downward, and the rate at which the width decreases varies at a plurality of points in the height direction.

[0012] The intervals between the plurality of points in the height direction may be different from each other. The vertical spacing between the points may increase going downwards. Preferably, the vertical spacing between the plurality of points increases by a constant value.

[0013] The plurality of points include first to fourth points which are points which are successively further below the height of the molten steel surface of the molten steel supplied inside the body, and it is preferable that a distance G1 between the height of the molten steel surface and the first point, a distance G2 between the first point and the second point, a distance G3 between the second point and the third point, and a distance G4 between the third point and the fourth point increase at a constant rate from the first distance G1 to the fourth distance G4. The inner wall surface of the body is formed as a slope that slopes away from the outer wall surface, which is the opposite surface of the inner wall surface, as it progresses toward the bottom, and the slope gradient of the inner wall surface of the body may be changed using the plurality of points as inflection points. The inclination of the inner wall surface of the body preferably decreases toward the bottom. The width at each of the plurality of points is preferably designed using the amount of solidification shrinkage at each height obtained by solidifying molten steel using a design base mold for designing the mold. [Effects of the Invention]

[0014] According to an embodiment of the present invention, the compensation rate for solidification shrinkage of the solidified shell can be improved. That is, by manufacturing a mold by designing the width for each height of the mold according to the amount of solidification shrinkage that differs from one another at each height, the compensation rate for solidification shrinkage at each height can be improved. Therefore, the occurrence of defects on the surface of the slab due to the shrinkage of the solidified shell can be suppressed or prevented. When manufacturing a mold, multiple types of molten steel are solidified to detect the solidification shrinkage rates, and the width of the inner wall surface of the mold for each height is designed based on the average solidification shrinkage rates. Therefore, it is possible to manufacture casts with reduced or prevented solidification shrinkage rates for multiple types of steel. [Brief explanation of the drawings]

[0015] [Figure 1]1 is a diagram showing a casting apparatus including a mold according to an embodiment of the present invention; [Figure 2] 1 is a three-dimensional view showing a mold according to an embodiment of the present invention. [Figure 3] FIG. 2 is an exploded perspective view of a mold according to an embodiment of the present invention. [Figure 4] 2A and 2B are diagrams for explaining the width and inclination of the inner wall surface of the first wall body at each height in a mold according to an embodiment of the present invention, where (a) is a front view seen from the "A" side of FIG. 2, and (b) is a front view seen from the "B" side of FIG. 2, showing only one of a pair of first walls. [Figure 5] 2A and 2B are diagrams for explaining the width and inclination at each height of the inner wall surface of the second wall in a mold according to an embodiment of the present invention, where (a) is a front view seen from the "B" side of FIG. 2, and (b) is a front view seen from the "A" side of FIG. 2, showing only one of a pair of second walls. [Figure 6] FIG. 2 is an exploded perspective view showing a portion of a master mold used to manufacture a mold according to an embodiment of the present invention. [Figure 7] FIG. 1 shows the width of each solidified shell (solidification width) and the width of the internal space to explain the amount of contraction of the solidified shell at each height when molten steel solidifies in the base mold, where (a) is the height PM of the molten steel surface in the base mold, (b) is a plan view at the first design point DP1 of the base mold, (c) is a plan view at the second design point DP2 of the base mold, (d) is a plan view at the third design point DP3 of the base mold, and (e) is a plan view at the fourth design point DP4 of the base mold. [Figure 8] 1 is a flow chart illustrating a method for manufacturing a mold according to an embodiment of the present invention. [Figure 9] 1 is a graph showing the amount of solidification shrinkage and the average amount of solidification shrinkage in a first direction for each height of a mother mold when first molten steel and second molten steel are charged into the mother mold and solidified. [Figure 10]Figures showing the surface condition of billets from the first to fifth experimental examples, where (a), (c), (e), (g), and (i) are photographs of the surfaces of billets from the first to fifth experimental examples, and (b), (d), (f), (h), and (j) are graphs showing the surface roughness (mm), i.e., the surface height (mm), of the billets from the first to fifth experimental examples. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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, and may be embodied in various different forms. The embodiments disclosed below are provided solely to complete the disclosure of the present invention and to inform those skilled in the art of the scope of the invention. In describing the present invention, the same reference numerals will be used to refer to the same components, and the drawings may be exaggerated to illustrate the embodiments of the present invention, and the same numerals will refer to the same components in the drawings.

[0017] FIG. 1 is a diagram showing a casting apparatus equipped with 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 the molten steel from the tundish 20 and initially solidifies it into a predetermined shape, and a nozzle 22 that supplies the molten steel from the tundish 20 to the mold 3000. The casting apparatus also includes a cooling section 40 disposed below the mold 3000, which sprays cooling water onto the unsolidified strand 1 extracted from the mold 3000 to completely solidify it. The cooling section 40 includes a plurality of segments 41. Each of the plurality of segments 41 preferably includes a plurality of rolls that can be rotated by the force that moves the strand 1, and a nozzle positioned between the plurality of rolls that sprays cooling water onto the strand 1.

[0018] Hereinafter, a mold according to an embodiment of the present invention will be described with reference to Fig. 2 to Fig. 5. The mold according to the embodiment may be used to cast a billet. Preferably, the mold is used to cast a billet made of low-carbon steel, medium-carbon steel, or high-carbon steel. Needless to say, the mold 3000 can be used to produce cast pieces of a wide variety of steel types in addition to the low carbon steel, medium carbon steel, and high carbon steel described above. Note that the mold 3000 may be used to produce a wide variety of cast pieces, such as slabs and blooms, in addition to billets.

[0019] FIG. 2 is a three-dimensional view of a mold according to an embodiment of the present invention. FIG. 3 is an exploded perspective view of a mold according to an embodiment of the present invention. FIG. 4 is a diagram illustrating the width per height relative to the inner wall surface of a first wall in a mold according to an embodiment of the present invention, where (a) is a front view viewed from the "A" side of FIG. 2 and (b) is a front view viewed from the "B" side, showing only one of a pair of first walls. FIG. 5 is a diagram illustrating the width per height and slope per height relative to the inner wall surface of a second wall in a mold according to an embodiment of the present invention, where (a) is a front view viewed from the "B" side of FIG. 2 and (b) is a front view viewed from the "A" side of FIG. 2, showing only one of a pair of second walls.

[0020] 2, the mold 3000 includes a body 3100 having an internal space IS. The mold 3000 may also include a cooling water passage (not shown) embedded inside the body 3100 so that cooling water can circulate. Referring to FIG. 3, the body 3100 has an inner wall surface IF:IF facing the internal space IS. L , IF S and the inner wall surface IF:IF L , IF S The outer wall surface OF:OF is the surface exposed to the outside and is located on the opposite side of the wall. L , OF S Equipped with.

[0021] As shown in FIG. 3, the body 3100 has an inner wall surface IF:IF L , IF S Width W:W L , W S At this time, the height P of the upper surface of the molten steel supplied into the body 3100, i.e., the height of the molten steel surface M Four or more points at different heights are set below the surface, and the widths at the points are made different. Here, the inner wall surface IF:IF L , IF S Width W:W L , W S means the horizontal length. More specifically, the inner wall surface IF:IF L , IF S Width W:W L , W S means the length in the first direction (X-axis direction) and the length in the second direction (Y-axis direction).

[0022] In the following, the mold 3000 according to the embodiment will be described taking as an example a case where four points are set. M It is assumed that the first point P1, the second point P2, the third point P3, and the fourth point P4 are set in this order below the map. When setting the first to fourth points P1 to P4, the distance between the first to fourth points P1 to P4 is set so that it decreases as it goes upward and increases as it goes downward. In other words, when setting the first to fourth points P1 to P4, the distance between the points positioned immediately above is set so that it decreases as it goes upward. In other words, the distance between the points positioned immediately above is set so that it increases as it goes downward. In other words, the height of the molten metal surface P M The distance G1 between the fourth point P4 and the third point P3 is the shortest, and the distance G4 between the fourth point P4 and the third point P3 is the longest. In other words, the distance between the first point P1 and the molten metal surface P MThe order is: distance G1 between the second point P2 and the first point P1 < distance G2 between the second point P2 and the first point P1 < distance G3 between the third point P3 and the second point P2 < distance G4 between the fourth point P4 and the third point P3.

[0023] The inner wall surface IF of the body 3100 is formed so that its width decreases as it goes downward. At this time, the width W:W at the first to fourth points P1 to P4 set as described above is L , W S However, the width is designed by a method according to an embodiment described later. Inner wall IF:IF L , IF S Width W:W L , W S The width decreases as it moves downward, and the rate at which the width decreases varies at a plurality of points P1 to P4 in the height direction. L , IF S Width W:W L , W S decreases as it moves downward, but the inner wall IF:IF L , IF S Width W:W L , W S The rate at which the upper end P decreases is not uniform in the height direction, but is different from one another. U It is preferable that the rate of decrease in width is constant in the region from the first point P1 to the first point P1, the rate of decrease in width is constant in the region from the first point P1 to the second point P2, the rate of decrease in width is constant in the region from the second point P2 to the third point P3, and the rate of decrease in width is constant in the region from the third point P3 to the fourth point P4.

[0024] And the inner wall IF:IF L , IF S Width W:W L , W S decreases as it moves downwards, U and the width W of the first point P1 L1 , W S1At this time, as described above, the difference in width between the upper end P U Since the rate of decrease in width in the region from the first point P1 to the first point P2 is constant, M If we compare the difference in width between the first to fourth points P1 to P4, the height of the molten metal surface P M Width W LM , W SM and the width W of the first point P1 L1 , W S1 The difference between the width W of the first point P1 and the width W of the second point P2 is the largest. L1 , W S1 and the width W of the second point P2 L2 , W S2 The difference between the width W of the second point P2 L2 , W S2 and the width W at the third point P3 L3 , W S3 The difference between the width W of the third point P3 L3 , W S3 and the width W at the fourth point P4 L4 , W S4 The difference between the height of the molten metal and the M Width W LM , W SM and the width W of the first point P1 L1 , W S1 The difference between the two is set to be even greater. This reduces the height of the molten metal surface P M The section where the width changes most rapidly is the section where the height of the molten metal surface P M From the first point P1 to the first point P1. M The distance G1 between the M Width W LM , W SM and the width W of the first point P1 L1 , W S1 The difference between the height of the molten metal and the M The change is most rapid when the width changes from the first point P1 to the first point P2.

[0025] In this way, the height of the molten metal surface P M Width W at LM , WSM and the width W at the first point P1 L1 , W S1 The reason why the difference between the height P and the molten metal surface is set to be the largest is that the closer the solidified shell approaches the molten metal surface when it contracts inside the body 3100, the greater the contraction amount of the solidified shell. M Width W at LM , W SM and the width W at the first point P1 L1 , W S1 By making the change in temperature sharp, the compensation rate for solidification shrinkage in the upper region of the body close to the molten metal surface can be improved. Also, as mentioned above, the inner wall surface IF:IF L , IF S Width W:W L , W S The rate at which the molten metal surface P decreases is not uniform in the height direction, but is set to be different from one another. M Width W at M :W LM , W SM and the width W at the first point P1 L1 , W S1 The difference between the width W of the first point P1 and L1 , W S1 and the width W of the second point P2 L2 , W S2 The difference between the width W of the second point P2 L2 , W S2 and the width W at the third point P3 L3 , W S3 The difference between the width W of the third point P3 L3 , W S3 and the width W at the fourth point P4 L4 , W S4 This is because when the molten steel solidifies and the solidified shell shrinks, the amount of shrinkage of the solidified shell may differ depending on the position at each height of the mold 3000.

[0026] In this way, since the amount of shrinkage of the solidified shell varies depending on the height of the mold 3000, in the embodiment, the inner wall surface IF:IF of the body 3100 is calculated using the amount of shrinkage of the solidified shell at each height of the mold. L , IFS Width W:W L , W S That is, after a mold for design (hereinafter referred to as a mother mold) is separately prepared, the height P M At least four or more points are set below the mold 3000. After detecting the amount of solidification shrinkage at each of the points, the width at each point is designed according to the amount of solidification shrinkage at each point, and the mold 3000 is manufactured. The inner wall surface IF of the mold 3000 to be manufactured, i.e., the body 3100, is determined according to the amount of solidification shrinkage at each height in the base mold. L , IF S Width W:W L , W S The method for designing or determining is described in detail below with reference to FIGS.

[0027] In the following, an example will be described in which the body 3100 is made up of a plurality of walls. 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), and a pair of second walls 3120 each extending in a second direction (Y-axis direction) intersecting the extension direction of the first walls 3110 and spaced apart in the first direction (X-axis direction).

[0028] The pair of first walls 3110 and the pair of second walls 3120 are connected to each other. 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 the other end of the pair of first walls 3110 is connected to one end and the other end of the remaining second wall 3120. Thus, an internal space IS surrounded by the pair of first walls 3110 and the pair of second walls 3120 is provided. Therefore, the inner wall surface IF of the body 3100 is the inner wall surface of the pair of first walls 3110 (hereinafter referred to as the first inner wall surface IF L) and the inner wall surfaces of the pair of second walls 3120 (hereinafter referred to as second inner wall surfaces IF S The outer wall surface OF of the body 3100 can be described as having the outer wall surfaces of the pair of first walls 3110 (hereinafter referred to as the first outer wall surfaces OF L ) and the outer wall surfaces of a pair of second walls 3120 (hereinafter referred to as second outer wall surfaces OF S ) can be explained as being equipped with.

[0029] Therefore, as shown in FIG. 3 and FIG. 4(a), the first inner wall surface IF L The length in the first direction (X-axis direction) of the first inner wall surface IF L Width W L :W LM , W L1 , W L2 , W L3 , W L4 3 and 5(a), the second inner wall surface IF of the second wall body 3120 is defined as follows. S The length in the second direction (Y-axis direction) at the second inner wall surface IF S Width W S :W SM , W S1 , W S2 , W S3 , W S4 It is defined as: The length of each of the first wall 3110 and the second wall 3120 in the horizontal direction intersecting with the width direction is defined as the "thickness." Therefore, the thickness T of the first wall 3110 L :T LM , T L1 , T L2 , T L3 , T L4 is the length in the second direction (Y-axis direction) (see FIG. 4(b)), and the thickness T S :T SM , T S1 , T S2 , T S3 , T S4 is the length in the first direction (X-axis direction) (see FIG. 5(b)).

[0030] Although the body 3100 has been described as being composed of a pair of first walls 3110 and a pair of second walls 3120, the pair of first walls 3110 and the pair of second walls 3120 may be integrally formed. That is, the pair of first walls 3110 and the pair of second walls 3120 may not be joined using a separate joining means, but may be manufactured as an integral body by a method such as compression molding. A mold having such a body 3100 is also called a "tube type mold." Needless to say, the body 3100 may be provided by connecting the first wall 3110 and the second wall 3120 by a separate connecting means.

[0031] As shown in FIG. 3, the body 3100 is provided so that its width varies depending on its position or height in the height direction (Z-axis direction), and the width W:W L , W S In this regard, the first inner wall surface IF of the first wall body 3110 will be described below. L and the second inner wall surface IF of the second wall 3120 S We will explain in more detail by dividing it into two parts. The first inner wall surface IF of the first wall 3110 L As shown in Figures 3 and 4(a), the width of the first inner wall surface IF decreases as it moves downward. L The widths at different positions in the height direction are different, but the height P M The width of the first inner wall surface IF is different at at least four different points on the lower side of the first inner wall surface IF. L The height of the molten metal surface P M The width W at first to fourth points P1 to P4, which are four positions at different heights below the L1 , W L2 , W L3 , W L4 At this time, the width W at the first to fourth points P1 to P4 is different. L1 ~W L4is the first inner wall surface IF L The height of the molten metal surface at P M Width at P LM It is narrower than

[0032] In addition, the second inner wall surface IF of the second wall body 3110 S In this case, the first inner wall surface IF L That is, the second inner wall surface IF of the second wall body 3110 is formed in the same shape as the second inner wall surface IF S The width of the first inner wall surface IF decreases as it moves downward. L The width W at the same position, that is, the first to fourth points P1 to P4 S1 , W S2 , W S3 , W S4 At this time, the width W at the first to fourth points P1 to P4 is different. S1 ~W S4 is the second inner wall surface IF S The height of the molten metal surface at P M Width at P SM It is smaller than First inner wall IF L The first to fourth points P1 to P4 and the second inner wall surface IF S The first to fourth points P1 to P4 are points at the same height. L , IF S The first to fourth points P1 to P4 at each of the points are the height P of the molten steel surface charged into the body 3100. M It is determined based on the following criteria.

[0033] Height of molten steel surface P M The upper end of the body 3100 U For example, the height of the upper end P of the body 3100 may be a predetermined distance below the upper end P of the body 3100. U Assuming that molten steel is charged so that the surface of the molten steel is located 100 mm below the lower end P B The distance from the upper end P of the body 3100 to the surface of the molten steel is the height of the molten steel surface. UThe position is O mm, and the height of the molten metal surface is P M The top of the body 3100 U If we use this as a reference, the height of the molten metal surface P M is the 100mm point. The first point P1 of the first and second walls 3110 and 3120 is the upper end P U The second point P2 is a point that is a distance corresponding to the first distance S1 downward from the upper end P U The third point P3 is a point that is spaced downward from the upper end P by a distance corresponding to the second distance S2 that is greater than the first distance S1. U The fourth point P3 is a point that is spaced downward from the upper end P by a distance corresponding to a third distance S3 that is greater than the second distance S2. U The point is located downward from the point S1 by a distance corresponding to a fourth distance S4 that is larger than the third distance S3.

[0034] Water surface height P M From bottom P B The section up to is divided into several sections in the height direction. M At the first to fourth points P1 to P4, the distance between adjacent points increases as the height of the molten metal surface P M The first distance G1 between the first point P1 and the second point P2, the second distance G2 between the first point P1 and the second point P2, the third distance G3 between the second point P2 and the third point P3, and the fourth distance G4 between the third point P3 and the fourth point P4 are set to be the smallest and the largest, respectively. M The interval G1 between the first point P1 and the first point P1 and the intervals G2 to G4 between the first to fourth points P1 to P4 may increase by a constant value. Preferably, the first to fourth points P1 to P4 are set so that the ratio of the first to fourth intervals G1 to G4 is 1:2:3:4 (G1:G2:G3:G4=1:2:3:4). For example, the height of the molten metal surface P M is the upper end P UWhen the point is 100 mm below the M (100mm) from the bottom P B The length is divided so that the ratio of the first to fourth intervals G1 to G4 is 1:2:3:4 (G1:G2:G3:G4=1:2:3:4).

[0035] At this time, the first point P1 is at the height of the molten metal surface P M The first point P1 is located at a distance corresponding to the first distance G1 downward from the molten metal surface P M The position of the third point P3 can be explained as the value obtained by adding the third distance G3 to the second point P2, and the position of the fourth point P4 can be explained as the value obtained by adding the fourth distance G4 to the third point P3. In this case, the position of the fourth point P4 can be explained as the value obtained by adding the third distance G4 to the third point P3. In this case, the position of the fourth point P4 is the value obtained by adding the fourth distance G4 to the bottom end P of the body. B This can sometimes happen. By setting the positions of the first to fourth points P1 to P4 in this way, the distances to the points immediately above become shorter as one moves upward, i.e., the order is "first distance G1 < second distance G2 < third distance G3 < fourth distance G4".

[0036] First and second inner wall surfaces IF L , IF S In each of the above, the widths at the first to fourth points P1 to P4, that is, the first to fourth widths W L1 ~W L4 , W S1 ~W S4 In this case, the width decreases as the distance from the first point P1 to the fourth point P4 increases. L1 , W S1 Compared to the second width W L2 , W S2 is small, and the second width W L2 , W S2 Compared to the third width WL3 , W S3 is small, and the third width W L3 , W S3 Compared to the fourth width W L4 , W S4 becomes smaller. In this way, the first and second inner wall surfaces IF L , IF S By providing each of the first inner wall surface IF such that its width decreases as it advances downward, it is possible to compensate for the shrinkage of the solidified shell in the first direction (X-axis direction) and the second direction (Y-axis direction). L Width W L1 , W L2 , W L3 , W L4 By providing the second inner wall surface IF so that it decreases as it moves downward, it is possible to compensate for the shrinkage of the solidified shell in the first direction (X-axis direction). S Width W S1 , W S2 , W S3 , W S4 By providing the thickness of the solidified shell such that it decreases as it moves downward, it is possible to compensate for the shrinkage of the solidified shell in the second direction (Y-axis direction).

[0037] Furthermore, the first and second inner wall surfaces IF L , IF S As the width of the inner wall IF decreases downward, L , IF S The rate at which the width of the groove decreases is not uniform or constant in the height direction, but is varied. In this case, the rate at which the width decreases varies at first to fourth points P1 to P4 in the height direction. Here, the width reduction rate can be calculated using the difference in width between two adjacent points and the distance between the adjacent points (see Equation 1). [Formula 1] Width reduction rate (%) = (((Width at top point - Width at bottom point) / Width at bottom point) x 100) / (Gap between bottom point and top point / Overall length of body)

[0038] The decrease rate will be explained using a specific example. M To this end, the overall height of the body 3100 or the first wall 3110 is set to 1000 mm, and the difference between the first point P1 and the height P M The distance G1 between the M The width of the first point P1 is 200 mm, and the width W L1 In this case, the height of the molten metal surface P M The rate of decrease in the width between the first point P1 and the first point P2 can be calculated using the following equation 1. [Equation 1] Width reduction rate (%) = (((200-199) / 199) x 100) / (210 / 1000) = 2.39%

[0039] The rate of decrease in width between the first point P1 and the second point P2, the rate of decrease in width between the second point P2 and the third point P3, and the rate of decrease in width between the third point P3 and the fourth point P4 can also be calculated using the same method as described above. The second inner wall surface IF of the second wall 3120 S The reduction rate of the width of the first inner wall surface IF S The reduction rate is calculated in the same manner as the reduction rate of the width of the

[0040] In this way, the first and second inner wall surfaces IF L , IF S As the width of the inner wall IF decreases downward, L , IF S The rate at which the width of the grooves decreases is not uniform or constant in the height direction, but is set to be different. In addition, the difference in width between the point immediately above and the height of the molten metal surface P M Width W LM , W SM and the width W of the first point P1 L1 , W S1 The difference between the width W and the width W at the third point P3 is maximized. L3 , W S3and the width W at the fourth point P4 L4 , W S4 This minimizes the difference between the height of the molten metal and the M The amount of change in width is most rapid in the section between the third point P3 and the fourth point P4, and the amount of change in width is most gradual in the section between the third point P3 and the fourth point P4. In this way, the height of the molten metal surface P M and the first point P1, the width of which changes more rapidly than in other sections, thereby making it possible to effectively compensate for solidification shrinkage in the upper part of the body 3100, where the solidified shell shrinks the most. Specifically, the solidified shell shrinks the most at a height adjacent to the molten metal surface in the upper part of the body 3100, and solidification shrinkage in this section can be effectively compensated for.

[0041] Width W at each of the first to fourth points P1 to P4 L1 ~W L4 , W S1 ~W S4 is a width designed according to the amount of solidification shrinkage of the solidified shell at the first to fourth points of the mother mold. In other words, the first width W at the first point P1 is L1 , W S1 , a second width W at a second point P1 L2 , W S2 , a third width W at a third point P1 L3 , W S3 , a fourth width W at a fourth point P1 L4 , W S4 Each of the above was designed using the amount of solidification shrinkage at each of the first to fourth points of the mother mold.

[0042] In this way, the inner wall IF L , IF S Adjusted width W for each height L1 ~W L4 , W S1 ~W S4This effectively compensates for the shrinkage of the solidified shell at each height. That is, in conventional molds, although the widths of the first and second inner wall surfaces are designed to decrease downward, the rate of decrease in width is constant or similar. In other words, the widths are designed to decrease at a constant rate regardless of the amount of shrinkage at each height position. In such cases, although compensation can be made for the tendency for the amount of solidification shrinkage to decrease downward, the tendency for the amount of solidification shrinkage to decrease does not appear to decrease at a uniform rate, and therefore compensation for the different amounts of solidification shrinkage at each height is insufficient. This results in a large number of surface defects due to solidification shrinkage occurring on the surface of a slab, e.g., a billet.

[0043] However, in this embodiment, the inner wall surface IF L , IF S Width W per height L1 ~W L4 , W S1 ~W S4 The actual amount of solidification shrinkage at each height is reflected in the inner wall IF. L , IF S Width W L1 ~W L4 , W S1 ~W S4 This design allows for more effective compensation for solidification shrinkage at each height, thereby minimizing or preventing defects on the surface of the slab due to solidification shrinkage. In addition, the first and second inner wall surfaces IF of the body 3100 L , IF S As each of these progresses downward, the outer wall surface of L , OF S In other words, the body 3100 is provided so that its thickness increases toward the bottom. More specifically, the first and second inner wall surfaces IF L , IF SAs shown in Fig. 4(b) and Fig. 5(b), each of the first and second inner wall surfaces IF L , IF S As each of these progresses downward, the outer wall surface of L , OF S The slope is preferably set so that the slope changes four or more times.

[0044] More specifically, the first and second inner wall surfaces IF L , IF S Each of the slopes F1 to F4 has a slope F2 whose gradient changes at at least first to third points P1 to P3 as inflection points. L1 ~F L4 , F S1 ~F S4 That is, the first and second inner wall surfaces IF L , IF S As shown in (b) of FIG. 4 and (b) of FIG. 5, the upper end P U As we move from the outer wall surface OF L , OF S A first slope F that moves away from L1 , F S1 , as it moves from the first point P1 to the second point P2, the outer wall surface OF L , OF S A second slope F that moves away from L2 , F S2 , as proceeding from the second point P2 to the third point P3, the outer wall surface OF L , OF S The third slope F, which is away from L3 , F S3 , as proceeding from the third point P3 to the fourth point P4, the outer wall surface OF L , OF S The fourth slope F, which is farther away from the fourth slope L4 , F S4 Includes:

[0045] And the first to fourth slopes F L1 ~F L4, F S1 ~F S4 are provided to have different gradients from one another. That is, the first to fourth gradients are different from one another, and the magnitude relationship between them is in the order of "first gradient > second gradient > third gradient > fourth gradient." In this way, the first inner wall surface IF L As you move downward, the first outer wall surface OF L By providing the first inner wall surface IF as an inclined surface so as to be away from the L The shrinkage of the solidified shell can be compensated in the direction intersecting the extension direction (X-axis direction) of the second inner wall surface IF, i.e., in the second direction (Y-axis direction). S As you move downwards, you will come across the second outer wall surface OF S By providing the second inner wall surface IF as an inclined surface so as to be away from the S The shrinkage of the solidified shell can be compensated in a direction intersecting the extension direction (Y-axis direction), i.e., in a first direction (X-axis direction).

[0046] Hereinafter, a method for manufacturing a mold according to an embodiment of the present invention will be described with reference to FIGS. Fig. 6 is an exploded perspective view showing a part of a base mold used to manufacture a mold according to an embodiment of the present invention, and Fig. 7 is a diagram for explaining the amount of shrinkage of a solidified shell at each height when molten steel solidifies in the base mold. Here, (a) in Figure 7 shows the height of the molten metal surface in the base mold, P M 7(b) is a plan view showing the width of the solidified shell (solidification width) and the width of the internal space at the first design point DP1 of the mother mold, FIG. 7(c) is a plan view showing the second design point DP2 of the mother mold, FIG. 7(d) is a plan view showing the third design point DP3 of the mother mold, and FIG. 7(e) is a plan view showing the width of the solidified shell and the width of the internal space at the fourth design point DP4 of the mother mold.

[0047] Hereinafter, the mother mold will be described first with reference to Fig. 6. At this time, for ease of description, the first and second inner wall surfaces IF L , IF S , height of the molten metal surface P M , width at the height of the molten metal surface W LM , WSM The same reference numerals as those used in the mold according to the embodiment will be used in the following description. And the height of the molten metal surface in the base mold is P M Four points below the design point DP1 are set, but the first to fourth design points are referred to as DP1 to DP4 to distinguish them from the mold according to the embodiment.

[0048] The mother mold 4000 preferably includes a body having an internal space IS and a cooling water passage (not shown) embedded inside the body so that cooling water can circulate. In this case, the body of the mother mold 4000 has an inner wall surface IF:IF facing the internal space IS. L , IF S Width W L , W S The inner wall surface IF:IF L , IF S As it moves towards the bottom, the width W L , W S As the width decreases, the rate of decrease is constant. More specifically, the body 4100 of the matrix 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), and a pair of second walls 4120 each extending in the second direction (Y-axis direction) and spaced apart in the first direction (X-axis direction). L Width W L and the second inner wall surface IF of the second wall body 4120 S Width W S Each of these decreases as you move towards the bottom.

[0049] However, in the case of the mother mold 4000, the first and second inner wall surfaces IF L , IF S Width W L , W S As the flow rate decreases toward the bottom, the gradient or rate of decrease is constant. L , IF S As the distance decreases, the first and second outer wall surfaces OFL , OF S As shown in Figure 6, the upper end of the U Lower end P B The slope is set to have a constant gradient. Such a mother mold 4000 may be a mold that has been used in the past. More specifically, it may be a mold that has caused surface defects due to solidification shrinkage and caused problems in the quality of cast pieces due to the surface defects. Needless to say, the mother mold 4000 may be a mold that is separately provided so as to have the shape and structure described above. The mother mold 4000 is sometimes called the first mold, and a new mold manufactured with a width designed according to the solidification shrinkage rate of the mother mold 4000 is called the second mold 3000.

[0050] A method for detecting the amount of solidification shrinkage for each height in the above-described base mold 4000 will be described below. Once 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 surface of the molten steel reaches a preset height. For example, the uppermost end P U The molten steel is charged so that the molten steel surface is located 100 mm below the The molten steel charged into the base mold 4000 is cooled by cooling water circulating inside the base mold 4000, and in this process, a solidified shell C is formed as shown in Fig. 7. At this time, the solidified shell starts to form at the height of the molten steel surface, and the thickness of the solidified shell C may increase as it progresses downward.

[0051] When the molten steel solidifies and a solidified shell C is formed, solidification shrinkage occurs in the solidified shell C. At this time, the amount of shrinkage of the solidified shell C may vary in the height direction, with greater shrinkage occurring in the upper part than in the lower part. In the embodiment, the amount of shrinkage of the solidified shell C at each height is detected and used to manufacture the mold 3000 of the present invention. For this purpose, first, a plurality of design points at different heights at which the amount of solidification shrinkage should be detected are set. In this case, it is preferable to set four or more design points and detect the amount of solidification shrinkage. In the embodiment, an example will be described in which the amount of solidification shrinkage is detected at four design points DP1 to DP4 at different heights. That is, the first and second inner wall surfaces IF L , IF S At each of these points, the height of the molten metal surface P M The amount of solidification shrinkage is detected at each of the following points: a first design point DP1 located downward from the first design point DP1 by an amount corresponding to the first distance G1; a second design point DP2 located downward from the first design point DP1 by an amount corresponding to the second distance G2; a third design point DP3 located downward from the second design point DP2 by an amount corresponding to the third distance G3; and a fourth design point DP4 located downward from the third design point DP3 by an amount corresponding to the fourth distance G4.

[0052] At this time, the first to fourth design points DP1 to DP4 are set so that the first to fourth intervals G1 to G4 increase as they move downward. At this time, it is preferable to set the first to fourth design points DP1 to DP4 so that the ratio of the first interval G1: the second interval G2: the third interval G3: the fourth interval G4 is 1:2:3:4 (G1:G2:G3:G4=1:2:3:4). At this time, the height P M is the upper end P U When the point is 100 mm below the M (100mm) from the bottom P B The length is divided so that the ratio of the first to fourth intervals G1 to G4 is 1:2:3:4 (G1:G2:G3:G4=1:2:3:4). The position of the first point P1 is at the height P MThe position of the second point P2 is set to a position obtained by adding the first interval G1 to the first point P1, and the position of the third point P3 is set to a position obtained by adding the third interval G3 to the second point P2, and the position of the fourth point P4 is set to a position obtained by adding the fourth interval G4 to the third point P3.

[0053] Solidification shrinkage amount per height SD:SD L , S.D. S is the length between both ends of the solidified shell C at each of the first to fourth points P1 to P4 and the height of the molten metal surface P M Width W of the internal space IS at LM , W SM Here, the length between both ends of the solidified shell C means the length between both ends of the solidified shell C based on the first direction (X-axis direction) and the length between both ends of the solidified shell C based on the second direction (Y-axis direction).

[0054] For ease of explanation, the length between both ends of the solidified shell C is referred to as the "solidification width SW:SW L , S.W. S ". This also determines the solidification width SW in the first direction (X-axis direction). L :SW L1 ~SW L4 is the first inner wall surface IF of the solidified shell C L Furthermore, the solidification width SW in the second direction (Y-axis direction) can be explained as the length between the two ends of the extension direction. S :SW S1 ~SW S4 is the second inner wall surface IF of the solidified shell C S It can be explained as the length between the two ends in the extension direction. Reflecting this definition, the calculation method for the amount of solidification shrinkage per height will be explained again. M Width W of the internal space IS LM , W SM and the solidification width SW at each of the first to fourth design points DP1 to DP4. L1 ~SW L4 , S.W. S1 ~SWS4 It can be calculated as the difference between

[0055] That is, the solidification width SW in the first direction at the first to fourth design points DP1 to DP4 L1 ~SW L4 and the height of the molten metal surface P M Width W in the first direction of the internal space IS LM The first to fourth design points DP L1 ~DP L4 The amount of solidification shrinkage SD L1 ~SD L4 In addition, the solidification width SW in the second direction at the first to fourth design points DP1 to DP4 can be calculated. S1 ~SW S4 and the height of the molten metal surface P M Width W in the second direction SM By calculating the difference between the first and fourth design points DP S1 ~DP S4 The amount of solidification shrinkage SD S1 ~SD S4 may be calculated.

[0056] The method for calculating the amount of solidification shrinkage for each height in the first direction will be described in more detail below with reference to FIG. 7. The amount of solidification shrinkage SD at the first design point DP1 L1 As shown in Figure 7(b), the height of the molten metal surface P M Width W in the first direction of the internal space IS LM and the solidification width SW at the first design point P1. L1 It is calculated by calculating the difference between L1 =W LM -SW L1 ) In addition, the solidification shrinkage amount SD at the second design point DP2 L2 As shown in Figure 7(c), the height of the molten metal surface P M Width W in the first direction of the internal space IS LM and the solidification width SW at the second design point P2. L2 It is calculated by calculating the difference between L2 =W LM -SWL2 ) The solidification shrinkage amount SD at the third design point P3 L3 and the solidification shrinkage amount SD at the fourth design point P4 L4 is calculated using the same method as above (SD L3 =W LM -SW L3 , S.D. L4 =W LM -SW L4 ).

[0057] The method for calculating the amount of solidification shrinkage for each height in the second direction is the same as the method for the first direction described above. That is, the amount of solidification shrinkage at the first design point DP1 SD S1 As shown in Figure 7(b), the height of the molten metal surface P M Width W in the second direction of the internal space IS SM and the solidification width SW at the first design point DP1 S1 It is calculated by calculating the difference between S1 =W SM -SW S1 ) In addition, the solidification shrinkage amount SD at the second design point DP2 S2 As shown in Figure 7(c), the height of the molten metal surface P M Width W in the second direction of the internal space IS SM and the solidification width SW at the second design point DP2 S2 It is calculated by calculating the difference between S2 =W SM -SW S2 ) The solidification shrinkage amount SD at the third design point P3 S3 and the solidification shrinkage amount SD at the fourth design point P4 S4 Even in this case, the calculation is performed in the same manner as above (SD S3 =W SM -SW S3 , S.D. S4 =W SM -SW S4 ). In this way, molten steel is charged into the base mold 4000 and solidified, and the solidification shrinkage amounts SD at the first to fourth design points DP1 to DP4 in the first direction (X-axis direction) and the second direction (Y-axis direction) are calculated. L1 ~SDL4 , S.D. S1 ~SD S4 The detection of can be carried out for a plurality of types of molten steel.

[0058] More specifically, among the multiple types of molten steel, a first type of molten steel (first molten steel) having the largest amount of solidification shrinkage and a second type of molten steel (second molten steel) having the smallest amount of solidification shrinkage are used. At this time, each of the multiple types of molten steel is supplied to the base mold 4000 to detect the amount of solidification shrinkage, and then the amounts of solidification shrinkage at the same height are compared to select the molten steel having the largest amount of solidification shrinkage as the first molten steel and the molten steel having the smallest amount of solidification shrinkage as the second molten steel. Here, the plurality of molten steels may be produced as billets. The contents of the main components in the first and second molten steels are as shown in Table 1, for example.

[0059] [Table 1]

[0060] Hereinafter, a method for manufacturing a mold according to an embodiment of the present invention using a first molten steel and a second molten steel will be described with reference to FIGS. Fig. 8 is a flow chart showing a method for manufacturing a mold according to an embodiment of the present invention. Fig. 9 is a graph showing the amount of solidification shrinkage and the average amount of solidification 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. Once the first and second molten steels are prepared, they are charged into the base mold 4000 and solidified (S110, S120). At this time, one of the first and second molten steels, for example, the first molten steel, is charged into the base mold first and solidified (S110). When the first molten steel starts to solidify, a solidification shrinkage amount 1SD at each of the first to fourth design points DP1 to DP4 in the first direction (X-axis direction) is calculated. L1 ~1SD L4 and the solidification shrinkage amount 1SD at each of the first to fourth design points DP1 to DP4 in the second direction. S1 ~1SD S4is detected (S211, S212).

[0061] When solidification using the first molten steel is completed, the solidified product of the first molten steel is carried out from the base mold 4000. Then, the second molten steel is charged into the base mold 4000 and solidified (S120). When solidification of the second molten steel begins, the amount of solidification shrinkage 2SD at each of the first to fourth design points DP1 to DP4 in the first direction (X-axis direction) is calculated. L1 ~2SD L4 and the solidification shrinkage amount 2SD at each of the first to fourth design points DP1 to DP4 in the second direction. S1 ~2SD S4 is detected (S221, S222). Next, the amount of solidification shrinkage 1SD in the first direction detected at each of the first to fourth design points DP1 to DP4 during solidification of the first molten steel L1 ~1SD L4 and the amount of solidification shrinkage 2SD in the first direction detected at each of the first to fourth design points DP1 to DP4 during solidification of the second molten steel. L1 ~2SD L4 Average shrinkage amount AS L1 , A.S. L2 , A.S. L3 , A.S. L4 In other words, the first to fourth average contraction amounts AS in the first direction are calculated (S310). L1 ~AS L4 is the first to fourth solidification shrinkage amounts 1SD in the first direction detected using the first molten steel. L1 ~1SD L4 and the first to fourth solidification shrinkage amounts 2SD in the first direction detected using the second molten steel. L1 ~2SD L4 It can be obtained by calculating the average of

[0062] This will be explained in more detail as follows: A first solidification shrinkage amount 1SD at a first design point DP1 during solidification of the first molten steel L1 and the first solidification shrinkage amount 2SD at the first design point DP1 during the solidification of the second molten steel. L1 The first average shrinkage amount AS is calculated by averaging L1Also, the second solidification shrinkage amount 1S at the second design point DP2 during the solidification of the first molten steel is calculated. L2 and a second solidification shrinkage amount 2S at a second design point DP2 during solidification of the second molten steel. L2 The second average shrinkage amount, AS, is calculated by averaging L2 Then, the third average shrinkage amount AS is calculated in the same way. L3 and the fourth average shrinkage amount AS L4 is calculated. Referring to FIG. 9 and Table 2, the first average shrinkage amount AS in the first direction L1 is 0.4 mm, the second average shrinkage amount AS L2 is 0.74 mm, the third average shrinkage AS L3 is 1.09 mm, the fourth average shrinkage AS L4 may be 1.36 mm.

[0063] [Table 2]

[0064] In addition, the amount of solidification shrinkage 1SD in the second direction detected at each of the first to fourth design points DP1 to DP4 during solidification of the first molten steel S1 ~1SD S4 and the amount of solidification shrinkage 2SD in the second direction detected at each of the first to fourth design points DP1 to DP4 during solidification of the second molten steel. S1 ~2SD S4 Average shrinkage amount AS S1 , A.S. S2 , A.S. S3 , A.S. S4 This is the same as the method for calculating the average shrinkage amount in the first direction described above, so a detailed explanation and specific numerical values ​​will be omitted. The first to fourth average contraction amounts AS in the first direction obtained by this method are L1 , A.S. L2 , A.S. L3 , A.S. L4 and the first to fourth average shrinkage amounts AS in the second direction. S1 , A.S. S2 , A.S.S3 , A.S. S4 That is, the first to fourth average shrinkage amounts AS in the first direction are L1 ~AS L4 The first inner wall surface IF of the mold to be manufactured is L The first to fourth widths W L1 ~W L4 In addition, the first to fourth average shrinkage amounts AS in the second direction are designed (S410). S1 ~AS S4 Using the second inner wall surface IF S The first to fourth widths W S1 ~W S4 is designed (S420).

[0065] First, the first inner wall IF L The first to fourth widths W L1 ~W L4 The method for designing the first inner wall surface IF (S410) will be described in more detail below. L The widths at the first to fourth points P1 to P4 in the first direction are the first to fourth average shrinkage amounts AS L1 ~AS L4 and the height of the water surface P M Width W in the first direction LM That is, the first inner wall surface IF L First width W at first point P1 L1 is the height of the molten metal surface P M Width W in the first direction LM to the first average shrinkage amount AS L1 is designed to a value minus (W L1 =W LM -AS L1 ) Also, the second width W at the second point P2 L2 is the height of the molten metal surface P M Width W in the first direction LM to the second average shrinkage amount AS L2 is designed to a value minus (W L2 =W LM -AS L2 ) In the same way, the third width W L3 and the fourth width W L4Each of these is the height of the molten metal surface P M Width W in the first direction LM to the third average shrinkage amount AS L3 and the fourth average shrinkage amount AS L4 It is designed to have a value obtained by subtracting each of the above (W L3 =W LM -AS L3 , W L4 =W LM -AS L4 ).

[0066] For more specific explanation, the first inner wall surface IF L The height of the molten metal surface at P M Width W at LM The first inner wall surface IF is 200 mm. L The first width W at the first point P1 L1 is the height of the molten metal surface P M Width W at LM (200mm) to the first average shrinkage amount AS L1 (0.4 mm) is subtracted from the first width W L1 is designed to be 199.6 mm (200 mm - 0.4 mm). M Width W at LM From the second to fourth average shrinkage amounts AS L2 ~AS L4 By subtracting the second to fourth widths W L2 ~W L4 can be designed. And the second inner wall surface IF S The first to fourth widths W S1 , W S2 , W S3 , W S4 is the first inner wall surface IF L The second inner wall surface IF is designed in the same manner as the first inner wall surface IF (S420). S The first width W at the first point P1 S1 is the height of the molten metal surface P M Width W at LM to the first average shrinkage amount AS S1The remaining second to fourth widths W S2 ~W S4 Each of these is the height of the molten metal surface P M Width W at LM to the first, second and third average shrinkage amounts AS S2 , A.S. S3 , A.S. S4 The design is made to have a value obtained by subtracting each of the above.

[0067] At this time, the first and second inner wall surfaces IF L , IF S The width W of the fourth point P4 at each L4 , W S4 is the height of the molten metal surface P M Width W at LM to the fourth average shrinkage amount AS L4 , A.S. S4 This is the value obtained by further subtracting 0.1 mm from the value obtained by subtracting 0.1 mm from the first and second inner wall surfaces IF L , IF S This is to reduce friction between the mold and the slab, thereby further extending the life of the mold. In this way, the first inner wall surface IF L The first to fourth widths W L1 ~W L4 Design of (S410), second inner wall IF S The first to fourth widths W S1 ~W S4 When the design of the first inner wall surface IF is completed (S420), the mold is manufactured using the design (S500). L The widths at the first to fourth points P1 to P4 are the designed first to fourth widths W L1 ~W L4 The second inner wall surface IF S The widths at the first to fourth points P1 to P4 are the designed first to fourth widths W S1 ~W S4 The body 3100 of the mold 3000 is manufactured so that:

[0068] (a), (c), (e), (g), and (i) in Figure 10 are photographs of the surfaces of the billets from the first to fifth experimental examples, and (b), (d), (f), (h), and (j) in Figure 10 are graphs showing the surface roughness (mm), i.e., the surface height (mm), of the billets from the first to fifth experimental examples. When measuring the roughness, the tip of the roughness tester was brought into contact with the surface of the billet, and the surface height was measured while the tip was moved in the width direction of the billet. When measuring the surface height while moving the tip in the width direction of the billet, measurements were taken at multiple positions in the direction intersecting the width direction, i.e., the longitudinal direction. The average height measured at multiple positions is shown in Figure 10 (b), (d), (f), (h), and (j). Here, the billet according to the first experimental example was manufactured using a base mold, and the billets according to the second to fifth experimental examples were manufactured using a mold according to the embodiment. The billets according to the second to fifth experimental examples were cast using molten steel of steel types with different contents of at least carbon (C) and manganese (Mn).

[0069] [Table 3]

[0070] 10(b), in the case of the billet manufactured using the master mold, a large defect was found, recessing from the surface to the inside by about 1.89 mm. It can be confirmed from FIGS. 10(a) and 10(b) that this defect occurred at a point about 120 mm away from one end (0 mm) of the billet in the width direction. 10(d), (f), (h), and (j), in the billets according to Experimental Examples 2 to 5, the size of the deepest recessed defect was less than 1 mm, which was significantly smaller than that of Experimental Example 1. That is, the deepest defect in Experimental Example 2 was 0.25 mm, in Experimental Example 3 was 0.71 mm, in Experimental Example 4 was 0.94 mm, and in Experimental Example 5 was 0.25 mm, all of which were smaller than that of Experimental Example 1.

[0071] This shows that, when a cast is produced using the mold according to the embodiment, surface defects can be reduced. This is because, in the case of the mold according to the embodiment, the inner wall surface IF reflects the different amounts of solidification shrinkage at each height. L , IF S Width W per height L1 ~W L4 , W S1 ~W S4 By designing and providing this, it is possible to effectively compensate for solidification shrinkage at each height. M By making the change in width in the section between the first point P1 and the first point P2 occur more rapidly than in other sections, solidification shrinkage in the upper part of the body 3100, where the solidified shell shrinks the most, can be effectively compensated for. When manufacturing the mold, the solidification shrinkage rates of a plurality of types of steel, i.e., molten steel, are solidified, and the width of the inner wall surface for each height is designed reflecting the average value of the solidification shrinkage rates. Therefore, in the case of the mold according to the embodiment, it is possible to manufacture a slab in which the solidification shrinkage rate is suppressed or prevented for a plurality of types of steel. [Industrial Applicability]

[0072] According to an embodiment of the present invention, the compensation rate for solidification shrinkage of the solidified shell can be improved. That is, by manufacturing a mold by designing the width for each height of the mold according to the amount of solidification shrinkage that differs from one another at each height, the compensation rate for solidification shrinkage at each height can be improved. Therefore, the occurrence of defects on the surface of the slab due to the shrinkage of the solidified shell can be suppressed or prevented. [Explanation of symbols]

[0073] 1. Castings 10 ladle 20 Tundish 22 nozzles 40 Cooling section 41 Segment 3000 mold 3100 Body 3110 First Wall 3120 Second Wall 4000 Mother Mold 4100 Body 4110 First Wall 4120 Second Wall Average solidification shrinkage between AS 1SD and 2SD AS L Average shrinkage AS L1 First average shrinkage in the first direction (X direction) AS L2 The second average shrinkage in the first direction (X direction) AS L3 The third average shrinkage in the first direction (X direction) AS L4 The fourth average shrinkage in the first direction (X direction) AS S1 The first average shrinkage in the second direction (Y direction) AS S2 The second average shrinkage in the second direction (Y direction) AS S3 The third average shrinkage in the second direction (Y direction) AS S4 The fourth average shrinkage in the second direction (Y direction) 1AS L2 Average shrinkage C Solidified shell DP design point DP1 First Design Point DP2 Second Design Point DP3 Third Design Point DP4 4th Design Point DP L Solidification width in the first direction DP L1 Solidification width in the first direction (X direction) at the first design point DP L2 Solidification width in the first direction (X direction) at the second design point DP L3 Solidification width in the first direction (X direction) at the third design point DP L4Solidification width in the first direction (X direction) at the fourth design point DP S Solidification width in the second direction DP S1 Solidification width in the second direction (Y direction) at the first design point DP S2 Solidification width in the second direction (Y direction) at the second design point DP S3 Solidification width in the second direction (Y direction) at the third design point DP S4 Solidification width in the second direction (Y direction) at the fourth design point FF L , F S Slope G interval G1P M Distance between and DP1 G2Dp1 and DP2 spacing Spacing between G3DP2 and DP3 Spacing between G4DP3 and DP4 IF:IF L , IF S Inner wall surface IS interior space IS DL Amount of solidification shrinkage IS DS Amount of solidification shrinkage OF:OF L , OF S exterior wall surface P point P1 First Point P2 Second Point P3 Third Point P4 Fourth Point P B lower end P U top end P M Height of molten steel surface S distance S1~S4 upper end P U Distance from the bottom to points P1 to P4 SD: Amount of solidification shrinkage of molten steel 1SD Solidification shrinkage of the first molten steel 2SD Secondary molten steel solidification shrinkage SD LAmount of solidification shrinkage 1SD L1 ~1SD L4 Amount of solidification shrinkage in the first direction (X direction) detected in DP1 to DP4 using the first molten steel 2SD L1 ~2SD L4 Amount of solidification shrinkage in the first direction (X direction) detected in DP1 to DP4 using the second molten steel SD S Amount of solidification shrinkage 1SD S1 ~1SD S4 Amount of solidification shrinkage in the second direction detected at DP1 to DP4 during solidification of the first molten steel 2SD S1 ~2SD S4 Amount of solidification shrinkage in the second direction detected at DP1 to DP4 during solidification of the second molten steel 1S L Amount of solidification shrinkage in the first direction (X direction) detected using the first molten steel 1S L2 Second solidification shrinkage at DP2 during solidification of the first molten steel 2S L Amount of solidification shrinkage in the first direction (X direction) detected using the second molten steel 2S L2 Second solidification shrinkage at DP2 during the solidification of the second molten steel SW solidification width SW L Solidification width in direction I (X direction) SW S Solidification width in the second direction (Y direction) T L First wall thickness T L1 ~T L4 , T LM Thickness of the first wall at each design point T S Thickness of the second wall 3110 T S1 ~T S4 , T SM Thickness of the second wall at each design point W: width of inner surface of mold W M The height of the first mold inner wall surface at the molten metal surface (P M ) width W L Width of the internal space IS in the first direction (X direction) W L1 ~W L4 Width in the first direction (X direction) at each point P1 to P4 W LM Water surface height P M Width of the internal space IS in the first direction (X direction) W S Width of the internal space IS in the second direction (Y direction) W S1 ~W S4 Width in the second direction (Y direction) at each point P1 to P4 W SM Water surface height P M Width of the internal space IS in the second direction (Y direction)

Claims

1. solidifying molten steel in a first mold; a step of calculating a solidification shrinkage (SD) that occurs when the molten steel solidifies in the first mold for each height of the first mold; a step of setting a design width for each height of the second mold to be manufactured using the calculated solidification shrinkage (SD) for each height; a step of providing a second mold so that the width (W) of the inner wall surface of the second mold per height is the designed width per height; Including, The step of calculating the amount of solidification shrinkage (SD) for each height of the first mold includes: The height of the molten steel surface (P Ｍ setting a plurality of design points (DPs) having different heights below the At each of the plurality of design points (DP) set in the first mold, the solidification width (S Ｗ ) and The height of the molten metal surface on the inner wall surface of the first mold (P Ｍ ) width (W Ｍ ) at each of the plurality of design points (DP) Ｗ ) to calculate the solidification shrinkage (SD) at each of the plurality of design points (DP); Including, The solidification width (S Ｗ ) is the length between both ends of the solidified shell in the width direction.

2. 2. The method for manufacturing a mold according to claim 1, wherein when the plurality of design points (DP) are set in the first mold, the distances between the plurality of design points (DP) are set to increase as they move downward.

3. 3. The method for manufacturing a mold according to claim 2, wherein when a plurality of design points (DP) are set in the first mold, the distances between the plurality of design points (DP) are set to increase by a constant value.

4. The plurality of design points (DP) set in the first mold are Ｍ ) are points that are successively farther away from the first to fourth design points (DP １ ~DP ４ ), The height of the molten metal surface (P Ｍ ) and the first design point (DP １ ) and the first interval (G １ ), the first design point (DP １ ) and the second design point (DP ２ ) and the second interval (G ２ ), the second design point (DP ２ ) and the third design point (DP ３ ) and the third interval (G ３ ), the third design point (DP ３ ) and the fourth design point (DP ４ ) and the fourth interval (G ４ ) in the first interval (G １ ) to the fourth interval (G ４ 4. The method for manufacturing a mold according to claim 3, wherein the temperature is adjusted so as to increase by a constant value as the temperature increases toward the target temperature.

5. The process of setting the design width for each height includes: setting a plurality of points (P) on an inner wall surface of the second mold at the same positions as the plurality of design points (DP) set on the first mold; The height of the molten metal surface in the first mold (P Ｍ ) the width of the inner wall surface (W Ｍ ) from which the amount of solidification shrinkage (SD) for each of the plurality of design points (DP) is subtracted (W Ｍ -SD) process, The deduction (W) at each of the plurality of design points (DP) Ｍ -SD) value as the width (W) at each of the plurality of points (P) set on the inner wall surface of the second mold; The method for manufacturing a mold according to claim 1, comprising:

6. The step of calculating the solidification shrinkage (SD) at each of the plurality of design points (DP) includes: a step of supplying and solidifying a first molten steel into the first mold and calculating a solidification shrinkage (1SD) of the first molten steel at the plurality of design points (DP); a step of supplying and solidifying second molten steel into the first mold and calculating 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 (2SD) of the second molten steel for each of the plurality of design points (DP); Including, The height of the molten metal surface of the first mold (P Ｍ ) the width of the inner wall surface (W Ｍ ) from which the amount of solidification shrinkage (SD) for each of the plurality of design points (DP) is subtracted (W Ｍ -SD) 6. The method for manufacturing a mold according to claim 5, wherein the solidification shrinkage (SD) for each of the plurality of design points (DP) is an average solidification shrinkage (AS) for each of the plurality of design points (DP).

7. selecting the first and second molten steels; The step of selecting the first and second molten steels includes: supplying each of a plurality of types of molten steel into the first mold and solidifying the molten steel; a step of calculating the amount of solidification shrinkage that occurs when each of the plurality of types of molten steel is solidified; a step of selecting the molten steel that has caused the largest amount of solidification shrinkage among the calculated amounts of solidification shrinkage as a first molten steel, and selecting the molten steel that has caused the smallest amount of solidification shrinkage as a second molten steel; The method for producing a mold according to claim 6, comprising:

8. A mold having an internal space into which molten steel can be poured, a body having the interior space; the body includes a pair of first walls each extending in a first direction and spaced apart from each other in a second direction intersecting the first direction, and a pair of second walls each extending in the second direction and spaced apart from each other in the first direction; A plurality of points at different heights are set on the inner wall surfaces of the first and second walls, the widths at each of the plurality of points on the inner wall surfaces of the first and second walls decrease as they progress downward; The rate at which the width decreases varies at a plurality of points in the height direction; The spacing between the plurality of points in the height direction is different from one another, and the spacing between the plurality of points in the height direction increases as the distance goes downward; a width of the inner wall surface of the first wall body is a length of the inner wall surface of the first wall body in the first direction, A mold characterized in that the width of the inner wall surface of the second wall is the length of the inner wall surface of the second wall in the second direction.

9. 9. The mold of claim 8, wherein the vertical spacing between the plurality of points increases by a constant value.

10. The plurality of points include first to fourth points which are points successively further below the height of a surface of molten steel supplied into the body, A first distance (G) between the height of the molten metal surface and the first point １ ), a second distance (G ２ ), a third distance (G ３ ), a fourth interval (G ４ ) in the first interval (G １ ) to the fourth interval (G ４ 10. The mold according to claim 9, wherein the value increases by a constant value as the distance from the center of the mold increases.

11. the inner wall surface of the body is provided as a slope that slopes away from the outer wall surface, which is the opposite surface of the inner wall surface, as it progresses downward; 9. The mold according to claim 8, wherein the gradient of the inner wall surface of the body is changed at the plurality of points as inflection points.

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