Casting method and cast product

Abstract

This casting method comprises: a pouring step for pouring a molten metal obtained from cast steel or non-ferrous metal into a mold in which a chiller is embedded; and a first cooling step for transforming the molten metal into a solidified body by cooling the poured molten metal so as to lower the temperature of the molten metal to the solidus temperature of the molten metal. The volume of the molten metal to be poured into the mold in the pouring step is 105-108% of the volume of the solidified body. The chiller is embedded in the mold so as to cause solidification of the molten metal to take place upward from the lower side thereof in the first cooling step.

Description

Casting method and cast product

[0001] This disclosure relates to a casting method for handling molten steel or non-ferrous metals, and to castings obtained therefrom. This application claims priority to Japanese Patent Application No. 2024-007916, filed with the Japan Patent Office on January 23, 2024, the contents of which are incorporated herein by reference.

[0002] Casting is a manufacturing method in which molten metal is poured into a mold and cooled to obtain a cast product, details of which are disclosed in, for example, Patent Document 1.

[0003] The solidification of molten metal that occurs during cooling generally progresses from the surface toward the interior. As the molten metal shrinks during solidification, shrinkage cavities form inside the casting. If shrinkage cavities exist in the part of the casting that will be used as the finished product, there is a risk that the finished product will break due to a decrease in strength when it is used.

[0004] Therefore, a method has been devised in which the amount of molten metal poured into the mold is greater than the amount corresponding to the finished product, and shrinkage cavities are generated in the excess portion above the finished product. The molten metal corresponding to this excess portion has traditionally been called a riser. If the riser is made to solidify last among the molten metal, the shrinkage cavities can be concentrated in the riser.

[0005] Japanese Patent Application Laid-Open No. 2002-346728

[0006] In order to ensure that the feeder head solidifies last, the proportion of the feeder head to the entire molten metal must be increased, and in some cases the feeder head may account for nearly 50% of the molten metal, which may result in an increase in the amount of molten metal to be poured.

[0007] Increasing the amount of casting can lead to various problems, such as an increase in the melting energy required to convert metal into molten metal, an increase in costs due to larger molds, or an increase in the time required for the casting process. Furthermore, when casting molten metal into a sand mold, the contact time between the sand mold and the molten metal is prolonged, which raises concerns that the sand may be seized onto the casting.

[0008] An object of the present disclosure is to provide a casting method and a casting product that reduce casting weight.

[0009] A casting method according to at least one embodiment of the present disclosure comprises: a pouring step of pouring molten metal of cast steel or non-ferrous metal into a mold having chills embedded therein; and a first cooling step of cooling the poured molten metal so that the temperature of the molten metal drops to the solidus temperature of the molten metal, thereby transforming the molten metal into a solidified body, wherein the volume of the molten metal poured into the mold in the pouring step is 105% or more and 108% or less of the volume of the solidified body, and the chills are embedded in the mold so that the solidification of the molten metal in the first cooling step progresses from bottom to top.

[0010] A casting according to at least one embodiment of the present disclosure is a casting obtained by the above-described casting method, and includes a top layer portion that is the final solidification portion of the molten metal and in which shrinkage cavities are formed.

[0011] According to the present disclosure, a casting method and a cast product with reduced casting weight can be provided.

[0012] FIG. 1 is a schematic view of a casting apparatus according to one embodiment; FIG. 2 is a schematic view of a casting apparatus immediately after molten metal has been poured according to one embodiment; FIG. 3 is a schematic view of a molten metal after liquid-phase shrinkage according to one embodiment; FIG. 4 is a schematic view of a solidified body which is the molten metal after solid-liquid phase shrinkage according to one embodiment; FIG. 5 is a schematic view of a cast product which is the solidified body after solid-phase shrinkage according to one embodiment; FIG. 6 is a schematic view of a removal step according to one embodiment; FIG. 7 is a flowchart showing a casting method according to one embodiment; FIG. 8 is a schematic graph showing the shrinkage rate of a molten metal body according to one embodiment.

[0013] Several embodiments of the present disclosure will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are not intended to limit the scope of the present disclosure and are merely illustrative examples. For example, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express relative displacements with a tolerance or angle or distance to the extent that the same function is achieved. For example, expressions expressing the equality of things, such as "same," "equal," and "homogeneous," not only express strict equality, but also express tolerance or differences to the extent that the same function is achieved. For example, expressions expressing shapes such as a square or cylindrical shape not only express shapes such as a square or cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is achieved. On the other hand, the expressions "comprise," "include," or "have" one component are not exclusive expressions that exclude the existence of other components. Note that similar components may be assigned the same reference numerals and descriptions thereof may be omitted.

[0014] <Overview of Casting Apparatus 1> FIG. 1 is a schematic diagram of a casting apparatus 1 according to an embodiment of the present disclosure. The casting apparatus 1 includes a sand mold 3 for casting a molten metal 10 (see FIG. 2 ) and chills 6 embedded in the sand mold 3. The primary heat retained by the molten metal 10 cast into the sand mold 3 is transferred to the chills 6, thereby cooling the molten metal 10. The cooling of the molten metal 10 includes a first cooling step in which the temperature of the molten metal 10 is lowered to a solidus temperature to produce a solidified body 20 (see FIG. 4 ), which is the molten metal 10 after solid-liquid phase contraction, and a second cooling step in which the temperature of the solidified body 20 is further lowered to room temperature to produce a casting 25 (see FIG. 5 ), which is the solidified body 20 after solid-liquid phase contraction. When at least a portion of the top layer 21 formed on the casting 25 removed from the sand mold 3 is removed, a finished product 23 (see FIG. 6 ) is obtained. The finished product 23 may have various shapes and is used for various applications. As an example, the finished product 23 may be applied to a housing that constitutes a part of an internal combustion engine.

[0015] The molten metal 10 of the present disclosure is a liquid of cast steel or a non-ferrous metal. The cast steel is iron with a carbon content of less than 2.14%. The non-ferrous metal is aluminum, magnesium, copper, or the like. Note that a metal mold may be used in the casting apparatus 1 instead of the sand mold 3.

[0016] An overview of the casting process of the present disclosure will be described with reference to Figures 2 to 6. First, molten metal 10 is poured into a sand mold 3 (see Figure 2). The molten metal 10 includes a molten metal main body 13 having a desired volume (i.e., a volume as a design value) of a solidified body 20 as an intermediate product, and a bulking portion 15 having a volume of 5% to 8% of the desired volume. In practice, it is difficult to distinguish between the molten metal main body 13 and the bulking portion 15, but in Figure 2 they are shown with different hatching (the same applies to the other drawings).

[0017] In some embodiments, a heat insulating material 5 may be placed above the molten metal 10 cast into the sand mold 3. The heat insulating material 5 is, for example, alumina powder, aluminum powder, or iron oxide powder. The heat insulating material 5 may also include a non-metallic material such as resin. Furthermore, alumina fiber or the like may be used instead of alumina powder. The heat insulating material 5 is placed on the liquid surface of the molten metal 10 (i.e., the liquid surface of the bulking portion 15).

[0018] Continuing with the explanation of the casting process, as shown in Figures 2, 3 and 4, the molten metal 10 is cooled by the chills 6. That is, first cooling and second cooling occur in sequence.

[0019] During the first cooling, the liquid-phase contraction and solid-liquid-phase contraction of the molten metal 10 occur sequentially, with the solidification of the molten metal 10 progressing from bottom to top. In other words, the chills 6 are positioned in advance to achieve directional solidification, in which the bottom portion of the molten metal 10 solidifies first and the surface portion of the molten metal 10 solidifies last. When the temperature of the molten metal 10 drops to the solidus temperature, the solid-liquid-phase contraction ends, and a solidified body 20 is obtained from the molten metal 10. At this stage after the first cooling is completed (see FIG. 4), shrinkage cavities 9 are formed in at least one of the interior of the bulking portion 15 and the liquid surface of the bulking portion 15 (the shrinkage cavities 9 are formed during the solid-liquid-phase contraction process). Subsequently, as shown in FIG. 5, the solidified body 20 is further cooled by the second cooling. The solid-phase contraction of the solidified body 20 occurs, and the temperature of the solidified body 20 drops to room temperature. This results in a cast product 25, and the second cooling is completed.

[0020] As shown in Fig. 6, the top layer 21 of the casting 25 corresponds to at least a part of the final solidification portion of the molten metal 10, and has shrinkage cavities 9 formed therein (the shrinkage cavities 9 are generated only during the first cooling step). Therefore, after the second cooling step, the top layer 21 may be machined to remove the shrinkage cavities 9 from the casting 25. The casting 25 from which the top layer 21 has been removed is used as the finished product 23.

[0021] 6, the top layer 21 and the other portions are hatched differently for the sake of clarity, but in reality, it is difficult to distinguish between them. Furthermore, at least a portion of the top layer 21 may remain after the shrinkage cavities 9 are removed. In other words, at least a portion of the top layer 21 may be included in the finished product 23.

[0022] <Casting Method> Fig. 7 is a flowchart showing the above-mentioned casting process. In the following, "step" may be abbreviated as "S".

[0023] First, a pouring step (S1) is performed in which molten metal 10 is poured into sand mold 3. The volume of molten metal 10 poured into sand mold 3 in the pouring step is 105% or more and 108% or less of the volume of solidified body 20.

[0024] Next, a heat insulating material placement step (S3) is performed in which a heat insulating material 5 is placed behind the poured molten metal 10. Next, a first cooling step (S5) is performed to transform the poured molten metal 10 into a solidified body 20. In the first cooling step, solidification of the molten metal 10 progresses from bottom to top. More specifically, the molten metal 10 is cooled so that solidification progresses from bottom to top as liquid-phase contraction and solid-liquid-phase contraction occur. When the liquid-phase contraction and solid-liquid-phase contraction are completed in order, the first cooling is completed. By the completion of the first cooling, shrinkage cavities 9 have been formed in the final solidified portion of the molten metal 10.

[0025] Thereafter, a second cooling step (S7) is performed so that the solidified body 20 becomes a casting 25. The temperature of the solidified body 20 is lowered to room temperature, thereby producing the casting 25. Note that no new shrinkage cavities 9 are formed during the second cooling. Thereafter, a removal step (S9) is performed to remove the top layer 21 of the casting 25, and the present flowchart ends.

[0026] <Amount of Molten Metal 10 Cast> The inventors of the present application decided to reconsider the conventional method of designing chills 6 and sand molds 3 on the assumption that a riser will be used. If the riser is to be eliminated, it is necessary to consider the minimum amount of molten metal 10 that must be cast.

[0027] During the first cooling, the molten metal 10 shrinks in the process of changing into the solidified body 20. Therefore, if only the molten metal main body 13 having a volume substantially equal to the desired volume of the solidified body 20 (i.e., the volume as a design value) is cast into the sand mold 3, the actual volume of the solidified body 20 obtained by cooling will be smaller than the desired volume.

[0028] According to the inventor's findings, the volume reduction due to shrinkage of the molten metal main body 13 during the first cooling step is 5% or less compared to the volume before shrinkage. Figure 8 shows the basis for this. The figure is a schematic graph showing the results of an analysis of the shrinkage volume of the molten metal main body 13. As the molten metal main body 13 solidifies from the liquid phase state indicated by point A to the solid phase state indicated by point B, liquid phase shrinkage and solid-liquid phase shrinkage occur in this order. As shown in the figure, the volume reduction due to shrinkage of the molten metal main body 13 is 5% or less compared to the volume before shrinkage.

[0029] In other words, if an additional amount of molten metal 10 having a volume of 5% to 8% of the volume of the molten metal main body 13 before contraction is prepared as the bulking portion 15, the minimum amount of molten metal 10 necessary to produce a solidified body 20 having a desired volume can be secured. Furthermore, if the chills 6 are designed so that the bulking portion 15 is the last to solidify in the molten metal 10 during the first cooling, the final solidified portion can be formed at the top of the molten metal 10. This allows shrinkage cavities 9 to be concentrated in the uppermost layer 21 of the casting 25 obtained by the second cooling. The chills 6 are designed by identifying the solidification process of the molten metal 10 through analysis.

[0030] In the second cooling step, the volume of solidified body 20 further shrinks by about 7% as it transforms into casting 25. Therefore, the design value for the volume of solidified body 20 needs to be set to a value that is about 7% higher than the desired volume of casting 25. The reason why the volume of solidified body 20 shown at point C in Figure 8 has changed by only about 1% compared to the volume of solidified body 20 shown at point B is because the temperature of the solid phase state shown at point C is higher than room temperature, and point C merely represents a state in the middle of the transformation of solidified body 20 into casting 25.

[0031] As described above, if the shrinkage cavities 9 can be concentrated at the top of the solidified body 20, the bulking portion 15 can serve the same role as a riser. In this regard, according to the casting method including the pouring step (S1) and the first cooling step (S5), the pouring volume of the molten metal 10 is set to 105% or more and 108% of the volume of the solidified body 20, and the molten metal 10 is cooled so that solidification proceeds from bottom to top. This allows the top part of the molten metal 10, which corresponds to the bulking portion 15, to solidify last. Therefore, a conventional riser is no longer necessary, and a casting method with reduced casting weight can be realized.

[0032] Furthermore, in some embodiments of the present disclosure, a removing step (S9) is performed in which the top layer 21, which is the final solidified portion of the molten metal 10, is removed from the casting 25 to obtain a finished product 23. According to the above configuration, a finished product 23 from which the shrinkage cavities 9 have been removed can be obtained, and damage to the finished product 23 due to insufficient strength can be suppressed.

[0033] In some embodiments of the present disclosure, a heat-insulating material arranging step (S3) is performed in which a heat-insulating material 5 is arranged above the poured molten metal 10. According to the above configuration, the heat-insulating material 5 prevents the bulking portion 15 from being exposed to the outside air. This prevents the bulking portion 15 from radiating heat to the outside air, and more reliably allows the bulking portion 15 to become the final solidification portion.

[0034] 1 , in some embodiments, the chills 6 include a lower chill 7 located below the vertical center (two-dot chain line M) of the casting space S formed inside the sand mold 3, and an upper chill 8 located above the vertical center of the casting space S, and the total volume of the lower chills 7 may be greater than the total volume of the upper chills 8. Here, the vertical center of the casting space S is the vertical center between the lowermost and uppermost ends of the inner surface 3 a of the sand mold 3 that defines the casting space S.

[0035] According to the above-described configuration, heat dissipation from the molten metal 10 in the lower portion of the sand mold 3 can be promoted, so that the solidification of the molten metal 10 can proceed more reliably from below to above.

[0036] <Summary> The contents described in the above-described embodiments can be understood, for example, as follows.

[0037] 1) A casting method according to at least one embodiment of the present disclosure comprises: a pouring step (S1) of pouring a molten metal (10) of cast steel and a non-ferrous metal into a mold (sand mold 3) having chills (6) embedded therein; and a first cooling step (S5) of cooling the poured molten metal so that the temperature of the molten metal drops to the solidus temperature of the molten metal, thereby transforming the molten metal into a solidified material (20), wherein the volume of the molten metal poured into the mold in the pouring step is 105% or more and 108% or less of the volume of the solidified material, and the chills are embedded in the mold so that the solidification of the molten metal in the first cooling step progresses from bottom to top.

[0038] The present inventors decided to reconsider the conventional approach of designing chills and molds with the assumption that a feeder is used. If a feeder is eliminated, the minimum amount of molten metal needed to be poured must be considered. Molten metal shrinks during its transformation into a solid. Therefore, if only a molten metal main body (13) having a volume approximately equal to the desired volume of the solidified body to be obtained after cooling is poured into the mold, the actual volume of the solidified body will be smaller than the desired volume. According to the inventors' findings, the volume reduction due to shrinkage of the molten metal main body is 5% or less compared to the volume before shrinkage. Therefore, by providing an additional molten metal with a volume of 5% to 8% of the desired volume of the solidified body as a bulking portion (15), the minimum amount of molten metal needed to obtain a solidified body with the desired volume can be secured. Furthermore, by designing the chills so that the bulking portion solidifies last in the molten metal, the top of the molten metal can be solidified last. Since shrinkage cavities can be concentrated at the top of the solidified body, the bulking portion can fulfill a similar role to a feeder. In this regard, according to the above-mentioned configuration 1), the molten metal is cooled so that the pouring volume of the molten metal is 105% or more and 108% or less of the volume of the solidified body, and solidification proceeds from bottom to top. This allows the uppermost part of the molten metal portion, which corresponds to the bulking portion, to finally solidify. Therefore, a conventional feeder is not required, and a casting method with reduced pouring weight can be realized.

[0039] 2) In some embodiments, the casting method described in 1) above further comprises, after the first cooling step, a second cooling step (S7) in which the solidified body is further cooled to change the solidified body into a casting (25), and a removal step (S9) in which a top layer (21), which is the final solidified portion of the molten metal, is removed from the casting to remove shrinkage cavities (9) formed in the top layer, thereby obtaining a finished product (23) from the casting.

[0040] According to the above-mentioned configuration 2), a finished product can be obtained from which shrinkage cavities have been removed, and therefore, the finished product can be prevented from being damaged due to insufficient strength.

[0041] 3) In some embodiments, the casting method according to 1) or 2) above further comprises a heat insulating material arrangement step (S3) of arranging a heat insulating material (5) above the poured molten metal before the first cooling step.

[0042] According to the above configuration 3), the heat insulating material can suppress the heat radiation from the bulky portion to the outside air, so that the bulky portion can be made into the final solidified portion more reliably.

[0043] 4) In some embodiments, in the casting method described in any one of 1) to 3) above, the chills include a lower chill (7) located below the vertical center of the casting space formed inside the mold, and an upper chill (8) located above the vertical center of the casting space, and the total volume of the lower chills is greater than the total volume of the upper chills.

[0044] According to the above configuration 4), heat dissipation from the molten metal at the lower part of the mold can be promoted, so that the solidification of the molten metal can proceed more reliably from below to above.

[0045] 5) A solidified body according to at least one embodiment of the present disclosure is a solidified body obtained by the casting method of 1) above, and includes an uppermost layer portion (21) which is the final solidified portion of the molten metal and in which shrinkage cavities are formed.

[0046] According to the configuration 5) above, the same technical advantages as those of the configuration 1) above can be obtained.

[0047] 1: Casting device 3: Sand mold 3a: Inner surface 5: Heat insulating material 6: Chills 7: Lower chills 8: Upper chills 9: Shrinkage cavities 10: Molten metal 13: Main body of molten metal 15: Bulking portion 20: Solidified body 21: Top layer 23: Finished product 25: Casting L1, L2: Dimensions M: Two-dot chain line S: Pouring space

Claims

1. A casting method comprising: a casting step of casting a molten steel or non-ferrous metal melt into a mold in which a chill is embedded; and a first cooling step of cooling the molten metal so that the temperature of the cast molten metal drops to the solidus temperature of the molten metal, thereby changing the molten metal into a solidified body, wherein the volume of the molten metal cast into the mold in the casting step is 105% or more and 108% or less of the volume of the solidified body, and the chill is embedded in the mold so that solidification of the molten metal in the first cooling step proceeds from the bottom upward.

2. The casting method according to claim 1, further comprising: a second cooling step of further cooling the solidified body after the first cooling step to change the solidified body into a casting; and a removing step of removing a shrinkage cavity formed in the uppermost layer portion, which is the final solidification portion of the molten metal, by cutting the uppermost layer portion from the casting to obtain a finished product from the casting.

3. The casting method according to claim 1 or 2, further comprising a heat insulating material arranging step of arranging a heat insulating material above the cast molten metal before the first cooling step.

4. The chill includes a lower chill located below the vertical center of the casting space formed inside the mold and an upper chill located above the vertical center of the casting space, and the total volume of the lower chill is larger than the total volume of the upper chill. The casting method according to claim 1 or 2.

5. A casting obtained by the casting method according to claim 2, the casting including an uppermost layer portion that is the final solidification portion of the molten metal and in which a shrinkage cavity is formed.

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