Method of casting and cast product

Abstract

To provide a method of casting that is reduced in the weight of pour, and a cast product.SOLUTION: A method of casting includes: a pouring step that pours a melt of cast steel or non-ferrous metal into a mold embedded with a chill; and a first cooling step that changes the melt into a solidification by cooling the melt such that the temperature of the melt poured lowers to a solid phase-line temperature of the melt. In the pouring step, the volume of the melt poured in the mold is 105% or more and 108% or less of the volume of the solidification, and the chill is embedded in the mold such that solidification of the melt proceeds from below to above in the first cooling step.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present disclosure relates to a casting method for handling molten steel or non-ferrous metal, and a casting obtained therefrom.

Background Art

[0002] Casting is a manufacturing method of obtaining a casting from a molten metal by pouring the molten metal into a mold and cooling it. The details are disclosed in, for example, Patent Document 1.

[0003] Solidification of the molten metal that occurs during cooling generally proceeds from the surface of the molten metal toward the inside. Since the molten metal shrinks due to solidification, shrinkage cavities are formed inside the casting. If there are shrinkage cavities in the part of the casting that is used as a finished product, there is a risk of breakage due to a decrease in strength during use of the finished product.

[0004] Therefore, a method has been devised in which the amount of molten metal poured into the mold is made larger than the amount corresponding to the finished product, and shrinkage cavities are generated in the surplus part above the finished product. The molten metal corresponding to this surplus part has conventionally been called riser metal. If the riser metal solidifies last in the molten metal, the shrinkage cavities can be concentrated in the riser metal.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In order for the riser metal to solidify last, it is necessary to increase the ratio of the riser metal to the entire molten metal, and in some cases, the riser metal may occupy nearly 50% of the molten metal. Therefore, there is a risk of increasing the amount of molten metal poured.

[0007] An increase in the casting volume can lead to various problems. For example, problems such as an increase in the melting energy required to change the metal into a molten metal, an increase in cost due to an increase in the size of the mold, or an increase in the required time for the casting process may occur. In addition, when pouring the molten metal into a sand mold, there is also a concern that the sand may stick to the cast product because the contact time between the sand mold and the molten metal becomes longer.

[0008] An object of the present disclosure is to provide a casting method with a reduced casting weight and a cast product.

Means for Solving the Problems

[0009] The casting method according to at least one embodiment of the present disclosure includes a casting step of pouring a molten steel or non-ferrous metal into a mold in which a chill is embedded, a first cooling step of changing the molten metal into a solidified body by cooling the molten metal so that the temperature of the poured molten metal drops to the solidus temperature of the molten metal and is provided with in the casting step, the volume of the molten metal poured into the mold is 105% or more and 108% or less of the volume of the solidified body, the chill is embedded in the mold so that solidification of the molten metal in the first cooling step proceeds from the bottom upward.

[0010] The cast product according to at least one embodiment of the present disclosure is a cast product obtained from the above casting method, including the uppermost layer portion where a shrinkage cavity is formed, which is the final solidification portion of the molten metal.

Advantages of the Invention

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

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

MODE FOR CARRYING OUT THE INVENTION

[0013] Hereinafter, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as embodiments or shown in the drawings are not intended to limit the scope of the present disclosure thereto, but are merely illustrative examples. For example, expressions representing relative or absolute arrangements such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric" or "coaxial" not only strictly represent such arrangements, but also represent a state of relative displacement with tolerances or at an angle or distance such that the same function can be obtained. For example, expressions representing that things such as "identical", "equal" and "homogeneous" are in an equal state not only strictly represent an equal state, but also represent a state in which there are tolerances or differences such that the same function can be obtained. For example, expressions representing shapes such as a rectangular shape or a cylindrical shape not only represent shapes such as a rectangular shape or a cylindrical shape in a geometrically strict sense, but also represent shapes including concave and convex portions, chamfered portions, etc. within a range where the same effect can be obtained. On the one hand, the expressions "comprising", "including", or "having" a component do not exclude the presence of other components. For components having the same configuration, the same reference numerals may be used and the description thereof may be omitted.

[0014] <Overview of the casting apparatus 1> FIG. 1 is a schematic view of a casting apparatus 1 according to an embodiment of the present disclosure. The casting apparatus 1 includes a sand mold 3 for casting molten metal 10 (see FIG. 2) and a chill 6 embedded in the sand mold 3. The main heat possessed by the molten metal 10 cast into the sand mold 3 is transferred to the chill 6, and the molten metal 10 is cooled. Here, the cooling of the molten metal 10 includes a first cooling for generating a solidified body 20 (see FIG. 4), which is the molten metal 10 after solid-liquid contraction, by lowering the temperature of the molten metal 10 to the solid phase temperature, and a second cooling for generating a cast product 25 (see FIG. 5), which is the solidified body 20 after the completion of solid phase contraction, by further lowering the temperature of the solidified body 20 to room temperature. When at least a part of the uppermost layer portion 21 formed on the cast product 25 removed from the sand mold 3 is removed, a finished product 23 (see FIG. 6) is obtained. The finished product 23 may exhibit various shapes and be used for various applications. Although merely an example, the finished product 23 may be applied to a housing constituting a part of an internal combustion engine.

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

[0016] With reference to FIGS. 2 to 6, an overview of the casting process of the present disclosure will be described. First, the molten metal 10 is cast into the sand mold 3 (see FIG. 2). The molten metal 10 includes a molten metal main body portion 13 having a desired volume (i.e., a volume as a design value) of the solidified body 20 as an intermediate product, and a bulging portion 15 having a volume of 5% or more and 8% or less with respect to this desired volume. Although it is actually difficult to distinguish between the molten metal main body portion 13 and the bulging portion 15, in FIG. 2, they are illustrated with different hatchings (the same applies to other drawings).

[0017] In some embodiments, a heat-insulating material 5 may be disposed 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 contain a non-metallic member such as a resin. Also, instead of alumina powder, alumina fiber or the like may be used. The heat-insulating material 5 is disposed on the liquid surface of the molten metal 10 (i.e., the liquid surface of the bulging portion 15).

[0018] Continuing the description of the casting process. As shown in FIGS. 2, 3, and 4, the molten metal 10 is cooled by the chill 6. That is, the first cooling and the second cooling occur in sequence.

[0019] In the first cooling, the liquid-phase shrinkage and the solid-liquid phase shrinkage of the molten metal 10 occur in sequence, and at this time, the solidification of the molten metal 10 proceeds from the bottom upward. In other words, the chill 6 is disposed in advance so that directional solidification is realized in which the bottom surface portion of the molten metal 10 solidifies first and the liquid surface portion of the molten metal 10 solidifies last. When the temperature of the molten metal 10 drops to the solid-phase temperature, the solid-liquid phase shrinkage ends, and a solidified body 20 is obtained from the molten metal 10. At this stage when the first cooling ends (see FIG. 4), a shrinkage cavity 9 is formed in at least one of the inside of the bulging portion 15 or the liquid surface of the bulging portion 15 (the shrinkage cavity 9 is formed during the solid-liquid phase shrinkage process). Then, as shown in FIG. 5, the solidified body 20 is further cooled by the second cooling. The solid-phase shrinkage of the solidified body 20 occurs, and the temperature of the solidified body 20 drops to room temperature. Thereby, a casting 25 is obtained and the second cooling ends.

[0020] As shown in FIG. 6, the uppermost layer portion 21 of the casting 25 corresponds to at least a part of the final solidification portion of the molten metal 10, and a shrinkage cavity 9 is formed (the shrinkage cavity 9 is generated only during the first cooling). Therefore, after the second cooling, the shrinkage cavity 9 may be removed from the casting 25 by, for example, machining the uppermost layer portion 21. The casting 25 from which the uppermost layer portion 21 has been removed is used as the finished product 23.

[0021] In addition, in FIG. 6, for the convenience of making the drawing easy to view, different hatches are given to the uppermost layer portion 21 and other portions. However, in reality, it is difficult to distinguish between the two. Further, at least a part of the uppermost layer portion 21 may remain after the removal of the shrinkage cavity 9. That is, at least a part of the uppermost layer portion 21 may be included in the finished product 23.

[0022] <Casting method> FIG. 7 is a flowchart showing the above-described casting process. Hereinafter, "step" may be abbreviated as "S".

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

[0024] Next, a heat insulating material arranging step (S3) of arranging the heat insulating material 5 after the cast molten metal 10 is executed. Next, a first cooling step (S5) for changing the cast molten metal 10 into the solidified body 20 is executed. In the first cooling step, the solidification of the molten metal 10 proceeds from the bottom upward. More specifically, the molten metal 10 is cooled so that the solidification proceeds from the bottom upward when the liquid phase shrinkage and the liquid-solid phase shrinkage occur. When the liquid phase shrinkage and the liquid-solid phase shrinkage are completed in sequence, the first cooling is completed. By the time the first cooling is completed, a shrinkage cavity 9 is formed in the final solidification portion of the molten metal 10.

[0025] Thereafter, a second cooling step is performed (S7) so that the solidified body 20 becomes the cast product 25. When the temperature of the solidified body 20 drops to room temperature, the cast product 25 is produced. Note that no new shrinkage cavity 9 is generated during the second cooling. Thereafter, a removing step (S7) of removing the uppermost layer portion 21 of the cast product 25 is executed, and this flowchart ends.

[0026] <Casting amount of molten metal 10> The inventors of the present application decided to review the conventional method of designing the chill 6 and the sand mold 3 on the premise of pouring hot water. If the pouring of hot water is eliminated, it is necessary to consider the minimum amount of molten metal 10 to be poured.

[0027] During the first cooling, the molten metal 10 shrinks as it changes into the solidified body 20. Therefore, if only the molten metal main body 13 having substantially the same volume as the desired volume of the solidified body 20 (i.e., the volume as the design value) is poured into the sand mold 3, the actual volume of the solidified body 20 obtained by cooling will be smaller than the above-mentioned desired volume.

[0028] According to the inventors' findings, the volume reduced by the shrinkage of the molten metal main body 13 during the first cooling is 5% or less compared to the volume before shrinkage. Fig. 8 shows the basis. The figure is a schematic graph showing the result of analyzing the shrinkage volume of the molten metal main body 13. During the process of the molten metal main body 13 solidifying from the liquid phase state indicated by point A to the solid phase state indicated by point B, liquid phase shrinkage and liquid-solid phase shrinkage occur in sequence. As shown in the figure, the volume reduced by the shrinkage of the molten metal main body 13 is 5% or less compared to the volume before shrinkage.

[0029] That is, if an additional amount of molten metal 10 having a volume of 5% or more and 8% or less with respect to the volume of the molten metal main body 13 before shrinkage is prepared as the bulging portion 15, the minimum necessary amount of molten metal 10 for generating the solidified body 20 having the desired volume can be ensured. Further, if the chill 6 is designed so that the bulging portion 15 solidifies last among the molten metal 10 during the first cooling, a final solidification portion can be formed at the uppermost part of the molten metal 10. Thereby, the shrinkage cavity 9 can be concentrated in the uppermost layer portion 21 of the casting 25 obtained by the second cooling. Note that the design of the chill 6 is performed by specifying the solidification process of the molten metal 10 through analysis.

[0030] In the second cooling, during the process in which the solidified body 20 changes into the cast product 25, its volume further shrinks by about 7%. Therefore, the designed value of the volume of the solidified body 20 needs to be set to a value about 7% higher than the desired volume of the cast product 25. Here, the reason why the volume of the solidified body 20 shown at point C in FIG. 8 has changed by only about 1% compared to the volume of the solidified body 20 shown at point B is that the temperature of the solid phase state shown at point C is higher than room temperature, and point C only shows a state during the process in which the solidified body 20 changes into the cast product 25.

[0031] As described above, if the shrinkage cavity 9 can be concentrated at the uppermost part of the solidified body 20, the bulging portion 15 can play the same role as the pressing hot water. In this regard, according to the casting method including the casting step (S1) and the first cooling step (S5), the casting 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 the bottom to the top. Thereby, the uppermost part of the molten metal 10 corresponding to the bulging portion 15 can be solidified last. Therefore, a casting method can be realized in which the pressing hot water as in the prior art can be made unnecessary and the casting weight can be reduced.

[0032] Also, in some embodiments of the present disclosure, a removal step (S7) of obtaining the finished product 23 by cutting off the uppermost layer portion 21, which is the final solidification portion of the molten metal 10, from the cast product 25 is executed. According to the above configuration, the finished product 23 from which the shrinkage cavity 9 has been removed can be obtained, and it is possible to suppress the finished product 23 from being damaged due to insufficient strength.

[0033] Also, in some embodiments of the present disclosure, a heat insulating material arranging step (S3) of arranging the heat insulating material 5 above the cast molten metal 10 is executed. According to the above configuration, the heat insulating material 5 suppresses the bulging portion 15 from being exposed to the outside air. Therefore, heat dissipation of the bulging portion 15 to the outside air is suppressed, and the bulging portion 15 can be made into the final solidification portion more reliably.

[0034] Returning to FIG. 1, in some embodiments, the chill 6 includes 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. The total volume of the lower chill 7 may be larger than the total volume of the upper chill 8. Here, the vertical center of the casting space S is the vertical center between the lowermost end and the uppermost end of the inner surface 3a of the sand mold 3 that defines the casting space S.

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

[0036] <Summary> The content described in some of the above-described embodiments is understood as follows, for example.

[0037] 1) The casting method according to at least one embodiment of the present disclosure includes a casting step (S1) of casting molten metal (10) of cast steel and non-ferrous metal into a mold (sand mold 3) in which a chill (6) is embedded, a first cooling step (S5) of changing the molten metal into a solid (20) by cooling the molten metal so that the temperature of the cast molten metal drops to the solidus temperature of the molten metal and is provided with in the casting step, the volume of the molten metal cast into the mold is 105% or more and 108% or less of the volume of the solid, 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.

[0038] The inventor of the present application decided to review the conventional method of designing chills and molds on the premise of pouring hot water. If the pouring of hot water is eliminated, it is necessary to consider the minimum amount of molten metal to be poured. Molten metal shrinks during the process of changing into a solid. Therefore, if only the main body portion (13) of the molten metal having a volume substantially the same as the desired volume of the solid to be obtained after cooling is poured into the mold, the actual volume of the solid will be smaller than the above-described desired volume. According to the inventor's findings, the volume reduced due to the shrinkage of the main body portion of the molten metal is 5% or less compared to the volume before shrinkage. Therefore, if an additional amount of molten metal having a volume of 5% to 8% with respect to the desired volume of the solid is prepared as the bulging portion (15), the minimum necessary amount of molten metal for obtaining a solid having the desired volume can be ensured. Furthermore, if the chill is designed so that the bulging portion solidifies last in the molten metal, the uppermost portion of the molten metal can be solidified last. Since shrinkage cavities can be concentrated at the uppermost portion of the solid, the bulging portion can play the same role as the pouring hot water. In this regard, according to the configuration of 1) above, the pouring volume of the molten metal is 105% or more and 108% of the volume of the solid, and the molten metal is cooled so that solidification proceeds from below to above. Thereby, the uppermost portion of the molten metal portion corresponding to the bulging portion can be finally solidified. Therefore, it is possible to eliminate the need for pouring hot water as in the conventional case, and to realize a casting method with reduced pouring weight.

[0039] 2) In some embodiments, the casting method described in 1) above After the first cooling step, a second cooling step of further cooling the solid to change the solid into a casting (25), and An removing step (S7) of removing shrinkage cavities (9) formed in the uppermost layer portion (21) which is the final solidification portion of the molten metal by cutting the uppermost layer portion from the casting to obtain a finished product (23) from the casting.

[0040] According to the configuration of 2) above, a finished product from which shrinkage cavities have been removed can be obtained. Therefore, it is possible to suppress the finished product from being damaged due to insufficient strength.

[0041] 3) In some embodiments, the casting method described in 1) or 2) above Before the first cooling step, a heat insulating material arrangement step (S3) of arranging a heat insulating material (5) above the cast molten metal is further provided.

[0042] According to the configuration of 3) above, the heat insulating material can suppress the heat dissipation of the bulging portion to the outside air, so that the bulging portion can be more surely made into the final solidification portion.

[0043] 4) In some embodiments, it is the casting method according to any one of 1) to 3) above, The chill block is A lower chill block (7) located below the vertical center of the casting space formed inside the mold, An upper chill block (8) located above the vertical center of the casting space, and includes The total volume of the lower chill block is larger than the total volume of the upper chill block.

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

[0045] 5) The solid according to at least one embodiment of the present disclosure is A solid obtained from the casting method of 1) above, which is the final solidification portion of the molten metal and includes the uppermost layer portion (21) where shrinkage cavities are formed.

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

Description of Reference Numerals

[0047] 1: Casting device 3: Sand mold 3a: Inner surface 5: Heat insulating material 6: Chill block 7: Lower chill block 8: Upper chill block 9: Shrinkage cavity 10: Molten metal 13: Molten metal body part 15: Bulging part 20: Solidified body 21: Topmost layer part 23: Finished product 25: Casting L1, L2: Dimensions M: Dashed double line S: Casting space

Claims

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

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

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

4. The chill is; A lower chill located below the vertical center of the casting space formed inside the mold; An upper chill located above the vertical center of the casting space; including; 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, A 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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