Metal-casting method and apparatus, casting system and cast-forging system

Abstract

[Purpose] To provide, in relation to casting of materials to be subjected to plastic working such as cold forging, hot forging, enclosed forging, rolling, extrusion, and roll-forming of metals, including nonferrous metals, such as aluminum and magnesium (inclusive of respective alloys), and ferrous metals (i.e., iron and steel) or to direct casting of products (i.e., castings), a metal casting method which is capable of yielding cast ingots of healthy interior metallographic structure with no cut surfaces, by making the solidification interface smooth so as to prevent generation of cracks in cast ingots which are otherwise unavoidable due to concentration of solidification shrinkage stress caused by the solidification interface becoming locally concave when the solidification interface arrives at the top surface of the mold to ultimately complete solidification, or by effecting local control of removal of heat from the mold so as to prevent generation of casting defects such as cavities and microshrinkages which are otherwise unavoidable due to the solidification interface of the molten metal in the mold forming a closed surface inside the cast ingot; a casting apparatus; and cast ingots.

Description

TECHNICAL FIELD TO WHICH THE INVENTION PERTAINS

[0001] The present invention relates to casting of materials to be subjected to plastic working such as cold forging, hot forming of metals, including nonferrous metals, such as aluminum and magnesium (inclusive of respective alloys), and ferrous metals (i.e., iron and steel), or to direct casting of products (i.e., castings). More particularly, the present invention relates to a metal casting method which is capable of yielding cast ingots of healthy interior metallographic structure with no cut surfaces, by making the solidification interface smooth so as to prevent generation of cracks in cast ingots which are otherwise unavoidable due to concentration of solidification shrinkage stress caused by the solidification interface becoming locally concave when the solidification interface arrives at the top surface of the mold to ultimately complete solidification, or by effecting local control of removal of heat from the mold so as to prevent generation of casting defects such as cavities and microshrinkages which are otherwise unavoidable due to the solidification interface of the molten metal in the mold forming a closed surface inside the cast ingot. The present invention also relates to a casting apparatus and to cast ingots.

BACKGROUND ART

[0002] In conventional metal mold casting, die casting, and low pressure or high pressure casting, molten metal is teemed into a casting apparatus to form a cast body, after which the sprue portion and feeder portion are cut off to thereby provide a stock material. These conventional methods require simple steps, and thus have an advantage of low production cost. However, they are not free from producing casting defects inside the cast bodies, including cavities, pin holes, shrinkage cavities, and engulfment of oxides.

[0003] As contrasted to such conventional methods, casting by way of unidirectional solidification provides excellent cast bodies in terms of quality regarding interior metallographic structure. However, if the molten metal has a free surface which is open to air, the meniscus portion that contacts side walls of the mold forms a curved surface having a large area, thus making it impossible to form a cast body having a top surface orthogonal to the circumferential side walls. Moreover, since controlling to a constant level the volume of molten metal to be teemed is difficult, various disadvantages result, including significant variation in weight of the as-produced stock material, halting of the forging machine due to overload imposed during forging, and significant dimensional variation in the resultant forged products.

[0004] In view of the foregoing, the present inventors have previously disclosed in Japanese Patent Application Laid-Open (kokai) No. 8-155627 a casting method and apparatus capable of solving the aforementioned problems inherent to the technique of unidirectional solidification.

[0005] Briefly, as shown in FIG. 15, a mold 2 is disposed on a cooling member 1, and molten metal 6 is introduced, from a molten metal reservoir 3 provided at an upper section of the mold 2 and via a molten metal inlet 4, into the inside of the mold 2 so as not to leave any space therein, and subsequently, the cooling member 1 is cooled with the inside of the mold 2 being isolated by means of closing the molten metal inlet 4 with an open/close plug 5, to thereby cause the molten metal 6 to solidify unidirectionally. In FIG. 15, reference numeral 7 denotes molten metal contained in the molten metal reservoir, reference numeral 8 denotes a spray nozzle, reference numeral 23 denotes an electric furnace for maintaining the molten metal at a predetermined temperature and for preventing cooling, from the side walls of the mold, of the molten metal poured into the mold, reference numeral 24 denotes an upper lid, reference numeral 25 denotes a casing, and reference numeral 26 denotes a discharge port for a cooling medium.

[0006] By the employment of the above-described method and apparatus, teeming of a precise, predetermined amount of molten metal 6 into the mold 2 can be performed quite easily without need for measurement of the molten metal. Moreover, serial operations, including teeming, cooling for solidification, and removing the cast product, can be performed continuously. In addition, since the molten metal is charged in the closed mold 2 without leaving any space therein, the resultant cast product has an outer surface conforming to the inner surface of the mold, thereby achieving high dimensional accuracy in thickness and shape. Also, the cast product has excellent quality in terms of internal metallographic structure, exhibiting no mold cavities, shrinkage cavities, pinholes, engulfment of oxides, or similar defects.

[0007] [Problems to be Solved by the Invention]

[0008] However, the aforementioned method and/or apparatus involves the following problem. That is, particularly when the cast body to be produced is a thin product having an axisymmetric disk shape of large outer diameter, time required for solidification of the molten metal at the molten metal inlet portion—which is located virtually at a central portion of the disk—is different from that at a peripheral portion of the disk which is the remotest from the molten metal inlet portion, and therefore, an ideal unidirectional solidification state cannot be maintained, causing a local depression of the solidification interface at a location directly below the molten metal inlet and in some cases producing cracks at a central portion of the cast ingot.

[0009] Under the above circumstances, the present inventors have continued further studies in an attempt to obtain cast ingots having more healthy internal metallographic structure, and have found that control of heat removal which is performed locally in accordance with the shape of the cast ingot to be produced; in other words, furnishing of a control mechanism that realizes a heat removal profile corresponding to the shape of the cast ingot to be produced, can contribute to attainment of a flat solidification interface and yield cast ingots which have no cut surfaces and have healthy interior metallographic structure. The present invention has been made on the basis of the above findings.

[0010] [Means for Solving the Invention]

[0011] The present invention, which has been made in view of the foregoing, is accordingly directed to a method for casting metal by charging molten metal into a closed-space-definable mold which includes a cooling member and in which an end surface of an open/close plug serves as a portion of an inner wall of the mold, characterized in that removal of heat from a mold member comprising the cooling member is locally controlled in accordance with the shape of cast ingot and the location and number of the molten metal inlet(s), to thereby solidify the molten metal in such a manner that the solidification interface advances to arrive at an end of an inner surface of the mold (claim 1); a metal casting apparatus for casting metal by charging molten metal into a closed-space-definable mold which includes a cooling member and in which an end surface of an open/close plug serves as a portion of an inner wall of the mold, characterized by comprising a cooling capacity control mechanism which imparts, to the mold member comprising the cooling member, a heat removal profile appropriate for the shape of the cast ingot to be produced and for the number and position of the molten metal inlet(s) (claim 3); and a cast ingot obtained by use of the method or apparatus (claim 24).

[0012] The above-mentioned prior art Japanese Patent Application Laid-Open (kokai) No. 8-155627 discloses the following methods for the forced cooling of a cooling member.

[0013] (1) Jetting, in the form of spray or shower, a medium onto the lower surface of the cooling member (to effect collision).

[0014] (2) Passing cooling water through cooling water piping provided in the cooling member.

[0015] (3) Installing a cooling water tank at a lower section of the cooling member for passing water therethrough.

[0016] However, any of these modes attains virtually uniform cooling of a cooling member. Also, the cast ingots to be produced are of simple disk shape, and this publication does not contain any specific disclosure for the case of cast ingots of three-dimensionally complicated shape.

[0017] As a result of continued energetic research, the present inventors have found that local control—in accordance with the shape of cast ingot, the location and number of molten metal inlet(s), etc.—of heat removal through augmenting or reducing the cooling capacity of the mold member having a cooling member or through intentional heating, whereby the molten metal is solidified in such a manner that the solidification interface advances to arrive at an end surface of the mold, eliminates the risk of a closed loop of solidification front surface being formed inside the mold and enables provision of a cast ingot having a healthy interior metallographic structure.

[0018] [Modes for Carrying Out the Invention]

[0019] The cooling capacity control mechanism employed in the method and apparatus of the present invention will next be described in more detail with reference to the drawings. Methods for forced cooling of a mold member having a cooling member are basically divided into two types: a method corresponding to the combination of the aforementioned methods (1) and (3); i.e., a method in which a cooling medium is brought into contact with an outer surface of a mold member having a cooling member, to thereby cool the cooling member; and a method corresponding to the aforementioned method (2); i.e., passing a cooling medium through the piping provided in a mold member having a cooling member. Either method, when combined with one of the following modes, establishes a cooling capacity control mechanism.

[0020] Although the following description mainly focuses on a cooling member, heat removal from not only the cooling member but from a mold member having a cooling member is locally controlled by the present invention.

[0021] 1. Mode in Which Cooling is Performed by Contacting a Cooling Medium with an Outer Surface of a Cooling Member (Claim 4);

[0022] Specifically, there are the following two types of methods: a method in which a cooling medium jetted in spray form or shower form hits against an outer surface of a cooling member; and a method in which a cooling bath to which a cooling medium is supplied is provided outside a cooling member. However, since local control of heat removal is difficult to attain when these methods (i.e., forced cooling methods) are used alone, one or more of the following modes “a” to “f” are combined with one of these two methods, to thereby establish a cooling capacity control mechanism that locally controls heat removal. In the accompanying drawings, only apparatuses applicable for top teeming (i.e., molten metal is poured from above the apparatus) are shown. However, the pouring direction of molten metal is not limited thereto, and bottom teeming may also be employed.

[0023] a. Mode Employing a Cooling Member in Which the Wall Thickness of a Certain Portion is Different from that of Other Portions (Claim 5);

[0024] The molten metal present at the location directly below the molten metal inlet is a lastly teemed portion, and accordingly, this portion of molten metal will be cooled and solidifies last. Therefore, the corresponding portion of a cast ingot directly below the molten metal inlet is prone to microshrinkage, or cracks caused by solidification stress due to temperature difference in the cast ingot. In order to cope with this problem, the cooling member is partially thickened or thinned, and a cooling medium is brought into contact with an outer surface of the cooling member, to thereby provide an appropriate profile of heat removal in accordance with the shape of cast ingot and the location and number of the molten metal inlet(s). Thus, formation of a local depression at the solidification interface can be prevented. Specifically, for example, when the cast ingot to be produced is of a simple disk shape, a portion of the cooling member which corresponds to the central portion of the ingot; i.e., the region where solidification of molten metal delays, is thinned to thereby enhance the cooling capacity; and a portion of the cooling member which corresponds to a peripheral portion of the cast ingot; i.e., the region where solidification of molten metal proceeds quickly, is thickened to thereby lower the cooling capacity. Moreover, in connection with the mechanism for supplying the cooling medium, the amount of the cooling medium to be jetted and the timings to initiate and terminate the cooling process may be determined in accordance with the shape of the cast ingot. For example, cooling may be started either after ultimate completion (the filled-up state) of teeming of molten metal, or before completion.

[0025] FIG. 1 is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode “a.”

[0026] In the embodiment shown in FIG. 1, a mold 2 (an upper mold 2a and a side mold 2b) is disposed on a cooling member 1. A reservoir 3 for receiving molten metal 7 from a melting furnace (not shown) or a similar apparatus is provided in the upper section of the mold 2, and is heated by means of an unillustrated electric furnace so as to maintain the molten metal at a predetermined temperature. The reservoir 3 is in communication with the interior space of the mold 2 (reference numerals 6a, 6b, and 6c represent solidified molten metal, solidification interface, and unsolidified molten metal, respectively) via a molten metal inlet 4. The molten metal inlet 4 is equipped with an open/close plug 5. Teeming of molten metal into the mold 2 is performed by elevating the open/close plug 5 by means of an open/close plug elevating means (not shown), and when the mold 2 is completely filled up with molten metal 6 without leaving any space therein, the open/close plug 5 is lowered, to thereby block the molten metal to be teemed.

[0027] The thickness of the cooling member 1 is smaller at the center portion, in which solidification of molten metal 6 delays, and the thickness gradually increases toward the periphery, where solidification rate of molten metal 6 is high. A spray nozzle 8 disposed below the center of the cooling member 1 jets a cooling medium such as water, supercooled water of 0° C. or lower (e.g., supercooled water of 0° C. or lower containing 0.5% or more sodium chloride, or supercooled water of 0° C. or lower containing a substance such as ethylene glycol), a volatile liquid such as ethyl alcohol, or an oil so that the cooling medium hits (or contacts) the lower surface of the cooling member 1, to thereby cool the cooling member 1.

[0028] Structures other than the above-described one may be appropriately selected and determined in accordance with needs as described, for example, in the aforementioned Japanese Patent Application Laid-Open (kokai) No. 8-155627. For example, when molten metal 7 (cast ingot) is Al, Mg, Zn, or an alloy thereof, the cooling member 1 is preferably made of Cu, Al, or any other metallic material endowed with excellent refractory property and mechanical strength, whereas when molten metal 7 (cast ingot) is Fe, Cu, or an alloy thereof, the cooling member 1 is preferably made of a ceramic material endowed with excellent refractory property such as graphite, SiC, Si3N4, or BN-containing Si3N4. Examples of the material that constitutes the mold 2 include a heat-insulating refractory material composed predominantly of an ordinary refractory material, CaO, SiO2, Al2O3, or MgO, among other materials; a single substance of SiC, Si3N4, black lead, BN, TiO2, ZrO2, or AlN, or a refractory mixture thereof; and metals such as Fe and Cu. Of these materials, the material to be employed may be selected in general consideration of the metal or alloy to be subjected to casting, temperature at use, wettability with molten metal, corrosion resistance, etc.

[0029] In order to supply the molten metal throughout the interior space of the mold without leaving any space, the molten metal 6 in the mold is preferably pressurized. In the apparatus shown in FIG. 1, pressurization is effected by the riser effect of the molten metal 7 in the reservoir 3. In this connection, the top surface of the molten metal 7 in the reservoir 3 is preferably 30 mm or more above the top surface of the molten metal 6 which fills the mold 2. When such a height difference is provided, oxides floating on the molten metal 7 contained in the reservoir 3 is prevented from entering the mold 2. Cooling of the molten metal 6 must be attained mainly by means of the cooling member 1, and cooling effected through side walls, etc. should be prevented. This allows the molten metal 6 to be solidified unidirectionally from the bottom toward above. Upon pouring the molten metal into the mold 2, the cooling member 1 preferably assume a temperature of at least 100° C. When teeming is performed at a lower temperature, disadvantageously, the phenomenon called “blow,” a type of defect typically found in metal mold casting, is caused. From the viewpoints of cooling efficiency and product quality, the upper limit would be approximately the temperature of molten metal. In order to prevent generation of blows, a mold release agent, which is widely used for the application to cooling member 1, is also effective.

[0030] b. Mode in Which an Interior Space is Provided in a Portion of a Cooling Member (Claim 6);

[0031] In the above-described mode “a,” the cooling member is partially thickened or thinned. Alternatively, when an interior space is provided in a part of a cooling member, thermal conductivity in the thickness direction can be varied even in the case in which, for example, the outer thickness of the cooling member is uniform, whereby cooling capacity control similar to that mentioned above can be attained. Moreover, the interior space prevents heat from flowing from molten metal to the outer surface of the cooling member, well-balanced cooling capacity can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape.

[0032] Although the interior space is essentially a closed space, it may be an open space unless it allows a cooling medium to enter therein deeply. Since the thermal conductivity of the interior space region is lower than that of the cooling member, which is generally formed of a material of high thermal conductivity, there can be attained a cooling capacity control similar to that through mode “a,” in which the cooling member is partially thickened or thinned. Moreover, the interior space prevents heat from flowing from the molten metal to the outer surface of the cooling member.

[0033] An example of mode “b” is shown in FIG. 8, and a detailed description therefor will be given herein later.

[0034] c. Mode in Which the Cooling Member is Made of a Composite Material of Different Thermal Conductivites (Claim 7);

[0035] In the above-described mode “a,” the cooling member is partially thickened or thinned. Alternatively, when a material segment having a thermal conductivity different from that of the remaining portion of the cooling member is integrally formed within the cooling member (FIG. 9(a)), or when a material segment having a thermal conductivity different from that of the remaining portion of the cooling member is integrally inserted into a portion of an outer surface of the cooling member (FIG. 9(b)), even when the outer thickness of the cooling member is uniform, the heat capacity in the thickness direction can be varied, attaining a function similar to the aforementioned one. Moreover, the material segment having a different thermal conductivity prevents heat from flowing from the molten metal to the outer surface of the cooling member, well-balanced cooling capacity can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape.

[0036] In this case, the cooling member preferably comprises a metallic material and a refractory heat-insulating material, which serves as the material segment having a different thermal conductivity, which is integrally formed inside or outside of the part made of metallic material. Examples of suitable metallic materials include aluminum, copper, iron, and an alloy thereof having a high thermal conductivity. Examples of suitable refractory heat-insulating materials incorporated into the inside of the part include a material in the form of plate, blanket, or sheet made of alumina fiber or fused silica fiber; or a single substance of Si3N4, SiC, BN, or graphite, or a mixture thereof. Examples of suitable refractory heat-insulating materials inserted from the outside of the part made of metallic material include a single substance of Si3N4, SiC, BN, or graphite, or a mixture thereof.

[0037] An embodiment of mode “c” is shown in FIG. 9, and a detailed description therefor will be given herein later.

[0038] d. Mode in Which an Outer Surface of the Cooling Member is Partially Provided with an Uneven Surface so that the Area that can Contact a Cooling Medium Locally Varies (Claim 9);

[0039] When a cast ingot to be produced does not have a simple disk shape but rather has, as viewed three-dimensionally, a non-uniform profile along the X-Y axis or, in addition thereto, also a non-uniform shape along the Z axis, cooling capacities of a cooling member and a mold member must be controlled in order to prevent formation of cracks in the resultant cast ingot, which are caused by the solidification interface being depressed locally; and to prevent formation of internal defects, such as blowhole defect and microshrinkage, which are generated when the solidification interface forms a closed surface within a cast ingot.

[0040] When a cooling member is excessively thin, rigidity of the cooling member lowers. Thus, heat cycle imposed upon each casting process distorts the cooling member, resulting in deformation thereof, and producing cast ingots of undesired shape. Furthermore, thermal shock or deterioration of the material of the cooling member produces cracks in the cooling member through which a cooling water leaks, leading to disturbed operation of the apparatus. Thus, in order to continue the casting process for a long period in a stable manner, the cooling capacity and the rigidity of the cooling member must be enhanced.

[0041] To this end, the cooling member is thickened so as to enhance the rigidity, and in addition, unevenness is provided on an outer surface of the cooling member and a cooling medium is supplied to the outer surface of the cooling member, whereby the contact area between the unevenness-imparted portion and the cooling medium (hereinafter referred to as “cooling-medium-contact-area”) is enhanced, leading to attainment of enhanced cooling capacity. The configuration of the unevenness is not particularly limited, and for example, a hole which does not reach the interior surface (blind hole) or a fin-like shape may be employed.

[0042] Usually, the cooling medium is jetted radially from a spraying means such as a cooling spray. Thus, even when such unevenness is uniformly provided, the cooling-medium-contact-area of the uneven portion directly above the nozzle of the cooling spray is different from that of other uneven portions.

[0043] The shape of the uneven portion (or dents) is determined so as to maintain the rigidity of the cooling member and to attain the desired cooling capacity. Preferably, a distance of at least 1 mm is left below the internal surface of the cooling member. If engraving is performed farther, rigidity of portions in the vicinity of dents cannot be secured, inviting the risk of generating cracks in the cooling member. Generally speaking, the cooling capacity of deeply engraved dents is higher than that of shallow dents due to larger cooling-medium-contact-area. Therefore, deep dents may be formed in a portion where high cooling capacity is desired, and shallow dents may be formed in a portion where low cooling capacity is desired.

[0044] The pitch of the dented portion (density of the formed dents) is determined in accordance with the shape of the cast ingot, and the pitch is not necessarily invariable. Depending on the case, the pitch may be long or short, and some portion may have no dents. On the other hand, when dents are formed at a certain unvaried pitch (uniform density of dents), cooling capacity can be controlled through regulating the diameter and/or depth of the dents. Thus, for example, portions for which high cooling capacity is desired may be provided with dents of narrow pitch (high density of dents), whereas other portions for which low cooling capacity is desired may be provided with dents of wide pitch (low density of dents).

[0045] In particular, when holes are provided as the dents, the diameter of the holes is preferably 3 mm or more for the following reasons. When cooling water in the form of spray or shower is jetted toward the holes each having a diameter of less than 3 mm, cooling water entered the holes is vaporized under heat, and the steam prevents jetted cooling water from entering the holes, lowering the cooling effect as compared to the case in which no hole is provided. The maximum diameter is determined in accordance with the size of the cast ingot and the cooling capacity profile to be attained. However, holes of any size may be formed so long as the rigidity of the cooling member is secured. Generally, large holes, realizing a large cooling-medium-contact-area, provide higher cooling capacity as compared with small holes. Thus, large holes may be provided at a site where high cooling capacity is desired, and small holes may be provided at a site where low cooling capacity is desired.

[0046] When the angle of the hole axis (“&agr;”; hereinafter referred to as “inclination angle”) coincides with the collision angle (&bgr;) at which the cooling water jetted in the form of spray or shower hits the cooling member, the maximum cooling capacity is attained. In other words, when high cooling capacity is desired, the following relation is preferably satisfied: &agr;=&bgr;±10°. When &agr; and &bgr; do not satisfy this relation, the cooling capacity may decrease.

[0047] FIG. 2 is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode “d.” Elements identical to those shown in FIG. 1 are denoted by the same reference numerals.

[0048] In this embodiment, molten metal is teemed through a single molten metal inlet 4 disposed at an approximately central portion, to thereby produce a cast ingot having an almost uniform thickness.

[0049] In this embodiment, a plurality of blind holes 9 which serve as the uneven portion are formed at almost the same intervals in an outer surface of a cooling member 1 having an almost uniform thickness, and a spray nozzle 8 for jetting a cooling medium is disposed beneath the approximately central portion of the cooling member 1.

[0050] As described above, holes 9 disposed directly above the spray nozzle 8, which are disposed at an approximately central position, have a larger cooling-medium-contact-area than holes 9 in peripheral portions. Thus, holes 9 disposed directly above the spray nozzle 8 provide higher cooling capacity. Therefore, in the cooling member 1, cooling capacity is high in the central portion and low in the peripheral portion.

[0051] In this connection, as shown in FIG. 3 for example, when holes 9 are formed in such a manner that the inclination angle a of each of the holes is identical with its corresponding collision angle &bgr; of the cooling medium, the maximum cooling capacity can be obtained.

[0052] The aforementioned controlling methods can be performed independently one from another, and they may be appropriately combined in accordance with needs. For example, the aforementioned modes “a” and “d” are combined, to thereby use a cooling member in which the thickness varies from portion to portion, and an outer surface thereof is partially provided with unevenness by means of holes, fins, etc.

[0053] FIG. 4 shows an embodiment in which molten metal is teemed through a molten metal inlet 4 disposed at an approximately central position and the cast ingot has a thick wall in the central to right portion (as viewed in the drawing) and a thin wall in the left portion (in the drawing).

[0054] The cooling member 1 of the present embodiment is designed such that the central to right portions, which correspond to the thicker portion of the cast ingot in which the solidification rate of molten metal 6 is slow, are formed to have a thin wall so as to lessen the heat capacity, and the thus-formed thin wall is provided with unevenness through formation of a plurality of holes 9 so as to increase the area that can contact a cooling medium jetted from a cooling spray 8 disposed below an approximately central portion of the cooling member 1, to thereby enhance the cooling capacity of the central portion and the right portion. In particular, the holes 9 are formed in such a manner that the inclination angles of the holes 9 coincide with corresponding collision angles of the cooling medium. In addition, the left portion of the cooling member 1, which corresponds to the thinner portion of the cast ingot in which molten metal solidifies faster, is thickened, and no hole 9 is formed in the left portion, to thereby lower the cooling capacity of the left portion.

[0055] e. Mode in Which a Cooling Medium Jetted in the Form of Spray or Shower from a Plurality of Nozzles Hits an Outer Surface of a Cooling Member (Claim 8);

[0056] FIG. 5(c) shows an exemplary apparatus according to mode “e” in which molten metal is teemed through two molten metal inlets 4 provided on the right side and the left side, to thereby produce a connecting rod member having a more complicated three-dimensional shape as shown in FIGS. 5(a) and 5(b).

[0057] In casting of such a product, a significant amount of molten metal 6 is accumulated in hemispheres directly below the two molten metal inlets 4, and the molten metal in the hemispheres has high heat capacity. Thus, the portion of the cast ingot directly below the two molten metal inlets 4 tends to generate cracks because local depressions corresponding to the two molten metal inlets 4 are produced in the solidification interface directly below the inlets 4. On the other hand, the space within the arm portion connecting the hemispheres is narrow and can contain less molten metal.

[0058] In order to cope with this problem, the cooling member 1 of the present embodiment has been designed such that specific portions of the cast ingot directly below the two hemispheres, in which the molten metal 6 solidifies slower, is thinned, and the thinned portion is provided with unevenness through formation of a plurality of holes 9, toward which a cooling medium is jetted from two spray nozzles 8, 8 disposed at locations corresponding to the locations of the hemispheres, to thereby enhance the cooling capacity of the portions directly below the two hemispheres. Moreover, the portion of the cooling member directly below the arm portion of the cast ingot, in which the molten metal 6 solidifies faster, is thickened, and the thickened portion is provided with no unevenness; i.e., no holes 9, to thereby lower the cooling capacity of the portion directly below the arm portion. Notably, the connecting rod member produced by use of the present apparatus is drilled at points corresponding to the locations of the molten metal inlets 4 on the right side and on the left side as shown in FIG. 5(a).

[0059] The present embodiment has been described as an embodiment of mode “e.” However, the present embodiment is also an embodiment according to the aforementioned mode “a” since the thickness of the cooling member 1 is locally varied, and is also an embodiment according to the aforementioned mode “d” since an unevenness (holes 9) is provided. The same applies, throughout the following embodiments, and even when any of the aforementioned modes is used in combination, no particular mention may be given.

[0060] FIGS. 6(a) and 7(a) are views showing other exemplary apparatuses for casting connecting rod members having a shape identical to that shown in FIG. 5. In both embodiments, molten metal is teemed through one molten metal inlet 4.

[0061] In the apparatus shown in FIG. 6(a), molten metal is teemed through one molten metal inlet 4 disposed at an approximately central position; and a cooling member 1 is formed in such a manner that the portion directly below the arm portion, in which solidification of the molten metal 6 delays, is thinned, and that the thinned portion is provided with unevenness through formation of a plurality of holes 9, toward which a cooling medium is jetted from a single spray nozzle 8 disposed at an approximately central position, to thereby enhance the cooling capacity of the portion directly below the arm portion. Moreover, the portions of the cooling member 1 directly below the right and left hemispheres are thickened outwardly; and the thickened portion is provided with no unevenness; i.e., no holes 9, to thereby lower the cooling capacity of the portions directly below the hemispheres. In this connection, the connecting rod member cast by use of the present apparatus is drilled at an approximately central portion corresponding to the location of the molten metal inlet 4 as shown in FIG. 6(b).

[0062] In the apparatus shown in FIG. 7(a), molten metal is teemed through one molten metal inlet 4 disposed on the left side; and a cooling member 1 is formed in such a manner that the portion directly below the left hemisphere, in which solidification of molten metal 6 delays, is thinned, and that the thinned portion is provided with a plurality of holes 9 serving as the uneven portion, and a cooling medium is jetted from a single spray nozzle 8 disposed on the left side, to thereby enhance the cooling capacity of the portion directly below the left hemisphere. Moreover, the portion directly below the central arm portion and the right hemisphere is thickened outwardly; and the thickened portion is provided with no uneven portions; i.e., no holes 9, to thereby lower the cooling capacity of the portion directly below the central arm portion and the right-side hemisphere. The portion directly below the arm portion, through which molten metal is introduced into the right-side hemisphere, is particularly thickened. In this connection, the connecting rod member cast by use of the present apparatus is drilled at a single point on the left side corresponding to the location of the molten metal inlet 4 as shown in FIG. 7(b).

[0063] As described above, when the number and the location of molten metal inlet(s) are varied for cast ingots of the same shape, the cooling capacity control mechanism is modified accordingly, and cooling capacity can be appropriately controlled and adjusted. Thus, the critical point is to carry out solidification so that the solidification interface advances to reach an inner end of the mold, to thereby produce a cast ingot having no cut surface or riser portion.

[0064] f. Mode in Which Unevenness is Provided Through Formation of Blind Holes in Such a Manner that Inclination Angles Differ from Corresponding Collision Angles of a Cooling Medium Jetted in the Form of Spray or Shower and Supplied to the Outer Surface of the Cooling Member (Claim 10);

[0065] Holes are formed in a portion of an outer surface of a cooling member in such a manner that inclination angles of the holes differ from corresponding collision angles of a cooling medium in the form of spray or shower so as to prevent direct entering of the cooling medium into the holes. In this manner, the cooling capacity of the aforementioned portion is lowered, and well-balanced cooling capacity can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape.

[0066] The relationship between inclination angle &agr; of the hole and collision angle &bgr; of the cooling medium is preferably &agr;>&bgr;±≅10°.

[0067] When the cooling medium does not enter the holes, the holes are cooled mainly through air-cooling, resulting in lower cooling capacity as compared with the case in which no holes are formed.

[0068] For example, in the aforementioned embodiment shown in FIG. 2, holes 9 in both the central portion and the peripheral portion of the cooling member 1 are vertically formed and have almost the same depth. However, the cooling medium can enter deeply in holes 9 in the central portion because the inclination angle a virtually coincides with the collision angle &bgr; of the cooling medium, leading to large cooling-medium-contact-area, which enhances the cooling capacity of the central portion, whereas the cooling medium is prevented from penetrating deeply in holes 9 in the peripheral portion because the inclination angle &agr; significantly differs from the collision angle &bgr; of the cooling medium, resulting in lowered cooling capacity at the peripheral portion.

[0069] g. Mode in Which a Portion of an Outer Surface of a Cooling Member is Provided with Means for Preventing the Cooling Member from Contacting a Cooling Medium (Claims 11 and 12);

[0070] As described above, forced cooling of a cooling member is performed through a method in which a cooling medium is supplied to an outer surface of the cooling member. In combination with this method, a portion of the outer surface of the cooling member is provided with a step, or a restriction plate for restricting the spray direction of the cooling medium is installed, to thereby prevent the cooling medium from contacting a portion of the cooling member. Thus, since the cooling capacity resulting from the heat of vaporization of the cooling medium decreases (masking effect), well-balanced cooling capacity can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape.

[0071] FIGS. 8 and 9 are cross-sectional views showing exemplary apparatuses of the present invention and depicting the cooling capacity control mechanisms of modes “f” and “g.” Elements identical to those shown in FIG. 1 are denoted by the same reference numerals.

[0072] Although the cast ingots schematically shown in FIGS. 8 and 9 may look similar to the cast ingot shown in FIG. 1, in the present embodiments, molten metal is teemed through a molten metal inlet 4 disposed at an approximately central position, and the cast ingots in the present embodiments are of a disk shape and have an almost uniform thickness which is extremely smaller than the outer diameter.

[0073] In such a casting process, in which the thickness of the cast ingot is extremely smaller than the outer diameter, an ideal unidirectional solidification state cannot be maintained because the time requires for solidification of the center portion is different from that required for solidification of the peripheral portion; i.e., the remotest portion from the molten metal inlet 4. Thus, the center portion of the cast ingot easily generates cracks.

[0074] In order to cope with this problem, in the present embodiment, blind holes 9 serving as unevenness are formed in a central outer surface of a cooling member 1 in such a manner that the inclination angles coincide with corresponding collision angles of a cooling medium, to thereby considerably enhance the cooling capacity. On the other hand, interior spaces 13 (in FIG. 9, material sections 14 having a different thermal conductivity) are provided in a peripheral portion in such a manner that the interior space 13 expands toward the periphery. Moreover, a spray nozzle 8 is provided with a restriction plate 15 for restricting the spray direction of a cooling medium so as to prevent the cooling medium from contacting the outer surface of the interior spaces 13 (the material sections 14). Moreover, a step 16 is provided in a intermediate portion of the slope surrounding the central portion so as to prevent the cooling medium from running down along the slope, to thereby considerably lower the cooling capacity.

[0075] h. Mode in Which a Portion of an Outer Surface of a Cooling Member is Covered with a Heat-Insulating Material (Claims 11, 13, and 14);

[0076] As described above, forced cooling of a cooling member is performed through a method in which a cooling medium is supplied to an outer surface of the cooling member. In combination with this method, a portion of the outer surface of the cooling member is covered with a heat-insulating material so as to prevent the portion from contacting the cooling medium, to thereby lower the cooling capacity attained through evaporation heat of the cooling medium (masking effect); and to prevent heat from radiating from the outer surface of the cooling member (insulation effect). Thus, well-balanced cooling can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape.

[0077] Examples of the heat-insulating material include heat-insulating rubber, ceramic material, heat-insulating material made of fire retardant fibers or non-combustible fibers.

[0078] FIG. 10 is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode “h.” Elements identical to those shown in FIG. 1 are denoted by the same reference numerals.

[0079] In the present embodiment, molten metal is teemed through a molten metal inlet 4 disposed on the left side, to thereby produce a cast ingot in which the left and center portions (as viewed in the drawing) are thicker and the right portion (as viewed in the drawing) is thinner.

[0080] In such a casting process, the left portion and the center portion of the cast ingot tend to generate cracks for the following reasons: the left portion and the center portion of the cast ingot, which are thick, have large heat capacity; and solidification of molten metal 6 in the left portion and the center portion delays because the molten metal inlet 4 is provided on the left side.

[0081] In order to cope with this problem, a cooling member 1 of the present embodiment is designed in the following manner. A plurality of holes 9, which serve as unevenness, are formed in the left portion and the center portion, toward which a cooling medium is jetted from a cooling spray 8 disposed below the holes 9, to thereby enhance the cooling capacity of the left portion and the center portion; and a heater 11 is incorporated into the right portion, and an outer surface of the right portion is covered with a heat-insulating material 12 so as to prevent the cooling medium from contacting the outer surface, to thereby lower the cooling capacity of the right portion.

[0082] 2. Mode in Which a Circulation Passage for a Cooling Medium is Incorporated into a Portion of a Cooling Member (Claims 15 and 16);

[0083] In mode 1 wherein an outer surface of a cooling member is cooled through contacting a cooling medium thereto, at least one of modes “a”-“h” must be employed in combination. In contrast, the present method can attain local cooling of the cooling member without employing such a mode in combination. Needless to say, the aforementioned mode may be used in combination in accordance with the shape of the cast ingot.

[0084] The diameter, location, shape, and depth from the upper surface of a circulation passage for the cooling medium are determined in accordance with the required cooling capacity. Flow rate and timings to initiate or terminate cooling are determined in accordance with the shape of the cast ingot. Examples of the cooling medium include, similar to the cooling medium for supplying to an outer surface of a cooling member as in the aforementioned mode, water, supercooled water of 0° C. or lower (e.g., supercooled water of 0° C. or lower containing 0.5% or more sodium chloride, or supercooled water of 0° C. or lower containing a substance such as ethylene glycol), and an oil.

[0085] FIG. 11 is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode 2. Elements identical to those shown in FIG. 1 are denoted by the same reference numerals.

[0086] In the present embodiment, molten metal is teemed through a molten metal inlet 4 disposed on the left side, to thereby produce a cast ingot in which the right portion and the center portion (in the drawing) is thicker, and the left portion (in the drawing) is thinner.

[0087] In such a casting process, the right portion of the cast ingot, which is thick, is high in heat capacity, whereas the left portion, which is thin, is disposed directly below the molten metal inlet 4. Thus, each portion involves a factor which can cause crack formation.

[0088] In order to cope with this problem, the cooling member 1 of the present embodiment is designed such that a plurality of holes 9, which serve as unevenness, are formed in the right-side portion, toward which a cooling medium is jetted from a single spray nozzle 8 disposed below the holes 9, and a circulation passage 10 through which a cooling medium flows is incorporated into the left portion, to thereby regulate the cooling capacity of respective portions through controlling their corresponding forced cooling mechanisms appropriately.

[0089] 3. Mode in Which a Temperature-Controlled Cooling Medium is Brought into Contact with a Cooling Member (Claim 17);

[0090] As described above, the cooling medium is selected from water, supercooled water of 0° C. or lower, a volatile liquid, and an oil, each of which can be used singly or in combination. Needless to say, the cooling capacity of water at room temperature is different from supercooled water of 0° C. or lower. In other words, the cooling capacity can be controlled through controlling the temperature of a cooling medium.

[0091] An exemplary method for attaining this purpose will be described with reference to the embodiment shown in FIG. 5, wherein the cooling medium jetted through the spray nozzles 8 on the right side and that jetted through the spray nozzles 8 on the left side are controlled to have different temperatures from each other. In this case, for example, room-temperature water is jetted from the right side, and supercooled water of 0° C. or lower is jetted from the left side, to thereby control the cooling capacity of the cooling member 1 such that the cooling capacity of the portion directly below the left hemisphere is higher than that of the right portion. In this manner, balancing in cooling capacity can be more precisely controlled between the left portion and the right portion.

[0092] 4. Mode in Which Contact History of a Cooling Medium with a Cooling Member is Controlled (Claim 18);

[0093] Needless to say, cooling capacity differs between the two cases; continuous contact between the cooling medium and the cooling member and intermittent contact therebetween. By the term “intermittent contact” is meant that contacting state and non-contacting state occur alternately, and thus, cooling capacity can also be controlled through controlling the ratio of contact time to non-contact time. In other word, cooling capacity can be regulated by modifying the contact history between a cooling medium and a cooling member.

[0094] For example, in the aforementioned embodiments shown in FIGS. 8 and 9, restriction plate 15, which regulates the spray direction, is made movable and a control mechanism (not shown) for controlling the motion of the restriction plate 15 is connected thereto. In this manner, cooling capacity can be enhanced as compared with the case in which the cooling medium does not at all contact the outer surface of the interior space 13 (material section 14). As a result, balance of cooling capacities between the center portion and the peripheral portion of the cooling member 1 is controlled more precisely.

[0095] 5. Mode in Which a Heater is Incorporated into a Portion of a Cooling Member (Claims 19 and 21);

[0096] Forced cooling of a cooling member is effected through a method in which either or both of the aforementioned modes 1 and 2 are implemented, and is controlled through implementing either or both of the aforementioned modes 3 and 4 in accordance with needs. In combination with the forced cooling, a heater for lowering cooling capacity is buried in a portion of a cooling member, to thereby block heat flow from molten metal to the outer surface of the cooling member. As a result, well-balanced cooling can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape.

[0097] The heater may be a resistance heater, superheated steam, or high-temperature gas.

[0098] As describe above with reference to, for example, FIG. 10, the left portion and the center portion of the molten metal 6 solidifies slowly, since in these portions the cast ingot is thick and the molten metal inlet 4 is disposed, and therefore, an attempt is made to enhance the cooling capacity of these portions. In contrast, the molten metal 6 in the right portion solidifies faster because the right portion of the cast ingot is thinner and is remote from the molten metal inlet 4. In order to attain a well-balanced cooling, the heater 11 is incorporated into the right portion, and the outer surface of the right portion is covered with the heat-insulating material 12 so as to prevent the cooling medium from contacting the outer surface of the right portion, to thereby lower the cooling capacity of the right portion.

[0099] 6. Mode in Which a Heater is Incorporated into a Portion of a Mold Member (Claims 20 and 21);

[0100] Forced cooling of a cooling member is effected through a method in which either or both of the aforementioned modes 1 and 2 is implemented, and the forced cooling is controlled through implementing either or both of the aforementioned modes 3 and 4 in accordance with needs. In combination with the forced cooling, a heater for lowering the cooling capacity is buried in a portion of a mold member, to thereby block heat flow from molten metal to the mold member. As a result, well-balanced cooling capacity can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape.

[0101] The aforementioned mode 5 is effective when a portion of cast ingot that lowers cooling capacity is relatively thin. When such a portion is relatively thick, solidification performance is affected by not only the cooling member but also the mold member, and therefore, a heater is incorporated into the mold member. The location of the incorporated heater is either or both of a side section and an upper section of the mold member. The mold may be divided into a side member and an upper member.

[0102] The heater may be a resistance heater, superheated steam, or a high-temperature gas.

[0103] FIG. 12(b) is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode 6. Elements identical to those shown in FIG. 1 are denoted by the same reference numerals.

[0104] The shape of the cast ingot in this embodiment is such that thick portions A and B are formed on the right side and left side (as viewed in the drawing), respectively, with a thin portion being interposed therebetween, and molten metal is teemed through a molten metal inlet 4 disposed at an upper end of left-hand space B providing a thicker ingot portion.

[0105] In such casting, molten metal filled in the smaller space A, which is remote from the molten metal inlet 4, solidifies faster than molten metal filled in the space B. While waiting for the completion of solidification of molten metal in space B, the mold material that defines space A is deprived of heat through the solidified cast ingot in space A, and therefore, the temperature of the side wall and upper wall of the mold member constituting space A becomes lower than the molten metal temperature. Since the molten metal in direct contact with the mold begins to solidify from the wall surfaces of the mold, the final solidification portion ris generated within the cast ingot in space A as shown in FIG. 12(a), leading to a defective cast ingot including a blowhole or microshrinkage in the portion corresponding to the final solidification portion.

[0106] In order to cope with this problem, as shown in FIG. 12(b), a heater 11 is buried in the mold material at the location directly above the space A so as to add heat commensurate with the amount of heat removed through the cast ingot, to thereby heat the mold to a temperature higher than the molten metal temperature. As a result, solidification of the molten metal proceeds without producing a closed solidification interface within the space A, and solidification is completed with the solidification interface coinciding with the interior upper surface of the mold. Thus, a wholly non-defective cast ingot can be obtained.

[0107] The heating conditions are preferably monitored through temperature measurement by means of a thermocouple buried in a representative position of the mold, to thereby maintain the solidification interface in a predetermined shape. The heater is preferably connected to a power source and a control box in order to control the heater automatically.

[0108] Unlike the case of application of heat by a heater, cooling does not provide any negative energy. However, in either of the aforementioned modes (1-b and 1-c) in which a space or a material section of different thermal conductivity is provided within the cooling member and the aforementioned mode (1-f) in which the inclination angle of holes formed in an outer surface of a cooling member is controlled in accordance with the collision angle of a cooling medium, similar to the case in which a heater is provided (modes 5 and 6), prevention of heat from flowing from the molten metal to the outer surface of the cooling member can be realized.

[0109] 7. Mode in Which a Plurality of Heating Sections and Cooling Sections are Provided Within a Cooling Member, and the Functions of the Respective Sections are Controlled (Claim 22);

[0110] When a mechanism which can be arbitrarily used for heating and cooling in accordance with needs is installed within a cooling member in advance, the temperature of an arbitrary portion of the cooling member can be arbitrarily controlled. Preferably, the heating section is similar to the aforementioned heater which performs heating in an arbitrary manner. The cooling section is a section or a chamber to which the aforementioned cooling medium is to be supplied, and preferably performs cooling in an arbitrary manner. These sections control temperatures (cooling capacity) of respective portions of the cooling member in accordance with the shape of the cast ingot and the number and the location of the molten metal inlet.

[0111] FIG. 13 is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode 7. Elements identical to those shown in FIG. 1 are denoted by the same reference numerals.

[0112] In the present embodiment, molten metal is teemed through a molten metal inlet 4 disposed at an approximately central position, to thereby produce a disk-shaped cast ingot having a shape similar to those shown in FIGS. 8 and 9; i.e., a cast ingot having a virtually uniform thickness wherein the thickness is extremely smaller than the outer diameter.

[0113] In such casting, as described above, the thickness of the cast ingot extremely smaller than the outer diameter causes solidification time difference between the center portion and the peripheral portion; i.e., the remotest portion from the molten metal inlet 4, of the disk. Thus, the center portion of the cast ingot easily produces cracks because an ideal unidirectionally solidification state cannot be maintained.

[0114] In order to cope with this problem, cooling sections (chambers) 19, which are provided independently from one another and each being connected to a cooling control unit 20, are disposed in an upper inner portion of a cooling member 1 of the present embodiment; and heating sections (chambers) 21, which are provided independently from one another and each being connected to a heating control unit 22, are disposed in a lower inner portion of the cooling member 1. The cooling control unit 20 can supply a cooling medium to an arbitrary cooling section 19, and the heating control unit 22 can make an arbitrary heating section 21 generate heat.

[0115] In this case, the cooling control unit 20 supplies the cooling medium to the cooling sections 19 that cool a center portion below the molten metal inlet 4, and supplies no cooling medium to the other cooling sections 19; and the heating control unit 22 make only the heating sections 21 that heat a peripheral portion of the disk generate heat.

[0116] In this manner, the cooling member 1 of the present embodiment shown in FIG. 13 can be appropriately applied to a cast ingot of any shape as long as the lower surface of the cast ingot is flat.

[0117] In the present invention, through use of a cooling capacity control mechanism that locally enhances or lowers cooling capacity of a cooling member or controls local heat removal through intentional heating in accordance with the shape of the cast ingot and the location and the number of the molten metal inlet—specifically, through the aforementioned method 1 (“a”-“h”) and 2 to 6, or appropriate combination thereof—control and regulation of solidification of a cast ingot is attained without producing a closed loop of solidification interface within the mold. The cast ingot obtained in the aforementioned manner does not include any riser portion or cut surface. Preferably, upper corners of the cast ingot has a radius of curvature of 1 mm or less.

[0118] Therefore, the cast ingot obtained through the aforementioned method and apparatus is a non-defective product having no cracks, blowhole defects, or internal defects, and can, of course, directly serve as a product (casting), or can be used as a material for plastic working for use in various processing such as forging.

[0119] Furthermore, according to the present invention, a mechanism may be provided for opening at least a portion (a portion or the entirety) of a cooling member in the course of solidification of molten metal within a mold; and a mechanism for supplying a cooling medium directly to an exposed outer surface of a cast ingot (claim 23).

[0120] The cast mechanism in the vicinity of a cooling member is finer because molten metal solidifies faster. As the solidification interface proceeds remote from the cooling member, the solidification rate decreases. In other words, when a cooling member is used for cooling, the thicker the cast ingot, the larger the solidification rate difference between at a lower section and at an upper section of a cast ingot, resulting in wide cast mechanism difference, which leads to difference in terms of cast quality or forging property. Furthermore, the upper section of the cast ingot is apt to generate internal microshrinkage and forging cracks.

[0121] The cooling capacity attained through indirect cooling by use of a cooling member is inferior to that of direct cooling in which a cooling medium is directly applied to the lower surface of a cast ingot. However, without using a cooling member, the aforementioned local control of heat removal from a mold member containing a cooling member cannot be performed. Thus, it is preferable to combine indirect cooling by use of a cooling member and direct cooling in order to enhance the cooling capacity.

[0122] At the beginning of casting, a cooling member, which serves as a portion of a mold, receives molten metal. For example, in the course of solidification, all or a portion of the cooling member contacting the lower surface of a cast ingot is opened, to thereby apply a cooling medium, which has been cooled the outer surface of the cooling member, directly to the lower surface of the cast ingot by means of cooling spray. As a result, the amount of heat removed from the cast ingot significantly increases, and the cooling rate and the solidification rate increase. In this manner, a cast ingot having small metallographic difference between an upper portion and a lower portion can be obtained. Alternatively, the cooling member may be lowered, after which a rotatable apparatus comprising a spray device and a pan for collecting the cooling medium may be used. In this case, the cast ingot is held so as not to fall, in a manner appropriate for ingot and the mold in terms of shape.

[0123] The present method is particularly effective when the ingot to be cast is thick, and enables casting of any species of alloy without involving difficulties associated with a conventional casting of an alloy.

[0124] FIG. 14 is a cross-sectional view showing an exemplary apparatus of the present invention in which a cooling member 1 is composed of a plurality of members 1a and 1b. The member 1b is connected to a driving means 18 via a piston rod 17 so that the member 1b can slidably move while contacting the lower surface of the member 1a.

[0125] The casting operation performed by use of the present apparatus is as follows.

[0126] During teeming of molten metal 6, the member 1b is placed at a position (1) in order to close a hole in the member 1a. Subsequently, the molten metal 6 in a mold 2 is solidified from the upper surface of the cooling member 1 by means of a cooling spray (spray nozzle 8) and the cooling member 1.

[0127] When the solidification interface 6b in the mold 2 has reached the position denoted by @, the driving means 18 is started to operate in order to slide the member 1b to the position (2) to thereby expose the lower surface of the cast ingot, to which a cooling medium is directly sprayed.

[0128] After completion of solidification, the cooling member 1 is lowered, and the cast ingot is removed.

[0129] As described above, the cooling member may comprise a plurality of members.

[0130] Each member constituting the cooling member is made of any of the aforementioned materials, and the member may be made up of homogeneous or heterogeneous material(s).

[0131] Preferably, respective members are processed to have optimal shapes from the viewpoints of rigidity and cooling capacity. A hole or holes may be formed in each member, or no hole may be formed, and the thickness may be controlled in an appropriate manner.

[0132] The driving means may be any apparatus such as an air cylinder, a hydraulic cylinder, or an electric cylinder. Although the driving means shown in FIG. 14 moves up and down along with the cooling member, the mechanism of the driving means is not limited thereto.

[0133] A series of operations of casting-related apparatus may be performed through a timer control in accordance with a predetermined time table, or alternatively, a measuring means such as a thermocouple may be inserted into a cooling member and/or a side and/or upper wall(s) of the mold so as to measure and monitor the temperature of respective portions, and the operation of each apparatus is started when the temperature has reached a predetermined point.

[0134] In particular, when a movable portion (member 1b in the illustrated embodiment) is opened excessively early, unsolidified molten metal flows out into a cooling case including a cooling spray, whereas when the movable portion is opened excessively early, microshrinkage is produced within the mold and the crystal grains become coarse.

[0135] When the movable portion (the member 1b in the illustrated embodiment) is opened, the cast ingot which is being solidified should not fall from the mold, and therefore, the cast ingot is designed to have a shape for allowing the ingot of as-cast shape to be retained by the mold, as shown in FIG. 14. Alternatively, it is also effective to provide, to a fixed portion (member la in the illustrated embodiment), a projection which does not impede the removal operation for the cast ingot. The projection, which forms a depression in a product, should have a shape which does not cause any problem during use of the cast ingot.

[0136] This method can be used in combination with the aforementioned various cooling control methods. Needless to say, the methods are preferably combined in accordance with the species of the alloy and the shape of the cast ingot, to thereby provide optimal operational conditions.

[0137] [Embodiments]

[0138] [Embodiment 1]

[0139] An aluminum alloy was melted in a separately provided melting furnace, and the molten metal was cast by use of the apparatus of FIG. 1. The thus-obtained cast ingot was examined for metallographic microstructure. The cooling member is made of copper, and the mold, the molten metal reservoir, and the open/close plug were made of a commercially available refractory heat-insulating material (Lumiboard; product of Isoraito Kogyo Kabushiki Kaisha). A liner was inserted between the side mold 2b and the upper mold 2a, to thereby secure a gas ventilation of the mold. The upper surface of the cooling member has a step-down center, and the slope angle of the step-down portion is 45°. The cast ingot to be produced has a disk shape having a convex portion in its lower surface, an outer diameter of 62.5&phgr;, an outer thickness at the periphery of 7 mm, a diameter of the central thick portion of 30&phgr;, and a thickness of the central thick portion of 12 mm. The cooling member has an outer shape depressed to form a hollow cone toward the center. The central portion of the cooling member has an inner diameter of 30&phgr; and a thickness of 5 mm. The thickness of the cooling member increases at 45° from the edge of the central portion toward the periphery. The casting conditions and the procedure are as follows.

[0140] 1) Alloy species: JIS 2218 alloy

[0141] 2) Temperature of molten metal contained in the molten metal reservoir: 720° C.

[0142] 3) Cooling member temperature before teeming: 150° C.

[0143] 4) Flow rate of cooling water: 5 liters/minute

[0144] 5) Diameter of molten metal inlet: 12&phgr;

[0145] 6) Casting procedure:

[0146] Close the molten metal inlet with the open/close plug two seconds after initiation of teeming.

[0147] Start water cooling when the cooling member temperature has reached 500° C.

[0148] Stop water cooling when the cooling member temperature has reached 30° C.

[0149] Start descending of the cooling member when the cooling member temperature has reached 200° C.

[0150] 7) The cast body was allowed to fall spontaneously together with the cooling member, and then collected.

[0151] [Embodiment 2]

[0152] The apparatus as shown in FIG. 2 was used, and cracks in the cooling member were investigated. The cooling member has a thickness of 12 mm, a hole diameter of 4&phgr;, and a hole depth of 10 mm. The holes were provided at nodes of 7 mm×7 mm grid. The casting conditions and the procedure were the same as in Embodiment 1. The cast ingot to be produced has an outer diameter of 62.5&phgr; and a thickness of 9 mm.

[0153] [Embodiment 3]

[0154] The apparatus as shown in FIG. 11 including a passage for circulating a cooling medium within the cooling member was used in order to produce a cast ingot having a three-dimensionally complicated shape with no plane of symmetry. The cast ingot to be produced has a thickness (thinner portion) of 9 mm, a thickness (thicker portion) of 15 mm, a longest edge of 50 mm, and a shortest edge of 35 mm. The casting conditions and the procedure are as follows.

[0155] 1) Alloy species: JIS 6061 alloy

[0156] 2) Temperature of molten metal contained in the molten metal reservoir: 720° C.

[0157] 3) Cooling member temperature before teeming: 100° C.

[0158] 4) Flow rate of cooling water: 8 liters/minute

[0159] 5) Diameter of molten metal inlet: 10&phgr;

[0160] 6) Casting procedure:

[0161] Close the molten metal inlet with the open/close plug three seconds after initiation of teeming.

[0162] Start water cooling when the cooling member temperature has reached 500° C.

[0163] Stop water cooling when the cooling member temperature has reached 30° C.

[0164] Start descending of the cooling member when the cooling member temperature has reached 200° C.

[0165] 7) The cast body was allowed to fall spontaneously together with the cooling member, and then collected.

[0166] 8) The metallographic microstructure of the cast ingot was investigated.

[0167] [Embodiment 4]

[0168] The apparatus as shown in FIG. 10 in which a heater was buried in a portion of the cooling member was used in order to produce a cast ingot having a three-dimensionally complicated shape with no plane of symmetry. The cast ingot to be produced had a thickness (of the thinner portion) of 9 mm, a thickness (of the thicker portion) of 15 mm, a longest side of 50 mm, and a shortest side of 35 mm. The casting conditions and the procedure are as follows.

[0169] 1) Alloy species: JIS AC2B alloy

[0170] 2) Temperature of molten metal contained in the molten metal reservoir: 720° C.

[0171] 3) Cooling member temperature before teeming: 150° C.

[0172] 4) Flow rate of cooling water: 8 liters/minute

[0173] 5) Diameter of molten metal inlet: 10&phgr;

[0174] 6) Casting procedure:

[0175] Close the molten metal inlet with the open/close plug three seconds after initiation of teeming.

[0176] Start water cooling when the cooling member temperature has reached 500° C.

[0177] Stop water cooling when the cooling member temperature has reached 30° C.

[0178] Start descending of the cooling member when the cooling member temperature has reached 200° C.

[0179] 7) The cast body was allowed to fall spontaneously together with the cooling member, and then collected.

[0180] 8) Heater capacity: 5 kW

[0181] 9) The metallographic microstructure of the cast ingot was investigated.

[0182] [Embodiment 5]

[0183] A material used for forging a VTR cylinder drum was produced by use of the apparatus of FIG. 8. The casting conditions and the procedure are as follows.

[0184] 1) Alloy species: JIS 2218 alloy

[0185] 2) Temperature of molten metal contained in the molten metal reservoir: 720° C.

[0186] 3) Cooling member temperature before teeming: 150° C.

[0187] 4) Flow rate of cooling water: 5 liters/minute

[0188] 5) Diameter of molten metal inlet: 12&phgr;

[0189] 6) Dimensions of the cast ingot: 62.5&phgr; (outer diameter)×7 mm (thickness)

[0190] 7) Casting procedure:

[0191] Close the molten metal inlet with the open/close plug 1.5 seconds after initiation of the teeming.

[0192] Start water cooling when the cooling member temperature has reached 500° C.

[0193] Stop water cooling when the cooling member temperature has reached 30° C.

[0194] Start descending of the cooling member when the cooling member temperature has reached 200° C.

[0195] 8) The cast body was allowed to fall spontaneously together with the cooling member, and then collected.

[0196] 9) Height of the step provided on the outer surface of the cooling member: 5 mm

[0197] 10) Slope angle of the outer surface of the cooling member: 45°

[0198] 11) Thickness between the inner surface of space 13 and the top surface or the lower surface of the cooling member: 4 mm

[0199] 12) Difference between the spray collision angle &bgr; and the hole inclination angle: within 10°

[0200] 13) The incidence of cracks of the cast ingot was investigated.

COMPARATIVE EXAMPLE 1

[0201] Casting was performed by use of the apparatus of FIG. 15 and a cooling member having a flat outer surface, a thickness of 10 mm, a diameter of the central depressed portion of 30 mm, and a depth of the central depressed portion of 5 mm. The casting conditions and the procedure were the same as in Embodiment 1.

[0202] The results of comparison of the thus-obtained cast ingot with the cast ingot obtained from Embodiment 1 are as follows.

[0203] Embodiment 1: No defect was observed directly below the molten metal inlet.

[0204] Comparative Example 1: A defect was observed directly below the molten metal inlet.

COMPARATIVE EXAMPLE 2

[0205] Casting was performed by use of the apparatus of FIG. 15 and a cooling member having a thickness of 5 mm. The casting conditions and the procedure were the same as in Embodiment 2.

[0206] The results of comparison of the thus-obtained cast ingot with the cast ingot obtained from Embodiment 2 are as follows.

[0207] Embodiment 2: No crack was observed in the cooling member.

[0208] Comparative Example 2: Cracks were observed in the central portion of the cooling member.

COMPARATIVE EXAMPLE 3

[0209] Casting was performed by use of the apparatus of FIG. 15 including a cooling member having no mechanism for enhancing cooling capacity. The casting conditions and the procedure were the same as in Embodiment 3.

[0210] The results of comparison of the thus-obtained cast ingot with the cast ingot obtained from Embodiment 3 are as follows.

[0211] Embodiment 3: No defect was observed in the portion of the cast ingot directly below the molten metal inlet.

[0212] Comparative Example 3: Defects were observed in the portion of the cast ingot directly below the molten metal inlet.

COMPARATIVE EXAMPLE 4

[0213] Casting was performed by use of the apparatus of FIG. 15 including a cooling member having no mechanism for enhancing cooling capacity. The casting conditions and the procedure were the same as in Embodiment 3.

[0214] The results of comparison of the thus-obtained cast ingot with the cast ingot obtained from Embodiment 3 are as follows.

[0215] Embodiment 4: No defect was observed in the portion of the cast ingot directly below the molten metal inlet.

[0216] Comparative Example 4: Defects were observed in the portion of the cast ingot directly below the molten metal inlet.

COMPARATIVE EXAMPLE 5

[0217] Casting was performed by use of the apparatus of FIG. 15 including a cooling member having a thickness of 5 mm. The casting conditions and the procedure were the same as in Embodiment 5.

[0218] The results of comparison of the thus-obtained cast ingot with the cast ingot obtained from Embodiment 5 are as follows.

[0219] Embodiment 5: No crack was observed in the cast ingot.

[0220] Comparative Example 5: Cracks were observed in a center portion of the cast ingot.

[0221] [Effects of the Invention]

[0222] As described above, the metal casting method and the apparatus of the present invention enables a cast ingot to solidify without forming a closed loop of solidification interface within a mold by means of a cooling capacity control mechanism which is adapted to locally enhance or lower the cooling capacity of a cooling member, or to control local heat removal through intentional heating in accordance with the shape of the cast ingot and the location and the number of the molten metal inlet. Thus, there can be produced non-defective cast ingots having no crack or blowhole therein can be obtained.

[0223] In other words, the metal casting method and the apparatus of the present invention controls the number and the location of the molten metal inlet in accordance with the shape of the cast ingot to be produced, to thereby produce healthy cast ingots of desired shape having no internal defects, such as cracks, blowholes, and microshrincage, can be obtained.

[0224] The cast ingots obtained through the aforementioned method and apparatus do not include any riser portion or cut surface, and can, of course, be directly used for casting of products (castings), or can be used for casting of a material for plastic working which is used in various processing such as forging.

BRIEF DESCRIPTION OF THE DRAWINGS

[0225] [FIG. 1] A schematic cross-sectional view showing an exemplary metal casting apparatus of the present invention.

[0226] [FIG. 2] A schematic cross-sectional view showing another exemplary metal casting apparatus of the present invention.

[0227] [FIG. 3] A cross-sectional view showing holes which are adapted to maximize the cooling capacity.

[0228] [FIG. 4] A schematic cross-sectional view showing another exemplary metal casting apparatus of the present invention.

[0229] [FIG. 5] (a) A plan view of a connecting rod member, (b) a side view thereof, and (c) a schematic cross-sectional view showing an exemplary metal casting apparatus for casting the connecting rod member.

[0230] [FIG. 6] (a) A schematic cross-sectional view showing another exemplary metal casting apparatus for producing a member having a shape identical with the connecting rod member shown in FIG. 5, and (b) a plan view showing the resultant connecting rod member.

[0231] [FIG. 7] (a) A schematic cross-sectional view showing another exemplary metal casting apparatus for producing a member having a shape identical with the connecting rod member shown in FIG. 5, and (b) a plan view showing the resultant connecting rod member.

[0232] [FIG. 8] A schematic cross-sectional view showing another exemplary metal casting apparatus of the present invention.

[0233] [FIG. 9] A schematic cross-sectional view showing another exemplary metal casting apparatus of the present invention.

[0234] [FIG. 10] A schematic cross-sectional view showing another exemplary metal casting apparatus of the present invention.

[0235] [FIG. 11] A schematic cross-sectional view showing another exemplary metal casting apparatus of the present invention.

[0236] [FIG. 12] (a) A schematic cross-sectional view showing the situation under which a closed loop of solidification interface is formed within the cast ingot. (b) A schematic cross-sectional view showing the situation under which solidification interface advances so as to reach the end portion of the mold.

[0237] [FIG. 13] A schematic cross-sectional view showing another exemplary metal casting apparatus of the present invention.

[0238] [FIG. 14] A schematic cross-sectional view showing another exemplary metal casting apparatus of the present invention.

[0239] [FIG. 15] A schematic cross-sectional view showing a conventional casting apparatus making use of unidirectional solidification.

[0240] [Description of Reference Numerals]

[0241] 1: cooling member

[0242] 2: mold

[0243] 3: molten metal reservoir

[0244] 4: molten metal inlet

[0245] 5: open/close plug

[0246] 6: molten metal

[0247] 6a: solidified molten metal

[0248] 6b: solidification interface

[0249] 6c: unsolidified molten metal

[0250] 7: molten metal in a reservoir

[0251] 8: spray nozzle

[0252] 9: hole

[0253] 10: circulation passage

[0254] 11: heater

[0255] 12: heat-insulating material

[0256] 13: interior space

[0257] 14: portion of material having different thermal conductivity

[0258] 15: restriction plate

[0259] 16: step

Claims

1. A method for casting metal by charging molten metal into a closed-space-definable mold which includes a cooling member and in which an end surface of an open/close plug serves as a portion of an inner wall of the mold, characterized in that

removal of heat from a mold member comprising the cooling member is locally controlled in accordance with the shape of cast ingot and the location and number of the molten metal inlet(s), to thereby solidify the molten metal in such a manner that the solidification interface advances to arrive at an end of an inner surface of the mold.

2. The metal casting method as described in claim 1, wherein an outer surface of at least one portion of the cooling member is opened during the course of solidification of the molten metal in the mold, whereby cooling an outer surface of the exposed cast ingot directly with a cooling medium.

3. A metal casting apparatus for casting metal by charging molten metal into a closed-space-definable mold which includes a cooling member and in which an end surface of an open/close plug serves as a portion of an inner wall of the mold, characterized by comprising a cooling capacity control mechanism which imparts, to the mold member comprising the cooling member, a heat removal profile appropriate for the shape of the cast ingot to be produced and for the number and position of the molten metal inlet(s).

4. The metal casting apparatus as described in claim 3, wherein the cooling member is cooled by bringing an outer surface of the cooling member into contact with the cooling medium.

5. The metal casting apparatus as described in claim 3 or 4, wherein the cooling member has a thickness which is partially different from the thickness of the remaining portion.

6. The metal casting apparatus as described in any one of claims 3 to 5, wherein a space is provided within a portion of the cooling member.

7. The metal casting apparatus as described in any one of claims 3 to 6, wherein the cooling member is made of a composite material of different thermal conductivites.

8. The metal casting apparatus as described in any one of claims 3 to 7, further comprising at least one nozzle for jetting the cooling medium toward an outer surface of the cooling member and causing the cooling medium in the form of spray or shower to hit the outer surface of the cooling member.

9. The metal casting apparatus as described in any one of claims 3 to 8, wherein an outer surface of the cooling member is partially provided with an unevenness so that the area that can contact a cooling medium locally varies.

10. The metal casting apparatus as described in claim 9, wherein the unevenness is holes which do not communicate with an interior surface and inclination angles of the holes are regulated to in accordance with collision angles of the cooling medium jetted in the form of spray or shower and supplied to the outer surface of the cooling member.

11. The metal casting apparatus as described in any one of claims 3 to 10, further comprising, on the outer face side of the cooling member, means for enabling local prevention of the cooling medium from contacting the cooling member.

12. The metal casting apparatus as described in claim 11, wherein the means for enabling prevention of the cooling medium from contacting the cooling member is a step provided at a portion of an outer surface of the cooling member.

13. The metal casting apparatus as described in claim 11, wherein the means for enabling prevention of the cooling medium from contacting the cooling member is a heat-insulating material which partially covers an outer surface of the cooling member.

14. The metal casting apparatus as described in claim 13, wherein the heat-insulating material is a species or a combination of species selected from the group consisting of rubber, ceramic material, and fibrous heat-insulating material.

15. The metal casting apparatus as described in any one of claims 3 to 14, further comprising a circulation passage for cooling medium which is provided within a portion of the cooling member.

16. The metal casting apparatus as described in any one of claims 3 to 15, wherein the cooling medium is a species or a combination of species selected from the group consisting of water, supercooled water of 0C or lower, a volatile liquid, or an oil.

17. The metal casting apparatus as described in any one of claims 3 to 16, wherein a temperature-controlled cooling medium is brought into contact with the cooling member.

18. The metal casting apparatus as described in any one of claims 3 to 17, wherein contact history of the cooling medium with a cooling member is controlled.

19. The metal casting apparatus as described in any one of claims 3 to 18, further comprising a heater provided within a portion of the cooling member.

20. The metal casting apparatus as described in any one of claims 3 to 19, further comprising a heater provided within a portion of the mold member.

21. The metal casting apparatus as described in claim 19 or 20, wherein the heater is a heating device making use of ohmic-resistance heating, superheated steam, or a high-temperature gas.

22. The metal casting apparatus as described in any one of claims 2 to 21, wherein a plurality of heating sections and a plurality of cooling sections are provided within the cooling member, and functions of respective sections are controlled.

23. The metal casting apparatus as described in any one of claims 2 to 22, further comprising a mechanism for opening at least a portion of the cooling member in the course of solidification of molten metal within a mold and a mechanism for supplying a cooling medium directly to an exposed outer surface of a cast ingot.

24. A cast ingot produced by charging molten metal into a closed-space-definable mold which includes a cooling member and in which an end surface of an open/close plug serves as a portion of an inner wall of the mold, effecting a local control in terms of removal of heat from a mold member in accordance with the shape of cast ingot and the location and number of the molten metal inlet(s), causing the molten metal to solidify in such a manner that the solidification interface advances to arrive at an end of an inner surface of the mold, to thereby provide a cast ingot having no cut surface or riser portion.