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Title:
UP-DRAWING CONTINUOUS CASTING APPARATUS AND UP-DRAWING CONTINUOUS CASTING METHOD
Document Type and Number:
WIPO Patent Application WO/2015/136347
Kind Code:
A1
Abstract:
An up-drawing continuous casting method that includes dipping a metal member (M3, M4) into molten metal (Ml) held in a holding furnace (101), and manufacturing a casting (M5) while drawing up the molten metal by the metal member (M3), includes dipping the metal member (M3, M4) into the molten metal (Ml), and then mixing the molten metal (Ml) near the dipped metal member (M4). As a result, an oxide film formed on, and foreign matter adhered to, the surface of the dipped metal member (M4), and the like, are able to be removed.

Inventors:
SUGIURA NAOAKI (JP)
YOKOTA YUSUKE (JP)
Application Number:
PCT/IB2015/000286
Publication Date:
September 17, 2015
Filing Date:
February 24, 2015
Export Citation:
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Assignee:
TOYOTA MOTOR CO LTD (JP)
International Classes:
B22D11/00; B22D11/01
Domestic Patent References:
WO2012035752A12012-03-22
WO2013136785A12013-09-19
Foreign References:
JP2012061518A2012-03-29
Other References:
L ZHANG ET AL: "On the mechanism of the formation of primary intermetallics under ultrasonic melt treatment in an Al-Zr-Ti alloy", IOP CONFERENCE SERIES: MATERIALS SCIENCE AND ENGINEERING, vol. 27, 12 January 2012 (2012-01-12), pages 012002, XP055185203, DOI: 10.1088/1757-899X/27/1/012002
ESKIN<1> G I: "Broad prospects for commercial application of the ultrasonic (cavitation) melt treatment of light alloys", ULTRASONICS: SONOCHEMISTRY, BUTTERWORTH-HEINEMANN, GB, vol. 8, no. 3, 1 July 2001 (2001-07-01), pages 319 - 325, XP004245625, ISSN: 1350-4177, DOI: 10.1016/S1350-4177(00)00074-2
ZHANG L ET AL: "Influence of ultrasonic melt treatment on the formation of primary intermetallics and related grain refinement in aluminum alloys", JOURNAL OF MATERIALS SCIENCE, KLUWER ACADEMIC PUBLISHERS, BO, vol. 46, no. 15, 18 March 2011 (2011-03-18), pages 5252 - 5259, XP019900827, ISSN: 1573-4803, DOI: 10.1007/S10853-011-5463-2
Download PDF:
Claims:
CLAIMS:

1. An up-drawing continuous casting method that includes dipping a metal member into molten metal held in a holding furnace, and manufacturing a casting while drawing up the molten metal by the metal member, comprising:

dipping the metal member into the molten metal; and

mixing the molten metal near the dipped metal member, after the metal member has been dipped into the molten metal.

2. The up-drawing continuous casting method according to claim 1, wherein when drawing up the molten metal by the metal member, the molten metal is drawn up while passing through a shape determining member that is arranged above a molten metal surface of the molten metal and determines a sectional shape of a casting.

3. The up-drawing continuous casting method according to claim 1 or 2, wherein the metal member is a casting; and

the molten metal is mixed after a portion of the casting that has been dipped into the molten metal has melted.

4. The up-drawing continuous casting method according to any one of claims 1 to 3, wherein

the molten metal is mixed by applying ultrasonic vibrations to at least one of the metal member and the molten metal.

5. An up-drawing continuous casting apparatus that dips a metal member into molten metal held in a holding furnace, and manufactures a casting while drawing up the molten metal by the metal member, comprising:

a molten metal mixing portion configured to mix the molten metal near the dipped metal member.

6. The up-drawing continuous casting apparatus according to claim 5, further comprising:

a shape determining member that is arranged above a molten metal surface of the molten metal and determines a sectional shape of the casting, wherein

the molten metal is drawn up while being passed through the shape determining member.

Description:
UP-DRAWING CONTINUOUS CASTING APPARATUS AND UP-DRAWTNG

CONTINUOUS CASTING METHOD

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to an up-drawing continuous casting apparatus and an up-drawing continuous casting method. 2. Description of Related Art

[0002] Japanese Patent Application Publication No. 2012-61518 (JP 2012-61518 A) proposes a free casting method as a groundbreaking up-drawing continuous casting method that does not require a mold. As described in JP 2012-61518 A, a starter is first dipped into the surface of molten metal (i.e., a molten metal surface), and then when the starter is drawn up, molten metal is also drawn up following the starter by surface tension and the surface film of the molten metal. Here, a casting that has a desired sectional shape is able to be continuously cast by drawing up the molten metal through a shape determining member arranged near the molten metal surface, and cooling the drawn up molten metal.

[0003] With a normal continuous casting method, the sectional shape and the shape in the longitudinal direction are both determined by a mold. In particular, with a continuous casting method, the solidified metal (i.e., the casting) must pass through the mold, so the cast casting takes on a shape that extends linearly in the longitudinal direction. In contrast, the shape determining member in the free casting method determines only the sectional shape of the casting. The shape in the longitudinal direction is not determined. Therefore, castings of various shapes in the longitudinal direction are able to be obtained by drawing the starter up while moving the starter (or the shape determining member) in a horizontal direction. For example, JP 2012-61518 A describes a hollow casting (i.e., a pipe) formed in a zigzag shape or a helical shape, not a linear shape in the longitudinal direction.

[0004] The inventors discovered the problem described below. With the free casting method described in JP 2012-61518 A, a casting that is difficult to form with a single casting may be divided up and cast in two parts (i.e., castings). In this case, the second casting is performed using the first casting as a starter. Therefore, the first casting and the second casting are joined together. Here, the strength of the joint portion of this kind of casting may end up being significantly lower than the strength of a non-joint portion. One conceivable reason for this is that an oxide layer formed on the surface of the first casting remains at the joint portion. A casting that uses a starter as part of the product, as well as of course a casting cast in three or more parts, has a joint portion, so the same problem may also arise.

SUMMARY OF THE INVENTION

[0005] The invention thus provides an up-drawing continuous casting apparatus and an up-drawing continuous casting method in which a decrease in strength of a joint portion of a casting is inhibited.

[0006] A first aspect of the invention relates to an up-drawing continuous casting method that includes dipping a metal member into molten metal held in a holding furnace, and manufacturing a casting while drawing up the molten metal by the metal member. This up-drawing continuous casting method includes dipping the metal member into the molten metal, and mixing the molten metal near the dipped metal member, after the metal member has been dipped into the molten metal. This kind of structure makes it possible to remove, for example, an oxide film formed on, and foreign matter adhered to, the surface of the dipped metal member. As a result, a decrease in the strength of the joint portion of the casting is able to be inhibited.

[0007] When drawing up the molten metal by the metal member, the molten metal may be drawn up while passing through a shape determining member that is arranged above a molten metal surface of the molten metal and determines a sectional shape of a casting. This kind of structure enables a casting to be accurately formed. Also, the metal member may be a casting, and the molten metal may be mixed after a portion of the casting that has been dipped into the molten metal has melted. This kind of structure may be used to join castings together. Moreover, the molten metal may be mixed by applying ultrasonic vibrations to at least one of the metal member and the molten metal. This kind of structure makes it possible to effectively remove, for example, an oxide film formed on, and foreign matter adhered to, the surface of the dipped metal member.

[0008] A second aspect of the invention relates to an up-drawing continuous casting apparatus that dips a metal member into molten metal held in a holding furnace, and manufactures a casting while drawing up the molten metal by the metal member. This up-drawing continuous casting apparatus includes a molten metal mixing portion configured to mix the molten metal near the dipped metal member. This kind of structure makes it possible to remove, for example, an oxide film formed on, and foreign matter adhered to, the surface of the dipped metal member. As a result, a decrease in the strength of the joint portion of the casting is able to be inhibited.

[0009] The up-drawing continuous casting apparatus described above may also include a shape determining member that is arranged above a molten metal surface of the molten metal and determines a sectional shape of the casting, and the molten metal may be drawn up while being passed through the shape determining member. This kind of structure enables a casting to be accurately formed.

[0010] According to the aspects of the invention described above, an up-drawing continuous casting apparatus and an up-drawing continuous casting method in which a decrease in strength of a joint portion of a casting is inhibited are able to be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a sectional view showing a frame format of a free casting apparatus according to a first example embodiment of the invention;

FIG 2 is a plan view of a shape determining member according to the first example embodiment;

FIG 3 is an enlarged sectional view showing a frame format of a case in which molten metal is drawn up diagonally;

FIG 4 is a sectional view showing a frame format illustrating a free casting method according to the first example embodiment;

FIG 5 is a sectional view showing a frame format illustrating the free casting method according to the first example embodiment;

FIG 6 is a sectional view showing a frame format illustrating the free casting method according to the first example embodiment;

FIG. 7 is a sectional view showing a frame format illustrating the free casting method according to the first example embodiment;

FIG 8 is a sectional view showing a frame format illustrating the free casting method according to the first example embodiment;

FIG. 9 is a sectional view showing a frame format illustrating the free casting method according to the first example embodiment;

FIG. 10 is a graph comparing tensile strengths of a non-joint portion, a joint portion of a comparative example, and a joint portion of the example embodiment;

FIG 11 is a microstructure of the joint portion of the comparative example; and

FIG. 12 is a plan view of a shape determining member according to a modified example of the first example embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0012] Hereinafter, specific example embodiments to which the invention has been applied will be described in detail with reference to the accompanying drawings. However, the invention is not limited to these example embodiments. Also, the description and the drawings are simplified as appropriate for clarity.

[0013] (First example embodiment) First, a free casting apparatus (up-drawing continuous casting apparatus) according to a first example embodiment of the invention will be described with reference to FIG. 1. FIG. 1 is a sectional view showing a frame format of the free casting apparatus according to the first example embodiment. As shown in FIG. 1, the free casting apparatus according to the first example embodiment includes a molten metal holding furnace 101, a shape determining member 102, a support rod 104, an actuator 105, a cooling gas nozzle 106, a cooling gas supplying portion 107, an up-drawing machine 108, a molten metal mixing member 109, and an actuator 110. Naturally, a right-handed xyz coordinate system shown in FIG 1 is for descriptive purposes in order to illustrate the positional relationship of the constituent elements. The x-y plane in FIG 1 forms a horizontal plane, and the z-axis direction is the vertical direction. More specifically, the plus direction of the z-axis is vertically upward.

[0014] The molten metal holding furnace 101 holds molten metal Ml such as aluminum or an aluminum alloy, for example, and keeps it at a predetermined temperature at which the molten metal Ml has fluidity. In the example in FIG. 1, molten metal is not replenished into the molten metal holding furnace 101 during casting, so the surface of the molten metal Ml (i.e., a molten metal surface MMS level) drops as casting proceeds. However, molten metal may also be replenished into the molten metal holding furnace 101 when necessary during casting so that the molten metal surface MMS level is kept constant. Here, the position of a solidification interface SIF can be raised by increasing a set temperature of the molten metal holding furnace 101, and lowered by reducing the set temperature of the molten metal holding furnace 101. Naturally, the molten metal Ml may be another metal or alloy other than aluminum.

[0015] The shape determining member 102 is made of ceramic or stainless steel, for example, and is arranged above the molten metal surface MMS. The shape determining member 102 determines the sectional shape of a cast casting M3. The casting M3 shown in FIG. 1 is a solid casting (a plate) having a rectangular cross-section in the horizontal direction (hereinafter, simply referred to as "transverse section"). Naturally, the sectional shape of the casting M3 is not particularly limited. The casting M3 may also be a hollow casting of a round pipe or a square pipe or the like.

[0016] In the example in FIG 1, a main surface (a lower surface) on a lower side of the shape determining member 102 is arranged contacting the molten metal surface MMS. Therefore, an oxide film that forms on the molten metal surface MMS and foreign matter floating on the molten metal surface MMS are able to be prevented from getting mixed into the casting M3. However, the lower surface of the shape determining member 102 may also be arranged a predetermined distance away from the molten metal surface MMS. When the shape determining member 102 is arranged away from the molten metal surface MMS, heat deformation and erosion of the shape determining member 102 are inhibited, so the durability of the shape determining member 102 improves.

[0017] FIG 2 is a plan view of the shape determining member 102 according to the first example embodiment. Here, the sectional view of the shape determining member 102 in FIG 1 corresponds to a sectional view taken along line I - I in FIG. 2. As shown in FIG. 2, the shape determining member 102 has a rectangular planar shape, for example, and has a rectangular open portion (a molten metal passage portion 103) having a thickness tl and a width wl through which the molten metal passes in the center portion. The xyz coordinates in FIG 2 match those in FIG. 1.

[0018] Here, FIG. 2 also shows the molten metal mixing member 109 that is positioned lower (farther toward the z-axis direction minus side) than the shape determining member 102. As shown in FIGS. 1 and 2, the rod-shaped molten metal mixing member 109 that extends in the x-axis direction moves back and forth in the y-axis direction by the actuator 110. This kind of structure enables the molten metal Ml that is positioned directly below the shape determining member 102 to be mixed.

[0019] Therefore, an oxide film formed on, and foreign matter adhered to, the surface of the casting and the starter ST that has been dipped into the molten metal Ml at the start of casting, are able to be effectively removed. As a result, foreign matter and an oxide film are inhibited from remaining on the joint surface of the starter ST and the casting, and the joint portion between castings, so a decrease in the strength of the joint portion with respect to a non-joint portion is able to be suppressed. [0020] The molten metal mixing portion is not limited to the molten metal mixing member 109. For example, the molten metal Ml may also be mixed by applying ultrasonic vibrations to the molten metal Ml. Alternatively, the molten metal Ml may be mixed by applying ultrasonic vibrations to the starter ST and the casting M3.

[0021] As shown in FIG. 1, the molten metal Ml is drawn up following the casting M3 by the surface tension and the surface film of the molten metal Ml, and passes through the molten metal passage portion 103 of the shape determining member 102. That is, by passing the molten metal Ml through the molten metal passage portion 103 of the shape determining member 102, external force is applied to the molten metal Ml from the shape determining member 102, such that the sectional shape of the casting M3 is determined. Here, the molten metal that is drawn up from the molten metal surface MMS following the casting M3 by the surface tension and surface film of the molten metal will be referred to as "retained molten metal M2". Also, the boundary between the casting M3 and the retained molten metal M2 is a solidification interface SIF.

[0022] The support rod 104 supports the shape determining member 102. The support rod 104 is connected to the actuator 105. The shape determining member 102 is able to move up and down (i.e., in the vertical direction, i.e., the z-axis direction) via the support rod 104, by the actuator 105. According to this kind of structure, the shape determining member 102 is able to be moved downward as the molten metal surface MMS level drops as casting proceeds.

[0023] The cooling gas nozzle (a cooling portion) 106 is cooling means for spraying cooling gas (e.g., air, nitrogen, argon, or the like) supplied from the cooling gas supplying portion 107 at the casting M3 to indirectly cool the retained molten metal M2. The position of the solidification interface SIF is able to be lowered by increasing the flow rate of the cooling gas, and raised by reducing the flow rate of the cooling gas. The cooling gas nozzle 106 is also able to be moved up and down (i.e., in the vertical direction, i.e., in the z-axis direction) and horizontally (i.e., in the x-axis direction and the y-axis direction). Therefore, for example, the cooling gas nozzle 106 can be moved downward, in concert with the movement of the shape determining member 102, as the molten metal surface MMS level drops as casting proceeds. Alternatively, the cooling gas nozzle 106 can be moved horizontally, in concert with horizontal movement of the up-drawing machine 108.

[0024] The casting M3 is cooled by the cooling gas while being drawn up by the up-drawing machine 108 that is connected to the starter ST via a chuck portion 108a. Therefore, the casting M3 is formed by the retained molten metal M2 near the solidification interface SIF progressively solidifying from the upper side (i.e., a plus side in the z-axis direction) toward lower side (i.e., a minus side in the z-axis direction). The position of the solidification interface SIF is able to be raised by increasing the up-drawing speed with the up-drawing machine 108, and lowered by reducing the up-drawing speed.

[0025] Also, the retained molten metal M2 is able to be drawn up diagonally by drawing the retained molten metal M2 up while moving the up-drawing machine 108 horizontally (in the x-axis direction and the y-axis direction). Therefore, the longitudinal shape of the casting M3 is able to be freely changed. The longitudinal shape of the casting M3 may also be freely changed by moving the shape determining member 102 horizontally, instead of by moving the up-drawing machine 108 horizontally.

[0026] Here, the chuck portion 108a has a hinge structure in which paired plate-like members are rotatably connected together by a pin extending in the y-axis direction. Therefore, the chucking angle of the starter ST (i.e., the chucking angle) is able to be changed. One of the plate-like members is fixed to a main body of the up-drawing machine 108, and the other plate-like member is fixed to the starter ST. Therefore, the starter ST is able to be rotated about an axis that is parallel to the molten metal surface MMS (the y-axis in the example in FIG 1). Here, the angle formed by the pair of plate-like members is able to be both changed and fixed. That is, after the angle is changed, it is fixed at that angle and used.

[0027] In this way, the chuck portion 108a is able to change the chucking angle by rotating the starter ST, while the starter ST is being chucked. Therefore, there is no need to re-chuck in order to change the chucking angle, which is advantageous for productivity of the casting. The chuck portion 108a is not limited to the hinge structure, as long as the structure enables the chucked starter ST to be rotated about an axis that is parallel to the molten metal surface MMS (i.e., the y-axis in the example in FIG. 1).

[0028] Here, a case in which the molten metal is drawn up diagonally will be described with reference to FIG 3. FIG. 3 is an enlarged sectional view showing a frame format of the molten metal being drawn up diagonally. The xyz coordinates in FIG. 3 also match those in FIG. 1.

[0029] As shown in FIG 3, the angle between the molten metal surface MMS and the up-drawing direction (i.e., the direction of the up-drawing speed V) is an up-drawing angle Θ (0° > Θ > 90°). Here, this up-drawing angle Θ is also an angle between an upper surface (the main surface on the upper side) of the shape determining member 102, and the up-drawing direction. The up-drawing speed V and the up-drawing angle Θ are determined from an up-drawing speed Vz in the vertical direction by the up-drawing machine 108, and a moving speed Vxy in the horizontal direction. In the example in FIG. 3, the up-drawing machine 108 moves only in the x-axis direction, and does not in the y-axis direction. Also, as shown in FIG 3, it is confirmed through testing that the solidification interface SIF is substantially perpendicular to the up-drawing direction.

[0030] As shown by the broken line in FIG 3, when the up-drawing angle Θ is reduced, the retained molten metal M2 that has passed through the shape determining member 102 ends up being offset with respect to the upper surface of the shape determining member 102, such that the sectional shape of the casting M3 is no longer able to be controlled. In the test, when the up-drawing angle Θ was 30° or less, an offset occurred between the retained molten metal M2 and the upper surface of the shape determining member 102. However, when the up-drawing angle Θ was 45° or greater, no offset occurred between the retained molten metal M2 and the upper surface of the shape determining member 102. Therefore, a casting in which the up-drawing angle Θ of the molten metal is 30° or less is unable to be formed. That is, with the free casting apparatus of the related art, there is a limit to the shape in which a casting can be formed.

[0031] In contrast, with the free casting apparatus according to the first example embodiment, the chucking angle of the starter ST is able to be changed by the chuck portion 108a of the up-drawing machine 108, just as described above. Therefore, with the free casting apparatus according to the first example embodiment, casting is temporarily stopped if the up-drawing angle Θ decreases to a predetermined reference angle (a first angle) at which no offset occurs. The reference angle is preferably greater than 30°. Also, when restarting casting, the chucking angle of the starter ST is changed so that the molten metal is initially drawn up in the vertical direction. Then, casting is restarted while maintaining this chucking angle. Moreover, if the up-drawing angle Θ decreases to the predetermined reference angle, the series of operations described above is repeated. Therefore, with the free casting apparatus according to the first example embodiment, it is possible to form a casting that was unable to be formed with the free casting apparatus of the related art.

[0032] Next, a free casting method according to the first example embodiment will be described with reference to FIGS. 4 to 9. FIGS. 4 to 9 are sectional views showing frame formats illustrating the free casting method according to the first example embodiment. Here, a case in which a casting with a longitudinal cross-section bent in a general L-shape (i.e., with a bending angle of approximately 90°) is cast will be described. This kind of casting is unable to be formed with the free casting apparatus of the related art.

[0033] First, the starter ST is lowered by the up-drawing machine 108 via the chuck portion 108a so that it passes through the molten metal passage portion 103 of the shape determining member 102, and the tip end portion of the starter ST is dipped into the molten metal Ml . As shown in FIG. 4, the chuck portion 108a that has the hinge structure is fixed open in a straight line to the starter ST, such that the longitudinal direction of the starter ST is the vertical direction.

[0034] Next, the starter ST starts to be drawn vertically upward at a predetermined speed, as shown in FIG. 4. Here, even if the starter ST separates from the molten metal surface MMS, the retained molten metal M2 that follows the starter ST and is drawn up from the molten metal surface MMS by the surface film and surface tension is formed. As shown in FIG. 4, the retained molten metal M2 is formed in the molten metal passage portion 103 of the shape determining member 102. That is, the shape detennining member 102 gives the retained molten metal M2 its shape. Here, the starter ST or the casting M3 is cooled by the cooling gas, so the retained molten metal M2 is indirectly cooled, and solidifies progressively from the upper side toward the lower side, thus forming the casting M3.

[0035] Next, casting is performed while drawing the molten metal up diagonally in order to form a bent portion. Here, the up-drawing angle Θ is gradually reduced as the bending angle of a bent portion increases.

[0036] Next, when the up-drawing angle Θ reaches a predetermined reference angle, a linear connecting portion M4 is cast while maintaining this up-drawing angle Θ, as shown in FIG 6. After casting the connecting portion M4, the connecting portion M4 is cut away from the retained molten metal M2 and casting temporarily stops. The connecting portion M4 is a portion that does not form the product, but instead will be dipped into the molten metal Ml and remelted when casting restarts. Here, the connecting portion M4 does not have to be cut away from the retained molten metal M2, but cutting it away makes it easy to change the chucking angle, and is therefore preferable.

[0037] Next, the starter ST is rotated around the y-axis so that the longitudinal direction of the connecting portion M4 is aligned with the vertical direction, by bending the chuck portion 108a that has the hinge structure, as shown in FIG. 7. The chuck portion 108a is fixed at that bending angle. Then the starter ST is once again lowered by the up-drawing machine 108 via the chuck portion 108a so that the starter ST passes through the molten metal passage portion 103 of the shape determining member 102, and the connecting portion M4 is dipped into the molten metal Ml. Aligning the longitudinal direction of the connecting portion M4 with the vertical direction (making the longitudinal direction of the connecting portion M4 perpendicular to the molten metal surface MMS) enables the connecting portion M4 to be easily dipped into the molten metal Ml .

[0038] Next, after the connecting portion M4 is melted as shown in FIG 8, the molten metal Ml is mixed by moving the molten metal mixing member 109 shown in FIGS. 1 and 2 back and forth in the y-axis direction. Accordingly, the oxide film formed on, and foreign matter adhered to, the surface of the connecting portion M4 that has been dipped into the molten metal Ml, are able to be inhibited from remaining on a joining surface BF (see FIG. 9) of the casting. As a result, a decrease in strength of the joint portion with respect to a non-joint portion is able to be inhibited. Then, the starter ST is drawn up in the vertical direction at a predetermined speed, and casting restarts. An up-drawing angle Θ (a second angle) when restarting casting does not have to be a right angle, and need only be greater than the reference angle.

[0039] Also, casting is performed while drawing up the molten metal diagonally in order to continuously form the bent portion, as shown in FIG 9. As a result, a casting with a generally L-shaped longitudinal cross-section that is made from the casting M3 and a casting M5 that are integrally connected together via the joining surface BF, is able to be obtained.

[0040] As described above, with the free casting method according to the first example embodiment, when casting restarts, the connecting portion M4 that has been dipped into the molten metal Ml is first melted, and the molten metal Ml near there is mixed. As a result, the oxide film formed on, and foreign matter adhered to, the surface of the connecting portion M4 are inhibited from remaining on the joining surface BF of the casting, so a decrease in the strength of the joint portion is able to be inhibited.

[0041] The free casting method of the first example embodiment of the invention may also be applied to a casting in which the starter ST is used as part of the product. That is, when casting starts, the molten metal Ml near the starter ST that has been dipped into the molten metal Ml may be mixed. As a result, the oxide film formed on, and foreign matter adhered to, the surface of the starter ST are removed, so a decrease in the strength of the joint portion between the starter ST and the casting M3 is able to be inhibited.

[0042] Here, FIG. 10 is a graph comparing the tensile strengths of a non-joint portion, a joint portion of a comparative example, and a joint portion of the example embodiment. In the comparative example, the molten metal Ml near the connecting portion M4 that was dipped into the molten metal Ml was not mixed. On contrast, with the example embodiment, the molten metal Ml near the connecting portion M4 that was dipped into the molten metal Ml was mixed. As shown in FIG 10, the tensile strength of the joint portion of the comparative example varies widely, with the average value being equal to or less than half the average value of the tensile strength of the non-joint portion. In contrast, the tensile strength of the joint portion of the example embodiment has approximately the same variability as the non-joint portion, with the average value being approximately 80 to 90 percent of the average value of the tensile strength of the non-joint portion. In this way, a decrease in the strength of the joint-portion is able to be effectively inhibited by mixing the molten metal Ml near the connecting portion M4 that has been dipped into the molten metal Ml .

[0043] FIG 11 is a view of the microstructure of the joint portion of the comparative example. An oxide was continuously confirmed on the joining surface between a casting A that was cast first (which corresponds to the casting M3) and a casting B that was cast later (which corresponds to the casting M5). In contrast, although not shown, with the microstructure of the joint portion of the example embodiment, only a slight amount of oxide was confirmed on the joining surface. From this, it can be inferred that the oxide film formed on, and foreign matter adhered to, the surface of the connecting portion M4 that has been dipped into the molten metal Ml are the cause of the decrease in the strength of the joint portion of the comparative example.

[0044] (Modified example of the first example embodiment)

Next, a free casting apparatus according to a modified example of the first example embodiment will be described with reference to FIG 12. FIG. 12 is a plan view of the shape determining member 102 according to the modified example of the first example embodiment. The shape determining member 102 of the first example embodiment shown in FIG. 2 is formed from one plate, so the thickness tl and width wl of the molten metal passage portion 103 are fixed. In contrast, the shape determining member 102 according to the modified example of the first example embodiment includes four rectangular shape determining plates 102a, 102b, 102c, and 102d, as shown in FIG 12. That is, the shape determining member 102 according to the modified example of the first example embodiment is divided into a plurality of sections. This kind of structure enables the thickness tl and width wl of the molten metal passage portion 103 to be changed. Also, the four rectangular shape determining plates 102a, 102b, 102c, and 102d are able to be synchronously moved in the z-axis direction.

[0045] As shown in FIG. 12, the shape determining plates 102a and 102b are arranged facing each other lined up in the x-axis direction. Also, the shape determining plates 102a and 102b are arranged at the same height in the z-axis direction. The distance between the shape determining plates 102a and 102b determines the width wl of the molten metal passage portion 103. The shape determining plates 102a and 102b are able to move independently in the x-axis direction, so they are able to change the width wl . A laser displacement gauge SI may be provided on the shape determining plate 102a, and a laser reflecting plate S2 may be provided on the shape determining plate 102b, as shown in FIG. 12, in order to measure the width wl of the molten metal passage portion 103.

[0046] Also, as shown in FIG 12, the shape determining plates 102c and 102d are arranged facing each other lined up in the y-axis direction. Also, the shape determining plates 102c and 102d are arranged at the same height in the z-axis direction. The distance between the shape determining plates 102c and 102d determines the thickness tl of the molten metal passage portion 103. Also, the shape determining plates 102c and 102d are able to move independently in the x-axis direction, so they are able to change the thickness tl. The shape determining plates 102a and 102b are arranged contacting upper surfaces of the shape determining plates 102c and 102d.

[0047] The invention is not limited to the example embodiment described above, and may be modified as appropriate without departing from the spirit of the invention. For example, the invention may also be applied to an up-drawing continuous casting method that does not use the shape determining member 102, as long as it is an up-drawing continuous casting method that draws up molten metal using the starter ST or the casting M3. However, an up-drawing continuous casting method that uses the shape determining member 102 is preferable because it is able to accurately form a casting.