JP2008254039A - Casting method and casting apparatus - Google Patents

Abstract

An object of the present invention is to unidirectionally solidify a molten metal containing a solute element, adjust the distribution of the concentration of the solute element in the solidification direction, and to obtain a portion with different performance such as mechanical strength in the solidification direction of the resulting ingot. A casting method and a casting apparatus that can be formed are provided.
In a casting method in which a molten metal containing a solute element is filled into a mold and the molten metal in the mold is solidified in one direction to obtain an ingot, the molten metal in the vicinity of a solid-liquid interface in the mold is obtained. By controlling the flow rate of the ingot, it is possible to obtain the ingot in which the concentration distribution of the solute element in the solidification direction is adjusted.
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Description

  The present invention relates to a casting method and a casting apparatus for obtaining an ingot by unidirectionally solidifying a molten metal containing a solute element.

Conventionally, as disclosed in Patent Document 1, for example, a casting method and a casting apparatus have been proposed in which cooling is performed from one side of a mold and the other side of the mold is heated to solidify the molten metal in the mold in one direction.
When casting is performed in this manner, solidification proceeds in one direction, and solidification shrinkage defects can be prevented from occurring in the resulting ingot. Thereby, it is possible to remarkably improve the creep rupture strength at a high temperature as compared with an ingot obtained by a general casting method.

  In addition, in an ingot obtained by unidirectional solidification, the crystal grains tend to be coarsened, so that improvement in tensile strength and fatigue strength at room temperature cannot be expected. Therefore, Patent Document 2 proposes a casting method and a casting apparatus in which a molten metal is solidified while stirring by applying vibration or swing to a mold in unidirectional solidification. Thereby, it becomes possible to refine the cast structure by dividing the dendrite growing at the solid-liquid interface and obtain an ingot having no solidification shrinkage defect.

By the way, when a metal containing a solute element solidifies, it is known that the solute element moves from the solid phase side to the liquid phase side due to the so-called insulator principle, and the concentration of the solute element in the liquid phase increases. ing. Here, when unidirectional solidification is performed as described above, since the solidification proceeds in one direction, for example, as shown in FIG. 5, the solute element concentration is made substantially constant from the solidification start portion. An ingot having a high solute element concentration in the solidified portion is obtained. In particular, when the molten metal is stirred as in Patent Document 2, the liquid phase trapped between the dendrite arms is discharged, and the solute element concentration in the final solidified portion is further increased.
Japanese Unexamined Patent Publication No. 57-1564 Japanese Patent No. 3194354

According to conventional unidirectional solidification, as described above, most of the ingot has a substantially constant solute element concentration, and a portion having a high solute element is formed at the end (final solidified portion) of the ingot. .
By the way, in a member such as a cylinder block, only a part in the longitudinal direction slides with another member, and it is possible to extend the life by improving the wear resistance of only this sliding part. It becomes. However, in the conventional casting method, it is not possible to obtain an ingot in which only a part of the longitudinal direction has different mechanical properties. Therefore, in the past, it was necessary to use a material that improved the mechanical properties of the entire member. For this reason, an ingot in which some properties in the longitudinal direction are changed is required.

  The present invention has been made in view of the above-mentioned circumstances, and solidifies a molten metal containing a solute element in one direction, adjusts the distribution of the concentration of the solute element in the solidification direction, and solidifies the obtained ingot. An object of the present invention is to provide a casting method and a casting apparatus capable of forming a part having different performance such as mechanical strength in part.

  In order to solve this problem, a casting method according to the present invention is a casting method in which a molten metal containing a solute element is filled in a mold, and the molten metal in the mold is unidirectionally solidified to obtain an ingot. The ingot in which the concentration distribution of the solute element in the solidification direction is adjusted is obtained by controlling the flow rate of the molten metal near the solid-liquid interface in the mold.

  The casting apparatus according to the present invention includes a mold filled with a molten metal containing a solute element, a cooling means for cooling the molten metal in the mold, and a heating means for heating the mold, The casting apparatus for unidirectionally solidifying the molten metal in the mold is characterized by comprising flow rate control means for controlling the flow rate of the molten metal near the solid-liquid interface in the mold.

In the casting method and casting apparatus having this configuration, the flow rate of the molten metal in the vicinity of the solid-liquid interface in the mold in which unidirectional solidification is progressing is adjusted, so the thickness of the diffusion layer of the solute element existing at the solid-liquid interface It is possible to change the height. More specifically, when the flow rate of the molten metal near the solid-liquid interface is decreased, the thickness of the diffusion layer is increased, and when the flow rate is increased, the thickness of the diffusion layer is decreased. Here, when the thickness of the diffusion layer is thick, the diffusion movement of the solute element from the solid phase to the liquid phase is hindered, and the difference in the solute element concentration between the solid phase and the liquid phase becomes small. On the other hand, when the thickness of the diffusion layer is small, the diffusion movement of the solute element from the solid phase to the liquid phase becomes easy, and the difference in the solute element concentration between the solid phase and the liquid phase becomes large.
Thus, by adjusting the flow rate of the molten metal near the solid-liquid interface in the mold, it becomes possible to change the concentration of the solute element near the solid-liquid interface, and change the distribution of the solute element concentration in the solidification direction. A cast ingot can be obtained.

Here, the flow rate control means is a mold rotation means capable of rotating the mold and adjusting the rotation speed thereof, and applying rotation to the mold and adjusting the rotation speed, thereby the solid-liquid interface in the mold. You may comprise so that the flow rate of the said molten metal of the vicinity may be adjusted.
In this case, by rotating the mold, it is possible to adjust the flow rate by applying a flow rate to the molten metal near the solid-liquid interface in the mold.

The flow rate control means is an electromagnetic stirring means for stirring the molten metal in the mold, and the molten metal in the mold is electromagnetically stirred to adjust the flow rate of the molten metal near the solid-liquid interface in the mold. It may be configured.
In this case, it is possible to adjust the flow rate of the molten metal near the solid-liquid interface in the mold by electromagnetically stirring the molten metal in the mold.

  According to the present invention, a molten metal containing a solute element is solidified in one direction, the distribution of the concentration of the solute element in the solidification direction is adjusted, and performance such as mechanical strength is partially present in the solidification direction of the ingot. It is possible to provide a casting method and a casting apparatus capable of forming different portions.

Hereinafter, a first embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a casting apparatus of the present invention.
The casting apparatus 10 according to the present embodiment heats the molten metal in the mold 11 by surrounding the mold 11 in which the molten metal is accommodated, the chill plate 12 on which the mold 11 is placed, and the mold 11. A heating furnace 13 and a cooling device 14 for cooling the molten metal in the mold 11 are provided.

In this embodiment, the casting_mold | template 11 has comprised the substantially cylindrical shape and obtains the column-shaped ingot. The material of the mold 11 is preferably selected as appropriate in consideration of casting conditions such as the metal to be cast and the molten metal temperature.
The chill plate 12 on which the mold 11 is placed is connected to a shaft 15 that can be moved back and forth in the vertical direction and can be rotated in FIG. 1. The mold 11 is configured to move up and down and rotate. The chill plate 12 is provided with a cooling pipe (not shown) through which cooling water flows.
The shaft 15 is provided with a rotation drive device 16 for rotating the connected mold 11 and chill plate 12 about the axis of the shaft 15 and a control unit 17 for controlling the rotation speed.

A heating furnace 13 and a cooling device 14 are connected in the vertical direction on the outer peripheral side of the moving space in which the chill plate 12 and the mold 11 move up and down. More specifically, a heating furnace 13 having a substantially cylindrical shape is disposed in an upper part of the moving space of the chill plate 12 and the mold 11, and a cooling device 14 is provided below the heating furnace 13.
The heating furnace 13 is provided with an induction coil (not shown) for heating the mold 11 disposed on the inner peripheral side thereof. A flange portion 18 is provided at the lower end portion of the heating furnace 13, and the upper surface of the gantry 19 of the heating furnace 13 and the lower surface of the flange portion 18 are brought into close contact with each other, so that the heat inside the heating furnace 13 is not transmitted downward. It is set as such.
The cooling device 14 is configured such that cooling pipes through which cooling water flows are arranged in a ring shape and can cool the mold 11 located on the inner peripheral side.

  In the casting apparatus 10 having such a configuration, the molten metal of the alloy containing the solute element is filled in the mold 11, and the molten metal temperature is adjusted to, for example, 720 ° C. by the heating furnace 13. With the cooling water flowing through the chill plate 12 and the cooling device 14, the shaft 15 is moved downward, and the chill plate 12 and the mold 11 are moved downward. Then, the chill plate 12 and the mold 11 exit from the heating furnace 13 and move to the cooling device 14 side, and the molten metal in the mold 11 is cooled from the contact surface between the chill plate 12 and the mold 11 to start solidification. . In this state, the portion of the mold 11 disposed inside the heating furnace 13 is set to, for example, 700 ° C., and the alloy in the mold 11 is kept in the liquid phase L state completely. In this way, as shown in FIG. 2, the solid phase S, the liquid phase L, and the diffusion layer D located at the interface between them exist in the mold 11.

  In this way, when the chill plate 12 and the mold 11 are moved downward to perform unidirectional solidification, the chill plate 12 and the mold 11 are rotated by the rotation driving device 16. The rotation speed is adjusted by the control unit 17. Thereby, the flow velocity of the molten metal near the solid-liquid interface in the mold 11 is adjusted.

Here, when the rotational speed of the mold 11, that is, the flow velocity of the molten metal near the solid-liquid interface is the angular velocity ω, the diffusion coefficient is D, and the kinematic viscosity coefficient is ν, the thickness of the diffusion layer D of the solute element existing at the solid-liquid interface. It is known that δ is expressed by the following equation (1).
δ = 2 ^2/3 × D ^1/3 × ν ^1/6 × ω ^−1/2 (1)
According to the equation (1), when the angular velocity ω (the flow velocity of the molten metal near the solid-liquid interface) is large, the thickness δ of the diffusion layer D decreases, and when the angular velocity ω (the flow velocity of the molten metal near the solid-liquid interface) is small, diffusion occurs. It can be seen that the thickness δ of the layer D increases.

When the thickness δ of the diffusion layer D is thick, the diffusion movement of the solute element from the solid phase S to the liquid phase L is hindered, and the difference in the solute element concentration between the solid phase S and the liquid phase L becomes small. When the thickness δ is small, diffusion movement of the solute element from the solid phase S to the liquid phase L becomes easy, and the difference in the solute element concentration between the solid phase S and the liquid phase L increases.
Therefore, by adjusting the rotational speed of the mold 11 during unidirectional solidification, it is possible to intentionally generate a portion having a high solute element concentration in a part of the solidification direction.

  Specifically, from the start of solidification, the rotation speed of the mold 11 is set to about 20 rpm, for example, the thickness δ of the diffusion layer D is reduced, the solute element is discharged to the liquid phase L side, and the solid phase S having a low solute element concentration is obtained. I will grow. When the mold 11 is moved downward by a predetermined length, the rotational speed of the mold 11 is reduced to, for example, 0.2 rpm or less, the thickness δ of the diffusion layer D is increased, and the liquid phase L to the liquid phase L are increased. Suppresses the discharge of solute element concentrations into Thereafter, the rotational speed of the mold 11 is returned to, for example, about 20 rpm, and the mold 11 is lowered. By doing so, as shown in FIG. 3, an ingot having a portion where the solute element concentration is increased in a part of the solidification direction can be obtained.

  As described above, according to the casting method using the casting apparatus 10 according to the present embodiment, the solid-liquid interface is adjusted by adjusting the flow rate of the molten metal in the vicinity of the solid-liquid interface in the mold 11 where the unidirectional solidification is progressing. It is possible to adjust the solute element concentration in the solid phase S portion by changing the thickness δ of the diffusion layer D of the solute element existing in the solid state, and to obtain an ingot in which the distribution of the solute element concentration in the solidification direction is adjusted. it can.

In the present embodiment, since the rotation driving device 16 for rotating the mold 11 is provided, the thickness δ of the diffusion layer D of the solute element existing at the solid-liquid interface is controlled by controlling the rotation speed of the mold 11. An ingot can be obtained in which the distribution of the solute element concentration in the solidification direction is adjusted.
Furthermore, in this embodiment, since the rotary drive device 16 is provided on the shaft 15 that moves up and down, the amount of lowering of the shaft 15 (the mold 11 and the chill plate 12), that is, the amount of growth of the solid phase S in the mold 11 is achieved. Accordingly, the rotational speed can be controlled in accordance with the above, and the solute element concentration can be adjusted with higher accuracy.

Next, a second embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 4 shows a casting apparatus according to the second embodiment of the present invention.
In this casting apparatus 20, an electromagnetic stirring device 26 is provided at the lower portion of the heating furnace 23, and the molten metal inside the mold 21 can be stirred at an arbitrary speed.

  In the casting apparatus 20 having this configuration, a molten alloy containing a solute element is filled in the mold 21, the molten metal temperature is maintained at, for example, 720 ° C. by the heating furnace 23, and cooling water is supplied to the chill plate 22 and the cooling device 24. The chill plate 22 and the mold 21 are moved downward in a distributed state. As a result, the chill plate 22 and the mold 21 exit from the heating furnace 23 and move to the cooling device 24 side, and the molten metal in the mold 21 is cooled from the contact surface between the chill plate 22 and the mold 21 to start solidification. Thus, the solid phase S, the liquid phase L, and the diffusion layer D located at the interface between these exist in the mold 21. In the present embodiment, the lowering speed and the cooling conditions are adjusted so that the solidification interface between the solid phase S and the liquid phase L is located in the vicinity of the electromagnetic stirring device 26.

When the chill plate 22 and the mold 21 are moved downward and unidirectional solidification proceeds, the molten metal in the mold 21 is stirred by the electromagnetic stirrer 26, and the speed of the molten metal near the solid-liquid interface is adjusted.
According to the casting method using the casting apparatus 20 according to the present embodiment, the solute existing at the solid-liquid interface is adjusted by adjusting the flow rate of the molten metal near the solid-liquid interface in the mold 21 in which the unidirectional solidification is proceeding. By changing the thickness δ of the element diffusion layer D, the solute element concentration in the solid phase S portion can be adjusted, and an ingot in which the distribution of the solute element concentration in the solidification direction is adjusted can be obtained.

  In the present embodiment, since the electromagnetic stirring device 26 for stirring the molten metal in the mold 21 is provided, the thickness of the diffusion layer D of the solute element existing at the solid-liquid interface is controlled by controlling the output of the electromagnetic stirring. δ can be adjusted, and an ingot in which the distribution of the solute element concentration in the solidification direction is adjusted can be obtained.

As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.
For example, the heating furnace is fixed and the chill plate and the mold are moved downward. However, the present invention is not limited to this. The chill plate and the mold are fixed and the heating furnace is moved upward. May be. That is, it is sufficient that the heating furnace and the mold are configured to be relatively separated from each other so that the unidirectional solidification can be performed.

Further, although the mold has been described as having a substantially cylindrical shape, the present invention is not limited to this, and the shape of the mold can be arbitrarily designed.
Further, the metal to be emphasized in the casting mold of the casting apparatus is not particularly limited as long as it contains a solute element. When the solute element is a heavy element, it is particularly effective because the solute element concentration is likely to change depending on the flow rate of the molten metal at the solid-liquid interface.
Moreover, although demonstrated as what provided the induction coil as a heating furnace, it is not limited to this, A resistance heating furnace etc. may be sufficient.

Below, the casting result by the casting apparatus which is 1st Embodiment is demonstrated as a specific Example.
An Al-10% Si alloy was used as an alloy containing a solute element. The mold was an alumina crucible having an inner diameter of 100 m, an outer diameter of 120 mm, and a height of 300 mm. This mold was placed on a chill plate and placed in a heating furnace. The mold was heated to 720 ° C. or higher by a heating furnace, and a molten Al-10% Si alloy was poured into the heated mold, and the chill plate and the mold were gradually lowered to perform unidirectional solidification.

At this time, the mold was lowered while rotating at a rotational speed of 20 rpm from the start of solidification, and when the mold was lowered by about 150 mm, the mold was lowered by 20 mm while stopping the rotation of the mold. Thereafter, the mold was lowered again while rotating at a rotational speed of 20 rpm.
As a result of analyzing the ingot thus obtained, a portion having a high Si concentration is formed only in the portion where the rotation of the mold is stopped, and an ingot having a portion having a different Si concentration in a part of the solidification direction is formed. It turns out that it is possible to obtain. In this way, it was confirmed that an ingot having a part with different mechanical properties (tensile strength, hardness, etc.) can be obtained.

It is a schematic explanatory drawing of the casting apparatus which is the 1st Embodiment of this invention. FIG. 2 is an enlarged explanatory view in the vicinity of an interface between a solid phase and a liquid phase in a mold in the casting apparatus shown in FIG. 1. It is a solute element concentration distribution map of the ingot obtained by the casting method which is an Example of the present invention. It is a schematic explanatory drawing of the casting apparatus which is the 2nd Embodiment of this invention. It is a solute element density | concentration distribution map of the ingot obtained by the conventional unidirectional solidification.

Explanation of symbols

10, 20 Casting device 11, 21 Mold 12, 22 Chill plate (cooling means)
13, 23 Heating furnace (heating means)
14, 24 Cooling device (cooling means)
16 Rotation drive device (mold rotation means)
26 Electromagnetic stirring device (electromagnetic stirring means)

Claims (6)

In a casting method in which a molten metal containing a solute element is filled in a mold and the molten metal in the mold is solidified in one direction to obtain an ingot.
A casting method characterized by obtaining the ingot in which the concentration distribution of the solute element in the solidification direction is adjusted by controlling the flow rate of the molten metal in the vicinity of the solid-liquid interface in the mold.   The casting method according to claim 1, wherein the flow rate of the molten metal near the solid-liquid interface in the mold is controlled by applying rotation to the mold and controlling the rotation speed.   The casting method according to claim 1, wherein the flow rate of the molten metal in the vicinity of the solid-liquid interface in the mold is controlled by electromagnetically stirring the molten metal in the mold. A casting that includes a mold filled with a molten metal containing a solute element, a cooling means for cooling the molten metal in the mold, and a heating means for heating the mold, and solidifies the molten metal in the mold in one direction. In the device
A casting apparatus comprising flow rate control means for controlling the flow rate of the molten metal near the solid-liquid interface in the mold.   5. The casting apparatus according to claim 4, wherein the flow rate control means is a mold rotating means capable of rotating the mold and adjusting a rotation speed thereof.   The casting apparatus according to claim 4, wherein the flow rate control means is an electromagnetic stirring means for stirring the molten metal in the mold.

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