JP5307640B2 - Casting core - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve mold releasing property of a molding by a simple device configuration without reducing production efficiency in a core for casting. <P>SOLUTION: The core 4 of a casting mold 10 includes: an outer core member 1 protruded from a cavity bottom face 5a toward an inner side of a cavity 6 along the drawing direction of the molding and having at an outer face a core mold face contacting with a melt introduced into the cavity 6; and an inner core member 3 extended along the drawing direction at the inner side of the outer core member 1 and fixed at the inner circumferential face 1c of the outer core member 1 is a state of interposing a heat insulating film 2 for suppressing heat transfer from the outer core member 1. The inner circumferential face 1c is arranged to restrain the deformation of the inner core member 3 to a taper part 3a. An interval between a side face 1a and the inner circumferential face 1c in a direction orthogonal to the extracting direction is arranged to be larger at a tip side than at a base end side on the inner circumferential face 1c. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a casting core.

Conventionally, when casting a member having a hollow shape such as a hole, a core (core for casting) is used in the cavity of the casting mold. For example, a cast product such as a long hole is used. Depending on the hollow shape required for the (molded product), the draft taper may not be sufficiently large. In this case, when the cast product contracts after casting, it is hugged by the core, and it becomes difficult to remove the core. It is also known to apply a mold release agent or to allow the core to be decomposed and removed, both of which cause the production efficiency of the molded product to deteriorate.
As a proposal for improving the releasability of such a core, for example, a technique described in Patent Document 1 is known.
In Patent Document 1, the outside is formed of a metal material having a large (small) linear expansion coefficient, and the inside is formed of a (large) metal material having a small linear expansion coefficient, and the direction in the direction perpendicular to the drawing direction of the molded product is described above. A casting mold core is described in which the proportion of a metal material having a small (large) linear expansion coefficient is made small (large) along the drawing direction.
According to the cores of these casting molds, the degree of thermal deformation of the cross section orthogonal to the drawing direction of the molded product is greater on the distal end side than on the base end fixed to the casting mold. Therefore, for example, a core that receives heat from the molten metal and has a straight shape at the time of molding is expected to be easy to release because the tip portion is further reduced in diameter and deformed into a tapered shape at the time of cooling. .

JP-A-5-104201

However, the conventional casting core as described above has the following problems.
In the technique described in Patent Document 1, a core having a double structure in which metal materials having different linear expansion coefficients are combined is used, and the outer shape of the core is formed at the time of filling the molten metal due to the difference in linear expansion coefficient of each metal material. The shape matches the hollow shape of the product, and the outer dimensions of the tip are reduced during cooling to improve the releasability. For this reason, since the heat from the molten metal is transferred to the entire core, the metal material having a small linear expansion coefficient is also heated and contributes to the thermal expansion.
In order to improve releasability, it is necessary to cause a large shape change in the core. However, depending on the hollow shape to be formed, the heat capacity of the entire core becomes too large and thermal deformation of the core during molding is small. As a result, there is a problem in that the taper size at the time of cooling becomes small and sufficient releasability may not be obtained.
In order to increase the thermal deformation of the core, it is conceivable to raise the temperature of the molten metal, but there are problems such as an increase in cooling time and a decrease in production efficiency and a decrease in the life of the molding equipment.
Similarly, it may be possible to cause a large shape change in the core by providing a cooling device for the casting mold or core. However, the structure of the casting mold and the casting apparatus are complicated, and the manufacturing cost increases. There is a problem that it ends up.

  The present invention has been made in view of the above problems, and provides a casting core that can improve the releasability of a molded product without reducing the production efficiency and with a simple apparatus configuration. The purpose is to provide.

  In order to solve the above-mentioned problem, in the invention according to claim 1, a casting core provided in a cavity of a casting mold for casting a molded product from a molten metal, the inner surface of the cavity from the inner surface of the cavity. An outer core member projecting along the drawing direction of the molded product toward the inner side and having a core mold surface formed on the outer surface contacting the molten metal introduced into the cavity; Inner core that is extended along the drawing direction inside the core member and fixed by a fixing portion inside the outer core member with a heat insulating layer portion that suppresses heat transfer from the outer core member interposed therebetween A fixing member on the inner side of the outer core member, and at least a base end fixing portion in the vicinity of the inner surface of the cavity and a tip fixing portion at a tip portion on the inner side of the cavity, respectively. The outer core with respect to the outer peripheral surface of the core member An outer peripheral surface of the outer core member on the side surface side with respect to the pulling direction and the fixing in each of the fixing portions from the base end fixing portion to the tip fixing portion. It is configured that each interval in a direction perpendicular to the drawing direction with respect to the portion is provided such that the distal end fixing portion side is larger than the proximal end fixing portion side.

  According to a second aspect of the present invention, in the casting core according to the first aspect, the inner core member has a convex portion whose outer dimension decreases from the inner surface of the cavity toward the inner side of the cavity. The outer core member has a concave portion along the convex portion of the inner core member, and has a cross section orthogonal to the extraction direction from the inner peripheral surface of the concave portion to the core mold surface. The thickness is provided in a shape that increases from the inner surface of the cavity toward the inner side of the cavity, and the heat insulating layer portion includes an outer peripheral surface of the convex portion of the inner core member and the outer core member. It is set as the structure pinched | interposed between the internal peripheral surfaces of a recessed part.

  According to a third aspect of the present invention, in the casting core according to the first aspect, the outer core member includes a cylindrical wall body portion having an opening on the inner surface side of the cavity, and the cylindrical wall. A distal end side wall body portion provided so as to cover the body portion on the inner side of the cavity, the proximal end fixing portion at the opening of the cylindrical wall body portion, and the distal end fixing portion at the distal end side wall body. An outer peripheral surface of the inner core member, and an inner peripheral surface of the cylindrical wall body portion and the distal side wall body portion between the proximal end fixing portion and the distal end fixing portion. It is set as the structure by which the space | interval was spaced apart and the hollow part was formed.

  According to a fourth aspect of the present invention, in the casting core according to the third aspect, the hollow portion is provided in a vacuum state.

  According to a fifth aspect of the present invention, in the casting core according to any one of the first to fourth aspects, the outer core member includes a heat radiating portion that radiates heat received from the molten metal to the outside of the cavity. It is set as the structure provided.

  In invention of Claim 6, in the core for casting in any one of Claims 1-5, the said heat insulation layer part is set as the structure which has a space | gap part.

  According to a seventh aspect of the present invention, in the casting core according to the sixth aspect, the gap is provided in a vacuum state.

  According to an eighth aspect of the present invention, in the casting core according to any one of the first to seventh aspects, a linear expansion coefficient of a material constituting the outer core member is a material constituting the inner core member. It is set as a structure larger than the linear expansion coefficient.

  According to the casting core of the present invention, the thermal expansion of the inner core member can be suppressed by the heat-insulating layer portion, and the outer core member mainly expands according to the temperature change by receiving heat from the molten metal. By shrinking, it is possible to form a shape in which the tip side is narrowed at the time of cooling, so that it is possible to improve the releasability of the molded product without reducing the manufacturing efficiency and with a simple device configuration. Play.

It is typical sectional drawing which shows schematic structure of the core for casting which concerns on the 1st Embodiment of this invention, the side view of the A view, and BB sectional drawing. It is a typical perspective view which shows an example of the molded product shape | molded with the casting die using the core for casting which concerns on the 1st Embodiment of this invention. It is process explanatory drawing explaining the shaping | molding process using the core for casting which concerns on the 1st Embodiment of this invention. It is typical sectional drawing which shows schematic structure of the core for casting which concerns on the modification of the 1st Embodiment of this invention, the side view of the C view, DD sectional drawing, and EE sectional drawing. It is typical sectional drawing which shows schematic structure of the core for casting which concerns on the 2nd Embodiment of this invention, the side view of the F view, and GG sectional drawing. It is process explanatory drawing explaining the shaping | molding process using the core for casting which concerns on the 2nd Embodiment of this invention. It is a typical partial expanded sectional view which shows the other example of the heat insulation layer part which can be used suitably for the core for casting which concerns on the 1st and 2nd embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In all the drawings, even if the embodiments are different, the same or corresponding members are denoted by the same reference numerals, and common description is omitted.

[First Embodiment]
The casting core according to the first embodiment of the present invention will be described.
Fig.1 (a) is typical sectional drawing which shows schematic structure of the core for casting which concerns on the 1st Embodiment of this invention. FIGS. 1B and 1C are a side view and a cross-sectional view taken along line BB in FIG. 1A, respectively. FIG. 2 is a schematic perspective view showing an example of a molded product molded with a casting mold using the casting core according to the first embodiment of the present invention.

The core 4 of this embodiment is a core for casting provided in a cavity 6 of a casting mold 10 for casting a molded product from a molten metal, as shown in FIG.
Hereinafter, an example in which the molded product to be cast is a molded product 8B as shown in FIG. 2 will be described.
Moldings 8B is a cylindrical surface shape of the side surface 8c of the diameter D ₀ is extended by a length L ₀ in one direction, one end face 8b is opened, a bottomed cylindrical member the other end face 8d is formed a bottom surface is there.
The molded product 8B has a diameter D (provided that D <D ₀ ) and a depth L (provided that L <L ₀ ) from the center of one end surface 8b in the longitudinal direction toward the inside, and a side surface 8c. A hole inner peripheral surface 8a constituting a coaxial cylindrical hole is provided. Here, the diameter D ₀ and the length L ₀ , and the diameter D and the length L are in a relationship of D ₀ <L ₀ and D <L, respectively.
The extraction direction of the molded product 8B (hereinafter simply referred to as the extraction direction) is a direction along the central axis of the cylindrical portion of the side surface 8c and the hole inner peripheral surface 8a.

In addition, the dimensional relationship in the temperature at the time of extracting the molded product 8B from the casting mold 10 and taking it out is important for the dimensional relationship of the present embodiment.
Therefore, in the following, the diameters D ₀ and D and the lengths L ₀ and L are the temperatures of the molded product 8B when the molded product 8B is taken out from the casting mold 10 after the molding of the molded product 8B is completed and cooled (hereinafter referred to as the temperature of the molded product 8B). , Referred to as take-out temperature _Tt ). However, regarding the diameter D and the length L, the take-out temperature T _t is strictly the temperature when the core 4 is removed from the molded product 8B, but the molded product 8B can be quickly extracted. For simplicity, it is assumed that the temperature change of the molded product 8B during the take-out operation can be ignored.
The take-out temperature T _t is equal to or lower than the solidification temperature T _k at which solidification of the entire molten metal ends, and an appropriate temperature at which the take-out operation can be performed smoothly can be employed. For this reason, the temperature may be higher than room temperature, for example, about 323K to 523K.
On the other hand, at the take-out temperature T _t , in order to form the dimension of the hole inner peripheral surface 8a to diameter D × length L, the diameter and length of the hole inner peripheral surface 8a at the solidification temperature T _k of the melt are respectively D _The dimensions need to be slightly larger than D and L, such as _k = D + ΔD and L _k = L + ΔL (ΔD> 0, ΔL> 0).
The values of ΔD and ΔL can be calculated in advance with dimensions obtained by combining the shape change due to molding shrinkage of the molten metal and the shape change due to heat shrinkage between the solidification temperature T _k and the take-off temperature T _t. .

As the material of the molded product 8B, an appropriate metal material that can be cast can be adopted by appropriately selecting the material of the casting mold 10 and the core 4.
For example, ADC12 is an example of an aluminum alloy, and MDC1D is an example of a magnesium alloy. In this case, the solidification temperature T _k may be a solidification temperature.
For example, an amorphous alloy having a glass transition region having a temperature width of 20 K or more is also suitable. In this specification, among amorphous alloys, an alloy having a glass transition region having a temperature range of 20 K or more is referred to as metallic glass. In this case, the glass transition temperature can be adopted as the solidification temperature T _k .

  The metallic glass is formed by rapidly cooling a molten metal raw material composed of a plurality of metallic elements until it reaches the glass transition temperature above the critical cooling rate. Amorphous alloys do not have the grain boundaries found in ordinary crystalline metals, and do not cause grain boundary corrosion (a phenomenon in which corrosion progresses along the grain boundaries) due to grain boundaries. Therefore, it has excellent corrosion resistance. Furthermore, since there is little occurrence of solidification shrinkage like crystalline metal, it has high-accuracy transferability to the molding die and low expansion against heat. Further, it is known that the physical properties are low Young's modulus, high strength, and high elasticity.

Further, the metallic glass is easily obtained when the metallic material satisfies the following three conditions (I) to (III), and is not determined only by the characteristics of the amorphous alloy.
(I) It contains three or more kinds of metal elements.
(II) The three or more metal elements have atomic diameters different by 12% or more. For example, large, medium, and small metal elements have atomic diameters different from each other by 12% or more.
(III) Each metal element is easily compounded. That is, each metal element has a property of attracting each other.
Examples of the metallic glass include a zirconium (Zr) based alloy, an iron (Fe) based alloy, a titanium (Ti) based alloy, and a magnesium (Mg) based alloy.
As a specific example, for _example, a composition, such as _{Zr 55 Cu 30 Ni 5 Al 10} , Fe 75 Ga 5 P 12 C 4 B 4, Ni 53 Nb 20 Ti 10 Zr 8 Co 6 Cu 3.

  In addition to the characteristics of the amorphous alloy described above, the metal glass has a characteristic that the glass transition region is larger and the critical cooling rate is slower than that of a normal amorphous alloy.

In order to cast such a molded product 8B, the casting mold 10 of this embodiment includes outer molds 5 and 7 and a core 4 as shown in FIGS. 1 (a), (b) and (c). .
The outer mold 5 constitutes a cavity 6 which is a cylindrical space composed of a cavity bottom surface 5a and a cavity side surface 5b corresponding to each of the end surface 8b and the side surface 8c of the molded product 8B. The size of the cavity 6 is set to a value slightly larger than the diameter D ₀ × length L ₀ in consideration of the molding shrinkage rate and linear expansion coefficient of the molten material.
In the center of the cavity bottom surface 5a, for attaching the core 4, which will be described later outer core member 1 of circular hole-shaped core mounting portion 5c of the diameter d ₂ which is matched to the outer diameter of the proximal end portion in the present embodiment Are provided penetrating in the thickness direction.

  The outer mold 7 forms the shape of the end face 8d by covering the cavity 6 with the side facing the cavity bottom surface 5a of the outer mold 5. In this embodiment, a disk member larger than the inner diameter of the cavity side surface 5b is employed. In the thickness direction of the outer mold 7, a runner portion 7 a for introducing molten metal into the cavity 6 is provided.

As the material of the outer molds 5 and 7, an appropriate metal material can be adopted according to the metal material of the molten metal as in the conventional casting mold. For example, SKD11 (k = 29 (W / mK), α = 12.1 × 10 ⁻⁶ (1 / K)) or cemented carbide (WC) (k = 85 ( W / mK), α = 5.5 × 10 ⁻⁶ (1 / K)) or the like can be employed.
Here, k represents thermal conductivity, and α represents a linear expansion coefficient (the same applies hereinafter).
The outer dies 5, 7 have a larger heat capacity than the core 4 so that the heat of the molten metal filled in the cavities 6 can be dissipated to the outer periphery of the casting mold 10 and cooled quickly.

  The core 4 is a round bar-shaped member that forms a cylindrical hole-shaped inner peripheral surface 8a that is a hollow shape of the molded product 8B. The outer core member 1, the inner core member 3, and the heat insulating film 2 (heat insulating layer) Part).

The outer core member 1 protrudes from the cavity bottom surface 5 a that is the inner surface of the cavity 6 toward the inside of the cavity 6 along the drawing direction of the molded product 8 </ b> B, and is in contact with the molten metal introduced into the cavity 6. A child mold surface is a member formed on the outer surface. In the following, particularly if no dimensional otherwise denote the value of the solidification temperature T _k.
The outer shape of the outer core member 1, in the projecting direction of the distal end portion, side view and circular distal end surface 1b of the diameter d ₁ at (A view of the FIG. 1 (a)), the outer peripheral edge portion of the front end surface 1b To the cavity bottom surface 5a of the outer mold 5, which is the base end portion in the projecting direction, and the side surface 1a.
The tip surface 1b and the side surface 1a constitute a core surface of the outer core member 1.
In the side surface 1a, the outer diameter of the base end portion is the diameter d ₂ and the outer diameter of the tip end portion is the diameter d ₁ (where d ₁ <d ₂ ), and the outer diameter of the intermediate portion between the base end portion and the tip end portion is the base. A frustoconical shape gradually decreasing from the diameter d ₂ to the diameter d ₁ from the end to the tip is provided.
The axial direction of the central axis of the side surface 1a is provided along the drawing direction.
In addition, an inner peripheral surface 1c constituting an axial through hole is formed inside the outer core member 1. The shape of the inner peripheral surface 1c has an inner diameter of the proximal end portion is the diameter d _2, and the inner diameter toward the distal side from the proximal end side is gradually reduced in diameter, the distal end surface 1b (see FIG. 1 (b)) A truncated cone-shaped concave portion having a diameter reduced toward the tip side so as to have a diameter d ₀ smaller than the diameter d ₁ is formed.
The central axis of the inner peripheral surface 1c is coaxial with the central axis of the side surface 1a.

Therefore, a cross section perpendicular to the opening direction of the outer core member 1, as shown in FIG. 1 (c), the outer diameter _{d 3 (however, d 2 ≧ d 3> 0} ) and the side surface 1a, an outer diameter _{d 3} Further, it is an annular shape surrounded by an inner peripheral surface 1c having a smaller diameter.
With such a shape, the radial thickness of the ring in the cross section perpendicular to the drawing direction of the outer core member 1 is from 0 to (d ₁ -d) from the cavity bottom surface 5 a toward the inside of the cavity 6. ₀ ) / 2 gradually increasing.

As the material of the outer core member 1, an appropriate metal material can be adopted, but it is preferable that the coefficient of thermal expansion is large. Moreover, it is more preferable that thermal conductivity is also large. For example, the magnitude of the linear expansion coefficient is preferably α ≧ 10 × 10 ⁻⁶ (1 / K), and the magnitude of the thermal conductivity is preferably k ≧ 10 (W / mK).
For example, SKD11 and SUS303 (k = 16.3 (W / mK), α = 17.2 × 10 ⁻⁶ (1 / K)) are used as iron-based alloys, and copper (Cu ) (K = 400 (W / mK), α = 16.8 × 10 ⁻⁶ (1 / K)) or the like can be employed.

The inner core member 3 includes a conical or frustoconical taper portion 3a that can be fixed to the inner peripheral surface 1c of the outer core member 1 via the heat insulating film 2, and the taper portion 3a. It is a rod-shaped member comprising a base end portion 3b fitted and attached to the attachment portion 5c. For this reason, the inner core member 3 is extended along the drawing direction of the molded product inside the outer core member 1. Further, the tapered portion 3 a constitutes a convex portion whose outer dimension decreases from the cavity bottom surface 5 a toward the inside of the cavity 6.
As the material of the inner core member 3, in this embodiment, an appropriate metal material, a cemented carbide, or a non-metallic material such as a ceramic having a smaller linear expansion coefficient than that of the outer core member 1 can be adopted. .
For example, SKD11 and SU303 are used as iron-based alloys, and tungsten carbide (WC) (k = 85 (W / mK), α = 5.5 × 10 ⁻⁶ (1 / K) as cemented carbide. )), Alumina (k = 32 (W / mK), α = 7.1 × 10 ⁻⁶ (1 / K)) or the like can be used as the nonmetallic material.

The heat insulating film 2 suppresses heat transfer between the outer core member 1 and the inner core member 3.
In the present embodiment, a thin film layer having a substantially constant film thickness is provided between the inner peripheral surface 1 c of the outer core member 1 and the tapered portion 3 a of the inner core member 3.
Although it is desirable that the amount of heat transfer through the heat insulating film 2 is smaller, it is difficult to reduce the heat conduction of the thin film layer to zero. Therefore, the material of the heat insulating film 2 is a material having a thermal conductivity lower than that of the material of the outer core member 1 and the inner core member 3, and the outer core member 1 and the inner core member 3 are used. Heat transfer is suppressed by reducing the heat conduction per unit time. The larger the difference between the thermal conductivity of the material of the outer core member 1 and the inner core member 3 and the thermal conductivity of the material of the heat insulating film 2, the better.

As a material of the heat insulating film 2, an appropriate material having a low thermal conductivity can be adopted. For example, ceramics can be preferably used.
Examples of the material of the heat insulating film 2 include silicon nitride (SiN) (k = 20 (W / mK), α = 2.6 × 10 ⁻⁶ (1 / K)), zirconia (ZrO ₂ ) (k = 3 (W / mK), α = 7.9 × 10 ⁻⁶ (1 / K)), sialon (Si _2-6 Al ₂ O ₃ N _2-8 ), for example, Si ₃ Al ₂ O ₃ N ₄ ( k = 21 (W / mK), α = 2.6 × 10 ⁻⁶ (1 / K)), Photovale (registered trademark) (manufactured by Sumikin Ceramics Co., Ltd., k = 1.67 (W / mK), α = 8.5 × 10 ⁻⁶ (1 / K)) or the like can be employed.
Although the heat insulating film 2 depends on the material, for example, a method of directly forming the taper portion 3a which is the surface of the inner core member 3 by a method such as vapor deposition or sintering, or a thin layer structure or a thin film shape. For example, a method of attaching and joining the inner core member 3 can be employed.

Further, when the inner core member 3 or the outer core member 1 can form an oxide film having high heat insulation properties, such as an iron alloy, for example, the tapered portion 3c of the inner core member 3 or the outer core member 3 is formed. The inner peripheral surface 1 c of the core member 1 may be oxidized and an oxide film formed on the surface may be used as the heat insulating film 2.
In this case, since a thicker heat insulating film can be formed as compared with the case where other materials are coated, it is easy to improve the heat insulating property.

The core 4 having such a configuration is formed by, for example, forming a heat insulating film (for example, ZrO ₂ ) by vapor deposition, sputtering, or the like on a tapered surface of an inner core formed by mechanical processing and mechanically processing the core 4. It can be manufactured by brazing with the outer core.
In addition, when using a material with a large linear expansion coefficient for the outer core, the outer core is heated and expanded, and then cooled by covering the inner core so that it is fixed as a tight fit. It is also possible to obtain a child 4.

With such a configuration, the inner peripheral surface 1c of the outer core member 1 constitutes a fixed portion inside the outer core member 1 that continues from the vicinity of the cavity bottom surface 5a to the inner tip of the cavity 6, It also serves as a base end fixing part and a tip fixing part. And the inner peripheral surface 1c is being fixed via the heat insulation film | membrane 2 so that the deformation | transformation with respect to the taper part 3a which is an outer peripheral surface of the inner core member 3 may be restrained, respectively. The distance (the thickness of the outer core member 1) in the direction perpendicular to the drawing direction between the side surface 1a that is the outer circumferential surface of the outer core member 1 on the side surface side and the inner circumferential surface 1c that is the fixed portion with respect to the drawing direction is At any position, the distal end fixing portion side is provided with a larger interval (thickness) than the proximal end fixing portion side.
Further, the thickness in the cross section perpendicular to the drawing direction from the inner peripheral surface of the recess of the outer core member 1 to the core mold surface is provided in a shape that increases from the cavity bottom surface 5 a toward the inside of the cavity 6. The heat insulating film 2 is sandwiched between the tapered portion 3 a that is the outer peripheral surface of the convex portion of the inner core member 3 and the inner peripheral surface 1 c that is the inner peripheral surface of the concave portion of the outer core member 1.

Next, the operation of the core 4 of the present embodiment will be described together with a method for forming the molded product 8B using the casting mold 10.
FIGS. 3A and 3B are process explanatory views illustrating a molding process using the casting core according to the first embodiment of the present invention.

First, as shown in FIG. 1A, a casting mold 10 is assembled.
Then, a molten metal 8A obtained by heating and melting a metal material for casting the molded product 8B is introduced from the runner portion 7a of the outer mold 7 into the cavity 6, and the molten metal 8A is filled into the cavity 6. Fig.3 (a) shows the part except the outer mold | type 7 after filling with this molten metal 8A.
The molten metal 8A comes into contact with the cavity bottom surface 5a and the cavity side surface 5b of the outer mold 5, the side surface 1a and the tip surface 1b of the outer core member 1, and the heat insulating film 2 exposed on the tip surface 1b.
Since the outer mold 5, the outer core member 1, and the heat insulating film 2 are lower in temperature than the molten metal 8A, the heat of the molten metal 8A is thermally conducted to the outer mold 5, the outer core member 1, and the heat insulating film 2, While the temperature of the molten metal 8A is lowered, the outer mold 5, the outer core member 1, and the heat insulating film 2 are heated. Thereby, each temperature distribution changes.
The outer mold 5, the outer core member 1, and the heat insulating film 2 are thermally expanded according to the magnitude of the respective temperature rises.

Most of the heat conducted to the outer mold 5 is radiated from the outer surface of the outer mold 5 to the outside after the temperature of the outer mold 5 is raised. The outer die 5 is in thermal contact with the inner core member 3 because it is in contact with the base end portion 3b of the inner core member 3 at the core mounting portion 5c, but the area of the base end portion 3b is the same as that of the outer die 5. Since it is smaller than the outer surface, the amount of heat transferred to the inner core member 3 is small.
On the other hand, the heat from the molten metal 8A conducted to the outer core member 1 is conducted to the inside of the outer core member 1 and reaches the heat insulating film 2, but the heat conductivity of the heat insulating film 2 is Since it is lower than the thermal conductivity of the core member 1, the amount of heat transferred to the inner core member 3 per unit time is significantly smaller than the amount of heat transferred to the outer mold 5, for example.
Heat of the molten metal 8A, since the outer mold 5 is quickly dissipated, within a short time the molten metal 8A reaches the solidification temperature T _k, the temperature rise of the inner core member 3 is negligible, the inner core member The outer diameter and length of the third tapered portion 3a do not change much.

Thus, the heat from the molten metal 8 </ b> A conducted to the outer core member 1 is accumulated in the outer core member 1. And, together with the small heat capacity of the outer core member 1, the temperature of the outer core member 1 rapidly rises to a temperature substantially equal to the molten metal 8 </ b> A in contact therewith.
As the material of the outer core member 1, it is preferable to select a material having a high thermal conductivity. In this case, since heat conduction is promoted as compared with the case where the thermal conductivity is small, the time required for the temperature rise is further shortened and it is easier to follow the temperature change of the molten metal 8A.
The heat insulating film 2 is in direct contact with the molten metal 8A at the exposed portion of the tip surface 1b, but the heat conductivity of the material of the heat insulating film 2 is small. For this reason, combined with the extremely small exposed area, the amount of heat directly conducted to the heat insulating film 2 is much smaller than the amount of heat conducted to the outer core member 1.

  Thus, the outer core member 1 that has been heated to a temperature substantially equal to the molten metal 8A is constrained to the shape of the tapered portion 3a of the inner core member 3 on the inner peripheral surface 1c side. The material expands thermally in proportion to the wall thickness (the dimension in the radial direction from the inner peripheral surface 1c to the side surface 1a). For this reason, the external dimension of the tapered side surface 1a before being heated from the molten metal 8A is thermally expanded to a shape in which the external dimension increases toward the tip side.

Melt 8A, since the solidification to be cooled to solidification temperature T _k is terminated, when the molten metal 8A reaches the solidification temperature T _k, melt 8A is a cavity bottom surface 5a and the cavity side surface 5b of the outer mold 5, the core 4 Are solidified along the shape of the cavity 6 surrounded by the side surface 1a and the front end surface 1b of the outer periphery 7 and the outer mold 7.
Therefore, a tapered outer shape of the outer core member 1 before subjected to heat from the molten metal 8A, when the molten metal 8A reaches the solidification temperature T _k, the diameter D _k of the hole inner peripheral surface 8a of the molded article 8B and thermal expansion × by preset so that the outer shape into a cylindrical shape length L _k, hollow shape of the hole inner peripheral surface 8a of the molded article 8B is formed.

When the cooling further proceeds, the outer mold 5, the molded product 8B, and the core 4 contract according to their respective thermal expansion characteristics. For the outer mold 5, since the contraction amount of the molded product 8 </ b> B is large, the side surface 8 c is separated from the cavity side surface 5 b.
Further, the inner peripheral surface 8a of the hole of the molded product 8B also shrinks. However, the outer shape of the core 4 is such that the amount of shrinkage at the time of cooling increases toward the tip side where the amount of thermal expansion is large at the time of heating. The side surface 1a of 1 has a tapered shape with a tapered end gradually with respect to the straight cylindrical surface of the hole inner peripheral surface 8a, and is spaced radially inward from the hole inner peripheral surface 8a of the solidified molded product 8B.
For this reason, even if the hole inner peripheral surface 8a contracts, the core 4 does not bite (hold), and when the removal temperature _Tt is reached, as shown in FIG. It will have a state. As a result, the releasability of the molded product 8B from the core 4 is improved. Therefore, after removing the outer mold 7, the molded product 8 </ b> B can be smoothly extracted from the outer mold 5 along the extraction direction and taken out of the casting mold 10.

  The heat insulating film 2 has a low thermal conductivity and suppresses heat transfer. However, the heat insulating film 2 is accumulated in the outer core member 1 during heating during cooling that requires a longer time than during heating. Heat is gradually transferred to the inner core member 3. For this reason, it also has a function as a transmission path for radiating heat through the base end 3d of the inner core member 3 and the outer mold 5 fitted with the base end 3d. Thereby, there also exists a function which assists the cooling from the inner side of the molded article 8B.

In the present embodiment, by appropriately selecting the shape and material of the core 4 in advance, the hollow shape of the molded product 8B is good, for example, even if the shape has no straight draft in the drawing direction. It can be formed with a good shape accuracy and can be taken out smoothly.
An example of a method for selecting the shape and material of the core 4 will be described.
First, the shape and material of the casting mold 10 and the core 4, the heat radiation conditions, the temperature of the molten metal to be introduced, etc. are set temporarily, and the temperature distribution in the casting mold 10 after the molten metal is introduced into the cavity 6 is analyzed. To do. As a result, the temperatures of the outer core member 1 and the inner core member 3 when the molten metal 8A in the cavity 6 is cooled to the solidification temperature T _k are, for example, T _out and T _in (where T _out > T _in ). As in the present embodiment, when the heat capacity of the outer core member 1 is small middle fraction, the temperature T _out is equal to the solidification temperature T _k, depending on the size of the heat capacity, met T _{out <T k} May be.

Next, the outer shape of the inner core member 3 at the temperature T _in is obtained.
Then, the inner peripheral surface 1c of the outer core member 1, under the condition that is constrained to the shape of the inner core member 3 of the tapered portion 3a at the temperature T _in, the outer core member 1 at the temperature T _out Find the outer shape. This shape is the outer shape of the core 4 in the cavity 6 during the solidification temperature T _k.
Next, the difference between this outer shape and the cylindrical shape of diameter D _k × length L _k is calculated, and the shape of the outer core member 1 that makes this difference zero, the diameter d _{2 of the} proximal end portion The diameter d ₁ and the length L ₁ of the tip are calculated and set as the outer shape of the outer core member 1.
Thereby, since the inner peripheral surface 8a of the molded product 8B is formed to have a diameter D _k × length L _k at the solidification temperature T _k , a cylinder having a diameter D × length L at the take-out temperature T _t. Shrink to hole shape.
Taper theta _t of side face 1a in extraction temperature T _t is calculated from the following equation.
However, since (d ₂ −d ₁ ) is sufficiently small compared to either L ₁ or L _k , it may be calculated as L ₁ = L _{k in} the following equation.

θ _t = tan ⁻¹ {(d ₂ −d ₁ ) / (2 · L ₁ )} (1)

Tapered theta _t is too small, if it can not be pulled out smoothly molded article 8B is a major material of more linear expansion coefficient material of the outer core member 1 or, more thermal conductivity of the material of the heat insulating layer 2 or changed to small, or by the material of the inner core member 3 and the smaller the material of the linear expansion coefficient, repeat the analysis described above, so that appropriate taper theta _t is obtained.
The appropriate taper θ _t has a relationship with the surface roughness of the outer core, but is preferably 0.1 (degrees) or more in general high-precision machining, and is 0.5 (degrees) or more. It is more preferable. If it is smaller than 0.1 (degrees), the influence of the surface roughness of the outer core is remarkably increased, and the release force tends to increase.

In the present embodiment, by providing the heat insulating film 2, a larger taper θ _t can be realized as compared with the case where the heat insulating film 2 is not provided. This will be described based on a specific example.
For simplicity, it is assumed that the thermal conductivity k2 of the heat insulating film ₂ is very small corresponding to the present embodiment. Also, heat conduction from the outer mold 5 to the inner core member 3 is very small.
In this case, since the thermal expansion and thermal contraction of the outer shape of the inner core member 3 having a linear expansion coefficient α ₃ can be ignored, the shape change of the outer shape of the core 4 is caused by the linear expansion coefficient α ₁ (where α It is determined only by the shape change in the radial direction of the outer core member 1 with ₁ > α ₃ ). Further, T _out = T _k may be set. Therefore, the following expressions (2) to (4) are established.

L ₁ = L = L _k (2)
D _k = d ₂ (3)
D _k = d ₁ · {1 + α ₁ · (T _k −T _t )} (4)

  Substituting equations (2) to (4) into equation (1) yields the following equation:

θ _t = tan ⁻¹ {d ₁ · α ₁ · (T _k −T _t ) / (2 · L _k )} (5)

Next, as a comparative example, considering the shape change in the case where the heat insulating film 2 is not provided, the heat of the molten metal 8A is easily conducted to the inner core member 3 via the outer core member 1, so that T _out , T _In is assumed to be equal to T _k for simplicity.
In this case, at the solidification temperature T _k, for inflating the diameter D _k × length L _k, the outer diameter d ₂ at the extraction temperature T _t of the proximal and distal ends ', d _1' is calculated using: It is done.

D _k = d ₂ ′ · {1 + α ₃ · (T _k −T _t )} (6)
D _k = d ₁ ′ · {1 + α ₁ · (T _k −T _t )} (7)
d ₂ ′ = d ₂ / {1 + α ₃ · (T _k −T _t )} (8)
d ₁ '= d ₁ (9)

For this reason, the taper θ _t ′ of the outer shape at the take-out temperature T _t in this case satisfies the relationship of the following equation.

tan θ _t ′ = (d ₂ ′ −d ₁ ′) / (2 · L _k )
= [D ₂ / {1 + α ₃ · (T _k −T _t )} − d ₁ )] / (2 · L _k )
... (10)

For example, the material of the outer core member 1 is SKD61 (α ₁ = 12.2 × 10 ⁻⁶ (1 / K)), and the material of the inner core member 3 is alumina (α ₃ = 7.8 × 10 ^−6). (1 / K)), and the shape of the hole inner circumferential surface 8a of the molded product 8B is D _k = φ10 (mm), L _k = 14 (mm), T _k = 993 (K), T _t = 523 Assuming (K), the taper θ _t ′ and θ _t are respectively _expressed by the following equations.

d ₁ = 10 / {(1 + 12.2 × 10 ⁻⁶ × (993-523)}
= 9.94 (mm)
d ₂ = 20 (mm)
θ _t = tan ⁻¹ {9.94 · 12.2 × 10 ⁻⁶ × 470 / (2 · 14)}
= 0.12 (degrees)
θ _t ′ = tan ⁻¹ [{(10 / (1 + 7.8 × 10 ⁻⁶ × 470)) − 9.94}
/(2.14)]
= 0.05 (degrees)

Thus, it can be seen that the taper θ _t according to the present embodiment is at least twice as large as the taper θ _t ′ when the heat insulating film 2 is not provided.
Therefore, since the thermal expansion of the inner core member 3 can be suppressed by the heat insulating film 2, the taper is larger than that without the heat insulating film 2, and the releasability of the core 4 can be improved. I understand.
The above example is an example in the case of T _k −T _t = 470 (K). However, when a metal material having a higher melting point, such as metal glass, is used as the molten metal 8A, the taper θ _t is used. Can be set to a larger value. For example, when T _k -T _t = 950 (K), θ _t = 0.24 (degrees).

  In the case of the prior art without the heat insulating film 2, there is a shape change on the base end side due to the temperature expansion of the inner core member 3. On the other hand, in the present embodiment, since the shape change on the base end side of the inner core member 3 hardly occurs, the processing accuracy on the end surface 8b side (the base end side of the core 4) of the molded product 8B is insulated. This can be improved as compared with the case without the film 2.

According to the core 4 of this embodiment, the thermal expansion of the inner core member 3 can be suppressed by the heat insulating film 2, and the outer core member 1 is mainly subjected to a temperature change by receiving heat from the molten metal 8A. By expanding and contracting accordingly, it is possible to form a shape in which the tip side is narrowed during cooling. Thereby, the utilization efficiency of the heat from the molten metal 8A is improved, and the shape change for obtaining a hollow shape necessary for molding and the shape change for obtaining a required taper during cooling can be caused with a small amount of heat.
Moreover, smooth mold release can be performed without complicating the casting mold 10 by using, for example, a slide mold.
That is, according to the core 4 of the present embodiment, the mold releasability of the molded product 8B can be improved without reducing the manufacturing efficiency and with a simple device configuration.

  In the present embodiment, in particular, when metallic glass is used as the material of the molten metal 8A, the molten metal temperature increases according to the height of the melting point, and therefore the deformation amount of the core 4 becomes larger, and the metallic glass Combined with the material having a small molding shrinkage at the time of solidification, the releasability can be further improved.

Moreover, in order to make a metallic glass amorphous, it is necessary to perform molding at a higher cooling rate than a general metallic material. That is, it is necessary to shorten the time from introduction of the molten metal 8A to solidification.
In the present embodiment, since the shape necessary for forming is obtained by transferring the heat from the molten metal 8A to only the outer core member 1, it is particularly suitable for forming in a short time such as forming such a metal glass. It becomes.

Next, a casting core according to a modification of this embodiment will be described.
Fig.4 (a) is typical sectional drawing which shows schematic structure of the core for casting which concerns on the modification of the 1st Embodiment of this invention. 4B, 4C, and 4D are a side view, a cross-sectional view taken along line DD, and a cross-sectional view taken along line EE in FIG. 4A, respectively.

As shown in FIG. 4A, the core 4A of the present modification is used for a casting mold 10A in order to cast a molded product 8B similar to that of the first embodiment.
The casting mold 10A is obtained by replacing the core 4 of the casting mold 10 of the first embodiment with a core 4A (core for casting). The core 4A includes an outer core member 1A and an inner core member 3A, respectively, instead of the outer core member 1, the inner core member 3, and the heat insulating film 2 of the core 4 of the first embodiment. .
Hereinafter, a description will be given centering on differences from the first embodiment.

The outer core member 1A includes a mold shape portion 1d having an outer shape made up of a side surface 1a and a distal end surface 1b similar to those of the outer core member 1, and a base end side of the mold shape portion 1d (opposite the distal end surface 1b). And a heat dissipating part 1e extending from the inner side of the outer mold 5 to the outer side.
Similar to the outer core member 1, the mold-shaped portion 1 d is projected from the cavity bottom surface 5 a, which is the inner surface of the cavity 6, toward the inside of the cavity 6 along the direction in which the molded product 8 B is pulled out, and is introduced into the cavity 6. It will be in contact with the molten metal.
Radiating portion outer peripheral surface 1g of the heat radiating portion 1e of this embodiment is the diameter d ₂ of the base end portion of the side surface 1a equal cylindrical surface, and is fixed by fitted into the core mounting portion 5c of the outer mold 5 Yes. Further, the heat radiating portion end face 1 h on the outer side of the outer mold 5 in the heat radiating portion 1 e is exposed to the outside of the outer die 5 at a position substantially aligned with the outer surface of the outer die 5.
Further, an inner peripheral surface 1f constituting an axial through hole is formed inside the outer core member 1A. The shape of the inner peripheral surface 1f is a cylindrical surface having an inner diameter d ₄ (where d ₄ <d ₂ ) in the heat radiating portion 1e. Further, the mold-shaped portion 1d, is connected to the cylindrical surface of the heat radiating portion 1e, gradually reduced in diameter from the inner diameter d ₄ toward the proximal end side to the distal side, the distal end surface 1b (see FIG. 4 (b)) , Having a conical concave shape with a reduced diameter on the tip side such that the inner diameter d ₀ is smaller than the outer diameter d ₁ .
The central axis of the inner peripheral surface 1f is coaxial with the central axes of the heat radiating portion outer peripheral surface 1g and the side surface 1a.

For this reason, as shown in FIG.4 (c), the cross section orthogonal to the extraction direction of the outer core member 1A in the cavity 6 has an outer diameter d ₃ (where d ₂ ≧ d ₃ > 0) side surface 1a, It is an annular surrounded by the small-diameter inner peripheral surface 1f than the inner diameter d ₄ of the base end side.
With such a shape, the radial thickness of the ring in the cross section orthogonal to the drawing direction of the outer core member 1A in the cavity 6 is (d ₂₎ from the cavity bottom surface 5a toward the inside of the cavity 6. It gradually increases from −d ₄ ) / 2 to (d ₁ −d ₀ ) / 2.

As the material of the outer core member 1A, the same metal material as that of the outer core member 1 of the first embodiment can be adopted.
In particular, in the outer core member 1A, a material having a higher thermal conductivity is preferable because the heat dissipation effect of the heat dissipation portion 1e can be enhanced.

The inner core member 3A includes a conical or truncated cone-shaped tapered portion 3c that can be fixed to the inner peripheral surface 1f of the mold-shaped portion 1d of the outer core member 1A via the heat insulating film 2, and heat dissipation of the outer core member 1A. This is a rod-shaped member composed of a columnar base end portion 3d fitted into the inner peripheral surface 1f of the portion 1e. For this reason, the inner core member 3A is extended along the drawing direction of the molded product inside the outer core member 1A.
The material of the inner core member 3A can be the same material as that of the inner core member 3 of the first embodiment.

Next, the operation of the core 4A of this modified example will be described focusing on differences from the first embodiment.
In the core 4A of the present modification, the radial thickness of the outer core member 1A along the pulling direction is closer to the proximal end side in the cavity 6 than in the outer core member 1 of the first embodiment. Although slightly thicker and the outer diameter of the inner core member 3A is slightly smaller on the proximal end side than the inner core member 3, the diameter of the outer core member 1A is gradually increased from the proximal end side toward the distal end side. It has the same action as the first embodiment in that the thickness in the direction gradually increases.
For this reason, by appropriately selecting the shape and material of the outer core member 1A, as in the first embodiment, the mold release of the molded product 8B can be performed without reducing the manufacturing efficiency and with a simple device configuration. Can be improved.
Here, the inner diameter d ₄ of the heat radiating portion 1e is too much small, the change in the radial direction of the outer core member 1A thickness is decreased, because good releasability can not be obtained, the heat radiating portion 1e The thickness (d ₂ -d ₄ ) / 2 in the radial direction is not excessively increased. For example, the thickness (d ₂ -d ₄ ) / 2 is preferably about 5% to 20% of the thickness (d ₁ -d ₀ ) / 2d ₁ of the front end portion of the outer core member 1A.

The core 4A includes the heat dissipating part 1e as described above, so that the heat transferred from the molten metal 8A to the outer core member 1A can be transferred to the outer mold 5 with good heat dissipation via the base end part 3d. The heat can be radiated to the outside of the outer mold 5 via the heat radiating portion end face 1h.
For this reason, since the outer core member 1A promotes heat dissipation compared to the outer core member 1 of the first embodiment that does not have any heat radiating portion, the cooling rate of the molten metal 8A can be improved. Therefore, when casting an amorphous alloy such as metallic glass (amorphous alloy), the possibility of crystallization can be reduced.
Moreover, since the front end side of the outer core member 1A is rapidly reduced in diameter, it can be released immediately after molding, and the productivity of casting can be improved.

  In addition, the thermal radiation part 1e of this embodiment is the thinnest thickness also in 1 A of outer core members with small heat capacity as a whole. For this reason, at the initial filling stage when the molten metal 8A is at a high temperature, the amount of heat transferred to the outer core member 1A is remarkably large, and the outer core member 1A thermally expands to a shape that forms the shape of the hole inner peripheral surface 8a. The time delay is almost negligible.

Further, by having the heat dissipating part 1e, the outer core member 1A has a double structure in close contact with the entire outer peripheral surface of the inner core member 3A, and the inner core member 3A and the outer core member 1A The holding power between is improved. For this reason, it is possible to prevent the outer core member 1 </ b> A from falling off due to the release force when the molded product 8 </ b> B is released. In particular, as described above, when the heat dissipating part 1e and the base end part 3b are in direct contact, the holding force between the outer core member 1A and the inner core member 3A can be further strengthened.
In addition, when a required holding force is obtained, the heat insulation film 2 may be provided to extend between the heat radiating portion 1e and the base end portion 3b. In this case, the heat insulation performance between the inner core member 3A and the outer core member 1A can be further improved.

[Second Embodiment]
A casting core according to a second embodiment of the present invention will be described.
Fig.5 (a) is typical sectional drawing which shows schematic structure of the core for casting which concerns on the 2nd Embodiment of this invention. FIGS. 5B and 5C are a side view and a GG cross-sectional view, respectively, as viewed in FIG. 5A.

As shown in FIG. 5A, the core 24 of the present embodiment is used for the casting mold 20 in order to cast the molded product 8B similar to that of the first embodiment.
The casting mold 20 is obtained by replacing the core 4 of the casting mold 10 of the first embodiment with a core 24 (a casting core). The core 24 includes an outer core member 21 and an inner core member 23 in place of the outer core member 1 and the inner core member 3 of the core 4 of the first embodiment, respectively. Instead of the heat insulating film 2 of the embodiment, heat insulating films 22a and 22b (heat insulating layer portions) are provided.
Hereinafter, a description will be given centering on differences from the first embodiment.

The outer core member 21 includes a cylindrical wall body portion 21A having an opening on the cavity bottom surface 5a side, and a distal end side wall body portion 21B provided so as to cover the cylindrical wall body portion 21A on the inner side of the cavity 6. Is provided.
The cylindrical wall portion 21A includes an outer peripheral side surface 21a of the same shape on the outer peripheral side corresponding to the side surface 1a of the outer core member 1 of the first embodiment, and the inner surface of the side portion is provided on the rear surface of the outer peripheral side surface 21a. A surface 21c is formed. In the present embodiment, the thickness of the cylindrical wall portion 21A is constant except for the opening.
In the opening portion of the cylindrical wall portion 21A, a tapered fixing portion 21e (base end) that decreases in diameter from the base end side to the tip end side of the outer core member 21 in order to contact and fix the heat insulating film 22b. Side fixing part) is provided.
Regarding the dimensions of the outer peripheral side surface 21a, the base end side is the outer diameter d ₂ and the tip end side is the outer diameter d ₁ .
Distal wall body 21B, in order to fix in contact with the heat insulating film 22a against the center is penetrated substantially circular hole-shaped fixing portion 21f (distal-side fixing portion), the outer peripheral portion of diameter d _1, a cylindrical wall It is connected to the end on the distal end side of the body part 21A. The distal end side wall 21B includes a distal end surface 21b on the outer surface side corresponding to the distal end surface 1b of the outer core member 1 of the first embodiment, and a bottom inner peripheral surface 21d on the rear surface of the distal end surface 21b. Is formed. In the present embodiment, the thickness of the tip side wall body portion 21B is constant.
The outer peripheral side surface 21a side of the inner diameter of the fixing portion 21f is the _{d 0} (see Figure 5 (b)).
However, distal wall body 21B, the distance from the cavity bottom surface 5a to the fixing portion 21f of the distal end face 21b is an _{L 1,} the distance _{L 2} from the cavity bottom surface 5a to the outer edge of the distal end surface 21b (where _{L 2} <L ₁ ).
As the material of the outer core member 21, the same material as that of the outer core member 1 of the first embodiment can be adopted.

The inner core member 23 includes a frustoconical taper portion 23a that can be fixed via the heat insulating films 22a and 22b at the fixing portions 21e and 21f of the outer core member 21, respectively. It is a rod-like member comprising a base end portion 23b fitted and attached to the child attachment portion 5c.
For this reason, the inner core member 23 is extended along the drawing direction of the molded product inside the outer core member 21.
The central axis of the inner core member 23 is coaxial with the central axis of the outer core member 21.
The outer diameter of the distal end portion of the tapered portion 23a is from the inner diameter d ₀ of the fixed portion 21f a circular minus twice the thickness of the heat insulating layer 22b. In this embodiment, the front end surface of the taper part 23a is aligned with the front end surface 21b of the outer core member 21, and is brought into contact with the molten metal.
As the material of the inner core member 23, the same material as that of the inner core member 3 of the first embodiment can be adopted.

The heat insulating films 22a and 22b suppress heat transfer between the outer core member 21 and the inner core member 23. In the present embodiment, the ranges facing the fixing portions 21e and 21f of the outer core member 21. Is provided as a thin film layer having a substantially constant film thickness on the tapered portion 23a of the inner core member 23.
The material of the heat insulation films 22a and 22b can be the same material as that of the heat insulation film 2 of the first embodiment.

With such a configuration, a hollow portion 22c including a closed space surrounded by the side inner peripheral surface 21c, the tapered portion 23a, and the bottom inner peripheral surface 21d is provided between the outer core member 21 and the inner core member 23. Is formed.
For this reason, the cylindrical wall body portion 21A and the distal side wall body portion 21B have the fixed portions 21e and 21f fixed to the inner core member 23, and the distal end portion of the cylindrical wall body portion 21A and the outer peripheral portion of the distal side wall body portion 21B. Can be thermally deformed in a connected state. For this reason, in particular, movement in the radial direction and the axial direction is easy at the intermediate portion of the cylindrical wall portion 21A.
Further, the side inner peripheral surface 21c and the bottom inner peripheral surface 21d of the outer core member 21 and the tapered portion 23a of the inner core member 23 are separated from each other by the hollow portion 22c, so that the heat insulating films 22a and 22b are separated from each other. Similarly, the heat insulation layer part which suppresses the heat transfer between the outer core member 21 and the inner core member 23 is comprised.
For example, atmospheric pressure air or inert gas may be sealed inside the hollow portion 22c, but in the present embodiment, it is in a vacuum state. For this reason, the hollow part 22c has a far superior heat insulating property as compared with the case where air at atmospheric pressure or inert gas is sealed.

With this configuration, the present embodiment is an example in which the fixing portion between the outer core member 21 and the inner core member 23 is composed of only the base end fixing portion and the tip end fixing portion.
In the proximal end fixing portion and the distal end fixing portion, each interval in the direction orthogonal to the extraction direction between the outer peripheral side surface 21a that is the outer peripheral surface of the outer core member 21 on the side surface side with respect to the extraction direction and the fixing portion is the proximal end. On the fixed portion side, the thickness is between the fixed portion 21e and the outer peripheral side surface 21a. On the distal end fixed portion side, the distance between the fixed portion 21f and the outer peripheral side surface 21a, that is, (d ₂ −d ₀ ) / 2. For this reason, the space | interval on the front-end | tip fixing | fixed part side is larger than the space | interval on the base end fixing | fixed part side.

Next, the operation of the core 24 of the present embodiment will be described together with a method for forming the molded product 8B using the casting mold 20.
6 (a) and 6 (b) are process explanatory views illustrating a forming process using the casting core according to the second embodiment of the present invention.

  The molding method of the present embodiment is performed by using the casting mold 20 instead of the casting mold 10 of the first embodiment, and the core 4 of the first embodiment and the core 24 of the present embodiment. They differ only in their thermal deformation based on the structural differences between the two. Below, it demonstrates centering on a different point from the said 1st Embodiment.

As shown in FIG. 5A, a molten metal 8A in which a metal material for casting the molded product 8B is heated and melted is introduced into the cavity 6 of the casting mold 20 assembled as shown in FIG. 5A, and the molten metal 8A is filled into the cavity 6. To do. FIG. 6A shows a portion excluding the outer mold 7 after filling with the molten metal 8A.
On the outer surface of the core 24, the molten metal 8 </ b> A comes into contact with the outer peripheral side surface 21 a and the front end surface 21 b of the outer core member 21, and the heat insulating film 22 b and the inner core member 23 exposed on the front end surface 21 b.
Here, the inner core member 23 is formed by the heat insulating films 22a and 22b and the hollow portion 22c in the same manner as the inner core member 3 of the first embodiment except that the tip of the small area comes into contact with the molten metal 8A. since the heat transfer from the outer core member 21 is suppressed, much like the inner core member 3, little temperature rise in time to melt 8A reaches the solidification temperature T _k.
For this reason, most of the heat from the molten metal 8 </ b> A contributes to the temperature rise of the outer core member 21.
Since the outer core member 21 has a smaller heat capacity than the outer core member 1 of the first embodiment, the temperature rises more quickly than the outer core member 1, and more It becomes almost the same temperature as the molten metal 8A in a short time.

The outer core member 21 whose temperature has been increased thermally expands in accordance with the temperature increase.
Since the outer core member 21 is fixed to the inner core member 23 by the fixing portions 21e and 21f, the outer peripheral side surface 21a and the distal end surface 21b have the same thicknesses as the cylindrical wall body portion 21A and the distal side wall body portion 21B. Regardless of the thickness, it is determined by the axial length of the cylindrical wall portion 21A and the thermal expansion of the outer diameter of the distal end side wall portion 21B. Therefore, together with the equations (2) and (3) of the first embodiment, the length L ₂ at the take-out temperature T _t and the outer diameters d ₂ and d ₁ satisfy the relationship of the following equation: Set it.

D _k = (d ₁ −d ₀ ) · {1 + α ₁ · (T _k −T _t )} + d ₀ (11)
L _k = L ₁ = L ₂ · {1 + α ₁ · (T _k -T _t )} (12)

Melt 8A, since the solidification reaches the solidification temperature _{T k} is terminated, when the molten metal 8A reaches the solidification temperature _{T k,} the outer surface of the core 24, the outer peripheral side surface 21a, the distal end surface 21b, and the distal end face 21b It is solidified along the shape of the front end surface of the aligned inner core member 23.
Accordingly, a hollow shape of diameter D _k × length L _k of the hole inner peripheral surface 8a of the molded product 8B is formed (see FIG. 6A).

Further, as the cooling progresses, the outer mold 5, the molded product 8B, and the core 4 contract according to their respective thermal expansion characteristics. For the outer mold 5, the side surface 8c gradually separates from the cavity side surface 5b, as in the first embodiment.
Also, the hole inner peripheral surface 8a of the molded product 8B shrinks evenly. However, as shown in FIG. 6B, the outer shape of the core 24 is such that the outer diameter of the tip side wall 21B is from _Dk to d. to shrink to the truncated cone shape such that _1, with respect to the side surface 8c, the more distal end side (opening direction inner side of the bore peripheral face 8a), shrinkage amount increases. For this reason, the outer peripheral side surface 21a of the outer core member 21 gradually has a tapered shape with a tapered tip with respect to the straight cylindrical surface of the hole inner peripheral surface 8a, and is spaced radially inward from the hole inner peripheral surface 8a. .
As a result, even if the hole inner peripheral surface 8a contracts, without bite in the core 24, upon reaching the extraction temperature T _t, a state with a moderate draft taper theta _t. Here, the taper θ _t is the same as the expression (1) in the first embodiment.
Therefore, the releasability of the molded product 8B from the core 24 is improved. As a result, after removing the outer mold 7, the molded product 8 </ b> B can be smoothly extracted from the outer mold 5 along the extraction direction and taken out of the casting mold 20.

According to the core 24 of the present embodiment, the thermal expansion of the inner core member 23 can be suppressed by the heat insulating films 22a and 22b and the hollow portion 22c, and the outer core is mainly received by receiving heat from the molten metal 8A. The member 1 expands and contracts according to the temperature change, so that a shape in which the tip side is narrowed during cooling can be formed. Thereby, the utilization efficiency of the heat from the molten metal 8A is improved, and a necessary shape change can be caused with a small amount of heat.
At the time of cooling, when the distal end side wall body portion 21B is cooled and contracts, it is separated from the inner peripheral surface 8a so as to be gradually separated from the distal end side of the outer core member 21. Accordingly, as in the first embodiment, the entire outer core member 1 is cooled, so that it is more easily separated as compared with the case where the outer core member 1 is separated from the hole inner peripheral surface 8a of the molded product 8B. .
In the present embodiment, since the outer core member 21 has a thin structure as described above, the thermal expansion during heating and the thermal contraction during cooling are performed more quickly than in the first embodiment. Can do.
Further, similarly to the first embodiment, for the purpose of causing a necessary shape change, for example, it is not necessary to add a heating mechanism to increase the temperature of the molten metal or to add a cooling device.
Moreover, smooth mold release can be performed without complicating the casting mold 20 by using, for example, a slide mold.
That is, according to the core 24 of the present embodiment, it is possible to improve the releasability of the molded product 8B without reducing the manufacturing efficiency and with a simple device configuration.

  In the present embodiment, since the outer core member 21 has a thin structure, the substantial heat capacity of the core 24 is reduced, so that the cooling effect for cooling the molten metal 8A is low. For this reason, for example, even if it contacts with the core 24, solidification of the molten metal 8A is difficult to proceed. Therefore, even if the molded product 8B is a thin-walled structure, a high filling property can be obtained.

Also in this embodiment, similarly to the first embodiment, when metal glass is used as the material of the molten metal 8A, the molten glass temperature becomes extremely high, and therefore the deformation amount of the core 24 is larger. In addition, the metallic glass is a material having a small molding shrinkage at the time of solidification, so that the mold release property can be further improved.
Moreover, since the shape required for shaping | molding is obtained because the heat | fever from the molten metal 8A is transmitted only to the outer core member 21, it becomes more suitable for shaping | molding performed in a short time, such as shaping | molding of metal glass.

Next, in the said 1st Embodiment, Examples 1-6 at the time of changing the material of the outer core member 1, the inner core member 3, the heat insulation film 2, and the molten metal 8A are demonstrated with Comparative Examples 1-3. To do.
Here, in order to evaluate the difference in releasability due to the difference in material and the like, in all examples and comparative examples, the shape of the molded product 8B is D = 10 (mm) and L = at a temperature of 298 (K). 14 (mm), D ₀ = 11 (mm), L ₀ = 15 (mm), and the dimensions of the core 4 are similarly d ₁ = 9.93 (mm) and d ₂ at a temperature of 298 (K). = 10 (mm), L ₁ = 10 (mm). Therefore, these dimensions are not optimized according to each material, and in Example 3, the taper at the take-out temperature T _t (298 K) is approximately θ _t = 0.1 (degrees). Selected.
The detailed conditions and evaluation results of each example and comparative example are shown in the following Table 1.

[Description of each example]
In Example 1, an aluminum alloy ADC12 was adopted as the molten metal 8A, the molten metal temperature T was T = 993 (K), the solidification temperature T _k was T _k = 843 (K), and the take-out temperature T _t was T _t = 298 (K). The material of the inner core member 3 was alumina, and the material of the outer core member 1 was SKD11 of an iron-based alloy. Further, the heat insulating layer 2 was adopted ZrO ₂ with a thickness of 10 [mu] m (Example 2-6 versa).
In Example 2, the material of the molten metal 8A in Example 1 is MDC1D (T = 923 (K), T _k = 783 (K), T _t = 298 (K)) which is a magnesium alloy instead of the ADC 12. In this example, the material of the heat insulating film 2 is replaced with alumina to form SKD11.
Example 3 is Zr ₅₅ Cu ₃₀ Ni ₅ Al ₁₀ (T = 1373 (K), T _k = 763) which is a material for forming metal glass instead of MDC 1D as the material of molten metal 8A in Example 2. (K), T _t = 298 (K)).
Example 4 is Fe ₇₅ Ga ₅ P ₁₂ C ₄ B ₄ (T = 1373 (K), T _k ), which is a material for forming metal glass instead of MDC 1D as the material of molten metal 8A in Example 2. = 823 (K), T _t = 298 (K)), and the material of the outer core member 1 is Cu instead of SKD11.
In Example 5, the material of the molten metal 8A is Ni ₅₃ Nb ₂₀ Ti ₁₀ Zr ₈ Co ₆ Cu ₃ (T = 1273 (K), which is a material for forming metal glass instead of the MDC 1D in Example 2. In this example, T _k = 823 (K) and T _t = 298 (K)), and SUS303 is adopted as the material of the outer core member 1 and the inner core member 3.
In Example 5, the material of the molten metal 8A in Example 5 was changed to Ni ₅₃ Nb ₂₀ Ti ₁₀ Zr ₈ Co ₆ Cu ₃ instead of Zr ₅₅ Cu ₃₀ Ni ₅ Al ₁₀ and the material of the inner core member 3 was: This is an example employing WC.

[Description of each comparative example]
Comparative Example 1 is an example in which, in Example 1, instead of the core 4, a core composed of an integrated cylindrical pin having a diameter 10 (mm) × length 14 (mm) by the SKD 11 is used. For this reason, this comparative example is an example in which the heat insulating film 2 is not provided and the taper of the core at the time of cooling does not occur as compared with the first embodiment.
The comparative example 2 is an example in which the heat insulating film 2 is removed and the inner core member 3 made of alumina and the outer core member 1 made of SKD11 are brought into direct contact with each other in the first embodiment.
Comparative Example 3 is an example in which, in Example 3, instead of the core 4, a core made of a cylindrical pin having a diameter 10 (mm) × length 14 (mm) by the SKD 11 is used.

[Explanation of evaluation method]
Based on the conditions of the above Examples and Comparative Examples, casting was performed, mold release was attempted, and the results were evaluated.
The evaluation result ○ indicates that the mold can be released with the same or better ease as the integral tapered core (taper angle is 0.5 degree), and the inner peripheral surface 8a of the molded product 8B and the core No damage was seen on the surface, indicating that the results were sufficiently practical.
The evaluation result Δ indicates that although the mold release was possible, damage such as scratches was observed on the inner peripheral surface 8a of the molded product 8B and the surface of the core, so that it was not acceptable.
Evaluation result x shows that mold release itself was difficult.

[About evaluation results]
As shown in Table 1 above, the evaluation results of the releasability in Examples 1 to 6 were good. In the integrated tapered core, a straight cylindrical hole shape as in each example cannot be formed, but in these examples, a straight cylindrical hole-shaped inner peripheral surface 8a can be formed.
On the other hand, Comparative Examples 1 and 3 correspond to Examples 1 and 3, respectively, and are examples in which casting is performed with a cylindrical core having no taper. In each case, the evaluation result was x, and it was difficult to release the mold.
Moreover, the comparative example 2 is an example at the time of removing only the heat insulation film 2 in the implementation house 1, and the difference in the linear expansion coefficient between the alumina and the SKD 11 and the change in the thickness of the outer core member 1 in the drawing direction. Since a tapered taper can be formed during cooling, it was not possible to release the mold as in Comparative Example 1 without the tapered taper, but the evaluation result was Δ.
Since there is no heat insulating film 2, a taper corresponding to the difference between the linear expansion coefficient of the inner core member 3 made of alumina and the linear expansion coefficient of the outer core member 1 made of MDC1D is formed. This is because only a smaller taper than that in Example 1 is formed.

Moreover, among Examples, when Examples 3 to 6 were compared with Examples 1 and 2, casting with metal glass as in Examples 3 to 6 was more excellent in releasability.
This is because metal glass has a melting temperature of about 1000 ° C., which is higher than that of an aluminum alloy or a magnesium alloy, so that the deformation amount due to temperature change of the outer core member 1 becomes large, and it is amorphous by rapid solidification. Therefore, the solidification shrinkage is remarkably smaller than that of the aluminum alloy or the magnesium alloy, and this is considered to be due to a synergistic effect that the degree of hugging the core by the solidification shrinkage is reduced.
That is, since the mold can be released after the core is deformed, the surface of the outer core member 1 is first peeled off from the metal glass having a high hardness, and then the surface of the outer core member 1 and the molded product are removed. Since the inner peripheral surface 8a of the hole 8B is not easily rubbed in the shearing direction, damage such as wear and scratches on the core 4 due to the high hardness metal glass can be effectively avoided.
Conversely, metallic glass has a higher modulus of elasticity and hardness than many mold materials, so if there is not enough taper, the mold is easily damaged during mold release. Requires a slide mold, and the mold structure is complicated and expensive.

In the above description, the heat insulating layer portion is described as an example of a thin film layer having a low thermal conductivity and a case of a hollow portion from which a heat conductive solid has been removed. It is good also as a structure which suppresses heat transfer by providing a space | gap part between a child member and reducing the contact area which contributes to heat conduction.
The case where such a heat insulation layer part has a space | gap part is demonstrated with reference to FIG.
FIG. 7 is a schematic partial enlarged cross-sectional view showing another example of the heat insulating layer portion that can be suitably used for the casting core according to the first and second embodiments of the present invention.

The heat insulation layer 2A shown in FIG. 7 is formed on the heat insulation film 2, the heat insulation films 22a, 22b, etc. in the outer core members 1, 1A, 21 and the inner core members 3, 3A, 23 of the above-described embodiments and modifications. It can be used instead. Below, the example at the time of applying to the outer core member 1 and the inner core member 3 is demonstrated.
2 A of heat insulation layer parts are the rough surface 100 which has the fine unevenness | corrugation formed in the internal peripheral surface 1c of the outer core member 1, and the rough surface which has the fine sinister unevenness formed in the taper part 3a of the inner core member 3 101 is abutted and joined, and is fixed so that the convex portions of the rough surfaces 100 and 101 are in point contact with each other, and a large number of minute voids 102 are formed between the rough surfaces 100 and 101. It is.
The rough surfaces 100 and 101 can be formed, for example, by performing machining with rough surface roughness, blasting, or increasing the unevenness of such rough surfaces by chemical treatment.
According to the heat insulating layer portion 2A having such a configuration, the real contact area between the outer core member 1 and the inner core member 3 is reduced, the area of the heat conduction path is reduced, and the gap portion 102 Heat transfer is suppressed.
It is more preferable that the void portion 102 is in a vacuum state since the heat insulation is further improved.

  As still another example of the heat insulating layer portion having such a void portion, a form of forming a layer film of a porous material having minute holes and bubbles can be exemplified.

Further, in the above description, an example in the case of casting a rod-shaped member having a straight cylindrical hole as a hollow shape of a molded product formed by a casting core is described as an example, and the molded product The shape is not limited to this. For example, an arbitrary shape such as a polygon or an ellipse can be adopted as the hollow cross-sectional shape.
Further, the hollow shape of the molded product formed of the casting core is not limited to a hole that is straight in the drawing direction, and may be a through hole that is straight in the drawing direction.
In addition, the hollow shape of the molded product formed by the casting core may be originally a shape with a draft, or a reverse taper as long as the outer core member can be pulled out in the drawing direction during cooling. It may be a shape with For this reason, the outer shape of the outer core member preferably has a taper that tapers along the drawing direction at the take-out temperature, but may be straight in the drawing direction depending on circumstances.
Further, the outer shape of the outer core member may be stepped.

  In the description of the modification of the first embodiment, the heat radiating portion 1e is described as an example in which the outer core member 1A is integrally formed of the same material, but the heat radiating portion 1e is formed on the molten metal 8A. Since it does not contact, for example, the melting point is low, but it may be constituted by another member made of a material having a higher thermal conductivity than the mold-shaped portion 1d.

  Further, in the above description, by providing the heat insulating layer portion, the temperature rise of the inner core member is suppressed, but in order to more efficiently suppress the temperature rise of the inner core member, or at the time of cooling In order to improve the cooling efficiency, for example, a cooling pipe through which a refrigerant flows inside the inner core member may be provided, and the inner core member may be cooled as necessary.

  Further, in the above description, the casting core is described as an example in which the casting core receives heat from the molten metal introduced into the cavity and is thermally expanded. However, the casting core is in contact with at least the molten metal. Casting may be performed after the outer core member to be heated is heated and sufficiently expanded before introducing the molten metal.

In the above description of the second embodiment, the inner core member 23 has been described as having the tapered portion 23a. However, in the second embodiment, the outer shape of the position at which the fixing portions 21e and 21f are fixed is changed. If you do. For this reason, any cross-sectional shape can be adopted in the intermediate portion in the axial direction of the taper portion 23a in contact with the hollow portion 22c as long as thermal deformation of the cylindrical wall portion 21A and the tip side wall portion 21B is not hindered. For example, it may be a stepped tapered from the distal end side of the fixing portion 21e, or in an extended cylindrical shape having an outer diameter d ₀ shape.

In the above description, the outer dimension of the proximal end portion of the inner core member is described as an example in which the outer diameter d ₂ that is the outer dimension of the proximal end of the outer core member 1 is the same value. Is an example, and the dimension of the proximal end portion of the inner core member may be different from the outer dimension of the proximal end side of the outer core member. In terms of promoting cooling of the molded product from the inner side during cooling, it is preferable that the base end portion of the inner core member is larger than the outer dimension on the base end side of the outer core member.

In addition, all the constituent elements described in the above embodiments, modifications, and the like can be implemented in appropriate combination within the scope of the technical idea of the present invention.
For example, the heat radiating portion 1e of the modification of the first embodiment may be combined with the outer core member 21 of the second embodiment.
Further, for example, the distal end portion of the inner core member 3 may have a shape in contact with the molten metal 8 </ b> A similarly to the distal end portion of the inner core member 23.

The invention according to claim 1 is a casting core provided in a cavity of a casting mold for casting a molded product from a molten metal, wherein the molded product is directed from the inner surface of the cavity toward the inner side of the cavity. An outer core member formed on the outer surface of a core mold surface that protrudes along the pulling direction and contacts the molten metal introduced into the cavity, and the pulling direction on the inner side of the outer core member And an inner core member fixed at an inner fixed portion of the outer core member across a heat insulating layer portion that suppresses heat transfer from the outer core member. The inner fixed portion of the child member includes at least a base end fixed portion in the vicinity of the inner surface of the cavity and a distal end fixed portion in the distal end portion on the inner side of the cavity, respectively, with respect to the outer peripheral surface of the inner core member. Constrain deformation inside the core member In each of the fixed portions from the base end fixing portion to the distal end fixing portion, the outer peripheral surface of the outer core member on the side surface with respect to the pulling direction and the fixing portion are orthogonal to the pulling direction. Each interval in the direction to be arranged is set to be larger on the distal end fixing portion side than on the proximal end fixing portion side.
According to this invention, when the molten metal is introduced into the cavity of the casting mold, the molten metal contacts the core surface, and the outer core member is heated and thermally expanded. The outer core member is an inner fixed part, and is fixed to the inner core member with a heat insulating layer portion that suppresses heat transfer from the outer core member interposed therebetween. It is used to thermally expand the child member, and the inner core member hardly thermally expands. Therefore, the shape of the core surface changes mainly due to the thermal expansion of the outer core member.
When the filling of the molten metal is completed and heat dissipation proceeds through the casting mold, the molten metal is cooled and solidified along the core surface of the outer core member that has been thermally expanded, and the hollow shape of the molded product is formed. At the same time, the outer core member contracts.
The inner core fixing portion includes at least a base end fixing portion in the vicinity of the inner surface of the cavity and a tip fixing portion at the inner end of the cavity, and the outer core with respect to the outer peripheral surface of the inner core member. The pulling direction between the outer peripheral surface of the outer core member on the side surface with respect to the pulling direction and the fixing portion at each fixing portion from the base end fixing portion to the distal end fixing portion, provided to restrain deformation inside the member. The intervals in the direction orthogonal to the front end fixing portion side are set to be larger than the base end fixing portion side.
For this reason, the outer core member has a thermal expansion amount at each fixed portion so that the outer peripheral surface of the outer core member on the side surface in the pulling direction from the fixed portion has a thermal expansion amount corresponding to the interval from the fixed portion to the outer peripheral surface. To do. Therefore, the amount of thermal expansion and heat shrinkage due to a constant temperature increase is greater on the distal end fixing portion side than on the proximal end fixing portion side. As a result, the shape of the core mold surface changes more greatly on the distal end side of the outer core member that is the back side of the hollow shape of the molded product, and the shape in which the distal end side becomes thinner as a whole compared to the time of thermal expansion during cooling. Become.

According to a second aspect of the present invention, in the casting core according to the first aspect, the inner core member has a convex portion whose outer dimension decreases from the inner surface of the cavity toward the inner side of the cavity. The outer core member has a concave portion along the convex portion of the inner core member, and has a cross section orthogonal to the extraction direction from the inner peripheral surface of the concave portion to the core mold surface. The thickness is provided in a shape that increases from the inner surface of the cavity toward the inner side of the cavity, and the heat insulating layer portion includes an outer peripheral surface of the convex portion of the inner core member and the outer core member. It is set as the structure pinched | interposed between the internal peripheral surfaces of a recessed part.
According to the present invention, the outer core member is fixed to the convex portion whose outer dimension decreases from the inner surface of the cavity toward the inner side of the cavity with the heat insulating layer portion interposed therebetween.
The outer core member has a concave portion shaped along the convex portion of the inner core member, and the thickness in a cross section perpendicular to the drawing direction from the inner peripheral surface of the concave portion to the core mold surface is the inner surface of the cavity. Since the inner peripheral surface of the concave portion of the outer core member hardly expands due to the action of the heat insulating layer portion, the shape of the outer peripheral surface of the convex portion of the inner core member is increased. Restrained by For this reason, the outer core member thermally expands in accordance with the thickness in the direction orthogonal to the drawing direction, and therefore, at the time of cooling, the distal end side of the outer core member that contacts the hollow side of the molded product contracts more greatly Thus, the core-shaped surface has a shape in which the tip side is thinner as a whole compared to the case of thermal expansion.

According to a third aspect of the present invention, in the casting core according to the first aspect, the outer core member includes a cylindrical wall body portion having an opening on the inner surface side of the cavity, and the cylindrical wall. A distal end side wall body portion provided so as to cover the body portion on the inner side of the cavity, the proximal end fixing portion at the opening of the cylindrical wall body portion, and the distal end fixing portion at the distal end side wall body. An outer peripheral surface of the inner core member, and an inner peripheral surface of the cylindrical wall body portion and the distal side wall body portion between the proximal end fixing portion and the distal end fixing portion. It is set as the structure by which the space | interval was spaced apart and the hollow part was formed.
According to this invention, the outer core member provided with the cylindrical wall body portion and the distal end side wall body portion includes the proximal end fixing portion of the opening outside the cylindrical wall and the distal end fixing portion at the center portion of the distal end side wall body portion. And each is fixed to the inner core member with the heat insulating layer portion interposed therebetween. A hollow portion is formed between the proximal end fixing portion and the distal end fixing portion, the outer peripheral surface of the inner core member being separated from the inner peripheral surfaces of the cylindrical wall body portion and the distal end side wall body portion. Therefore, heat transfer from the outer core member to the inner core member is suppressed by the action of the heat insulating layer portion and the hollow portion.
The cylindrical wall body portion and the tip side wall body portion of the heated outer core member are thermally expanded in a state where the inner peripheral surface is constrained by the inner core member at a position where each is fixed, and the thermal expansion amount is It is proportional to the interval in the direction orthogonal to the drawing direction between the inner peripheral surface and the outer peripheral surface of the outer core member in each. For this reason, the outer dimensions at the proximal end fixing portion of the cylindrical wall portion hardly change, and the outer dimensions at the distal end side of the core mold surface are caused by thermal expansion in a direction perpendicular to the drawing direction of the distal end sidewall body portion. Change.
Therefore, at the time of cooling, the front end side of the outer core member corresponding to the back side of the hollow shape of the molded product is contracted more greatly, and the core mold surface has a shape in which the front end side is thinner as a whole than at the time of thermal expansion.

According to a fourth aspect of the present invention, in the casting core according to the third aspect, the hollow portion is provided in a vacuum state.
According to this invention, the heat insulation by a hollow part can be improved.

According to a fifth aspect of the present invention, in the casting core according to any one of the first to fourth aspects, the outer core member includes a heat radiating portion that radiates heat received from the molten metal to the outside of the cavity. It is set as the structure provided.
According to this invention, the heat of the outer core member heated by the molten metal is quickly radiated to the outside of the cavity through the heat radiating portion.

In invention of Claim 6, in the core for casting in any one of Claims 1-5, the said heat insulation layer part is set as the structure which has a space | gap part.
According to this invention, since a heat insulation layer part is provided with a space | gap part, heat transfer can be suppressed with a simple structure.

According to a seventh aspect of the present invention, in the casting core according to the sixth aspect, the gap is provided in a vacuum state.
According to this invention, the heat insulation by a space | gap part can be improved.

According to an eighth aspect of the present invention, in the casting core according to any one of the first to seventh aspects, a linear expansion coefficient of a material constituting the outer core member is a material constituting the inner core member. It is set as a structure larger than the linear expansion coefficient.
According to this invention, even if heat is transferred to the inner core member and the inner core member is thermally expanded to some extent, the shape change due to the temperature change of the outer core member is relatively less than that of the inner core member. growing.

1, 1A, 21 Outer core member 1a Side surface 1b Tip surface 1c, 1f Inner peripheral surface 1d Mold shape portion 1e Heat radiation portion 2, 22a, 22b Heat insulation film (heat insulation layer portion)
3, 3A, 23 Inner core member 3a, 3c, 23a Taper part 3b, 3d, 23b Base end part 4, 4A, 24 Core (core for casting)
5, 7 Outer mold 5a Cavity bottom (inside of cavity)
6 Cavity 8A Molten metal 8B Molded product 8a Hole inner peripheral surface 10, 10A, 20 Casting mold 21A Cylindrical wall portion 21B Tip side wall portion 21a Outer peripheral side surface 21b Tip end surface 21c Side inner peripheral surface 21d Bottom inner peripheral surface 21e Fixed portion (base End fixing part)
21f Fixed part (tip fixed part)
22c Hollow part (heat insulation layer part)

Claims (8)

A casting core provided in a cavity of a casting mold for casting a molded product from a molten metal,
A core mold surface that protrudes from the inner surface of the cavity toward the inner side of the cavity along the drawing direction of the molded product and contacts the molten metal introduced into the cavity is formed on the outer surface. An outer core member;
The inner core member is extended along the drawing direction and fixed by a fixing portion inside the outer core member with a heat insulating layer portion for suppressing heat transfer from the outer core member interposed therebetween. An inner core member,
The fixed portion inside the outer core member is
At least at the proximal end fixing portion in the vicinity of the inner surface of the cavity and the distal end fixing portion at the distal end portion on the inner side of the cavity, the deformation inside the outer core member with respect to the outer peripheral surface of the inner core member is restrained. As well as
Each interval in the direction orthogonal to the extraction direction between the outer peripheral surface of the outer core member on the side surface with respect to the extraction direction and the fixed portion in each of the fixation portions from the proximal end fixation portion to the distal end fixation portion. However, the core for casting is characterized in that it is provided so that the gap on the distal end fixing portion side is larger than the base end fixing portion side. The inner core member is
From the inner surface of the cavity toward the inner side of the cavity, a convex portion whose outer dimension decreases,
The outer core member is
The inner core member has a concave portion shaped along the convex portion, and the thickness in a cross section perpendicular to the drawing direction from the inner peripheral surface of the concave portion to the core mold surface is from the inner surface of the cavity. Provided in a shape that increases toward the inside of the cavity;
The said heat insulation layer part is pinched | interposed between the outer peripheral surface of the said convex part of the said inner core member, and the inner peripheral surface of the said recessed part of the said outer core member. Casting core. The outer core member is
A cylindrical wall body portion having an opening on the inner surface side of the cavity, and a tip side wall body portion provided so as to cover the cylindrical wall body portion on the inner side of the cavity,
The proximal end fixing portion is provided in the opening of the cylindrical wall body portion, and the distal end fixing portion is provided in a central portion of the distal end side wall body portion;
Between the base end fixing portion and the distal end fixing portion, the outer peripheral surface of the inner core member and the inner peripheral surface of the cylindrical wall body portion and the distal end side wall body portion are separated from each other so that a hollow portion is formed. The casting core according to claim 1, wherein the casting core is formed.   The casting core according to claim 3, wherein the hollow portion is provided in a vacuum state.   5. The casting core according to claim 1, wherein the outer core member includes a heat radiating portion that radiates heat received from the molten metal to the outside of the cavity.   The core for casting according to any one of claims 1 to 5, wherein the heat insulating layer portion has a void portion.   The casting core according to claim 6, wherein the gap is provided in a vacuum state.   8. The medium for casting according to claim 1, wherein a linear expansion coefficient of a material constituting the outer core member is larger than a linear expansion coefficient of a material constituting the inner core member. Child.

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