JP3597679B2 - Sand core - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a sand core used for high-pressure casting such as melt forging and die casting.
[0002]
[Prior art]
Conventionally, as a sand core used for high-pressure casting, a first coating layer made of powdered refractory or the like is formed on the surface of a core body, and a second coating layer made of synthetic mica or the like is formed on the first coating layer. A sand core having a mold layer is known (for example, described in Japanese Patent Publication No. 60-15418).
[0003]
[Problems to be solved by the invention]
In the conventional sand core, the surface of the core body is smoothed by the first coating layer, the molten metal pressure acting on the surface of the sand core is made uniform, and the inside of the core body is formed by the second coating layer. It is formed so as to suppress the intrusion of the molten metal into the metal. However, the second coating layer is merely formed on the surface of the first coating layer, and the adhesion between the first coating layer and the second coating layer is weak. When the molten metal is filled into the mold at high speed and in a turbulent flow, there is a problem that the second coating layer is washed away by the molten metal and the molten metal is inserted into the sand core.
Then, this invention is made in order to solve such a problem, and makes it a subject to obtain the sand core which has a smooth surface and does not generate | occur | produce a molten metal even at the time of high pressure casting.
[0004]
[Means for Solving the Problems]
The present invention relates to a core formed from a small core sand having an average particle diameter of 100 to 150 μm, and an outer shell formed from a large core sand having an average particle diameter of 350 to 450 μm and covering the core. And a mold filling layer that fills a space between adjacent large-diameter core sands on the surface of the core body and covers the core body.
[0005]
Since the sand core having the above configuration has a high sand filling rate at the core, it is difficult to shrink even when a high melt pressure is applied, and also, a coating mold of a mold filled in the space between the large-diameter core sands. Since the thickness of the layer is large, no molten metal is inserted into the sand core.
[0006]
The reason why the average particle size of the small-diameter core sand is 100 to 150 μm is that if it is smaller than 100 μm, it becomes difficult to apply a binder resin such as a phenol resin, and if it is larger than 150 μm, the shrinkage of the sand core increases. Because.
The reason why the average particle size of the large-diameter core sand is 350 to 450 μm is that if the average diameter is smaller than 350 μm, the space between the large-diameter core sands becomes small, and the thickness of the mold filling layer filled in the space becomes small. Is more likely to occur, and if it is larger than 450 μm, the smoothness of the surface of the sand core decreases.
The thickness of the outer shell is preferably 5 mm or less, and more preferably 3 mm or less, from the viewpoint of reducing shrinkage of the sand core.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
It is preferable that the particle size distribution of the small-diameter core sand and the large-diameter core sand is narrow, but as the small-diameter core sand, it is sufficient that the particle size falls within the range of 50 to 200 μm. Is sufficient if the particle size falls within the range of 200 to 600 μm. When the adjacent large-diameter core sands are in contact with each other, the coating mold to be filled in the space between the large-diameter core sands is formed from the radial outer edge of the large-diameter core sands in the contact portion. In the case where the large-diameter core sand is separated and has a gap, the mold is applied not only to the space up to the contact portion but also to the space inside the gap and the gap. Can be filled.
[0008]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
As shown in FIGS. 1 and 2, a sand core 1 is formed from a core 3 formed from a small-diameter core sand 2 having an average particle diameter of 120 μm, and a large-diameter core sand 4 having an average particle diameter of 400 μm. A mold layer 7 is applied to a core body 6 composed of an outer shell 5 covering the core 3 and molded. As shown in FIG. 3, the small-diameter core sand 2 forming the core portion 3 is distributed in a mountain shape having a single peak in a range from about 90 μm to about 170 μm, and the large-diameter core sand forming the outer shell portion 5. The child sand 4 is distributed in a mountain shape having a single peak in a range from about 280 μm to about 520 μm.
As shown in FIG. 2, the coating layer 7 applied to the surface of the core body 6 is filled in the space 8 between the adjacent large-diameter core sands 4 on the surface of the core body 6, and No. 6 is coated. For example, when adjacent large-diameter core sands 4 are in contact with each other, such as large-diameter core sand 4a and large-diameter core sand 4b, the coating layer 7 is filled in the space 8a up to the contact portion 9 thereof. When the adjacent large-diameter core sand 4 has a gap 10 such as the large-diameter core sand 4b and the large-diameter core sand 4c, the coating layer 7 forms the gap 8 and the space 8b inside the gap 10. Is also filled.
[0009]
The sand core 1 was formed in the following procedure.
A large-diameter core sand 4 coated with a phenol resin is blow-filled into a mold heated to 250 to 270 ° C., and after 10 to 15 seconds, the mold is inverted and sand is discharged to form an outer shell layer 5. After that, a small-diameter core sand 2 coated with a phenol resin is blow-filled into the mold and heated for 1 minute to mold the core body 6. Next, an aqueous mold is applied to the core body 6 to form the mold layer 7.
[0010]
The sand core 1 is set in a mold, and an aluminum casting is die-cast under the conditions of a casting pressure of 50 MPa, a plunger speed of 0.1 to 0.3 m / sec, and a casting temperature of 680 ° C., and the surface of the casting is cast. Observed. As a result, the casting surface was smooth and no insertion was observed.
[0011]
【The invention's effect】
The sand core of the present invention is formed of a core formed from a small core sand having an average particle diameter of 100 to 150 μm and a large core sand having an average particle diameter of 350 to 450 μm, and covers the core. Since the core body composed of the outer shell portion and the mold filling layer that fills the space between the large-diameter core sand adjacent to the core body surface and covers the core body, Since the sand filling rate is increased and the shrinkage of the sand core is suppressed, the dimensional accuracy of the sand core is improved, and the thickness of the mold filling layer filled in the space between the large-diameter core sand is large. In addition, casting defects such as insertion do not occur, and the quality of the casting is improved.
[Brief description of the drawings]
FIG. 1 is a sectional view of a sand core according to an embodiment of the present invention.
FIG. 2 is a partially enlarged sectional view of the sand core of FIG.
FIG. 3 is a view showing a particle size distribution of a small core sand and a large core sand forming the sand core of FIG. 1;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sand core 2 Small diameter core sand 3 Core part 4 Large diameter core sand 5 Outer shell part 6 Core body 7 Coating layer 8 Space

Claims (1)

A core comprising a core formed from a small-diameter core sand having an average particle diameter of 100 to 150 μm, and an outer shell formed from a large-diameter core sand having an average particle diameter of 350 to 450 μm and covering the core. A sand core comprising: a main body; and a coating layer that fills a space between adjacent large-diameter core sands on the surface of the core main body and covers the core main body.

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