JPH1110279A - Sand core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sand core which is difficult to be shrunk even if high molten metal pressure is loaded. SOLUTION: This sand core is composed of small diameter fluttery sand 1 having 90-110 μm average grain diameter and large diameter fluttery sand 2 having 280-320 μm and the mixed ratio of both fluttery sands is regulated to 20-50 wt.% small diameter fluttery sand 1 and 50-80 wt.% large diameter fluttery sand 2 to mold the sand core. In the sand core, the small diameter fluttery sand 1 is closely filled into gaps formed among the large diameter fluttery sand 2 and since the sand filling ratio is high, this sand core is difficult to be shrunk even if the high molten metal pressure is loaded at the time of casting at high pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sand core used for high-pressure casting such as molten metal forging and die casting.

[0002]

2. Description of the Related Art Conventionally, as a sand core used for casting,
A material obtained by sintering and molding a core sand having a mountain-like particle size distribution having a single peak and an average particle size of about 200 to 300 μm is used.

[0003]

However, when the above-mentioned conventional sand core is used for high-pressure casting such as melt forging or die casting, a gap is formed between the core sands forming the sand core. Therefore, when a high melt pressure is applied to the sand core, there is a problem that the core sand is pushed into the gap and the sand core shrinks. Then, this invention is made in order to solve such a problem, and makes it a subject to provide the sand core which does not contract easily even if a high molten metal pressure is applied.

[0004]

The sand core according to the present invention comprises a small core sand having an average particle diameter of 90 to 110 μm and an average particle diameter of 280 μm.
It is composed of a large core sand of up to 320 μm, and the mixing ratio of the two core sands is such that the small core sand is 20 to 50% by weight and the large core sand is 50 to 80% by weight. And The reason for setting the average particle size and the mixing ratio of the two core sands in the above ranges is that the small core sand is densely filled in the gaps formed between the large core sands during sand core molding. To do that.

When small diameter core sand and large diameter core sand are mixed,
Small-diameter core sand densely penetrates into the gaps formed between the large-diameter core sands and increases the sand filling rate of the sand cores. When I was
The shrinkage of the sand core is suppressed.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION It is desirable that the particle size distribution of the small-diameter core sand and the large-diameter core sand is narrow. However, the small-diameter core sand may have a particle size within a range of 50 to 200 μm. The large-diameter core sand may have a particle size falling within a range of 150 to 430 μm. The type of the core sand is not particularly limited, but preferably has a round particle shape and a high sand filling property at the time of core molding. For example, a flattery sand is suitable.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. Small diameter flattery sand 1 with average particle size of 106 μm
And 50% by weight of each of the large-sized flattery sands 2 having an average particle size of 300 μm to prepare mixed sand, and then 98.5% by weight of the mixed sand and 1.5% by weight of a phenol resin. The mixed sand was coated with the phenol resin, and a cylindrical core having a diameter of 100 mm and a length of 150 mm was molded at a mold temperature of 250 to 270 ° C. As shown in FIG. 1, the particle size distribution of the mixed sand has peaks at an average particle diameter of 106 μm for the small diameter fattery sand 1 and an average particle diameter of 300 μm for the large diameter fattery sand 2. The large particle size portion 1 and the small particle size portion of the large diameter flattery sand 2 have a shape overlapping each other. As shown in FIG. 2, the filling form of the two sand flutes in the sand core of the present embodiment is such that the small diameter fattery sand 1 is densely packed in the gap 3 formed between the large diameter fattery sands 2. And the sand filling rate was 63%.

After applying a mold-coating agent to the sand core of this embodiment in a thickness of 0.1 mm, the sand core is set in a mold to form a cylindrical cavity in the mold, and a casting pressure of 50 MPa. Plunger speed 0.1-0.3 m / sec, casting temperature 680
A cylindrical aluminum casting having an outer diameter of 120 mm and a length of 130 mm was die-cast under the condition of ° C., and the inner diameter of the casting was measured to calculate the shrinkage of the sand core due to the pressure of the molten metal. When the sand core does not shrink, the casting thickness is 9.9 mm
On the other hand, the thickness of the casting cast using the sand core was 10.2 mm, and the sand core of the present example contracted 0.6 mm in the diameter direction due to the pressure of the molten metal during casting.

Next, as a comparative example, an average particle size of 150 μm
98.5% by weight of a phenolic resin is mixed with 98.5% by weight of the flattery sand, and the phenolic resin is coated on the flattery sand, and the mold temperature is 250 to 270 ° C
Below, a cylindrical sand core having a diameter of 100 mm and a length of 150 mm was formed. In addition, the particle size distribution of the core sand was a mountain shape having a single peak, and the sand filling rate was 56%.

[0010] After a coating agent is applied to the sand core of this comparative example in a thickness of 0.1 mm, the sand core is set in a mold to form a cylindrical cavity in the mold, and a casting pressure of 50 MPa. Plunger speed 0.1-0.3 m / sec, casting temperature 680
A cylindrical aluminum casting having an outer diameter of 120 mm and a length of 130 mm was die-cast under the condition of ° C., and the inner diameter of the casting was measured to calculate the shrinkage of the sand core due to the pressure of the molten metal. When the sand core does not shrink, the casting thickness is 9.9 mm
On the other hand, the thickness of the casting cast using the sand core was 10.8 mm, and the sand core of this comparative example contracted 1.8 mm in the diameter direction due to the molten metal pressure at the time of casting.

From the above results, the sand core of the example has a higher sand filling rate than the sand core of the comparative example, and therefore, the sand core of the example is higher than the sand core of the comparative example. Thus, it was revealed that the amount of shrinkage due to the pressure of the molten metal was small during die casting.

[0012]

According to the present invention, the sand core has an average particle size of 90.
~ 110 μm small core sand, average particle size 280-320
μm of large-diameter core sand, and the mixing ratio of the two cores is such that the small-diameter core sand is 20 to 50% by weight and the large-diameter core sand is 50 to 80% by weight. Since the sand is densely penetrated into the gap formed between the large core sand and the sand filling rate of the sand core is increased, it does not easily shrink even when a high melt pressure is applied by pressure casting such as die casting, The dimensional accuracy of a casting cast using the sand core is improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the particle size distribution of core sand used in Examples.

FIG. 2 is a view showing a state in which the sand core of the embodiment is filled with sand.

[Explanation of symbols]

 1 small diameter flattery sand 2 large diameter flattery sand 3 gap

Claims (1)

[Claims] 1. A small core sand having an average particle size of 90 to 110 μm and a large core sand having an average particle size of 280 to 320 μm. ~ 50
A sand core, wherein the weight of the core sand is 50 to 80% by weight.