JPH04253549A - Molding method of sand core - Google Patents

Abstract

PURPOSE:To lessen the generation of the defects of products in casting by preventing the accumulation of gases in a recessed part 32 of a sand core 30 without increasing the working of the sand core 30 and without limiting the shape of the cast products. CONSTITUTION:Air is blown into a point 14a to be molded with the recessed part 32 where the escape of the gases generated at the time of casting is difficult, simultaneously with blowing of molding sand, such as shell sand, into a cavity 14 for molding the sand core 30 at the time of molding the sand core 30 having the above-mentioned recessed part 32.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for molding a sand core that is placed in a mold during casting.

BACKGROUND OF THE INVENTION During casting, a sand core is generally wrapped in molten metal and reaches a high temperature, generating a large amount of gas. One means for discharging these gases from the inside of the sand core to the outside of the mold is disclosed in Japanese Patent Laid-Open No. 114554/1983. In other words, in this structure, a pipe passing through the mold is connected to a part of the sand core, and during casting, gases inside the sand core are discharged out of the mold through the pipe. However, in this publication, since the pipe crosses the cavity for casting products between the mold and the sand core, the shape of the product cast in this cavity is limited.

[0002] Also in the technique disclosed in the above-mentioned publication, if the sand core has a recess from which it is difficult for gases to escape, gases may accumulate there and cause defects in the cast product. Therefore, when the sand core has such a recess, it has been proposed to form gas holes 54 that penetrate above and below the recess 52 after molding the sand core 50, as shown in FIG. There is.

0003

In the sand core 50 shown in FIG. 9, gases that collect in the recess 52 escape through the gas hole 54, but the molten metal also escapes through the gas hole 54.
I get into it. Therefore, the gas holes 54 cannot be used unless the shape of the cast product is changed. Furthermore, when molding the sand core 50, it is necessary to open the gas holes 54 after firing the molding sand, which increases the number of steps.

[0004] The technical problem of this invention is to reduce the bulk density of the part of the sand core where the recesses are formed to improve the passage of gases generated during casting, thereby increasing the amount of processing required for the sand core. The object of the present invention is to reduce the occurrence of defects in cast products caused by gases being collected in the recesses without limiting the shape of the cast products.

[0005]

[Means for Solving the Problems] Therefore, the method for molding a sand core according to the present invention is a method for molding a sand core having a concave portion from which it is difficult for gases generated during casting to escape. The method is characterized in that, at the same time as the molding sand is blown into the cavity, air is blown into the area where the recess is to be molded.

[0006]

[Function] According to the present invention, by blowing air into the part where the recess is to be formed during molding of the sand core, a large amount of air is contained in the sand in the part forming the recess, and the bulk of this part is increased. Density decreases. This improves the flow of gases generated during casting, and prevents the gases from accumulating in the recesses.

[0007]

[Embodiment] Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 9. First, FIG. 2 shows a cross section of the sand core 30 after molding. This sand core 30 is used by being placed in a mold (not shown) for the purpose of creating a hollow inner surface of a product to be cast in the mold. The sand core 30 has a recess 32 corresponding to the shape of the cast product (the shape of the hollow part). This concave portion 32 is a place where it is difficult for gases generated from the sand core 30 to escape during the above-mentioned casting, and where these gases tend to accumulate. FIG. 1 shows the sand core 30.
A core mold (mold) 10 for molding is shown in a cross-sectional view. As is clear from FIG. 1, the core mold 10 consists of an upper mold 11 and a lower mold 12, and a cavity 14 is formed by these. Further, the upper die 11 is formed with a sand blowing port 16 that communicates with the cavity 14 from the upper surface thereof. A device (not shown) that instantaneously fills the cavity 14 with a predetermined molding sand (shell sand) is connected to the sand blowing port 16 .

On the other hand, the lower mold 12 has an air blowing port 2.
2 is formed. This air blowing port 22 is connected to a nozzle block 26 that is pre-assembled into the lower mold 12.
The central part of the cavity 14, that is, the part 14 where the concave part 32 of the sand core 30 is formed through the air nozzle 24 of
It is connected to a. A device (not shown) capable of supplying compressed air is connected to the air inlet 22. Figure 3
The nozzle block 26 is shown in FIG. As is clear from these drawings, the air nozzle 2
4 is formed in the center of the nozzle block 26, and its hole diameter is set to a minute size (about 0.3 mm) so that the molding sand blown into the cavity 14 does not enter. Further, as is clear from FIG. 1, the upper mold 11 includes a lower mold 1.
An air escape port 18 is formed at a position corresponding to the second air nozzle 24. An air vent 20 is set at a portion of the air escape port 18 facing the cavity 14 to prevent the molding sand in the cavity 14 from passing through.

Next, the molding of the sand core 30 will be explained. First, the core mold 10 is heated by a heating device (not shown) for about 20 minutes.
It is heated to 50°C and the upper mold 11 and lower mold 12 are set in a closed state. Therefore, molding sand such as shell-coated sand of No. 6 silica sand is blown into the cavity 14 from the sand blowing port 16 of the upper mold 11. At the same time, air is blown from the air blowing port 22 of the lower die 12 through the air nozzle 24 into the portion 14a of the sand core 30 where the concave portion 32 is to be formed. As a result, the molding sand is instantly filled into the cavity 14, but the portion of the sand core 30 constituting the recess 32 contains a large amount of air, and its bulk density (sand filling rate) is low. Thereafter, the sand core 30 is fired for about 1 minute, and then the upper mold 11 and the lower mold 12 are opened and the sand core 30 is taken out. The blowing pressure of the molding sand and the blowing pressure of air are both about 196 KP.
a (2Kgf/cm2).

Now, when the bulk density of the sand core 30 molded by the above method was measured, the bulk density of the part constituting the concave portion 32 was 1.1 g/cm3 compared to the previous 1.2 g/cm3.
m3, a decrease in bulk density was observed. Therefore, during casting, gases generated from the sand core 30 can easily pass through the part where the recess 32 of the sand core 30 is formed.
Gases are less likely to accumulate in this recess 32.

Modifications of the nozzle block 26 are shown in FIGS. 5 to 8. First, in FIGS. 5 and 6, a plurality of air nozzles 24 are formed along the circumferential direction of a nozzle block 26. As shown in FIG. As a result, the cavity 1
Air is uniformly blown into the portion 14a of the sand core 30 where the concave portion 32 is to be formed. In this case, a counterbore portion 28 is formed on the lower surface of the nozzle block 26. This counterbore portion 28 serves to communicate each air nozzle 24 with the air blowing port 22 of the lower mold 12. The number and shape of the air nozzles 24 may be appropriately selected. For example, as shown in FIGS. 7 and 8, some of the two air nozzles 24 may be
It is also possible to set it as a. As a result, each air nozzle 24 opens at a position offset toward the center of the upper surface of the nozzle block 26.

[0013]

[Effects of the Invention] As described above, in the present invention, a large amount of air is contained in the sand in the part constituting the recess of the sand core, and the bulk density of this part is lowered, making it easier for gases to pass through. The occurrence of defects in cast products due to the accumulation of gases in these recesses is reduced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a core mold (mold) for molding a sand core.

FIG. 2 is a sectional view of the sand core after molding.

FIG. 3 is an enlarged sectional view of the nozzle block.

FIG. 4 is a plan view of the nozzle block.

FIG. 5 is an enlarged sectional view showing a modified example of the nozzle block.

FIG. 6 is a plan view of the nozzle block of FIG. 5;

FIG. 7 is an enlarged sectional view of an example in which the nozzle block is further modified.

8 is a plan view of the nozzle block of FIG. 7. FIG.

FIG. 9 is a sectional view of a conventional sand core.

[Explanation of symbols]

14 Cavity 16　Sand blowing port 22 Air inlet 30 Sand core 32 Recess

Claims (1)

[Claims] 1. A method for molding a sand core having a recess from which it is difficult for gases generated during casting to escape, wherein the recess is molded at the same time as molding sand is blown into a cavity for molding the sand core. A sand core molding method characterized by blowing air into the areas where the sand cores are formed.