JPH05285589A - Production of shell core - Google Patents

Abstract

PURPOSE:To prevent the degradation in a sand discharge rate at the time of production of the shell core by cooling the discharged shell sand to a specific temp. and reusing the sand. CONSTITUTION:The shell sand is blown into a metallic mold and is calcined by which the shell sand is cured inward from the surface in contact with the metallic mold; thereafter, the internal uncured shell sand is discharged. The discharged shell sand is cooled to the temp. exceeding room temp. and below room temp. +10 deg.C and is reused. The melt sticking of the shell sand decreases to approximately the same level as the fusibility of the fresh sand and, therefore, the sand discharge rate does not fall. About the same sand discharge rate is thereby obtd. in spite of repetitive use. The formation of the cured layer to a smaller thickness is possible and the collapsing property of the shell core is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a shell core for forming a hollow portion in a casting.

[0002]

2. Description of the Related Art As is well known, a core is used when forming a hollow portion in a casting. And this core uses shell sand which made resin a binder, and the shell core shape | molded by the shell machine is used often. That is, the core molding die attached to the shell machine is 200 to 300
The mixture is heated to 0 ° C., shell sand is blown into the heated mold through a blow head of a shell machine, and firing is performed in the mold.

By this firing, the shell sand hardens inward from the surface in contact with the inner surface of the mold, so when the shell sand is hardened to the required thickness, the firing is stopped, and the uncured portion inside the hardened portion is uncured. The shell sand of is discharged from the discharge port by tilting the mold. Then, the discharged shell sand (hereinafter referred to as "sand discharge") is returned to the sand tank of the shell machine, and the shell core is manufactured as described above together with fresh sand (unused shell sand) separately supplied to this sand tank. Use again (repeat) to do.

[0004]

However, it is desirable that the thickness of the hardened portion of the shell core is thin as far as the strength required during casting can be obtained. This improves the disintegration of the shell core during sand removal after casting, and increases the sand removal rate (ratio (%) of the weight of discharged sand to the weight of blown shell sand) to remove sand. This is for the purpose of improving efficiency and reducing shell sand consumption. And, in particular, when casting a light alloy casting, it has been considered to increase the amount of sand discharged during shell core production.

However, when the shell sand is reused repeatedly, the temperature of the discharged sand is high (about 10
Even when it is returned to the sand tank, it is still considerably high at 45 to 50 ℃, and new sand (room temperature (about 25 ℃))
The temperature of the shell sand becomes high even if mixed with a certain temperature). And when the temperature of the shell sand becomes high,
The shell sands tend to fuse together. That is, when the shell core is manufactured by a shell machine, the work temperature is controlled by setting the mold heating temperature and the holding time after the shell sand is blown according to the shape, size, etc. of the shell core. As described above, when the temperature of the shell sand rises and it becomes easy to fuse with each other, when the fusion starts early and reaches the set time, a hardened layer thicker than the designed thickness is formed.

When the thickness of the hardened layer is increased, the sand removal rate is reduced and the shell core disintegration property during sand removal is deteriorated. It is an object of the present invention to solve the above-mentioned problems, to improve the sand removal rate by thinning the hardened layer, and to provide a production method capable of obtaining a shell core having good disintegration property. is there.

[0007]

The first constitution of the method of the present invention for achieving the above object is to blow shell sand into a mold for core molding which is mounted on a shell machine and heated, and the shell sand is blown. In a method for manufacturing a shell core, which comprises a step of firing sand to cure it inward from a surface in contact with the mold, and discharging an uncured shell sand inside,
The discharged shell sand is cooled to a temperature higher than room temperature and not higher than room temperature + 10 ° C. and reused, and the second structure is the shell sand cooled after being discharged in the first structure. Is mixed with unused shell sand and reused.

[0008]

[Function] By cooling the discharged sand to room temperature, the fusion property of the shell sand is reduced and becomes equal to that of the new sand. Therefore, it is possible to obtain a sand removal rate similar to that of fresh sand. Further, if the temperature of the discharged sand is up to 10 ° C. higher than the room temperature, the fusion property is considerably reduced and there is not much difference from the case of cooling to the room temperature, and the almost same degree of the discharged sand is obtained. It is a gift. This also applies to repeated reuse. further,
Even if the discharged sand that has been cooled to a temperature higher than room temperature and not higher than room temperature + 10 ° C. is mixed with fresh sand and reused repeatedly, the same ratio of discharged sand can be obtained.

[0009]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a front sectional view of a test shell molded product (hereinafter referred to as a test product), and FIG. 2 is a graph showing test results. First, using fresh sand at room temperature (25 ° C.), it is blown into a mold heated to 200 ° C. to form a test product 1 having the shape and dimensions (numerical values within the dimension line) shown in FIG. Test product 1
Sand properties such as fusion point transverse rupture strength and sand removal rate were measured. Next, after the discharged sand, that is, the returned sand of the fresh sand, was cooled to room temperature again, the test product 1 was molded in the same manner as in the case of the fresh sand, and the properties of the sand were measured and compared with the case of molding with the fresh sand. The results are shown in Table 1.

[0010]

[Table 1]

As can be seen from Table 1, there was almost no difference between the sand properties when the test product 1 was formed by using the new sand and the sand properties when the test product 1 was formed by the return sand of the new sand. .. That is, it was found that by cooling the discharged sand to room temperature, it can be reused repeatedly like new sand. Further, it was also found in another experiment that the sand properties were almost unchanged even when the cooling was 10 ° C. higher than room temperature. As a result, it was found that the shell core may be formed by using only the returned sand of the fresh sand, or the fresh sand and the returned sand of the fresh sand may be mixed and used. Almost the same result as the broken line A in FIG. 2 showing the sand removal rate when the product 1 was formed was obtained).

Next, after molding the test product 1 using new sand at room temperature (25 ° C.), the returned sand (exhaust sand) is not cooled but kept at room temperature in a sand tank (not shown) as usual. While mixing with fresh sand, 18 test pieces 1 were molded including molding with fresh sand (Fig. 1) (molding tact about 3
0 ″). The change in sand removal rate at this time is shown in Fig. 2 by the broken line B.
Indicate. As can be seen from Fig. 2, if the number of moldings exceeds a certain number (6 in this case) without cooling the sand, the sand removal rate decreases rapidly, and a certain number (13 in this case)
When it is above, the sand removal rate does not decrease any more, and it remains stable.

This means that when the sand discharge is used without being cooled, the temperature of the sand gradually rises and the time to start the fusion becomes shorter, and the thickness t of the hardened layer 2 when the set time is reached. Indicates that the sand gradually becomes thicker and the sand removal rate decreases. Therefore, it is understood that if the discharged sand is cooled and reused, the decrease of the discharged sand ratio can be suppressed.

[0014]

As described above, according to the present invention, it is possible to improve the collapsibility of the shell core and reduce the sand removal by suppressing the decrease of the sand removal rate during the production of the shell core and thinning the hardened layer. The work efficiency can be improved and the consumption of shell sand can be reduced to contribute to the cost reduction of castings. The discharged sand may be cooled, for example, while being transferred to a sand tank, before being mixed with fresh sand, or may be transferred to another place and separately.

[Brief description of drawings]

FIG. 1 is a front sectional view of a test product showing an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the number of molded shell cores and the sand removal rate.

[Explanation of symbols]

 1 Test product 2 Hardened layer t Hardened layer thickness

Claims (2)

[Claims] 1. After the shell sand is blown into a mold for core molding which is mounted on a shell machine and heated, and the shell sand is baked and hardened inward from the surface in contact with the mold. In the method for producing a shell core, which comprises the step of discharging the uncured shell sand inside, the shell is characterized in that the discharged shell sand is cooled to a temperature above room temperature and below room temperature + 10 ° C. and reused. Core manufacturing method. 2. The method for producing a shell core according to claim 1, wherein the shell sand cooled after discharge is mixed with an unused shell sand and reused.