JPH0339774B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a casting mold using a core and a core used directly in carrying out this method.

(Background of the Invention) Ceramic cores used for casting are required to have a sufficiently smooth surface, high precision, and high strength. Conventional cores were formed using alumina, zircon, fused silica, etc. as aggregates, and the cores were fired and sintered individually. However, in this case, since there is a sintering process for the core, there is a problem that productivity and dimensional accuracy are poor and the cost is very high.

In addition, in the investment casting method using a core, there is a method in which the disappearing model is coated with a refractory material multiple times, but this method requires long drying times after each coating. Because of this, it takes a very long time to complete the mold.
A major problem was that productivity could not be increased.

(Object of the Invention) The present invention was made in view of the above circumstances, and provides a casting tool that significantly increases productivity and accuracy in investment casting using cores, and enables inexpensive mold manufacturing. The first objective is to provide a method for manufacturing a mold.

A second object of the present invention is to provide a core that can be used directly in carrying out this manufacturing method.

(Structure of the Invention) According to the present invention, the first object is a method for manufacturing a casting mold, which is characterized by comprising the following steps: (a) Adding an alkaline substance to a kneaded mixture of aggregate and a sodium silicate solution. A step of producing coated sand in which the aggregate is coated with sodium metasilicate produced by adding and spacing and evaporating water; (b) flowing the slurry into the core mold to coat the inner surface of the core mold; (c) filling the coated sand in the core mold; (d) filling the coated sand in the core mold; (e) removing the core from the core mold; (f) impregnating the core with a high-temperature binder having high high-temperature strength and then drying it; Step; (g) Step of positioning this core within the outer mold for the main mold, injecting the disappearing model material into the outer mold for the main mold, and forming a disappearing model by casting the core; ( h) Coating the vanishing model with slurry; (i) Placing the vanishing model coated with the slurry in a frame and filling the frame with the coated sand; (j) Passing high-temperature steam through A step of heating and curing the coated sand that will become the main mold; (k) A step of making the disappearing model disappear to form a mold consisting of the core and the main mold; (l) A step of making the core and the main mold The process of simultaneously firing: This is achieved by:

As claimed in claim 5, if the coated sand is coated with a high-temperature binder when making the coated sand, the strength during firing can be increased. As in the invention, the step of impregnating a high temperature binder (step (f) of the invention described in the first paragraph) can be omitted.

The second purpose is to add an alkaline substance to a kneaded mixture of aggregate and aqueous sodium silicate solution, melt it, and evaporate the water to coat the aggregate with sodium metasilicate to coat the inner surface of the coated sand. This is achieved by a core characterized in that a core mold on which a coating layer of slurry is formed is filled, the coated sand is heated and hardened by passing high-temperature steam, the surface is impregnated with a high-temperature binder, and the core is dried.

(Example) FIG. 1 is a process flowchart of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of each process.

First, coated sand is made by coating silica sand with sodium metasilicate. Sodium metasilicate (N _a2 O・S _i O ₂ ) itself is in the form of colorless crystals or white powder, and if it is mixed directly into aggregates such as silica sand, it is difficult to uniformly coat the surface of the silica sand. Not only that, but because this sodium metasilicate is expensive, the coated sand is also expensive. Therefore, in the present invention, a coated sand is prepared using sodium silicate which is in the form of a solution and is inexpensive (for example, No. 3 Na2 _{O.3S i} O ₂ ).

As shown in Fig. 1, the method is as shown in Fig.
2 is added little by little and kneaded, and a small amount of caustic soda (N _a OH) aqueous solution 104 is added thereto to melt the sodium silicate with an alkali. Sodium metasilicate is produced by this reaction in the presence of an alkali. Since the sodium silicate solution adheres uniformly to the surface of the aggregate, the generated sodium metasilicate also adheres uniformly to the surface of the aggregate. Note that if the high-temperature binder 106 is also kneaded, the hot strength of the molded product will be further improved. The amount of kneading of this high-temperature binder 106 is not particularly specified, and if this amount of kneading is sufficiently large, there is no need to immerse the core 18 in the high-temperature binder. In this case, it is only necessary to increase the time of immersion in the high-temperature binder. The alkaline reaction is preferably carried out with caustic soda, although other alkaline solutions can be used.

If the alkali-reacted material is heated to evaporate the moisture (Fig. 1, step 108), the dried sodium metasilicate remains on the surface of the aggregate, resulting in highly fluid coated sand. .

This sodium metasilicate has the effect of ensuring the strength of the mold at low temperatures and quickly hardening it.
As the aggregate, for example, a mixture of 90% by weight of silica sand and 10% by weight of silica flour is used. The silica sand here is JIS standard.
A grain size of about No. 7 according to G5901 (1954) is preferable.

Ethyl silicate and colloidal silica are used as the high temperature binder. This high temperature binder has the function of ensuring the strength of the mold at high temperatures. Generally, the cohesive strength of sodium metasilicate decreases rapidly when the temperature exceeds 200°C, but a high-temperature binder compensates for this decrease in the cohesive strength of sodium metasilicate and improves the strength at high temperatures. The amount of high-temperature binder mixed should be increased as the size and weight of the mold increase to increase the strength of the mold at high temperatures, but it is better to keep the amount mixed as low as possible considering the mold's disintegration. desirable.

Next, a core mold 10 is prepared, and slurry (coating liquid) is poured into this mold. This slurry preferably contains a binder and filler using 50% by weight of ethyl silicate and 50% by weight of Zircon flour No. 350. After a suitable period of time has elapsed after the slurry is injected into the core mold 10, the core mold 10 is turned upside down and the slurry inside is discharged. As a result, a slurry coating layer 12 of an appropriate thickness is formed on the inner surface of the core mold 10. (Figure 2A).

Next, the already prepared coated sand 14 is inserted into the core mold 1 on which the slurry coating layer 12 is formed.
0 and is filled with vibration (step 112, Figure 2B).

High temperature steam is passed through the core mold 10 filled with the coated sand 14 as shown in FIG. 2C (step 114). For example, high-temperature steam is sent through a core-shaped blowhole, split surface, etc., or high-temperature steam is sent through an inlet of the coated sand 14. When this high-temperature steam passes through the coated sand 14, it dissolves the sodium metasilicate that coats the surface of the aggregate such as silica sand,
Allow to dry and harden. As a result, coated sand 14
and coating layer 12 are integrated and cured, and sufficient low-temperature strength is obtained.

After hardening the coated sand 14 by passing high-temperature steam in this way, the core mold 10 is divided and demolded (step 116), thereby obtaining a core 18 having a slurry coating layer 12 on its surface.

If enough high-temperature binder is added when making the coated sand 14 (step 106), it will have sufficient hot strength, but if this high-temperature binder is not added or the amount added is small, Hot strength will be insufficient. In this case, it is desirable to further immerse the core 18 in a high-temperature binder for several minutes to form a binder-impregnated layer (step
118) As this high-temperature binder, ethyl silicate or colloidal silica is used like the high-temperature binder mixed in the coated sand 10. This binder penetrates from the surface of the core 18 to an appropriate depth and has the effect of increasing hot strength.

Next, paraffin wax is applied to the core 18 obtained in this way as necessary (step
120, Figure 2D). This coating is carried out by immersing the core 18 with the coating layer 12 in paraffin wax melted at 80 to 90 DEG C. for about 10 minutes.
As a result, a wax layer 20 is formed on the surface of the coating layer 12, thereby preventing sand from falling off the coating layer 12. Furthermore, the strength of the core 18 can be increased, preventing the core from being damaged during transportation, and also preventing the core from absorbing moisture during storage. In this way, the core 18 is completed.

This core 18 is fixed inside the outer mold 22 for the main mold,
A vanishing model material such as wax or styrofoam is injected into the mold 22 to form a vanishing model 24 (step 122, FIG. 2E). Like this, core 18
A slurry coating layer 26 coated with slurry is formed on the outside of the vanishing model 24 in a state in which it has been cast (step 124, FIG. 2F).

Disappearance model 24 with core 18 cast in this way
is placed in a frame 28 that is shaped to have an appropriate distance between it and the outer surface of the disappearing model 24 (step 126), and coated sand 30 is placed in the gap between the frame 28 and the disappearing model 24. Fill (step
128). Then, in the same manner as in step 114, the coated sand 30 is heated and cured by passing high-temperature steam through it (step 130, Fig. 2G).Then, the frame mold 28 is removed (Fig. 2H), and the disappearing model 24 is removed. If the core 18 and the main mold 30A surrounding it are simultaneously fired and the mold 3
2 is completed. A casting gap 34 is formed in the mold 32, which is sandwiched between the slurry coating layer 12 on the outer surface of the core 18 and the slurry coating layer 26 on the inner surface of the main mold 30A (FIG. 2).

Next, molten metal is poured into this casting gap (step 136), and after cooling, the mold is released, and the core 1
8. Main mold 30A and coating layers 12, 26
is removed (step 138). This mold breaking is performed by removing most of the mold by physical means such as vibration or impact, and then immersing the remaining part in molten caustic soda to melt it. This results in a product 36 (Figure 2J).

In the above embodiment, the manufacturing process of the main mold 30A includes a step of impregnating it with a high-temperature binder.
118) is omitted. If sufficient high-temperature binder is kneaded in advance into the coated sand 30 used for the main mold 30A , step 118 can be omitted, but if the amount of high-temperature binder kneaded is small or not kneaded at all. In this case, it is desirable to impregnate the main mold 30A with a high-temperature binder by immersing it in a high-temperature binder in the state shown in FIG. 2H as in step 118, thereby improving the high-temperature strength.

(Effect of the invention) Invention described in claim 1 (first invention)
As described above, coated sand with high fluidity, which is made by adding an alkali substance to a mixture of aggregate and an inexpensive sodium silicate solution and melting it, is placed in a core mold whose inner surface has been coated with slurry in advance. A core is made by filling the core, heating and hardening it by passing high-temperature steam, and immersing it in a high-temperature binder.The core and the main mold are simultaneously fired. That is, this core does not need to be fired alone, but is fired at the same time as the main mold is fired. In addition, since the core and main mold are hardened using high-temperature steam, drying time can be significantly shortened, and coated sand is highly fluid, making it easy to fill the core mold with coated sand. . Therefore, the productivity of molds using this core is greatly improved. This coated sand does not require the use of expensive sodium metasilicate, making it inexpensive.

Also, since the inner surface of the core mold is coated with slurry and then coated sand is filled into the core mold, the surface of the core is covered with a coating layer of this slurry, resulting in a smooth surface. can be made into a high-precision core. Therefore, molds using this core also have high precision.

Further, as in the invention of claim 5 (second invention), when the coated sand is kneaded with a high-temperature binder in advance, the core is immersed in the high-temperature binder to impregnate it. It is possible to provide sufficient high-temperature strength without any heat loss, and it is possible to reduce the number of steps.

Furthermore, according to the invention set forth in claim 6 (third invention), it is possible to provide a core that is directly used in carrying out the manufacturing method set forth in claims 1 and 5.

[Brief explanation of drawings]

Fig. 1 is a process flow diagram of one embodiment of the present invention;
The figure is an explanatory diagram of each step. 10... Core mold, 12, 26... Slurry coating layer, 14, 30... Coated sand,
18... Core, 22... Outer mold for main mold, 24... Vanishing model, 28... Frame mold, 30A... Main mold, 32...
…template.

Claims (1)

[Claims] 1. A method for producing a casting mold, characterized by comprising the following steps: (a) Adding an alkaline substance to a kneaded mixture of aggregate and a sodium silicate solution and separating the mixture to remove moisture. Step of producing coated sand by coating the aggregate with sodium metasilicate produced by evaporation; (b) flowing slurry into a core mold to form a coating layer of the slurry on the inner surface of the core mold to remove excess (c) filling the coated sand into the core mold; (d) passing high-temperature steam through the coated sand in the core mold to heat the coated sand; (e) A step of removing the core from the core mold; (f) A step of impregnating this core with a high-temperature binder having high high-temperature strength and then drying it; (g) A step of drying this core as a main material. A process of positioning within the outer mold for a mold and injecting a dissipative model material into the outer mold for the main mold to form a dissipative model in which the core is cast; (h) coating the dissipative model with slurry; Steps: (i) Place this vanishing model coated with this slurry in a frame and fill the frame with the coated sand; (j) Heat and harden the coated sand, which will become the main mold, by passing high-temperature steam through it. (k) A step of causing the disappearing model to disappear to form a mold consisting of the core and the main mold; (l) A step of simultaneously firing the core and the main mold. 2. The method for manufacturing a casting mold according to claim 1, wherein in the step (a), the alkaline substance is a caustic soda aqueous solution. 3. The method for manufacturing a casting mold according to claim 1, wherein the aggregate is mainly composed of silica sand. 4. The method for manufacturing a casting mold according to claim 1, wherein in step (f), the high-temperature binder contains at least one of ethyl silicate and colloidal silica. 5. A method for manufacturing a casting mold characterized by comprising the following steps: (a) Adding an alkaline substance to a kneaded mixture of aggregate, sodium silicate solution, and high-temperature binder, followed by separation and evaporation of water. (b) flowing slurry into a core mold to form a coating layer of slurry on the inner surface of the core mold; (c) filling the coated sand into the core mold; (d) passing high-temperature steam through the coated sand in the core mold; (e) removing the core from the core mold and drying it; (f) positioning the core within the outer mold for the main mold and creating a disappearing model within the outer mold for the main mold; (g) coating the vanishing model with slurry; (i) placing the vanishing model coated with the slurry in a frame; and filling this frame with the coated sand; (i) heating and hardening the coated sand, which will become the main mold, by passing high-temperature steam; (j) making the disappearing model disappear, and forming the core and the main mold together. (k) A step of simultaneously firing the core and the main mold. 6 Add an alkaline substance to a kneaded mixture of aggregate and sodium silicate aqueous solution, melt it, and evaporate the water to form coated sand in which the aggregate is coated with sodium metasilicate, and a slurry coating layer is formed on the inner surface. 1. A core characterized in that the coated sand is filled into a core mold, heated and cured by passing high-temperature steam through the coated sand, and the surface is impregnated with a high-temperature binder and dried.