JPH0557395A - Method for molding ceramic mold for precision casting - Google Patents

Abstract

PURPOSE:To prevent a crack from being generated in a mold by separately molding a backup mold and a ceramic shell layer, combining the backup mold and the ceramic shell layer after executing heat treatment only to the ceramic shell layer and forming the mold. CONSTITUTION:The backup mold 7 is hardened at the room temp. with CO2 by using water glass in CO2 sand as the ordinary method. On the other hand, the primary burning and the secondary burning heat treatments are executed to the ceramic shell layer 13 at the desired temp. At last, by fitting the ceramic shell layer 13, which is heat treated, to the backup mold 7, the ceramic shell mold is formed. By this method, the crack in the backup mold can be prevented. Further, only the ceramic shell layer can be burnt at high temp. and entrapping defect of the sand into ceramic slurry is eliminated and the backup mold can be repeatedly used.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a ceramic mold,
In particular, the present invention relates to a method for producing a ceramic mold for precision casting, which is suitable for producing medium-sized and large-sized castings with high dimensional accuracy.

[0002]

2. Description of the Related Art A method of using a ceramic mold is known as one of precision casting methods. Above all, the composite mold method using a ceramic mold composed of a backup mold and a ceramic shell layer is used to cast a relatively large casting. It is used when 2 (a) to 2
(F) is an explanatory view showing a molding method of the conventional composite molding method, and the molding was performed in the following order. The backup model 3 and the flask 2 are set on the surface plate 1. (FIG. 2A) CO ₂ sand 5 is filled to mold the backup mold 7. (FIG. 2B) After the cover 8 having the CO ₂ gas blowing hole 8a is attached to the upper portion of the casting mold ₂ , CO ₂ gas is blown from the CO ₂ gas blowing hole 8a to cure the backup mold 7. (Fig. 2
(C)) After removing the backup model 3, the model 9 is set on the surface plate 1 and the backup mold 7 is covered. (Fig. 2
(D)) The backup mold 7 is placed on the model 9, and the ceramic slurry 12 is injected from the ceramic slurry inlet 10 into the gap 11 between the backup mold 7 and the model 9. (Fig. 2
(E)) When the injected ceramic slurry 12 has gelled and solidified, the model 9 is demolded and the surface of the ceramic shell layer 13 is rapidly heated (primary firing) with a burner for propane or the like, and then the ceramic mold 20 is fired at high temperature ( Secondary firing).
(Fig. 2 (f))

[0003]

However, there are the following problems in forming the ceramic mold 20 as described above. When the ceramic mold 20 is fired at a high temperature (secondary firing) at 600 to 1000 ° C., the water glass used as a binder for the CO ₂ sand 5 in the backup mold 7 undergoes a rapid heat shrinkage change and cracks in the backup mold 7. Occurs, and thus the ceramic shell layer 13 also cracks. This is because the ceramic shell layer 13 undergoes a thermal expansion change when the secondary firing temperature of the ceramic mold 20 exceeds 650 ° C., whereas the backup mold 7 has a ceramic shell layer 13 due to a rapid thermal contraction change of water glass. This is because a pressing force is generated between the backup molds 7. As a measure against the firing cracking of the backup mold 7, the secondary firing temperature is 600 ° C. or lower, for example, 500 to 60
Although a method of performing it at 0 ° C. has been proposed, although the ceramic shell layer 13 and the backup mold 7 have little thermal change in this firing temperature range, the ceramic shell layer 13 is insufficiently hardened. When the ceramic slurry 12 is poured into the cavity 11, a part of the CO ₂ sand 5 falls off from the backup mold 7 and the ceramic shell layer 13 corresponding to the molding surface is apt to have defects such as sand bite.

[0004]

In order to solve the above-mentioned problems, in the present invention, in a method for producing a precision casting ceramic mold comprising a backup mold and a ceramic shell layer, the backup mold and the ceramic shell layer are used. Were separately molded, and only the ceramic shell layer was heat treated, and then the backup mold and the ceramic shell layer were combined to form a mold.

[0005]

In the backup casting, water glass is used to mold CO ₂ sand as in the conventional case, and CO ₂ gas is circulated to cure at room temperature. The ceramic shell layer is separately molded, and after microcrazing is generated by primary firing, secondary firing is performed at a desired temperature in an electric furnace to perform heat treatment.
The ceramic shell layer is fitted to the backup mold thus formed to complete the combination. As a result, the backup mold does not have to be heat-treated together with the backup mold to heat-treat the ceramic shell layer of the ceramic mold, so that the backup mold is prevented from cracking.

[0006]

EXAMPLES The present invention will be described in detail below with reference to examples. 1 (a) to 1 (e) are explanatory views showing a molding method of the composite molding method of the present invention.

In this embodiment, the ceramic shell layer 13 and the backup mold 7 are molded separately. First, the ceramic shell layer 13 is molded in the following order. The model 9 and the flask 15 are set on the surface plate 1. The flask 15 has a similar shape to the backup model 3 which is slightly larger than the model 9, and forms a space 11 between the frame 15 and the model 9. (FIG. 1A) Next, the ceramic slurry 12 is injected from the ceramic slurry inlet 10 into the cavity 11. (Fig. 1
(B)) When the injected ceramic slurry 12 has gelled and solidified, the casting frame 15 and the model 9 are inverted to remove the model 9, and then the ceramic shell layer 13 is extracted. (Fig. 1
(C)) The surface of the obtained ceramic shell layer 13 is immediately heated rapidly by the propane burner 16 (primary firing) to generate microcrazing, and thereafter 650 to 10
High temperature heating in an electric furnace (not shown) heated to 00 ° C (2
Next firing) and completely solidified. The secondary firing temperature varies depending on the type of cast metal, and this means that the heat treatment temperature of the ceramic shell layer 13 is changed depending on the temperature at which each cast metal is cast. That is, in order to prevent casting defects due to gas generation from the ceramic shell layer 13 and obtain necessary strength, for example, the secondary firing temperature is determined as follows. A1 alloy: Casting temperature 600 to 700 ° C Secondary firing temperature 650 to 750 ° C Alloy steel: Casting temperature 1400 to 1600 ° C Secondary firing temperature 900 to 1000 ° C

The composition of the ceramic slurry 12 used in this example is shown below. Binder: Hydrolysis solution of ethyl silicate Refractory: Mixture of Zr sand and Zr flower due to fire resistance, thermal expansion and surface transferability, etc. Curing agent: 10% NH ₄ HCO ₃ solution 2-8% Addition

Apart from the molding of the ceramic shell layer 13 described above, the molding of the backup mold 7 is performed as follows. As in the conventional case, the backup model 3 and the flask 2 are set on the surface plate 1, and then CO ₂ sand 5 is filled to mold the backup mold 7. Further, CO ₂ gas is blown into the backup mold 7 to cure the backup mold 7 at room temperature. After this, the backup model 3 is removed and the backup template 7 is inverted and set. (FIG. 1D) Here, the ceramic shell layer 13 that has been subjected to the heat treatment is fitted into the backup mold 7. (Fig. 1
(E)) The composition of the backup mold 7 used in this example is shown below. Refractory: From the perspective of fire resistance and cost, a binder using chamotte sand .... Adding 4-8% of water glass

[0010]

As is apparent from the above description, in the present invention, in the method for producing a precision casting ceramic mold comprising a backup mold and a ceramic shell layer, the backup mold and the ceramic shell layer are separately provided. By performing separate molding and heat-treating only the ceramic shell layer, the backup mold and the ceramic shell layer are combined to form a mold, whereby cracking of the backup mold that occurs during heat treatment of the ceramic shell layer can be prevented. Depending on the type of cast metal, only the ceramic shell layer can be fired at a high temperature of 650 ° C. or higher. The defect of sand entrapment in the ceramic slurry is eliminated. Conventionally, after casting, the backup mold and the ceramic shell layer were collapsed to take out the product.
According to the present invention, since only the product and the ceramic shell layer can be extracted from the backup mold when the product is taken out, the backup mold can be repeatedly used several times. Such an excellent effect can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a ceramic mold making method according to the present invention.

FIG. 2 is an explanatory view showing a conventional ceramic mold making method.

[Explanation of symbols]

1 Surface Plate 2, 15 Mold 3 Backup Model 5 CO ₂ Sand 7 Backup Mold 11 Void 13 Ceramic Shell Layer 16 Propane Burner 20 Ceramic Mold

Claims (1)

[Claims] 1. A method of molding a ceramic mold for precision casting comprising a backup mold and a ceramic shell layer, wherein the backup mold and the ceramic shell layer are separately molded separately, and only the ceramic shell layer is heat treated, and then the backup mold is formed. A method for producing a ceramic mold for precision casting, comprising forming a mold by combining ceramic shell layers.