JPH0387202A - Slip casting molding process - Google Patents

Abstract

PURPOSE:To lower the viscosity of a slip, rise the gluing density of a molded material and prevent the generation of cracks by casting a slip prepared, adding an ungluing agent to a ceramic stock and another ungluing agent to a sintering stock into a mold having absorbing properties and molding. CONSTITUTION:A slip is prepared by adding an ungluing agent to ceramic stock powder and another ungluing agent to a sintering assistant respectively. When said slip is cast into a mold having absorbing properties, a solvent is absorbed into a mold leaving a solid component on the inner periphery of the mold to form a molding material, uniform and of high bulk density. In that case, ceramic powder is composed of 90wt.% of silicon nitride powder as main stock, 5wt.% of alumina as sintering assistant and 5wt.% of ytteria, and slip composition is composed of 80wt.% of ceramic powder and 20wt.% of ion exchange water to the ceramic powder. Further, 0.6wt.% of polyacryl acid ammonium is added as the ungluing agent, and 0.1wt.% of polyacryl acid olygomer is added as the ungluing agent for the sintering auxiliary material.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a slip casting method for ceramics.

The conventional slip casting molding method involves injecting a slip, in which ceramic raw material powder is dispersed in a solvent, into an absorbent mold such as plaster to absorb the solvent, and only the solid content in the slip is transferred to the inner surface of the mold. This is a molding method in which a predetermined shape is obtained by leaving a blank. Therefore, in the slip casting method, preparation of the slip is important in order to obtain a defect-free and homogeneous molded product. When preparing this slip, ceramic raw material powder is first dispersed in a dispersion medium such as water to form a slurry. During dispersion, a peptizer is used to peptize the aggregated particles of the raw material powder into primary particles. It is common to add sintering aids to promote sintering during firing (Japanese Patent Application Laid-open No. 158403/1983, Japanese Patent Application Laid-open No. 61-158403,
No. 0-176963.

(Refer to various publications such as Japanese Patent Laid-Open No. 59-213675).

Problems to be Solved by the Invention As described above, a slip to which a sintering aid is added has a higher viscosity than a slip made only of ceramic raw material powder at the same concentration. Therefore, in order to make a high-density compact, the slip raw material must be prepared with a high-concentration slip composition containing this sintering aid, and a deflocculant must be added to ensure that the finished re-slip remains stable without reducing the powder content. It was necessary to prepare it so that the viscosity was reduced.

On the other hand, in the conventional slip casting method, the amount of sintering aid is less than 0% by weight based on the main raw material. In the slurry casting method, only 0.4% by weight of ammonium salt of polyacrylic acid was added as a peptizer to the ceramic raw material powder, and no peptizer was added to the sintering aid.

Further, when a high viscosity slip is used, there is a problem that the bulk density of the resulting molded product is low and cracks are likely to occur due to drying shrinkage.

The present invention was made in view of the above circumstances, and an object thereof is to provide a slip casting molding method that can reduce the viscosity of slip to prevent molding defects, and can also obtain a high-density molded product.

Means for Solving the Problems In order to achieve the above object, the slip casting formability method of the present invention uses a slip casting method in which a ceramic raw material powder is added with a metal oxide as a sintering aid. , the slip is prepared by adding a peptizer for the ceramic raw material powder and a peptizer for the sintering aid, respectively, and the slip is poured into an absorbent mold and molded.

Effect According to the above method, the viscosity of the slip decreases because a peptizer for the ceramic raw material powder and a peptizer for the sintering aid are added to the slip used. Therefore, when performing casting molding, when this slip is injected into an absorbent mold, the solvent is absorbed into the mold and solids remain on the inner periphery of the mold, forming a homogeneous molded product with high bulk density. Ru. Therefore, cracks and deformation will not occur in the molded body.

Example An embodiment of this invention will be described below.

The ceramic powder used in the slip casting molding method contains 90% by weight of silicon nitride powder with an average particle size of 0.8 μm as the main raw material, and 90% by weight of silicon nitride powder with an average particle size of 0.8 μm as a sintering aid.
The slip composition consists of 5% by weight of alumina with a diameter of 1 μm and 5% by weight of ittria with an average particle size of 0.3 μm, and the slip composition is 80% by weight of ceramic powder and 2% by weight of ion-exchanged water.
It is 0% by weight.

Furthermore, the ceramic powder contains 0.6% by weight of polyacrylic acid ammonium salt as a peptizing agent for silicon nitride powder, which is the main raw material, and polyacrylic acid oligomer as a peptizing agent for a sintering aid. Add 0.1% by weight of
After stirring in a ball mill for 48 hours, the viscosity was measured using a Brookfield viscometer, and the results are shown in Table 1.

In addition, as a comparative example, 0.0% ammonium polyacrylate salt was added to the ceramic powder as a deflocculant for silicon nitride powder, which is the main raw material. Only 6% by weight was added and no deflocculant was added to the sintering aid, and this was stirred in a ball mill for 48 hours, and the viscosity was measured in the same manner as in the examples. The results are shown in Table 1.

Next, using the two types of slips obtained by stirring, Example and Comparative Example, a hollow round bar with an outer diameter of 50 m5φ, an inner diameter of 30 mm, and a length of 150 m was cast and left in the atmosphere for 20 days. After drying, both were inspected for the occurrence of cracks, and the results are also shown in Table 1.

As can be seen from Table 1, ammonium polyacrylate salt is added as a deflocculant for the main raw material to ceramic powder made by adding a sintering aid to the main raw material, and a deflocculant for the sintered ribs. The viscosity of the slip of the example prepared by adding polyacrylic acid oligomer as 260 cP (centipoise)
The viscosity of the slip of the comparative example in which no deflocculant for sintering aid was added was as high as 760 cP. As a result, among the molded bodies (hollow tubes) molded using both slips, cracks did not occur in the molded body using the slip of the example, but the molded body using the slip of the comparative example did not crack. In this case, cracks occurred. The relationship between slip viscosity and crack occurrence is that if the viscosity of the slip is 400 cP or less, no cracks will occur when the molded product is dried, but if the viscosity of the slip exceeds approximately 400 cP, the molded product will not be dried. It is known that cracks may occur.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, this invention involves adding a peptizer to the ceramic raw material and a peptizer to the sintering aid, and molding the slip by injecting it into an absorptive mold. By adding a deflocculant to the binder, it is possible to further reduce the viscosity of the slip, increasing the bulk density of the molded product, making it difficult for cracks to occur, and improving the yield rate of molded products. In addition, it has the effect of reducing the variation in the time for applying metal to the inner periphery of the mold, and greatly improving controllability during mass production.

Claims (1)

[Claims] In a slip casting molding method that uses a slip in which a metal oxide is added as a sintering aid to ceramic raw material powder, the slip is added with a peptizer for the ceramic raw material, which is the main raw material, and a peptizer for the sintering aid. A slip casting molding method characterized in that the slip is prepared by preparing a slip and then being molded by injecting the slip into an absorbent mold.