JPH0469843B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a ceramic mold, and also relates to a ceramic injection molding method. [Prior art] Ceramic molding methods include plastic molding methods that utilize the plasticity of molding materials such as extrusion molding, slurry casting molding methods that inject a slurry made by suspending ceramic raw material powder in water into a mold, and adjusted molding methods. Dry pressure molding methods, in which powder is placed in a mold and molded under pressure, are well known. In addition to these methods, injection molding, which is often used for plastics, has recently come to be used for ceramics with irregular shapes or complex shapes. Injection molding is a plastic molding process that is mainly performed using thermoplastic resin, and is a process in which plastic raw materials that have been heated and fluidized are pressed into a cooled mold using a plunger, etc., and then cooled and solidified to form an integral piece. Up to now, various improvements have been made based on many years of experience. In addition, in recent years, a method has been developed in which ceramic powder is mixed with an organic binder, mainly water as a plasticizing medium, and this mixed raw material is cooled to give it plasticity, and then injected into a mold for molding. Some studies have also considered a method of obtaining a ceramic sintered body by removing the binder from the obtained molded body and firing it. However, in the ceramics industry, it has traditionally been believed that the fine powder used as the raw material determines the quality and properties of the final molded product, so while there has been much technological development for adjusting the raw material fine powder, there has been little research on molding methods. The current situation is that it is delayed. In recent years, it has been found that molding methods have a large effect on the quality of molded products, and molding methods are being reconsidered. In particular, the injection molding method for ceramic molding is still in its infancy and is at a stage where various improvements in injection machines, molds, etc. must be made in the future. [Problems to be Solved by the Invention] In the injection molding of ceramics, since the raw material fine powder of ceramics itself has no plasticity unlike plastic, molding materials made plastic by adding thermoplastic resin to the raw material fine powder, or A molding material (clay) obtained by adding water, proposed by the applicant in Japanese Patent Application No. 62-180584, is used for injection molding. However, these molding materials have poor fluidity compared to thermoplastic plastics, resulting in the creation of voids or non-homogeneous molding during molding. In particular, as shown in the earlier Japanese Patent Application No. 180584/1984, the properties of molding materials that mainly use water as a plasticizer are not yet clear, so it is desired to develop conditions for applying them to injection molding. Ta. In view of the above-mentioned current situation, the inventors have conducted intensive studies on homogeneously injecting a molding material into a mold in injection molding of ceramics, and have arrived at the present invention. [Means for Solving the Problems] According to the present invention, there is provided a mold for a ceramic molded article having a single wall thickness portion with a difference in wall thickness,
A mold for ceramics is provided, characterized in that an injection gate having a cross-sectional area corresponding to the shape of a molded article is disposed in a thick portion. In addition, there is a difference in wall thickness,
Provided is a mold for a ceramic molded body having a plurality of thick parts, characterized in that an injection gate having a cross-sectional area corresponding to the shape of the molded body is arranged in each part of the plurality of thick parts. . Further, according to the present invention, in a method for injection molding ceramics, a ceramic molded body having a thickness difference including a single thick part is molded, and the molded body has a shape corresponding to the shape of the molded body disposed in the thick part of the mold. Provided is a method for injection molding ceramics, characterized in that molding is performed by injecting a molding material through a gate having a cross-sectional area. In addition, in a ceramic injection molding method, a ceramic molded body having a wall thickness difference including a plurality of thick parts is molded, and the ceramic molded body has a cross-sectional area corresponding to the shape of the molded body placed in each thick wall part of the mold. Provided is a method for injection molding ceramics, characterized in that molding is performed by injecting a molding material through a gate. In the present invention, the thick wall portion and the thin wall portion refer to the diameter of the largest sphere inscribed in the molded body when the diameter of the largest sphere inscribed in the molded body is the maximum wall thickness of the molded body, and the diameter of the largest sphere inscribed in each part of the molded body is determined. The part where the diameter is 40% or more of the maximum wall thickness is called the thick wall part, and the part where the diameter is less than 40% is called the thin wall part. A molded article having a plurality of thick portions refers to a molded article having one or more of the thin portions between the thick portions. [Function] Injection molding of ceramics involves forcing a molding material from an injection molding machine into a mold such as a metal mold using a plunger, screw, or the like. A mold generally consists of a molding die and a sprue gate or an introduction section consisting of a sprue, runner and gate, which directs the molding material from the injection machine nozzle into the molding die. In this case, the introduction port, ie, the gate, into the molded body is preferably arranged in a thicker part in a mold for a ceramic molded body having different wall thicknesses. For example, when injection molding a molded body A as shown in FIG. 1a, in conventional injection molding, the sprue 1 and gate 3 are usually arranged as shown in FIG. 1a. The molding die of the present invention has an injection gate in the thick part as shown in FIG. molded. By arranging the gate on the thick wall part in this way, the resulting molded product is produced using the method described in ``Fine Ceramics Injection Molding Technology'' (published by Nikkan Kogyo Shimbun).
The occurrence of defects such as weld lines and pore entrainment due to jetting, which are observed in conventional methods, as shown in Figures 6 and 24 on page 122 and Figures 6 and 27 on page 123, can be prevented. These reasons are caused by the lack of fluidity of the material, as the molding material is injected from the thick part along the shape of the molded object, so that jetting does not occur, and the material is less likely to cool down and can maintain its fluidity for a long time. This is because weld lines can be prevented. In addition, a mold for a ceramic molded body having a plurality of thick portions with different wall thicknesses, for example molded body B shown in front and side views in FIGS. 2b and 2c, has thick portions of 4 and 4' If the sprue 1 and the gate 3 are located at two or more locations, as shown in FIG. 3', but the mold of the present invention is provided with injection gates 3 and 3' at each thick wall part 4 and 4' as shown in E, and from each injection gate to the thick wall part of the molded body. Injection mold the molding material. In this case, it is preferable to maximize the amount of molding material injected into at least one of the plurality of thick parts. This means that it is better to join the molding materials from each thick part at the thick part than at the thin part.
This is because defects such as welds can be prevented. For example, in Figure 2 E, runner 2 to gate 3
By making the diameter of the runner 2' larger than that of the runner 2' to the gate 3', or by making the distance of the runner 2 connected to the sprue 1 shorter than that of the runner 2',
The amount of injection into the thick portion 4 can be controlled to be greater than the amount of injection into the thick portion 4'. Of course, in this case, even if the runners have the same shape, there is no need to control them unless the molding material joins at the thin section. Furthermore, the introduction part of the mold of the present invention, that is, the injection sprue gate or the injection sprue, the runner, and the gate, may have a constant taper in the part or runner part continuous from the injection gate to the sprue. Particularly in the case of a sprue gate consisting of a sprue and a gate, it is preferable to have the above-mentioned taper. The taper angle may be selected appropriately depending on the molding material used, etc.
Generally it is about 2 to 10 degrees. The reason for providing the taper is to allow the injected molding material to spread from the injection molding machine nozzle through the gate into the cavity, that is, the molded body, and to allow smooth release from the mold. In the present invention, the molding material used is a mixture of ceramic raw material fine powder such as silicon nitride, silicon carbide, or inorganic oxide, and water or/and an organic binder, and is a so-called organic molding material that uses the organic binder as a plasticizer. or a molding material that mainly uses water as a plasticizer (referred to as a water-based molding material). [Example] Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 Injection molding of an organic molding material will be explained according to the process diagram shown in FIG. The raw material mixture is ceramic raw material Si ₃ N ₄ powder 100
parts by weight and 2 parts by weight of SrO ₂ powder as a sintering aid,
Mix 3 parts by weight of MgO powder and 3 parts by weight of CeO ₂ ,
It was ground to an average particle size of 0.5 μm. Then, spray drying was performed to obtain granules with an average particle size of 30 μm. The granules were pressurized at a pressure of 3 t/cm ² using a hydrostatic isostatic pressurization method. There is a method in which after pressurization, the material is crushed and the average particle size is 30 μm again (referred to as the method), and a method in which it is calcined in the atmosphere at 450°C for 5 hours and then crushed to have an average particle size of 30 μm (referred to as the method). Two methods of preparation were performed. After crushing, 100 parts by weight of the obtained powder, 3 parts by weight of binder,
15 parts by weight of a plasticizer and 2 parts by weight of a lubricant were mixed and kneaded using a kneader to obtain an organic molding material. The obtained molding material was made into pellets using an extruder. The obtained pellets were injected and filled into the molds of molded bodies A and B shown in FIG. 1a and FIGS. 2b and c, respectively, using an injection molding machine. The filling method for the molded body A was as shown in FIG. 1 (a) and (b), respectively. The angle of the sprue part in Figure 1A was 2 degrees, and the angle in B was 5 degrees. In addition, the filling method for the molded body B was carried out as shown in FIG. The taper angle of the sprue part in Figure 2C was 10 degrees, and the taper angle of the sprue part in Figure 2 was 5 degrees. In FIG. 2 E, the length and diameter of runners 2 and 2' are the same, and the taper angle is 5 degrees. In FIG. 2 E, runner 2 diameter>runner 2' diameter,
The taper angle of runner 2 is 5 degrees, runner 2'
A filling method was carried out in which the taper angle was 10 degrees and the flow rate of the molding material was controlled. A schematic diagram of each filling process is shown in FIG. 4, and the molding results are shown in Table 1. As can be seen from the schematic diagram of the filling process in FIG. 4, filling method A in which the molding material is filled from the thinner part of the molded body A is undesirable because it causes jetting of the molding material in the thicker part. On the other hand, the filling method B, in which the molding material was filled from the thick part along the shape of the molded object, did not cause jetting and was preferable because the material was filled uniformly, and as shown in Table 1, the molding yield was also improved. . Moreover, in the molded body B having a plurality of thick parts,
Filling methods c and d in which the molded body is filled from one of the thicker parts are undesirable because the other thicker part is filled from the thinner part, which causes the same problem as the filling method in b above. I understand. On the other hand, filling methods (E) and (F) in which the molding material is filled from both thick parts are preferable because the molding material is filled uniformly, and the molding yield is improved as shown in Table 1. Furthermore, compared to the filling method (E), the molding material (F) was adjusted so that the bonding was performed in the thick part, so defects were less likely to occur and the results were more favorable.

[Table] Example 2 Injection molding of a water-based molding material will be explained according to the process diagram shown in FIG. The steps of raw material preparation, mixing and pulverization, and spray drying were carried out in the same manner as in Example 1. 100 parts by weight of granules with an average particle size of 30 μm obtained by spray drying,
30 parts by weight of water, 7 parts by weight of a binder and 1 part by weight of a surfactant were mixed and kneaded in a kneader to obtain a water-based molding material. The obtained aqueous molding material was formed into a cylinder with a diameter of 52 mm and a length of 340 mm using a vacuum extruder, and the cylindrical molding material was isostatically pressurized using a rubber press at a pressure of 2.5 t/cm ² . The obtained water-based molding material is
Molded bodies A and B were injection molded in the same manner as in Example 1 using an injection molding machine. A schematic diagram of each filling process is shown in FIG. 6, and the molding results are shown in Table 2. These results show that almost the same results as the organic molding material of Example 1 can be obtained.

〔Effect of the invention〕

The present invention makes it possible to obtain a molded body without defects such as welds and pores with a high yield by providing an injection gate in the thick part of the molded body when molded bodies with different wall thicknesses are manufactured by injection molding. can. Also,
When there are a plurality of thick parts, by providing an injection gate in each thick part and performing injection molding, it is possible to similarly obtain a molded product without defects. The present invention can be applied to both so-called organic molding materials and aqueous molding materials, and is extremely useful industrially.

[Brief explanation of the drawing]

FIG. 1a is a cross-sectional view of molded body A, b and c
are a front view and a side view of molded body B, respectively.
2A and 2B are schematic diagrams of a mold for the molded body A, and FIGS. 2A, 2, and 3 are schematic diagrams of the mold for the molded body B. FIG. 3 is a process diagram of the preparation and injection molding of an organic molding material, and FIG. 4 is a schematic diagram of the injection filling process of the organic molding material. FIG. 5 is a process diagram of the preparation and injection molding of a water-based molding material, and FIG. 6 is a schematic diagram of the injection filling process of the water-based molding material. 1... Injection sprue, 2, 2'... Injection runner, 3, 3'... Injection gate, 4, 4'... Thick part of molded body B, 5... Thin part of molded body B.

Claims (1)

[Scope of Claims] 1. A mold for a ceramic molded body having a single wall thickness with a difference in wall thickness, wherein an injection gate having a cross-sectional area corresponding to the shape of the molded body is disposed in the thick wall part. A mold for ceramics characterized by: 2. A mold for a ceramic molded body having a plurality of wall thickness parts with different wall thicknesses, characterized in that an injection gate having a cross-sectional area corresponding to the shape of the molded body is disposed in each of the plurality of wall thickness parts. Molding mold for ceramics. 3. In a ceramic injection molding method, a gate having a cross-sectional area corresponding to the shape of the molded body in which the thick part of the mold is arranged, in which a ceramic molded body having a wall thickness difference including a single thick part is molded. An injection molding method for ceramics characterized by injecting a molding material through a . 4 In a ceramic injection molding method, a ceramic molded body having a plurality of wall thicknesses and a difference in wall thickness is molded, and a gate having a cross-sectional area corresponding to the shape of the molded body placed in each thick walled part of the mold. An injection molding method for ceramics characterized by injecting a molding material through a .