JPH064502B2 - Ceramics manufacturing method - Google Patents

Description

The present invention relates to a method for producing ceramics, and more particularly to a method for producing ceramics by injection molding using kneaded clay.

[Conventional technology]

Conventionally, a casting method and an injection molding method are known as molding methods for manufacturing ceramic parts having a complicated shape such as a turbine wheel.

The cast molding method is a method in which a slurry of ceramic powder is poured into a casting mold such as gypsum and solidified to obtain a molded body. The casting mold of gypsum or the like can form a complicated shape, but the precision of the mold and the precision of the molded body sometimes deteriorate. Also,
Since a large amount of water is generally used as a medium, a long time is required for molding.

The injection molding method usually involves adding 1 as a plasticizer to ceramic powder.
This is a method in which one or several kinds of thermoplastic polymers, that is, organic binders are added, mixed and heated, injected into a mold and cooled and solidified to obtain a molded body. This injection molding method can mold complicated shapes and is suitable for mass production, but in the organic binder removal so-called degreasing process, it usually requires a long time heating of 100 hours or more to prevent cracking and deformation of the molded body, Moreover, it was only applicable to thin parts. Further, there are many cracks and the like in the process of degreasing and firing the obtained molded body, and improvement has been desired.

[Problems to be Solved by the Invention]

The present invention eliminates the above-mentioned drawbacks of the prior art, obtains a molded body by injection molding using kneaded clay, removes the organic binder, reduces the number of process days in the method of manufacturing a ceramic for firing, and further comprises binder removal and firing. The aim is to improve the yield of ceramics throughout the process.

For this reason, the inventors have mainly applied water to a plasticizing medium, which has not been conventionally used for injection molding, and applied a kneaded material using an organic binder as a plasticizer to the injection molding, and have diligently studied the conventional manufacturing process. As a result, the present invention has been achieved.

[Means for Solving the Problems]

According to the present invention, there is provided a method for producing ceramics, which comprises drying a binder obtained by injection-molding a kneaded material containing a ceramic powder, a sintering aid, water and an organic binder, removing the binder, and then firing it. Therefore, there is provided a method for producing ceramics, characterized in that isostatic pressing is performed before the binder is removed.

[Work]

The present invention is injection-molded using a kneaded material obtained by adding water and an organic binder as a plasticizer to a ceramic powder such as an inorganic solid material containing a sintering aid, and the molded body has good dimensional accuracy and release yield. In the production of ceramics by manufacturing, then drying, removing the organic binder, and firing.In the conventional production of ceramics by injection molding, isostatic pressing with a rubber press or the like is performed after the step of removing the organic binder, that is, degreasing. In contrast to firing after application, hydrostatic isostatic pressing is performed before removing the organic binder. In the present invention, the yield of ceramics in the binder removal and firing process can be improved by performing isostatic pressing with hydrostatic pressure before removing the organic binder.

Ceramic powder used for the kneaded clay of the present invention, silicon carbide, silicon nitride, sialon, carbide such as boron nitride,
Any ceramic material such as a non-oxide type such as a nitride and an oxide such as zirconia may be used. The ceramic raw materials may be used alone or in combination of two or more, depending on the intended use of the obtained molded part. When a molded part to be manufactured is required to have high heat resistance and mechanical strength, such as a structural ceramic part, it is preferable to use silicon nitride as a main component.

The ceramic powder used in the present invention is (1) excellent in miscibility with water and an organic binder, formability by vacuum clay kneading, and becomes a good kneaded clay with good shape retention, (2) between powder particles Has a low slip resistance, excellent fluidity, does not cause defects such as flow patterns in the molded body, (3) does not cause defects during drying and binder removal, and does not reduce the strength of the sintered body, etc. It is better to have the requirements of. The ceramic powder satisfying these requirements is preferably particles within the range represented by the following formula.

In the present invention, the average particle diameter according to the particle size distribution of the above formula is based on the particle size distribution according to the laser diffraction method measured by Microtrack 79957-30 type particle size distribution measuring device manufactured by Leeds & Northrup. Further, the specific surface area particle diameter by the adsorption method of the above formula is obtained from the specific surface area by the BET adsorption method measured by, for example, Shimazu Seisakusho Flow Soap Model 2300 Specific Surface Area Measuring Device, based on the following equation. In this case, the density depends on the ceramic powder used, for example, silicon nitride (Si ₃ N ₄ ) is 3.18.
Is.

Specific surface area particle size by adsorption method = 6 / density / specific surface area ... The kneaded material using the ceramic powder satisfying the above formula has excellent formability, and the resulting formed body has no defects.
The sintered body has no defects. If the condition of the above formula is not satisfied, the flowability of the kneaded material is deteriorated, and the flow pattern at the time of molding remains in the molded body, or pores and cracks occur.

The sintering aid used in the present invention is alumina, magnesia, beryllia, cerium oxide, strontium oxide, titania,
Oxides such as zirconia and yttria, beryllium titanate, complex oxides such as lead zirconate titanate, mullite,
It is an oxide such as a multi-component oxide such as aluminum zirconate titanate. The sintering aid preferably has a particle shape similar to that of the ceramic powder.

The water added as a plasticizing medium to the ceramic powder is
It is 10 to 50 parts by weight with respect to 100 parts by weight of the ceramic powder in the kneaded material to be used for injection molding. When the water content is less than 10 parts by weight, the kneading property is poor and a homogeneous kneaded material cannot be obtained. When the water content exceeds 50 parts by weight, a slurry state is formed and dehydration treatment is required at the time of molding, which is not preferable.

The organic binder used in the present invention is a water-soluble or water-absorbing organic compound, for example, a water-soluble cellulose ether derivative such as methylcellulose or hydroxypropylmethylcellulose, a water-soluble polymer such as polyvinyl alcohol or polyethylene glycol, and a water-absorbing polymer of those derivatives. Using. Preferably, at least thermal gel curing (thermogel curing means, for example, the phenomenon described in "New ceramics extrusion molding using methylcellulose" in "New Ceramics Adhesive Technology Lecture" held in February 1984. Possible examples include methyl cellulose, hydroxypropyl methyl cellulose, and alkylene oxide cellulose derivatives. The organic binder improves the water retention of the kneaded material used in the present invention and acts to maintain the plasticity, and when a heat-gel curable material is used, the heat-gel is cured during injection molding to improve shape retention and release. The moldability is improved.

The content of organic binder in the kneaded clay is 10 ceramic powder.
0.1 to 15 parts by weight is preferable to 0 parts by weight. If it is less than 0.1 part by weight, the strength of the molded product is low and the shape retention is poor, and if it exceeds 15 parts by weight, the binder removal time becomes long and cracks are easily generated in the molded product, which is not preferable.

The above-mentioned ceramic powder, sintering aid, water and organic binder are mixed, then kneaded and vacuum kneaded to prepare a kneaded clay. All components may be mixed to form a kneaded clay, but it is preferable to first mix the ceramic powder and the sintering aid. In this case, the crushed ceramic powder having the above-mentioned particle shape and the sintering aid may be mixed, but the mixture of the ceramic powder and the sintering aid is crushed and mixed together to obtain the particle shape used in the present invention. It is good to say The pulverization and mixing can be carried out, for example, with an attritor by adding water using boulders such as silicon nitride.

The ground mixture of ceramic powder and sintering aid is then dried. If necessary, you may remove iron before drying. Iron removal can be performed using, for example, a wet ferro filter. The drying is preferably spray drying with a spray dryer. The treatment in the spray dryer has an advantage that granulation can be performed at the same time as drying, and the organic binder can be easily removed later. After drying, if necessary, the particles can be sized using a vibrating screen.

Water and an organic binder are added to the dried pulverized mixture, and the mixture is kneaded. The kneaded material is defoamed using a vacuum clay kneader to obtain, for example, a cylindrical kneaded material. Examples of the kneading machine for preparing kneaded clay (extruder) include a pug mill, a vacuum pug mill, an auger machine, a piston type extruder, and the like, and a kneading machine combining these may be used. A homogenous kneaded clay is usually prepared by a vacuum clay kneader, but if it is difficult to obtain a homogeneous kneaded clay, isostatically press the kneaded clay with a rubber press machine to further defoam and homogenize it. May be. The kneaded material obtained as described above is subjected to injection molding, but it may be subjected to injection molding after being aged in a dark place.

The injection molding of the present invention (for example, a vertical type, a horizontal type plunger type, and an inline screw type is used) means a mold such as a mold closed through an injection molding nozzle, that is, an injection sprue, an injection runner, and an injection gate. Or, it is carried out by injecting a kneaded material into a molding die injection introducing part and a molding body die which are composed of an injection sprue and an injection gate. Any injection molding nozzle may be used, and a known one may be used. The shape of the injection introducing portion is not particularly limited, but it is preferable to use one in which the injection sprue and the injection runner are formed in a tapered shape having a certain angle from the injection gate. Generally, the taper angle is 5 to 10 degrees.

For injection molding, the molding conditions may be selected depending on the type of kneaded clay, injection machine, molding die, and the like to be used. In the present invention, the pressure is usually 50 to 1000 kg / cm ² , and the pressure time is 1 to 200.
The injection speed may be 50 seconds to 1000 cc / sec. The kneaded clay temperature is usually 5 to 20 ° C.

The kneaded material poured into the molded body mold is formed into a molded body by the molded body mold. In this case, when the kneaded clay to which the heat gel-curable organic binder is added is used, the heat gel is cured by the action of the added organic binder. By preheating the mold to a temperature close to the heat gel curing temperature of the organic binder for heat gel curing, the shape retention of the molded body can be imparted, so mold release can be performed in a short time, and the molded body can be thermally gel cured. Since the strength is imparted to the molded article, the dimensional accuracy of the molded article is good, the handling becomes easy, and the molded article can be manufactured with high molding yield. The molding die in this case, for example, the conditions of the die,
Appropriate selection is made according to the type and amount of the added organic binder, the injection temperature and water content of the kneaded clay, the shape and size of the molded product. Generally, the temperature is (T-10) ° C to (T + 25) ° C with respect to the heat gel curing temperature T of the heat gel curable organic binder.
The mold temperature should be set within the range. For example, when methyl cellulose is used as the organic binder, the gel can be hardened by preheating and treating the mold, and the process is usually performed at 45 to 75 ° C.

The molding die preferably has a water-repellent inner surface. The water-repellent treatment preferably has a contact angle with water of about 80 ° or more. The water-repellent treatment may be silicone-treated or Teflon-treated. When these water-repellent molds are used, the dimensional accuracy of the molded product is good, the surface roughness of the molded product is small, and the separation yield is high.

After injection molding, dry, isostatically pressurize, then calcine,
After removing the water content and the organic binder, firing is performed to obtain a molded product. Drying is performed by humidity conditioning drying, dielectric drying, current drying, induction heating drying, etc. Usually, humidity conditioning drying is performed using a constant temperature and constant humidity dryer. The drying temperature varies depending on the size of the molded product and the like, but is generally 40 to 100 ° C. Drying is performed while sequentially lowering the humidity, and finally lowering the humidity to about 10%.

The dried injection-molded body is subjected to hydrostatic isostatic pressing. Hydrostatic isostatic pressing encloses a molded body in a flexible container (rubber mold) such as rubber, and applies uniform pressure to the molded body through a liquid. You can call.
The pressure applied in this isostatic pressing is 1 to 10
t / cm ² is preferable, more preferably 2.5 to 8 t / cm ^2.
Is. Water contained in the molded body is removed by drying,
The molded body became porous, and the molded body shrank by about 7% by this isostatic pressing.

In the conventional drying / degreasing process of injection molding, that is, binder removal / firing process, binder removal treatment is performed before isostatic pressing, resulting in cracks in the molded product and the yield was not high. Further, when the kneaded material used in the present invention was similarly applied, the yield was improved as compared with the conventional injection molding, but it was also insufficient. When the binder removal treatment is performed after isostatic pressing is carried out as in the present invention, no cracks are formed in the molded product, and the strength of the molded product after the binder removal treatment is the binder removal before isostatic pressing. The yield is about 3 times that of the molded product after removal of the treated binder, and the yield is further improved without the occurrence of cracks or the like during subsequent firing or the like.

After the isostatic pressing treatment, the organic binder is removed from the molded body. The removal of the organic binder depends on the type of the molded product, but is usually performed by heating the molded product at about 500 ° C. for 5 to 10 hours to remove the organic binder. After removing the organic binder, a hydrostatic isostatic pressing process may be further performed if necessary.

After removing the organic binder, the molded body is fired to obtain a sintered body.
The firing conditions are appropriately determined depending on the type of ceramics, purpose of use, and the like. For example, when manufacturing a silicon nitride sintered body,
1600 to 1800 ℃ in normal pressure firing, 17 in pressure firing
It is preferable to perform firing in a nitrogen gas atmosphere at 00 to 2000 ° C. In the case of producing a silicon carbide sintered body, it is preferable to carry out firing under normal pressure in an argon atmosphere at 1900 to 2200 ° C. Further, when producing a partially stabilized zirconia sintered body, it is preferable to perform firing in an air atmosphere at 1300 to 1500 ° C. under normal pressure.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to examples.
However, the present invention is not limited to this embodiment.

(Preparation of Kneaded Material) 100 parts by weight of silicon nitride, 2 parts by weight of strontium oxide, 3 parts by weight of magnesia, and 3 parts by weight of cerium oxide were wet-ground and mixed with an attritor. The crushed mixture after crushing had an average particle size of 0.6 μm and a specific surface area of 6.3 m ² / g. The value of the above formula in this case is 2.0 as the density of silicon nitride 3.18.
Met. The crushed mixture was deironed with a crushed wet type ferrofilter mini-shifter, and then dehydrated and dried with a spray dryer.

100 parts by weight of the dried and ground mixture obtained as described above, methyl cellulose (trade name: SM-4000) 7
Parts by weight and surfactant (trade name: Cedran FF-20
0) 1 part by weight and 30 parts by weight of water were kneaded while cooling with an open kneader. Then, using a vacuum kneader, extrude three times at a vacuum degree of 700 mmHg or more, diameter 52 mm, length 50
It was a 0 mm columnar kneaded clay. A rubber press machine was used to add pressure at 2.5 t / cm ² to obtain a homogeneous kneaded clay. (Injection molding) The kneaded material was aged in a refrigerator at 12 ° C overnight and then used for injection molding.

(1) Turbine wheel sintered body Diameter 13 shown in FIG. 2 along with the process chart shown in FIG.
A 0 mm turbine wheel sintered body was manufactured. The molded body was integrally injection-molded by the method schematically shown in FIG. The dies used were Teflon processed with a pressure of 20 μm on the inside of both the upper and lower dies, and had a contact angle with water of 105 degrees. The kneaded clay temperature was 12 ° C., the mold temperature was 60 ° C., the pressure was 300 kg / cm ² , the pressing time was 10 seconds, and the injection rate was 300 cc / sec.

After the injection molding, the molded body was taken out of the mold and dried. Dry 6
In a thermo-hygrostat heated to 0 ° C., the temperature was kept at 60 ° C. for 2 hours, then the temperature was raised at 10 ° C./hr, and the temperature was kept at 100 ° C. for 3 hours. The humidity inside the thermo-hygrostat was initially 98%, but the humidity was reduced to about 10% / hr and the humidity was dried to 20%.

After drying, the molded body was subjected to isostatic pressing with a rubber press at a pressure of 7 tons.

After the rubber press, the organic binder was removed. In the binder removal treatment, the temperature was raised in air at 50 ° C./hr and heated at 500 ° C. for 5 hours to remove the organic binder. The obtained molded body was fired. The firing was carried out by raising the temperature in a nitrogen atmosphere at 700 ° C./hr and holding at 1650 ° C. for about 1 hour to obtain a turbine wheel sintered body. The number of days required for all the above steps was 10 days. In this case, the yield through drying, binder removal and firing was 100%. The results are shown in Table-1.

[Comparative example]

A turbine wheel sintered body was obtained in the same manner as in the example, except that isostatic pressing was performed after removing the binder of the molded body. The results are shown in Table-1.

EFFECTS OF THE INVENTION According to the present invention, since water is mainly used as the plasticizing medium, the amount of the organic binder used as the plasticizer can be reduced. By using a water-soluble or water-absorbing polymer as the organic binder, preferably by injection-molding a kneaded material using a gelable water-soluble or water-absorbing polymer such as methylcellulose, drying, removing the binder, and firing. In the step of obtaining the ceramics, the hydrostatic isostatic pressing treatment is performed before removing the binder, so that the yield after removing the binder is improved to almost 100%.

In addition, molded products with multiple shapes and thick parts that could not be integrally molded by conventional injection molding were obtained by integrally injection molding with good moldability and shape retention. Can be manufactured with an extremely high yield.

Further, according to the method of the present invention, degreasing, which took a long time in the conventional injection molding, can be completed in about 2 days, and moreover, the ceramics having the same accuracy and performance as the conventional injection molded product can be obtained. You can get well. Further, in the present invention, as described above, a molded product sintered body having a wall thickness larger than that of conventional injection molding can be manufactured, and a structural ceramic component having a complicated shape can be obtained by injection molding, which is extremely useful industrially.

[Brief description of drawings]

FIG. 1 is a process block diagram of the method for producing a ceramics sintered body of the present invention. FIG. 2 is a sectional view of a turbine wheel molded body, and FIG. 3 is a schematic sectional view of an injection molding system. DESCRIPTION OF SYMBOLS 1 ... Kneaded clay, 2 ... Piston, 3 ... Cylinder, 4 ... Nozzle, 5 ... Movable plate, 6 ... Mold upper mold, 7 ... Metal lower mold, 8 ... Molded body, 9 ... Exhaust hole.

Claims (1)

[Claims] 1. A method for producing ceramics, which comprises drying a binder obtained by injection-molding a kneaded material containing a ceramic powder, a sintering aid, water and an organic binder, removing the binder, and then firing. Then, after the drying, a hydrostatic pressure isotropically applied before removing the binder.