JPH02171205A - Injection molding method of ceramics - Google Patents

Abstract

PURPOSE:To obtain a homogeneous molded body, by controlling a temperature distribution of the molded body in the vicinity of a molding mold at the time of completion of pressurization so that the same falls within a specific temperature range. CONSTITUTION:In the title method, a temperature distribution of a molded body in the vicinity of a molding mold at the time of completion of pressurization is so controlled that the same falls within the specific temperature + or -0.5. Therefore, a temperature gradient of the mold is set up so that a range of a formula x<=y<=5x is imparted when an arrival time of a molding material extending from an inlet part of the mold to a temperature measuring part and a temperature difference of the mold extending from the inlet part of the mold to the temperature measuring part are made respectively x (sec) and y( deg.C). When the temperature gradient is set up like this, a temperature in the vicinity of the injection-molded body becomes almost uniform so as to fall within the temperature + or -0.5 deg.C irrespective of a part, a homogeneous molded body and sintered body following to the molded body are obtained and a high- strength ceramic sintered body whose dimensional accuracy is favorable is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for injection molding ceramics.
This invention relates to a ceramic injection molding method for producing injection molded products with excellent performance.

[Prior Art] Silicon ceramics such as silicon nitride, silicon carbide, and sialon are more stable at high temperatures than metals, and are less susceptible to oxidative corrosion and creep deformation, so in recent years, research has been conducted into using them as engine parts. It is actively carried out. For example, radial turbine rotors made of these ceramic materials are lighter than metal rotors, can raise the operating temperature of the engine, and have excellent thermal efficiency, so they are used in automobile turbocharger rotors, gas turbine rotors, etc. is attracting attention as

Since such a turbine rotor has blades with a complicated three-dimensional shape, it is possible to use a simple sintered material such as a rod-like or square-like material such as a dense silicon nitride or silicon carbide sintered body. It goes without saying that it is nearly impossible to finish a material with a simple shape into a desired shape by grinding, but it is also nearly impossible to obtain a molded object with such a complex shape in just one molding operation. is extremely difficult. Conventionally, injection molding has been widely used as a method for manufacturing such complex ceramic molded bodies.

The injection molding method for ceramics is a molding method that applies plastic molding, and uses ceramic powder, polyethylene,
A method in which an organic binder consisting of a thermoplastic resin such as polystyrene, a plasticizer, a dispersant, a wax, etc. is mixed, the mixed raw material is heated to give it plasticity, and the mixture is injected into a mold for molding. A ceramic molded body can be obtained by degreasing the obtained molded body and firing it.

According to this molding method, a complex part that would otherwise require a considerable number of man-hours can be quickly and precisely molded with a small finishing allowance in one operation.

In such conventional injection molding methods, molding is usually carried out by keeping the mold temperature constant from the inlet to the tip.

[Problem to be solved] However, if the temperature of the molding die is kept constant, a temperature difference will occur in the molding material between the entrance and the tip of the mold during injection molding, and the resulting molded product will be affected. The density distribution of the molded body becomes uneven, and as a result, cracks or deformations occur in the sintered body produced by firing the molded body, resulting in uneven dimensional accuracy, strength, etc., making it difficult to produce a uniform sintered body. I couldn't get it.

[Means for Solving the Problems] Therefore, as a result of intensive research in order to solve the above-mentioned conventional problems, the present inventors created a temperature gradient in the molding die to control the molding material at a uniform temperature. We have discovered that it is possible, and have arrived at the present invention.

That is, according to the present invention, a method for injection molding ceramics is characterized in that the temperature distribution of the molded body near the molding die at the end of pressurization is controlled to be within ±0.5°C. A method of injection molding ceramics is provided.

[Function] In the present invention, the temperature distribution of the molded article near the molding die at the end of pressurization is controlled to be within ±0.5°C. There are two methods, such as a method of setting a slope from the tip to the tip, and a method of controlling the speed at which the molding material is filled into the mold (injection speed). As a specific example of the present invention, as shown in FIG. When the difference is y ('C), X≦y≦5
Set the temperature gradient of the mold to be within the range of x *'/
The reason for the range from = Because the shape and wall thickness of
■Because the molding conditions etc. are different, etc. Since a molding material with a large specific heat and a low thermal conductivity is not easily affected by the mold temperature, the mold temperature difference y can be small even if the molding material arrival time X is long, for example, y=x. Also, molding materials with low specific heat and high thermal conductivity are easily affected by the mold temperature, so if the molding material arrival time X becomes longer, the mold temperature difference y must be increased. Become.

Specifically, for example, the composition of the ceramic material, ceramic powder 48-60vol%, organic binder 52-40%
vo1%, and the composition of the organic binder has a molecular weight of 10,000 to 50,000 or 3 to 15 wt%, and a molecular weight of 200 to 100.

85 to 97 wt%, and when the molding conditions are a molding material temperature of 60 to 80°C and a mold temperature of 40 to 52°C, a range of X≦y≦5x is preferable.

When the mold temperature gradient is set as described above, the temperature near the mold of the injection-molded molded product becomes almost uniform within ±0.5°C regardless of the part, making it possible to produce a homogeneous molded product. This is preferred for the subsequent production of a homogeneous sintered body. If the temperature distribution of the molded body exceeds ±0.5°C, the density distribution of the molded body obtained will become uneven, and as a result, the sintered body produced by firing the molded body will have more racks and deformation. etc., resulting in nonuniform dimensional accuracy, strength, etc., and it was not possible to obtain a uniform sintered body.

Also, the temperature distribution of the molded product near the molding die is ±0.5°.
The point at which it is necessary to be at least C is when the pressurization ends.

Generally, in injection molding, after filling the molding material, high pressure is applied for a predetermined period of time, and then the molded object is held at low pressure for a predetermined period of time in order to impart a shape to the molded object or to prevent defects such as sink marks occurring inside the molded object. The term "completion of pressurization" refers to the time of completion of the high-pressure pressurization process that is carried out for the predetermined period of time.

The preferable temperature conditions for the mold as described above are as follows: In the injection molding method using an organic binder, in which a large amount of organic binder such as a binder, wax, lubricant, etc. is added to the raw material blended powder and kneaded, the injection molding material Since the temperature is higher than the mold temperature, the molding material is cooled as it goes from the inlet to the tip, and the temperature of the molded body also decreases as it goes from the inlet to the tip. In order to compensate for this and keep the temperature of the molded body constant, the temperature of the mold is increased from the inlet to the tip. As a method for heating the mold, for example, a general heater (rod, hand, etc.) may be used, or a liquid (water, oil) may be used.

In addition, in injection molding methods that use clay made by adding a small amount of organic binder and mainly water to the raw material blended powder, the temperature of the clay (molding material) is lower than the mold temperature. The temperature of the molding material increases from the inlet to the tip.

In order to compensate for this and keep the temperature of the molded product constant, the temperature of the mold is lowered from the inlet to the tip. The ceramic powder used in the present invention includes:
In addition to conventionally known resistant materials such as alumina and zirconia, nitrides such as silicon nitride, known as so-called new ceramics, carbides such as silicon carbide, and composite materials thereof can be used.

[Examples] The present invention will be explained in more detail based on Examples below.
The present invention is not limited to these examples.

(Example 1) An injection molding method using an organic binder was carried out. Hereinafter, a description will be given according to a flow sheet showing an injection molding method using an organic binder shown in FIG.

To 100 parts by weight of silicon nitride powder as a ceramic raw material, 2 parts by weight of SrO, 3 parts by weight of MgO+, and 3 parts by weight of CeO2 as sintering aids were added, and these were pulverized and mixed to obtain an average particle size of 0.5 pm. After preparing a blended powder and then spray drying to obtain granules with an average particle size of 30 m, 2.
The pellets were granulated by isostatic isostatic pressurization at a pressure of 5 ton/cm2, and the pellets were crushed to obtain particles with an average particle size of 30 gm.

Next, to 100 parts by weight of this mixed powder, binder: 3
parts by weight, wax = 15 parts by weight, and lubricant: 2 parts by weight were added and kneaded to form a pellet.Then, this was heated at a material temperature of 68°C, an injection pressure of 400 kg/cm2, and an injection speed of 100 to 300 cc/sec. After 15 seconds of pressure time,
Injection molding was performed in the molding die shown in Figure 3 while controlling the temperature of each part A, B, and C according to the mold temperature shown in Table 1 to produce a molded product with a length of 150 mm, width of 65 mm, and thickness of 15 mm. Obtained. Table 1 shows the temperature of the molded body at that time.

Here, the mold shown in FIG. 3 includes a thermocouple 10 for mold temperature control.
．． 10', 10'', thermocouple for measuring temperature of compact 11.11
', 11'' and mold warming heater 12.12', 1
2" is provided to control the mold temperature and measure the temperature of the molded product. 13 is the gate (inlet part) of the mold;
4.14'14'' indicates the pressure detection sensor inside the mold.The temperature and pressure sampling interval of these sensors is 10
It was conducted in Le sec.

Next, the molded body was heated to 400°C at a heating rate of 1 to 3°C/h.
Then, the temperature was raised, held at that temperature for 5 hours to perform degreasing treatment, then hydrostatically isostatically pressurized at a pressure of 7 ton/cm2, and then heated at 1700°C under a nitrogen atmosphere at normal pressure for 1 hour. A square sintered body was obtained by firing for a time.

Table 1 shows the dimensional accuracy and strength of the obtained sintered body.

(Comparative Examples 1 and 2) A molded body was produced under the same conditions as in Example 1, except that the control temperature of the molding die was set to the conditions shown in Table 1, and a rectangular sintered body was obtained. Table 1 shows the dimensional accuracy and strength of the obtained sintered body.

(Example 2) Injection molding was performed in the same manner as in Example 1, except that the same raw materials as in Example 1 were used, the mold shown in FIG. 4 was used, and the controlled temperature was changed as shown in Table 1. conduct, diameter 301mφ,
A molded body with a length of 200 cm was obtained, and further degreased and fired in the same manner as in Example 1 to obtain a round bar-shaped sintered body. Table 1 shows the dimensional accuracy and strength of the obtained sintered body.

(Comparative Example 3) A round bar-shaped sintered body was obtained by manufacturing under the same conditions as in Example 2 except that the control temperature of the molding die was changed to the conditions shown in Table 1. Table 1 shows the dimensional accuracy and strength of the obtained sintered body.
Shown below.

(Example 3) Same as Example 1 except that the same raw materials as in Example 1 were used, the molds shown in FIGS. 5(a) and 5(b) were used, and the controlled temperature was changed as shown in Table 1. A turbine rotor molded body having a tip diameter of 150 mφ and a blade height of 100 ts was obtained by injection molding according to the method, and further degreased and fired in the same manner as in Example 1 to obtain a turbine rotor sintered body. Table 1 shows the dimensional accuracy of the obtained sintered body.

(Comparative Example 4) A sintered body of a turbine rotor was obtained under the same conditions as in Example 3 except that the control temperature of the molding die was set to the conditions shown in Table 1. Table 1 shows the dimensional accuracy of the obtained sintered body.

If the temperature rise falls within the temperature gradient range shown in Figure 1, the temperature of the compact at the end of pressing will be within ±0.5°C at any location, and the dimensions will be within ±0.5°C. It can be seen that a sintered body with good precision and high strength can be obtained.

(Hereafter, blank spaces) As is clear from the above Examples and Comparative Examples, an injection molding method was carried out in which the temperature control of the mold was changed from the inlet to the tip (Example 4). The following will explain the flow sheet of the water-based injection molding method shown in FIG.

For 100 parts by weight of silicon nitride powder as a ceramic raw material, SrO: 2 parts by weight and CEO2: 3 as sintering aids.
parts by weight and pulverized and mixed to obtain an average particle size of 0.6.
A blended powder of JLm was prepared, and then spray-dried to obtain granules with an average particle size of about 30 gm. To 100 parts by weight of the granules, 8 parts by weight of an organic binder (methyl cellulose near weight, Cedran FF-200: 1 part by weight) and approximately 30 parts by weight of water were added and kneaded, and then kneaded at a vacuum degree of 70.
Vacuum soil kneading was performed at cmHg, and the diameter was 52 mm and the length was 50 mm.
A clay of 0.0 cm was obtained. This was subjected to hydrostatic isostatic pressurization at a pressure of 2.5 ton/c 2, then aged overnight in a cool, dark place at a temperature of 12°C, and then molded at a clay temperature of 12°C and an injection pressure of 1.
50-300kg/cm2, injection speed 100-300
cc/sec, gel curing time is 1 to 3 minutes, and the temperature of each part of A, B, and C is controlled according to the mold temperature shown in Table 2. injection molded, length 150m1z, width 65mm, thickness 15mm
A molded body was obtained. Table 2 shows the temperature of the molded body at that time.

Next, the molded body was placed in a constant temperature and humidity chamber to increase the temperature from 60°C to 10°C.
The temperature was raised to 0°C, the humidity was lowered from 98% to 20% and dried, then the temperature was raised to 500°C at a heating rate of 50°C/h, and the binder After removal and isostatic isostatic pressurization at a pressure of 7 ton/c+*2, the sample was heated at 700°C/in a nitrogen atmosphere at normal pressure.
The temperature was raised to h''??1650''C, and firing was performed at that temperature for 1 hour to obtain a square sintered body. Table 2 shows the dimensional accuracy and strength of the obtained sintered body.

(Comparative Examples 5 and 6) A rectangular sintered body was obtained under the same conditions as in Example 4 except that the control temperature of the molding die was set to the conditions shown in Table 2. Table 2 shows the dimensional accuracy and strength of the obtained sintered body.

(Example 5) Example 4 except that the same raw materials as in Example 4 were used, the mold shown in FIG. 4 was used, and the controlled temperature was changed as shown in Table 2.
Injection molding was carried out in the same manner as in Example 4 to obtain a molded body having a diameter of 30 mm and a length of 2005 m, and the binder was removed and sintered in the same manner as in Example 4 to obtain a round bar-shaped sintered body. Table 2 shows the dimensional accuracy and strength of the obtained sintered body.

(Comparative Example 7) A round bar-shaped sintered body was obtained by manufacturing under the same conditions as in Example 5 except that the control temperature of the molding die was set to the conditions shown in Table 2. Table 2 shows the dimensional accuracy and strength of the obtained sintered body.
Shown below.

(Example 6) Same as Example 4 except that the same raw materials as in Example 4 were used, the molds shown in FIGS. 5(a) and (b) were used, and the controlled temperature was changed as shown in Table 2. A molded turbine rotor having a tip diameter of 150 mmφ and a blade height of 100 cm was obtained by injection molding using the same method as in Example 4, and the binder was removed and sintered in the same manner as in Example 4 to obtain a sintered turbine rotor. Table 2 shows the dimensional accuracy of the obtained sintered body.

(Comparative Example 8) A sintered body of a turbine rotor was obtained under the same conditions as in Example 6 except that the control temperature of the molding die was set to the conditions shown in Table 2. Table 2 shows the dimensional accuracy of the obtained sintered body.

From the above-mentioned Example 4.5.6 and Comparative Example 5.6.7.8, the control temperature of the mold is lowered from the inlet to the tip, and the temperature drop is caused by the temperature gradient shown in Figure 1. If the temperature is within the range of ±0.
It can be seen that the temperature is within 5°C, and a sintered body with good dimensional accuracy and high strength can be obtained.

(Hereinafter, blank space) [Effects of the Invention] As explained above, according to the injection molding method for ceramics of the present invention, a molded product that is homogeneous throughout can be obtained, and as a result, a molded product with good dimensional accuracy, high strength, and uniformity can be obtained. It is possible to obtain a ceramic sintered body.

[Brief explanation of the drawing]

Figure 1 is a graph showing the temperature gradient of the molding die in the present invention, Figure 2 is a flow sheet showing an example of an organic injection molding method, and Figures 3, 4, and 5 (a) are respectively FIG. 5(b) is a schematic diagram showing an example of temperature control in a molding die used in the present invention, FIG. 5(b) is a schematic diagram of a molded article seen from direction D in FIG. It is a flow sheet showing an example of a molding method. 10.10', 10''...Thermocouple 1 for mold temperature control
1.11', 11"...Thermocouple for measuring molded body temperature, 1
2.12', 12"...Mold warming heater 13-
・・Mold gate (entrance part), 14.14'14″・・
・Mold pressure detection sensor

Claims (1)

[Claims] (1) In the method of injection molding ceramics, the temperature distribution of the molded body near the molding die at the end of pressurization is ±0.5°C.
A method for injection molding ceramics, characterized in that the injection molding method is controlled so that