JPH0470122B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a ceramic injection molding method for producing injection molded products with excellent performance when injection molding ceramics. [Prior Art] Silicon ceramics such as silicon nitride, silicon carbide, and sialon are more stable at high temperatures than metals.
Because it is resistant to oxidative corrosion and creep deformation,
In recent years, research into using it as engine parts has been actively conducted. For example, radial turbine rotors made of these ceramic materials,
Compared to metal rotors, they are lightweight, can raise the operating temperature of the engine, and have excellent thermal efficiency, so they are attracting attention as automotive turbocharger rotors, gas turbine rotors, etc. 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. Finishing a material with a simple shape into a desired shape by grinding,
Needless to say, it is extremely difficult to obtain a molded article with such a complicated shape in just one molding operation. Conventionally, injection molding has been widely used as a method for manufacturing such complicated ceramic molded bodies. Ceramics injection molding is a molding method that applies plastic molding. Ceramics powder is mixed with an organic binder consisting of thermoplastic resins such as polyethylene and polystyrene, plasticizers, dispersants, wax, etc., and this mixed raw material is heated. This is a method in which the ceramic is molded to give it plasticity and then injected into a mold for molding. By degreasing the obtained sintered body and firing it, a ceramic molded body can be obtained. 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. A method of obtaining a ceramic sintered body by removing the binder from the obtained molded body and firing it has also been considered in some cases. 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. [Problems to be Solved by the Invention] However, when the temperature of the molding die is kept constant, a temperature difference occurs in the molding material between the mold entrance and the tip during injection molding, and the resulting molded product The density distribution 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., resulting in a uniform sintered body. I couldn't do 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 temperature of the molding material to be uniform. The present invention was achieved based on the discovery that the present invention can be obtained. That is, according to the present invention, in a method for injection molding ceramics, the temperature of the molded product near the molding die at the end of pressurization is measured and a temperature gradient is provided in the mold, thereby reducing the molding temperature near the molding die. Provided is a method for injection molding ceramics, characterized in that the body temperature distribution is within ±0.5°C. [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. Therefore, there are methods such as setting the temperature of the mold so that it has a gradient from the inlet to the tip, and 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), the temperature gradient of the mold is set so that x≦y≦5x. y=
The reason for the range from x to y = 5x is that the specific heat or thermal conductivity of the molding material varies depending on the type and amount of organic binder in the molding material or the type and amount of ceramic powder added. Because the shape and wall thickness are different, the molding conditions etc. are different, etc. Molding materials with high specific heat and low thermal conductivity are less affected by mold temperature, so
Even if the molding material arrival time x is long, the mold temperature difference y can be made small, for example, y=x. In addition, molding materials with low specific heat and high thermal conductivity are easily affected by mold temperature, so as molding material arrival time x increases, mold temperature difference y must be increased.
For example, y=5x. Specifically, for example, the composition of the ceramic material is ceramic powder 48~
60vol%, organic binder 52 to 40vol%, and the composition of the organic binder is a molecular weight of 10,000 to 50,000.
~15wt%, molecular weight 200-1000 is 85-97wt%, and the molding conditions are molding material temperature 60-80℃ and mold temperature 40-52℃, the 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 product becomes almost uniform within ±0.5℃ regardless of the part, making it possible to produce a homogeneous molded product and the resulting This is preferable for the subsequent production of a homogeneous sintered body. Temperature distribution of molded body is ±0.5
If the temperature exceeds ℃, the density distribution of the obtained compact becomes uneven, and as a result, the sintered compact produced by firing the compact becomes cracked, deformed, etc., and the dimensional accuracy, strength, etc. become unstable. It was not possible to obtain a uniform sintered body. In addition, the temperature distribution of the molded object near the molding die is ±
The point at which the temperature needs to be 0.5°C or higher is at the end of pressurization. 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. After setting the mold temperature and injection speed, the thermocouple for measuring the temperature of the molded object is removed and injection molding is started. The preferred 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 object constant,
The temperature of the mold is increased from the inlet to the tip. As a method of heating the mold, for example, a general heater (rod, band, 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 molding material becomes higher 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 conventionally known oxides such as alumina and zirconia, as well as nitrides such as silicon nitride, known as new ceramics, and carbides such as silicon carbide. Composite materials, etc. can be used. [Examples] Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to these Examples. Example 1 An injection molding process 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. 2 parts by weight of SrO as a sintering aid for 100 parts by weight of silicon nitride powder as a ceramic raw material;
Add 3 parts by weight of MgO and 3 parts by weight of CeO ₂ , grind and mix these to obtain a blended powder with an average particle size of 0.5 μm, and then spray dry to reduce the average particle size.
After obtaining granules of 30 μm, they were granulated by isostatic isostatic pressurization at a pressure of 2.5 ton/cm ² and crushed to obtain particles with an average diameter of 30 μm. Next, this mixed powder 100
Binder: 3 parts by weight, Wax:
15 parts by weight and 2 parts by weight of lubricant were added and kneaded to form pellets, which were then heated at a material temperature of 68°C.
Injection pressure 400Kg/cm ² , injection speed 100~300c.c./sec,
With a pressurizing time of 15 seconds, injection molding was performed in the mold shown in Figure 3 while controlling the temperature of each part A, B, and C according to the mold temperature shown in Table 1, and the length was 150 mm.
A molded body with a width of 65 mm and a thickness of 15 mm was obtained. Table 1 shows the temperature of the molded body at that time. Here, the mold shown in FIG. 3 includes thermocouples 10, 10', 10'' for controlling mold temperature, thermocouples 11, 11', 11'' for measuring molded body temperature, and heater 12, 12' and 12'' are provided to control the mold temperature and measure the temperature of the molded product. Reference numeral 13 is the gate (inlet part) of the mold, and 14, 14', and 14'' are for detecting the pressure inside the mold. Showing the sensor. The temperature and pressure sampling intervals of these sensors were 10 μsec. Next, the molded body was heated to 400 °C at a heating rate of 1 to 3 °C/h.
℃, held at that temperature for 5 hours to perform degreasing treatment, then subjected to isostatic isostatic pressurization at a pressure of 7 tons/ ^cm2 , and then heated to 1700℃ for 1 hour under a nitrogen atmosphere at normal pressure. Firing was performed to obtain a square sintered body. 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 carried out 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. A molded body with a diameter of 30 mmφ and a length of 200 mm 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 temperature control of the molding die was as shown in Table 1. Table 1 shows the dimensional accuracy and strength of the obtained sintered body. Example 3 Injection molding was carried out in the same manner as in Example 1, except that the same raw materials as in Example 1 were used, the molds shown in Figure 5 a and b were used, and the controlled temperature was changed as shown in Table 1. A turbine rotor molded body having a chip diameter of 150 mmφ and a blade height of 100 mm was obtained, 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 by manufacturing 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. As is clear from the above examples and comparative examples, the control temperature of the mold is increased from the inlet to the tip, and the temperature rise falls within the range of the temperature gradient shown in Figure 1. In this case, the temperature of the compact at the end of the pressurization will be ±0.5 at any location.
℃ or less, indicating that a sintered body with good dimensional accuracy and high strength can be obtained.

【table】

[Table] Example 4 An injection molding method using clay was carried out. below,
This will be explained according to the flow sheet of the water-based injection molding method shown in FIG. 2 parts by weight of SrO as a sintering aid for 100 parts by weight of silicon nitride powder as a ceramic raw material;
Add 3 parts by weight of MgO and 3 parts by weight of CeO ₂ , grind and mix these to obtain a blended powder with an average particle size of 0.6 μm, and then spray dry to reduce the average particle size.
Granules of about 30 μm were obtained. For 100 parts by weight of this granule, 8 parts by weight of organic binder (methylcellulose: 7 parts by weight, Cedran FF-200: 1 part by weight),
Add about 30 parts by weight of water and knead, then vacuum at 70%.
Perform vacuum soil kneading at cmHg, diameter 52 mm, length 500 mm
Obtained the right to do so. This is subjected to isostatic pressurization at a pressure of 2.5 ton/cm ² , and then left to rest overnight in a cool, dark place at a temperature of 12°C.
Kg/cm ² , injection speed 100-300 c.c./sec, gel curing time 1-3 minutes, and mold temperature shown in Table 2.
Injection molding was carried out in a mold shown in FIG. 3 having the same shape as in Example 1 while controlling the temperature of each part of B and C to obtain a molded article having a length of 150 mm, a width of 65 mm and a thickness of 15 mm. Table 2 shows the temperature of the molded body at that time. Next, the molded body is kept in a constant temperature and humidity chamber at a temperature of 60℃.
The temperature was raised to 100°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 was removed by holding at that temperature for 5 hours. Then, after performing isostatic pressurization at a pressure of 7 ton/cm ² , it was heated to 700 m
The temperature was raised to 1650°C at a rate of 1650°C and fired 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 temperature control 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 Using the same raw materials as in Example 4, injection molding was performed in the same manner as in Example 4, except that the mold shown in FIG. 4 was used and the controlled temperature was changed as shown in Table 2.
A molded body with a diameter of 30 mmφ and a length of 200 mm was obtained, and the binder was removed and fired 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 temperature control of the molding die was as shown in Table 2. Table 2 shows the dimensional accuracy and strength of the obtained sintered body. Example 6 Injection molding was carried out in the same manner as in Example 4, except that the same raw materials as in Example 4 were used, the molds shown in Figure 5 a and b were used, and the controlled temperature was changed as shown in Table 2. A molded turbine rotor having a chip diameter of 150 mmφ and a blade height of 100 mm was obtained, and the binder was removed and fired 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.
Shown below. Comparative Example 8 A sintered body of a turbine rotor was obtained by manufacturing 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. Examples 4, 5, 6 and Comparative Examples 5, 6,
7 and 8, the control temperature of the mold is lowered from the inlet to the tip, and the temperature drop is
It can be seen that when the temperature gradient is within the range shown in FIG. 1, the temperature of the compact at the end of pressurization is within ±0.5° C., and a sintered compact with good dimensional accuracy and high strength can be obtained.

【table】

[Table] [Effects of the Invention] As explained above, according to the injection molding method for ceramics of the present invention, a molded body that is homogeneous throughout can be obtained, and as a result, a homogeneous ceramic with good dimensional accuracy and high strength can be obtained. A sintered body can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the temperature gradient of the molding die in the present invention, FIG. 2 is a flow sheet showing an example of an organic injection molding method, and FIGS. 3, 4, and 5.
Figure a is a schematic diagram showing an example of temperature control in a molding die used in the present invention, and Figure 5 b is a schematic diagram of a molded body viewed from direction D in Figure 5 a.
FIG. 6 is a flow sheet showing an example of a water-based injection molding method. 10, 10', 10''...Thermocouple for mold temperature control,
11, 11', 11''...Thermocouple for measuring temperature of molded object,
12, 12', 12''...Mold warming heater, 13
...Mold gate (entrance), 14, 14', 14''
...In-mold pressure detection sensor.

Claims (1)

[Claims] 1. A method for injection molding ceramics,
By measuring the temperature of the molded object near the molding die at the end of pressurization and creating a temperature gradient in the mold, the temperature distribution of the molded object near the molding die is within ±0.5℃. An injection molding method for ceramics. 2. The ceramic injection molding method according to claim 1, further comprising controlling the injection speed of the molding material into the mold.