JPH01200907A - Method and apparatus for cast molding of powder - Google Patents

Abstract

PURPOSE:To obtain a molded body containing no air bubble, by reducing the internal pressure of a slurry tank to remove air from a slurry and subsequently casting the degassed slurry in a casting mold in a reduced pressure state. CONSTITUTION:A raw material powder such as a metal powder or a ceramic powder, a binder and an additive are charged in a slurry tank 1 from the charging port 2 thereof and a heating apparatus is operated while the slurry tank 1 is evacuated to be reduced in pressure to form the charged materials into a slurry and this slurry is heated to predetermined temp. to be stirred continuously. The slurry is continuously stirred for about 1hr under reduced pressure while being recirculated by starting a slurry pump 7 to remove the air in the slurry. Next, the valve 9 of a recirculation slurry circuit is opened to cast the slurry in a casting mold 11 and the air cylinder 13 of a mold clamping apparatus is opened and a molded body is demolded to be taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for casting metal powder or ceramic powder.

[Prior art] Perlaman molding is known as a method for molding metal powder or ceramic powder, particularly for obtaining complex molded bodies (Molding of Fine Ceramics and Organic Materials, published by CMC Co., Ltd., 1985). , this method is 2%
Ni98, Fe, metal powder such as 5US316, aluminum t.

It can be applied to the molding of a wide variety of powders, including ceramic powders such as silicon carbide, zirconia, and ferrite, and mixed powders of metals and ceramics such as tungsten carbide-cobalt and titanium carbide-nickel. The outline of the molding method is to add a binder mainly consisting of paraffin to the above-mentioned powder to form a slurry, and then press-fit this slurry into a mold for molding. Paraffin is generally used as the binder, but other substances such as stearyl alcohol and stearic acid that have low viscosity when melted and are easily solidified by cooling are also used. Small amounts of oleic acid, beeswax, etc. are also added to improve the plasticity of the slurry.

FIG. 2 is an explanatory diagram of an apparatus for the Perlaman molding method. This device is equipped with an agitator 3, which prepares a uniform slurry by mixing raw material powder and a binder such as paraffin, a slurry tank 1 for temporarily storing this slurry, and means for reducing the pressure inside this slurry tank 1. It is composed of a vacuum pump 5, an air compressor 20, which is a means for pressurizing the inside of the slurry tank 1, and a mold 11, which is equipped with a mold clamping device. Further, the slurry tank 1 and its connecting piping can be heated externally if necessary.

In order to mold powder using the device configured as described above, raw material powder, paraffin, beeswax, etc. are introduced from the inlet 2 of the slurry supply tank 1, and are stirred by the agitator 3 to form a slurry. Next, the vacuum pump 5 is started to reduce the pressure inside the C slurry supply tank 1, and air mixed in the slurry is removed. After the air in the slurry has been removed, the agitator 3
．． The vacuum pump 5 is stopped, and the air compressor fi 20 is started to pressurize the inside of the slurry tank 1. This pressurized slurry is injected into the mold 11, which is cooled by a mold clamping device installed in advance and cooled by cooling water 12.

After the slurry in the mold 11 has solidified, the air compressor 20 is stopped, the pressure in the slurry tank 1 is returned to atmospheric pressure, the mold clamping device is removed, the casting 11 is disassembled, and the molded body is produced. Get it out.

[Problems to be Solved by the Invention] However, the prior art has the following problems. The air in the slurry is removed by reducing the pressure inside the slurry tank, but since the inside of the slurry tank is pressurized during casting, the free surface of the slurry comes into contact with the pressurized air and the air is drawn into the slurry. This causes re-entrainment of air into the slurry. For this reason, the density of the cast molded body is 2 to 5% lower than the theoretical density (value calculated from the blending ratio of powder and binder and their respective true densities), and the density decrease is contained in the molded body. pores corresponding to . The formation of pores adversely affects the properties of the product.

In addition, when pouring slurry by pressurizing the inside of the slurry tank, since the slurry has a high viscosity, the surface of the slurry does not fall uniformly as the slurry is discharged, and the slurry falls at the position where it contacts the wall surface or the agitator. is delayed, and only the slurry at the top of the discharge section tends to fall faster, forming a recess on the slurry surface at the top of the discharge section. Depending on the conditions, this recess can become very deep, causing the surrounding slurry to collapse and a large amount of air to be drawn into the slurry. In such cases, the air in the cast slurry blows out through the gaps in the mold, and even though there is slurry remaining in the slurry tank, only air is sent into the mold, causing the air to flow continuously. Blowouts and casting may become impossible.

The present invention was made in order to solve the problems of the prior art, and there is no mixing of air into the slurry, and therefore no pores are generated in the molded product.
Another object of the present invention is to provide a powder casting method and an apparatus therefor, which can perform continuous and stable casting without entraining a large amount of air into the slurry during slurry casting.

[Means for Solving the Problems] The present invention involves preparing a slurry of metal powder or ceramic powder in a slurry tank, casting it into a mold under pressure, cooling and solidifying the slurry through the mold, and then removing the slurry. A powder casting method for molding powder, characterized in that the inside of the slurry tank is reduced in pressure to remove air in the slurry, and the slurry is cast into a mold while maintaining the reduced pressure state. It is a method for casting and molding a metal powder or ceramic powder, and also includes a slurry tank capable of preparing a slurry of metal powder or ceramic powder and maintaining a reduced pressure inside, a depressurizing means for reducing the pressure inside the slurry tank, and a method for depositing and transporting the slurry. This is a powder casting apparatus consisting of a pump and a mold equipped with a cooling mechanism.

[Function] If air is mixed in the slurry, it will impair the characteristics of the molded product, and if air is mixed in even in a small amount, it will increase the viscosity of the slurry, making the casting operation difficult. However, in the present invention, the air is removed by reducing the pressure inside the slurry tank, and then the slurry is sent to a mold under reduced pressure for casting, so that no air is mixed in. By keeping the degree of pressure reduction during cast molding, that is, the pressure of the atmospheric gas in the slurry tank, at 100 Torr or less and 10-' Torr or more, it is possible to obtain a molded article free from air inclusion. If the pressure in the slurry tank is 100 Torr or more, it is difficult to remove air from the slurry.Also, the lower limit of the pressure varies depending on the type of binder, slurry concentration, etc., but under all conditions, the pressure is up to 10-3 Torr. Re-entrainment of air can be prevented by selecting . Another limiting condition is that in order to reduce the pressure to 10-' Torr or less, expensive equipment such as a diffusion pump must be used as a means of reducing the pressure, and in the apparatus of the present invention,
As a means for transporting the slurry to the mold, a push-in type pump is used that does not allow foreign matter such as gas or oil to be mixed in.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described based on the drawings. 1st
The figure is an explanatory view of a powder casting apparatus showing an embodiment of the present invention. In FIG. 1, 1 is a slurry tank;
A raw material inlet 2 is provided at the top, and an agitator 3 is provided inside, so that the inside can be maintained at reduced pressure. An exhaust pipe 4 is provided at the top thereof, and this exhaust pipe 4 is connected to a vacuum pump (rotary pump) 5 which is a pressure reducing means. Further, a pipe 6 is provided at the bottom of the slurry tank 1 and is connected to a slurry pump 7. A pipe 8 is provided at the discharge portion of the slurry pump 7, and a valve 9 is provided at the end of the pipe 8, which is connected to a lower pedestal 10 of the mold clamping device. A non-liquid-absorbing mold 11 made of metal is arranged on the upper surface of the lower pedestal 10 of the mold clamping device, so that slurry can be cast. Furthermore, a flow path for passing cooling water 12 is formed in the mold 11, thereby providing a mechanism for cooling the slurry in the cavity. The mold 11 is an air cylinder 1 of the mold clamping device.
3, it is tightened from above, from the lateral direction, or from both vertical and lateral directions to prevent the mold from opening due to the internal pressure of the slurry in the cavity. The piping 8 is branched before the valve 9 and is provided with a piping 14 that connects to the slurry tank 1. By providing this piping 14, the slurry sent out from the slurry tank 1 can be circulated back to the slurry tank 1. And piping 1
4 is equipped with a pressure regulating valve 15, so that the pressure at which the slurry is cast into the mold 11 can be set.

Although not shown in the drawings, it is necessary to maintain the temperature of the slurry above the melting point of the binder, so the slurry tank 1. The slurry pump 7, piping 8.degree. 14, and other equipment and piping for storing or transporting the slurry are equipped with heating devices so that they can be heated to the required temperature. Further, the pump that can be used in the device according to the present invention is a push-in type pump, and a tube pump, monopump, diaphragm pump, etc. can be applied.

Next, a method of operating the device will be explained. Slurry tank 1
Raw material powders such as metal powders and ceramic powders, binders, and additives are introduced through the inlet 2 of the machine, and the stirring fi3 is started.

The vacuum pump 5, which is a pressure reducing means, is started to exhaust the air in the slurry tank 1 to reduce the pressure, and a heating device (not shown) is operated to turn the input material into slurry and raise the temperature to a predetermined temperature. . After the slurry reaches a predetermined temperature, stirring is continued for about 3 hours. The slurry pump 7 is started, and while the slurry is circulated through the pipes 8 and 14, stirring is continued under reduced pressure for about one hour to remove air from the slurry.

Next, the mold 11 is placed on the pedestal 10 of the mold clamping device, the air cylinder 13 of the mold clamping device is set, and the cooling water 12 is passed through. Further, the pressure regulating valve 15 is adjusted to set the pressure of the circulating slurry to a predetermined value. Then, the valve 9 is opened and the slurry is poured into the mold 11. After a predetermined period of time has elapsed after casting, the valve 9 is closed, the air cylinder 13 of the mold clamping device is opened to remove the mold, and the molded product is taken out.

<Example> Using an apparatus having the configuration shown in Fig. 1, a silicon nitride-based ceramic mixed powder was cast and formed into a 70 mm x lOO
The results of producing a flat plate of mmxlOmm will be explained. As shown in Table 1, SiN4. 1000g of mixed powder containing Y2O5 and Aρ203 powder, 7g of paraffin, and 25g of beeswax
was put into slurry tank 1, and a slurry portion was prepared according to the above-mentioned operating procedure. The temperature of the slurry at the time when the slurry tank 1 was depressurized and the air in the slurry was removed was 9.
The temperature was 2°C, and the pressure inside slurry tank 1 was 0.05 Torr. This slurry is pumped into 3 kg by slurry pump 7.
The mixture was poured into a mold 11 at a pressure of /m2 to obtain a molded body.

As shown in Table 2, the density of the molded body was a value consistent with the theoretical density.

(Comparative Example) The following flat plate molded body was produced using the same raw materials as in the example using a prior art apparatus having the configuration shown in FIG.

70mmX100mmX10mm The removal of air in the slurry was the same as in the example, the temperature of the slurry was 92°C, and the pressure inside the slurry tank 1 was 0.05To.
I went by rr. Then, the air compressor 20 was started to increase the pressure in the slurry tank 1 to 3 kg/m'', and the slurry was cast into the mold 11 at this pressure to obtain a molded body.The density of this molded body is shown in Table 2. As shown, 96 for the theoretical density
%Met. In addition, during the slurry casting process, air was frequently drawn into the slurry from the time when the slurry in the slurry tank 1 was reduced to about 1/2, making stable casting operation difficult.

Table 1 Table 2 [Effects of the Invention] In the present invention, the slurry is sent to the mold while the pressure inside the slurry tank remains reduced to carry out casting, so air is not mixed into the slurry and the pores are reduced. It is possible to obtain a molded body without any oxidation. In addition, when the slurry in the slurry tank decreases during the process of casting, even if only the slurry near the top of the discharge port falls quickly and a recess is formed on the slurry surface, the inside of the slurry tank is maintained at a reduced pressure. Therefore, there is no trapped air, and continuous and stable casting can be performed.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a powder casting apparatus showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram of a conventional apparatus. DESCRIPTION OF SYMBOLS 1... Slurry tank, 5... Vacuum pump, 7... Slurry pump, 11... Mold, 12... Cooling water.

Claims (2)

[Claims] (1) Powder casting forming by preparing a slurry of metal powder or ceramic powder in a slurry tank, casting it into a mold under pressure, cooling and solidifying the slurry through the mold, and then removing it from the mold. A powder casting method, characterized in that the inside of the slurry tank is reduced in pressure to remove air in the slurry, and the slurry is poured into a mold while maintaining the reduced pressure state. (2) A slurry tank capable of preparing a slurry of metal powder or ceramic powder and maintaining a reduced internal pressure, a decompression means for reducing the internal pressure of the slurry tank, a pump for transporting the slurry, and a cooling mechanism. A powder casting molding device consisting of a mold provided.