JPH03219003A - Method and apparatus for forming with pseudo hot isostatic pressing - Google Patents

Abstract

PURPOSE:To make heat loss as less as possible and to form a product having stable quality by using an electric insulating material as powdery pressurized medium for embedding a powder formed body and embedding the heating means near the powder body in the medium. CONSTITUTION:The powder pressurized medium 5 (SiO2 particles or Al2O3 particles having spherical or almost spherical shape of about 100-300mu particle diameter) is charged into a pressurized vessel 1 with an exothermic body 3 and a sensor 4 inserted to lower part of the exothermic body 3. Successively, the powder formed body 6 is set inside the exothermic body 3, and the powdery pressurized medium 5 is packed around the circumference thereof and the pressurizing die 2 is fitted. Under this condition, the pressurization is executed with the pressurizing means from the arrow marked direction through the pressurizing die 2 and electric current is conducted to the exothermic body 3 so as to be heated to the solid-forming temp., and the forming temp. is controlled to almost the fixed temp. based on the measured temp. with the sensor 4. In this way, the temp. control of powder forming body 6 is easily executed to produce a high density sintered body.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is directed to so-called pseudo-hot isostatic pressing (hereinafter referred to as pseudo-hot isostatic pressing).
It's called IP. ) concerning improvements in the law.

(Conventional technology) Hot isostatic pressing (hereinafter referred to as HIP) is used for forming true density sintered bodies using various metal powders and manufacturing functional intermetallic compounds.
That's what it means. ) law is applied.

The HIP method uses an inert gas as a pressurizing medium, and is a method of sintering and solidifying powder molded material in a high-pressure container filled with inert gas. However, the HIP method requires an airtight high-temperature, high-pressure resistant container and a high-pressure gas generator, and has the disadvantage that the equipment is expensive and the operation takes time.

Therefore, in recent years, a pseudo-HIP method has been developed in which a conventional press device can be used as a pressurizing equipment, although it is difficult to obtain perfect isostatic pressure. In this method, a powder preheated to the sintering temperature is embedded in preheated ceramic powder (pressurizing medium) and placed in a pressurized container, and pressed against the ceramic powder in the container. This method applies a load in the same direction, densifies the powder molded material through ceramic powder, and solidifies it by sintering. Compared to the HIP method, it can reduce equipment costs, shorten operation time, and ensure a higher pressure state.
There is a point.

(Problem to be Solved by the Invention) However, the temperature during powder compaction under pressure depends on the preheating temperature of the compact and ceramic powder, and it is difficult to control the same temperature under pressure, resulting in poor product performance. Not stable. Furthermore, since the ceramic powder is taken out of the pressurized container along with the product each time it is molded, there is a problem in that heat loss is large.

The present invention was devised in view of these problems, and is a pseudo-H
The purpose is to provide an IP method and a molding device for the same.

(Means for Solving the Problems) The method of the present invention, which has been made to achieve the above object, involves embedding a powder-formed powder in a pressurized medium in a pressurized container, and heating it. In a pseudo hot isostatic pressing method in which a sintered compact at or near the true density is obtained by pressurizing the powder compacted material through the medium, an electrically insulating material is used as the powder press medium. The present invention is characterized in that the molded body is heated by a heating means buried within the medium and near the powder molding station. At this time, it is preferable to pressurize and heat under vacuum conditions.

The molding apparatus of the present invention suitable for carrying out the molding method includes a pressurized container 1 containing a powder pressurized medium 5 in which a heating means 3 is embedded, and a pressurized container 1 that is attached to the pressurized container 1. The pressurizing container 1 is provided with a pressurizing means for pressurizing the powder pressurizing medium 5 in the pressurizing container 1 through the pressurizing mold 2, and the pressurizing container 1 is disposed in a chamber 11 connected to an exhaust means. This is the structure of the invention.

(Function) The powder molded material embedded in the powder pressurized medium is heated by a heating means embedded within the medium and in the vicinity thereof. Therefore, only the portion of the powder pressurized medium near the powder molding stage is heated, resulting in less thermal energy loss, and the temperature at the powder molding stage can be easily controlled.

In addition, the temperature of the powder pressurized medium around the powder compaction is lower than that of the medium in the vicinity, so the pressure transmission performance is good.
The transmission of pressure becomes smoother, it becomes easier to obtain an isostatic pressurized state, and the shape of the powder molded product is more easily maintained. Furthermore, it is easy to take out the product after molding.

When heating and pressurizing the powder molding process, performing it under a vacuum condition promotes the evacuation of gases such as air inside the powder molding process, resulting in dense sintered crystals with a density of 99% or more, close to the true density. can be obtained easily. In addition, depending on the situation, gas such as air may be mixed into the preformed powder compact, and this may remain as voids. It is difficult to obtain a dense sintered body.

Further, according to the molding apparatus of the present invention, since the pressurized container containing the powder molding chamber is disposed in the chamber, when the gas in the chamber is exhausted by the exhaust means, the gas in the powder molding chamber is The powder is exhausted to the outside through the gap between the pressurized medium and the gap between the pressurized container and the pressurized mold. At this time, the pressure applied by the pressure means is carried by the pressurized container via the powdered pressurizing medium, so the chamber does not need to have high pressure resistance.
A simple closed container allows the pseudo-HIP method to be carried out under vacuum conditions.

(Example) In the present invention, the powder molding material to be molded is powder molded from various metal powders, ceramic powders, and mixed powders thereof by compression molding or direct powder forging using mold lubrication. . Moreover, in order to improve handling properties, it may be lightly sintered.

As the powder pressure medium, an electrically insulating material is used which does not itself sinter, does not react during powder compaction, and has a shape and particle size that allows pressure to spread uniformly. For example, spherical or approximately spherical SiO□ particles or N2O3 particles with a particle size of about 100 to 300 μm are preferable. In the case of 5iOz grains, foundry sand containing silica sand as a main component can be used.

FIG. 1 shows a molding apparatus for carrying out the present invention, and the pressurized container is generally a cylindrical container 1 with a bottom as shown in the figure. A pressure medium 5 is accommodated, and a pressure mold 2 is attached to the upper opening. These members are usually made of mechanical structural carbon steel or stainless steel. The powder-like pressurizing medium 5 is pressurized via the pressurizing mold 2 by a pressurizing means such as a hydraulic press (not shown).

The wall thickness of the pressurized container 1 (particularly the wall thickness of the peripheral side wall) is appropriately determined depending on the molding pressure (usually 500 kgf/c+f1 or more).

A coil-shaped heating element 3 is embedded inside the powder pressurizing medium 5 housed in the pressurizing container 1 as a heating means. As the heating element 3, a resistance heating element such as a Kanthal wire is generally used, but if the powder molded material is a magnetic material, an induction heating element such as a high frequency coil may be used. In this case, the pressurized container is preferably made of a non-magnetic material. Moreover, an ignition electrode (igniter) can also be used as a heating means. In addition, 4 is a sensor (for example, a thermocouple) for temperature greenhouses.

To carry out the present invention, a powder pressurizing medium 5 is first added to a pressurizing container 1 in which a heating element 3 and a sensor 4 are installed.
A powder molding chamber 6 is installed inside the heating element 3, a powder pressurizing medium 5 is filled around it, and a pressurizing mold 2 is attached.

Next, this pressurized container 1 is pressurized from one direction via a pressurizing mold 2 by a pressurizing means such as a hydraulic press (not shown). In this state, electricity is applied to the heating element 3 to heat it to the solidification molding temperature, and based on the temperature measured by the sensor 4, the power supplied to the heating element 3 is controlled so that the molding temperature is approximately constant. When this state is maintained for a certain period of time, the powder particles of the powder compaction 6 are mutually diffused and bonded and become dense, resulting in a sintered body having approximately true density. Thereafter, the electricity is turned off, and after cooling under pressure, the upper mold 2 is removed and the product is taken out together with the powdered press medium.

In the above example, pressure molding is performed in the atmosphere, but by performing the molding under a vacuum condition, the discharge of gas such as air inside the powder molding chamber is promoted, and more dense sintered crystals can be easily obtained. be able to.

FIG. 2 shows a molding apparatus for performing pseudo HIP molding under a vacuum condition, and members having the same configuration as the molding apparatus of FIG. 1 are given the same reference numerals.

In this device, a pressurized container 1 is installed in a closed chamber 11. The chamber 11 is composed of a main body 12 and a lid 13 for closing an opening at the upper end of the main body 12, and the two are airtightly connected by bolts and bolts 15 via a sealing material 14. The lid 12 has a through hole through which the pressure mold 2 can be freely inserted, and a ring 18 with a sealing material 17.17 attached to the inner peripheral surface is attached to the top of the lid 13 with a holding nut 19. .

The pressurizing mold 2 includes the presser pad 9, the ring 18 and the lid 1.
3 and is attached to the pressurized container 1 installed in the main body 12, and is allowed to slide vertically in an airtight manner by the sealing material 17, 17 of the ring 18. Further, an exhaust pipe 21 and a replacement gas supply pipe 22 are attached to the main body 12,
Exhaust valve 23. Each of them is connected via a replacement gas supply valve 24 to an exhaust means such as a vacuum pump and a replacement gas supply source. The lead wires of the heating element 3 and the temperature sensor 4 which are drawn out from the pressurized container 1 are drawn out of the main body 12 through a hermetic seal.

To use the molding apparatus, first, the heating element 3 and the powder molding chamber 6 are embedded in the powder pressurizing medium 5, and the pressurizing container 1 equipped with the pressurizing mold 2 is placed inside the main body 12 of the chamber 11. Then, the lid 13, ring 18, and retaining nut 19 are attached. Then, the replacement gas supply valve 24 is closed, the exhaust valve 23 is opened, and the air inside the chamber 11 is exhausted to create a vacuum state.

As a result, the gas in the powder molding chamber 6 is exhausted through the exhaust pipe 21 from the gap between the inner circumferential surface of the pressurized container 1 and the outer circumferential surface of the pressurized mold 2. Then, as described above, pseudo HIP molding is performed by applying pressure with the pressure mold 2 and heating with the heating element 3.

According to this device, after the chamber 11 is evacuated, the exhaust valve 23 is closed or opened, the replacement gas supply valve 24 is opened, and N is supplied from the replacement gas supply pipe 22.
2. A sintered body made of a desired compound can be produced by sintering while filling or flowing a reactive gas such as Co, 02, etc. into the chamber 11 and reacting with the powder-formed particles.

Next, specific examples are listed.

(1) Mix l and Ti powder at an atomic ratio of 1=1 and seal it in a thin stainless steel tube with an outer diameter of φ20 mm.
It was stretched to φ10 [IR] by a rotary swage method. Scrape off the stainless steel outer skin, eight! A powder molding process was obtained using a mixed powder of Ti and Ti.

(2) As shown in Fig. 1, the powdered powder is charged into a pressure-resistant container made of stainless steel along with commercially available foundry sand (average particle size: 80 mesh), a Kanthal wire, and a thermocouple as described above, The upper mold was attached.

(3) This pressure-resistant container is heated to 100,100 O by a hydraulic press.
It was pressurized with a surface pressure of /cffl, electrically heated to 1100°C, and held for 2 hours. At this time, the temperature of the sand at the bottom of the container was maintained at approximately room temperature. Thereafter, the electricity was turned off and the tube was cooled while being kept under pressure.

(4) The reaction sintered body taken out from the pressure vessel had a relative density of 98.5% or more. Further, the bending strength at 700°C was 90 kgf/mm'', the compressive strength at room temperature was 220 kgf/mm2, and the elongation was 20%, confirming that the desired TiA2 compound molded product was obtained.

(Effects of the Invention) As explained above, according to the pseudo-HIP method of the present invention, a powder pressurized medium made of an electrically insulating material is used, and a heating means buried within the medium and near the powder molding hole is heated. Since the molded body is heated, there is no need to heat the entire powder pressurized medium in the pressurized container, resulting in less heat loss. In addition, the heating means facilitates temperature control during powder molding, making it possible to stabilize product performance. Furthermore, since the temperature of the pressurizing medium around the powder compaction is lower than the temperature in the vicinity, pressure is transmitted smoothly, it is easier to achieve an isostatic pressurized state, and the shape of the powder compaction is less likely to change. (It is easy to mold a product with a shape similar to the molded body.

Further, by performing pressure molding under a vacuum condition, gas during powder molding is discharged, and a high-density sintered body can be easily produced.

Further, according to the molding apparatus of the present invention, the chamber does not require high pressure resistance, and pseudo HIP molding can be easily performed under a vacuum condition during powder molding.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a main part of a molding apparatus for carrying out the method of the present invention, and FIG. 2 is a cross-sectional view of a main part of a molding apparatus for carrying out the method of the present invention under a vacuum condition. 1... Pressurized container, 2... Pressurized type, 3... Heating element (
heating means), 5... powder pressurized medium, 6... powder molding rest, 11... chamber

Claims (3)

[Claims] (1) A powder compact is embedded in a powder pressurized medium in a pressurized container, and the heated powder compact is pressurized through the medium to achieve a sintered body that is at or near the true density. In the pseudo hot isostatic pressing method for obtaining a compacted body, an electrically insulating material is used as a powder pressurizing medium, and the compacted body is heated by a heating means embedded within the medium and near the powder compact. A pseudo-hot isostatic pressing method characterized by heating. (2) Claim (1) of pressurizing and heating under vacuum conditions
) The pseudo hot isostatic pressing method described in ). (3) A powder pressurized medium (5) in which a heating means (3) is embedded.
) is housed in the pressurized container (1), and the pressurized medium (5) in the pressurized container (1) is pumped through the pressurized mold (2) attached to the pressurized container (1). Equipped with a pressurizing means for pressurizing,
A pseudo hot isostatic pressing apparatus, characterized in that the pressurized container (1) is disposed in a chamber (11) connected to an exhaust means.