JPH0754010A - Method for degassing metal power in metal vessel by vacuum heating - Google Patents

Abstract

PURPOSE:To shorten the time required to release gas existing in gaps in metal powder filled into a metal vessel and gas adsorbed on the surface of the powder from the vessel by making the inside of the vessel vacuum and heating the powder. CONSTITUTION:The apparent density of metal powder in a metal vessel is regulated to >=72% to considerably increase the heat conductivity of the powder and to shorten the time required to soak the powder up to the central part at the time of heating. Space for releasing gas is held by regulating the apparent density to <=90%. Since the central part of the powder is rapidly heated, the release of adsorbed gas dependent on temp. is rapidly carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a method for converting a metal powder filled in a metal container (hereinafter referred to as a container) having a shape similar to that of a product to be molded into a metal powder into a metal powder prior to HIP treatment. The present invention relates to a method for efficiently degassing adsorbed gas components such as water and oxygen in air.

[0002]

2. Description of the Related Art In a method of filling a metal powder into a container having a similar shape to that of a metal powder and sintering it by HIP, the gap space of the powder in the container and the gas component adsorbed to the powder are released prior to HIP. In order to achieve this, a method is often adopted in which the mouthpiece of the container is connected to a vacuum pump, heating is also used in some cases, vacuum deaeration is performed, and then the mouthpiece is sealed to make an airtight state and then HIP. .

The reason why heating is used together in the vacuum degassing step is to accelerate the release of gas from the powder surface by heating. That is, the powder is in contact with the gas during the manufacturing process and the transportation process, and therefore the gas is adsorbed on the surface. In particular, the powder handled in the air adsorbs moisture, oxygen, etc. in the air. Generally, these gas components are often solid-dissolved in the powder or remain as a compound and often have a harmful effect on the HIPed product. To reduce these effects, the adsorbed gas is released. .

Since heating under vacuum as a means for releasing the adsorbed gas on the solid surface is commonly used in vacuum equipment, a detailed description thereof will be omitted here, and the peculiarities in heating the metal powder in the container will be described below. Describe.

[0005]

As a method for filling a metal powder into a container, a vibration filling method is generally used when the powder has good fluidity and a high tap density. In this case, the average contact number of the metal powder in the container is small, and the upper point contact is made. Therefore, the thermal conductivity of the metal powder in such a state is very small.

On the other hand, as a means for heating the powder in the container, generally, a means for heating the outer circumference of the container is often used because of easiness of heating, and in this case, the heat conduction filled by the conventional vibration filling method is used. In the case of a powder having a low rate, it takes a long time to uniformly heat the powder to the center. Since the release state of the adsorbed gas by heating in vacuum varies depending on the heating temperature, it is necessary to determine the time by the temperature of the central portion where the temperature rise is delayed.
Therefore, the vacuum heating and deaeration work requires a long time.

As another method, as a means for improving the thermal conductivity of the powder in the container, it has been proposed to introduce high-pressure gas into the container to improve heat transfer in the powder gap space. .

However, in the case of this method, heating is performed while the high-pressure gas is introduced, and in some cases, the powder and the introduced gas or the adsorbed gas may react during heating, and the product characteristics obtained after HIP It takes time and effort to confirm the impact on Further, it is necessary to prepare a jig for improving the rigidity of the capsule that can withstand the pressure or for preventing the expansion of the capsule, which is a drawback that it cannot be easily adopted. From the above, in order to shorten the time of the vacuum heating degassing step and reduce the cost, it is necessary to heat the powder after improving the thermal conductivity of the powder by another method, which is the object of the present invention. .

[0009]

In order to solve the above-mentioned problems, the present invention is to fill a metal container with metal powder, evacuate the inside of the container, and fill the container with the metal powder. A method of heating a body to release the gas existing in the gap space of the metal powder and the gas adsorbed on the surface of the metal powder to the outside of the container, in which the apparent density of the metal powder inside the container is set in advance. It is characterized in that the container is evacuated and heated after it is adjusted to 72% or more and 90% or less.

[0010]

[Function] The metal powder filled in the container is pressurized prior to the HIP treatment to make the apparent density of the powder 64% or more and 90% or less, thereby significantly improving the thermal conductivity of the powder. The vacuum heating degassing time, which is a process, is significantly shortened.

More specifically, when pressure is applied to the metal powder, the metal powder easily rearranges from the initial filling state, and then the contact state with the adjacent particles changes from point contact to surface contact, and then the pressure is applied. The contact area between adjacent particles is increased while increasing the average number of contacts as

When the contact state of adjacent powder particles changes from the point contact state to the surface contact, the thermal conductivity sharply increases. As a result, the thermal conductivity of the metal powder as vibrated and filled is 1
It can be 0 to 100 times. A means for industrially obtaining this state at around room temperature can be achieved by pressurizing the metal powder at a high pressure.

On the other hand, if the pressure applied to the metal powder is too large, the contact area of the powder increases, the space between the powder particles becomes narrow, and the conductance, which is an index of gas passage, decreases. . As a means for bringing the inside of the powder into a vacuum state, the gas originally existing in the powder gap space and the gas released from the powder surface are guided to the vacuum pump through the powder gap space. Must be secured to some extent. The size of the gap space of the powder can be controlled by the pressing force.

[0014]

EXAMPLES As the method of the present invention and a comparative example, the following experiment was conducted by using the steel powder which was actually gas-atomized by the conventional method using the equipment shown in FIG. In FIG. 2, 3 is a container filled with the powder, 1 is a heating furnace in which a heater 2 is arranged, and 4 is a vacuum pump.

The implementation conditions are shown below. (Conditions) Powder used: Gas atomized high-speed steel powder having an average particle size of 150 μm Filling ratio into containers: 70% and 75% (apparent density) The containers 3 filled with the powder as described above were placed in the heating furnace 1, respectively. While keeping the same atmosphere temperature in the furnace, the temperature versus elapsed time was measured on the container surface and in the center. Table 1 shows the measurement positions. The result is shown in FIG.

[0016]

[Table 1]

As is apparent from FIG. 1, at the filling rate of 75%, which is an embodiment of the method of the present invention, the temperature at the center of the container is almost equal to the surface of the container, and the time until the temperature is soaked is much larger than that of the conventional method. You can see that it is shortened to.

Since generally available metal powders have a particle size distribution, the initial packing density is higher than that of a single particle size. Based on such a situation, an appropriate range of apparent density was determined. FIG. 3 shows the relationship between the apparent density and the thermal conductivity of the gas atomized high-speed steel powder shown in the example. The thermal conductivity greatly changes when the apparent density is around 70%.
For this reason, the lower limit of the apparent density is set to 72% in order to stably obtain high thermal conductivity. Further, as an upper limit, when the apparent density is 90% or more, the contact area between the powder particles becomes large as shown in FIG. 4, the space between the powder particles becomes small, and the degree of decrease in conductance is large, so that the surface adsorption gas is not released. not enough. Further, as shown in FIG. 5, a high pressure is required to consolidate the apparent density to 90% or more, so that it is not practical for a hard alloy.

In this embodiment, the powder container in the HIP is described, but after filling the metal container with the metal powder,
It can also be applied to vacuum heating degassing during hot extrusion. Further, although the powder is shown as the gas atomized powder, the same effect can be obtained by the present invention even for the powder mechanically alloyed by a ball mill or the like. There are a CIP method and a pressing method as methods for making the apparent density of the metal powder 72% or more and 90% or less. Both
It can be used before or after filling the powder into the container.

[0020]

As shown in the examples, according to the present invention, the temperature of the powder central portion rises very quickly, so that the vacuum heating and deaeration process can be shortened. Therefore, when a large number of containers are targeted, the equipment and place required for vacuum deaeration can be reduced, and the occupancy time of the device in each individual container can be reduced, so that the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 shows the experimental results of the method of the present invention and a conventional example.

FIG. 2 shows the equipment used in the above experiment.

FIG. 3 is a diagram showing a relationship between apparent density and heat conduction.

FIG. 4 is a diagram showing a relationship between an apparent density and a contact area ratio of a powder surface.

FIG. 5 is a diagram showing a relationship between apparent density and pressure required for consolidation / yield point of powder metal.

[Explanation of symbols]

 1 Heating furnace 2 Heating heater 3 Container 4 Vacuum pump

Claims (1)

[Claims] 1. A metal container is filled with metal powder, the inside of the container is evacuated, and the metal powder filled in the container is heated to remove the gas existing in the metal powder gap space. A method of releasing the gas adsorbed on the surface of the metal powder to the outside of the container, comprising vacuuming the container after setting the apparent density of the metal powder inside the container to 72% or more and 90% or less in advance. A method for vacuum heating and deaerating a metal powder in a metal container, which comprises heating.