JPS62124203A - Method for cold caking powder having regular shape under isotropic pressure - Google Patents

Abstract

PURPOSE:To prevent the production of ununiform stress in a formed body and to inhibit the cracking of the formed body by adopting a two-step pressure reducing method consisting of rapid reduction from the maximum pressure to a prescribed set pressure and slow reduction from the set pressure to atmospheric pressure. CONSTITUTION:Powder having a regular shape such as spherical or flaky powder as starting material is filled into rubber dies and cold caked under isotropic pressure. The pressure is then reduced in two steps. The pressure is rapidly reduced from the maximum pressure to >=100kg/cm<2> set pressure at >=1,000kg/ cm<2>/min reduction rate and the pressure is slowly reduced from the set pressure to atmospheric pressure at <=100kg/cm<2>/min reduction rate.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is applied to cold isostatic pressure of raw material powder in fields such as powder metallurgy and fine ceramics.
ic Press, hereinafter abbreviated as CIP. ) The present invention relates to a solidification method, particularly a method for efficiently solidifying regularly shaped powder by CIP treatment.

(Prior Art) In recent years, in fields such as powder metallurgy and fine ceramics, it has often been adopted to densify raw material powder by CIP treatment.

This CIP treatment is performed using hot isostatic pressure (Hot l5ostat).
icPress, usually abbreviated as HIP. Although the density of the molded body is lower than that of methods such as ), it is an effective treatment as a pretreatment technique for sintering treatment and HIP treatment.

Figure 2 shows an outline of the equipment generally adopted for CIP processing as described above, which consists of a pressure vessel (1), an upper M (2) and a lower lid (3) that seal the upper and lower openings of the vessel. The processing chamber is divided into sections, and houses a rubber container filled with the powder to be processed (6), that is, a rubber mold (5), and pressure medium such as water is pumped through the pressure medium distribution pipe (4). The solidification process is performed by doing this. And in processing, the fifth
As shown in the figure, pressure cover turns such as 1 to 5 demarcation pressure, 0 to 5 minutes of holding, and 1 to 5 minutes of pressure reduction are normally carried out, and especially when the pressure is reduced, the pattern is one step.

(Problems to be Solved by the Invention) By the way, the shape of metal powder most commonly used in the field of powder metallurgy and the like has been an irregular shape as shown in FIG. 4(a). For example, metal powder produced by a water atomization method or an air atomization method has irregularities on its surface when surface oxide is formed, resulting in an irregular shape. Therefore, such irregularly shaped powders are easy to manufacture and are inexpensive, so they are used in large quantities in fields such as powder metallurgy.

When such irregularly shaped powder is subjected to CIP treatment, the powder particles become intertwined with each other due to the unevenness of the surface, so that a green compact with high strength can be obtained.

However, in recent years, along with the trends of the times, there has been a strong demand for improving the quality of products, and regularly shaped powders have often been used for this purpose.

For example, metal powder manufactured by an inert atomization method to prevent surface oxidation has a spherical shape as shown in Figure 4 (b), and powder obtained by pulverizing a thin ribbon rapidly solidified for the purpose of improving properties is generally It has a flaky shape as shown in FIG. 4(c).

When these regular-shaped powders are solidified by CIP processing, the entanglement (bonding property) between the powders is reduced.
Since the number of particles is smaller than that of the irregularly shaped powder, the molded product tends to crack, and it is difficult to maintain a good shape.

That is, as shown in FIG. 3, the regularly shaped powder is molded into a rubber mold (
5) and perform CIP treatment, first fill the rubber mold (5) with CIP treatment.
The regularly shaped powder (6) (see FIG. 3(A)) filled in the container (El) is compressed under isostatic pressure and its volume contracts as shown in FIG. 3(A). Of course, the higher the pressure at this time, the more the deformation of the powder is promoted and the density of the green compact increases.

When the molded body (6) thus obtained is then subjected to reduced pressure after the required time, the deformation resistance of the rubber mold (5) is smaller than that of the powder, so it sticks to the molded body until the pressure is relatively low. However, when the pressure is lower than the required pressure, the rubber mold (5) begins to return to its original state due to the elastic restoring force of the rubber itself and the expansion of the internal gas.

At this time, since the adhesion force of the rubber mold (5) to the surface of the molded body (6) generally varies locally, the rubber mold (5) peels off unevenly from the molded body (d). Non-uniform tensile stress is generated, and as a result, cracks (7) occur in the molded body (6) as shown in FIG. 3(c).

The occurrence of cracks due to uneven peeling of the rubber mold (5) is not much of a problem with irregularly shaped powders where the strength of the molded product is high, but when regular shaped powders are subjected to CIP treatment, cracking occurs frequently due to the weak bonding properties. This is an important problem.

The present invention focuses on the occurrence of cracks in such regularly shaped powder, and
In particular, the objective is to improve the pressure cover pattern of CIP treatment and obtain good solidification of compacts even in CIP treatment of regularly shaped powder.

(Means for Solving the Problems) Therefore, the feature of the present invention that satisfies the above object is that in the method of solidifying the regular-shaped powder as a raw material powder by CIP treatment, as shown in FIG. The pattern has two stages (n-11) and (Harney), first, the pressure is rapidly reduced from the highest pressure to a predetermined set pressure (o-A), and then the pressure is reduced rapidly from the set pressure to atmospheric pressure (8). -2) is to gradually reduce the pressure.

Therefore, the above-mentioned set pressure is usually set to an appropriate pressure of 100 kglct1 or more, preferably 100 to 300 kg/ci, and from the maximum pressure to this set pressure, the rate is 1/min.
The pressure is rapidly decelerated at a pressure reduction rate of 000 kg/i or more, and the pressure is gradually reduced from the set pressure to atmospheric pressure at a pressure reduction rate of 100 kg/cat or less per minute.

Here, the purpose of carrying out the two-step depressurization is for the following reasons.

That is, the faster the depressurization speed is, the higher the number of CIP treatment cycles and the higher the productivity. Therefore, it is desirable that the initial pressure be reduced rapidly. However, in the relatively low pressure range where the rubber mold peels off from the molded object, the slower the decompression rate, the slower the recovery speed of the rubber mold. It is possible to prevent uniform stress from being generated.

Therefore, it is preferable that the pressure reduction be slower in the lower pressure range than in the initial high pressure range, and for this reason, it is preferable that the pressure reduction pattern be two-stage.

Although the present invention describes two-stage depressurization in the above description, this is because dividing the pressure into three or more stages would complicate the control, and this does not negate separate provision.

Furthermore, in the above two-stage pressure reduction pattern, the switching setting pressures of the first stage and second stage are set to 100 kg/cd or more based on the following reasons.

That is, from the gist of the above description, it is desirable that the set pressure in the present invention be just above the pressure at which the rubber mold starts to peel off from the molded article.

The pressure at which this peeling begins is generally determined by the adhesion force between the rubber mold and the molded body, the elastic restoring force of the rubber mold, and the expansion force of the gas (atmosphere) existing within the rubber mold. In particular, when the adhesive force between the rubber mold and the molded body is greater than the restoring force of the rubber mold, the state shown in FIG. 3(0) is maintained until the pressure reaches a relatively low state.

However, in the case of commonly used rubber molds for CIP processing,
At pressures below 100 kg/cal, the restoring force of the rubber mold overcomes the adhesion force between the molded body and the rubber mold due to the expansion of internal pressure and elastic force, so if rapid deceleration is performed at pressures below this, Figure 3 (c) This results in cracking (7).

Therefore, it is effective to suppress the lower limit of the set value to 100 k[/cd.

Furthermore, even if the upper limit of the set value is the one with the highest restoring force among the commonly used rubber molds for CIP processing, restoring will not start at a pressure higher than this, and if the pressure is higher than this, the second stage low-speed decompression will start. It is desirable to keep the rate at about 300 kg/cd because productivity will drop significantly if the rate is changed to 300 kg/cd.

Next, regarding the decompression speed, the decompression speed in the first stage is unrelated to the occurrence of cracks, and as mentioned above, the faster the better for the purpose of improving productivity, but depending on the capacity of the existing equipment,
It is preferable to reduce the pressure to 0 kg/ad or more. Further, the slower the second stage depressurization speed, the more effective it is in preventing cracking, but when productivity is taken into consideration, a lower speed is not desirable. Therefore, we determined the maximum decompression speed that can prevent cracking, and
g/cd or less.

Therefore, although both the pressure reduction speeds of the first stage and the 72nd stage cannot be said to be critical, they are within a practical range.

Specific examples of the present invention are listed below.

(Example) Aluminum alloy powder (Samples 1 to 15) and pure iron powder (Sample 16)
~18) respectively as powders to be treated, with inner dimensions of diameter 50w1Φ,
Using a rubber mold with a length of 150fl, the maximum pressure is 5000kg/
CIP treatment was performed using CD, and the state was observed while changing the switching setting pressure, first stage B pressure reduction speed, and second stage pressure reduction speed.

It should be noted that the decompression speed of the first stage is preferably as fast as possible in order to shorten the working time, but due to the equipment, it is only 1500kl/cI+ per minute!
It was held constant.

In addition, the rubber mold is a urethane rubber mold with a large restoring force (male pressure 8
fl) and a natural rubber mold with low restoring force (muscle pressure 11 degrees) were used.

The above observation results are shown in the table below.

As seen in samples 1 to 3 and 16, 1 of the regular shaped powder was
When the molded body was treated by stage vacuum, cracking was observed in the molded body. In addition, in the case of rubber molds with large restoring force, samples 4 to 6
．． 100 as shown on each side of 13-15 and 17
It is understood that if the switch to the second stage is performed at a pressure of kg/d or more, a good molded product without cracking can be obtained.

This tendency is the same for rubber molds with weak restoring force, but
As shown in the examples of Samples 7 to 9, the peeling of the molded body from the rubber mold starts on the low pressure side, making it possible to switch to a lower pressure side.

In either case, switching to the second stage is 100kg/ctA.
It can be seen that cracking of the molded product can be prevented by applying the above pressure.

On the other hand, the decompression speed of the second stage was for samples 4, 5, 7, 10.11
．． 100+ per minute by comparing each example of 12 and 16-18
r/an! It can be seen that if the pressure is reduced below, molding can be performed without inducing cracking in any case.

From the above results, if the method and conditions of the present invention are applied,
It has been found that even powders with regular shapes can be subjected to CIP treatment and good molded bodies without cracks can be obtained.

(Effects of the Invention) As described above, according to the method of the present invention, a two-stage pressure reduction is adopted, and the pressure is rapidly reduced from the maximum pressure to a predetermined set pressure, and gradually from the set pressure to atmospheric pressure, so that the rubber The recovery speed of the rubber mold can be slowed down in the relatively low pressure range where the mold starts to peel off the molded body, and therefore,
Peeling becomes uniform, preventing uneven stress from occurring inside the molded body, and preventing cracking of the molded body caused by this,
Good quality molded bodies can be obtained even in CIP treatment of regularly shaped powders with low strength.

In response to the current demand for quality improvement, CIP treatment has a remarkable effect on increasing the solidification efficiency of powder.

Moreover, since the method of the present invention reduces the pressure at a high pressure reduction rate in the first step, it does not hinder the number of cycles of CIP treatment and ensures sufficient productivity, making it a practical method for powder metallurgy, fine ceramics, etc. Future practical application in this field is expected.

[Brief explanation of drawings]

FIG. 1 is a diagram showing pressure cover turns in the method of the present invention;
FIG. 2 is a sectional view showing an outline of the equipment used for CIP processing,
Figure 3 (() (U) (A) is an explanatory diagram of the processing state of the powder to be treated during CRP treatment, Figure 4 (A) (O) (
+t) is an explanatory diagram showing the shape of the powder, where (a) shows an irregularly shaped powder, and (U) and (11) both show a regularly shaped powder with two spherical pieces. FIG. 5 is a chart showing pressure cover turns during conventional CTP processing. Calyx 1 diagram Vz diagram 3 times (a) (b) Rod 4 old (a) (b) 1, old (c) (c)

Claims (1)

[Claims] 1. In a method in which raw material powder with regular shapes such as spherical or flaky shapes is filled into a rubber mold and solidified by cold isostatic pressure treatment, the pressure reduction process is performed in two stages, and 100 kg from the highest pressure is used.
1000 per minute up to the set pressure set at /cm^2 or higher
Cold processing of regularly shaped powder, etc. characterized by rapid depressurization at a decompression rate of kg/cm^2 or more, and gradual depressurization from the set pressure to atmospheric pressure at a decompression rate of 100 kg/cm^2 or less per minute. Direct pressure solidification method.