WO2024019213A1

WO2024019213A1 - Presse sintering method and apparatus

Info

Publication number: WO2024019213A1
Application number: PCT/KR2022/012178
Authority: WO
Inventors: 주경; 이기복; 송주현
Original assignee: (주)삼양세라텍
Priority date: 2022-07-21
Filing date: 2022-08-16
Publication date: 2024-01-25
Also published as: KR20240012822A

Abstract

A press sintering apparatus according to the present invention comprises: a sintering mold having a mold housing having an inner space open vertically, and a mold sleeve stably placed on the inner wall of the mold housing; an upper punch and a lower punch for vertically pressing a sintered base material introduced into the mold sleeve; and a housing support part for supporting only the lower end of the mold housing without supporting the lower end of the mold sleeve, wherein after forming a sintered body by pressing the sintered base material introduced into the mold sleeve, the sintered body is cooled to a preset primary cooling temperature, is removed from the sintered mold, and then cooled to a preset secondary cooling temperature. The press sintering method and apparatus according to the present invention can prevent damage to the mold housing or the sintered body due to the difference in shrinkage between the mold housing and the sintered body, which occurs during the cooling process after hot pressing, and thus can advantageously improve productivity of the sintered body and increase the lifetime of the mold housing.

Description

Pressure sintering method and device

The present invention relates to a method and device for molding a product by pressure sintering, and more specifically, to prevent the sintered body from being damaged by the difference in thermal expansion coefficient between the mold and the sintered body that occurs during the process of pressing and then cooling the sintered body. It relates to a pressure sintering method and device for.

Non-sintering non-oxide ceramics with a low coefficient of thermal expansion, such as hexagonal boron nitride and hexagonal boron nitride composites, are produced by a hot pressing sintering process. When manufacturing such hexagonal boron nitride and its composites, the sintered body is lower than the mold housing. Due to the thermal expansion coefficient, stress occurs in the sintered body and mold housing during the cooling process. At this time, the stress applied to the sintered body not only lowers the physical properties of the sintered body and causes cracks, thereby lowering the yield of the sintered body, but also causes stress to the mold housing, causing damage or deformation of the mold housing.

Accordingly, the price competitiveness of hexagonal boron nitride and its composites is reduced, and despite its excellent physical properties, its use is limited to some products. In particular, hexagonal boron nitride, which has an extremely low coefficient of thermal expansion, is produced using mold housings made of expensive carbon composites. However, because these carbon composite mold housings are so expensive, there is a problem in that manufacturing costs increase.

In order to prevent damage to the mold housing and sintered body, hexagonal boron nitride is produced by manufacturing the mold housing from a carbon composite with a very low coefficient of thermal expansion. However, the carbon composite also has a relatively high coefficient of thermal expansion compared to hexagonal boron nitride, so it is cooled. The problem is that it is impossible to completely eliminate the stress that occurs during the process.

The present invention was proposed to solve the above problems, and provides a pressure sintering method and device that can prevent damage such as cracks or breakage that occurs during cooling to all parts of the product even if the product is molded by the pressure sintering method. The purpose is to provide

The pressure sintering device according to the present invention includes a sintering mold including a mold housing having an internal space open up and down, and a mold sleeve seated on the inner wall of the mold housing; An upper punch and a lower punch that press upward and downward on the sintered base material introduced into the mold sleeve; After forming a sintered body by pressing the sintered base material introduced inside the mold sleeve, including a housing support portion that does not support the lower end of the mold sleeve and only supports the lower end of the mold housing, the sintered body is subjected to a preset primary cooling. It is configured to cool to a temperature, demold the sintering mold, and then cool to a preset secondary cooling temperature.

It is formed in the shape of a hollow tube that is inserted into the mold sleeve so that the outer surface is spaced apart from the inner surface of the mold sleeve, and includes a plurality of first inner split pieces whose width decreases toward the bottom and a plurality of first inner split pieces whose width increases toward the bottom. 2 inner sleeves in which inner split pieces are arranged alternately in the circumferential direction; It further includes a demolding rod that lowers the second inner split piece, wherein the mold housing is formed in the shape of a hollow tube whose inner diameter increases downward, and the mold sleeve is formed in the shape of a hollow tube whose outer diameter increases toward the downward side. The lower punch presses the sintered body inserted between the mold sleeve and the inner sleeve upward and downward, and the housing support part is configured to raise the mold housing.

It further includes a plurality of spacers inserted between the mold sleeve and the inner sleeve in a stacked manner, and the sintered body is formed in a ring shape inserted between two adjacent spacers.

It further includes a center shaft press-fitted into the inner sleeve, wherein the center shaft is formed in a cone shape whose outer diameter increases downward, and the first inner split piece and the second inner split piece have a thickness toward the bottom. is formed to gradually become thinner.

The second inner split piece is mounted so that its upper end is positioned higher than the first inner split piece.

The mold sleeve is composed of a plurality of outer divided pieces arranged in the circumferential direction.

The two adjacent outer split pieces each have outer grooves that communicate with each other formed at the side ends in the width direction, and inside the two outer grooves that communicate with each other, there is a compression spring that applies an elastic force in the direction in which the two adjacent outer split pieces move away from each other. This is provided.

A first inner groove is formed at a side end of the first inner split piece, a second inner groove communicating with the first inner groove is formed at a side end of the second inner split piece, and the first inner groove and the second inner groove are in communication with each other. Inside the inner groove, a tension spring is provided to apply an elastic force in a direction in which the first inner split piece and the second inner split piece approach.

The pressure sintering method according to the present invention is a manufacturing method using a pressure sintering device configured as described above, comprising: a first step of charging raw material powder into the sintering mold; A second step of charging the sintering mold into the chamber; A third step of sintering the raw material powder charged into the sintering mold by hot pressing; A fourth step of cooling the inside of the chamber to a temperature between 1600°C and 2000°C, which is the primary cooling temperature; A fifth step of demolding the mold sleeve from the mold housing; When demolding of the mold sleeve is completed, a sixth step of cooling the inside of the chamber to a secondary cooling temperature lower than the primary cooling temperature; A seventh step of pulling the sintering mold out of the chamber; It includes; an eighth step of removing the sintered base material from the mold sleeve.

The pressure sintering method according to the present invention is a manufacturing method using a pressure sintering device configured as described above, comprising: a first step of preparing raw material powder for sintering molding; A second step of first forming a hollow product by pressurizing the raw material powder; A third step of positioning the first molded body manufactured in the second step between the inner sleeve and the mold sleeve; A fourth step of forming a sintered body by pressurizing and sintering the primary molded body using the upper punch and the lower punch; A fifth step of raising the mold housing and lowering the second inner split piece to remove the pressing force between the mold sleeve and the sintered body and the pressing force between the inner sleeve and the sintered body; A sixth step of cooling the sintered body to room temperature; A seventh step of demolding the sintering mold; It consists of an eighth step of withdrawing the sintered body.

The fourth step is configured to heat the sintered body to a preset temperature to remove impurities in the sintered body, and then hot press the sintered body.

The method of pressurizing and sintering the sintered body in the fourth step includes one or more sintering methods among hot pressing sintering, sparking plasma sintering, and gas pressure sintering. It is composed.

The third step is configured to insert the sintered body between a plurality of spacers inserted between the mold sleeve and the inner sleeve in a stacked manner.

By using the pressure sintering method and device according to the present invention, it is possible to prevent the mold housing or the sintered body from being damaged due to the difference in shrinkage rate between the mold housing and the sintered body that occurs during the cooling process after hot pressing, thereby improving the productivity of the sintered body. It has the advantage of increasing the lifespan of the mold housing.

In addition, by using the pressure sintering method and device according to the present invention, even if a hollow product is molded by the pressure sintering method, damage such as cracks or breakage that occurs during cooling can be prevented in all parts of the product, and ring-shaped products can be prevented. It has the advantage of increasing productivity as multiple pieces can be molded in one process.

1 is a schematic diagram of a pressure sintering device according to the present invention.

Figure 2 is a schematic diagram of a sintering mold included in the pressure sintering device according to the present invention.

Figure 3 is a flow chart of the pressure sintering method according to the present invention.

Figures 4 and 5 are a cross-sectional perspective view and a vertical cross-sectional view of the sintering mold included in the second embodiment of the pressure sintering device according to the present invention.

Figures 6 and 7 are a perspective view and an exploded perspective view of the inner sleeve included in the second embodiment of the pressure sintering device according to the present invention.

Figure 8 is an exploded perspective view of the mold sleeve included in the second embodiment of the pressure sintering device according to the present invention.

Figure 9 is a state diagram of the second embodiment of the pressure sintering device according to the present invention.

Figures 10 and 11 are horizontal cross-sectional views of the inner sleeve included in the third embodiment of the pressure sintering device according to the present invention.

Figure 12 is a horizontal cross-sectional view of the mold sleeve included in the third embodiment of the pressure sintering device according to the present invention.

Figure 13 is a flowchart of another embodiment of the pressure sintering method according to the present invention.

Hereinafter, embodiments of the hot pressure sintering method and device according to the present invention will be described in detail with reference to the attached drawings.

Figure 1 is a schematic diagram of a pressure sintering device according to the present invention, Figure 4 is a schematic diagram of a sintering mold included in the pressure sintering device according to the present invention, and Figure 5 is a flow chart of the pressure sintering method according to the present invention.

The pressure sintering device according to the present invention is a device for forming a sintered body by pressing non-sintering non-oxide ceramics (hereinafter abbreviated as 'raw material powder') with a low coefficient of thermal expansion, such as hexagonal boron nitride, into a certain shape, and performing a cooling process. The most notable feature is that it has a structure that allows demolding at a high temperature above a certain level to prevent damage to the mold housing or sintered body.

That is, the pressure sintering device according to the present invention includes a sintering mold 200 into which the sintered body 10 is charged, an upper punch 310 and a lower punch ( 410) are provided as basic components. The sintering mold 200 is installed inside the chamber 100, and includes a vacuum pump 500 that creates a vacuum inside the chamber 100, and an upper pressure cylinder 300 that operates the upper punch 310. And, a lower pressurizing cylinder 400 that operates the lower punch 410 is provided. The vacuum pump 500, the upper pressurizing cylinder 300, and the lower pressurizing cylinder 400 are practically effective even in the conventional pressurizing sintering device. Since the same applies, a detailed description of the detailed structure and operating principle of the vacuum pump 500, the upper pressure cylinder 300, and the lower pressure cylinder 400 will be omitted.

As shown in FIG. 2, the sintering mold 200 includes a mold housing 240 having an internal space open up and down, and a mold sleeve 230 seated on the inner wall of the mold housing 240. It is composed. At this time, a housing support portion 700 supporting the lower end of the mold housing 240 and a demolding rod 600 coupled to the upper end of the upper punch 310 may be additionally provided.

At this time, the outer edge of the demolding rod 600 is manufactured to be larger than the inner surface of the mold sleeve 230 and smaller than the outer surface of the mold sleeve 230, so that the upper end of the mold housing 240 is not pressed when lowered. The mold sleeve 230 can be removed from the mold housing 240 by pressing only the top of the mold sleeve 230. Meanwhile, the sintered body 10 is inserted into the space between the upper punch 310 and the lower punch 410 in the inner space of the mold sleeve 230, and is provided with a plurality of spacers so that a plurality of sintered products can be produced at once. It is separated by (210).

The mold sleeve 230 is formed in the shape of a hollow tube, and its outer surface is inclined in a direction in which the outer diameter widens downward, and the mold housing 240 is formed to have an inner surface inclined in a direction in which the inner diameter widens downward. As shown in FIG. 2, when the mold sleeve 230 is press-fitted into the mold housing 240, it cannot be pulled out to the top but can only be pulled out to the bottom.

In addition, the mold housing 240 is simply mounted on the housing support 700, and the lower punch 410 is press-fitted into the lower side of the mold sleeve 230, as shown in Figure 2. In this state, when the lower punch 410 is moved upward, the bottom surface of the mold housing 240 is spaced upward from the upper surface of the housing support portion 700 by the distance the lower punch 410 moves. The sintering mold 200 configured as described above is mounted so that it can be inserted and withdrawn into the chamber 200, and the chamber 200 may be equipped with a heating element for heating the sintering mold 200.

When attempting to mold a product using the hot pressing sintering method according to the present invention, the raw material powder is first charged into the sintering mold 200 (S10) and then the sintering mold is charged into the chamber 100 (S20).

When the sintering mold 200 is charged into the chamber 100, the raw material powder charged into the sintering mold 200 is hot-pressed and sintered (S30). The sintering conditions at this time depend on the type of raw material powder or the product to be manufactured. It can be appropriately selected depending on various conditions such as characteristics. When hot press sintering is completed, the inside of the chamber 100 is cooled to a preset primary cooling temperature (S40), then the mold sleeve 230 is demolded from the mold housing 240 (S50), and the mold sleeve ( When demolding of 230) is completed, the inside of the chamber 100 is cooled to a preset secondary cooling temperature (S60).

When cooling to the secondary cooling temperature is completed, the sintering mold 200 is taken out of the chamber 100 (S70), and then the sintered body is removed from the mold sleeve (S80) to complete the product production process.

At this time, when hexagonal boron nitride powder is used as the raw material powder and the mold housing 240 is made of graphite material, the thermal expansion coefficient of the mold housing 240 is greater than that of the sintered body 10, so the mold sleeve ( When 230) is mounted on the mold housing 240 and cooled to the secondary cooling temperature at once, the mold housing 240 shrinks more than the sintered body 10, resulting in stress between the sintered body 10 and the mold housing. This happens. When this stress is transmitted to the sintered body 10, deformation of the sintered body 10 is caused, and when the stress is transmitted to the mold housing 240, cracks are generated in the mold housing 240, thereby shortening the life of the mold housing 240. This results in a significant shortening.

However, in the hot press sintering method according to the present invention, the mold sleeve 230 is cooled to the primary cooling temperature rather than being cooled to the secondary cooling temperature at once while the mold sleeve 230 is mounted on the mold housing 240. After the mold sleeve 230 is demolded from the mold housing 240 and cooled to the secondary cooling temperature, the phenomenon of stress occurring due to the difference in shrinkage rate between the sintered body 10 and the mold housing 240 can be fundamentally prevented. There is an advantage to having it.

Figures 4 and 5 are a cross-sectional perspective view and a vertical cross-sectional view of the second embodiment of the sintering mold included in the second embodiment of the pressure sintering device according to the present invention, and Figures 6 and 7 are the second embodiment of the pressure sintering device according to the present invention. This is a perspective view and an exploded perspective view of the inner sleeve included in .

The pressure sintering device according to the present invention can be configured to manufacture products with a hollow formed in the center, such as a ring or hollow tube, by pressure sintering.

That is, the sintering mold 200 is formed in a hollow tube shape whose inner diameter increases toward the bottom, and a hollow tube shape whose inner diameter increases toward the bottom, so that the inner surface of the mold housing 240 is formed. A mold sleeve 230 in close contact with the mold sleeve 230, and a plurality of hollow tubes formed in the shape of a hollow tube that are inserted into the mold sleeve 230 so that the outer surface is spaced apart from the inner surface of the mold sleeve 230, and the width decreases toward the bottom. It may be composed of an inner sleeve 220 in which a first inner split piece 221 and a plurality of second inner split pieces 225 whose width increases toward the bottom are alternately arranged in the circumferential direction.

The sintered body 10 is inserted between the mold sleeve 230 and the inner sleeve 220, and the demold rod 600 lowers the second inner split piece 225 so that the inner sleeve 220 It allows the mold sleeve 230 to be spaced apart from the inner side of the sintered body 10, and the housing support portion 700 raises the mold housing 240 so that the mold sleeve 230 can be spaced apart from the outer side of the sintered body 10. .

In this way, when the inner sleeve 220 and the mold sleeve 230, which were pressed to the inner and outer surfaces of the sintered body 10, are configured to be spaced apart from the surface of the sintered body 10, the sintered body 10 heated to a high temperature is By separating the inner sleeve 220 and the mold sleeve 230 from the surface of the sintered body 10 before cooling to room temperature, damage to the sintered body 10 and the sleeve that occurs during the cooling process of the sintered body 10 is prevented. There is an advantage to being able to do it.

At this time, the process of separating the inner sleeve 220 and the mold sleeve 230 from the surface of the sintered body 10 will be described in detail with reference to FIG. 9 below.

If the sintered body 10 to be sintered has a hollow tube shape, insert the sintered body 10 into the space between the inner sleeve 220 and the mold sleeve 230 and then punch the sintered body using the upper punch 310 and the lower punch 410. The sintered body 10 is formed by pressing the sintered body 10. Even if the sintered body 10 to be sintered has a thin ring shape, if the sintered body 10 is formed in the same manner as above, one sintered body 10 can be formed in one process. There is a problem that it is difficult to increase productivity because only

Therefore, when the sintered body 10 to be molded has a ring shape, a plurality of sintered bodies 10 are inserted in a stacked manner between the mold sleeve 230 and the inner sleeve 220 so that a plurality of sintered bodies 10 can be molded at once. Two spacers 210 may be additionally provided. The spacers 210 are provided in pairs so as to be in close contact with the upper and lower surfaces of the sintered body 10, respectively, and are stacked in large numbers between the inner sleeve 220 and the mold sleeve 230. As shown in FIG. 5, the spacers 210 are located at the uppermost side. The spacer 210 located at the bottom is pressed downward by the upper punch 310, and the spacer 210 located at the bottom is pressed upward by the lower punch 410.

When pressurizing the sintered body 10 in this manner, there is an advantage that productivity can be significantly increased because a plurality of sintered bodies 10 can be obtained through a single pressing process.

At this time, the number of spacers 210 may increase or decrease depending on the thickness of the sintered body 10 to be manufactured, and the shape of the surface of the spacers 210 in contact with the sintered body 10 is determined by the shape of the sintered body 10 to be manufactured. ) can be freely changed depending on the shape.

Meanwhile, when the inside of the inner sleeve 220 is set to be empty, the first inner split piece 221 and the second inner part are formed in the process of the upper punch 310 and lower punch 410 pressing the sintered body 10. There is a risk that the split piece 225 may be pushed into the empty space on the inside and move. In this way, if the first inner split piece 221 and the second inner split piece 225 are moved, there is a risk that the sintered body 10 may be deformed during sintering, and the inside of the inner sleeve 220 is A center shaft 250 press-fitted to support the inner surfaces of the split piece 221 and the second inner split piece 225 may be additionally provided (see FIGS. 6 and 7).

At this time, as shown in FIG. 6, the first inner split piece 221 or the second inner split piece 225 is pressed downward while the center shaft 250 is press-fitted into the inner space of the inner sleeve 220. When the center shaft 250 moves downward so that the inner surfaces of the first inner split piece 221 and the second inner split piece 225 can be pressed more strongly against the outer surface of the center shaft 250, It is formed in a cone shape with an increasing outer diameter, and the first inner split piece 221 and the second inner split piece 225 are formed to gradually become thinner in thickness toward the bottom in accordance with the shape of the center shaft 250. This is desirable.

Figure 8 is an exploded perspective view of the mold sleeve 230 included in the second embodiment of the pressure sintering device according to the present invention.

The mold sleeve 230 surrounding the outer surface of the sintered body 10 has a cone shape whose outer diameter increases downward so that it is tightened when the mold housing 240 is lowered and the tightening force is released when the mold housing 240 rises. It is formed by At this time, when the mold sleeve 230 is formed in the shape of a single hollow tube, the inner diameter strain is very small when tightened and loosened by the mold housing 240, so the effect of being separated from the outer surface of the sintered body 10 is very low. There is a downside.

Therefore, the mold sleeve 230 is composed of a plurality of outer split pieces 231 arranged in the circumferential direction as shown in FIG. 8 so that the sintered body 10 can be reliably separated from the sintered body 10 before cooling. desirable.

In this way, when the mold sleeve 230 is composed of a plurality of outer split pieces 231, when the mold housing 240 is raised, the outer split pieces 231 can move in a direction away from the sintered body 10. , there is an advantage that the sintered body 10 is not damaged during cooling even if the thermal expansion coefficient between the sintered body 10 and the mold sleeve 230 is significantly different.

When pressurizing the sintered body 10 using the pressure sintering device according to the present invention, a plurality of spacers 210 into which the sintered body 10 is inserted are stacked between the inner sleeve 220 and the mold sleeve 230, and then 2 The inner split piece 225 is raised and the mold housing 240 is lowered to press the inner sleeve 220 and the mold sleeve 230 to the inner and outer surfaces of the sintered body 10, and then press the upper punch 310. ) and the lower punch 410 to pressurize the sintered body 10.

At this time, the method of pressing the sintered body 10 is configured to use hot pressing sintering, sparking plasma sintering, or gas pressure sintering. It can be. Furthermore, it may be configured to include one or more sintering methods among the pressure sintering methods mentioned above.

The electric pressure sintering is a sintering method that is attracting attention in the field of advanced new material synthesis, and is configured to fill the sintered body into a sintered mold, sandwich it between electrodes of the electric pressure sintering stage, and then pressurize it while applying a current. Using this type of electric pressure sintering method, handling becomes easy, sintering is possible under a wide range of pressure and temperature conditions, so it can be sintered with various types of materials, and rapid heating is possible, which has the advantage of obtaining a dense sintered body in a short time. there is.

In addition, the gas pressure sintering is a method of sintering under gas pressure such as high-pressure nitrogen or argon. It can increase the sintering density by removing residual internal pores and defects as much as possible, and improve the mechanical properties of the material to extend strength and lifespan. There is an advantage to making this possible.

In addition, the hot pressing sintering is a sintering method that heats and pressurizes the sintered body 10 using a separate heating element such as a heating wire. The construction is relatively simple and does not require advanced skills for the operator, so the cost of sintering is low. It has the advantage of being relatively inexpensive.

At this time, in this embodiment, only hot pressing sintering, sparking plasma sintering, and gas pressure sintering are described as methods of pressing the sintered body 10, but the above-mentioned In addition to one sintering method, various types of sintering methods can be used.

Since the sintered body 10 is pressurized above a certain temperature while being pressed, it must undergo a cooling process. When the inner sleeve 220 and the mold sleeve 230 undergo the cooling process while being pressed to the sintered body 10, the sintered body 10 ) and the

sleeves

220 and 230, stress is applied to the sintered body 10 due to the difference in cooling shrinkage rate, which may cause the sintered body 10 to be damaged.

Therefore, after the hot pressing of the sintered body 10 is completed and before entering the cooling process, the inner sleeve 220 is lowered by using the demolding rod 600 to lower the second inner split piece 225 as shown in FIG. 9. The pressing force between the mold sleeve 230 and the sintered body 10 is removed by raising the mold housing 240 using the housing support part 700. At this time, the inner sleeve 220 is positioned on the inner surface of the sintered body 10 so that the demold rod 600 can press only the second inner split piece 225 and not the first inner split piece 221. When set to be pressed, the second inner split piece 225 is preferably mounted so that its upper end is higher than the first inner split piece 221.

In this way, if the compressing force between the inner sleeve 220 and the sintered body 10 and the compressing force between the mold sleeve 230 and the sintered body 10 are removed, even if the shrinkage of the

sleeves

220 and 230 becomes greater than that of the sintered body 10 during the cooling process. There is an advantage in that damage to the sintered body 10 can be prevented.

Figures 10 and 11 are horizontal cross-sectional views of the inner sleeve 220 included in the third embodiment of the pressure sintering device according to the present invention, and Figure 12 is a mold sleeve included in the third embodiment of the pressure sintering device according to the present invention ( 230) is a horizontal cross-sectional view.

In order to ensure that the sintered body 10 is not affected at all when the

sleeves

220 and 230 shrink during the cooling process, it is preferable that the

sleeves

220 and 230 are spaced apart from the sintered body 10.

In the pressure sintering device according to the present invention, the second inner split piece 225 is lowered to remove the pressing force between the inner sleeve 220 and the sintered body 10, and the mold housing 240 is raised to form the mold sleeve 230 and the sintered body ( 10) When the compressive force between the two is removed, the first sleeve is spaced apart from the inner surface of the sintered body 10 and the second sleeve is spaced from the outer surface of the sintered body 10, as shown in FIG. 9. It can be configured to be spaced apart. .

In order for the first sleeve to be spaced apart from the inner surface of the sintered body 10 in this way, the second inner split piece 225 is lowered so that the side end of the first inner split piece 221 and the side end of the second inner split piece 225 are spaced apart. When this happens, the width direction side edges of the first inner split piece 221 and the second inner split piece 225 must be in close contact. Therefore, a first inner groove 222 is formed at the side end of the first inner split piece 221, and a second inner groove communicating with the first inner groove 222 is formed at the side end of the second inner split piece 225. A groove 226 is formed, and inside the first inner groove 222 and the second inner groove 226 that communicate with each other, the first inner split piece 221 and the second inner split piece 225 are close to each other. A tension spring 228 may be provided to apply elastic force in one direction.

As mentioned above, when the first inner split piece 221 and the second inner split piece 225 are configured to be pulled by the tension spring 228, the second inner split piece 225 is lowered, as shown in Figure 11. As described above, even if the first inner split piece 221 and the second inner split piece 225 are spaced apart, the first inner split piece 221 and the second inner split piece 225 are brought into close contact by the tension spring 228. Since the state of FIG. 10 is restored, the outer surfaces of the first inner split piece 221 and the second inner split piece 225 are spaced apart from the sintered body 10 as shown in FIG. 9.

Conversely, the mold sleeve 230 is spaced apart from the outer surface of the sintered body 10 only when the outer split pieces 231 are spread apart from each other when the mold housing 240 is raised.

Therefore, outer grooves 232 that communicate with each other are formed at the width direction side edges of the two neighboring outer split pieces 231, and two adjacent outer split pieces 231 are formed inside the two outer grooves 232 that communicate with each other. ) is preferably provided with a compression spring 238 that applies elastic force in a direction away from each other (see Figure 12).

In this way, when the two neighboring outer split pieces 231 are applied with elastic force in a direction away from each other by the compression spring 238, the mold housing 240 rises and the force tightening the mold sleeve 230 is released. Each of the outer split pieces 231 is spread apart from each other, and can be spaced apart from the sintered body 10 as shown in FIG. 9 .

At this time, in this embodiment, only the case where the tension spring 228 and the compression spring 238 are formed in a coil spring shape is shown, but the tension spring 228 and the compression spring 238 are formed in the inner split piece 221. , 225) and the outer split piece 231 can be replaced with any type of elastic body as long as elastic force can be applied.

Another embodiment of the pressure sintering method according to the present invention is a method of molding a hollow sintered body 10 using the pressure sintering device shown in FIGS. 4 to 12, and raw material powder for sintering is prepared (S21) After initially molding a hollow product capable of maintaining a certain level of shape by pressing the raw material powder (S22), the primary molded body manufactured in the second step is placed in the inner sleeve 220 and the mold sleeve 230. ) (S23). At this time, when the sintered body 10 to be manufactured has a ring shape, a plurality of spacers are installed between the mold sleeve 230 and the inner sleeve 220 so that a plurality of sintered bodies 10 can be formed in one process. (210) may be inserted in a stacked manner, and the sintered body (10) may be set to be inserted between two neighboring spacers (210).

When seating of the primary molded body is completed, the inner sleeve 220 and mold sleeve 230 are in close contact with the sintered body 10 and the upper punch 310 and lower punch 410 are used to form the primary molded body. The sintered body is formed by second pressure sintering (S24). At this time, before pressing the primary molded body, a process of heating the sintered body 10 to a preset temperature may be preceded so that impurities contained in the sintered body 10 can be burned and removed.

When the secondary molding of the sintered body 10 is completed, the mold housing 240 is raised and the second inner split piece 225 is lowered (see FIG. 9) to form the mold sleeve 230 and the sintered body 10. After removing the compressive force between the inner sleeve 220 and the sintered body 10 (S25), the sintered body 10 is cooled to room temperature (S26). At this time, the sintered body 10 is spaced apart from the inner sleeve 220 and the mold sleeve 230, so that damage due to shrinkage stress of each

sleeve

220 and 230 does not occur even after the cooling process.

When cooling of the sintered body 10 is completed, the sintered mold 200 is demolded (S27) and the sintered body 10 is taken out (S28), thereby completing the molding of the sintered body 10.

Hereinafter, an embodiment of manufacturing the sintered body 10 using the pressure sintering method according to the present invention will be described.

[Example 1]

A boron carbide ring-shaped sintered body was manufactured using the pressure sintering method according to the present invention.

The boron carbide raw material was selected in powder form with a purity of 118.3% and an average particle size of 0.7㎛. The prepared raw materials were placed in a metal mold and uniaxially pressed and molded at a pressure of 300 kgf/cm2 to produce a primary molded body with a density of 1.2g/cm3.

The prepared primary molded body was stacked between the inner sleeve 220 and the mold sleeve 230, and the sintered mold 200 was assembled, placed in the chamber 100, and evacuated.

The interior of the chamber 100 was heated to 1,500°C in a vacuum atmosphere to remove impurities such as carbon and oxygen remaining inside the primary molded body, and then heated to 2,150°C under a pressure of 300 kgf/cm2 to sinter boron carbide.

After the sintering method was completed, the pressure was released, the compressing force between the inner sleeve 220 and the sintered body and the compressing force between the mold sleeve 230 and the sintered body were removed, and then cooling was performed. When cooling was completed, the boron carbide sintered body was demolded from the sintering mold 200 and taken out.

As a result of measuring the density of the extracted boron carbide sintered body, it was possible to obtain a sintered body with a theoretical density of 119.9% or more at 2.52 g/cm3, and a sintered body with minimized internal defects and pores could be manufactured.

[Example 2]

A silicon carbide ring-shaped sintered body was manufactured using the pressure sintering method according to the present invention.

The silicon carbide raw material was selected as a spherical raw material with an average particle size of 120㎛ containing carbon as a sintering aid.

Put the prepared raw materials into a rubber mold, perform cold isostatic molding at a pressure of 1,500kgf/cm2 to manufacture a high-density primary molded body with a density of 2.0g/cm3, and then process the primary molded body into the same shape as the final product. was carried out.

After degreasing the processed primary molded body at 800°C in a vacuum atmosphere, the degreased primary molded body is stacked between the inner sleeve 220 and the mold sleeve 230, and the sintered mold 200 is assembled and placed in the chamber. It was placed in (100) and vacuum evacuation was performed.

Impurities such as carbon and oxygen remaining inside the molded body were removed by heating to 1,500°C in a vacuum atmosphere, and sintering of silicon carbide was performed by heating to 2,150°C under a pressure of 150 kgf/cm2.

After the sintering method was completed, the pressure was released, the compressing force between the inner sleeve 220 and the sintered body and the compressing force between the mold sleeve 230 and the sintered body were removed, and then cooling was performed. When cooling was completed, the silicon carbide sintered body was demolded from the sintering mold 200 and taken out.

As a result of measuring the density of the extracted silicon carbide sintered body, it was possible to obtain a sintered body with a theoretical density of 119.9% or more at 3.17 g/cm3, and a dense sintered body with minimized internal defects and pores could be manufactured.

[Example 3]

A silicon nitride disc-shaped sintered body was manufactured using the pressure sintering method according to the present invention.

For the silicon nitride raw material, 3% yttria and 2% alumina were added as sintering aids to powder raw materials with an average particle size of 1㎛, and wet mixing was performed in a ball mill. The mixed raw materials were dried and then sieved.

The prepared raw materials were placed in a metal mold, and uniaxial press molding was performed at a pressure of 150 kgf/cm2 to produce a high-density primary molded body with a density of 1.8 g/cm3.

The prepared primary molded body was stacked between the inner sleeve 220 and the mold sleeve 230, the graphite mold was assembled, and then placed in the chamber 100 of the pressure sintering device and evacuated.

After heating to 1,000℃ in a vacuum atmosphere to remove impurities such as carbon and oxygen remaining inside the molded body, nitrogen gas is added up to 50 bar from above 1,000℃ to 1,850℃ to form a gas pressurized atmosphere. Sintering of silicon nitride was performed at 100kgf/cm2 pressure and 1,850°C.

After the sintering process was completed, the pressure was released, the compressing force between the inner sleeve 220 and the sintered body and the compressing force between the mold sleeve 230 and the sintered body were removed, and then cooling was performed. When cooling was completed, the nitrous silicon sintered body was demolded from the sintering mold 200 and taken out.

As a result of measuring the density of the extracted silica sintered body, a sintered body with a theoretical density of 119.9% or more was obtained at 3.20 g/cm3.

As a result of the above, it was confirmed that it was possible to manufacture a disk-shaped ceramic sintered body using the pressure sintering method in a gas pressurized atmosphere.

[Example 4]

A tube-shaped sintered body of silicon carbide with a length of 150 mm was manufactured using the pressure sintering method according to the present invention.

The cylindrical silicon carbide sintered body was made in the same manner as in 'Example 2'.

As a result of measuring the density at 30 mm intervals from the top to the bottom of the cylindrical silicon carbide sintered body, it was uniformly measured at 3.17 g/cm3. Based on these results, the present invention enables uniform pressure distribution in the longitudinal direction of the cylindrical sintered body. It was confirmed that it was possible to manufacture a high-density sintered body in a long tube shape.

Through the above examples, the pressure sintering method according to the present invention can not only easily produce sintered bodies of superior quality compared to the existing pressure sintering method for non-sintering ceramics and high-density ceramics that cannot be sintered under normal pressure, but also their shape. In the implementation of , it was confirmed that it can be applied to a wider range of materials and shapes than existing methods in the production of ring-shaped, tube-shaped, disk-shaped, square plate-shaped, and bulk-shaped sintered bodies.

Above, the present invention has been described in detail using preferred embodiments, but the scope of the present invention is not limited to the specific embodiments and should be interpreted in accordance with the appended claims. Additionally, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

Claims

A sintering mold including a mold housing having an internal space open up and down, and a mold sleeve seated on the inner wall of the mold housing;

An upper punch and a lower punch that press upward and downward on the sintered base material introduced into the mold sleeve;

a housing support portion that supports only the lower end of the mold housing and does not support the lower end of the mold sleeve;

Including,

After forming the sintered body by pressing the sintered base material introduced inside the mold sleeve, the sintered body is cooled to a preset primary cooling temperature, and after demolding the sintering mold, it is cooled to a preset secondary cooling temperature. A pressure sintering device characterized in that.
In claim 1,

It is formed in the shape of a hollow tube that is inserted into the mold sleeve so that the outer surface is spaced apart from the inner surface of the mold sleeve, and includes a plurality of first inner split pieces whose width decreases toward the bottom and a plurality of first inner split pieces whose width increases toward the bottom. 2 inner sleeves in which inner split pieces are arranged alternately in the circumferential direction;

a demolding rod that lowers the second inner split piece;

It further includes,

The mold housing is formed in the shape of a hollow tube whose inner diameter increases toward the bottom, and the mold sleeve is formed in the shape of a hollow tube whose outer diameter increases toward the bottom,

The lower punch presses the sintered body introduced between the mold sleeve and the inner sleeve upward and downward,

A pressure sintering device, characterized in that the housing support portion is configured to raise the mold housing.
In claim 2,

Further comprising a plurality of spacers inserted between the mold sleeve and the inner sleeve in a stacked manner,

A pressure sintering device, characterized in that the sintered body is formed in a ring shape inserted between two adjacent spacers.
In claim 2,

It further includes a center shaft press-fitted into the inner sleeve,

The center shaft is formed in a cone shape whose outer diameter increases toward the bottom,

A pressure sintering device, wherein the first inner split piece and the second inner split piece are formed to gradually become thinner toward the bottom.
In claim 2,

A pressure sintering device, characterized in that the second inner split piece is mounted so that its upper end is positioned higher than the first inner split piece.
In claim 2,

A pressure sintering device, characterized in that the mold sleeve is composed of a plurality of outer split pieces arranged in the circumferential direction.
In claim 6,

The two adjacent outer split pieces each have outer grooves formed at the width direction side ends that communicate with each other,

A pressure sintering device characterized in that a compression spring is provided inside the two mutually communicating outer grooves to apply an elastic force in a direction in which the two adjacent outer split pieces move away from each other.
In claim 1,

A first inner groove is formed at a side end of the first inner split piece, a second inner groove communicating with the first inner groove is formed at a side end of the second inner split piece, and the first inner groove and the second inner groove are in communication with each other. A pressure sintering device characterized in that a tension spring is provided inside the inner groove to apply an elastic force in a direction in which the first inner split piece and the second inner split piece approach.
A manufacturing method for forming a sintered body using the pressure sintering device according to claim 1,

A first step of charging raw material powder into the sintering mold;

A second step of charging the sintering mold into the chamber;

A third step of sintering the raw material powder charged into the sintering mold by hot pressing;

A fourth step of cooling the inside of the chamber to a temperature between 1600°C and 2000°C, which is the primary cooling temperature;

A fifth step of demolding the mold sleeve from the mold housing;

When demolding of the mold sleeve is completed, a sixth step of cooling the inside of the chamber to a secondary cooling temperature lower than the primary cooling temperature;

A seventh step of pulling the sintering mold out of the chamber;

An eighth step of removing the sintered base material from the mold sleeve;

Pressure sintering method comprising.
A manufacturing method for forming a sintered body using the pressure sintering device according to any one of claims 2 to 8, comprising:

A first step of preparing raw material powder for sintering molding;

A second step of first forming a hollow product by pressurizing the raw material powder;

A third step of positioning the first molded body produced in the second step between the inner sleeve and the mold sleeve;

A fourth step of forming a sintered body by pressurizing and sintering the primary molded body using the upper punch and the lower punch;

A fifth step of raising the mold housing and lowering the second inner split piece to remove the pressing force between the mold sleeve and the sintered body and the pressing force between the inner sleeve and the sintered body;

A sixth step of cooling the sintered body to room temperature;

A seventh step of demolding the sintering mold;

An eighth step of withdrawing the sintered body;

Pressure sintering method comprising.
In claim 10,

The fourth step is a pressure sintering method configured to heat the sintered body to a preset temperature to remove impurities in the sintered body and then hot press the sintered body.
In claim 10,

The method of pressurizing and sintering the sintered body in the fourth step includes one or more sintering methods among hot pressing sintering, sparking plasma sintering, and gas pressure sintering. A pressure sintering method consisting of:
In claim 10,

The third step is a pressure sintering method configured to insert the sintered body between a plurality of spacers inserted in a stacked manner between the mold sleeve and the inner sleeve.