KR102145545B1 - Method and apparatus of hot pressure sintering - Google Patents

Abstract

The hot pressure sintering method according to the present invention comprises: a first step of charging raw material powder into a mold assembly; A second step of charging the mold assembly into the chamber; A third step of hot pressing and sintering the raw material powder charged into the mold assembly; A fourth step of cooling the inside of the chamber to a pre-set primary cooling temperature; A fifth step of demolding the mold sleeve of the mold assembly from the mold housing inside the chamber; A sixth step of cooling the inside of the chamber to a predetermined secondary cooling temperature when the mold sleeve is demolded; A seventh step of drawing the mold assembly out of the chamber; And an eighth step of removing the sintered body from the mold sleeve. By using the hot press sintering method and apparatus according to the present invention, it is possible to prevent damage to the mold housing or the sintered body due to the difference in shrinkage between the mold housing and the sintered body occurring in the cooling process after hot pressing, thereby improving the productivity of the sintered body. And can increase the life of the mold housing.

Description

Hot press sintering method and apparatus {METHOD AND APPARATUS OF HOT PRESSURE SINTERING}

The present invention relates to a hot press sintering method and apparatus, and more particularly, to a hot press sintering method and apparatus for preventing damage to a mold housing or a sintered body due to a difference in thermal expansion coefficient between the mold housing and the sintered body occurring in the cooling process. About.

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-press sintering process. When manufacturing such a hexagonal boron nitride and its composite, a sintered body lower than that of a mold housing Due to the coefficient of thermal expansion, stress is generated in the sintered body and the mold housing during the cooling process. At this time, the stress applied to the sintered body deteriorates the physical properties of the sintered body and causes cracking, thereby lowering the yield of the sintered body, and stress is applied to the mold housing, causing breakage or deformation of the mold housing.

Accordingly, the price competitiveness of the hexagonal boron nitride and its composite is reduced, and despite its excellent physical properties, it is limitedly used for some products. In particular, although hexagonal boron nitride having an extremely low coefficient of thermal expansion is produced using a mold housing made of an expensive carbon composite, there is a problem in that manufacturing cost increases because such a carbon composite mold housing is very expensive.

In order to prevent damage to the mold housing and the sintered body, a mold housing is produced with a carbon composite having a very low coefficient of thermal expansion to produce hexagonal boron nitride, but the carbon composite also has a relatively high coefficient of thermal expansion compared to hexagonal boron nitride, so it is cooled. It is a situation that has a problem that cannot completely remove the stress generated in the process.

KR 10-0816371 B1

The present invention has been proposed to solve the above problems, and is sintered by a hot pressing method, but hot pressing is constructed so that the mold housing or the sintered body is not damaged due to the difference in shrinkage between the mold housing and the sintered body occurring in the cooling process. It is an object to provide a method and apparatus for sintering.

The hot-pressing sintering method according to the present invention for achieving the above object includes: a first step of charging raw material powder into a mold assembly; A second step of charging the mold assembly into the chamber; A third step of hot pressing and sintering the raw material powder charged into the mold assembly; A fourth step of cooling the inside of the chamber to a pre-set primary cooling temperature; A fifth step of demolding the mold sleeve of the mold assembly from the mold housing inside the chamber; A sixth step of cooling the inside of the chamber to a predetermined secondary cooling temperature when the mold sleeve is demolded; A seventh step of drawing the mold assembly out of the chamber; And an eighth step of removing the sintered body from the mold sleeve.

The first step further includes a process of pressing and pressing the raw material powder loaded into the mold assembly after charging the raw material powder into the mold assembly.

The second step further includes forming a vacuum in the chamber and introducing an inert gas after the mold assembly is loaded into the chamber.

In the third step, the mold housing is separated from the upper surface of the mold housing support by 10 mm to 30 mm, and then hot press sintering is performed.

The raw material powder is a hexagonal boron nitride powder, the sintering temperature is 2000 ℃ to 2200 ℃, the third step, when the raw material powder is heated to 1600 ℃ to 2000 ℃ pressure of 100kgf / ㎠ to 200 kgf / ㎠ It is configured to pressurize sintering, and the pressurization sintering time is set to 3 to 6 hours.

The primary cooling temperature is 1600 ℃ to 2000 ℃.

The hot press sintering apparatus according to the present invention includes a mold housing having an inner space open up and down, a mold sleeve seated on the inner wall of the mold housing, and inserted into the upper and lower sides of the mold sleeve, respectively, but the raw material powder loading space A mold assembly including an upper punch and a lower punch spaced vertically to secure the upper and lower punches, a mold housing support for supporting a lower end of the mold housing, and a mold support plate on which the mold housing support is mounted; A chamber provided with an internal space into which the mold assembly can be inserted, a heat insulating material surrounding the mold assembly, a heating element heating the mold assembly, and a mold support supporting the mold assembly; A vacuum exhaust system for forming a vacuum in the chamber; An upper cylinder and a lower cylinder for pressing the upper and lower punches of the mold assembly charged into the chamber; It comprises a; mold support driving device for lifting the mold support.

The mold assembly further includes a demolding punch coupled to an upper end of the upper punch.

It further includes a load measuring unit for sensing a downward load applied to the mold support.

By using the hot press sintering method and apparatus according to the present invention, it is possible to prevent damage to the mold housing or the sintered body due to the difference in shrinkage between the mold housing and the sintered body occurring in the cooling process after hot pressing, thereby improving the productivity of the sintered body. And can increase the life of the mold housing.

1 is a flow chart of a hot press sintering method according to the present invention.
2 is a schematic diagram of a hot press sintering apparatus according to the present invention.
3 is a schematic diagram of a mold assembly included in the hot press sintering apparatus according to the present invention.

Hereinafter, embodiments of the hot press sintering method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a flow chart of a hot press sintering method according to the present invention.

The hot press sintering method according to the present invention is a manufacturing method for sintering non-sintering non-oxide ceramics having a low coefficient of thermal expansion such as hexagonal boron nitride into a certain shape, so that damage to the mold housing or the sintered body does not occur during the cooling process. The biggest feature is that it demolds at a high temperature above a certain level.

That is, in the hot press sintering method according to the present invention, a non-sintering non-oxide ceramics such as hexagonal boron nitride (hereinafter abbreviated as'raw material') is charged into the mold assembly (S10), and then the raw material powder is charged. The mold assembly is charged into the chamber (S20). At this time, the mold assembly is configured to include a mold housing having an inner space open up and down, a mold sleeve mounted inside the mold housing to which the raw material powder is charged, and an upper punch and a lower punch for pressing the raw material powder. Although (see Fig. 3), such a mold assembly is used in the same manner in a conventional hot press sintering apparatus, and a detailed description thereof will be omitted.

When the mold assembly is charged into the chamber, the raw material powder charged in the mold assembly is hot-pressed and sintered (S30), and the sintering conditions at this time are appropriate depending on various conditions such as the type of raw material powder or the characteristics of the product to be manufactured. Can be chosen. When hot press sintering is completed, the chamber is cooled to a pre-set primary cooling temperature (S40), and then the mold sleeve is demolded from the mold housing (S50), and when the mold sleeve is demolded, the inside of the chamber is preliminarily removed. Cool down to the secondary cooling temperature set in (S60).

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

At this time, when the raw material powder is used as hexagonal boron nitride powder and the mold housing is made of graphite material, the thermal expansion coefficient of the mold housing is higher than that of the sintered product. When cooled to the second cooling temperature at once, the mold housing shrinks more than the sintered product, and stress is generated between the sintered product and the mold housing. When such stress is transferred to the sintered product, deformation of the sintered product is caused, and when the stress is transferred to the mold housing, cracks are generated in the mold housing, resulting in a remarkably shortened life of the mold housing.

However, in the hot press sintering method according to the present invention, the mold sleeve is not cooled to the secondary cooling temperature at one time while the mold sleeve is mounted on the mold housing, but is cooled to the primary cooling temperature, and the mold sleeve is removed from the mold housing. After demolding, it is cooled down to the secondary cooling temperature, which has the advantage of fundamentally preventing the occurrence of stress due to the difference in shrinkage between the sintered product and the mold housing.

On the other hand, in order to minimize the amount of shrinkage of the raw material powder in the hot press sintering step (S30), it is preferable to add a process of pressing the raw material powder loaded into the mold assembly with a press after charging the raw material powder into the mold assembly. Do. In this way, if the press-pressing process of the raw material powder is additionally preceded by the hot pressing sintering, the raw material powder is pressed in two steps, so that the raw material powder compressibility increases, and accordingly, the structure of the sintered product becomes more dense. Can be obtained.

In addition, a process of forming a vacuum inside the chamber and introducing an inert gas after the mold assembly is charged into the chamber may be added so that an unexpected chemical reaction does not occur during the hot pressurization sintering process in the chamber. At this time, the inert gas introduced into the chamber can be applied to various gases such as nitrogen gas, provided the interior of the chamber can be made into an inert atmosphere.

On the other hand, the mold housing charged with the raw material powder is seated on the mold housing support when it is inserted into the chamber, and when the mold housing is heated for hot pressurization sintering, the mold housing expands thermally, so that the mold housing support is pressed. A phenomenon in which the mold housing support is damaged may occur. Therefore, when hot pressing sintering after inserting the mold assembly into the chamber, it is preferable to perform hot pressing sintering after the mold housing is separated from the upper surface of the mold housing support by 10 mm to 30 mm.

In addition, since the hexagonal boron nitride powder undergoes sintering shrinkage at 1600°C to 2000°C, in the case of selecting the hexagonal boron nitride powder as the raw material powder, the sintering temperature is heated to 2000°C to 2200°C, but sintering shrinkage occurs. It is preferable to pressurize sintering at a pressure of 100 kgf/cm 2 to 200 kgf/cm 2 at 1600°C to 2000°C. At this time, the pressure sintering time is preferably set to 3 to 6 hours.

In addition, the hexagonal boron nitride powder does not undergo deformation until it is cooled to 1600°C to 2000°C after pressing sintering is completed, and the primary cooling temperature is preferably set to 1600°C to 2000°C.

2 is a schematic diagram of a hot press sintering apparatus according to the present invention, and FIG. 3 is a schematic diagram of a mold assembly included in the hot press sintering apparatus according to the present invention.

The hot press sintering apparatus according to the present invention is an apparatus manufactured to perform the above-mentioned hot press sintering method, and has the greatest feature of construction in that it is configured to be demolded at a high temperature.

That is, as shown in FIG. 2, the hot press sintering apparatus according to the present invention includes a mold assembly 100 for pressing and sintering the charged raw material powder 10, and an interior into which the mold assembly 100 can be inserted. A chamber provided with a space provided with an insulating material 210 surrounding the mold assembly 100, a heating element 220 for heating the mold assembly 100, and a mold support 230 supporting the mold assembly 100 200, a vacuum exhaust system 300 for forming a vacuum in the chamber 200, and an upper punch 132 and a lower punch 134 of the mold assembly 100 charged in the chamber 200. It is configured to include an upper cylinder 410 and a lower cylinder 420 to pressurize, and a mold support driving device 500 for raising and lowering the mold support 230.

As shown in FIG. 3, the mold assembly 100 includes a mold housing 110 having an inner space open up and down, a mold sleeve 120 seated on the inner wall of the mold housing 110, and the Supports the upper and lower punches 132 and 134, which are respectively inserted into the upper and lower sides of the mold sleeve 120, and spaced up and down so as to secure a loading space for the raw material powder 10, and the lower end of the mold housing 110 A mold housing support 150, a mold support plate 160 on which the mold housing support 150 is seated, and a demolding punch 136 coupled to the upper end of the upper punch 132 are included. At this time, the demolding punch 136 has an outer edge that is larger than the inner surface 121 of the mold sleeve 120 and smaller than the outer surface 122 of the mold sleeve 120. When descending, the mold housing 110 By pressing only the upper end of the mold sleeve 120 without pressing the upper end, the mold sleeve 120 can be removed from the mold housing 110. On the other hand, the raw material powder 10 is charged in the space between the upper punch 132 and the lower punch 134 of the inner space of the mold sleeve 120, so that a plurality of sintered products can be produced at once. Separated by the diaphragm 140.

The mold sleeve 120 is formed in the shape of a hollow tube, the outer surface is formed to be inclined in the direction that the outer diameter increases toward the lower side, and the inner surface of the mold housing 110 is formed to be inclined toward the inner diameter increases toward the lower side. As shown in FIG. 3, when the mold sleeve 120 is press-fitted into the mold housing 110, the mold sleeve 120 cannot be pulled out upwards, but can be pulled out only downwards.

In addition, the mold housing 110 is simply mounted on the mold housing support 150, and the lower punch 134 is press-fitted to the lower side of the mold sleeve 120, as shown in FIG. When the lower punch 134 is moved upward while the lower punch 134 is moved, the bottom surface of the mold housing 110 is spaced upward from the upper surface of the mold housing support 150 by the moving distance of the lower punch 134.

The mold assembly 100 configured as described above is mounted so as to be able to be inserted and withdrawn into the chamber 200, and when the mold assembly 100 is brought into the chamber 200, the heat insulating material 210 is formed as a mold assembly ( Since the heating element 220 is arranged to surround 100 and is positioned between the mold assembly 100 and the heat insulating material 210, the heat radiated from the heating element 220 is effectively utilized to heat the mold assembly 100.

In addition, the mold support 230 may be manufactured in any shape as long as it can effectively support the mold support plate 160 of the mold assembly 100, and the mold support driving device 500 stably lifts and lowers the mold support 230 If you can, it can be applied in any structure.

At the upper and lower sides of the chamber 200, the upper cylinder 410 which presses the upper punch 132 downward by penetrating the upper wall of the chamber 200 and the lower punch 134 through the lower wall of the chamber 200, respectively. ), the lower cylinder 420 that pressurizes upward is mounted, and the raw material powder charged into the mold assembly 100 by operating the upper cylinder 410 and the lower cylinder 420 even when the chamber 200 is not opened. (10) It becomes possible to pressurize sintering.

In addition, a load measurement unit 600 for sensing a downward load applied to the mold support 230 is provided below the mold support 230, and for the function of the load measurement unit 600, refer to the following examples. It will be described in detail.

Hereinafter, an embodiment of manufacturing a sintered product using the hot press sintering apparatus according to the present invention will be described.

[Example]

First, a hexagonal boron nitride powder having a purity of 95% to 99% and an average particle diameter of 2 μm to 4 μm, and a mold assembly for pressure sintering are prepared. After the hexagonal boron nitride powder is charged into the mold housing made of graphite, the hexagonal boron nitride powder is first compressed by pressing at a pressure of 10 kgf/cm 2 to 50 kgf/cm 2 using a hydraulic press.

When the pressurization of the hexagonal boron nitride powder using a hydraulic press is completed, the mold assembly is charged into the chamber of the hot pressurized sintering apparatus, and when the charging of the mold assembly is completed, the door of the chamber is closed and vacuum exhaust is performed. When vacuum exhaust is completed to 5.0×10-2 Torr or less, nitrogen gas is injected to 1 atmosphere and nitrogen gas is flowed into the chamber at 5L/min to make the interior of the chamber an inert atmosphere.

When the nitrogen gas input is completed to 1 atm, the sintering temperature is heated to about 2,000°C to 2,200°C. At this time, the mold housing and the mold are not excessively pressurized during the thermal expansion of the mold housing. The process of setting the height of the mold housing so that the spacing of the housing support is between 10 mm and 30 mm is preceded. Position setting of the mold housing is performed by raising and lowering the lower punch pressed into the lower side of the mold sleeve.

When the sintering shrinkage of the hexagonal boron nitride powder reaches 1,600°C to 2,000°C during heating, pressure sintering is performed at a pressure of 100kgf/cm2 to 200kgf/cm2 over about 3 to 6 hours.

When the pressure sintering process is completed, perform primary cooling to 1,600°C to 2,000°C where hexagonal boron nitride deformation does not occur, release the pressure in the chamber, and then until a load due to the weight of the mold occurs in the load measuring unit (i.e. , Lower punch is lowered until the mold housing is seated on the upper surface of the mold housing support, and the mold sleeve is demolded from the mold housing in the chamber. At this time, the demolding of the mold sleeve is performed by lowering the upper punch and the demolding punch. The raw material powder is formed into a sintered product through the process of hot pressing sintering and is fixed to the inner surface of the mold sleeve, so that the upper punch is a sintered product. The sintered product and the mold sleeve fixed thereto may be demolded from the mold housing by the force to lower the sintered product. Of course, when the sintered product is drawn to the lower side of the mold sleeve by the downward pressing force of the upper punch, the mold sleeve is demolded from the mold housing by a demoulding punch.

The lowering of the upper punch and the demolding punch is continued until the sintered product and the mold sleeve completely come out of the mold housing, that is, the load on the mold support continuously increases and then decreases.

When demoulding is completed, secondary cooling is performed to room temperature. When secondary cooling is completed, the mold assembly is removed from the chamber, and the sintered product is removed from the mold sleeve to complete all processes.

When the characteristics of the hexagonal boron nitride sintered body manufactured through the above example are analyzed, it is shown in Table 1 below.

division In use
Hexagonal boron nitride Produced by the present invention
Hexagonal boron nitride Mil degree (g/cm3) 1.6 1.89 Porosity (%) - 18.3 Mechanical properties Bending strength (MPa) 20 26 Modulus of elasticity (GPa) - 43 Thermal
Characteristics Thermal conductivity (W/mK) 60 58 Coefficient of thermal expansion (ppm/K) -0.6 -1.93 Electrical
Characteristics Volume resistance (Ω·cm) 10 ¹⁵ 10 ¹⁵ Permittivity (1MHz) 4.9 4.0

As shown in Table 1 above, it can be seen that the hexagonal boron nitride sintered body according to the present invention has superior density and strength compared to the hexagonal boron nitride sintered body currently commercially available.

Therefore, the present invention removes the stress generated in the cooling process in hot press sintering of a non-sinterable non-oxide system having a small coefficient of thermal expansion such as hexagonal boron nitride to improve physical properties of sintered products, production yield and mold life. Cost savings can be made possible. In addition, by using the hot press sintering method and apparatus according to the present invention, it is possible to easily manufacture a hexagonal boron nitride sintered body that is difficult to manufacture and has a high manufacturing cost, so that the hexagonal boron nitride sintered body can be more usefully utilized throughout the industry. There is an advantage of being there.

In the present invention, a non-sintering non-oxide-based structural material having a small coefficient of thermal expansion such as hexagonal boron nitride as a raw material powder is described, but the raw material powder includes silicon carbide (SiC), boron carbide (BC), and silicon nitride (SiN). Non-oxide based structural materials may also be included.

As described above, the present invention has been described in detail using preferred embodiments, but the scope of the present invention is not limited to specific embodiments, and should be interpreted by the appended claims. In addition, those skilled in the art will have to understand that many modifications and variations are possible without departing from the scope of the present invention.

10: raw material powder 100: mold assembly
110: mold housing 120: mold sleeve
132: upper punch 134: lower punch
136: demoulding punch 140: diaphragm
150: mold housing support 160: mold support plate
200: chamber 210: insulation
220: heating element 230: mold support
300: vacuum exhaust system 410: upper cylinder
420: lower cylinder 500: mold support drive device
600: load measurement unit

Claims (9)

A mold housing having an inner space open up and down, a mold sleeve seated on the inner wall of the mold housing, and an upper punch that is respectively inserted into the upper and lower sides of the mold sleeve and spaced vertically so as to secure a space for charging raw material powder, and A lower punch, a mold housing support that does not support the lower end of the mold sleeve but supports only the lower end of the mold housing, a mold support plate on which the mold housing support is seated, and the mold housing when lowered by being coupled to the upper end of the upper punch In the method of hot pressing and sintering raw material powder using a mold assembly having a demolding punch for pressing only the upper end of the mold sleeve without pressing the upper end of,
A first step of charging raw material powder into the mold assembly;
A second step of charging the mold assembly into the chamber;
A third step of hot pressing and sintering the raw material powder charged into the mold assembly;
A fourth step of cooling the inside of the chamber to a temperature between 1600°C and 2000°C, which is a primary cooling temperature;
A fifth step of demolding the mold sleeve from the mold housing by lowering the demolding punch so that only the mold sleeve is pressed downward without the mold housing being pressed downward;
A sixth step of cooling the inside of the chamber to a secondary cooling temperature lower than the primary cooling temperature when the demolding of the mold sleeve is completed;
A seventh step of drawing the mold assembly out of the chamber;
An eighth step of removing the sintered body from the mold sleeve;
Including,
The third step is a hot-press sintering method, characterized in that the mold housing is separated from the upper surface of the mold housing support by 10mm to 30mm, and then hot-pressed sintering. The method according to claim 1,
The first step further comprises a step of press-pressing the raw material powder loaded into the mold assembly after charging the raw material powder into the mold assembly. The method according to claim 1,
The second step further includes forming a vacuum in the chamber and introducing an inert gas after the mold assembly is charged into the chamber. delete The method according to claim 1,
The raw material powder is a hexagonal boron nitride powder,
The sintering temperature is 2000°C to 2200°C,
The third step is configured to press sinter at a pressure of 100 kgf/cm 2 to 200 kgf/cm 2 when the raw material powder is heated to 1600° C. to 2000° C., and the press sintering time is set to 3 to 6 hours. Hot-press sintering method. delete A mold housing having an inner space open up and down, a mold sleeve seated on the inner wall of the mold housing, and an upper punch that is respectively inserted into the upper and lower sides of the mold sleeve and spaced vertically so as to secure a space for charging raw material powder, and A lower punch, a mold housing support that does not support the lower end of the mold sleeve but supports only the lower end of the mold housing, a mold support plate on which the mold housing support is seated, and the mold housing when lowered by being coupled to the upper end of the upper punch A mold assembly having a demolding punch for pressing only the upper end of the mold sleeve without pressing the upper end of the mold;
A chamber provided with an inner space into which the mold assembly can be inserted, a heat insulating material surrounding the mold assembly, a heating element heating the mold assembly, and a mold support supporting the mold assembly;
A vacuum exhaust system for forming a vacuum in the chamber;
An upper cylinder and a lower cylinder for pressing the upper and lower punches of the mold assembly charged into the chamber;
Including,
The raw material powder charged in the mold assembly is hot-pressed and sintered, the inside of the chamber is cooled to a pre-set primary cooling temperature, and then the mold sleeve of the mold assembly is demolded from the mold housing inside the chamber, and the mold sleeve When the demolding of is completed, the hot pressurized sintering apparatus is configured to cool the inside of the chamber to a predetermined secondary cooling temperature. delete The method of claim 7,
The hot pressurized sintering apparatus further comprises a mold support driving device for raising and lowering the mold support, and a load measuring unit detecting a downward load applied to the mold support.

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