JPH07330446A - Sintering method and device therefor - Google Patents

Abstract

PURPOSE:To suppress dissipation due to oxidation in dies or the like and to reduce the cycle time of sintering when a powder material is sintered with an electric current under pressure. CONSTITUTION:An electric current is applied on side faces of dies 25 to supply heat to the powder material 28, while the powder material 28 in the dies 25 is pressed in the vertical direction by ceramic upper and lower punches 26 and 27. Thus, large pressing force is given to the powder material 28 so that the sintering temp. is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintering method and an apparatus therefor.

[0002]

2. Description of the Related Art As a sintering method, there is a method in which a powder material is pressed and energized to be sintered (current sintering). Specifically, as shown in FIG. 11, this sintering method is performed by the powder material 101.
A cylindrical mold 102 (for example, a carbon (graphite) die) for accommodating a mold, and a conductive punch 10 that is displaceably movable with respect to the mold 102 and presses the powder material 101 in the mold 102.
3 (for example, made of carbon) and a current supply means (power source) 104 for supplying an electric current to the conductive punch 103 to apply the Jule heat to the powder material. As a result, the powder material 101 is formed into a sintered body.

[0003]

However, in the above sintering apparatus, the punch 103 must be a conductor because it is necessary to supply an electric current to the powder material 101 through the punch 103 as described above. Since it is not possible to use a punch having a strong strength, it is not possible to sufficiently increase the pressure applied to the powder material 101, and accordingly, the pressure applied to the powder material 101 cannot be increased. Only the sintering temperature is increased. Therefore, from the viewpoint of suppressing the oxidative consumption of the punch 103, the mold 102, etc., although the sintering process by such a sintering device is performed in a vacuum device, a complete vacuum state cannot be obtained. The binding temperature has a great influence on the oxidative consumption of the mold 102 and the like. Moreover, in the above apparatus, if the vacuum apparatus is opened immediately after sintering, the amount of residual heat will significantly accelerate the oxidative consumption of the mold and the like.
After sintering, it cannot be opened unless the mold is cooled to such an extent that the oxidation consumption rate does not matter, and the cycle time (time required for one sintering step) must be lengthened accordingly. I don't get it. The present invention has been made in view of the above circumstances, and an object thereof is to suppress oxidation consumption in a mold or the like and shorten the cycle time of the sintering process in the case of sintering by applying electricity while pressing a powder material. Especially.

[0004]

In order to achieve the above object, according to the invention of claim 1, in a sintering method in which a powder material is pressed and energized to sinter, the pressing is applied. ,
The punch is made of a high-strength material, and the energization is performed from the side in the pressing direction of the punch without passing through the punch. With the above configuration, heat can be supplied to the powder material by energization as usual, while pressing the powder material with a high strength material without considering the energization by the punch (which must be a conductor). Since it is performed by the punch used, it is possible to increase the pressing force on the powder material more than ever,
Along with this, the sintering temperature can be lowered. Therefore, the influence of the sintering temperature on the oxidation consumption rate can be reduced, and the time for cooling the mold or the like after sintering can be shortened to such an extent that the oxidation consumption rate does not matter. As a result, it is possible to suppress the oxidation consumption of the mold and the like and to shorten the cycle time of the sintering process.

In order to achieve the above-mentioned object, the invention of claim 2 has a constitution in which the high-strength material is an insulator. With the above configuration, the same strength as that of the insulator is utilized to produce the same effect as that of the first aspect.

In order to achieve the above-mentioned object, the invention of claim 3 is the structure of claim 1 or 2, wherein the high-strength material is ceramics. With the above configuration, the sintering temperature is lowered by increasing the pressure applied to the powder material, and the properties of the ceramic showing high strength in a certain temperature range from the low temperature side are combined, and the ceramic is effectively used. According to claim 1 or 2
Will produce the same effect as.

In order to achieve the above-mentioned object, in the invention of claim 4, according to any one of claims 1 to 3, a plurality of sets of the powder material and the punch are prepared, and each powder material is prepared. While pressurizing, each set is energized to perform sintering. With the above configuration, in addition to producing the same effect as in any one of claims 1 to 3 described above, it is not necessary to supply an electric current to the powder material through the punch,
When each punch is pressed by the common conductive pressing means, even if some of the punches have some rattling, it is possible that the temperature distribution becomes non-uniform because no current flows. It can be suppressed. Therefore, it is possible to obtain a plurality of sintered bodies having a uniform temperature distribution in the radial direction.

In order to achieve the above-mentioned object, according to the invention of claim 5, a cylindrical mold for containing the powder material, and a powder in the mold provided so as to be displaceable with respect to the mold. In a sintering apparatus comprising a punch for pressing a material and an electric current supply means for applying a Jule heat to the powder material, the mold is a conductor, and the electric current supply means supplies electric current to the mold. And the punch is made of a high-strength material. With the above configuration, since current is supplied through the mold, heat can be supplied to the powder material as before, but there is no need to consider the energization by the punch (must be a conductor). The pressing of the body material can be performed by a punch using a high-strength material such as an insulator, and like the invention of claim 1 described above.
It is possible to increase the pressure applied to the powder material and lower the sintering temperature more than ever. For this reason, the influence of the sintering temperature on the oxidation consumption rate can be reduced, and the time for cooling the mold etc. after sintering to the extent that the oxidation consumption rate does not become a problem can be shortened, and the oxidation consumption in the mold etc. can be reduced. The cycle time of the sintering process can be shortened as well as suppressed.

In order to achieve the above-mentioned object, the invention of claim 6 provides the structure according to claim 5, wherein the punch is made of ceramics. With the above configuration, the punch has the same strength as the properties of ceramics, so that the same effect as that of the second aspect of the invention can be obtained.

In order to achieve the above-mentioned object, the invention of claim 7 is the structure according to claim 5 or 6, wherein the inner peripheral surface of the mold is covered with an insulating coating. With the above configuration, in addition to producing the same effect as in claim 5 or 6, only heat is supplied from the mold to the powder material inside the mold, whereby the powder material is conductive or non-conductive. Regardless of the material, as in the case of supplying heat from the radial center of the powder material to the radial outside of the powder material (conventional case), the radial outside portion of the powder material is It is possible to prevent the heat from being radiated to the outside, and it is possible to prevent the heat radiation phenomenon from occurring in the powder material. Therefore, it is possible to prevent the temperature distribution in the radial direction of the sintered body (powder material) from becoming non-uniform.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. First, before describing the sintering method according to the present invention, a sintering apparatus using the sintering method will be described. Figure 1
In the figure, 1 is a frame, and a lower pedestal 2 is provided at the bottom of the frame 1.
Is provided, and the cylinder device 3 is fixed to the lower pedestal 2. This cylinder device 3 includes a lower pedestal 2
The mold lift bar 4 is connected on the upper side of the mold lift bar 4, and the mold lift bar 4 is vertically displaced based on the expansion and contraction of the cylinder device 3. As shown in FIG. 1, a cylindrical stopper 5 is fitted around the die lift rod 4. A support plate 6 is attached to the outer periphery of the stopper 5, and the support plate 6 is a side frame 1 a of the frame body 1.
Is fitted and held (fixed).

A vacuum chamber 7 is mounted on the stopper 5, as shown in FIGS. The vacuum chamber 7 is composed of a chamber body 8 and a lid 9, and the inside of the vacuum chamber 7 is evacuated by a vacuum pump (not shown). The die lift rod 4 is inserted into the chamber body 8 of the vacuum chamber 7 from the lower portion of the chamber body 8 so that the die lift rod 4 can be displaced. The airtightness is maintained between the die lift rod 4 and the chamber body 8. Has been done.

An upper pedestal 10 is provided on the upper portion of the frame 1, and a cylinder device 1 is provided on the lower surface of the upper pedestal 10.
1 is fixed. A die pressure rod 12 is connected to the cylinder device 11 on the lower side of the cylinder device 11, and the die pressure rod 12 is displaced in the vertical direction based on the expansion and contraction of the cylinder device 11. ing. As shown in FIGS. 1 and 2, a cylindrical sliding cylinder 13 is slidably fitted around the outer periphery of the die pressure rod 12. A lid 9 of the vacuum chamber 7 is fixed to a lower portion of the sliding cylinder 13, and the die pressure bar 12 is movably inserted into the lid 9 while ensuring airtightness. ing. A support plate 14 is attached to the outer periphery of the sliding cylinder 13 above the lid body 9, and the support plate 14 is slidably fitted to the side frame 1a of the frame body 1. ing. A plurality of guide rods 15 are fixed to the upper surface of the support plate 14 at their one ends, and the other ends of the guide rods 15 extend upward through the upper pedestal 10 and the other ends thereof. The parts are connected by a connecting plate 16. A cylinder device 17 fixed to the upper pedestal 10 is connected to the connecting plate 16, so that the expansion and contraction of the cylinder device 17 causes the lid body to pass through the guide rod 15 and the support plate 14. 9 moves toward and away from the chamber body 8 (opens and closes).

As shown in FIGS. 1 to 3, two insertion ports 18 communicating with the inside of the vacuum chamber 7 are provided on the side of the vacuum chamber 7 so as to face each other. An electrode 19 and a cooling rod 20 are movably inserted into the opening 18 while ensuring airtightness. Each electrode 19
Is provided with a graphite part 21 at the tip (left end in FIG. 3), and a DC power supply 22 is connected to each base end (right end in FIG. 3) in this embodiment, The electrode 19
Is to be displaced by a cylinder device 23 fixed to a fixing means (not shown). On the other hand, the cooling rod 2
In No. 0, the inside thereof is hollow, and cooling water is to be supplied to the inside thereof. Like the electrode cylinder device 23, this cooling rod 20 is fixed to a fixing means (not shown). It is supposed to be displaced by the cylinder device 24.

As shown in FIGS. 1 to 3, a mold 25 and upper and lower punches 26 and 27 are to be housed in the vacuum chamber 7 (in FIGS. 1 to 3, the upper and lower punches 26 are arranged). , 27 are omitted). The mold 25 has a function of accommodating a powder material (for example, copper, aluminum, powder for cemented carbide (WC-10CO)) 28 as a material of the sintered body, and therefore the mold 25 is As shown in FIGS. 5 and 6, it has a tubular shape (for example, a cylindrical shape). In the present embodiment, the mold 25 has a graphite portion 29 formed of graphite on the outer peripheral portion and a ceramic portion 30 formed of ceramics on the inner peripheral portion thereof. In the above, the mold 25 is arranged so that its axis is oriented in the vertical direction.
Therefore, when the tip portion of the electrode 19 is contacted and a current is supplied to the mold 25, the current passes through the graphite portion 29 as shown by a dotted line in FIGS. It is supposed to flow from 19 to the other electrode 19. On the other hand, the upper punch 26 is fitted to the inner periphery of the die 25 so as to be displaceably movable from the upper side while ensuring liquid tightness, and the lower punch 27 is fluidly fitted to the inner periphery of the die 25 from the lower side. It is supposed to be fitted so as to be displaceable while ensuring tightness (see FIG. 5). In the vacuum chamber 7, the die 25 is set on the die lift rod 4 via the lower punch 27, and the die pressure rod 12 applies a pressure to the upper punch 26. It has become. The upper and lower punches 26 and 27 are made of ceramics as an insulator in this embodiment. The main components of this ceramic are alumina (Al ₃
O ₂ ), zirconia (ZrO), silicon nitride (Si ₃ N
₄ ), silicon carbide (SiC), etc. are used, and those containing silicon nitride as a main component are preferable from the viewpoint of thermal shock resistance. Regarding the strength of this ceramics (for example, the one whose main component is silicon nitride), as for the bending strength, as shown in FIG. 8, when the temperature is up to about 1000 ° C., graphite is 2 to 4 (Kgf / mm ^2). ), While 60 to 8
It is 0 (Kgf / mm ² ), and regarding the compressive strength, graphite is 3 to 9 (Kgf / mm ² ), while ceramics is 200 (Kgf / mm ² ) or more. In this case, the fact that the bending strength is emphasized in addition to the compressive strength is, as a practical matter, due to the pressurization movement by the punch 26 (27),
Based on the friction between the inner periphery of the die 25 and the outer periphery of the punch 26 (27), the center portion of the punch 26 (27) in the radial direction and the punch 26 (27).
This is because a force that causes bending is generated between the outer peripheral portion of (27) and it cannot be ignored.

Next, the method according to the present invention will be described together with the operation of the above-mentioned sintering apparatus. First, as shown in FIG. 5, a powder material 28 (copper powder is used in this embodiment) is filled in a die 25, and the powder material 28 is placed in the die 25 between upper and lower punches 26, 27. To be stored in. Next, as shown in FIG. 3, in the vacuum chamber 7, the above-mentioned mold 25 is moved by the mold lift bar 4 and the mold pressure bar 12.
The upper and lower punches 26, 27 and the mold 2
The electrode 19 is brought into contact with the five side surfaces, and the setting of the sintering process is completed.

Thereafter, in this embodiment, the sintering process is performed based on the time chart shown in FIG. That is, first, evacuation of the vacuum chamber 7 is started, then the die pressure rod 12 is lowered by the cylinder device 11, and the ceramic upper and lower punches 26, 27 are made into the powder material 2.
Start to pressurize 8 with a large pressure. Next, a predetermined time has elapsed from the start of the sintering process (30 seconds in this embodiment).
Then, the power supply 22 is turned on and the mold 2 is inserted through the electrode 19.
Current is supplied to 5. This gives the mold heat to the mold 25, and the heat is applied to the powder material 28 under pressure.
Will be supplied to. As a result, the mold temperature (powder material temperature) rises as shown in FIG. 7, and when the temperature reaches a predetermined temperature (800 ° C. in this embodiment), the predetermined temperature is held for a certain period of time. Then, the pressed powder material is heated before being melted to obtain a sintered body.

After the mold temperature has reached a certain time, the power source 22 is turned off and the electrode 19 is separated from the mold 25. Instead, the cooling rod 20 is replaced by the mold 2 as shown in FIG.
The mold 25 is forcedly cooled by being brought into contact with the five side surfaces. Then, when the die temperature is cooled to a predetermined take-out temperature (200 ° C. in this embodiment), the upper and lower punches 26, 27.
2 is stopped, the lid 9 of the vacuum chamber 7 is opened by the cylinder device 17, and the mold 25 is moved to the position shown in FIG.
As shown in FIG. 3, the mold lift bar 4 removes it from the vacuum chamber 7. After that, the sintered body as a product is taken out of the mold 25, and the mold 25 is on standby for the next sintering process.

Therefore, according to the above contents, the upper and lower punches 26, 27 are made of ceramics, and the strength thereof is larger than that of the conventional artificial graphite punch as shown in FIG. The pressing force of the powder material can be made higher than the pressing force using the conventional artificial graphite punch, and the sintering temperature when the ceramic punch is used is the same as the conventional artificial graphite punch. If so, the sintering temperature can be lowered.

To support this, an artificial graphite punch that is not made of ceramics is used, and the pressing force of the powder material is P ₁ (= 0.91 Kgf / mm ² ), P ₂ (= 4.
55 Kgf / mm ² ), an experiment was conducted to find out what the sintering temperature would be. As shown in FIG. 9, when the pressure P ₁ was applied, the temperature at a certain density d ₁ was T ₁ , While the sintering end point is T ₂ (= 845 ° C),
In the case of the pressing force P ₂ , the temperature at a certain density d ₁ is T
₃ , the sintering end point is T ₄ (= 680 ° C), and the pressing force P
_In the case of _2, the pressure could be lowered by 165 ° C. than in the case of the pressure P ₁ . Therefore, it can be understood that if the ceramic punch is used instead of the artificial graphite punch to further increase the pressing force, the sintering temperature is lowered accordingly.

As described above, although the sintering is performed in the vacuum chamber 7 under vacuum (not completely vacuum, for example, 0.01 Torr), the sintering temperature can be lowered. As is clear from the relationship between the oxidation rate of graphite and the temperature, not only the graphite portion 21 of the electrode 19 but also the oxidation portion of the graphite portion 29 of the mold 25 is further reduced, and the oxidation consumption of the graphite is reduced. This can be suppressed compared to the conventional case. In this embodiment, the mold 25
The inner peripheral surface is the ceramic part 30, and the upper and lower punches 26,
No. 27 is made of ceramics. With respect to these, the oxidation consumption of graphite does not pose a problem, and liquid phase sintering can be performed without problems. However, even when the inner peripheral surface of the mold 25 is not coated with ceramics, as described above. As a result of the decrease in the sintering temperature, oxidation consumption of graphite on the inner peripheral surface of the die is suppressed, so that no gap is produced early between the punch 26 (27) and the inner peripheral surface of the die 25. Liquid phase sintering can be performed.

Further, since the sintering temperature can be lowered, the mold 25 is cooled by the cooling rod 20.
The time required to lower the temperature to a predetermined take-out temperature is shortened, and the cycle time that was conventionally required for about 10 minutes is shortened to about 2 minutes.

Further, in this embodiment, the inner peripheral surface of the mold 25 is coated with ceramics, and only the heat is applied to the powder material 2.
Since it is supplied from the outer peripheral surface side of 8, the diameter of the powder material can be reduced as in the case of supplying heat from the central portion in the radial direction of the powder material to the outside in the radial direction of the powder material. It is possible to prevent the portion on the outer side in the direction from easily radiating heat to the outside, and it is possible to prevent the heat radiation phenomenon from occurring in the powder material 28. As a result, the temperature distribution in the radial direction of the powder material 28 is prevented from becoming non-uniform.

Although the embodiments have been described above, the present invention includes the following. The powder material 28 may be either a conductive material or a non-conductive material. A conductive material is used as the powder material 28, and the powder material 2
When a current is also applied to 8, the coating of the inner peripheral surface of the mold 25 with ceramics should be omitted. A plurality of filling holes for the powder material 28 are formed in the mold 25, punches are fitted in the respective filling holes, and all the punches are simultaneously pressed by the die pressure rod 12, so that the powder material in each filling hole is formed. Pressurize 28. As a result, no electric current is applied to the powder material through the punch as in the prior art. It is possible to suppress the formation of materials having different temperature distributions for each body material).

[0025]

As described above, according to the inventions of claims 1 to 4, when the powder material is pressed and energized to be sintered, oxidation consumption in the mold or the like is suppressed and the sintering treatment is performed. It is possible to provide a sintering method that shortens the cycle time. According to the invention of claim 4, it is possible to obtain a plurality of sintered bodies having a uniform temperature distribution in the radial direction. According to the inventions of claims 5 to 7, it is possible to provide a sintering apparatus which suppresses the oxidation consumption in the mold and the like and shortens the cycle time of the sintering process. According to the invention of claim 7, it is possible to prevent the temperature distribution in the radial direction of the sintered body (powder material) from becoming non-uniform.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a sintering device according to an embodiment.

FIG. 2 is a view for explaining insertion and removal of a mold and the like in the sintering machine of FIG.

FIG. 3 is a partially enlarged explanatory view of the sintering device of FIG.

FIG. 4 is a view for explaining forced cooling of a mold in the sintering apparatus of FIG.

5 is a view showing a relationship between a die and upper and lower punches in the sintering machine of FIG.

6 is a cross-sectional view of FIG.

7 is a time chart for explaining the operation of the sintering apparatus of FIG.
To.

FIG. 8 is a diagram comparing the strength of ceramics with the strength of artificial graphite.

FIG. 9 is a diagram for explaining the influence of the pressure applied to the powder material on the sintering temperature.

FIG. 10 is a graph showing the relationship between the oxidation consumption of graphite and temperature.

FIG. 11 is an explanatory view showing a conventional sintering device.

[Explanation of symbols]

 19 Electrode 22 DC Power Supply 25 Type 26 Upper Punch 27 Lower Punch 28 Powder Material 29 Graphite Part 30 Ceramics Part

Claims (7)

[Claims] 1. A sintering method in which a powder material is pressed and energized to sinter, and the pressing is performed by a punch using a high-strength material, and the energization is performed on the side in the pressing direction of the punch. From one side, the sintering method is performed without using the punch. 2. The sintering method according to claim 1, wherein the high-strength material is an insulator. 3. The sintering method according to claim 1, wherein the high-strength material is ceramics. 4. The burner according to claim 1, wherein a plurality of sets of the powder material and the punch are prepared, and each of the powder materials is pressurized while being energized. A sintering method characterized in that the sintering is performed. 5. A cylindrical die for accommodating the powder material, a punch for displaceably moving with respect to the die for pressurizing the powder material in the die, and a die heat for the powder material. In a sintering apparatus comprising: a current supply means for imparting a current, the mold is a conductor, the current supply means is set to supply a current to the mold, the punch is formed of a high-strength material, A sintering machine characterized by the above. 6. The sintering apparatus according to claim 5, wherein the punch is made of ceramics. 7. The sintering machine according to claim 5, wherein the inner peripheral surface of the mold is insulation-coated.