Patent Application
20060104849
1. Field of the Invention
The present invention relates to a method and device for sintering a material in a short period of time by directly applying pressure and current as a result of relatively moving the sintering subject material and heating area while restricting the heating area of the sintering subject material, such as metal and ceramics, to a specific position. The present invention provides a manufacturing method and device suitable for obtaining a sintered body in the form of a long rod or having an uneven cross section.
2. Description of the Related Art
According to the pressurized sintering method employing a direct current, since it is possible to raise the temperature of the sintering subject material at high speed, the manufacturing time can be significantly shortened in comparison to the conventional sintering method employing atmosphere heating.
Generally, the conventional heat sintering method pursuant to a direct current adopts a method of disposing and pressurizing electrodes for current heating at both ends in the axial direction of the sintering subject and simultaneously applying heat thereto (for example, c.f. Japanese Patent Laid-Open Publication No. 2000-239707).
Nevertheless, when heating with such direct current, since the heating value at the contact site of the two in a current path will become considerably larger in comparison to the portions of other sintering subject powders, a thermal gradient will occur from the electrode contact surface toward the center of the sintering material (position that is distant from the electrode).
Therefore, when manufacturing a sintered product having a long current path such as a rod-shaped material, there is a problem in that it is extremely difficult to sinter the overall material at an even temperature.
Further, with a material in which the cross section of the sintered body is uneven in the lengthwise direction in relation to the current path (i.e., materials with irregular section profiles), since the electrical resistance will change pursuant to the area difference of the cross section perpendicular to the current path, there is a problem in that the heating value will change and an even sintered body cannot be obtained.
Therefore, with the conventional pressurized sintering method employing a direct current, there is a problem in that it is difficult to manufacture a product having an even material quality from a rod-shaped material of a certain length or longer and a stepped material which has an uneven cross section.
Accordingly, a proposal has been made for a method of disposing and heating electrodes at both sides of a sintering subject in substitute for the conventional method of disposing and pressing electrodes for current heating at both ends in the axial direction of the sintering subject (for example, c.f. Japanese Patent Laid-Open Publication No. H10-259405). Nevertheless, here, since the electrodes and sintered body are subject to the processes at a fixed position, it is not possible to continuously sinter a long material.
Moreover, from the perspective of performing continuous sintering, a proposal has been made for sandwiching the sintering subject powder between rolls to be made a thin plate and electrifying and heating it with roll-shaped electrodes (for example, c.f. Japanese Patent Laid-Open Publication No. H9-268302). Nevertheless, this method is limited to the manufacture of thin plates, and there is a problem in that it is not possible to sinter components of other shapes.
In view of the foregoing circumstances, an object of the present invention is to provide a sintering method and device that are superior in sintering ability, wherein even if the sintered body is in the form of a long rod or has an uneven cross section, the sintered body is uniform in quality.
As a result of conducting intense study to obtain a sintered body in a rod shape or which has an uneven cross section, the present inventors discovered that the foregoing object can be achieved by restricting (limiting) heating zone in the sintering subject material, and effecting sintering while relatively and successively moving the sintering subject material and current portion.
In other words, based on the foregoing discovery, the present invention provides:
1. A method of performing direct current pressurized sintering to powder in a mold having a cylindrical molding space, wherein sintering is continuously effected while relatively moving a current portion and a sintering subject;
2. A sintering method according to paragraph 1 above, wherein the sintering powder material disposed in the cylindrical mold is pressurized from the end of the mold, an electrode movable in the lengthwise direction of the mold is disposed around the mold, and sintering is effected by energizing and heating the sintering powder material;
3. A sintering method according to paragraph 2 above, wherein the sintering powder material is pressurized from both ends of the mold;
4. A sintering method according to any one of paragraphs 1 to 3 above, wherein an electrode connection terminal assembly affixed to the periphery of the mold and having a space portion capable of moving freely on a single axis is provided, and sintering is effected by the connection terminal assembly moving the current portion;
5. A sintering method according to paragraph 1 above, wherein fixed electrodes are disposed around a fixed cylindrical die, sintering powder material is filled in the die and subject to current pressurized sintering, the raw material powder is pressed from one side of die, the obtained sintered body is pressed from the opposite side of die, and successive sintering is effected thereby;
6. A sintering method according to any one of paragraphs 1 to 5 above, wherein the sintering powder material is sintered in one direction;
7. A sintering method according to any one of paragraphs 1 to 6 above, wherein a long sintering powder material is sintered;
8. A sintering method according to any one of paragraphs 1 to 7 above, wherein a material with an uneven cross section is sintered while setting the heating area;
9. A sintering device for performing direct current pressurized sintering to powder in a mold having a cylindrical molding space while relatively moving a current portion and a sintering subject, comprising an elevation ram capable of position control and which successively moves the mold and sintering subject;
10. A sintering device according to paragraph 9 above, further comprising a pressurizing ram capable of load control and which pressurizes the sintering powder material disposed in the cylindrical mold from one end of the mold;
11. A sintering device according to paragraph 9 or paragraph 10 above, further comprising an electrode ram which presses the current electrodes disposed around the mold or performs such pressing via the current plate;
12. A sintering device according to any one of paragraphs 9 to 11 above, wherein the sintering powder material is sintered in one direction;
13. A sintering device according to any one of paragraphs 9 to 12 above, wherein a long sintering powder material is sintered; and
14. A sintering device according to any one of paragraphs 9 to 13 above, wherein a material with an uneven cross section is sintered while setting the heating area.
With the present invention, instead of integrally and wholly heating the sintering subject material and the mold comprising a sintering space as conventionally, a method has been developed, based on the publicly known current press sintering method, of limiting the current portion to a specific position of the mold, relatively moving the sintering object and the heating portion and continuously effecting sintering in one direction so as to enable the manufacture of a sintered material of a rod shape or having an uneven cross section in which the sintering quality is favorable.
As shown in
Meanwhile, the filled sintering powder 2 is pressurized from both ends in the mold with a punch 4. Reference numeral 5 indicates a pressurizing disk. In this situation, the powder is energized to the movable electrode 1 while pressurizing the powder, and the electrode 1 is moved while controlling it to become a desired temperature and speed. As a result, a sintered body having a rod shape or an uneven cross section can be obtained.
Meanwhile, as shown in
Here, by disposing a roll 7 having a rotational resistance or the likes of a secondary die (not shown) having a slightly smaller diameter than the energizing die 6 at the exit side, the raw material powder is pressurized while taking measures to generate a resistance against the progress of the sintered product 9.
According to the foregoing method, a sintered product in the form of a rod shape or having an uneven cross section in which the uniformity of the sintered product is superior can be obtained.
Further, the device according to the present invention, as shown in
Although the lower punch 25 is usually fixed, and is constituted to press (apply a load to) the sintering subject powder 29 in the mold with the upper punch 24, a constitution of moving the lower punch 25 may also be adopted. The upper punch 24 is pressurized with the pressurizing ram 21. As shown in
The lower punch 25 is supported with an elevation ram 22 via a movable elevation stage 34. The elevation stage 34 is constituted to support the mold 23 having a cylindrical molding space, and adjusts the height of the mold 23 having a molding space with the elevation thereof.
The electrode 28 for energizing and heating the sintering subject powder in the mold 23 is designed such that it is able to move in the horizontal direction. This is required to avoid complicating the mechanism of the energization device from the power source.
Further, provided is an electrode pressurizing ram 30 for pressing the current portion of the electrode 28 to the mold. As shown in
This current plate 26 has a width that corresponds to the heating area 27 of the raw material powder 29 to be sintered. When performing energization directly with the electrode 28 without the current plate 26, the electrode 28 delinates the foregoing heating zone (area).
In
In the foregoing device, powder 29 is filled in the mold 23 having a cylindrical molding space, the elevation stage 34 is temporarily fixed to adjust the height thereof, and the raw material sintering powder 29 is thereafter pressed with the upper punch 24 for pressurizing the mold 23 from the upper end thereof.
Meanwhile, the upper and lower position of the current electrodes 28 is set to match the position of the heating portion of the raw material sintering powder 29, and energization is simultaneously commenced. Current sintering is conducted in a short period of time. When sintering a long rod-shaped material, the adjustment of the stage position may be conducted in steps or continuously. Further, the stage position may be adjusted while performing energization, or upon performing energization intermittently.
In other words, sintering may be performed by pressing the raw material sintering powder 29 with the punch 24 for pressurizing the mold 23 from one end thereof by arbitrarily adjusting the stage position in steps or continuously, and while simultaneously performing energization, or upon performing energization intermittently.
As a result, even if it is a long rod material, the sintering subject can be successively moved from the upper end of the mold 23 and successively (continuously) sintered in steps.
Further, as a result of adjusting the current for energizing the electrode 28 and the load of the pressurizing ram 21 in conjunction with the position of the freely settable stage elevation ram 22, an arbitrary position of the long material may be sintered at an arbitrary temperature while controlling the pressurizing force.
Moreover, even if the cross section shape (electrical resistance) in the sintering subject material changes, so as long as the heating area is made smaller, the absolute value of the different of the heating value at the respective positions pursuant to the change in shape will be small. Therefore, if the thickness t of the current plate 26 for determining the heating area is made sufficiently thin to an extent of not influencing the quality of sintering, a material having an uneven cross section can be sintered favorably.
As described above, the current value for each portion of the sintering powder raw material 29 can be controlled precisely to match the electrical resistance.
With the present sintering method, the sintering powder material 29 can be sintered in one direction, and, as described above, a long sintering powder material 29 can also be sintered with ease. Further, when a material having an uneven cross section is sintered while setting the heating area, for instance, a rod-shaped material having a small diameter portion and a large diameter portion; that is, a stepped rod-shaped material can also be sintered with ease.
In other words, the present invention yields a significant characteristic in that it is able to easily sinter a long or irregular rod-shaped material with a relatively simple device constitution.
The present invention is now explained in detail with reference to the Examples. These Examples are merely illustrative, and the present invention shall in no way be limited thereby. In other words, the present invention shall only be limited by the scope of claim for a patent, and shall include the various modifications other than the Examples of this invention.
As shown in
Results of the temperature distribution measured in Example 1 are shown in
Even when the cross section shape (electrical resistance) in the sintering subject material changes, so as long as the heating area is made smaller, the absolute value of the difference of the heating value at the respective positions pursuant to the change in shape will be small. Therefore, if the thickness t of the electrode connection terminal assembly 11 for determining the heating area is made sufficiently thin to an extent of not influencing the quality of sintering, a material having an uneven cross section can be sintered favorably.
Further, since heat generation will not occur in an area outside the electrode connection terminal assembly 11, the temperature of this portion will not become higher than the portion covered with the terminal assembly, and the raw material will therefore not overheat or melt.
As shown in
A graphite electrode connection terminal assembly (perforated square plate) 11 having a φ30 mm hole in the center and in which the length of one side thereof is 70 mm and the thickness is t=10.0 to 13.2 mm was fitted so as to be attached to the side wall of the cylinder.
Here, the material of the electrode connection terminal assembly (perforated square plate) 11 used is the same as the material of the cylinder. As a result, the current will flow to the cylinder, and the raw material powder will be heated with energization when the electrical resistance of the raw material powder in the cylinder is small. Further, when the electrical resistance of the raw material powder is large, the cylinder will generate heat, and the raw material powder will be indirectly heated and sintered.
Incidentally, a method of dividing and attaching the electrode connection terminal assembly 11 to the cylinder, and energizing and heating the cylinder or the powder in such cylinder may also be employed. There is no particular limitation on the current heating method, and any one of the known methods may be employed.
The electrode 1 was mounted to the terminal board 11 so as to enable energization in the vertical direction with the pressurizing axis. Further, the electrode connection terminal assembly (square plate) was perforated in the center of the mold (cylinder) 3 to form a 7 mm hole, and the thermocouple 12 was inserted therein so as to control the temperature and for monitoring.
After the foregoing preparation, pressurization was performed with a load of approximately 10 kN while energizing between the electrodes so as to heat the center of the mold (cylinder) to 580° C. to 640° C. and effect sintering.
Results of the measurement regarding the temperature change of the mold (cylinder) in foregoing Example 2 are shown in
In other words, even when energization is effected via the electrode connection terminal assembly 11 fitted in the mold (cylinder), it is possible to control the sintering subject material 2 to become a desired temperature.
Further, results regarding the density of the aluminum sintered product obtained from Example 2 are shown in
Since the terminal assembly connecting the electrodes is merely fitted in the mold (cylinder), it is able to freely move in the lengthwise direction of the cylinder. Therefore, if sintering is effected while moving the terminal assembly, a long and uniform sintered body can be manufactured so as to implement the present invention.
As shown in
Upon examining the density of the aluminum sintered product obtained in Example 3, the relative density showed a value of 99% or more. If the distance to be moved is made longer, the manufacture of an even longer product is possible. Thus, it is evident that a rod-shaped sintered product superior in density can be manufactured with this method.
Next, as an example of sintering a material having an uneven cross section while setting the heating area, when considering sintering a stepped component as illustrated in
The current area is the heating area 15 shown with the diagonal line at the upper diagram of
Next, the electrode connection terminal assembly 11 is moved to the small diameter portion 14, and similarly sintered via current heating. The current heating portion is the center heating area 16 in the lower diagram of
At the respective positions, energization matching the electrical resistance can be effected independently. As a result, a stepped component can also be evenly energized and sintered. Incidentally, while the electrode connection terminal assembly 11 is moving, the energization may be stopped, or current for keeping a specific temperature may be flowed. This can be set arbitrarily.
Further, as shown in
As shown in
The height of this sample was adjusted such that the distance from the lower end of the cylinder 23 to the center of the electrode 28 will become 80 mm and placed on the stage, and sandwiched with the current plates 26 having a height of 30 mm×width of 40 mm mounted to the center of the electrode 28.
A punch 24 having a length of 40 mm was mounted on the cylinder 23, and subject to powder compacting at a load of 900 kgf. Under these conditions, the electrodes 28 were energized and heated up to 650° C. Incidentally, for temperature control, the thermocouple inserted in the hole having a depth of 12.0 mm formed at the center of the side face at a height of 80 mm from the lower end of the cylinder was used.
Next, as shown in
Thereafter, this was repeated twice, and a total of four heating steps were conducted to manufacture a rod-shaped sintered product. Incidentally, in the fourth heating step, as shown in
In this Example, an aluminum sintered body having a length of approximately 55 mm was obtained. Upon examining the density of this sintered product, a relative density having a value of 99.7% was obtained.
This result shows that a sufficient numerical value was obtained as the density of the sintered product, and it has been confirmed that the present invention was able to obtain a favorable rod-shaped sintered product. Incidentally, as necessary, as shown in
If the scale-up of the device is sought to enable the mold (cylinder) 23 to move even longer, an even longer sintered product can be manufactured by increasing the number of heating steps.
Moreover, if the heating area is made small and the current value is controlled to match the electrical resistance for each portion, sintering can be effect at a fixed temperature even if the cross section shape is changed. Therefore, the present invention enables the sintering and manufacture of a favorable long product or a component having an uneven cross section.
Incidentally, although only aluminum was used in the Examples, the present invention is not limited to such aluminum material. Powders of other metals or ceramics may also be sufficiently employed.
The present invention proposes a method of sintering while relatively moving the raw material and electrode, and, since it is not necessary to sinter the enter product at once, there is an effect in that the heating area can be made small. Further, since energization is effected through the electrode connection terminal assembly mounted on the mold, heat generation will only occur to the portion corresponding to the thickness of the electrode connection terminal assembly. Therefore, if the thickness of the electrode connection terminal assembly is made thin to a range where the cross section of the sintering subject material will be even, the heat generation of the sintering subject material at such position will become even.
As a result, the temperature variation during sintering can be restrained, and a significant effect is yielded in that a long sintered body or a sintered body having an uneven cross section with superior quality can be manufactured.
Further, as a result of employing the method of sequentially supplying the raw material powder, the continuous manufacture of a rod-shaped material is enabled. As a result, in comparison to the conventional batch production method, a significant effect is yielded in that a considerable improvement in productivity in the sintered material can be expected.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200346661 | Feb 2003 | JP | national |
| 200346690 | Feb 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP03/16155 | 12/17/2003 | WO | 7/7/2005 |
