JP2000301395A - Powder molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the yield of a powder molded product by mounting an auxiliary pressurizing device having a plurality of coned disk springs to apply pressing force to an upper punch immediately after passing the maximum pressure point of a pressure roller to maintain the specified pressure on the molded product on a pressure roller bearing part to be vertically moved synchronously with the pressure roller to apply the pressure to at least the upper punch among upper and lower punches. SOLUTION: A cylinder 28 to be opened downwardly is provided on a bearing part 17 which is located on the axis side of a rotary panel with respect to a pressure roller 15 and synchronous to the shaft action of the pressure roller 15, and a plurality of coned disk springs 30 are interposed between a piston member 29 which is vertically movable in the cylinder 28 and the inner surface of a top wall of the cylinder 28. When upper and lower punches are at the position immediately before the completion of the pressing stroke, an upper cam body and an upper inside cam body 31 are engaged with guide rollers 13a, 13b of an upper punch holder, and the pressing force synthesized by both cam bodies is applied to the molded product until the push-out process is completed while the force is successively reduced, and generation of cracks is thereby suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder molding machine for molding a powder metallurgy material such as a fuel pellet for a nuclear fuel.

[0002]

2. Description of the Related Art Generally, when a powder metallurgical material such as the above-mentioned fuel pellet is formed, powder supplied into a die is compressed by both upper and lower punches.

FIG. 4 is a vertical sectional view of a powder molding machine for performing the above-described compression molding, particularly a rotary type powder molding machine. The frame 1 includes a stand frame 2 provided above the frame 1 and a stand frame 2. A vertical shaft 3 is provided between them. A vertical shaft oil receiver 4 is fixedly mounted on the upper surface of the frame 1 concentrically with the vertical shaft 3, and above the vertical shaft oil receiver 4, a turntable 5 is provided with respect to the vertical shaft 3. It is mounted rotatably.

The rotary disk 5 has an upper flange portion 5a, a central flange portion 5b and a lower flange portion 5c integrally formed on the outer peripheral portion thereof. As shown in the figure, a large number of dice 6 are provided in the circumferential direction.

Further, an upper punch holder 7 for holding an upper punch 7a on the same axis as each of the dies 6 is disposed on the upper flange-like portion 5a so as to be vertically movable.
A lower punch holder 8 that holds a lower punch 8a on the same axis as each of the dies 6 is also disposed on the lower flange-like portion 5c so as to be vertically movable.
A drive gear 10 driven by a drive mechanism is meshed with a gear 9 formed on the outer periphery of the drive gear.

On the other hand, the lower punch holder 8 is provided with a guide roller 1 outside a portion protruding downward from the turntable 5.
The guide groove 11 is provided on the frame 1 over a predetermined range in the circumferential direction.
2 is engaged.

The rotary plate 5 of the upper punch holder 7
Guide rollers 13 on both sides of the part projecting upward from
And is engaged with a guide groove 14 provided over a predetermined range in the circumferential direction at a position above the turntable 5.

The upper punch 7a and the lower punch 8
a is inserted into the die 6 from above and below, and in a pressurizing process section for compressing and molding the powder raw material supplied into the die 6, the abutment respectively contacts the top end of the upper punch holder 7 and the lower end of the lower punch holder 8, Pressure rollers 15 and 16 for applying pressure to both punches are provided, respectively. Bearing members 17 and 18 that support the pressure rollers 15 and 16
Is provided on the stand frame 2 or the frame 1 by a mechanism (not shown) so that it can only move up and down within a certain range, and between the top or bottom of the bearing members 17 and 18 and the stand frame 2 or the frame 1, respectively. Cylinder device 17
a, 18a are interposed.

Reference numeral 19 in FIG. 4 denotes a powder feeder.

When the powder is compacted, the rotary disk 5 is rotated via the drive gear 10, and the powder is supplied from the powder feeder 19 into the die 6 at a predetermined position. Accordingly, the lower punch 8a is moved up to a predetermined filling depth via the guide groove 12 and the guide roller 11 according to the rotation of the rotary disk 5, and after the excess powder is removed, the upper punch 8a is removed. 7a is gradually lowered, and the powder in the die 6 is removed by the upper and lower punches 7a, 8a.
It becomes a pinched state between a. When the upper and lower punches 7a and 8a, which hold the powder in the die 6 in a sandwiched state, enter between the pressing rollers 15 and 16 in this manner, the cylinder device 17
a, a pressure roller 1 to which a predetermined pressure is applied by 18a
The upper and lower punches 7a, 8a are pressed by the 5, 5 in the direction approaching each other, and the powder is compacted. When the pressing process is completed in this way, the upper and lower punches are moved upward while the molded product is held between the upper and lower punches 7a and 8a, and the upper surface of the lower punch 8a is the same as the upper surface (die table) of the die 6. When the surface becomes
a is moved further upward, and then the molded article is paid out. Thereafter, in a similar manner, compression molding of the powder is sequentially performed in each die 6.

[0011]

However, in general, at the time of powder molding, a pressure on the order of several tons / cm ² is applied to the molded product in the die, and when the molded product is extracted from the die, about 1 to 1. Expands about 5%.

Accordingly, if the pressure is rapidly released when the extrusion process is started after the completion of the molding, there are problems such as the occurrence of defects such as cracks in the molded product.

Accordingly, in order to maintain a predetermined pressure on the molded product during the extrusion process of extruding the molded product from the inside of the die while being sandwiched between the upper and lower punches, a cam mechanism for applying a pressure to at least one of the upper and lower punches. And the cam bodies 22 and 23 of the cam mechanism are constituted by a plurality of cams divided from each other in the rotating direction of the turntable so that the pressing force of the pressurizing cylinder of each cam is gradually reduced. It has been proposed (Act 2-435)
No. 95).

However, as described above, in the case where the pressing force is applied to the cam mechanism by the pressing cylinder, the pressing force is applied to the punch by air pressure.
When the filling amount of powder changes, the length of the molded product fluctuates, the position of the punch is constantly displaced by the fluctuation, and the pressing force varies, making it difficult to keep the pressing force constant. There is a problem that the occurrence of cracks and the like in the molded product cannot always be sufficiently suppressed.

As shown in FIG. 6, in the pressure step, two pressure roller pairs are provided in the rotation direction, and the first upper and lower pressure rollers 15a and 16a perform main pressure forming. Excessive pressure molding is performed by the upper and lower pressure rollers 15b and 16b so that the pressure is rapidly released from the molded article, or the first upper and lower pressure rollers 15a and 16a are used to form the preform. ,
It has also been proposed to perform the main pressure molding with the second upper and lower pressure rollers 15b and 16b.

However, even in the case of providing a plurality of pairs of pressure rollers as described above, it is necessary to adjust the position of the pressure roller in order to maintain a predetermined pressure, and it is difficult to adjust the position. It becomes complicated, and there is a problem that occurrence of cracks or the like of a molded product cannot always be sufficiently suppressed.

In view of the foregoing, the present invention is intended to maintain a sufficient pressing force on a molded product immediately after pressure molding, sufficiently suppress cracks or the like in the molded product, and improve the yield of the molded product. It is an object of the present invention to obtain a powder molding machine.

[0018]

The invention according to claim 1 is
In a rotary-type powder molding machine that pressurizes and forms powder by the pressing force of both upper and lower punches, pressurization that moves up and down in synchronization with the vertical position movement of a pressing roller that applies a pressing force to at least the upper punch of the upper and lower punches A pressure assist device with a plurality of disc springs is attached to the roller bearing to apply a predetermined pressing force to the upper punch immediately after passing the maximum pressing point of the pressing roller and maintain a predetermined pressing force on the molded product. It is characterized by having done.

According to a second aspect of the present invention, in the first aspect of the present invention, the conical spring is disposed in the cylinder, and the pressing force of the conical spring is provided on the punch holder via the cam body. Characterized in that it is configured to be added to

According to a third aspect of the present invention, in the first or second aspect, the pressing force of the auxiliary pressing device immediately after passing the maximum pressing point of the pressing roller is 5 to 20 times the forming pressing force. %, And the disc springs are combined so as to be%.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

In the figure, the same parts as those shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 is an exploded view showing each molding step of the rotary powder molding machine, in which guide rails such as guide grooves 14 and 12 provided with an upper punch 7a and a lower punch 8a along their moving direction. Following the pressing step A in which the powder is pressed and molded by the pressing rollers 15 and 16 while being guided up and down by the guides 20 and 21, the molded article extruding step B, the molded article discharging step C and the powder filling step D , The weight adjustment process E and the pressurization preparation process F are sequentially repeated.

The upper punch holder 7 extends over a range G from a position immediately before the end of the powder pressing process A by the pressing rollers 15 and 16 to the end of the molded product extruding process B.
The upper cam body 22 that engages with the guide roller 13a from above and applies a hold-down pressure to the upper punch 7a via the upper punch holder 7 is located on the side opposite to the vertical shaft 3 with respect to the pressure roller 15, that is, outward. On the other hand, in a period H between the position immediately before the end of the pressurizing process A and the extrusion process B of the molded product, the lower roller 8 engages the lower outer guide roller 11a of the lower punch holder 8 from below and holds the lower punch 8a. A lower cam body 23 for applying an up pressure is provided.

The cam body 22 is provided with five cams 22a, 22b, 2 in the direction of rotation of the turntable 5 holding both punches and the like.
2c, 22d, and 22e.
As shown in the figure, each of the cams 22a, 22b, 22c, 22
d and 22e are pressure cylinders 24a, 24b and 2 respectively.
4c, 24d, 24e pistons 25a, 25b, 25
c, 25d and 25e are connected. On the other hand, the lower cam body 23 has three cams 23a,
23b, 23c, each cam 23a, 23c
The pistons of the pressure cylinders are similarly connected to b and 23c, respectively.

The above structure is the same as that of a conventional powder molding machine, but in the present invention, as shown in FIGS.
A pressure assisting device 26 for applying a pressing force to the upper punch holder 7 is provided on a bearing portion 17 which supports the pressure roller with respect to the pressure roller 15 or moves in synchronization with the pressure roller 15.

That is, a cylinder 28 that opens downward is provided in the bearing portion 17 that is located on the axial center side of the rotating disk 5 with respect to the pressure roller 15 and is synchronized with the axial operation of the pressure roller 15. A piston member 29 is accommodated in the cylinder 28 so as to be vertically movable within a predetermined range, and a plurality of disc springs 30 are interposed between the piston member 29 and the inner surface of the cylinder 28 top wall.

An upper inner cam body 31 is fixed to the lower surface of the piston member 29.
1 is a position immediately before the end of the pressing process A, that is, the pressing roller 1
The guide roller 13b is engaged with the inner guide roller 13b mounted on the inside of the upper punch holder 7 from above in the range from the lowest point where the maximum pressure 5 is applied to the end of the molded product extruding process.

When the upper and lower punches 7a, 8a have moved to positions immediately before the end of the pressing stroke, the upper cam 2
2 and the upper inner cam body 31 are engaged with the guide rollers 13a or 13b of the upper punch holder 7, respectively, and the pressing force synthesized by the two cam bodies is applied to the molded product. Then, until the end of the extrusion process of the molded product, the pressing force is gradually reduced according to the shape of the cam bodies 22 and 31.

Therefore, immediately after the start of the extruding process of the molded product, the pressing force synthesized by the two cam bodies is applied to the formed product, so that a large force is applied to the formed product and the powder having large springback is held down. The force acts, and the occurrence of cracks in the molded body is further suppressed.

That is, a roller position adjusting mechanism 27 is provided between the bearing 17 of the pressure roller 15 and the piston of the cylinder device 17a, and the vertical position of the bearing 17 is adjusted by the roller position adjusting mechanism 27. By adjusting the position, the position of the pressure roller 15 and the position of the cam body 31 are set from the height of the molded body to be manufactured first. Therefore,
If a certain amount of powder is constantly inserted into the die, there is no particular variation in the height of the compact, but in practice, a certain amount of powder is always filled into the die due to various conditions such as fluidity and bulk density of the powder. It is not always the case, and when molded under the same pressure, the height of the molded body varies. In particular, when the filling amount is small, the piston of the cylinder device 17a is pressed down by pressing in the pressing process, and the powder is pressed while the pressing roller 15 is slightly lowered. Therefore, the pressure cylinder 24 fixed to the stand frame 2 as in the prior art
In the one in which the cam body 22 is merely added to the upper punch by the piston 25a or the like, since the pressure cylinder is at a fixed position, the upper punch holder by the cam body 22 immediately after the pressing by the pressing roller 15 is completed. 7 is not sufficient and cracks may occur in the molded body due to the spring bag.

However, in the present invention, since the pressure assist device 26 having the disc spring 30 is mounted on the bearing 17, the pressure assist device 26 moves up and down following the pressure roller 15. Therefore, immediately after the upper punch holder 7 has passed the lowermost point of the pressure roller, the pressure assisting device 26 is immediately activated, and a time lag occurs until the cam body 31 is sufficiently operated on the upper punch holder 7 as described above. Thus, cracks in the molded body due to springback are reliably prevented.

Incidentally, the pressing force by the upper inner cam body 31 can be adjusted by a combination of the disc springs 30. In the case of normal nuclear fuel, the pressure is 5 to 20% of the pressing force of 3 to 5 ton / cm ^2. Ie, about 150-800
Preferably, a pressure of kg / cm ² is applied to the compact.

Although the above embodiment has been described with the upper inner cam body 31 provided, a lower inner cam body engaging with the guide roller 11 of the lower punch holder 8 may be provided.

Table 1 shows the test results of the pressing force of the cam body and the frequency of occurrence of cracks.

[Table 1] As shown in Table 1, it can be seen that the generation of cracks is effectively suppressed by removing the molded product immediately after molding with a pressure as high as possible with respect to the molding pressure and extracting the molded product from the die. The pressing force is 5 to 2 of the molding pressure.
0% is optimal.

[0036]

As described above, the present invention applies a pressing force to at least the upper punch of the upper and lower punches during the extrusion process of extruding the molded product from the inside of the die while holding it between the upper and lower punches, and applying a predetermined pressure to the molded product. Since the pressurizing auxiliary device having a plurality of disc springs for maintaining the pressing force is provided, it is possible to maintain a state in which a relatively high pressure is applied to the compact during the extrusion process, and to rapidly release the pressure during the extrusion process. Thereby, generation of cracks in the molded body can be prevented. In addition, since a disc spring is used as the pressurizing assist device as described above, there is not much space restriction,
It can be arranged inside the pressure roller, that is, on the rotating disk axis side with respect to the pressure roller, and can be used in combination with the conventional pressing cam continuous mechanism.

[Brief description of the drawings]

FIG. 1 is a development view of a molding process of a powder molding machine according to the present invention.

FIG. 2 is a longitudinal sectional view of a compact pressing device during an extrusion process of the powder compacting machine of the present invention.

FIG. 3 is a plan view of an upper cam body.

FIG. 4 is a longitudinal sectional view showing a schematic configuration of a powder molding machine.

FIG. 5 is a plan view of a die plate portion.

FIG. 6 is a development view of a molding process of a conventional powder molding machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 5 Rotating disk 6 Dice 7 Upper punch holder 7a Upper punch 8 Lower punch holder 9 Lower punch 11, 13, 13a, 13b Guide roller 15, 16 Pressure roller 17, 18 Bearing part 26 Pressure auxiliary device 28 Cylinder 29 Piston member 30 Disc Springs 31 Upper Inner Cam Body

Claims (3)

[Claims] 1. A rotary-type powder molding machine for press-forming a powder by a pressing force of both upper and lower punches, in synchronization with a vertical position movement of a pressing roller for applying a pressing force to at least an upper punch of the upper and lower punches. A pressure assist having a plurality of disc springs for applying a predetermined pressing force to the upper punch immediately after passing the maximum pressing point of the pressing roller to the pressing roller bearing part which moves up and down to maintain a predetermined pressing force on the molded product. A powder molding machine equipped with an apparatus. 2. A disc spring is provided in a cylinder, and is configured such that a pressing force of the disc spring is applied to a guide roller provided on a punch holder via a cam body. The powder molding machine according to claim 1, wherein 3. The pressing force of the auxiliary pressing device immediately after passing through the maximum pressing point of the pressing roller is 5 to 20% of the forming pressure.
The powder molding machine according to claim 1 or 2, wherein a coned disc spring is combined so that