阅读说明：本技术 一种球形燃料元件无燃料区预成型下半模的加粉造窝装置 (Powder adding and dimpling device for spherical fuel element fuel-free zone preforming lower half mold ) 是由 刘兵 张�杰 周湘文 卢振明 唐亚平 史小龙 于 2020-03-18 设计创作，主要内容包括：本发明的一种球形燃料元件无燃料区预成型下半模的加粉造窝装置,粉末料仓固定设置在机架顶部,导料装置的顶端与粉末料仓的底部下料口紧密连接,导料装置下方的机架上设有加粉工位和造窝工位,成型下模放置在加粉工位上；模具上盖总成的加粉位部设置在成型下模的上方,导料装置的底部通过加粉位部与成型下模连接,模具上盖总成的造窝位部的底部固定连接球形造窝头。导料装置的上导料管、直料管和下导料管之间通过筛网旋转,实现定量给料,且给料均匀松散,加料过程中,模具上盖总成始终在成型下模上方,防止基体石墨粉的外溢,保护生产车间环境。加粉完成后在造窝工位进行造窝,多个工位同时完成多个成型下模的加粉和造窝,大大提高了生产效率。(According to the powder adding and nest making device for the spherical fuel element fuel-free zone pre-forming lower half die, the powder bin is fixedly arranged at the top of the frame, the top end of the material guide device is tightly connected with the bottom feed opening of the powder bin, the frame below the material guide device is provided with the powder adding station and the nest making station, and the forming lower die is placed on the powder adding station; the powder adding part of the upper die cover assembly is arranged above the forming lower die, the bottom of the material guide device is connected with the forming lower die through the powder adding part, and the bottom of the nest making part of the upper die cover assembly is fixedly connected with a ball-shaped nest making head. The upper material guide pipe, the straight material guide pipe and the lower material guide pipe of the material guide device are rotated through the screen mesh, so that quantitative feeding is realized, the feeding is uniform and loose, and in the feeding process, the upper cover assembly of the mold is always above the lower forming mold, so that the overflow of matrix graphite powder is prevented, and the environment of a production workshop is protected. After the powder is added, the nest is made at the nest making station, and the powder adding and nest making of a plurality of forming lower dies are completed simultaneously at a plurality of stations, so that the production efficiency is greatly improved.)

1. The powder adding and nest making device for the pre-forming lower half die of the fuel-free area of the spherical fuel element is characterized by comprising a rack, a powder bin (1), a material guide device, a die upper cover assembly and a forming lower die (12), wherein the powder bin (1) is fixedly arranged at the top of the rack, the top end of the material guide device is tightly connected with a bottom feed opening of the powder bin (1), a powder adding station and a nest making station are arranged on the rack below the material guide device, and the forming lower die (12) is placed on the powder adding station;

mould upper cover assembly is including adding powder position portion and making nest position portion, add the top that powder position portion set up at shaping lower mould (12), the bottom of guide device is connected with shaping lower mould (12) through adding powder position portion, it sets up in making nest station top to make nest position portion, the bottom fixed connection ball shape of making nest position portion makes nest head (10).

2. The device for powdering and dimpling a spherical fuel element fuel-free zone preforming bottom half-mold according to claim 1, wherein the mold upper cover assembly is provided with a powdering and dimpling lifting cylinder (9).

3. The powder adding and nest making device for the spherical fuel element fuel-free zone preforming lower half die is characterized in that the material guiding device comprises an upper material guiding pipe (2), a straight material guiding pipe (4) and a lower material guiding pipe (8), the top of the upper material guiding pipe (2) is tightly connected with a bottom blanking opening of the powder storage bin (1), an upper screen assembly (3) is arranged between the upper material guiding pipe (2) and the straight material guiding pipe (4), and a lower screen assembly (5) is arranged between the straight material guiding pipe (4) and the lower material guiding pipe (8).

4. The powder adding and nest making device for the spherical fuel element fuel-free zone preforming lower half die is characterized in that the upper screen assembly (3) comprises an upper screen, an upper screen frame, an upper screen gear and an upper screen motor (6), the upper screen is arranged at the joint of the upper material guide pipe (2) and the straight material pipe (4), the upper screen frame is fixedly arranged at the outer edge of the upper screen, the upper screen frame is fixedly arranged in the center of the upper screen gear, the upper screen gear is fixed on a rack through a gear shaft, and the upper screen motor (6) drives the upper screen gear to rotate horizontally.

5. The powder feeding and dimpling device for the spherical fuel element fuel-free zone preforming lower mold half according to claim 4, wherein the lower screen assembly (5) comprises a lower screen, a lower screen frame, a lower screen gear and a lower screen motor (7), the lower screen is arranged at a joint of the straight pipe (4) and the lower guide pipe (8), the lower screen frame is fixedly arranged at the outer edge of the lower screen, the lower screen frame is fixedly arranged at the center of the lower screen gear, the lower screen gear is fixed on the machine frame through a gear shaft, and the lower screen motor (7) drives the lower screen gear to rotate horizontally.

6. The powder adding and dimpling device for the spherical fuel element fuel-free zone preforming lower die half according to claim 1, characterized in that a mechanical claw (11) is further provided on the machine frame, the shape of the mechanical claw (11) is matched with that of the forming lower die (12), and the mechanical claw (11) horizontally reciprocates at the powder adding station and the dimpling station.

7. The powder adding and dimpling device for the spherical fuel element fuel-free zone preforming lower mold half according to claim 3, wherein the diameters of the upper guide pipe (2), the straight guide pipe (4) and the lower guide pipe (8) are all 55mm to 65 mm.

8. The powder-adding and dimpling device for the spherical fuel element non-fuel area preforming lower mold half, according to claim 5, characterized in that the upper screen is 6-15 mesh, the rotation speed of the upper screen is 50-100 rpm, the rotation speed of the lower screen is 8-16 mesh, and the rotation speed of the lower screen is 50-100 rpm.

9. The powder adding and dimpling device for the spherical fuel element fuel-free zone preforming lower die half according to claim 1, characterized in that a double helix stirrer is arranged in the powder bin (1).

10. The powder-coating and dimple-forming device for the lower half of the nonfuel area preform of spherical fuel element as claimed in claim 1, wherein the spherical dimple forming head (10) is shaped as a hemisphere with a diameter of 53 ± 1 mm.

Technical Field

The invention relates to the technical field of nuclear technical devices, in particular to a powder adding and pit making device for a spherical fuel element fuel-free area preforming lower half mold.

Background

The fuel used in the pebble-bed high-temperature gas-cooled reactor is a spherical fuel element with the diameter of about 60mm and a certain amount of coating particles uniformly distributed inside, wherein the area containing the fuel in the center of a sphere is called a fuel area, and the area at the periphery of the fuel area is called a fuel-free area. The forming process of the fuel zone and the fuel-free zone comprises a preforming process and a final pressing forming process. The pre-forming of the fuel area is that under the pressure condition of 0.3-4MPa, the material which is obtained by uniformly mixing quantitative matrix graphite powder and quantitative dressing particles is pressed and formed in a rubber soft film; the preforming of the fuel-free area is to add a certain amount of matrix graphite powder to the lower half die of the rubber soft film for nest making, then position the preformed fuel area in the lower half die of the rubber soft film after powder nest making, and fill the whole die cavity with the matrix graphite powder after the upper half die is added. At present, the powder adding and nest making of the lower half die adopts a spiral feeding open type, the nest making is completed while the powder is added, the powder adding and nest making period is long, the dust overflows, and the capacity can not meet the requirement of large-scale production of spherical fuel elements.

Therefore, a powder adding and nest making device for the spherical fuel element fuel-free zone preforming lower half mold is needed, the problem of dust overflow is effectively solved while the production efficiency is greatly improved, and the production environment of a workshop is well improved.

Disclosure of Invention

In view of the above, the present invention provides a powder adding and dimpling device for a spherical fuel element non-fuel area pre-forming lower mold half, which realizes uniform and quantitative feeding, and an upper mold cover assembly of a mold is always on a forming lower mold in a powder adding process, so as to avoid pollution to workshop environment due to overflow of matrix graphite powder in the powder adding process, and improve production efficiency.

In order to solve the technical problems, the invention adopts the following technical scheme:

a powder adding and nest making device for a spherical fuel element fuel-free zone pre-forming lower half die comprises a rack, a powder bin, a material guide device, a die upper cover assembly and a forming lower die, wherein the powder bin is fixedly arranged at the top of the rack, the top end of the material guide device is tightly connected with a bottom blanking port of the powder bin, a powder adding station and a nest making station are arranged on the rack below the material guide device, and the forming lower die is placed on the powder adding station; mould upper cover assembly is including adding powder position portion and making nest position portion, add the top of powder position portion setting at the shaping lower mould, the bottom of guide device is connected with the shaping lower mould through adding powder position portion, it sets up in making nest station top to make nest position portion, the bottom fixed connection ball of making nest position portion makes a nest head.

Preferably, a powder adding and pit making lifting cylinder is arranged on the die upper cover assembly. The up-and-down movement of the die upper cover assembly and the spherical nest forming head is realized by the up-and-down movement of a fixed plate fixed on the frame, and the up-and-down movement of the fixed plate is realized by a powder adding nest forming lifting cylinder under the action of a guide shaft. Add powder and make nest lift cylinder and drive mould upper cover assembly and rise and descend, whole powder in-process that adds, mould upper cover assembly is in the next all the time, and the powder position portion that adds presses all the time on the shaping lower mould to prevent to add the production environment in powder in-process matrix graphite powder and spill over, effectual improvement workshop.

Preferably, the material guiding device comprises an upper material guiding pipe, a straight material pipe and a lower material guiding pipe, the top of the upper material guiding pipe is tightly connected with a bottom feed opening of the powder storage bin, an upper screen assembly is arranged between the upper material guiding pipe and the straight material guiding pipe, and a lower screen assembly is arranged between the straight material guiding pipe and the lower material guiding pipe. The upper material guide pipe, the straight material guide pipe and the lower material guide pipe are fixed on a transverse plate of the rack through bases of the pipe clamps.

Preferably, the upper screen assembly comprises an upper screen, an upper screen frame, an upper screen gear and an upper screen motor, the upper screen is arranged at the joint of the upper material guide pipe and the straight material pipe, the outer edge of the upper screen is fixedly provided with the upper screen frame, the upper screen frame is fixedly arranged at the center of the upper screen gear, the upper screen gear is fixed on the rack through a gear shaft, the upper screen motor drives the upper screen gear to rotate horizontally, and the upper screen rotates along with the upper screen gear. The powder bin is used for storing a certain amount of matrix graphite powder, and the matrix graphite powder in the upper material guide pipe falls into the straight material pipe with the same looseness through the rotation of the upper screen.

Preferably, the lower screen assembly comprises a lower screen, a lower screen frame, a lower screen gear and a lower screen motor, the lower screen is arranged at the joint of the straight material pipe and the lower material guide pipe, the lower screen frame is fixedly arranged at the outer edge of the lower screen, the lower screen frame is fixedly arranged at the center of the lower screen gear, the lower screen gear is fixed on the rack through a gear shaft, the lower screen motor drives the lower screen gear to horizontally rotate, and the lower screen rotates along with the lower screen gear. The matrix graphite powder in the straight material pipe falls into the lower material guide pipe with the same looseness through the rotary screen movement of the lower screen, and a certain looseness is formed and falls into a forming lower die of the fuel-free area preforming die.

The upper screen motor and the lower screen motor drive the upper screen gear and the lower screen gear to drive the upper screen and the lower screen to rotate, so that the graphite powder is conveyed, the rotating speed of the upper screen and the lower screen is changed or the operating time of the upper screen motor and the lower screen motor is changed by adjusting the rotating speed of the upper screen motor and the lower screen motor, and the purpose of controlling the quantitative feeding is achieved.

Preferably, the rack is further provided with a mechanical claw, the shape of the mechanical claw is matched with that of the lower forming die, and the mechanical claw horizontally reciprocates at the powder adding station and the nest forming station. The mechanical claw is connected with the upper part and the lower part of the side surface of the frame by a connecting rod through a hard link.

After matrix graphite powder is added into a forming lower die through a lower guide pipe, a powder feeding and nest making lifting cylinder controls an upper cover assembly of the die to ascend, then a grabbing mechanism of a mechanical claw clamps the forming lower die to move forwards, the forming lower die above a preparation position is conveyed to a powder feeding station, the forming lower die of the powder feeding station is conveyed to a nest making station, and the forming lower die of the nest making station is conveyed to a conveying chain; meanwhile, the powder adding and pit making lifting cylinder controls the upper cover assembly of the die to move downwards in place, pit making is carried out on the powder adding lower die, powder is added to the powder adding lower die above the powder adding station, and the whole process of powder adding and pit making is completed. The upper cover assembly of the die is pressed on the lower forming die all the time in the powder adding process to prevent the matrix graphite powder from overflowing, and the air in the lower forming die in the powder adding process is discharged through an exhaust hole between the dust cover of the upper die and the upper edge interface of the lower forming die and is discharged through a public exhaust dust removal system.

Preferably, the diameters of the upper material guide pipe, the straight material pipe and the lower material guide pipe are 55mm-65mm, and preferably 57-60 mm; the upper material guide pipe and the straight material guide pipe as well as the straight material guide pipe and the lower material guide pipe are connected in a tight fit mode, and sealed by an inner sealing piece and an outer sealing piece.

Preferably, the upper screen is 6-15 meshes, preferably 8-12 meshes, and the rotating speed of the upper screen is 50-100 revolutions/minute, preferably 60-90 revolutions/minute; the lower screen is 8-16 meshes, preferably 10-12 meshes, and the rotating speed of the lower screen is 50-100 revolutions per minute, preferably 60-90 revolutions per minute.

Preferably, a double-helix stirrer is arranged in the powder bin. The double helix agitator can make the basal body graphite powder in the powder bin continuously and uniformly disperse and fall into the upper material guide pipe through the feed opening.

Preferably, the spherical dimple forming head is hemispherical in shape and 53 ± 1mm in diameter. The height of the spherical steamed corn bread is adjusted to adjust the depth of the steamed corn bread, and the adjusting range is 1mm-3 mm.

The powder adding and nest making device is provided with a plurality of stations, the screen meshes at different stations rotate through a motor to drive the gear of the first station below the screen mesh, and the gear of the first station drives the screen meshes at other stations to rotate through gear transmission. The upper screen mesh gear meshing transmission between a plurality of stations, the lower screen mesh gear meshing transmission between a plurality of stations, the upper screen mesh motor and the lower screen mesh motor drive the upper screen mesh and the lower screen mesh rotation of different stations through gear transmission, and the powder is simultaneously added to the forming lower dies of different stations.

The invention has the following beneficial effects:

according to the invention, by adopting the technical scheme, the upper material guide pipe, the straight material guide pipe and the lower material guide pipe of the material guide device rotate through the screen, so that quantitative feeding is realized, the feeding is uniform and loose, the upper cover assembly of the mold is always arranged above the lower molding die in the feeding process, the overflow of matrix graphite powder is prevented, and the environment of a production workshop is protected. After the powder is added, the nest is made at the nest making station, and the powder adding and nest making of a plurality of forming lower dies are completed simultaneously at a plurality of stations, so that the production efficiency is greatly improved.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly understood and to make the technical means implementable in accordance with the contents of the description, and to make the above and other objects, technical features, and advantages of the present invention more comprehensible, one or more preferred embodiments are described below in detail with reference to the accompanying drawings.

Drawings

One or more embodiments are illustrated by way of example in the accompanying drawings, which correspond to the figures in which like reference numerals refer to similar elements and which are not to scale unless otherwise specified.

Fig. 1 shows a schematic structural view of a powdering and dimpling device of a spherical fuel element fuel-free zone preforming lower mold half according to the present invention in a front view direction.

Fig. 2 shows a schematic left-side view of a powder feeding and dimpling device of a spherical fuel element fuel-free zone preforming lower mold half of the present invention.

Description of the main reference numerals:

1-a powder bin, 2-an upper material guide pipe, 3-an upper screen assembly, 4-a straight material pipe, 5-a lower screen assembly, 6-an upper screen motor, 7-a lower screen motor, 8-a lower material guide pipe, 9-a powder adding nest lifting cylinder, 10-a spherical nest making head, 11-a mechanical claw and 12-a forming lower die.

Detailed Description

The following detailed description of the present invention is provided in conjunction with the accompanying drawings, but it should be understood that the scope of the present invention is not limited to the specific embodiments.

Throughout the specification and claims, unless explicitly stated otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or component but not the exclusion of any other element or component.

Spatially relative terms, such as "below," "lower," "upper," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the object in use or operation in addition to the orientation depicted in the figures. For example, if the items in the figures are turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the elements or features. Thus, the exemplary term "below" can encompass both an orientation of below and above. The article may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative terms used herein should be interpreted accordingly.

As shown in fig. 1 and 2, a powder adding and dimpling device for a spherical fuel element fuel-free zone pre-forming lower half mold comprises a frame, a powder bin 1, a material guiding device, a mold upper cover assembly and a forming lower mold 12.

Powder feed bin 1 is fixed to be set up at the frame top, the top of guide device is connected with powder feed bin 1's bottom feed opening is close, be equipped with the powder station in the frame of guide device below and nest station, shaping lower mould 12 is placed on the powder station.

The material guiding device comprises an upper material guiding pipe 2, a straight material guiding pipe 4 and a lower material guiding pipe 8, the top of the upper material guiding pipe 2 is tightly connected with a bottom feed opening of the powder storage bin 1, an upper screen assembly 3 is arranged between the upper material guiding pipe 2 and the straight material guiding pipe 4, and a lower screen assembly 5 is arranged between the straight material guiding pipe 4 and the lower material guiding pipe 8. The upper material guide pipe 2, the straight material guide pipe 4 and the lower material guide pipe 8 are fixed on a transverse plate of the frame through bases of pipe clamps.

The diameters of the upper material guide pipe 2, the straight material guide pipe 4 and the lower material guide pipe 8 are all 55-65 mm, and preferably 57-60 mm; the upper material guide pipe 2 and the straight material guide pipe 4 as well as the straight material guide pipe 4 and the lower material guide pipe 8 are connected in a tight fit mode, and sealed by an inner sealing piece and an outer sealing piece.

The upper screen assembly 3 comprises an upper screen, an upper screen frame, an upper screen gear and an upper screen motor 6, the upper screen is arranged at the joint of the upper material guide pipe 2 and the straight material guide pipe 4, the outer edge of the upper screen is fixedly provided with the upper screen frame, the upper screen frame is fixedly arranged at the center of the upper screen gear, the upper screen gear is fixed on the rack through a gear shaft, the upper screen motor 6 drives the upper screen gear to rotate horizontally, and the upper screen rotates along with the upper screen gear. The upper screen is 6-15 meshes, preferably 8-12 meshes, and the rotating speed of the upper screen is 50-100 r/min, preferably 60-90 r/min.

The powder bin 1 is used for storing a certain amount of matrix graphite powder, and a double-helix stirrer is arranged in the powder bin 1. The double helix agitator can make the matrix graphite powder in the powder bin 1 continuously and uniformly dispersed and fall into the upper material guide pipe 2 through the feed opening. The matrix graphite powder in the upper material guide pipe 2 falls into the straight material pipe 4 with the same looseness through the rotation of the upper screen.

The lower screen assembly 5 comprises a lower screen, a lower screen frame, a lower screen gear and a lower screen motor 7, the lower screen is arranged at the joint of the straight material pipe 4 and the lower material guide pipe 8, the outer edge of the lower screen is fixedly provided with the lower screen frame, the lower screen frame is fixedly arranged at the center of the lower screen gear, the lower screen gear is fixed on the rack through a gear shaft, the lower screen motor 7 drives the lower screen gear to rotate horizontally, and the lower screen rotates along with the lower screen gear. The matrix graphite powder in the straight material pipe 4 falls into the lower material guide pipe 8 with the same looseness through the rotary sieving of the lower screen, and a certain looseness is formed and falls into a forming lower die 12 of a fuel-free area preforming die. The lower screen is 8-16 meshes, preferably 10-12 meshes, and the rotating speed of the lower screen is 50-100 revolutions per minute, preferably 60-90 revolutions per minute.

The upper screen motor 6 and the lower screen motor 7 drive the upper screen gear and the lower screen gear to drive the upper screen and the lower screen to rotate, so that the matrix graphite powder is conveyed, the rotating speed of the upper screen and the lower screen is changed or the running time of the upper screen motor 6 and the lower screen motor 7 is changed by adjusting the rotating speed of the upper screen motor 6 and the lower screen motor 7, and the purpose of controlling the quantitative feeding is achieved.

The mould upper cover assembly includes powder position portion and makes nest position portion, add the top that powder position portion set up at shaping lower mould 12, the bottom of guide device is connected with shaping lower mould 12 through adding powder position portion, it sets up in the position top of making the nest to make nest position portion, the bottom fixed connection ball of making nest position portion makes nest head 10. The spherical steamed corn bread 10 is hemispherical and has a diameter of 53 +/-1 mm. The height of the spherical steamed corn bread 10 is adjusted to adjust the depth of the steamed corn bread, and the adjusting range is 1mm-3 mm.

And a powder adding and pit making lifting cylinder 9 is arranged on the die upper cover assembly. The up-and-down movement of the die upper cover assembly and the spherical nest forming head 10 is realized by the up-and-down movement of a fixed plate fixed on the frame, and the up-and-down movement of the fixed plate is realized by the powder adding nest forming lifting cylinder 9 under the action of the guide shaft. Add powder and make nest lift cylinder 9 and drive mould upper cover assembly and rise and descend, whole powder in-process that adds, mould upper cover assembly is in the next all the time, and the powder position portion that adds presses all the time on shaping lower mould 12 to prevent to add the production environment in powder in-process matrix graphite powder and spill over, effectual improvement workshop.

The machine frame is also provided with a mechanical claw 11, the shape of the mechanical claw 11 is matched with that of the lower forming die 12, and the mechanical claw 11 horizontally reciprocates at a powder adding station and a nest forming station. The gripper 11 is connected to the upper and lower sides of the frame side by a connecting rod using a hard link.

After matrix graphite powder is added into a lower forming die 12 through a lower material guide pipe 8, a powder feeding nest making lifting cylinder 9 controls a die upper cover assembly to ascend, then a grabbing mechanism of a mechanical claw 11 clamps the lower forming die 12 to move forwards, the lower forming die 12 above a preparation position is conveyed to a powder feeding station, the lower forming die 12 of the powder feeding station is conveyed to a nest making station, and the lower forming die 12 of the nest making station is conveyed to a conveying chain; meanwhile, the powder adding and nest making lifting cylinder 9 controls the upper cover assembly of the die to move downwards in place, the powder adding lower die 12 is subjected to nest making, the powder is added to the lower die 12 above the powder adding station, and the whole process of powder adding and nest making is completed. The upper cover assembly of the die is pressed on the lower forming die 12 all the time in the powder adding process to prevent the matrix graphite powder from overflowing, and the air in the lower forming die 12 in the powder adding process is exhausted through an exhaust hole between the dust cover of the upper die and the upper edge interface of the lower forming die 12 and is exhausted through a public exhaust dust removal system.

The powder adding and nest making device is provided with a plurality of stations, the screen meshes at different stations rotate through a motor to drive the gear of the first station below the screen mesh, and the gear of the first station drives the screen meshes at other stations to rotate through gear transmission. The upper screen mesh gears between the stations are in meshing transmission, the lower screen mesh gears between the stations are in meshing transmission, and the upper screen mesh motor 6 and the lower screen mesh motor 7 drive the upper screen mesh and the lower screen mesh of different stations to rotate through gear transmission, so that the lower molding dies 12 of different stations are simultaneously powdered.

The working process of the powder adding and dimpling device for the spherical fuel element non-fuel area preforming lower half mold comprises the following steps:

the matrix graphite powder in the powder bin 1 enters an upper material guide pipe 2 connected with a bottom feed opening through the dispersion of a double-helix stirrer, passes through an upper screen assembly 3 between the upper material guide pipe 2 and a straight material pipe 4, and falls into the straight material pipe 4 through the rotation of an upper screen.

Through installing lower screen assembly 5 between straight material pipe 4 and lower baffle pipe 8, through the rotary screen of lower screen cloth move, form certain bulk to the base member graphite powder in straight material pipe 4 and fall into in the shaping lower mould 12 of the no fuel zone preforming mould of baffle pipe 8 bottom down, and mould upper cover assembly is in the next position in this process, presses on shaping lower mould 12 all the time to prevent that base member graphite powder from overflowing.

After matrix graphite powder is added into a lower forming die 12 of a fuel-free area preforming die through a material guide device, a powder adding and pit making lifting cylinder 9 drives a die upper cover assembly to ascend, then a grabbing mechanism of a mechanical claw 11 clamps the lower forming die 12 to move forwards, the lower forming die 12 above a preparation position is conveyed to a powder adding station, the lower forming die 12 of the powder adding station is conveyed to a pit making station, and the lower forming die 12 of the pit making station is conveyed to a conveying chain; meanwhile, the powder adding and pit making lifting cylinder 9 drives the die upper cover assembly to move downwards in place, pit making is carried out on the powder adding lower die 12, powder is added to the forming lower die 12 above the powder adding station, and the whole process of powder adding and pit making is completed.

Experimental example 1:

the experimental example adopts a powder adding and nest making device with six stations, the diameters of an upper material guide pipe 2, a straight material guide pipe 4 and a lower material guide pipe 8 are 56-58mm, the rotating speeds of an upper screen and a lower screen are 79 rpm, the upper screen is 10 meshes, the lower screen is 12 meshes, the powder adding and nest making time is 21s, and the productivity is 1028 pieces/hour.

The test process is as follows: the parallelism analysis of the tests at different times at six stations and the powder adding precision and error analysis of the test results of 15 times at the same station are shown in the data of the following tables 1 and 2.

TABLE 1-parallelism analysis of six stations at different trials

TABLE 2 powder addition accuracy and error analysis of 15 test results at the same station

	Maximum value/g	Minimum value/g	Average value/g	Upper deviation/%)	Lower deviation/%)	Maximum error/g
							1	73.32	71.23	72.02	1.80	1.10	2.09
2	72.76	70.03	71.63	1.34	1.63	2.13
							3	73.18	71.63	72.38	1.10	1.04	1.55
4	72.41	70.92	71.64	1.07	1.01	1.49
							5	73.34	70.45	72.13	1.68	2.32	2.89
6	73.14	71.84	72.60	0.74	1.05	1.30
							7	71.96	70.54	71.15	1.13	0.86	1.42
8	72.21	70.45	71.30	1.28	1.19	1.76
							9	72.30	70.84	71.62	0.96	1.08	1.46
10	72.01	70.08	70.92	1.53	1.19	1.93
							11	71.61	70.85	71.26	0.50	0.57	0.76
12	72.06	70.99	71.41	0.91	0.59	1.07
							13	72.57	71.09	71.77	1.12	0.94	1.48
14	72.40	70.72	71.55	1.19	1.16	1.68
							15	72.31	71.10	71.49	1.14	0.55	1.21

Experimental example data show that the powder adding and nesting device for the spherical fuel element fuel-free zone preforming lower half mold can enable matrix graphite powder to be uniformly dispersed and quantitatively added into the forming lower mold 12, and the powder adding precision can be controlled within 3%.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications as are suited to the particular use contemplated. Any simple modifications, equivalent changes and modifications made to the above exemplary embodiments shall fall within the scope of the present invention.