JPH03181326A - Pellet formation device - Google Patents

Abstract

PURPOSE:To produce the green pellets of uniform density by feeding back the compared result between the measured value and the set value of the density of green pellet to a hydraulic unit and adjusting the formation pressure. CONSTITUTION:The control unit 13 for the hydraulic unit 12 which gives a constant upward pressure FU to an upper punch 2 at the bottom dead center of press is constituted of a pellet density measuring unit 14, a density setting unit 15, and the comparator 16 which feeds back the hydraulic pressure control signal based on the compared result between the measured value and the set value to the hydraulic unit 12. The control unit 17 for the motor 9 adjusting a floating die 3 is constituted of the lower load cell 18 for a lower punch 4, an FL/FU measuring unit 19 which measures the ratio between the downward pressure FL detected by the cell 18 just before the upper punch 2 starts pressing with the definite force at the bottom dead center of press and the upper pressing force FU, and FL/FU setting unit 20, and the comparator 21 which feeds back the motor control signal based on the compared result between the measured value and the set value to the motor 9.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an apparatus for molding various ceramic powders, uranium dioxide powder, mixed oxide powder of plutonium and uranium, etc. into pellets.

[Conventional technology]

Taking the example of green pellets, in order to produce nuclear fuel pellets with uniform and consistent sintered density,
Green pellets obtained by molding nuclear fuel powder must have a uniform density. A conventional molding device is shown in FIG. 9 and briefly explained. A fixed lower bunch 4
The through hole 11 of the floating die 3 is 1% tifi
Above the through hole 11, an upper punch 2 held by an upper ram 1 to which a hydraulic damper 5 is attached is arranged so as to be able to be pushed down into the through hole li. The powder filled in the through hole 11 of the floating die 3 is pressed by the upper punch 2 and the lower punch 4 to form green pellets. The powder filling amount is adjusted by moving the floating die 3 up and down by rotating the adjustment motor 9 in the forward or reverse direction. 6, a height setting device 7,
The comparator 8 compares the value measured by the height detector 6 with the value set in the height setting device 7 and feeds back a forward/reverse operation signal to the motor 9 if the value is out of a certain range. was. The movement of this molding device is summarized using the cam diagram shown in FIG. 1O. I, II, and ■ are the trajectories of the lower surface of the upper bunch 2, the upper surface of the floating die 3, and the upper surface of the lower punch 4, respectively. In the powder filling step (2), the depth of the inner part of the through hole It filled with the powder to be molded is represented by filling ff1a, which is the difference between (2) and (2). In the first stage compression process (■), the upper bunch 2 descends by the upper pressure jib to apply upper pressure to the stationary floating die 3, and in the second stage compression process (■), the upper bunch 2 and the floating die The die 3 descends to the bottom dead center of the press while maintaining a constant relative positional relationship, and then comes to rest. This is the amount of downward pressure C on the lower bunch 4.
Since it is the same as pushing in only 1, this means applying downward pressure. In the extrusion process (2), the floating die 3 is lowered by an amount of extrusion Ete until the upper surface of the floating die 3 coincides with the upper surface of the lower bunch 4, while the upper bunch 2 escapes upward. The height h of the green pellet compressed by the lowering amount of the upper ram 1 is detected by the height detector 6, and based on the result of comparison with the set value by the comparator 8, the motor 9 rotates forward or backward to move the floating die 3. Move up and down, fill, fill
Adjustment of a is made. At that time, if the change in pellet height h is within the allowable range Y of the hydraulic damper 5, when excessive pressure is applied to the upper punch 2, the hydraulic damper 5 will move as shown in the hydraulic damper operating area shown by the diagonal line. This allows the pressure to be released and molding to be performed at a constant molding pressure. However, the above-mentioned molding apparatus is incapable of dealing with changes in the density of the green pellets, and an operator has no choice but to manually adjust the molding pressure based on the density measurement results of the green pellets.

[Problem to be solved by the invention]

Generally, the particle size distribution of powder filled into a die changes due to drifting and segregation, so even if pressed at a constant molding pressure, the density of the obtained green pellets will change. In the past, workers manually adjusted the molding pressure based on the density measurement results of the green pellets as described above, but this work was rather troublesome, and with the hydraulic damper type, the molding pressure was reduced during molding. In addition to not being able to easily change the pressure, there were times when there was a time delay in releasing the pressure, resulting in pressure exceeding the specified value being applied to the green pellets. Furthermore, in conventional molding equipment, when the floating die 3 is slightly raised to increase powder filling Eta due to a decrease in bulk density or to increase the height of green pellets, the lower pressure, lc, increases. lower bunch 4
Since the lower pressure increases and the density of the lower side of the green pellet locally increases, sintering in this state has the disadvantage that the lower shrinkage is low and the pellet becomes distorted in the shape of a truncated cone. The purpose of the present invention is to obtain a density balance between the upper and lower parts of a molded green pellet even when the amount of powder packed is changed, to make the height of the green pellet almost constant, and to maintain a constant density. Propose a molding device that can ensure uniformity13! - It's about doing.

[Means for resolving issues]

In the molding device of the present invention, a lower punch fixed to the lower part of the through hole of the floating die, which can be raised by an adjustment motor, is slidably fitted, and a lower punch held by the upper ram is provided above the through hole. The pellet molding device is the same as the conventional one in that it is equipped with a press that allows the punch to be pushed in and compresses the powder filled in the through hole with the upper punch and lower punch, but Apply a foot of upper pressure F to the upper punch! A hydraulic unit is provided for The control device for the hydraulic unit includes a pellet density measuring device, a density setting device, and a comparator that feeds back a hydraulic control signal to the hydraulic unit based on the comparison result between the measured value and the set value. The control device for the floating die adjustment motor includes a load cell installed below the lower punch, and a lower pressing force F1 detected by the load cell just before the upper punch starts applying constant pressure at the bottom dead center of the press. Also, an FL/FU measuring device that measures the ratio to the upper pressure FU, an FL/FU set value, and a comparator that feeds back a motor control signal to the adjustment motor based on the comparison result between the measured value and the set value. It is made up of the following. The upper limit ■ and lower limit values manually input to the density setter and FL/Fu setter described above are H=A+α L−A −Ji. However, A is the target value, ■ is the pellet density or F
It is the unbiased variance of the mean value of t/F u. When the measured value is within the range between the upper limit H and the lower limit, it is better not to provide feedback. It is also preferable that the control device for the floating die adjustment motor constantly monitors the upper limit of the amount of downward pressurization, and stops the molding device 11 times when the upper limit is reached.

[For use]

For example, if the properties of the powder change during molding and the pellet height h changes (higher) due to molding with a lower (higher) bulk density, the lower pressing force F will decrease (increase) from the normal value and the upper Pressure FU is constant and Alcala, F t / F u rf
il, go down (go up). In this way, since the F L / F u value is correlated with the density of the upper and lower parts of the pellet and the pellet height, F
When the comparison result between the measured value and the set value regarding the t/Fu value is fed back to the floating die lifting motor and the floating die is raised and lowered, the density of the upper and lower parts of the pellet is made uniform and the pellet height is also made uniform. become Furthermore, the hydraulic unit generating pressure control device changes the molding pressure according to the pellet density, thereby making the pellet density uniform.

【Example】

In the embodiment of the present invention shown in FIG. 1, the same parts as in FIG. 9 are given the same reference numerals. In the non-simultaneous three-stage compression type with-draw mechanical press used, a fixed lower bunch 4 is slidably fitted and pressed below a through hole 11 of a floating die 3 that can be moved up and down by an adjustment motor 9. Further, the upper punch 2 held by the upper ram 1 can be pushed down into the through hole 11, so that the powder filled in the through hole 11 can be compressed by the upper punch 2 and the lower punch 4. A unit 12 is provided so that a constant upward pressure FU can be applied to the upper punch 2 at the bottom dead center of the press. The movement of this press is shown in Figure 2, the cam diagram is shown in Figure 3, and when compared with Figure 9, the powder filling process ■, the first compression process ■, and the second compression process ■ There is no change in the extrusion process (2), but following the compression process (2) at the second stage opening, at the bottom dead center of the press where the floating die 3 is stationary, the upper punch 2 is pressed against a constant pressure (P) generated by the pressure unit 12. kg/cal), the pressure drops by a constant pressure jld, and the compression process at the third stage is continued for a constant pressurization time■
There is. The operating range of the upper punch 2 that guarantees a constant pressurization amount d is about 4 to 6III m, and the constant pressurization time t is about 0.5 to 5 seconds. In the figure,
The constant pressure operation range can be changed as appropriate within the range of about 6 Ton/c4, and the shaded area is the constant pressure operation range. As shown in FIG. 1, the pressure control device I3 of the above-mentioned hydraulic unit It is comprised of a comparator 16 that compares the output with the value set in the density setter 15 at every predetermined sampling point and feeds back a pressurization control signal to the hydraulic unit 12 according to the result. The initial value of the pellet density manually entered into the density setting device 15 is:
When the unbiased variance of the average value of pellet density is V (this unbiased variance is based on the measurement results in a short time when it is assumed that there is no change in the average value over time), and the target value is A,
The upper limit H and lower limit are determined from the following formula. In the example of FIG. 5, which shows the relationship between pellet density and molding pressure, one sampling point is taken every 50 punches. To explain using the flowchart of pressurization control shown in FIG. 6, Step! It is determined whether or not it is a sampling point in step 01, and if it is a sampling point, the average value of one or more of the densities of the green pellets measured by the density 1111 measuring device 14 is determined by step +02.
and send the result to the comparator 16 to input the pellet density initial value range (H, L
) and step +03 and! 04, and if it is out of the range, the extraction pressure unit 12 sends a control signal to increase or decrease the molding pressure by one step in steps 105 and 108.
The generated pressure P of the pressurizing unit 12 is fed back to the pressurizing unit 12. Adjust kg/c-. In the example shown in FIG. 5, since the molding pressure exceeds the set value H at the second sampling point, the molding pressure is decreased by one step from the initial value. Further, in the example shown in FIG. 5, the third and fourth sampling points are within the set range (HSL). In such a case, it is better not to perform feedback as it is essentially a control-unnecessary range in order to improve the stability of the control system. Note that FIG. 5 also shows the relationship between the lower pressurizing force/upper pressurizing force and the lower pressurizing amount, but in this case, one sampling point is taken every five punches. The pellet density setting value manually entered into the density setting device 15 is as follows:
It is not limited to the above upper limit H and lower limit. If necessary, it may be further subdivided into H, H, . . . LlLl . . . to perform multi-stage feedback control. To give an example, the setting values (H, L) when divided into three groups
(H+L+) (H2, L2) is A+Jv A±2 to i A+3Jv its step m
(+), (2), (3) are 0.8162.09a3
．． 21%/V. FIG. 7 is a flowchart in the case of subdivision, and steps 107 to 110 are increased. Returning again to FIG. 1, the control device 17 for the floating die adjustment motor 9 will now be described. This control device 17 has F1. / F u 1l II regulator 19
, F L / F u setting device 20, and the above F t /
A comparator 21 that compares the output of the F u measuring device and the value set in the F L/F u setting device at each predetermined sampling point, and feeds back a motor control signal to the adjustment motor 9 according to the result. It consists of Here, the lower pressure F is referred to in FIG. 4, which shows the output of the load cell 18 installed below the lower punch 4.
It refers to the output sampled just before the third stage compression process (2) when the press reaches the bottom dead center and the second stage compression process (2) ends and the upper bunch 2 starts applying constant pressure. Also, upper shelf pressure FU
is the product P of the constant pressurization applied to the upper punch 2, that is, the pressure generated by the hydraulic unit 11, P□kg/cl#, and the head area 5ocj (constant) of the upper punch 2. XSo(kg)
It is defined as The upper limit H and lower limit manually input to the F L/Fu setting device 20 are determined by the above formula, where V is the unbiased variance of the average value of F L/FU, and the target value A is the upper and lower limits of the diameter of the pellet after sintering. F where the difference is close to zero and the upper shelf pressure Fu and lower pressing force FL are well balanced 1. / F u value. PoxSo and Fl, /F 11 are calculated by a microcomputer within the device. To explain with the flowchart of lower pressurization amount control shown in Fig. 8, F +, / F
u aPl setter 19 The average value of one or more of the set flF+ is calculated in step 202, and the result is sent to the comparator 21, and the F L/F u setter 20
The initial value range (H, L) manually entered is compared in steps 203 and 204, and if it is outside the range, step 20
By feeding back to the motor 9 a control signal that increases or decreases the amount of lower pressurization by one step at 5 and 20B,
The floating die 3 is raised and lowered to adjust the filling amount, in other words, the lower pressurization amount. In this example, the upper limit of the lower pressure amount C is constantly monitored in step 207, and if the lower pressure amount C reaches the upper limit, it is determined that it means that there is no more powder to be supplied to the molding device. , the molding device is automatically stopped and the process is finished. The above-mentioned feedback of molding pressure and lower pressure (filling amount) operates independently without excessive interference, and if the operating point deviates from the optimum value, they work together to return it to its original value. Work with. All of the above are medium-sized die sets, but in the case of a molding machine having a plurality of die sets, feedback control of the density upper and lower balance may be independently provided for each die set. This suppresses variations in filling amount between die sets. ■Effects of the Invention The present invention feeds back the comparison result between the measured value of Ft/Fu and the set value to the floating die lifting motor to raise and lower the floating die to increase or decrease the filling amount. Even if the properties of the powder change during molding, it not only helps to suppress the density deviation between the upper and lower parts of the green pellet, in other words, it contributes to reducing the diameter distortion of the sintered pellet, but also contributes to reducing the height of the pellet. It is extremely superior in that it can approach a predetermined value at the same time. Further, in the present invention, the comparison result between the measured value of the green pellet density and the set value is fed back to the hydraulic unit to adjust the molding pressure, so that green pellets having a uniform density can be obtained. Both of these effects can improve the yield of products. 4. ffl'l 111- Explanation of the drawings Fig. 1 is an explanatory diagram of the pellet molding apparatus according to the present invention, Fig. 2 is an explanatory diagram showing the molding process in order, Fig. 3 is a cam diagram thereof, Fourth
The figure shows the output of the load cell, Figure 5 shows the relationship between the green pellet density and molding pressure during the molding process, the relationship between the lower pressurizing force/upper pressurizing force and the lower pressurizing amount, and Fig. 6
The figure is a flowchart of pellet density control, and Figure 7 is a flowchart of pellet density control.
Figure 8 is a flowchart for equalizing the density of the upper and lower parts of the pellet; Figure 9 is an explanatory diagram of a conventional pellet molding device;
Figure 0 is its cam diagram. DESCRIPTION OF SYMBOLS 1... Upper ram, 2... Upper punch, 3... Floating die, 4... Lower punch, 9... Adjustment motor, 11... Through hole, 12... Hydraulic unit, 13.
... Hydraulic unit control device, 14... Density measuring device,
15... Density setter, 1B... Comparator, 17
...Floating die adjustment motor control device, 1
8...Load cell, 19...Lower pressure Ft/upper pressure FU measuring device, 20...Ft/Fu setting device,
21... Comparator. Fig. U "Sweet Diagram" ■ ■ ■ ■ ■ Flute Diagram Diagram 1 Time Diagram Diagram 7 Diagram Flute Diagram

Claims (1)

[Claims] 1. A fixed lower punch is slidably inserted into the lower part of the through hole of the floating die which can be moved up and down by an adjustment motor, and a lower punch held by the upper ram is inserted above the through hole. In a pellet molding device equipped with a press in which the punch can be pushed in and the powder filled in the through hole can be compressed with an upper punch and a lower punch, a constant upper pressing force F_U is applied to the upper punch at the bottom dead center of the press. The control device for the hydraulic unit includes a pellet density measuring device, a density setting device, and a comparator that feeds back a hydraulic control signal to the hydraulic unit based on the comparison result between the measured value and the set value. The control device for the floating die adjustment motor is composed of a load cell installed below the lower punch, and a load cell that detects the lower pressure immediately before the upper punch starts applying constant pressure at the bottom dead center of the press. An F_L/F_U measuring device that measures the ratio of the pressurizing force F_L and the above-mentioned upper pressurizing force F_U, and an F_L/F_U setting device, and a motor control signal is sent to the above-mentioned adjustment motor based on the comparison result between the measured value and the set value. A pellet molding device characterized by comprising a feedback comparator. 2. The setting values of the upper limit H and lower limit L input to the density setter and F_L/F_U setter are determined by the following formula, where A is the target value and V is the unbiased variance of the pellet density or the average value of F_L/F_U. The molding apparatus according to claim 1, obtained by. H=A+√V L=A−√V 3. The molding apparatus according to claim 1, wherein the feedback is not performed when the measured value is within the range between the upper limit H and the lower limit L. 4. The molding apparatus according to claim 1, wherein the control device for the floating die adjustment motor constantly monitors the upper limit of the amount of downward pressurization and automatically stops the molding apparatus when the upper limit is reached.