Powder forming method and system for manufacturing rare earth sintered magnet

Abstract

The invention discloses a powder forming method and system for manufacturing a rare earth sintered magnet. The system comprises a supply device, a powder feeding device and an extrusion forming device. The supply device comprises a stock bin, a powder feeding dustpan, a vibration feeder, a metering tipping bucket, a discharging bowl and a discharging barrel, the powder feeding dustpan is located below the stock bin, and the vibration feeder is located below the powder feeding dustpan; the metering tipping bucket is located below the outlet end of the powder feeding dustpan, and the discharging bowl is located below the metering tipping bucket. The discharging barrel is located below the discharging bowl and communicates with the discharging bowl. A vibrator is arranged on a powder feeding box of the powder feeding device, when powder falls into the powder feeding box, the powder feeding box starts to vibrate under the action of the external vibrator, and vibration is stopped after powder receiving is completed. The problems that vibration is not generated when a traditional oval-opening discharging barrel and a powder feeding box are used for receiving powder, the dimensional tolerance in the height direction of a sintered blank is larger than or equal to 0.7 after the pressed blank is sintered, the contact face between the upper pressing head and the powder and the contact face between the lower pressing head and the powder are planes are solved, the material utilization rate and the blank qualification rate are greatly increased, and the machining load of subsequent procedures is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of R-Fe-B series permanent magnet materials. Specifically, it relates to a powder molding method and system for manufacturing rare earth sintered magnets. Background Art

[0002] Sintered Nd-Fe-B has excellent magnetic properties. As the main component, the rare earth element Nd is rich in resources and inexpensive, and is widely used in fields such as computers, machinery, and electronic products. Generally, powder metallurgy is often used to prepare sintered Nd-Fe-B. Its technological process includes composition design - batching - smelting - powder making - mixing - magnetic field orientation and pressing - isostatic pressing - sintering - magnetic detection - machining - surface coating treatment - quality inspection - magnetization - finished product. The purpose of orientation and pressing is to press the powder filled into the cavity in the mold into a green compact with a predetermined size, density, and magnetic field orientation under the action of a certain pressure and an external magnetic field, with the upper and lower punches moving synchronously. The filling state of the powder in the cavity not only affects the height direction size, density uniformity, appearance, and magnetic field orientation of the powder of the pressed green compact, but also affects the geometric size, surface state, magnetic properties, and density of the final blank.

[0003] During the pressing process, due to factors such as powder fluidity and relative movement of the powder, the density of the pressed green compact is uneven, which easily causes cracks in the green compact and poor dimensional accuracy, further leading to problems such as cracks in the sintered blank, poor dimensional accuracy, and appearance state, increasing the workload of the post-sintering processing procedures.

[0004] Therefore, how to improve the powder filling uniformity, green compact density uniformity, powder utilization rate during the molding process, and the qualified rate of the sintered blank has become an urgent problem to be solved currently. Summary of the Invention

[0005] To solve the above problems, the present invention provides a powder molding method and system for manufacturing rare earth sintered magnets, which can improve the powder filling uniformity, green compact density uniformity, powder utilization rate during the pressing process, and the qualified rate of the sintered blank.

[0006] Specifically, the present invention provides the following technical solutions:

[0007] A powder molding system for manufacturing rare earth sintered magnets, comprising a feeding device, a powder feeding device, and an extrusion molding device;

[0008] The feeding device includes a bin, a powder feeding chute, a vibrating feeder, a metering hopper, a feeding bowl, and a feeding tube. The powder feeding chute is located below the bin, and the vibrating feeder is located below the powder feeding chute; the metering hopper is located below the outlet end of the powder feeding chute, and the feeding bowl is located below the metering hopper; the feeding tube is located below the feeding bowl and is connected to the feeding bowl;

[0009] The powder feeding device includes a powder feeding box and a pressing plate; the powder feeding box is located directly below the blanking cylinder and on the pressing plate; a vibrator is provided on the powder feeding box. When the powder in the feeding device starts to fall into the powder feeding box through the blanking cylinder, the powder feeding box starts to vibrate under the action of the externally added vibrator, and the uniformity of the powder distribution in the powder feeding box is greatly improved through vibration.

[0010] In an embodiment of the present invention, the inlet of the blanking cylinder is flange-connected to the upper blanking bowl through a base, and a vibrator is also provided on the side wall of the blanking cylinder.

[0011] In an embodiment of the present invention, the blanking cylinder is a flat-mouth blanking cylinder, the main body of the flat-mouth blanking cylinder is an oval shape that is thick at the top and thin at the bottom, and the lower opening is a rectangle with different widths.

[0012] In an embodiment of the present invention, the width of the lower opening of the flat-mouth blanking cylinder is 7 mm to 17 mm.

[0013] In an embodiment of the present invention, the extrusion molding device includes a mold, and the mold has a hollow cavity inside, and two upper pressing heads and lower pressing heads with the same structure and symmetrically arranged are at both ends of the cavity.

[0014] In an embodiment of the present invention, both the upper pressing head and the lower pressing head include a convex arc surface in contact with the material, a valid surface of the pressing head, and a base of the pressing head. The convex arc surfaces of the upper pressing head and the lower pressing head are arranged opposite to each other, and when extrusion molding, the two arc surfaces squeeze towards the middle powder body.

[0015] Preferably, the structures of the upper pressing head and the lower pressing head are in an inverted "I" shape.

[0016] Preferably, the highest point of the convex arc surface is 0.3 mm.

[0017] In an embodiment of the present invention, the powder feeding device further includes a clip, and the clip is fixed on the powder feeding box and is directly in front of the powder feeding box.

[0018] In an embodiment of the present invention, the powder feeding box includes a powder feeding box body and a heightening cover located outside the powder feeding box body, and the heightening cover is used to prevent the powder from falling outside.

[0019] In an embodiment of the present invention, the bottom of the powder feeding box body has a powder feeding box opening, and the size of the powder feeding box opening in the orientation direction is smaller than the size of the cavity opening.

[0020] The present invention also provides a powder molding method for manufacturing rare earth sintered magnets, including the following steps:

[0021] S1. The powder in the silo falls into the powder feeding scoop under the action of gas pressure and gravity.

[0022] S2. The powder in the powder feeding scoop is sent to the weighing tipping bucket for weighing under the vibration of the vibrating feeder. When the weight reaches the set value, the weighing tipping bucket opens, and the powder falls into the flat-mouth feeding cylinder through the feeding bowl. The powder in the flat-mouth feeding cylinder falls into the powder feeding box of the powder feeding device under the vibration of the vibrator.

[0023] S3. After all the powder has fallen into the powder feeding box, the powder feeding box moves forward in contact with the pressing plate above the mold. There is a hollow mold cavity inside the mold. The powder feeding box vibrates and moves back and forth above the mold cavity, and the powder falls evenly under the action of gravity and fills the mold cavity.

[0024] S4. After the powder filling is completed, the upper punch and the lower punch move simultaneously in two directions in the mold cavity of the mold to extrude the powder into a shape. After the magnetic field orientation pressing is completed, isostatic pressing is carried out. The green compact obtained by isostatic pressing is put into a sintering furnace for sintering treatment to obtain a blank.

[0025] In an embodiment of the present invention, in step S2, when the powder feeding box is receiving powder, it is in a vibrating state and stops vibrating after receiving the powder.

[0026] In an embodiment of the present invention, in step S4, after the powder filling is completed, the upper punch and the lower punch press simultaneously, the applied pressure is 6 - 14 MPa, and the external magnetic field strength is 1.5 - 2.0 T to obtain a compact.

[0027] In an embodiment of the present invention, step S4 further includes placing the obtained compact in an isostatic press, setting the isostatic pressure value to 150 - 190 MPa, and maintaining the pressure for 6 - 15 s to obtain a green compact.

[0028] In an embodiment of the present invention, it further includes putting the formed green compact into a sintering furnace for sintering, the sintering temperature is 1000 - 1100 °C, the sintering time is 5 - 9 hours, and a blank is obtained after the cooling is completed.

[0029] Advantages of the present invention:

[0030] 1) The present invention provides a powder molding method and system. When the powder in the metering tipping bucket starts to fall into the powder feeding box through the blanking cylinder, the powder feeding box starts to vibrate under the action of an external vibrator. The neodymium iron boron powder falls into the powder feeding box more evenly through the blanking cylinder. The powder feeding box is in a vibrating state when receiving powder, and the vibration stops after the powder receiving is completed. By vibrating, the uniformity of the powder distribution in the powder feeding box before the powder feeding device feeds the powder into the mold cavity is greatly improved, and further the uniformity of the powder falling from the powder feeding box of the powder feeding device into the mold cavity is improved, thus solving the problem of uneven feeding distribution, greatly improving the powder utilization rate, and solving the problems such as poor dimensional accuracy of the sintered blank and low qualified rate of the blank. And when the powder filling ends, the vibration of the powder feeding box stops, and the pressing cycle will not increase due to improving the powder filling uniformity.

[0031] 2) A flat-mouth blanking cylinder is adopted in the feeding device of the present invention. Since the lower opening is a rectangle with different widths and matches the rectangular shape of the cavity of the powder feeding box, the powder will not accumulate in the center of the powder feeding box and is more evenly distributed in all directions in the cavity of the powder feeding box. Therefore, the powder distribution falling into the powder feeding box is more uniform. By adopting the flat-mouth blanking cylinder and the vibration of the powder feeding box when receiving powder, the uniformity of the powder distribution in the powder feeding box is greatly improved, and the uniformity of the powder filling in the cavity is improved. Compared with the existing powder filling system, the dimensional tolerance of the sintered blank in the height direction of the powder molding system optimized by the present invention is below 0.2 mm, greatly improving the dimensional accuracy of the sintered blank and reducing the production cost.

[0032] 3) The powder feeding box moves above the mold cavity, vibrates and moves back and forth to fill the powder. After the magnetic field orientation pressing is completed, isostatic pressing is carried out. The green compact obtained by isostatic pressing is put into a sintering furnace for sintering treatment. The dimensional tolerance of the sintered blank in the height direction is ≤0.2 mm. On the basis of not extending the production cycle and not significantly increasing the production cost, the present invention greatly improves the dimensional accuracy of the sintered blank. The dimensional tolerance of the blank in the height direction is below 0.2 mm. At the same time, the rejection rate of the pressed blank caused by cracks is greatly reduced, the dimensional accuracy and appearance qualified rate of the sintered blank are improved, and the production cost is reduced.

[0033] 4) The present invention solves the problem that the dimensional tolerance in the height direction of the pressed blank obtained by using a traditional oval opening blanking cylinder, a traditional powder feeding device without vibration when the powder feeding box receives powder, and a traditional process with a flat contact surface between the upper and lower punches and the neodymium iron boron powder is ≥0.7 after isostatic pressing and sintering. The effect is more significant for large-sized pressed blanks with a length greater than 150 mm, greatly improving the material utilization rate, increasing the qualified rate of the blank, and reducing the processing load of the subsequent processes. Description of the Drawings

[0034] Figure 1 is a schematic diagram of the overall composition of the powder molding system of the present invention;

[0035] Figure 2 Schematic structural diagram of the flat-mouth blanking cylinder of the present invention;

[0036] Figure 3 Schematic structural diagram of the powder feeding box in the powder feeding device of the present invention;

[0037] Figure 4 Schematic structural diagram of the upper and lower pressing heads of the present invention. Detailed implementation manners

[0038] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be emphasized that the specific embodiments described herein are only used to better illustrate the present invention and are partial embodiments of the present invention, rather than all embodiments, so they are not used to limit the present invention. In addition, the technical features involved in the embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] As Figure 1 shown, the present invention provides a powder molding system for manufacturing rare earth sintered magnets, including a feeding device, a powder feeding device and an extrusion molding device; the feeding device includes a material bin 1, a powder feeding scoop 2, a vibrating feeder 3, a metering tipping bucket 4, a blanking bowl 5 and a blanking cylinder. The powder feeding scoop 2 is located below the material bin 1, the vibrating feeder 3 is located below the powder feeding scoop 2, the metering tipping bucket 4 is located below the outlet end of the powder feeding scoop 2, and the blanking bowl 5 is located below the metering tipping bucket 4; the blanking cylinder is located below the blanking bowl 5 and is communicated with the blanking bowl 5.

[0040] Among them, the powder feeding device includes a powder feeding box 7 and a pressing plate 12. The powder feeding box 7 is located directly below the blanking cylinder 6 and on the pressing plate 12. A vibrator 14 is provided on the powder feeding box 7. When the powder in the feeding device starts to fall into the powder feeding box 7 through the blanking cylinder, the powder feeding box 7 starts to vibrate under the action of the externally added vibrator 14, and the uniformity of the powder distribution in the powder feeding box is greatly improved through vibration.

[0041] As Figure 2 shown, the inlet of the blanking cylinder is flange-connected to the upper blanking bowl through a base 13, and a vibrator 14 is also provided on the side wall of the blanking cylinder.

[0042] Preferably, the blanking cylinder is a flat-mouth blanking cylinder 6, the main body of which is an oval shape that is thick at the top and thin at the bottom, and the lower opening 15 is a rectangle with different widths.

[0043] When the powder from the traditional oval-opening blanking cylinder falls into the powder feeding box, it will cause more powder in the middle and less powder at both ends in the cavity of the powder feeding box, and the powder distribution is extremely uneven. After the powder feeding box moves above the mold and the powder falls into the mold cavity, the height tolerance between the middle and both ends of the sintered blank is about 0.5. Compared with the traditional blanking cylinder with an oval opening, the present invention adopts an optimized rectangular flat-mouth blanking cylinder with different opening widths. Since the lower opening is a rectangle with different widths, which matches the rectangular shape of the cavity of the powder feeding box, when the powder falls, the powder will not gather in the center of the powder feeding box, but is distributed in all directions in the cavity of the powder feeding box. In this way, the powder distribution in the powder feeding box is more uniform, and the height dimension tolerance of the blank obtained after sintering the powder falling into the mold cavity is below 0.3, improving the dimensional accuracy of the sintered blank.

[0044] Preferably, the width of the lower opening of the flat-mouth blanking cylinder 6 is 7 mm to 17 mm. Different widths can be set according to the weight of the compacted green body. For example, for a green body with a weight of less than 200 g, the width can be 7 mm; for a green body with a weight between 200 g and 350 g, the width can be 12 mm; for a green body with a weight between 351 g and 500 g, the width can be 17 mm.

[0045] As Figure 3 shown, the powder feeding box 7 includes a powder feeding box body 17 and a heightening cover 16 located outside the powder feeding box body 17. The heightening cover is provided to prevent the powder from falling outside. The bottom of the powder feeding box body 17 is provided with a powder feeding box opening 18, and the dimension of the powder feeding box opening 18 in the orientation direction is smaller than the dimension of the mold cavity opening.

[0046] Preferably, a vibrator 14 is further provided on the side wall of the powder feeding box 7.

[0047] As Figure 1 and Figure 4 shown, the extrusion molding device includes a mold 11. The mold 11 has a hollow mold cavity 10 inside. Two upper pressing heads and lower pressing heads 9 with the same structure and symmetrically arranged are at both ends of the mold cavity 10. The upper pressing head and the lower pressing head both include a convex arc surface 19 in contact with the material, a valid surface 20 of the pressing head, and a pressing head base 21. The convex arc surfaces 19 of the upper pressing head and the lower pressing head are arranged opposite to each other.

[0048] Preferably, the chord height of the convex arc surface 19 is 0.3 mm.

[0049] Preferably, the structures of the upper pressing head and the lower pressing head are in an inverted "I" shape.

[0050] After all the powder has fallen into the mold cavity, the upper punch and the lower punch move simultaneously for double-sided pressing and forming. Traditional double-sided pressing uses flat punches, and the surface of the punch in contact with the powder is a plane. When pressing large-sized compacts with a pressing length of more than 150 mm, due to the large size of the compact, it is extremely easy to cause extremely poor uniformity in the density distribution of the pressed compact. After sintering, the height tolerance of the blank is more than 0.7 mm, and the dimensional tolerance in the height direction generally exceeds the industry requirement of more than 0.5 mm. The dimensional accuracy of the sintered blank is poor, and subsequent processing is difficult. Moreover, during the pressing process of the compact, due to poor density uniformity, it is extremely easy for uneven internal stress release caused by uneven density, resulting in cracks on the surface of the compact, causing material waste and reducing the powder utilization rate.

[0051] The present invention uses a punch with a circular arc surface to improve the uniformity of the density distribution of the pressed compact after pressing, and greatly reduces the waste caused by cracks generated by uneven internal stress release. After sintering, the dimensional tolerance in the height direction of the blank is below 0.2 mm, far lower than the 0.5 mm tolerance required by the industry. It improves the appearance qualification rate and dimensional accuracy of the sintered blank, reduces the production cost, and reduces the processing load of the subsequent processes.

[0052] For example, for large-sized compacts with a pressing length of more than 150 mm, the present invention uses a punch with a circular arc surface with a chord height of 0.3 mm for double-sided pressing of large-sized green compacts. After sintering, the height tolerance of the blank is below 0.3 mm, improving the dimensional accuracy of the blank, greatly improving the powder utilization rate and the qualification rate of the sintered blank, and reducing the processing cost.

[0053] According to the present invention, the powder feeding device further includes a clip 8, and the clip 8 is fixed on the powder feeding box 7 and is located directly in front of the powder feeding box.

[0054] The present invention also provides a powder molding method for manufacturing rare earth sintered magnets, including the following steps:

[0055] S1, the powder in the storage bin 1 falls into the powder feeding scoop 2 under the action of gas pressure and gravity;

[0056] S2, the powder in the powder feeding scoop 2 is sent to the metering tipping bucket 4 for weighing under the vibration of the vibrating feeder 3. When the weight reaches the set value, the metering tipping bucket 4 opens, and the powder falls into the flat-mouth feeding tube 6 through the feeding bowl 5. The powder in the flat-mouth feeding tube 6 falls into the powder feeding box 7 of the powder feeding device under the vibration of the vibrator 14; when the powder falls into the powder feeding box 7 through the feeding tube 6, the vibrator is in a vibrating state when the powder feeding box 7 receives the powder.

[0057] S3. After all the powder has fallen into the powder feeding box 7, the powder feeding box 7 moves forward under the control of the lead screw of the electric telescopic component to fit against the pressing plate 12 and reaches above the mold 11. There is a hollow mold cavity 10 inside the mold 11. The powder feeding box 7 vibrates and moves back and forth above the mold cavity 10, and the powder falls evenly under the action of gravity and fills the mold cavity 10;

[0058] S4. After the powder filling is completed, the upper punch and the lower punch move in both directions simultaneously inside the mold cavity 10 to extrude the powder into a shape. After the magnetic field orientation pressing is completed, isostatic pressing is carried out. The green compact obtained by isostatic pressing is put into a sintering furnace for sintering treatment to obtain a blank, and then it is sent to the plane of the pressing plate 12 by the lower punch and clamped by the clamp 8 and sent out of the forming device.

[0059] Preferably, in step S2, when the powder feeding box 7 is receiving powder, it is in a vibrating state and stops vibrating after the powder receiving is completed. In the prior art, the powder feeding box itself does not vibrate when receiving powder, and only when the powder feeding box with an open bottom moves forward above the mold cavity and starts to drop powder does it move back and forth and vibrate to feed powder.

[0060] The forming method of the present invention improves the uniformity of the powder distribution in the powder feeding box. When the powder starts to fall into the powder feeding box 7 through the blanking tube, the powder feeding box 7 starts to vibrate under the action of an external vibrator, and the vibration is used to greatly improve the uniformity of the powder distribution in the powder feeding box 7. When the powder receiving ends, the vibration of the powder feeding box stops, and the pressing cycle will not increase due to improving the powder filling uniformity. Compared with the original powder filling system, the size tolerance of the blank sintered by the optimized powder filling system in the height direction is below 0.3 mm, greatly improving the dimensional accuracy of the sintered blank and reducing the production cost.

[0061] Preferably, in step S4, after the powder filling is completed, the upper punch and the lower punch press simultaneously, the applied pressure is 6 - 14 MPa, and the external magnetic field strength is 1.5 - 2.0 T to obtain a compact.

[0062] Preferably, step S4 further includes placing the obtained compact in an isostatic press, setting the isostatic pressure value to 150 - 190 MPa, and maintaining the pressure for 6 - 15 s to obtain a green compact.

[0063] According to the present invention, the powder forming method further includes putting the formed green compact into a sintering furnace for sintering. Preferably, the sintering temperature is 1000 - 1100 °C, the sintering time is 5 - 9 hours, and a blank is obtained after the cooling is completed.

[0064] Example 1

[0065] The neodymium iron boron powder in the silo falls into the powder feeding scoop under the action of gas pressure and gravity. The powder in the powder feeding scoop is sent into the metering tipping bucket under the vibration of the vibrating feeder. When the powder weight reaches the set value, the metering tipping bucket opens, and the powder falls into the flat-mouth feeding cylinder through the feeding bowl. The powder in the feeding cylinder of the feeding device falls into the powder feeding box of the powder feeding device under the vibration of the vibrator.

[0066] When all the neodymium iron boron powder has fallen into the powder feeding box through the flat-mouth feeding cylinder, the powder receiving is completed. The powder feeding box moves in contact with the pressing plate to the upper part of the die cavity and drops powder while vibrating. The contact surfaces of the upper and lower pressing heads with the material are flat. After the powder is filled in the die cavity, the upper and lower pressing heads of the magnetic field orientation are opened for two-way pressing, the two-way pressing pressure is 10 MPa, and the external magnetic field is about 2.0 T to obtain a green compact; the obtained green compact is placed in the isostatic press cavity, the pressure set value is 165 MPa, and the pressure is maintained for 12 s to obtain a green body; after isostatic pressing, the green body is placed in a sintering furnace for sintering, the sintering temperature is 1070 °C, and the sintering time is 6.5 h. After cooling, a blank is obtained.

[0067] Test the height tolerance in the height direction, and the data is shown in Table 1.

[0068] Example 2

[0069] The steps are basically the same as those in Example 1, except that: the neodymium iron boron powder falls into the powder feeding box through the oval opening feeding cylinder. The vibrator is in a vibrating state when the powder feeding box receives powder, and stops vibrating after the powder receiving is completed, and moves to the upper part of the die cavity and drops powder while vibrating. The contact surfaces of the upper and lower pressing heads with the material are flat. After the powder is filled in the die cavity, the upper and lower pressing heads of the magnetic field orientation are opened for two-way pressing, the two-way pressing pressure is 10 MPa, and the external magnetic field is about 2.0 T to obtain a green compact; the obtained green compact is placed in the isostatic press cavity, the pressure set value is 175 MPa, and the pressure is maintained for 9 s to obtain a green body; after isostatic pressing, the green body is placed in a sintering furnace for sintering, the sintering temperature is 1060 °C, and the sintering time is 7 h. After cooling, a blank is obtained. Test the height difference in the height direction, and the data is shown in Table 1.

[0070] Example 3

[0071] The steps are basically the same as those in Example 1, except that: the neodymium iron boron powder falls into the powder feeding box through the oval opening feeding cylinder. After the powder feeding box finishes receiving powder, it moves to the upper part of the die cavity and drops powder while vibrating. The contact surfaces of the upper and lower pressing heads with the material are arcs with a chord height of 0.3. After the powder is filled in the die cavity, the upper and lower pressing heads of the magnetic field orientation are opened for two-way pressing, the two-way pressing pressure is 10 MPa, and the external magnetic field is about 2.0 T to obtain a green compact; the obtained green compact is placed in the isostatic press cavity, the pressure set value is 175 MPa, and the pressure is maintained for 10 s to obtain a green body; after isostatic pressing, the green body is placed in a sintering furnace for sintering, the sintering temperature is 1060 °C, and the sintering time is 7 h. After cooling, a blank is obtained. Test the height tolerance in the height direction, and the data is shown in Table 1.

[0072] Example 4

[0073] The steps are basically the same as those in Example 1, except that: the neodymium iron boron powder falls into the powder feeding box more evenly through the flat-mouth feeding cylinder. The vibrator is in a vibrating state when the powder feeding box is receiving powder, stops vibrating after the powder receiving is completed, moves above the mold cavity and feeds powder while vibrating. The contact surfaces of the upper and lower punches with the material are arc surfaces with a chord height of 0.3. After the powder is filled in the mold cavity, the upper and lower punches with magnetic field orientation are opened for double-sided pressing, the double-sided pressing pressure is 10 MPa, and the external magnetic field is about 2.0 T to obtain a green compact; the obtained green compact is placed in the cavity of an isostatic press, the pressure setting value is 165 MPa, and the pressure is maintained for 11 s to obtain a green body; after isostatic pressing, the green body is placed in a sintering furnace for sintering, the sintering temperature is 1065 °C, and the sintering time is 6.5 h. After cooling, a blank is obtained. Measure the height difference in the height direction, and the data are shown in Table 1.

[0074] Example 5

[0075] The steps are basically the same as those in Example 1, except that: the neodymium iron boron powder falls into the powder feeding box more evenly through the flat-mouth feeding cylinder. The vibrator is in a vibrating state when the powder feeding box is receiving powder, stops vibrating after the powder receiving is completed, moves above the mold cavity and feeds powder while vibrating. The contact surfaces of the upper and lower punches with the material are flat surfaces. After the powder is filled in the mold cavity, the upper and lower punches with magnetic field orientation are opened for double-sided pressing, the double-sided pressing pressure is 10 MPa, and the external magnetic field is about 2.0 T to obtain a green compact; the obtained green compact is placed in the cavity of an isostatic press, the pressure setting value is 175 MPa, and the pressure is maintained for 9 s to obtain a green body; after isostatic pressing, the green body is placed in a sintering furnace for sintering, the sintering temperature is 1065 °C, and the sintering time is 6.5 h. After cooling, a blank is obtained. Measure the height difference in the height direction, and the data are shown in Table 1.

[0076] Comparative Example 1

[0077] The feeding cylinder has an oval opening. The neodymium iron boron powder falls into the powder feeding box through the oval-opening feeding cylinder. The powder feeding box is stationary and not in a vibrating state when receiving powder. After the powder feeding box finishes receiving powder, it moves above the mold cavity and feeds powder while vibrating. The contact surfaces of the upper and lower punches with the material are flat surfaces. After the powder is filled in the mold cavity, the upper and lower punches with magnetic field orientation are opened for double-sided pressing, the double-sided pressing pressure is 10 MPa, and the external magnetic field is about 2.0 T to obtain a green compact; the obtained green compact is placed in the cavity of an isostatic press, the pressure setting value is 175 MPa, and the pressure is maintained for 9 s to obtain a green body; after isostatic pressing, the green body is placed in a sintering furnace for sintering, the sintering temperature is 1060 °C, and the sintering time is 7 h. After cooling, a blank is obtained. Measure the height difference in the height direction, and the data are shown in Table 1.

[0078] Table 1

[0079]

[0080] As can be seen from Table 1, the height dimension tolerances of the sintered blanks in Examples 1-5 are all less than 0.3. In particular, in Example 4, the use of a flat-mouth blanking cylinder, upper and lower punches with a chord height of 0.3, and the vibration of the powder feeding box during powder receiving achieves the best effect. Even for large-sized compacted blanks with a length of more than 150 mm, the height range is within 0.2 mm, far lower than the industry requirement of a dimensional tolerance of 0.5 mm. In Comparative Example 1, a traditional flat punch, an oval-opening blanking cylinder, and no vibration during powder receiving by the powder feeding box were used, and its height dimension tolerance was 0.72, far exceeding the industry requirement.

[0081] The above are only the preferred application embodiments of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the technical principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A powder molding system for manufacturing rare earth sintered magnets, characterized in that, It includes a feeding device, a powder feeding device, and an extrusion forming device; The feeding device includes a silo (1), a powder feeding scoop (2), a vibrating feeder (3), a weighing hopper (4), a feeding bowl (5), and a feeding tube. The powder feeding scoop (2) is located below the silo (1), and the vibrating feeder (3) is located below the powder feeding scoop (2); the weighing hopper (4) is located below the outlet end of the powder feeding scoop (2), and the feeding bowl (5) is located below the weighing hopper (4); the feeding tube is located below the feeding bowl (5) and is connected to the feeding bowl (5); The powder feeding device includes a powder feeding box (7) and a pressing plate (12); the powder feeding box (7) is located directly below the feeding tube (6) and on the pressing plate (12); a vibrator (14) is provided on the powder feeding box (7). When the powder in the feeding device starts to fall into the powder feeding box (7) through the feeding tube, the powder feeding box (7) starts to vibrate under the action of the external vibrator (14), and the uniformity of the powder distribution in the powder feeding box is greatly improved through vibration.

2. The powder molding device according to claim 1, wherein, The inlet of the feeding tube is flange-connected to the upper feeding bowl (5) through a base (13), and a vibrator (14) is also provided on the side wall of the feeding tube.

3. The powder molding device according to claim 2, wherein The feeding tube is a flat-mouth feeding tube (6). The main body of the flat-mouth feeding tube (6) is an oval shape that is thicker at the top and thinner at the bottom, and the lower opening (15) is a rectangle with different widths.

4. The powder molding device according to claim 3, wherein The width of the lower opening of the flat-mouth feeding tube (6) is 7 mm to 17 mm.

5. The powder molding device according to claim 1, characterized in that, The extrusion forming device includes a mold (11). The mold (11) has a hollow cavity (10) inside. Two upper pressing heads (9) and lower pressing heads (9) with the same structure and symmetrically arranged are at both ends of the cavity (10); Preferably, both the upper pressing head and the lower pressing head include a convex arc surface (19) in contact with the material, a valid surface of the pressing head (20), and a base of the pressing head (21). The convex arc surfaces (19) of the upper pressing head and the lower pressing head are arranged oppositely, and when extrusion forming, the two arc surfaces squeeze towards the middle powder body; Preferably, the structures of the upper pressing head and the lower pressing head are in an inverted "I" shape; Preferably, the highest point of the convex arc surface (19) is 0.3 mm.

6. The powder molding device according to any one of claims 1 to 5, characterized in that The powder feeding device further includes a clip (8). The clip (8) is fixed on the powder feeding box (7) and is located directly in front of the powder feeding box (7).

7. The powder molding device according to claim 1, wherein The powder feeding box (7) includes a powder feeding box body (17) and a heightening cover (16) located outside the powder feeding box body (17). The heightening cover (16) is configured to prevent the powder from falling outside.

8. The powder molding device according to claim 1, characterized in that, The bottom of the powder feeding box body (17) has a powder feeding box opening (18), and the size of the powder feeding box opening (18) in the orientation direction is smaller than the size of the cavity opening.

9. A powder molding method for manufacturing a rare earth sintered magnet, characterized in that, It includes the following steps: S1. The powder in the silo (1) falls into the powder feeding scoop (2) under the action of gas pressure and gravity; S2. The powder in the powder feeding scoop (2) is sent into the weighing hopper (4) for weighing under the vibration of the vibrating feeder (3). When the weight reaches the set value, the weighing hopper (4) opens, and the powder falls into the flat-mouth feeding tube (6) through the feeding bowl (5). The powder in the flat-mouth feeding tube (6) falls into the powder feeding box (7) of the powder feeding device under the vibration of the vibrator (14); S3. After all the powder has fallen into the powder feeding box (7), the powder feeding box (7) moves forward to fit against the pressing plate (12) under the control of the lead screw of the subsequent electric telescopic component until it is above the mold (11). The mold (11) has a hollow cavity (10) inside. The powder feeding box (7) vibrates and moves back and forth above the cavity (10), and the powder falls under the action of gravity and is evenly filled into the cavity (10). S4. After the powder filling is completed, the upper punch and the lower punch (9) move in both directions simultaneously inside the cavity (10) to extrude the powder into a shape. After the magnetic field orientation pressing is completed, isostatic pressing is carried out. The green compact obtained by isostatic pressing is put into a sintering furnace for sintering treatment. The dimensional tolerance of the sintered blank in the height direction is ≤0.2 mm. Then it is sent to the plane of the pressing plate (12) by the lower punch, and then clamped by the clamp (8) and sent out of the forming device.

10. The powder molding method according to claim 9, characterized in that, In the step S2, when the powder feeding box (7) is receiving powder, it is in a vibrating state and stops vibrating after the powder receiving is completed. Preferably, in the step S4, after the powder filling is completed, the upper punch and the lower punch press simultaneously, the applied pressure is 6 - 14 MPa, and the external magnetic field strength is 1.5 - 2.0 T to obtain a compacted blank. Preferably, the step S4 further includes placing the obtained compacted blank in an isostatic press, setting the isostatic pressure value to 150 - 190 MPa, and maintaining the pressure for 6 - 15 s to obtain a green compact. Preferably, it further includes putting the formed green compact into a sintering furnace for sintering, the sintering temperature is 1000 - 1100 °C, the sintering time is 5 - 9 hours, and a blank is obtained after the cooling is completed.

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