JP5179133B2 - Sintered body manufacturing equipment - Google Patents

Description

  The present invention relates to an apparatus for manufacturing a sintered body, and more specifically, a high-performance permanent magnet is manufactured by preferentially evaporating rare earth elements from an Nd—Fe—B (neodymium iron boron) sintered magnet. The present invention relates to an apparatus for manufacturing a sintered body used for the purpose.

  Nd-Fe-B based sintered magnets (so-called neodymium magnets) can be manufactured at low cost by being made of a combination of iron and Nd and B elements that are inexpensive and abundant in resources and can be stably supplied. In addition, since it has high magnetic properties (the maximum energy product is about 10 times that of ferrite magnets), it is used in various products such as electronic equipment, and is also used in motors and generators for hybrid cars. is increasing.

  Nd-Fe-B magnets are mainly produced by powder metallurgy. In this method, Nd, Fe, and B are first blended at a predetermined composition ratio, and melted and cast to produce an alloy raw material. For example, it is roughly pulverized by, for example, a hydrogen pulverization step, and then finely pulverized by, for example, a jet mill pulverization step to obtain an alloy raw material powder. Next, the obtained alloy raw material powder is oriented in a magnetic field (magnetic field orientation), and compression molded in a state where a magnetic field is applied to obtain a compact. And this sintered compact is sintered on predetermined conditions, and a sintered magnet is produced (refer patent document 1).

Here, the R ₂ T ₁₄ B phase (main phase component) responsible for the magnetism of the Nd—Fe—B based sintered magnet is not generated directly from the liquid phase in the equilibrium state, and firstly γ iron is generated as the initial phase. It is formed by a reaction (peritectic reaction) between the liquid phase and its iron (γ iron transforms into α iron with a decrease in temperature). In this case, for example, even if the alloy raw material is melted and cast by the strip casting method (SC method), which is a rapid cooling method with a rapid solidification cooling rate, if the Nd content is 28.5% or less, the production of α iron It is known that it is difficult to suppress, and it is formed in a dendrite form in the alloy.

  If alpha iron is formed in a dendritic form in the alloy and is three-dimensionally connected, the pulverizability of the alloy in the subsequent pulverization step is significantly impaired. In other words, if the grindability is poor, the particles are once coarsely pulverized by the hydrogen pulverization process, and then the particle shapes suitable for producing sintered magnets with high magnetic properties are prepared even if the pulverization is attempted by the jet mill pulverization process. It is difficult to obtain fine powder particles. In addition, coarse grains (due to α-iron produced in a dendritic form) remain in the jet mill, and composition deviation tends to occur due to an increase in the amount of fine powder collected by the bag filter, making quality control difficult. There is a problem that there is.

On the other hand, if the Nd content is more than 28.5%, it is possible to produce an ingot that does not produce α iron, but the R-rich phase increases and the volume ratio of the R ₂ T ₁₄ B phase that plays a role in magnetism. Therefore, there arises a problem that it becomes difficult to manufacture an ultra-high performance magnet having a maximum energy product ((BH) max) and a large residual magnetic flux density (Br) exhibiting magnetic characteristics.

Therefore, after obtaining a sintered magnet by liquid phase sintering, heating the sintered magnet in a vacuum atmosphere at a temperature lower than the sintering temperature gives priority to rare earth elements having a high vapor pressure in the liquid phase component. It has been proposed by the present applicant to reduce the volume ratio of the liquid phase by evaporation (see Japanese Patent Application No. 2007-200845).
Japanese Unexamined Patent Application Publication No. 2004-6761 (for example, see the description of the prior art)

According to the above method, the rare earth element is efficiently evaporated to reduce the volume ratio of the R-rich phase, thereby increasing the volume ratio of the R ₂ T ₁₄ B phase (main phase component) that plays a role in magnetism. The maximum energy product ((BH) max) and the residual magnetic flux density (Br) exhibiting characteristics can be improved. However, such sintered magnets often contain rare earth elements such as dysprosim and terbium, which are scarce in resources and cannot be expected to provide a stable supply. In such a case, if the evaporated element is evacuated as it is by the vacuum evacuation means, not only valuable rare earth elements are wasted, but also the production cost is increased.

  Therefore, in view of the above points, an object of the present invention is to provide an apparatus for manufacturing a sintered body in which evaporated elements are efficiently recovered when improving product functions such as improvement of magnetic characteristics of a magnet. It is to provide.

In order to solve the above problems, a sintered body manufacturing apparatus of the present invention includes a vacuum chamber having a vacuum exhaust means, and a sintered body containing a primary sintered body obtained by liquid phase sintering in the vacuum chamber. A unit case and a heating unit that enables heating of the sintered body case, and the heating unit is operated to heat the primary sintered body at a temperature lower than the sintering temperature in a vacuum atmosphere. An apparatus for manufacturing a sintered body configured to preferentially evaporate an element having a high vapor pressure in a liquid phase component to reduce or eliminate the volume ratio of the liquid phase, and the evaporated element is attached the trapping means so as to provided the sintered body case is of box-shaped having an open one surface, the trap means, and the opening surface at a predetermined interval from the opening surface of the front Symbol sintered body It is composed of plate materials arranged to cover the whole And butterflies.

  According to the present invention, by preferentially evaporating an element having a high vapor pressure among the liquid phase components contributing to the promotion of sintering (evaporation process), the volume ratio of the liquid phase is reduced or eliminated, The characteristics can be exhibited. In this case, since the sintered body manufacturing apparatus of the present invention includes the trap means to which the evaporated element adheres, the evaporated element is sequentially attached to the trap means during the evaporation process. In addition, after the treatment, the element can be recovered only by peeling the element from the trap means using a known peeling method. As a result, when an expensive rare earth element such as dysprosim is evaporated from a neodymium iron boron based sintered magnet, the rare earth element may be recovered.

  On the other hand, the trap means is composed of a storage chamber provided in communication with an exhaust passage leading from the vacuum chamber to the vacuum exhaust means, and at least one plate material disposed in the storage chamber, and the drive means is connected to the plate material. And the plate member can be moved forward and backward with respect to the exhaust passage, the trap means may be allowed to enter the exhaust passage only when performing the evaporation process.

  In this case, in order to efficiently attach the evaporated elements to the plate material, the plate material is preferably arranged so as to be alternately arranged in two rows inclined with respect to the gas flow direction.

  Moreover, it is preferable that the trap means is freely movable back and forth in a range that becomes a viscous flow region in the exhaust passage.

  Furthermore, if a configuration in which a cooling means by circulating a refrigerant is incorporated in the trap means, the element evaporated by the temperature difference may be efficiently attached to the trap plate.

  In addition, in order to peel off the element from the trap unit using a known stripping method after the treatment, at least a portion of the trap unit to which the evaporated element is attached is formed of a material that does not react with the element.

Referring to FIG. 1, reference numeral 1 denotes a vacuum evaporation apparatus 1 which is a sintered body manufacturing apparatus according to the present invention. In particular, a neodymium iron boron-based sintered magnet (primary sintered body) S is placed in a vacuum atmosphere. It is suitable for producing an ultra-high performance magnet (permanent magnet) by performing a process (vacuum evaporation process) of preferentially evaporating rare earth elements from the sintered magnet S. The vacuum evaporation apparatus 1 has a vacuum chamber 12 that can be held at a reduced pressure to a predetermined pressure (for example, 10 ⁻⁵ Pa) through a vacuum exhausting means 11 such as a turbo molecular pump, a cryopump, or a diffusion pump. A cylindrical sintered body case 2 having an upper surface opened is installed in the vacuum chamber 12, and a space surrounded by the sintered body case 2 constitutes a processing chamber 20. The sintered body case 2 is made of a material that does not react with the rare earth element R when the rare earth element R such as Nd and Pr in the liquid phase, which is a liquid phase, is preferentially evaporated from the sintered magnet S by heating. ing.

  That is, if the evaporated rare earth element R adheres to the surface of the sintered body case 2 and forms a reaction product on the surface, it may be difficult to recover the rare earth element R. For this reason, the sintered body case 2 is manufactured from Mo or SUS from which the rare earth element R adhering to the surface is easily peeled, or Mo or the like is formed as a lining film on the surface of another heat insulating material. It is composed. In the processing chamber 20, for example, a plurality of Mo-shaped plate-like mounting portions 3 are arranged at predetermined intervals from the bottom surface to the upper surface of the sintered body case 2. Can be mounted side by side on the sintered magnet S formed by sintering into a predetermined shape such as a rectangular parallelepiped.

  The vacuum chamber 12 is provided with a heating unit 4 so as to surround the sintered body case 2. The heating means 4 is an electric heater (not shown) composed of a plurality of annular filaments arranged over the entire length so as to surround the periphery of the sintered body case 2, and each filament is a vacuum chamber. 12 is supported by a support piece (not shown) provided in the inside. In this case, the filament is also composed of Mo or the like that does not react with the rare earth element R. Then, by heating the sintered body case 2 by the heating means 4 under reduced pressure, the sintered magnet S placed on the processing chamber 20 and thus on the placement portion 3 indirectly through the sintered body case 2. Can be heated substantially evenly.

  A trap plate (trap means) 5 is detachably set above the sintered body case 2 so as to cover the opened upper surface. Similar to the sintered body case 2, the trap plate 5 is made of a material that does not react with the evaporated rare earth element R and that adheres to the surface easily peels off, for example, Mo. Further, although not shown, the trap plate 5 incorporates a cooling means by circulation of the refrigerant, and when the trapped plate 5 is cooled to a predetermined temperature, the evaporated rare earth element R reaches the trap plate 5. In addition, the rare earth element R efficiently adheres to and accumulates on the trap plate 5 due to the temperature difference.

  Considering the mean free path of the evaporated rare earth element R, the volume of the processing chamber 20 is set to the outside through the upper surface opening through repeated collision of the evaporated rare earth element R directly or on the inner wall of the sintered body case 2. The interval from the upper end of the sintered body case 2 to the trap plate 5 is set so that most of the rare earth element R discharged from the upper surface opening of the sintered body case once faces the trap plate 5. Is set to be guided. Thereby, in the evaporation processing apparatus 1 of the present embodiment, during the evaporation process, the evaporated elements can be sequentially attached to the trap plate 5, and after the trap plate 5 is detached after the process, By simply peeling the element from the trap plate 5 using a known peeling method, the element can be recovered.

  Next, the operation of the evaporation processing apparatus 1 of the present invention will be described by taking the production of an ultra-high performance permanent magnet as an example. First, the raw material alloy powder is produced as follows. That is, industrial pure iron, metallic neodymium, and low carbon ferroboron are blended and dissolved using a vacuum induction furnace so that Fe, Nd, and B have a predetermined composition ratio, and then quenched by a rapid cooling method such as a strip casting method. First, a raw material alloy of 05 mm to 0.5 mm is prepared. Alternatively, an alloy raw material having a thickness of about 5 to 10 mm may be produced by a centrifugal casting method, and Dy, Tb, Co, Cu, Nb, Zr, Al, Ga, or the like may be added during blending. . In this case, the total content of rare earth elements is set to more than 28.5%, and an ingot that does not produce α iron is obtained.

  Next, the produced raw material alloy is coarsely pulverized by a known hydrogen pulverization step, and then finely pulverized in a nitrogen gas atmosphere by a jet mill fine pulverization step to obtain an alloy raw material powder having an average particle size of 3 to 10 μm. Next, the raw material alloy powder is compression molded into a predetermined shape in a magnetic field using a known compression molding machine. Next, the molded body taken out from the compression molding machine is housed in a sintering furnace (not shown), sintered in a vacuum at a predetermined temperature (for example, 1050 ° C.) for a predetermined time (sintering process), and further, a predetermined temperature (500 ° C), a primary sintered body S is obtained.

Next, the produced primary sintered body S is placed on the placement portion 3 of the vacuum evaporator 1 and the trap plate 5 is set at a predetermined position (the state shown in FIG. 1), and then the vacuum evacuation means is used. The vacuum chamber 12 is depressurized until it reaches a predetermined pressure (for example, 10 ⁻⁵ Pa). After the inside of the vacuum chamber 12 reaches a predetermined pressure, the heating means 4 is operated to heat the processing chamber 20 and eventually the sintered magnet S, and after reaching the predetermined temperature, this state is maintained for a predetermined time (vacuum evaporation process). ).

In this case, the heating temperature of the processing chamber 20, and consequently the sintered magnet S, is set to 900 ° C. or higher and lower than the sintering temperature. When the temperature is lower than 900 ° C., the evaporation rate of the rare earth element R is slow, and when the sintering temperature is exceeded, abnormal grain growth occurs and the magnetic properties are greatly deteriorated. In addition, an open / close valve 11b whose opening degree can be adjusted is provided in an exhaust passage (exhaust pipe) 11a that connects the vacuum chamber 12 and the vacuum exhaust means 11, and the opening degree of the open / close valve 11b is adjusted so that the vacuum chamber 11, As a result, the pressure in the processing chamber 20 is set to a pressure of 10 ⁻³ Pa or less. When the pressure is higher than 10 ⁻³ Pa, the rare earth element R cannot be efficiently evaporated.

Thereby, due to the difference in vapor pressure at a constant temperature (for example, at 1000 ° C., the vapor pressure of Nd is 10 ⁻³ Pa, the vapor pressure of Fe is 10 ⁻⁵ Pa, and the vapor pressure of B is 10 ⁻¹³ Pa). Only the rare earth element R in the R-rich phase evaporates. At that time, most of the evaporated rare earth element R adheres to the cooled trap plate 5 and accumulates.

  When the evaporation process is performed in this way, the ratio of the Nd-rich phase is reduced, and the maximum energy product ((BH) max) and residual magnetic flux density (Br) showing magnetic characteristics can be improved, and a high-performance permanent magnet can be obtained. It is done. In this case, in order to obtain a high-performance permanent magnet, the rare earth element R content of the permanent magnet is less than 28.5 wt%, or the average concentration reduction of the rare earth element R is 0.5 wt% or more. Heat treatment.

  Then, after the vacuum evaporation process is performed, the operation of the heating unit 4 is temporarily stopped, the open / close valve 11b is fully opened and the vacuum chamber 12 is evacuated and cooled, and the temperature in the process chamber 20 is set to 500 ° C., for example. Lower until. Subsequently, the heating means 4 is actuated again, the temperature in the processing chamber 20 is set in the range of 550 ° C. to 650 ° C., and heat treatment for further improving the magnetic properties is performed. Finally, it is cooled to approximately room temperature, and the permanent magnet that is a sintered body is taken out. On the other hand, the trap plate 5 is also detached from the vacuum chamber 12 and recovered by separating the rare earth element R from the trap plate 5 using a known peeling method.

  In the present embodiment, the trap plate 5 disposed above the sintered body case 2 has been described. However, the present invention is not limited to this. For example, an exhaust passage leading from a vacuum chamber (not shown) to the vacuum exhaust means. You may arrange | position the trap means 6 to 11a (refer Fig.2 (a) and FIG.2 (b)). The trap means 6 has a storage chamber 62 that communicates with the exhaust passage 11 a via a gate valve 61. A storage frame 62 having a substantially rectangular cross section is stored in the storage chamber 62. A number of trap plates 64 are arranged. The support frame 63 is connected to a driving means 65 such as an air cylinder that allows the support frame 63 to move forward and backward with respect to the exhaust passage 11a when the gate valve 61 is open.

  Similarly to the above, the trap plate 64 is made of Mo, SUS, or the like that does not react with the rare earth element R, and is alternately arranged in two rows in an inclined manner with respect to the gas flow direction so as to block the gas flow in the exhaust passage 6. . Then, only when the vacuum chamber 12 is depressurized to a predetermined pressure and the heating means 4 is operated to heat the sintered magnet S, the trap means 6 enters the exhaust passage 11a and the evaporated rare earth element R is attached. To collect. In order to allow the evaporated element to adhere to the trap means 6 efficiently, the trap means 6 is provided in the exhaust passage 11b in a range that becomes a viscous flow region.

  By the way, even if the trap plate 5 is arranged above the sintered body case 2, the evaporated element may wrap around and adhere to the wall surface of the vacuum chamber. For this reason, a trap plate made of, for example, Mo may be disposed on the inner wall of the vacuum chamber 12 and may also be used as a shield for preventing contamination of the wall surface of the vacuum chamber 12.

  Furthermore, in the present embodiment, the manufacture of the sintered magnet S has been described as an example. However, the sintered body of the present invention can be used as long as it can improve the function of the sintered body by evaporating a specific substance from the sintered body. The manufacturing method can be applied. For example, a case of a sintered body obtained by mixing metal carbide powder into silicon carbide (SiC) powder as a sintering aid and performing liquid phase sintering at a temperature equal to or higher than the melting point of silicon after molding.

  In Example 1, a permanent magnet was obtained by subjecting the primary sintered body S to vacuum evaporation using the vacuum evaporator 1 shown in FIG. First, industrial pure iron, metallic neodymium, low carbon ferroboron, electrolytic cobalt, and pure copper are used as raw materials so that the composition is 29Nd-1B-0.1Cu-1Co-BalFe (wt%), and vacuum induction melting is performed. And a flaky ingot having a thickness of about 0.3 mm was obtained by a strip casting method. Next, it was coarsely pulverized once by a hydrogen pulverization step, and then finely pulverized by, for example, a jet mill pulverization step to obtain a raw material alloy powder.

  Next, a molded body was obtained using a transverse magnetic field compression molding apparatus having a known structure, and then sintered in a vacuum sintering furnace at a temperature of 1050 ° C. for 2 hours to obtain a primary sintered body S. . Then, the primary sintered body was processed into a shape of φ10 × 5 mm by wire cutting, and then finished to have a surface roughness of 10 μm or less, and then the surface was etched with dilute nitric acid.

Next, using the vacuum evaporation apparatus 1 shown in FIG. 1, after placing the 100 primary sintered bodies S on the mounting part 3 in the processing chamber 20, the pressure in the vacuum chamber 12 reaches 10 ⁻⁵ Pa. It was evacuated until. After the pressure in the vacuum chamber 12 reached a predetermined position, the heating unit 4 was activated to heat the processing chamber 20. In this case, the heating temperature was set to 975 ° C., and the opening of the opening / closing valve 11b was adjusted to set the pressure in the vacuum chamber 12 to 5 × 10 ⁻⁵ Pa. Next, heat treatment was performed to improve the coercive force. In this case, the heat treatment temperature was set to 530 ° C., and the treatment time was set to 60 minutes.

  FIG. 3 shows the amount of change in the Nd content (wt%) of the material to be treated when the above-described vacuum evaporation treatment is performed at different treatment times, and the average value of the magnetic properties after heat treatment (measured by a BH curve tracer) It is a table | surface which shows these relationships. According to this, as the evaporation process time becomes longer, the Nd content decreases, and when the vacuum evaporation process for 24 hours is performed, the Nd content can be reduced by about 2 wt%. In this case, the maximum energy product showing the magnetic characteristics is 55.1MG0e, the residual magnetic flux density is 14.88 kG, and it can be seen that the magnetic characteristics can be improved.

The figure which illustrates schematically the structure of the vacuum evaporation apparatus which is a manufacturing apparatus of the sintered compact of this invention. The figure explaining the trap means which concerns on another modification. The table | surface which shows the variation | change_quantity and magnetic characteristic of content of rare earth elements of the sintered magnet material produced in Example 1. FIG.

Explanation of symbols

1 Vacuum evaporator (sintered body manufacturing equipment)
DESCRIPTION OF SYMBOLS 11 Vacuum exhaust means 12 Vacuum evaporation apparatus 2 Sintered body case 20 Processing chamber 3 Placement part 4 Heating means 5 Trap plate (trap means: plate material)
S Primary sintered body (sintered magnet)
R Rare earth elements

Claims (3)

A vacuum chamber having a vacuum evacuation means, a sintered body case for storing a primary sintered body obtained by liquid phase sintering in the vacuum chamber, and a heating means for enabling heating of the sintered body case; And by heating the primary sintered body in a vacuum atmosphere at a temperature lower than the sintering temperature by operating the heating means, the element having a high vapor pressure in the liquid phase component is preferentially evaporated, An apparatus for manufacturing a sintered body configured to reduce or eliminate the volume ratio of the liquid phase, provided with trap means so that the evaporated element adheres,
The sintered body case is of box-shaped having an open one surface, the trap means, disposed from the opening surface of the front Symbol sintered body so as to cover the entire presence to and the opening surface by a predetermined distance An apparatus for producing a sintered body comprising a plate material. Wherein the trap means, apparatus for producing a sintered body according to claim 1, wherein the cooling means is incorporated by circulation of the refrigerant. 3. The apparatus for manufacturing a sintered body according to claim 1, wherein at least a portion to which the evaporated element of the trap means adheres is formed of a material that does not react with the element.

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