JPH08333166A - Mold for molding rare earth magnet powder and molding method - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To achieve excellent seizure resistance with R-Fe-B alloy powder, and to reduce the number of times lubricant is applied to a die hole.
To provide a die for molding rare earth magnet powder, which improves productivity and prevents deterioration of magnetic properties of the obtained rare earth magnet material. SOLUTION: The inner ring 12 made of Si ₃ N ₄ material is shrink-fitted to the mold body 11, or the intermediate ring 13 made of WC-Ni sintered cemented carbide is shrink-fitted to the mold body 11. After that, by further shrink-fitting the inner ring 12, the seizure resistance is significantly improved and the height L of the molded body is significantly improved as compared with the conventional configuration in which the inner ring 14 is made of a WC-Ni sintered cemented carbide. It is possible to efficiently obtain a long green compact having an L / D ratio of the diameter and the diameter or width D of more than 1.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to Sm-Co type and R-Fe-B type (R is L) used as a permanent magnet material.
at least one of a series and rare earth elements including Sc and Y
(More than one kind) related to a molding die used for producing a green compact by press molding a ferromagnetic alloy powder for a rare earth magnet, such as an inner ring made of Si ₃ N _{4 in the} die. By forming holes and preventing seizure of the molded product and mold with excellent seizure resistance, the number of times lubricant is applied to the mold holes is greatly reduced, and the deterioration of magnetic properties of the obtained rare earth magnet material is prevented. By using the molding die for molding the rare earth magnet powder thus prevented, the L / D ratio between the height L of the compact and the diameter or width D is 1.
The present invention relates to a molding die for rare earth magnet powder and a molding method for efficiently obtaining a long green compact exceeding 0.

[0002]

2. Description of the Related Art As shown in FIG. 1, for example, a manufacturing process of an R-Fe-B type anisotropic sintered magnet is performed by melting a raw material alloy to obtain a slab, and then squeezing the H ₂ storage property. The slab is naturally disintegrated by utilizing it, and further finely pulverized in an inert gas stream to obtain fine powder with a predetermined average particle size, which is filled in a molding die and oriented by applying a magnetic field. , Molding, sintering, and aging treatment.

In particular, in the magnetic field pressing process, R ₂ F produced by a hydrogenation crushing process or a crushing process using a jet mill is used.
supplying R-Fe-B alloy powder for the main phase of the e ₁₄ B phase to the mold holes of the forming die, it is to press-molding while applying a magnetic field to the after accordingly. At the time of press molding, generally, a means for applying a lubricant or the like to a mold hole of a molding die to prevent seizure between the molded product and the die is taken.

As shown in FIG. 2, the molding die has one or more die holes 2 having a required space shape for filling the alloy powder in the die 1. 2 is formed by fitting an inner mold ring 4 having a required space shape inside the main mold body 3, and the inner mold ring 4 is generally made of cemented carbide such as WC sintered alloy. It is used because it has excellent wear resistance and is non-magnetic.

The outer ring with respect to the inner ring 4, that is, the mold body 3 is generally made of austenitic stainless steel in the case of ordinary magnetic field molding. Further, when no magnetic field is applied or when a radial anisotropic ring is molded, a ferromagnetic material such as JIS-S45C is generally used for the outer ring.

Recently, as disclosed in Japanese Patent Laid-Open No. 5-186805, 87 wt% of Si ₃ N ₄ powder, 5 wt% of Y ₂ O ₃ powder, ₃ wt% of AlN powder, 5 wt% of Al ₂ O ₃ powder.
45% by volume of TiN powder to the powder adjusted to the composition
A mold material produced by using a so-called conductive sialon sintered material, which is manufactured by adding and sintering, is used for press molding of rare earth magnet powder.

This is because when a normal cemented carbide die is used at the time of magnetic field pressing, if a pulsed magnetic field with a large current is applied,
Eddy current is generated in the mold by electromagnetic induction by a pulsed magnetic field, and a reverse magnetic field that cancels the pulsed magnetic field is generated, weakening the magnetic field strength and used to improve the orientation of the magnet powder. is there. Even in an ordinary cemented carbide die, no eddy current is generated when the pulsed magnetic field is not used, and no significant decrease in orientation is observed.

[0008]

An example of industrial production of an R-Fe-B system permanent magnet material is as follows. The magnetic field press-molding time is usually about 1 minute per cycle, of which the mold lubrication time is The occupancy rate is very large, about 30% during the cycle. Therefore, it is necessary to reduce the number of lubrication times and improve the productivity. However, in the cemented carbide inner ring, if a lubricant is not applied every few strokes, seizure occurs and the molded product is defective.

As a method of reducing the number of lubrication, as shown in JP-A-4-214803 and JP-A-4-214804, stearic acid, zinc stearate, solid paraffin, etc. are previously added to the alloy powder as a lubricant. There is a method of molding after mixing. However, with this method, there is a risk of residual carbon even after the sintering process in the subsequent step, and the magnetic properties were not sufficient compared with the mold lubrication molded product.

Therefore, a material that is more resistant to seizure with R-Fe-B alloy powder than cemented carbide, is non-magnetic, and has no problem in working into a mold is required, and a magnetic field such as a bond magnet is required. Even in a molding die for producing an isotropic magnet that is not applied, the seizure resistance of the inner ring made of a cemented carbide is a problem, and a die material having good seizure resistance is required.

A rare earth magnet having an L / D ratio of the height L of the compact to the diameter or width D of more than 1.0 is press-formed (L
Is the length in the molding direction of the press, and D is the length in the direction perpendicular to the molding direction), the contact area between the press molded body and the cemented carbide die surface is large and friction is large. Even if die lubrication is applied, there are problems that seizure flaws occur, variations in green density become large, and abnormal deformation and cracking occur after sintering, so magnets with long L / D have not been produced.

The long rare earth magnet is assumed to be used as a long one depending on the application, or used as a thin and thick magnet by cutter cutting or wire saw cutting. In the latter case, it is considered that the longer the length, the better the cutting efficiency, the higher the productivity and the lower the cost. Therefore, the yield will be higher than the case of pressing and compacting one by one, and then sintering and grinding. To be

The present invention is based on Sm-Co, R-Fe-B.
In view of the above-mentioned problems in a molding die used for producing a green compact by press molding of a ferromagnetic alloy powder for a rare earth magnet such as a magnet system, in particular, seizure resistance with an R-Fe-B alloy powder It has excellent properties, reduces the number of times lubricant is applied to the mold holes, improves productivity, and prevents deterioration of the magnetic properties of the rare earth magnet material obtained.
An object of the present invention is to provide a molding die and a molding method for molding rare earth magnet powder, which can easily and efficiently obtain a long rare earth magnet having a D ratio of more than 1.0.

[0014]

DISCLOSURE OF THE INVENTION The inventors of the present invention aimed at a material having a better resistance to seizure with an R-Fe-B alloy powder than a conventional cemented carbide for a die, for the purpose of R-Fe-B. As a result of various studies on sliding wear between the system-based sintered magnet and various non-magnetic materials, it is difficult to say that the sialon sintered body has good seizure resistance with the R—Fe—B system alloy powder, but Si ₃ N ₄ It was found that the best seizure resistance can be obtained by using ceramics containing as a main component.

Furthermore, the inventors actually pressed one-side press-pressing a long green compact having L / D> 1 with a mold using the above-mentioned ceramics in a contact portion with the rare earth magnet alloy powder. , Sintered product with no seizure and small sinter deformation can be obtained in the subsequent sintering process, and by double press molding, sinter with less sinter deformation can be obtained. Si ₃ N ₄ through the intermediate ring made of cemented carbide in the mold
The present invention has been completed by finding that a die having a die hole formed by an inner ring made of can be used to form a long green compact having a larger L / D without seizure.

That is, according to the present invention, in the molding die for filling and molding the rare earth magnet alloy powder, the portion in contact with the rare earth magnet alloy powder is composed of 90 wt% or more of Si ₃ N ₄ and the sintering aid. Is a mold for molding rare earth magnet powder.

Further, according to the present invention, in the above-mentioned molding die, a molding die of rare earth magnet powder in which a molding hole is formed by an inner ring made of Si ₃ N _{4 in} the molding die, A mold for molding rare earth magnet powder in which a mold hole is formed by an inner ring made of Si ₃ N ₄ through an intermediate ring made of cemented carbide is also proposed in the mold.

Further, according to the present invention, a material comprising 90 wt% or more of Si ₃ N ₄ and a sintering aid is used as the material of the portion of the mold which is in contact with the powder to be molded, and the height L and the diameter of the obtained molded body or After the alloy powder for rare earth magnets is filled in the molding die in which the dimension ratio of the molding die is set so that the L / D ratio with the width D exceeds 1.0, one-sided pressing or double-pressing is applied. This is a method for molding a rare earth magnet powder, which is obtained by pressing with a punch to obtain a long green compact having an L / D ratio of more than 1.0.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION As the rare earth magnet powder to which the present invention is applied, any known Sm-Co-based, R-Fe-B-based, or other rare-earth magnet powder can be used. The molding die is particularly excellent in seizure resistance to the R-Fe-B magnet powder, and the following composition is preferable as the R-Fe-B magnet powder. That is, R-
As a Fe-B magnet powder composition, R8 at% to 30 at
% (R is at least one of La series and rare earth elements including Sc and Y), B2 at% to 28 at%, Fe4
2 at% to 90 at% as a main component and R ₂ F as a main phase
e ₁₄ B compound, other unavoidable impurities in industrial production, 50% or less of Fe partially replaced with Co, and usually 10 at% or less in total amount, depending on the additive element. The total amount is 5 at% or less and 3 at% or less is appropriately selected, and Ti, Ni, V, Nb, Ta, Cr, M is selected.
o, W, Mn, Al, Sb, Ge, Sn, Zr, Bi,
Hf, Cu, Si, S, C, Ca, Mg, P, H, L
i, Na, K, Be, Sr, Br, Ag, Zn, N,
Some include one or more of F, Se, Te, and Pb added.

For example, in the case of a powder for a sintered magnet, the R-Fe-B magnet powder was rapidly solidified by ingot or strip casting produced by high frequency melting, arc melting, etc., as shown in FIG. The flakes are roughly crushed by a jaw crusher, and then hydrogenated and jet milled to obtain finely pulverized powder having an average particle size of 1 to 10 μm.

In the molding die according to the present invention, the material of the inner ring of the die, that is, the portion in contact with the rare earth magnet powder is 90 w.
It is characterized by using t ₃ or more of Si ₃ N ₄ (silicon nitride) and a sintering aid. Here, Si ₃ N ₄ is not particularly limited, but it is manufactured by an ordinary powder metallurgy method and has a density of 3.
1 to 3.3 g / cm ³ , Young's modulus of about 30.000 kgf
/ Mm ² , bending strength of 50 to 80 kgf / mm ² , and Vickers hardness (Hv) of about 1200 to 1600 are preferably used. Further, as a sintering aid, Y ₂ O ₃ ,
It means Al ₂ O ₃ , MgO.Al ₂ O ₃ , AlN, etc., and may be contained in a total amount of 10 wt% or less.

[0022] In the mold of the present invention, to form the mold hole at an inner ring made of Si ₃ N _4, it is necessary to fix the inner ring of Si ₃ N ₄ in the mold body, sticking As a method, besides shrink-fitting, a method of mechanically joining to a non-magnetic iron-based alloy mold part, brazing, joining using an adhesive, or the like can be adopted.

When shrink-fitting to the mold body, it is necessary to mold from a Si ₃ N ₄ material that has been fired to a predetermined size into a predetermined inner ring outer diameter dimension determined by considering the shrinkage allowance rate. There is. It should be noted that the shrinkage allowance rate is obtained by the following formula, but it was found from experiments by the inventor that about 0.1 to 0.20 (%) is preferable. Shrink fit rate = (Inner ring outer diameter-Outer ring inner diameter) /
(Inner ring outer diameter) x 100 (%)

Next, an example of a method of manufacturing a die in which a die hole is formed by an inner ring made of Si ₃ N ₄ in a die body made of a non-magnetic iron alloy according to the present invention will be described. The manufacturing method is as follows. First, by grinding a Si ₃ N ₄ material made to a predetermined size into an outer diameter of the inner ring in consideration of the shrink fit margin ratio described above, in the case of a single-fitting die, The Si ₃ N ₄ inner ring is shrink-fitted directly to the mold body made of a non-magnetic iron-based alloy, or in the case of a double-fitting mold, the intermediate ring is attached to the mold body. For example, for example, after shrink-fitting a cemented carbide (WC-Ni), further shrink-fitting the inner ring of Si ₃ N ₄ , finishing the inner surface of the inner ring to the required hole size, and lapping (Ra <0. 0.1 μm)
By performing the above, the mold can be completed.

In the mold of the present invention, when the mold material is, for example, an isotropic magnet such as an isotropic bond magnet or a radial anisotropic ring magnet, the mold body is made of, for example, Ferromagnetic iron-based materials such as JIS-S45C, WC-Co type cemented carbide can be used for the intermediate ring. When manufacturing anisotropic magnets, austenite stainless steel is used for the die body and intermediate ring is used for the intermediate ring. Is non-magnetic WC-N
An i-based cemented carbide can be used.

In the double-fitting die, since the intermediate ring is made of cemented carbide having a high Young's modulus, the deformation of the inner ring is small, and the frictional force when the molded product is taken out of the die is small. Compared with the heavy-fitting die, it has the effect that seizure is less likely to occur. Therefore, it is optimal for obtaining a long green compact having a large L / D ratio.

The mold according to the present invention is particularly suitable for R-Fe-
A die for forming an anisotropic bonded magnet, which has a seizure resistance effect, is used as a die for forming a B-based alloy powder.
Also it exhibits the preferred operational effects as injection mold R ₂ Fe ₁₄ B magnet powder shown in 77029. Moreover, since the mold material of the present invention is non-conductive, even when a pulsed magnetic field is applied during molding, eddy current is not generated during use,
This has the effect of improving the orientation.

In the present invention, the material of the inner ring of the mold for obtaining the molded product of L / D> 1 is 90 wt% or more of S
If the amount of i ₃ N ₄ and the sintering aid is less than 90 wt%, it is easy to seize even if the mold is lubricated as in the case of the conventional mold, and the dispersion of the green density becomes large, so that a good sintered body can be obtained. This is because you cannot get

Press molding methods include one-side pressing, withdrawal, and both-side pressing methods. The withdrawal molding method is a method in which the die moves downward in the pressing direction due to the friction with the compact as the upper punch is pressed, and the friction between the die and the compact is reduced. In the molding, under the condition of parallel magnetic field (the pressing direction and the magnetic field direction are the same), the attraction force by the magnetic field does not cause the withdrawal molding but the normal one-sided pressing.

As a press-molding method for producing a long green compact having L / D> 1, one-sided pressing and both-sided pressing methods are preferable. In the one-sided pressing method, a press device is simple and can be manufactured at low cost.
In the double-press molding, since the upper and lower punches are respectively molded, the green densities in the vicinity of the upper and lower surfaces are equal to each other, variation in green density and sintering deformation after sintering are drastically reduced, and a high quality sintered body is obtained.

Further, 90% by weight or more of S according to the present invention
If a long green compact is formed by double-press molding with die lubrication and / or internal lubrication using a circular ring mold made of i ₃ N ₄ and a sintering aid, the green density variation of the green compact becomes more A compact compact without seizure is obtained, and a sintered compact with a small sintering deformation is inevitably obtained. The internal lubricant is a boric acid ester or a fatty acid ester of 0.1 to 0.3 w.
It is advisable to mix t%. It has an effect of improving the seizure property as well as the orientation property. Since Si ₃ N ₄ has excellent seizure resistance with the rare earth alloy powder, an appropriate amount of internal lubricant should be mixed to
By performing press molding, die lubrication is completely unnecessary and the press cycle time can be further shortened.

[0032]

【Example】

Example 1 After smelting a raw material alloy to obtain a slab, the slab is naturally disintegrated by utilizing the H ₂ occlusion property, and further finely pulverized in an inert gas stream to obtain a predetermined average particle size. Obtaining a fine powder, filling it in a molding die and orienting by applying a magnetic field, then molding,
A sintered magnet having an outer diameter of 25 N, an inner diameter of 22 and a height of 7 (mm), which was created by a process of sintering and aging treatment and which was not subjected to rust-prevention treatment, of 15Nd-8B-77Fe (at%) component.
Outer diameter 25 x height 15 made of various mold materials shown in Table 1
A ring-on-disc test with a disc of (mm) was conducted, and the result of evaluating the seizure resistance as the seizure condition is shown in Table 1.

In the ring-on-disc test, as shown in FIG. 3, a fatty acid ester was applied only once on a disc D having an outer diameter of 25 and a height of 15 (mm), and then a sintered magnet M was placed on the disc D to give a weight of 20 kg. It was carried out by a method of applying a load and rotating at a sliding speed of 0.8 m / sec for 30 minutes. As is clear from the results in Table 1, Si ₃ N ₄ of the present invention is Nd-Fe-B.
Although it has the best seizure resistance to magnets, the sialon sintered body and the conductive sialon sintered body of JP-A-5-186805 have poor seizure resistance with Nd-Fe-B magnets. I know that

[0034]

[Table 1]

Example 2 15Nd-8B-77Fe (at
%) Component, a magnet powder having an FSS particle size of 3.5 μm, which is compounded under the condition of 3 wt% of an epoxy resin, is used for a bond magnet powder, using the mold of the present invention shown in FIG. 4B and the comparative mold shown in FIG. 4C. No mold lubrication, molding pressure 6 ton / c
When continuous molding was performed under the conditions of m ² , non-magnetic field, and molded product size φ25 × 15t (mm), the comparative mold produced a flaw at the 100th stroke, whereas the mold according to the present invention produced 1000 strokes. There was no flaw. In addition,
The mold of the present invention has the same 92 wt% Si as in the first and second embodiments.
₃ N ₄ and sintering aid (4 wt% Y ₂ O ₃ + 4 wt% MgO · A
It is a ceramic composed of 1 ₂ O ₃ ).

Example 3 15Nd-8B-77Fe (at
%) Component of FSS particle size 3.5 μm magnet powder using the two types of molds of the present invention shown in FIGS. 4A and 4B described later and the comparative cemented carbide mold shown in FIG. 4C under the molding conditions shown in Table 2. , Φ2
5 × 15 l, 50 l, and 75 l (mm) molded products were continuously molded. The mold of the present invention is the same as that of the first embodiment.
wt% Si ₃ N ₄ and sintering aid (4 wt% Y ₂ O ₃ +4 wt
% MgO.Al ₂ O ₃ ).

The results of the molding test are shown in Table 3. In the cemented carbide mold, seizure flaws did not occur up to 300 strokes in the 15 l product (L / D = 0.6), but in the 50 l product (L / D = 2). ．
0), 75l product (L / D = 3.0), seizure flaws occur within 10 strokes, and it is found that it is difficult to mold a long green compact with a cemented carbide die. On the other hand, with the circular ring Si ₃ N ₄ die, even with a die that does not use an intermediate ring (Fig. 4A), a product with L / D> 2 or more can be formed for 1000 strokes or more without seizure flaws. The die using carbide for the ring (FIG. 4B) showed even better seizure resistance.

All of the molds have a bottom surface outer diameter of 160 mm, a top surface outer diameter of 140 mm, a height of 60 mm, and a mold hole inner diameter of 2 mm.
It is 5 mm. The mold 10A shown in FIG. 4A is a mold body 1
1 is austenitic stainless steel, inner ring 12 is Si ₃
The mold 10B shown in FIG. 4B is made of N ₄ material, and the mold body 1
1 is austenitic stainless steel, W in the intermediate ring 13
Si is used for the inner ring 12 by using a C-Ni sintered cemented carbide.
₃ N ₄ material is used. Comparative mold 1 shown in FIG. 4C
In 0C, the die body 11 is austenitic stainless steel and the inner ring 14 is made of WC-Ni sintered cemented carbide.

[0039]

[Table 2]

[0040]

[Table 3]

Example 4 Using the powder of Example 3, using a mold shown in FIG. 4B, a molding having φ25 × 75 l of molding conditions (excluding the molding method) shown in Table 2 was molded by an electric press. At this time, the molding method was double press molding. Let the sample be D. Let S be the φ25 × 75 l compact formed in the same die of FIG. 4B by the one-sided pressing of Example 3. After sintering the D and S samples in a vacuum at 1075 ° C. for 4 hours, the amount of change in the outer diameter of the sintered body in the vertical direction was measured.
Although there was a difference in m, the double-pressed product had a small center diameter of about 200 μm, and only half the sintering strain of the S product was produced. From this, the advantage of double-press molding became clear.

[0042]

As is apparent from the examples, by press-molding R-Fe-B magnet powder using the mold according to the present invention, the number of mold lubrications can be reduced, so that the molding cycle time can be shortened. Further, the productivity is dramatically improved, it is extremely advantageous in industrial production, and it is also extremely useful for reducing the manufacturing cost of magnets. In particular, long molded products that could not be mass-produced in the past can be manufactured without seizure, which is extremely advantageous in industrial production. In addition, if this long product is sintered and then cut to make a thin product, the material yield is improved and the productivity is good, compared to the conventional method of forming thin products by molding one piece at a time. It also contributes to the reduction of magnet production costs.

A mold in which a mold hole is formed in the mold body by an inner ring made of Si ₃ N _{4 according} to the present invention has excellent seizure resistance to prevent seizure between the molded product and the mold. The number of times lubricant is applied to the holes can be significantly reduced, and the deterioration of the magnetic properties of the rare earth magnet material obtained can be prevented.
The double-fitting die, in which the inner ring made of Si ₃ N ₄ is used for the middle of the die main body using cemented carbide with high Young's modulus,
Further, when the molded product is taken out of the mold, the frictional force is small and the seizure resistance is excellent.

The mold according to the present invention has a preferable effect not only for sintered magnets and bonded magnets but also as a mold for injection molding. Furthermore, the mold material of the present invention is non-conductive. Even when a pulsed magnetic field is applied during molding, there is an effect that orientation is improved without generating an eddy current.

[Brief description of drawings]

FIG. 1 is a chart showing an example of a manufacturing process of an R—Fe—B anisotropic sintered magnet.

FIG. 2 is a perspective explanatory view showing a mold for molding rare earth magnet powder, where A is a plurality of mold holes and B is a single mold hole.

FIG. 3 is an explanatory diagram showing a ring-on-disk test method.

FIG. 4 is a longitudinal sectional view showing a molding die, where A is Si ₃ N ₄
The structure of the present invention having an inner ring consisting of B is the structure of the present invention having an intermediate ring, and C is the conventional structure.

[Explanation of symbols]

 1 Mold 2 Mold Hole 3 Mold Body 4 Inner Ring 10A, 10B, 10C Mold 11 Mold Body 12 Inner Ring 13 Intermediate Ring 14 Inner Ring D Disk M Sintered Magnet

Claims (4)

[Claims] 1. A molding die for filling and molding a rare earth magnet alloy powder, wherein a material of a portion in contact with the rare earth magnet alloy powder is 90 wt% or more of Si ₃ N ₄ and a rare earth magnet powder. Mold for. 2. The S according to claim 1, wherein S is placed in the molding die.
A die for molding rare earth magnet powder in which a die hole is formed by an inner ring made of i ₃ N ₄ . 3. The molding of rare earth magnet powder according to claim 1, wherein a mold hole is formed in an inner ring made of Si ₃ N ₄ through an intermediate ring made of cemented carbide in a forming die. Mold for. 4. A material comprising 90 wt% or more of Si ₃ N ₄ and a sintering aid is used as a material of a portion of the die which is in contact with the powder to be molded, and the height L and the diameter or width D of the resulting compact are obtained. L
After the alloy powder for rare earth magnets is filled in the molding die in which the dimension ratio of the molding die is set so that the / D ratio exceeds 1.0, pressing by one-sided pressing or double-pressing punch is performed. L /
A method for molding a rare earth magnet powder, which obtains a long green compact having a D ratio exceeding 1.0.