JPH09104902A - Powder compacting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the friction among powder particles or between a mold and powder particles at a low level or below and to improve the properties of a sintered product by forming a coating film consisting of a solid lubricant on the surface of at least any one of the powder and the mold inner wall and, thereafter, compacting the powder. SOLUTION: In powder metallurgy, a coating film consisting of a lubricant is formed on the surface of at least any one of the powder and the mold inner wall before filling a mold with a powder, by heating a solid lubricant consisting of a fatty acid or metallic soap to a temp. at or above the melting point of the lubricant to melt it and, thereafter, atomizing and spraying the melted lubricant. At this time, the atomized lubricant is allowed to impact on the surface of the powder or mold inner wall to stick it to the surface and, concurrently, the lubricant is cooled to instantaneously form a uniform lubricant coating film without requiring any drying time. By using this method, since the rotation of each of magnetic particles in the compacting process in a magnetic field becomes smooth, an anisotropic rare earth sintered magnet having a high degree of orientation, and accordingly, a high residual flux density can be manufactured. Further, the content of oxygen or hydrogen in the sintered magnet can be controlled at a low level or below to improve the coercive force of the magnet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder molding method, and more particularly to a die lubrication method at the time of molding in the molding step of powder metallurgy.

[0002]

BACKGROUND OF THE INVENTION The present invention relates to a powder metallurgical molding process. Powder metallurgy is a method of filling powders made of metal or ceramics such as oxides, carbides, and nitrides into a mold and applying the powder. This is a method in which pressure molding is performed, and the obtained molded body is heated and sintered. Products manufactured by powder metallurgy include magnetic materials, cemented carbides, mechanical parts, oil-impregnated bearing parts, heat-resistant materials, contact materials, etc., and in recent years the development of fields such as the automobile industry, mechanical industry, electronic and electrical industry, etc. Due to
The products produced by these powder metallurgy methods are becoming increasingly important.

A lubricant is often used in the powder metallurgical molding process, and the use of the lubricant in the molding process reduces the friction between particles and the friction between the powder and the inner wall of the mold. Therefore, the fluidity of the powder is improved, and the agglomeration of the powder is prevented. As a result, it is possible to obtain a molded product having a uniform molded product density and excellent strength, and further, it is possible to reduce the wear of the mold and to reduce the take-out pressure when taking out the molded product. Also in, it is possible to obtain a great effect.

Lubricants used in this molding process include metal soaps such as stearic acid, zinc stearate, lead stearate and calcium stearate, stearic acid bisamide, paraffin wax, graphite and molybdenum disulfide. Whether a different lubricant is used is determined by the composition and particle size of the powder, molding conditions, sintering conditions, finish of the product, and the like. These lubricants are generally used in the form of granules, mixed with powder before the molding step, and supplied to the molding step. The amount of lubricant added and the particle size have a great influence on the properties and finish of the molded product and the sintered product, so they are carefully selected. If the amount of lubricant added is too large, the lubricant components may remain in the product after sintering is complete, and the desired product characteristics may not be obtained. .

In particular, in the process of molding a sintered permanent magnet, by applying an external magnetic field, the easy magnetization direction of the magnetic particles is aligned in the direction of the external magnetic field to form an anisotropic sintered magnet having a high residual magnetic flux density. However, in this case, in order to smoothly rotate each magnetic particle by applying an external magnetic field, it is necessary to suppress the frictional force acting between the particles. After the magnetic particles are oriented by the external magnetic field, the compression force of molding disturbs the orientation due to the frictional force, so it is necessary to suppress the friction between the magnetic particles and the inner wall of the mold. Plays a big role.

[0006]

However, in the powder metallurgy method, a lubricant is mixed with a powder, but since this lubricant is generally used in the form of particles, even if it is mixed sufficiently uniformly. Even if it does, the lubricant should not be able to act on the entire surface of the powder, so the effect of the lubricant will be localized and the effect will be limited. However, there is a limit to the amount that can be added.

Therefore, for this, a method of dissolving the lubricant in an appropriate solvent and mixing the solvent with the powder, or immersing the powder in the solvent, or spraying the solvent to the powder is also available. However, in this method, a large amount of oxygen and carbon as solvent components may remain in the sintered product to deteriorate the characteristics of the product, and in the case of a metal product, such a situation may occur. Many. In the production of anisotropic rare earth sintered magnets, the presence of oxygen and carbon may be fatal because rare earth elements that easily react with oxygen and carbon are included as constituent components.

[0008]

The present invention relates to a powder molding method in the powder metallurgy method which solves the above disadvantages and problems, and in the molding step of the powder metallurgy method, the powder is formed into a mold. Before filling, at least one of the powder and the mold inner wall is heated and melted with a solid lubricant consisting of fatty acid or metal soap above its melting point, and then sprayed to the surface of the powder and the mold inner wall. The method is characterized in that after forming a film of a lubricant on, molding is performed. This will be described in more detail below.

As described above, the powder molding method according to the present invention involves melting and spraying a solid lubricant consisting of fatty acid or metallic soap on the inner wall of the powder or mold in the molding step of powder metallurgy. According to the method, a lubricious coating can be formed uniformly on the entire surface of the powder or the inner surface of the die, so that the friction between the powder particles and the friction between the powder and the die are not locally but Therefore, the characteristics of the molded body, the characteristics of the sintered product are improved, the workability thereof is improved, and the step of mixing the lubricant can be omitted, so that the steps can be simplified, In particular, in the production of a sintered magnet, the orientation due to an external magnetic field is improved and the disorder of the orientation due to a mold can be suppressed, which gives an advantage that an anisotropic sintered magnet with high magnetic properties can be produced. To be

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The solid lubricant composed of fatty acid or metallic soap used in the powder molding method of the present invention has a chemical formula of CH ₃ (CH ₂ ) _n COOH or CH ₃ (CH ₂ ) _n COOM (M is Pb. , M
1 of n, Al, Cu, Zn, Cr, Ca, Li
The typical substances are stearic acid, zinc stearate, calcium stearate and the like. Since their melting points are as low as around 100 ° C, they can be melted and sprayed with a simple device.In the molten state, the viscosity is sufficient for spraying, so spraying can be done using a lubricant tank and a spray nozzle that retain heat. it can.
If the amount of solid lubricant sprayed is less than 0.001% by weight of the powder, the lubrication performance will be insufficient, and if it exceeds 2% by weight, a large amount of carbon will remain after sintering and the magnetic properties will deteriorate.
2% by weight is good.

Further, the lubricant sprayed here collides with the powder surface and the inner wall of the mold and adheres to the powder, and at the same time, it is cooled, and a uniform lubricating film is instantaneously formed, so that no drying time is required. By selecting the shape of the nozzle, the shape and thickness of this lubricating coating can be made arbitrary.
However, when spraying a lubricant onto powder, it is preferable to spray the powder while shaking the powder so that the lubricant adheres to the entire powder. When the process is carried out in an inert gas, the spray of the lubricant should also be carried out in an inert gas, since the product dislikes oxidation.

In the powder molding method according to the present invention, the surface of the powder and the surface of the inner wall of the mold can be entirely coated with a lubricant film without using a solvent. This is an effective method for manufacturing a magnet. That is, according to the method of the present invention, since the rotation of the magnetic particles in the molding process in the magnetic field becomes smooth, the degree of orientation is high, and thus it is possible to manufacture an anisotropic rare earth sintered magnet having a large residual magnetic flux density, Furthermore, since the amounts of oxygen and carbon in the sintered magnet can be suppressed, its coercive force is improved.

The anisotropic rare earth magnets include R-Co type and R-Fe-B type.
System (R is at least one of rare earth elements including Y)
and so on. RCo system rare earth magnet RCo ₅ system, there are such R ₂ Co ₁₇ series, what is put into practical use is mostly R ₂ Co ₁₇ series, 20 to 28% of R in normal weight percentage , 5-30% F
e, 3 to 10% Cu, 1 to 5% Zr, and the balance Co, but the raw material metal is weighed, melted and cast,
The obtained alloy is pulverized to an average particle size of 1 to 20 μm, shaped in a magnetic field, and then 0.5 to 100 at 1,100 to 1,250 ℃.
Sinter for 5 hours. Then, this is 0 ~ 50
℃ lower temperature for 0.5 ~ 5 hours, and finally 700 ~
It is manufactured by first-stage aging treatment at 950 ° C and then continuous cooling or multiple-stage aging.

The R-Fe-B rare earth magnet is usually composed of 5-40% R by weight, 50-90% Fe, and 0.2-8% B by weight. C, Al, Si, Ti, V, Cr, Mn, Co, for improving magnetic properties
Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, S
Additive elements such as n, Hf, Ta, and W are often added. The amount of these additives added is 30% by weight or less in the case of Co,
It is usual that the content of the other elements is 8% by weight or less. Note that this
R-Fe-B rare earth magnets are manufactured by weighing raw material metals, melting and casting, and crushing the resulting alloy to an average particle size of 1 to 20 μm, then molding in a magnetic field, 1,200
Sintering may be performed at 0.5 ° C for 0.5 to 5 hours, and finally aging may be performed at 400 to 1,000 ° C.

[0015]

【Example】

Example 1 Using the spraying device shown in FIG. 1, stearic acid was melted by heating with a heater, and this was sprayed by spraying air from an atomizing nozzle onto R-Fe-B magnetic powder having an average particle size of 5 μm. The amount of this spray was 0.1% by weight based on the weight measured value of the magnet powder, and this stearic acid was also sprayed on the inner wall of the mold using this spray device.

Then, this magnet powder was fed into a mold, a magnetic field of 15 kOe was applied by an electromagnet, and a pressure of 1 ton / cm ² was applied in a direction perpendicular to the magnetic field application direction while the magnetic field was applied. When this molded body was sintered in vacuum at 1,060 ° C for 90 minutes and then aged at 540 ° C, R-
Since a Fe-B system sintered magnet was obtained, this magnetic property was measured by B-H
When measured using a tracer, this residual magnetic flux density was 12.73 kG.

Example 2 0.1% by weight of stearic acid heated and melted by the spraying device shown in FIG. 1 was sprayed on R-Fe-B magnetic powder having an average particle size of 5 μm. A magnet powder obtained by spraying stearic acid into the mold without supplying the acid was supplied and treated in the same manner as in Example 1 to produce an R-Fe-B system sintered magnet.
When its magnetic characteristics were measured using a BH tracer, its residual magnetic flux density was 12.65 kG.

Example 3 In the method of Example 1, the mold was sprayed with stearic acid, but the R-Fe-B magnet powder was not sprayed with stearic acid. When an R-Fe-B system sintered magnet was manufactured and its magnetic characteristics were measured using a BH tracer, its residual magnetic flux density was 12.51 kG.

Comparative Example 1 No stearic acid was sprayed on the R-Fe-B magnet powder or the mold, and this R-Fe-B magnet was supplied into the mold, and When an R-Fe-B system sintered magnet was manufactured in the same manner and its magnetic characteristics were measured using a BH tracer, its residual magnetic flux density was 12.08 kG.

Comparative Example 2 0.1% by weight of stearic acid was added to the R-Fe-B magnet powder of Example 1.
Added and mixed. A mold was filled with this magnet powder and the same experiment as in Example 1 was performed. As a result, the residual magnetic flux density of the obtained magnet was 12.38 kG.

Comparative Example 3 The molten stearic acid shown in FIG. 1 was used as an ethanol solution in which stearic acid was dissolved in ethanol. The R-Fe-B magnet powder used in Example 1 contained 0.1% by weight of stearic acid. And spray it into the mold, and
When an R-Fe-B system sintered magnet was manufactured by the same treatment as
In this case, since the R-Fe-B magnet powder was oxidized during sintering, the magnetic characteristics could not be measured.

Example 4 0.1 wt% of stearic acid was sprayed onto R ₂ Co ₁₇ magnet powder having an average particle diameter of 5 μm by using the spraying device shown in FIG. 1, and the inner wall of the mold was stearic acid. Is sprayed, R ₂ Co ₁₇ system magnet powder is supplied to this mold, and 1
A magnetic field of 8 kOe was applied, and a pressure of 0.8 ton / cm ² was applied in the direction perpendicular to the magnetic field application direction while the magnetic field was applied.

Next, this compact was sintered at 1,200 ° C. in an argon gas atmosphere, solutionized at 1,180 ° C., and held at 850 ° C. for 2 hours as a first stage aging, and then continuously cooled to 400 ° C. at a cooling rate of 1 ° C./min. When cooled and then rapidly cooled, an R ₂ Co ₁₇ series sintered magnet was obtained. When its magnetic characteristics were measured using a BH tracer, its residual magnetic flux density was 10.46 kG.

[0024] While using R ₂ Co ₁₇ magnet powder used in Comparative Example 4 Example 4, the R ₂ Co
Stearic acid was not sprayed on the _17- based magnet powder and the mold, and this R ₂ Co _17- based magnet powder was supplied to the mold and treated in the same manner as in Example 4 to produce a R ₂ Co _17- based sintered magnet. The magnetic characteristics of B-
When measured with an H tracer, the residual magnetic flux density was 10.19 kG.

Examples 5 to 7 and Comparative Examples 5 to 6 Metal Fe powder having a particle size of 100 mesh or less or stainless steel powder and the lubricants (zinc stearate, calcium stearate or lithium stearate) shown in Table 1 were used. 0.1% by weight based on the metal powder using the spraying device shown in
Along with spraying, the lubricant was also sprayed on the inner wall of the mold, and the fluidity of the Fe powder and the stainless steel powder thus treated was measured, and the results as shown in Table 1 were obtained.

Then, the metallic Fe powder or stainless steel powder treated in this way is filled in a mold, and the molding pressure is 6 ton / cm.
^When molded with No. ² , the density of this compact was as shown in Table 1, but this powder was
When sintered at 00 ° C. for 1 hour and the tensile strength of this sintered body was measured, the results shown in Table 1 were obtained. In addition, Comparative Examples 5 to 6 are examples in which the lubricant is not sprayed on the metallic Fe powder and the stainless steel powder, and the fluidity, compact density, and tensile strength of the sintered body of these are as shown in Table 1. It was a thing.

[0027]

[Table 1]

[0028]

INDUSTRIAL APPLICABILITY The present invention relates to a powder molding method, and more particularly to a powder molding method in the powder metallurgy method. According to this method, a lubricant film is provided on the powder surface and / or the mold inner wall surface. The friction between the particles and the friction between the powder and the mold are suppressed, so that the molded product made from this has improved physical properties and workability, which is particularly important in the production of sintered magnets because of the magnetic properties. It provides the advantage of being effective in the manufacture of highly anisotropic sintered magnets.

[Brief description of the drawings]

FIG. 1 shows a longitudinal sectional view of a stearic acid spraying device using stearic acid as a lubricant.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiro Takaguchi 2-15-5 Kitafu, Takefu City, Fukui Prefecture Shin-Etsu Chemical Co., Ltd.

Claims (2)

[Claims] 1. In the molding step of powder metallurgy, before filling the mold with the powder, at least one of the powder and the inner wall of the mold is filled with a solid lubricant composed of fatty acid or metallic soap to a temperature not lower than its melting point. After heating and melting, spray and
A powder molding method, comprising forming a film of a lubricant on the surface of the powder and the inner wall of the mold, and then molding. 2. The powder molding method according to claim 1, wherein the powder is an alloy powder for a rare earth magnet.