JP4509862B2 - Method for manufacturing sintered soft magnetic member - Google Patents

Description

  The present invention relates to a method for producing a sintered soft magnetic member having soft magnetic characteristics, particularly high magnetic flux density and high permeability, suitable for actuators such as electromagnetic valves, electromagnetic clutches, and injectors for electronically controlled fuel injection devices. .

  Soft magnetic members used in magnetic cores of actuators such as solenoid valves, electromagnetic clutches, and injectors for electronically controlled fuel injection devices are required to have a high magnetic flux density, but the magnetic flux density is the occupation of the Fe component in the magnetic core. Therefore, the sintered soft magnetic member needs to be compacted at a high density in order to produce a member having a high magnetic flux density. Further, in applications where a quick response is required, it is necessary to increase the magnetic permeability. Therefore, a sintered soft magnetic member such as pure iron is compacted by applying a molding pressure that is at least twice as high as that for manufacturing a general sintered machine part.

General sintered machine parts contain about 0.3 to 1.2% by mass of carbon in order to improve the strength of the iron base, but this carbon content is usually imparted by adding graphite powder to the raw material powder. . For this reason, in general sintered parts, graphite powder functions as a lubricant. Therefore, combined with the effect of a molding lubricant added separately to the raw material powder, the extraction pressure when the molded product is extracted from the mold after compacting. It works in a direction that is advantageous for the lubrication effect of the molded body, for example, reducing squeezing and no galling of the molded body.
By the way, sintered soft magnetic members are pure iron, silicon iron alloy (Fe-1-6Si alloy), permalloy (Fe-30-30Ni alloy), permendur (Fe-30-60Co alloy), electromagnetic Powder of stainless steel (Fe-5-13Cr-2-6Si alloy) or the like is used. Of these, pure iron and permalloy are soft and viscous materials. When the molded product is extracted from the mold after compacting, it easily adheres to the mold, and the extraction pressure increases and is difficult to extract. In addition, silicon iron alloy, permendur, and electromagnetic stainless steel are hard in powder, and are easily removed by scratching the mold when the molded product is extracted from the mold after compacting. It becomes difficult to pull out. In a sintered soft magnetic member that uses a powder having a problem when extracted from the mold as a raw material, when carbon content is added to the raw material powder, the carbon dissolves in the iron base, and the magnetic properties, particularly the magnetic permeability. Since graphite deteriorates, graphite powder is not added. For this reason, in the sintered soft magnetic member, it is not possible to obtain a lubricating effect by adding graphite powder, and the lubricating effect of the compact is only due to the effect of the molding lubricant added to the raw material powder. Therefore, it is more difficult to improve the lubricity than in the case of general sintered machine parts.
When manufacturing a sintered soft magnetic member using such raw material powder, when the compact molded at high pressure and high density is extracted from the mold, the extraction pressure is high because the lubrication effect of the compact is low. Therefore, there is a problem that mold galling is likely to occur. This problem is conspicuous in a soft magnetic sintered member having a large product height, that is, a long sliding distance between the mold and the molded product when the molded product is extracted after compacting. If it exceeds 25 mm, the film of the forming lubricant formed on the surface of the mold hole of the molding die is broken to cause metal contact, and the molded body is galling. In the worst case, molding after compacting is performed. The body cannot be extracted.
Even if the size of the molded body is large, that is, when the sliding area of the mold is large, if the product has a large bottom area of the molded body, that is, a pressing area of the punch, The pressurizing area of the punch is relatively large with respect to the moving area, and the load per unit area during extraction can be reduced. However, since a relatively large extraction load is required when the sliding area of the mold becomes larger than the pressing area of the punch, the ratio of the sliding area of the mold to the pressing area of the punch exceeds 1. In products, the above problems are more prominent.

  On the other hand, when manufacturing such a sintered soft magnetic member, if a large amount of molding lubricant is added to increase the lubrication effect of the molded body, even if compression molding is performed at a high pressure, only the volume of the molded lubricant is The density of the molded body is lowered, the space factor of the Fe component is lowered, and the magnetic flux density is lowered. In addition, the molding lubricant should be removed by volatilization during sintering, but since the molded body is compacted at high pressure and has a high density, it is difficult to remove the entire amount of the molding lubricant. The carbon component produced by the decomposition of the molded lubricant during sintering diffuses and dissolves in the Fe matrix and degrades the magnetic properties, particularly the magnetic permeability.

Under such circumstances, as a method for producing a sintered soft magnetic member, Patent Document 1 fills a molding die in which a higher fatty acid-based lubricant is applied on the inner surface with a magnetic powder mainly composed of Fe, Disclosed is a sintered soft magnetic material obtained by sintering a powder compact obtained by press-molding warm at a compacting pressure of 784 MPa or more. In this molding process, a mechanochemical reaction is caused between the higher fatty acid lubricant applied to the inner surface of the molding die and at least the magnetic powder in contact with the inner surface of the molding die, thereby causing the magnetic powder and the higher fatty acid lubricant. And a metal soap film is formed on the surface of the magnetic powder compact.
JP 2003-82401 A

Generally, the lubrication method for compacting is a mixed lubrication method (internal lubrication method) in which a molding lubricant is added to the raw material powder, and a mold lubrication method (external lubrication method) in which a molding lubricant is applied to the mold hole wall surface. There is.
The mixed lubrication method requires only adding a molding lubricant at the time of blending the raw material powder, whereas the mold lubrication method requires a device for applying the molding lubricant and is troublesome to apply the molding lubricant. This is a lubrication method that is necessary and has a higher manufacturing cost than the mixed lubrication method.
Patent Document 1 is based on the mold lubrication method having a high manufacturing cost. In addition, the mold hole depth of the mold is required to be 2 to 2.5 times the height of the compact after compacting to fill the raw material powder. If the compact has a large height, The depth increases. For this reason, in the mold lubrication method, it is difficult to uniformly apply the molding lubricant only to the required amount over the entire inner surface of the molding die, and even more difficult to uniformly apply the molding lubricant if the product shape is complicated. Become. In this respect, Patent Document 1 does not necessarily solve the above problem. Furthermore, Patent Document 1 requires warm molding, that is, molding under heating conditions, in order to perform the above mechanochemical reaction. Compared to ordinary cold molding, a heating device and energy for heating are used. Therefore, a molding method requiring a high manufacturing cost is essential.

  The present invention has been made in view of such circumstances, and when an inexpensive mixed lubrication method is used, it can be implemented by inexpensive cold forming, and the size of the molded body in the extraction direction exceeds 25 mm. However, it is an object of the present invention to provide a method for producing a sintered soft magnetic member that does not cause mold galling on the surface of the molded body and can be pulled out with good pullability.

  In order to solve the above-mentioned problems, the method for producing a sintered soft magnetic member of the present invention is a method for forming a raw material powder obtained by adding a molding lubricant to a soft magnetic powder into a desired shape and sintering the resulting molded body. In the manufacturing method of a soft magnetic member, as the molding lubricant, a molding lubricant in which ethylene bisstearamide and an aliphatic carboxylic acid monoamide are mixed in a mass ratio of 6: 4 to 8: 2 is 0.4 to 1. .2% by mass is used.

  In the method for producing a sintered soft magnetic member of the present invention, in molding soft magnetic powder, ethylene bisstearamide and aliphatic carboxylic acid monoamide are used in a mass ratio of 6: 4 to 8: 2 as a molding lubricant. In this method, 0.4 to 1.2% by mass of the molding lubricant mixed in 1) is used, and the soft magnetic powder molded body having a dimension in the extraction direction of 25 mm or more can be satisfactorily extracted from the mold after compacting. can get.

  Ethylene bisstearamide (ethylene bis aliphatic monocarboxylic acid amide) has a melting point of about 120 to 145 ° C. and does not contain a metal component, so that the metal component does not vaporize and accumulate in the furnace. , All are converted to hydrocarbon gas and discharged outside the furnace, so they are used as molding lubricants for powder metallurgy. In addition, ethylene bisstearamide has the advantage of higher compressibility of raw material powder and higher extractability of molded product compared to commonly used zinc stearate, but the apparent density and flow of raw material powder It has the disadvantage of low degree. Even with such ethylene bisstearamide having excellent pullability, mold galling occurs when the molded product of the soft magnetic sintered member having a dimension in the pulling direction exceeding 25 mm is extracted.

  For this reason, in the method for producing a soft magnetic sintered member of the present invention, a product obtained by adding an aliphatic carboxylic acid monoamide to ethylene bisstearamide to improve the extraction property is used as a molding lubricant. Aliphatic carboxylic acid monoamide (hereinafter referred to as “monoamide”) is the most common acid amide and has a melting point of about 40 to 110 ° C. and is used as a lubricant or a release agent. Specifically, lauric acid amide (melting point 87 ° C.), palmitic acid amide (melting point 100 ° C.), stearic acid amide (melting point 101 to 107 ° C.), behenic acid amide (melting point 98 to 110 ° C.), hydroxy stearic acid amide (melting point) 107 ° C.), oleic acid amide (melting point 75 ° C.), erucic acid amide (melting point 81 to 82 ° C.), ricinoleic acid amide (melting point 62 ° C.), or a mixture thereof.

  FIG. 1 shows the extraction pressure of a molded product and the apparent density and fluidity of a raw material powder when a mixture of ethylene bisstearamide and stearamide as a monoamide with different addition amounts is used as a molding lubricant. It shows a change. FIG. 1 shows a raw material powder in which 1.5% by mass of copper powder and 1.0% by mass of graphite powder are added to iron powder, and 0.8 parts by mass of molding lubricant is added to 100 parts by mass of the raw material powder. It is an example in the case of the added raw material for sintered machine parts. From FIG. 1, it can be seen that the extractability is further improved by adding 20% by mass or more of monoamide to ethylene bisstearamide. On the other hand, however, when monoamide is added, the apparent density of the raw material powder decreases, and particularly when the amount of monoamide added exceeds 40% by mass, the rate of decrease increases rapidly. From these facts, it can be seen that the addition of monoamide to ethylene bisstearamide can improve the extraction pressure without causing a significant decrease in apparent density and fluidity in the range of 20 to 40% by mass.

FIG. 1 shows an example of a sintered machine part. When a mixture of ethylene bisstearamide and monoamide in this range is used as a molding lubricant for a soft magnetic sintered member, the sintered soft magnetic member is used. It has been found for the first time that the same effect can be obtained and the molded product can be satisfactorily extracted with a dimension in the extraction direction of the molded product exceeding 25 mm.
The present invention is derived from this finding, and the gist of the present invention is that such a molding lubricant is applied to the production of a soft magnetic sintered member.

  Sintered soft magnetic members are compacted with high density and tend to have fewer pores than conventional sintered machine parts, making it difficult to remove molding lubricants. The molding lubricant mixed with is easily decomposed during dewaxing, especially during dewaxing, and is easy to remove by volatilization. In this respect, it is suitable for a sintered soft magnetic member. However, if the amount added is less than 0.4% by mass, the lubrication effect is poor and the molded product after compacting cannot be extracted well. In particular, when a molded product having a dimension in the extraction direction of 25 mm or more is extracted, it is preferable to add 0.6% by mass or more. On the other hand, when the addition amount exceeds 1.2% by mass, the density of the compact is lowered and the magnetic flux density is lowered. In addition, it becomes difficult to remove the carbon content generated by the decomposition of the molding lubricant, which may diffuse into the iron base and cause a decrease in magnetic properties, particularly permeability, so the amount added is 1.2 mass. % Should be kept below.

  If a molding lubricant that is a mixture of ethylene bisstearamide and monoamide is used, pure iron powder or permalloy powder that has low powder hardness and easily adheres to the mold, and the powder has high hardness and is easy to scratch the mold. In any case of silicon iron alloy powder, permendur powder or electromagnetic stainless steel powder, an excellent lubricating effect is exhibited and good extraction can be performed.

  The molding pressure is determined by the raw material powder used and the magnetic properties (magnetic flux density and permeability) required for the product, and is not particularly limited. As an example, when adding Si powder to the raw material powder in a soft magnetic material using Si, if the molded body density is more than a certain level, it shrinks during sintering and a high sintered body density can be obtained. Is about 700 MPa or more. In the case of a pure iron material or the like having a small amount of sintering shrinkage, a product with a high sintered body density cannot be obtained unless the molded body density is increased in advance. Therefore, the molding pressure needs to be 800 MPa or more. On the other hand, an excessive molding pressure is not preferable because it causes wear of the mold, and about 1200 MPa is recommended.

  As the soft magnetic powder, pure iron powder having a soft average particle diameter of 65 μm and soft powder having a hard average particle diameter of 65 μm, Cr: 6% by mass, Si: 3% by mass, the balance being Fe and inevitable impurities Two types of electromagnetic stainless steel raw material powder made of an Fe—Cr—Si alloy were prepared. In addition, as a molding lubricant, ethylene bisstearamide and monoamide mixed with stearamide in a mass ratio of 75:25, and for comparison only ethylene bisstearamide and zinc stearate are prepared. Then, using a raw material powder obtained by adding 1.0% by mass to soft magnetic powder and molding it at a molding pressure of 800 MPa, a molded body having an outer diameter of φ11.3 mm and different dimensions in the extraction direction was molded. The extracted state was observed. The results are also shown in Table 1.

When a mixture of ethylene bisstearamide and monoamide is used as a molding lubricant, the extraction pressure is low in the dimensions in the extraction direction of all molded products, regardless of whether the raw material powder is soft or hard. I know that there is. On the other hand, when the molding lubricant is only ethylene bisstearamide or zinc stearate, the extraction pressure of ethylene bisstearamide is lower than the mixture of ethylene bisstearamide and monoamide, although the extraction pressure is lower.
Further, when the dimension in the drawing direction of the molded body is 25 mm, even if ethylenebisstearamide is used, the mold galling is large and the pulling property is poor, and if it exceeds 25 mm, the molded body cannot be pulled out. In the example using zinc stearate, the molded product could not be extracted at 25 mm or more.
From the above, it was confirmed that when a mixture of ethylene bisstearamide and monoamide was used as a molding lubricant, the soft magnetic powder molded body could be satisfactorily extracted.

  As soft magnetic powder, Fe-47Ni alloy (permalloy) powder, Fe-50Co (permendur) powder, and pure iron powder having an average particle diameter of 65 μm and Si fine powder having an average particle diameter of 10 μm are 3.5. Three types of silicon iron raw material powders, which are added by mass% and coated with Si fine powder on the surface of pure iron powder, are molded lubricants in which ethylene bisstearamide and monoamide used in Example 1 are mixed at 75:25. The raw material powder was mixed with 1.0% by mass and molded under the same molding conditions. The dimensions of the molded body were an outer diameter of φ11.3 mm and a dimension in the extraction direction of 40 mm, and the extraction state at the time of molding was observed. However, in any of the soft magnetic powders, good extraction was performed.

  As the soft magnetic powder, a raw material powder was used which was added and mixed with the pure iron powder used in Example 1 while changing the addition amounts of the ethylene bisstearamide and monoamide molding lubricants used in Example 1. This raw material powder was molded under the same molding conditions as in Example 1 and molded bodies with dimensions in the extraction direction of 20, 25, and 50 mm. Table 2 shows the results of observation of the extracted state at this time.

From the results shown in Table 2, when the addition amount of the molding lubricant is 0.2% by mass, the addition amount is insufficient, and it cannot be extracted with a sample having a dimension in the extraction direction of the molded body of 25 mm or more, but it is not less than 0.4% by mass. It can be seen that the extraction pressure can be reduced with the addition of 0.6% by mass or more.
On the other hand, if the added amount of the molding lubricant exceeds 1.2% by mass, the added amount becomes excessive, resulting in incomplete removal of the molding lubricant in the sintering process, and the magnetic properties of the sintered soft magnetic sintered member. A decrease in properties was observed.
From these facts, the amount of molding lubricant added is in the range of 0.4 to 1.2% by mass, and the soft magnetic powder molded product can be extracted. In particular, in the molded product whose dimension in the extraction direction is 25 mm or more, 0.6 to It was found that good extraction can be performed in the range of 1.2% by mass.

Addition amount of the mixture of ethylene bisstearamide and monoamide used in Example 1 as the molding lubricant, only ethylene bisstearamide, and zinc stearate to the magnetic stainless steel raw material powder used in Example 1 as the soft magnetic powder The raw material powder which was added and mixed while changing was used. A compact formed by compacting this raw material powder into a shape having an outer diameter of 30 mm, an inner diameter of 20 mm, and a dimension in the extraction direction of 25 mm is sintered in a reduced gas atmosphere of 10 ⁻² Torr at 1250 ° C. for 60 minutes. The obtained sintered body was processed to a height of 5 mm for measurement to obtain ring-shaped samples of sample numbers 49 to 69 shown in Table 3. These samples were wound 100 times on the primary side and 20 times on the secondary side, the DC BH curve was measured at room temperature (20 ° C.), and the magnetic flux density B at a magnetic field strength of 2500 (A / m). ₂₅₀₀ (T) result of obtaining and permeability mu _m shown in Table 3.

From the results shown in Table 3, when a mixture of ethylene bisstearamide and monoamide is used as the molding lubricant, the magnetic flux density is almost constant in the range of 0.2 to 1.2% by mass of the molding lubricant addition amount. A slight decrease is observed when the amount of molding lubricant added exceeds 1.2% by mass. Moreover, the magnetic permeability has also shown the high value which exceeds 4000 in the range whose addition amount is 0.2-1.4 mass%.
On the other hand, when only ethylene bisstearamide is used as the molding lubricant, the same high magnetic flux density as that of the mixture of ethylene bisstearamide and monoamide is shown up to 0.6% by mass of the molding lubricant. When the amount exceeds 0.6 mass%, the tendency to decrease the magnetic flux density becomes prominent. Further, the magnetic permeability decreases as the amount of the molding lubricant added increases, and when it exceeds 0.6% by mass, the magnetic permeability decreases until it falls below 4000. This is presumably because the removal of the molding lubricant becomes difficult as the amount of the molding lubricant added increases, and the carbon component decomposed by the molding lubricant dissolves in the base.
And when zinc stearate is used as a molding lubricant, these tendencies are more prominent, the magnetic flux density tends to decrease when the amount of molding lubricant added exceeds 0.6% by mass, and the permeability decreases. It can be seen that the tendency is greater than when only ethylene bisstearamide is used.
From these facts, it was confirmed that when a mixture of ethylene bisstearamide and monoamide was used as a molding lubricant, there was almost no decrease in magnetic properties when the amount of molding lubricant added was in the range of 0.2 to 1.2% by mass. It was done.

  Even when a sintered soft magnetic member having a dimension in the extraction direction of 25 mm or more suitable for a magnetic core of an actuator such as an electromagnetic valve or an electromagnetic clutch is manufactured by the manufacturing method of the present invention, the extraction from the mold is easy. It becomes possible to mold without forming mold on the surface of the molded body.

It is a graph which shows the influence which the mixing ratio of the ethylenebisstearoamide and aliphatic carboxylic acid monoamide in the raw material powder for sintered machine parts has on the extraction pressure of the molded product, the apparent density of the raw material powder, and the fluidity.

Claims (2)

In the method for producing a sintered soft magnetic member, a raw material powder obtained by adding and mixing a molding lubricant to soft magnetic powder is molded into a desired shape, and the resulting molded body is sintered.
As the molding lubricant, 0.4 to 1.2% by mass of a molding lubricant in which ethylene bisstearamide and an aliphatic carboxylic acid monoamide are mixed at a mass ratio of 6: 4 to 8: 2 is used. A method for producing a sintered soft magnetic member. 2. The sintered soft magnetic member according to claim 1, wherein the sintered soft magnetic member is a molded body having a dimension in a drawing direction of 25 mm or more, and the molding lubricant is blended by 0.6 mass% or more. Production method.

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