JP4462967B2 - Method for producing soft magnetic member by powder metallurgy - Google Patents

Description

  The present invention relates to a dust core suitable for various electrical parts such as a transformer, a reactor, a stator core, a thyristor valve, a noise filter, a choke coil, and a motor core, or an iron core (core, yoke) such as a relay or a transformer, an electromagnetic clutch The present invention relates to an improvement in a method for producing a sintered soft magnetic member by powder metallurgy suitable for a rotor, a plunger of various actuators, and the like.

  As a soft magnetic member using a powder material as a raw material powder, after the raw material powder is compacted, it is heat-treated at about 150 to 600 ° C., and in addition to the powder magnetic core having no metallurgical bond between the powders, the raw material powder After compacting, there is a sintered soft magnetic member in which each powder is metallurgically diffusion-bonded by heat treatment (sintering) at about 800 to 1200 ° C. The present invention relates to an improvement of a powder forming method of a raw material powder common to a dust core and a sintered soft magnetic member. Therefore, the following description proceeds with a dust core as an example.

  The powder magnetic core is manufactured by powder-molding a mixed powder obtained by using iron powder as magnetic particles and adding and mixing an insulating resin to the iron powder as a raw material powder, followed by heat treatment (Patent Document 1, etc.), Alternatively, iron powder having an insulating film formed on the surface is used as a raw material powder as it is (Patent Document 2, etc.), or a mixed powder obtained by further adding an insulating resin is used as a raw material powder (Patent Document 3, etc.) In any case, a magnetic core having a relatively high magnetic flux density and low iron loss can be obtained.

  The magnetic flux density of such a dust core depends on the space factor of the iron powder in the dust core, that is, the density of the dust core. For this reason, increasing the density of the powder magnetic core has become an essential requirement. Under these circumstances, in order to increase the density of the powder magnetic core, iron powder with good compressibility is used, and a small amount is required. Research has been progressing on resins that can ensure insulation (Patent Document 4, etc.).

Japanese Examined Patent Publication No. 4-12605 JP 2003-332116 A JP-A-11-251131 JP 2002-246219 A

  When powder molding is performed at a high pressure using the conventional powder magnetic core powder as described above, the powder compact has a high density, and thus a high magnetic flux density powder magnetic core can be obtained. When a product is molded at a high pressure, the surface area is large, so that the amount of deflection of the mold, core, etc. increases, and there is a problem that the green compact is galling or cannot be extracted. For this reason, it is difficult to increase the density in the case of such complicated shape products, and only products that have been molded at a low density that can be extracted, or that have been shaped from simple shapes by processing, are currently in practical use. is there.

  Therefore, an object of the present invention is to provide a manufacturing method capable of compacting at a high pressure even in a complicated shape and improving the pullability of the compact after compacting.

The method for producing a soft magnetic member by the powder metallurgy method of the present invention for solving the above-mentioned problem is that a molding lubricant is applied to the mold hole wall surface of the mold, and then the raw material powder is filled in the mold hole, and then this raw material powder In a method for producing a soft magnetic member by a powder metallurgy method in which the green compact is extracted from the mold, and thereafter heat-treated or sintered, the molding powder is used as a molding lubricant. The melting point is higher than the temperature of the mold hole wall surface when the molding lubricant is applied to the mold hole wall surface, and lower than the temperature of the mold hole wall surface raised by extracting the green compact from the mold. Use a mold that is in a solid state when applied to the mold hole wall surface and compacted, and when the compact is extracted from the mold, it melts due to the heat generated at that time and becomes a liquid state. It is characterized by that.

  The compacting process in the present invention can be performed by cold forming, and the molding lubricant used in this case is selected from unsaturated fatty acid amides having 12 to 22 carbon atoms, cetyl alcohol, and stearyl alcohol. It is recommended to use at least one selected from the above.

  Further, in the present invention, as a method for applying the molding lubricant, a method in which a solution obtained by dissolving or dispersing the molding lubricant in a liquid is sprayed onto the mold wall surface is preferable. Furthermore, in this invention, it is set as a preferable form that the metal mold | die is equipped with the cooling means.

  According to the present invention, since the molding lubricant to be used is in a solid state at the time of compaction molding, it is possible to prevent the molding lubricant from penetrating into the compact and obtain a healthy compact. At the same time, the coefficient of static friction is reduced at the beginning of extraction of the green compact from the mold. The molding lubricant to be used melts due to the heat generated between the compact and the mold hole wall surface when the compact is removed from the mold after compacting. As a result, it is possible to obtain a good extraction property, that is, a characteristic that it is easy to extract. Therefore, this method is very promising as a method for producing a soft magnetic member having a high density and a complicated shape.

Embodiments of the present invention will be described below.
When molding a green compact by filling a mold hole with raw material powder and molding it, then opening the mold and extracting the green compact, and repeatedly molding the green compact, the mold temperature is the number of moldings It is known that it increases with an increase and almost reaches equilibrium at a certain number or more. The heat generation and temperature rise of the mold mainly occur in the extraction process of extracting the green compact from the mold. Specifically, the direction perpendicular to the direction in which the raw material powder is compressed, that is, the direction of the mold wall in the mold It is generated by the frictional heat generated between the elastic deformation force of the green compact to swell and the wall surface of the mold hole. Compared to such a temperature rise at the time of extracting the green compact, it can be said that the amount of heat generated at the time of compacting is much smaller because the movement of the powder is relatively free.

  Normally, in compacting with a mold, a lubricant is applied to the wall surface of the mold hole, and then the raw material powder is filled into the mold hole. Therefore, the lubricant application process, the raw material powder filling process, and the compacting process. ~ In a series of molding processes such as the extraction process, frictional heat is generated on the mold hole wall surface during the extraction process and the temperature rises. In other processes, the heat generated on the mold hole wall surface is diffused and dissipated throughout the mold. Thus, compaction molding is performed while repeating a cycle in which the temperature decreases.

  In the case of continuous molding that repeats such processes, the amount of heat generated during the extraction process is greater than the cooling effect during the other processes because the mold is at room temperature at the beginning of molding, and therefore the amount of heat stored in the mold. The mold temperature rises with the number of moldings, and after a certain number of moldings, the amount of generated heat and the cooling effect reach an equilibrium state, and the mold temperature almost reaches equilibrium.

  The present invention was made by paying attention to the temperature difference of the mold hole wall surface of the mold in the above one molding cycle, that is, the lubricant application step, the raw material powder filling step, the compacting step, and the extracting step. In the low-lubricant coating step, the raw material powder filling step, and the compacting step, a lubricant that exists in a solid state and melts due to heat generated in the extraction step and exists in a liquid state is used.

  If the lubricant is liquid during filling of the raw material powder into the mold and compacting, the melted lubricant is absorbed by the capillary force and penetrates between the powders or in the pores of the compact, The amount of lubricant required when the green compact is extracted is reduced, and the density increase at the time of compacting is hindered to cause a decrease in magnetic flux density. In addition, it may cause defective appearance such as rough skin on the product after heating, or decrease the mechanical strength.

  On the other hand, if the lubricant is solid from the time of filling the raw material powder to the compacting process, the lubricant is not absorbed into the compact, and the initial stage of extracting the compact That is, the effect of reducing the friction (static friction) at the stage where the green compact has not yet started to move is more noticeable with solid lubrication than with liquid lubrication. However, liquid lubrication is superior in reducing friction after moving, and liquid lubrication is a factor that hinders density improvement because the green compact has already been densified by high-pressure compacting. In addition, absorption of the liquid lubricant due to the capillary force inside the green compact is only slightly generated on the surface layer, so that it can be easily removed in the subsequent heating step.

  From these findings, it is most suitable that the lubricant used in the molding of the powder magnetic core is solid in the raw material powder filling process to the powder molding process and melts due to the heat generated during extraction to become a liquid state. Will be. Since the temperature difference between the raw material powder filling step to the compacting step and the extraction step is, for example, about 10 to 40 ° C., a lubricant having a melting point in this range may be used.

  The present invention can be carried out regardless of the distinction between cold forming, warm forming and hot forming. For example, in the case of cold forming, when the temperature of the mold reaches equilibrium by continuous forming. Is, for example, 40 to 50 ° C. in the raw material powder filling step to the compacting step, and the temperature of the mold hole wall surface of the mold is 50 to 90 ° C. in the extraction step. In this case, the melting point is 47 to 53 Cetyl alcohol having a melting point, stearyl alcohol having a melting point of 56 to 62 ° C., unsaturated fatty acid amide having a melting point of 40 to 90 ° C., and the like can be used. Among these, unsaturated fatty acid amides can be applied in a wide range because the melting point can be adjusted by the number of carbon atoms, and are particularly suitable. In order to set the melting point of the unsaturated fatty acid amide to 40 to 90 ° C., the carbon number may be 12 to 22.

  In addition, in the case of warm forming or hot forming, the heating temperature of the raw material powder and the mold is adjusted according to the melting point of the lubricant to be used, and the temperature of the raw material powder filling process to the compacting process and during the extraction process Since the melting point of the lubricant to be used should exist between the temperature of the mold hole wall surface, a wide range of lubricants can be selected.

  In addition, when using a mixed lubrication method in which the entire amount of the raw material powder is given and compacted, the lubricant must be added in a large amount to ensure the amount necessary for lubrication. As a result, the density of the green compact is lowered and a high-density powder magnetic core cannot be obtained. In addition, dust compaction of the dust core is performed at a high pressure to increase the magnetic flux density. Therefore, the amount of pores is small, making it difficult to remove sufficient lubricant during subsequent heating or sintering. It remains inside and causes a decrease in strength and magnetic properties. Therefore, a pressing lubrication method in which a lubricant is applied to the mold hole wall surface is suitable for compacting the soft magnetic member.

  However, the combined use of the push-type lubrication method and the mixed lubrication method in which a lubricant of 0.3% by mass or less with respect to the raw material powder is given to the inside of the raw material powder promotes densification due to slipping between the powders during compaction molding. It is recommended because of the small amount of lubricant added, because it is easy to remove the lubricant during subsequent heating or sintering. In this way, when the die-type lubrication method and the mixing lubrication method are used in combination, the lubricant to be mixed may be added to and mixed with the raw material powder as a lubricant powder, or may be provided by adhering to or covering the raw material powder.

  Further, in the present invention, the press-type lubrication method has the following advantages. In other words, as a push-type lubrication method, an electrostatic coating method in which a charged lubricant powder is sprayed and attached to the mold hole wall surface together with air, or a solution in which a lubricant is dissolved or dispersed in a volatile liquid such as alcohol is sprayed. Although there is a wet coating method to apply, especially when electrostatic spraying method is adopted, the lubricant powder is sprayed with air, so the heat generated during extraction can be taken away when air is blown, and the mold wall surface It has the effect of lowering the temperature. Furthermore, such a temperature lowering effect of the mold hole wall surface is a cooling that reduces the temperature by removing heat from the mold wall surface when the volatile liquid evaporates in addition to the cooling effect by air. Since the effect | action works, since the temperature difference between the raw material powder filling process-a compacting process, and the extraction process can be expanded, it is preferable. In the case of the wet coating method, the liquid for dissolving or dispersing the lubricant is not limited to the volatile liquid such as the alcohol, but an appropriate type of liquid that evaporates when applied to the mold wall surface is heated. It can be selected according to the temperature of the mold.

  In order to cool the mold hole wall surface of the mold effectively, for example, a mold cooling means such as providing a cooling pipe between the die supporting the mold and the die plate and circulating cooling water or the like through the cooling pipe is provided. The temperature difference between the raw material powder filling process to the compacting process and the extraction process can be expanded by cooling the mold in this way, which is preferable.

  As described above, the dust core has been mainly described as an example of the soft magnetic member by the powder metallurgy method, but the sintered soft magnetic member is common in terms of increasing the density of the green compact for improving the magnetic flux density. Since the green compact is different in that it is sintered at a temperature at which metallurgical bonding occurs or is heat-treated at a temperature at which it does not occur, the sintered soft magnetic member has the same effect.

  Moreover, in the manufacturing method of the soft magnetic member by the powder metallurgy method of this invention, as raw material powder to be used, for example, iron powder, Fe-Si alloy powder, Fe-Co alloy powder, Fe-Ni alloy powder, electromagnetic stainless steel powder In the case of a dust core, an insulating film may be formed on the surface of the powder, and a binder component may be added or coated. The same effect can be obtained.

[Example 1]
The raw material powder which added the 0.3% imide resin using the insulating film formation iron powder which formed the insulating layer of the phosphate on the surface of iron powder was prepared. Using this raw material powder, the lubricants of sample numbers 01 to 06 shown in Table 1 were applied to the mold hole wall surface of the mold by electrostatic spraying, and the green compact serving as the material of the motor core having the shape shown in FIG. Continuous molding in which molding was performed at a molding pressure of 980 MPa and cold was performed at a molding speed of 5 pieces / minute, and 500 compacts were formed for each sample number. In this motor core, a plurality of ribs 2 extend radially from a central cylindrical inner ring portion 1, and an arc-shaped outer ring portion 3 concentric with the inner ring portion 1 is formed at the tip of these ribs 2. The inner ring portion 1 has an inner diameter of φ16 mm, an outer diameter of φ25.6 mm, and an overall outer diameter of φ80 mm.

In this example, during the above-described continuous molding, the ability to pull out the green compact from the mold was verified and observed. The results are also shown in Table 1. Note that the motor core having the shape shown in FIG. 1 has a very large mold wall surface area, and thus cannot be formed with high density by the conventional lubrication method, and only a molding density of about 7.1 Mg / m ³ has been put to practical use. It is of shape. Under the molding pressure of this example, the molding density is about 7.5 Mg / m ³ , and this example is a test at a molding density in a region that has not been put into practical use at present.

  From the results in Table 1, it was confirmed that when the lubricants of sample numbers 01 to 04, which are examples of the present invention, were used, all (500 pieces) could be extracted although the extraction sound at the initial stage of the molding was large. Further, the green compact surface after extraction showed wet luster, and it was clear that the lubricant was melted at the time of extraction, which is considered to indicate good extraction performance. On the other hand, it was found that when the lubricants of Sample Nos. 05 and 06, which are conventional examples, were used, mold galling occurred during molding, making it impossible to extract and molding was impossible. As described above, according to the present invention, it was confirmed that even a complicated shape that could not be molded in the past was excellent in the drawability and could be continuously continuously molded. In addition, although it is about the problem that the extraction sound at the initial stage of molding is large, this can be avoided beforehand if only the mold is preheated to an equilibrium temperature reached by the mold during continuous molding.

[Example 2]
A molding test was conducted in the same manner as in Example 1 except that the molding pressure was increased to 1200 MPa and the molding density was increased to about 7.65 Mg / m ³ . As a result, as in Example 1, when cetyl alcohol, stearyl alcohol, and unsaturated fatty acid amide were used as the molding lubricant, the extractability was excellent and good continuous molding was achieved. When zinc stearate and ethylene bisstearoamide were used, mold galling occurred and extraction was impossible.

  According to the method for producing a soft magnetic member by the powder metallurgy method of the present invention, it is possible to obtain a high-density soft magnetic member because good drawability is obtained, which is particularly suitable for producing a soft magnetic member having a complicated shape. Suitable for various electrical parts such as transformers, reactors, stator cores, thyristor valves, noise filters, choke coils, motor cores, etc., or iron cores (cores, yokes) such as relays and transformers, electromagnetic clutches It is possible to form a soft magnetic member by a powder metallurgy method, such as a sintered soft magnetic member suitable for the rotor of this type, and the plunger of various actuators, at a high density.

It is a top view which shows the green compact used as the raw material of the stator core shape | molded in the Example of this invention. It is the II-II sectional view taken on the line of FIG.

Claims (4)

After applying molding lubricant to the mold hole wall surface of the mold, the mold hole is filled with the raw material powder, then the raw material powder is compacted, and the obtained green compact is extracted from the mold, In the method for producing a soft magnetic member by a powder metallurgy method in which the green compact is heat-treated or sintered,
As the molding lubricant, the melting point of the mold hole wall surface is higher than the temperature of the mold hole wall surface when the molding lubricant is applied to the wall surface of the mold hole, and has been raised by extracting the green compact from the mold. When the green compact is extracted from the mold, it is melted by the heat generated at that time. Then, a method for producing a soft magnetic member by powder metallurgy is used, which is in a liquid state.   The compacting is cold forming, and as the forming lubricant, at least one selected from unsaturated fatty acid amides having 12 to 22 carbon atoms, cetyl alcohol and stearyl alcohol is used. Item 2. A method for producing a soft magnetic member by powder metallurgy according to Item 1.   The method of applying the molding lubricant comprises spraying a solution obtained by dissolving or dispersing the molding lubricant in a liquid onto the wall surface of the mold hole, according to claim 1 or 2, Production method.   The said metal mold | die is equipped with the cooling means, The manufacturing method of the soft magnetic member by the powder metallurgy method in any one of Claims 1-3 characterized by the above-mentioned.

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