DE112007001311T5 - Process for the preparation of a magnetic powder and process for the production of a molding compound core - Google Patents

Abstract

A process for producing a magnetic powder by a water atomization method, wherein
the magnetic powder produced by water atomization is used as a raw powder, and
a spheroidizing treatment is performed by applying mechanical forces to the powder to spheroidize a form of the powder.

Description

Technical area

The The present invention relates to a method for producing a Earth's core used in a rotating electric machine is to be, and a method for producing a magnetic powder, which are used as a material for the ground core is intended, and in particular, a method for producing a magnetic powder for producing a ground core with low core losses and a method of manufacturing the compound core.

Technical background

• Patentschrift 1: JP8(1996)-37107A
• Patentschrift 2: JP7(1995)-245209A

So far, in rotating electric machines, a ground core made of a magnetic metal powder has been used by compaction. As a method for producing this magnetic metal powder to be used for the ground core, for example, a sputtering method such. A water atomization method and a gas atomization method (see, for example, Patent Documents 1 and 2).

• Patent document 1: JP8 (1996) -37107A
• Patent document 2: JP7 (1995) -245209A

Disclosure of the invention

Task of the invention

The Particles of the conventional one given above Water atomizing method produced magnetic Metal powders, however, tend to be irregular shaped as well as very pointed and strongly gerieft. This results in the Disadvantage that the compacted core has a high iron loss value having. According to the water atomization method also forms on the surface of the particles a thick oxide layer. It is therefore difficult to get one in the powder reducing carbon content, which leads to that the core has a high hysteresis loss.

on the other hand For example, a powder can be produced by the gas atomizing method compared to the powder produced by the water atomization process produced, has an almost rather spherical shape. Accordingly, a core with a favorable iron loss getting produced. The powder particles, however, are smooth and therefore, even after compression, they are relatively weak Connect with each other. This complicates the production of a Kerns, which has a sufficiently high strength. In a motor stator For example, a plurality of cores is arranged in a ring shape and from outside by shrink fit or the like with each other connected. Furthermore, such a stator will occur cyclically Subjected to thermal cycling. If the core that out the powder produced by the gas atomizing method exists, there is a problem that it leads to a destruction of the edge area or cracking can come. Furthermore, it is the gas atomization process a costly manufacturing process that acts as a process less common for making a large number of cores is.

The The present invention has been developed in order to achieve the above Problems in the conventional mass-core manufacturing process to solve. In particular, it is an object of the present invention a method for producing a magnetic powder and a method for producing a ground core with sufficiently low core losses, such as B. iron loss and hysteresis loss, and a satisfactory To create strength.

Solution of the task

to To solve the above object, the present invention provides Invention a method for producing a magnetic powder by a water atomization process, which by a water atomization produced magnetic powder is used as a raw powder and a Einformungsbehandlung or a Sphäroidisierungsbehandlung executed is exerted by applying mechanical forces to the powder to spheroidize the shape of the powder particles.

According to the Production method according to the invention for a magnetic powder passes through the water atomization process manufactured magnetic powder together with used for spheroidization mechanical forces for use. Thus be through the water atomization method produced largely spheroidized particles of irregular shape; but the degree of spheroidization is in this process moderate. The shape of this manufacturing process Magnetic powder produced is thus slightly different. Of the made of this powder by compaction core has a satisfactory Strength on.

According to the The present invention is preferably a grain-enlarging treatment carried out by the powder after the spheroidization treatment is annealed at a temperature that is greater or equal to an austenite transformation point. This will do that Crystal grain increases and the carbon content reduced in the powder. The use of this magnetic powder allows consequently, the production of a core of satisfactorily low Ummagnetisiserungsverlusten.

When In another aspect, the present invention provides a method for producing a ground core by compacting a magnetic powder, wherein the magnetic powder produced by water atomization is used as a raw powder and a spheroidization treatment Running is done by the powder before compressing mechanical forces is exposed to spheroidize the shape of the powder.

In the molding compound core production process according to the invention is preferably a grain enlargement treatment carried out by the powder after the spheroidization treatment, however before compacting, annealing at a temperature, which is greater than or equal to an austenite transformation point is.

According to the Magnetic powder production method according to the invention and the molding compound core production method of the present invention the prepared mass core or molding compound core satisfactorily low re-magnetization losses, such. B. iron and hysteresis loss, as well a satisfactorily high strength.

Brief description of the drawing

1 Fig. 12 is a perspective view showing an example of the shape of a ground core in a preferred embodiment;

2 FIG. 10 is a flowchart showing a molding compound core manufacturing process in the embodiment; FIG.

3 Fig. 10 is an enlarged view of a powder obtained by a water atomization method;

4 Fig. 10 is an enlarged view of the powder obtained by the water atomization method, which was then subjected to a jet mill treatment and an annealing treatment;

5 Fig. 10 is a sectional view of the powder showing an example of a crystal grain boundary and a periphery of a powder particle;

6 Fig. 12 is a graph illustrating a difference in the spheroidized shape corresponding to each jet mill treatment period;

7 Fig. 12 is a graph illustrating differences in crystal grain diameter when the jet mill treatment and the annealing treatment are performed and not carried out;

8th Fig. 10 is a graph showing changes in the amount of carbon in jet mill treatment and annealing treatment;

9 Fig. 10 is a graph showing a difference in hysteresis loss between the powder processing methods;

10 Fig. 4 is an explanatory view showing a method of a compression test performed in the radial direction; and

11 Fig. 10 is a graph showing a difference in strength between the powder processing methods.

Best way to run the invention

It Now, a detailed description of a preferred Embodiment of the present invention with reference on the attached drawing. In the present embodiment the invention is based on a magnetic powder Earth core applied by compaction applied.

1 shows an example of the shape of a molding compound core of this embodiment. This molding compound core 20 is made from a magnetic metal powder by compaction, using a molding tool to form a tooth 21 and a yoke 22 to train in one piece. At the tooth 21 it is a part on which a coil with a concentrated winding is wound so as to function as a core. According to the invention, the molding compound core can have any shape.

• (1) Herstellung eines Rohpulvers
• (2) Strahlmühlenbehandlung
• (3) Glühbehandlung
• (4) Beschichtungsbehandlung
• (5) Verdichten
• (6) Erwärmungsbehandlung

The molding compound core manufacturing method of this embodiment becomes, as in FIG 2 shown following the order of the following six steps:

• (1) Preparation of a raw powder
• (2) jet mill treatment
• (3) annealing treatment
• (4) Coating treatment
• (5) compacting
• (6) heating treatment

In the raw powder manufacturing step (1), first, a raw magnetic metal is pulverized by the water atomizing method. The magnetic raw metal is preferably an Fe-Si material containing 1% or more of Si. As in 3 is shown schematically, the powder obtained by the water atomization method contains differently shaped particles. In addition, they have largely different sizes to each other. On the surface of the particles also forms an oxide layer.

In the subsequent jet mill treatment step (2) The powder obtained in step (1) becomes jet mill treatment subjected or subjected to a ball mill treatment become. Accordingly, the convex-shaped portions of a respective slightly spheroidized powder particle removed, and at the same time the oxide layer from the surface away.

Thereafter, the annealing treatment is carried out at the annealing treatment step (3). In this treatment, the annealing temperature is preferably set at about 980 ° C or more, at which temperature austenite transformation occurs. Even more preferred, however, is vacuum annealing. In this sputtering treatment, the term "vacuum" does not stand for a so-called ultra-high vacuum, but represents a condition in which a pressure is reduced to a certain value. 4 Fig. 12 is a schematic representation of the powder obtained after the jet mill treatment (2) and the annealing treatment (3) applied to the water-atomized powder obtained in the step (1). As in 4 is shown, the powder is, after it has been subjected to the annealing treatment opposite to that in 3 The water-atomized powder shown is almost spherical, and the crystal grain diameter of the powder has also increased. As stated later, this powder is more decarburized than before annealing.

According to a study of the cross section of a respective powder particle, which in 5 schematically, inside the powder particle, a crystal grain boundary (a broken line L1 in FIG 5 ). In particular, several crystal grains have been bonded together to form a single particle. Therefore, the inventors of the present invention carried out an image analysis by photographing a cross section of the powder and comparing the following two sizes to compare the powders prepared by the different production methods. Degree of spheroidization = length of the powder perimeter / area of the powder Crystal grain degree = length of crystal grain boundary / area of crystal grain

Here, the term "length of the powder periphery" is understood to mean the length of an outer circumference of a particle in cross section (the length in 5 indicated by a thick line L2). The area inside the outer circumference represents the "area of the powder." According to the above expression, if the value of the "spheroidization degree" is smaller, the shape of the particle is closer to a spherical shape. Further, the term "crystal grain boundary length" means the length of an outer circumference of a crystal grain, ie, the length of the crystal grain boundary L1 and an outer circumference surrounding a grain, in a cross-sectional view, and the surface area surrounded by the crystal grain boundary and the outer circumference represents the "area of the crystal grain boundary crystal grain. " If a value defined by the above expression is smaller, the crystal grain diameter is larger, making it clear that the grains have become larger. In this embodiment, by the treatment steps (2) and (3), a powder approximated to a spherical shape and including larger crystal grains could be obtained.

Thereafter, in the coating treatment step (4), the powder obtained in step (3) is subjected to silicone resin coating. In the compacting step (5), the magnetic metal powder thus obtained is densified by using a mold. Subsequently, in the heating treatment step (6), a heating operation is carried out. In this treatment, the temperature is preferably set at 750 ° C or less. If it is exceeded, destruction of a SiO ₂ -coated layer generated from the silicone resin in the coating treatment step (4) may occur. The ground core fabrication steps are completed as indicated above. The step (1) corresponds to the conventional water atomization method. Steps (4) through (6) are identical to the conventionally generally performed steps for the bulk core fabrication.

According to the Manufacturing process of this embodiment is the water-atomized Powder which has an irregular shape and is largely different, before the coating treatment a jet mill treatment and annealing treatment subjected. Accordingly, the powder particles become spheroidized and their crystal grain diameter above enlarged. Further, in the annealing treatment reduces the carbon content contained in the powder. The through Use of such a powder shaped mass core can be reduced Have hysteresis loss. In the jet mill treatment (2) the powder could not be spheroidized be like the gas atomization process, and thus kept the powder particles up their irregular shape to a degree. Consequently, the particles go through in the Use of this powder shaped earth core a strong connection one another, so that they have a satisfactory strength exhibit.

<Example>

below an explanation of an example of the present embodiment. In this example was used an Fe-Si material as a raw metal and by the water atomization method pulverized (step (1)). The particle diameter of the powder was about 75 to 350 microns. With the help of a through The company NPK manufactured jet mill became the jet mill treatment under conditions at an air pressure of about 0.6 MPa (Step 2)). This treatment time is preferably 30 minutes or more and 60 minutes or less.

A cross section of the powder prepared as described above was photographed and subjected to image analysis to calculate the degree of spheroidization (length of the powder / surface area of the powder particle) of the powder. The spheroidization degree was compared with respect to the jet mill treatment time. The resulting result is in 6 shown. In the present example, a change in the spheroidization degree corresponding to the jet mill treatment time is 6 indicated by a solid line. 6 shows that a powder in the lower region more closely approximates a spherical shape than another powder. As can be seen from this figure, the degree of spheroidization of the powder which had not been subjected to jet mill treatment was about 0.053, whereas the powder subjected to a 60 minute jet mill treatment had a value of about 0.044.

It turns out in other words that the powder through the jet mill treatment is spheroidized. In this figure, a dashed line represents the degree of spheroidization (about 0.04) of the gas atomizing process Powder. The spheroidization of the by the water atomization process and the jet mill treatment obtained powder did not reach the value of that obtained by the gas atomization method Powder.

Further, the powder subjected to the jet mill treatment was subjected to the annealing treatment (step (3)). In this example, the annealing treatment was carried out under vacuum at 1100 ° C for 3 hours. As in 7 is shown, while the crystal grain was increased. Here, the cross sections of each particle produced were photographed and subjected to image analysis. Based on the resulting result, the crystal grain degree (length of the crystal grain boundary / surface area of the crystal grain) was calculated. In 7 is a lower area for a larger crystal grain. More specifically, the powder that has undergone water atomization and then annealing has a larger grain size than the water atomized powder. If the powder had additionally been subjected to the jet mill treatment before the annealing treatment, its crystal grain diameter would have been further increased.

A change in the carbon content contained in the powder subjected to the jet mill treatment and the annealing treatment was examined. The amount of carbon per se contained in the water-atomized powder is about 0.014% by weight. The proportion of carbon in the powder after the jet mill treatment and the annealing treatment was examined at a changed jet mill treatment time. The resulting result is in 8th shown. That is, in the case where only the vacuum annealing treatment was performed without the jet mill treatment (which corresponds to a jet mill treatment time of 0 minutes in the figure), the content of the carbon was reduced to about 0.0045% by weight. Further, when the jet mill treatment was carried out for a period of 30 minutes or more and then the vacuum annealing treatment, the carbon content was reduced to about 0.0013% by weight.

In The coating treatment step (4) was 0.2 to 0.5% by weight. Added silicone resin, stirred in and dried. In the compaction step (5), a molding operation was performed at a surface pressure from 1200 to 1600 MPa performed by a compaction process, in which a mold wall is heated and provided with lubricant becomes. In the subsequent heating treatment step (6) The heating treatment was in a nitrogen atmosphere Run at 600 to 750 ° C for 30 minutes. The molding compound core of the present example was then as above specified manufactured.

<comparison between the present example and a comparative example>

A comparison test was made on the present example and various comparative examples. First, the hysteresis loss between test pieces made of four types of powders, namely, the present example in which the water atomized powder was subjected to the jet mill treatment and the annealing treatment, and the three comparative examples, ie, the gas atomized powder, the atomized atomized water atom, and the water-atomized powder which had only been subjected to jet mill treatment. Accordingly, the above steps (4) to (6), by using these four types of powders to produce annular test pieces T, as shown in FIG 10 is shown. Here, a respective test piece T having an outer diameter of 39 mm, an inner diameter of 30 mm and a thickness of 5 mm was produced.

On each test piece T, an exciting coil and a detection coil were wound. To measure hysteresis loss, a BH curve was acquired using a DC BH analyzer. The resulting result is in 9 shown. The test piece T made of the powder of the present example had the second lowest hysteresis loss after the test piece T made of the gas atomized powder. This value turned out to be unproblematic when using the test piece.

Subsequently, various types of test pieces T were compared with each other in terms of their strength. As stated above, for the comparison, the test pieces T were prepared by using the powder of the present embodiment, the gas-atomized powder and the sputtered powder in the atomized state. These were subjected to a strength test. As a strength test, a compression test was carried out in the radial direction by placing a respective test piece T vertically on a flat plate, as in 10 is shown, wherein exerted on a respective test piece T a pressure in the diametrical direction and the destruction inducing pressure was measured. The resulting result is in 11 shown. The test piece T made of the powder of the present example had a strength nearly equal to the test piece made of the water-atomized powder. This value turned out to be unproblematic when using the test piece.

For example, a motor core may be made such that a plurality of ground cores, each in correspondence to those in FIG 1 have shown shape, arranged in a ring shape and connected by shrink fit or the like. When the mass cores are connected together in such a ring shape, a maximum stress acts at the boundary between the yoke and the tooth of a respective core molding mass. Accordingly, there is a fear that cracking may occur in such a place in a compacted core having low strength. In view of the cycling thermal cycling that occurs when the ground core is installed in a motor and actually operated, the strength of such a ground core needs to be increased. In the case of a compression-molded core with insufficient strength, destruction or removal of material can take place at the edge region if the core of the pressed-material core is installed. According to the manufacturing method of the present embodiment, a molding compound core having a satisfactorily high strength can be produced without causing the defects mentioned above.

As has been described in detail above, in the mass-core manufacturing process In the present embodiment, the water-atomized Powder, the jet mill treatment and the annealing treatment is used as raw powder used. The jet mill treatment increased the spheroidization degree of the magnetic powder particles. About that In addition, the annealing treatment provides for an enlargement of the crystal grain and a reduction of the carbon content. Accordingly, can by applying these treatment methods a mass nucleus with a satisfactorily low hysteresis loss. In addition, the degree of spheroidization of a each particle is not excessive to, and thus can a mass core with sufficient strength getting produced. Consequently, a manufacturing method for a mass core with a sufficiently low hysteresis loss and a sufficiently high strength.

The The above embodiment is only an example and not a limitation of the present invention. The present invention may therefore be understood in other specific forms be executed without their essential features departing. For example, the shape of the ground core is in the figure by way of example and the invention is not limited to the same. The term "water" in the water atomization process and water-atomized powder is not alone on pure water limited but may conveniently also contain a mixture that is in a sputtering process is generally used. The annealing treatment can also in an inert atmosphere, such as In nitrogen, rather than under vacuum become.

Summary

Process for the preparation of a magnetic powder and method for producing a molding compound core

A method for producing a magnetic powder, which in terms of Ummagnetisierungsverluste, such. Iron loss and hysteresis loss, is sufficiently reduced and has sufficient strength; and a method for producing a ground core. The method for producing a magnetic powder includes using a sputtered powder of a magnetic material as a raw powder and applying spheroidization to the powder; wherein mechanical forces are applied to the powder to spheroidize the powder particles. After spheroidization, the powder is subjected to a grain enlargement treatment in which the powder is annealed at a temperature not lower than the austenite transformation point. The ground core manufacturing method comprises compacting the magnetic powder thus produced.

20

Dust core

step (2)

Jet mill treatment step

step (3)

annealing step

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - JP 8-37107 A [0002]
• JP 7-245209 A [0002]

Claims (4)

Process for producing a magnetic powder by a water atomization method, wherein that through a water atomization produced magnetic powder as a Raw powder is used, and a spheroidization treatment is performed by mechanical forces The powder may be applied to a form of powder spheroidizing. Magnetic powder production method according to claim 1, where a grain enlargement treatment is carried out by after the spheroidization treatment the powder is annealed at a temperature greater than or equal to is equal to an austenite transformation point. Method for producing a ground core by compacting a magnetic powder, wherein that by water atomization produced magnetic powder is used as a raw powder, and a Spheroidization treatment is performed by before compressing mechanical forces on the powder be applied to spheroidize a form of the powder. Magnetic powder production method according to claim 3, where a grain enlargement treatment is performed by after the spheroidization treatment, however, before compacting, the powder is annealed at a temperature which is greater than or equal to an austenite transformation point is.