JP2019062085A - Dust core and method of manufacturing the same - Google Patents

Abstract

To provide a dust core excellent in strength, in which the occurrence of cracking and chipping is suppressed, and a method of manufacturing the same.SOLUTION: The dust core is provided that is constituted using particles of an Fe-based alloy and formed by bonding particles through an oxide layer. The dust core is formed in a columnar body or a cylindrical body and has a length dimension larger than an outer diameter dimension. The dust core includes at the end part, a tapered part which is formed of a worked surface, the tapered part is equipped with a striation in a direction along an axial direction, and the entire surface of the dust core is a sintered skin. The striation of the tapered part is formed by grinding, and the surface of the dust core is covered with an oxide derived from the Fe-based alloy.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cylindrical or cylindrical dust core provided with a tapered portion tapering to an end, and a method of manufacturing the same.

  2. Description of the Related Art An electronic device such as a smartphone or a tablet adopts an input unit that allows a user to easily input operation information and character information. As such input means, there is a position detection device configured by combining a pen-type device for specifying a position and a device called a sensor substrate for detecting the position.

  For example, in the position detection device disclosed in Patent Document 1, a pulse signal is applied from a coil provided in a pen-shaped device to a sensor coil group in each of the X-Y directions provided on the sensor substrate side, and the principle of electromagnetic induction. The position information of the XY coordinates is obtained by the electromotive force generated in the coil group at. In the electronic device, a sensor substrate is provided at the lower part of the display panel, and information such as information displayed on the display can be interlocked with the position information by various software to facilitate information input to the electronic device. There is.

  In a pen-type device used for such a position detection device, a columnar magnetic core is disposed at the air core portion of the coil so as to enhance coupling with the coil group on the sensor substrate side and to improve the accuracy of position information. An inductance element is used. FIG. 10 shows the internal structure of a pen-type device used in the position detection device described in Patent Document 1. As shown in FIG. In this pen type device, a cylindrical ferrite core is adopted as the magnetic core. A ferrite core 506 in which a coil 509 is wound is housed inside the housing 501. In the illustrated configuration of the ferrite core 506, the tip end portion 507 is reduced in diameter in accordance with the internal structure of the housing 501 and formed in a tapered shape. The ferrite core 506 is cylindrical, and a switch rod 502 whose tip is covered with a cap-like cover is slidably passed through the hollow portion. The rear end side of the ferrite core 506 is passed through the support 508 and fixed in the housing 501. Further, the rear end of the switch rod 502 is connected to an operation switch 505 fixed to the circuit board 511.

Japanese Patent Application Publication No. 08-050535

  A magnetic core such as that used for a pen-type device is a thin shaft and has an elongated shape whose length is longer than its diameter. In order to be contained in the housing, for example, the small diameter of 5 mm or less, the thin thickness of 1 mm or less, and the length of 10 mm or more. Therefore, a strength that does not easily break even when an impact is applied by a drop or the like is required, but a ferrite core generally has a side of being vulnerable to an impact because it is easily fragile. In particular, since the tapered tip portion is thin, there is a problem that it is easily affected.

  Therefore, an object of the present invention is to provide a dust core having excellent strength and suppressing occurrence of cracking and chipping as a magnetic core replacing a ferrite core, and a method of manufacturing the same.

  The first invention is composed of particles of an Fe-based alloy, is a cylindrical body or cylindrical body, has a large axial length with respect to the outer diameter, and has a tapered portion at its end. The tapered portion is provided with streaks in a direction along the axial direction, and the entire surface is a dust core having a sintered skin.

  Preferably, the surface of the dust core of the present invention is covered with the oxide derived from the Fe-based alloy, and an oxide derived from the Fe-based alloy is present between the particles.

  In the second invention, a forming step is performed by using particles of an Fe-based alloy to form a cylindrical or cylindrical body into a green body having a large axial length relative to the outer diameter, and the above-mentioned green body Including a chamfering step of centerless grinding to form a tapered portion with streaks at the end by tapering at the end, and a heat treatment step of heat-treating the formed body after the chamfering step in an atmosphere containing oxygen, In the chamfering step, the streaks are formed in a direction along the axial direction of the formed body, and in the heat treatment step, the surface of the dust core is covered and the oxidation derived from the Fe-based alloy bonding the particles together It is a manufacturing method of a dust core which forms a thing.

  ADVANTAGE OF THE INVENTION According to this invention, it is excellent in intensity | strength and can provide the powder magnetic core which suppressed generation | occurrence | production of a crack and a chip | tip as a magnetic core replaced with a ferrite core, and its manufacturing method.

It is a flowchart for demonstrating the process of the manufacturing method of the powder magnetic core which concerns on one Embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a general view which shows an example of the centerless grinding apparatus used for the manufacturing method of the dust core of this invention. It is a principal part enlarged view of XY cross section for explaining the centerless grinding device shown in Drawing 2 in detail. It is an enlarged view of the BB cross section of the principal part of the centerless grinding apparatus shown in FIG. It is a figure for demonstrating the method of centerless grinding in the manufacturing method of the powder magnetic core which concerns on one Embodiment of this invention. It is a figure which shows the state of the molded object accommodated in the groove part in the centerless grinding apparatus shown in FIG. It is the figure which extracted and showed the workpiece feeder and the carrier guide in the centerless grinding apparatus shown in FIG. They are a perspective view (a) of a dust core produced with a manufacturing method of a dust core concerning one embodiment of the present invention, and a sectional view (b) cut in the direction of an axis. It is an enlarged view of the taper part of the dust core shown in FIG. It is a sectional view showing an example of composition of a pen type device in which a ferrite core is used.

  Hereinafter, although the manufacturing method of the powder magnetic core which concerns on one Embodiment of this invention, and the powder magnetic core obtained by it are demonstrated concretely, this invention is not limited to this, The technical idea It can be suitably changed within the range. In the drawings used for the description, main parts are mainly described so that the gist of the invention can be easily understood, and the details are appropriately omitted. Further, the configuration of the diagram may be described using operation / functional expressions for easy understanding, but it is not uniquely limited, and may include other operations or functions.

  FIG. 1 is a flow chart showing a method of manufacturing a dust core according to the present invention. In the present invention, a cylindrical or cylindrical shaped body is obtained from the powder of the Fe-based alloy in the forming step S1, and the end face of the shaped body is ground by centerless processing in the chamfering step S2 to form a tapered shape. . Next, heat treatment is performed at a predetermined temperature and condition in an atmosphere containing oxygen in a heat treatment step S3 to prepare a cylindrical or cylindrical powder magnetic core whose surface is substantially as sintered skin. Here, the shape of the dust core may be a shape that can be rotated by centerless grinding, which will be described in detail later, but it is preferable that the shape is a cylindrical shape or a cylindrical shape.

  The Fe-based alloy is preferably at least one of FeSiCr alloy, FeSiAl alloy, FeAlCr alloy, and FeAlCrSi alloy. These Fe-based alloys include Al (aluminum), Cr (chromium), and Si (silicon) which are non-ferrous metals having a greater affinity for Fe (iron) and O (oxygen) than Fe, and the Fe-based alloys thereof. The elements constituting the alloy form an oxide in a heat treatment step described later to cover the surface of the dust core and bond the particles of the Fe-based alloy. As a result, the dust core after the heat treatment step becomes excellent in strength.

  The particles of the Fe-based alloy used in the present invention are preferably fine particles having an average particle diameter of 1 to 100 μm in median particle diameter d50 in cumulative particle size distribution, and the atomizing method (water atomizing method or gas atomizing method) Etc.) is preferred, and in particular, water atomization is preferred because it is easy to obtain small diameter particles. The small average particle diameter improves the strength of the dust core, reduces the eddy current loss, and improves the core loss. The above-mentioned median diameter d50 is more preferably 30 μm or less, still more preferably 20 μm or less. On the other hand, when the average particle diameter is small, the magnetic permeability tends to be low, so the median diameter d50 is preferably 5 μm or more.

  According to the water atomization method, a raw material weighed to have a predetermined alloy composition is melted by a high frequency heating furnace, or an alloy ingot manufactured to have an alloy composition in advance is melted by a high frequency heating furnace The molten metal (hereinafter referred to as "molten metal") is made to collide with water jetted at high speed and high pressure, whereby it is cooled together with fine graining to obtain a powder of an Fe-based alloy. It is preferable to classify the particles of the obtained Fe-based alloy according to the particle size, and to remove particles with large particle diameter. It is preferable to use sieving classification etc. as a classification method. Further, particles having different particle sizes may be mixed and used.

  In the forming step S1, it is possible to employ a method of dry-forming granules in which particles of an Fe-based alloy are aggregated particles of an appropriate size suitable for forming. In dry forming, granules (also called formed particles) in which particles of an Fe-based alloy are formed into agglomerated particles of a suitable size for forming, are filled by pressing the granules into a mold, pressed and compressed. It is a method of obtaining a shaped body. In order to make the tip end portion tapered by molding, it is preferable to use a cylindrical or cylindrical molded body, since it is difficult for the granules to be filled in the tapered portion at the end and the molding density is likely to be uneven. In the forming step S1, in addition to dry forming, for example, a water-soluble binder such as methyl cellulose is added to a powder of an Fe-based alloy, and kneaded by a high shear kneader such as a Banbury mixer or mixing roll It is also possible to adopt a method of extruding the clay as the clay.

  Preferably, the granules are prepared (also referred to as granulation) such that particles of a plurality of Fe-based alloys are bound by an organic binder. The organic binder binds the granules together in pressure molding, and gives the molded body a strength that can withstand handling and processing after molding. Although the kind of binder is not specifically limited, For example, various organic binders, such as polyethylene, polyvinyl alcohol, an acrylic resin, can be used. The amount of the binder to be added may be a sufficient amount among the particles of the Fe-based alloy, and it may be an amount that can ensure a sufficient molded body strength, but if the amount is too large, the density and the strength tend to decrease. The amount of the binder added is preferably 0.2 to 10 parts by weight with respect to 100 parts by weight of the powder of the Fe-based alloy, for example.

As a granulation method, for example, a wet granulation method such as rolling granulation or spray drying granulation can be adopted. Among them, spray drying granulation using a spray drier is preferable. According to this, the state of the obtained granules is close to a spherical shape, and the time of exposure to heated air is short, and a large amount of granules can be obtained. The obtained granules preferably have a bulk density of 1.5 to 2.5 g / cm ³ and an average granule diameter (d50) of 60 to 150 μm. According to the granules composed of the powder of the Fe-based alloy configured in this way, the formed body is excellent in fluidity at the time of molding, and it is difficult for a gap to be generated between particles to increase the filling property into the mold. A high density magnetic core having a high permeability can be obtained after heat treatment.

  Further, in order to reduce the friction between the powder during molding and the molding die, it is preferable to add a lubricant such as stearic acid or a stearate. The amount of the lubricant added is preferably 0.1 to 2.0 parts by weight with respect to 100 parts by weight of the Fe-based alloy powder.

The above-mentioned granules are pressure-formed into a predetermined shape using a molding die. The particles of the Fe-based alloy after forming are in point contact or surface contact with each other through a binder or a natural oxide film, and partially adjacent to each other through an air gap. For pressure forming, a press machine such as a hydraulic press or a servo press is used. The flowability of the granules in the mold can be improved by the shape of the alloy particles, the shape of the granules, the selection of their average particle diameter, and the effects of the binder and the lubricant. Moreover, the powder of the above-mentioned Fe-based alloy can obtain a sufficiently high molding density and a radial crushing strength of a molded product even when molding is performed at a low molding pressure of 1 GPa or less. The molding density is preferably 5.7 × 10 ⁻³ kg / m ³ or more, more preferably 5.95 × 10 ⁻³ kg / m ³ or more, but according to the granules of such Fe-based alloy, low pressure molding is possible. Even if there is, good molding density can be easily obtained. The radial crushing strength of the molded body is preferably 3 MPa or more. The molding may be performed at room temperature, or may be performed warmly by heating the granules to around the glass transition temperature at which the binder softens, depending on the material of the binder, to the extent that the binder does not disappear.

  Next, the chamfering step S2 will be described. In the chamfering step S2, the end of the cylindrical or cylindrical molded body is processed into a tapered shape by grinding. It is preferable to employ centerless grinding. When a compact is chucked as a workpiece using a cylindrical grinder and the tapered portion at the end is ground, the compact is susceptible to cracking or chipping during chucking, but there is no such risk in centerless grinding.

  Hereinafter, a configuration example of the centerless grinding apparatus will be described. FIG. 2 is an overall view of a centerless grinding apparatus used in the method of manufacturing a dust core according to the present invention. Moreover, the principal part enlarged view of a centerless grinding apparatus is shown in FIG. Moreover, the enlarged view which looked at the principal part of the centerless grinding apparatus shown in FIG. 3 from the other direction in FIG. 4 is shown. FIG. 5 is a figure for demonstrating the method of centerless grinding in the manufacturing method of a dust core. FIG. 6 is a view showing the state of the compact stored in the groove portion of the work feeding portion in the centerless grinding apparatus. FIG. 7 is a view showing the carrier guide and the workpiece feeder.

  As shown in FIG. 2, the centerless grinding apparatus 200 includes, as its main components, a work feed unit 210 and a work grinding unit 220 disposed on a base 250. The workpiece feeding unit 210 includes a cylindrical carrier guide 104, a workpiece feeder 101 disposed inside the carrier guide 104, and a workpiece holder 102 for facing the workpiece feeder 101 and supporting a workpiece (formed body). . The workpiece feed wheel 101 is disposed so that the X axis in FIG. 2 is the rotation axis, and is connected to drive means 260 including a servomotor and the like. Further, the carrier guide 104 is provided with slits 109 at a predetermined pitch, and the outer peripheral surface of the workpiece feeder 101 forms a plurality of groove portions 16 for accommodating the molded body. The workpiece grinding unit 220 includes a grinding stone 100 which is disposed so that the Z axis in FIG. 2 is the rotation axis and is connected to a driving unit such as a servomotor (not shown).

  The workpiece feeder 210 is mounted on the base 250 via the movable bed 230. The movable bed 230 is composed of a plurality of slide members, and in FIG. 2, the work feeding unit 210 is slidable in the XZ plane, and the positional relationship with the grindstone 100 can be adjusted.

  The main structural portion of the centerless grinding apparatus will be described using FIGS. 3, 4 and 7. 3 is an enlarged view of a cross section obtained by cutting the A-indicator in FIG. 2 in the X direction passing through the rotation axis of the workpiece feeder, and FIG. 4 is a cross section of the centerless grinding apparatus as viewed from the B-B direction in FIG. It is an enlarged view. FIG. 7 is a perspective view of the workpiece feeder and the carrier guide.

  The rotational axis of the grinding wheel 100 is positioned below the rotational axis of the disk-like workpiece feeder 101 that provides a rotational force for the molded body 10 to rotate. In the illustrated example, the rotational axes of the grinding wheel 100 and the workpiece feed wheel 101 are substantially orthogonal to each other. The term "orthogonal" as used herein is not a geometrically strict orthogonal state, but also includes the case of having an inclination of about 2 degrees to 3 degrees.

  A cylindrical carrier guide 104 provided with a comb-like slit 109 opening toward the grindstone 100 is disposed so as to cover the outer periphery of the workpiece feed wheel 101. The slit 109 of the carrier guide 104 and the outer periphery of the workpiece feeder 101 constitute a groove portion 16 capable of containing the formed body 10, and the carrier guide 104 has the same direction as the workpiece feeder 101 and a slower speed than the workpiece feeder 101. Rotate at.

  Below the workpiece feed wheel 101, a workpiece holder 102 facing the circumferential surface is installed. In the illustrated example, the work presser 102 is fixed and has an arc-shaped surface substantially concentric with the outer peripheral surface of the work carriage 101, and the distance between the work carriage 101 and the work presser 102 is the work feed. The diameter of the molded body 10 disposed in the groove 16 of the portion 210 is set to be approximately equal.

  The grindstone 100 is rotating in the direction of the arrow shown in FIG. The rotational direction of the grindstone 100 is set such that the grinding force acts in the direction of pushing the formed body 10 to the work stopper 103 side. Although the details will be described later, the formed body 10 is chamfered by the grindstone 100 while being rotated by the rotational force applied to the outer periphery of the workpiece feed wheel 101.

  The molded body 10 disposed one by one in the groove portion 16 from a supply device (not shown) rotates on its one end face in contact with the work stopper 103, and the other end projecting from the work feeding portion 210 is a grindstone 100. Grinding forms a tapered portion. Since the diameter of the grindstone 100 is sufficiently larger than that of the molded body 10, the angle of the tapered portion is set to the virtual line segment of the molded body 10 in the Y direction in FIG. It is substantially equal to the angle θ formed by the point at which the end contacts the outer peripheral surface of the grindstone 100 and the imaginary line connecting the central point.

  The state where the molded body passes between the workpiece feeder and the workpiece presser will be described with reference to FIG. A part of the outer peripheral surface of the workpiece feed wheel 101 faces the workpiece retainer 102 to clamp the molded body 10. It is preferable that the side of the work pressing member 102 in contact with the formed body is made of a member 108 such as super steel which is excellent in rigidity and wear resistance. Further, in the workpiece feed wheel 101, it is preferable that at least an outer peripheral portion in contact with the molded body is formed of an elastic body such as urethane rubber having appropriate elasticity and frictional resistance. By pressing the formed body 10 against the work presser 102 by the work feed wheel 101, the rotation of the work mover 101 is transmitted to the formed body 10, and it rolls while sliding on the surface of the work presser 102, so that the formed body 10 While rotating in a direction opposite to that of the workpiece feed wheel 101, it moves in an arc-shaped space between the workpiece feed wheel 101 and the workpiece holder 102. The rotational speed of the carrier guide 104 is sufficiently slower than that of the workpiece feeder 101, for example, it is rotated so as to be 1/2 or less, and the workpiece 10 stored in the groove 16 of the workpiece feeder 210 is fed. The circumference of the car 101 is forcibly moved at a predetermined speed in an arc-like locus. The state of such movement may be called revolution in the following description in contrast to rotation.

The groove portion 16 of the workpiece feeding unit 210 is preferably formed so as to be inclined at a predetermined angle with respect to the rotational axis direction of the workpiece feed wheel 101. FIG. 6 is a view of the workpiece feeding unit from the lower side of the drawing in the Y axis direction of FIG. The grindstone 100 (not shown) is at the upper side of the figure, and the workpiece feed wheel 101 and the carrier guide 104 are rotating in the right direction of the figure with a predetermined speed difference. For example, when the groove portion 16 is configured such that the grindstone 100 side is inclined to the delay side in the rotational direction, the outer peripheral surface of the molded body 10 is the slit 109 of the carrier guide 104 due to the speed difference between the workpiece feeder 101 and the carrier guide 104. It rotates while contacting the side (left side of the drawing) The molded body 10 receives a force to move forcibly to the work stopper 103 side on the lower side of the drawing by a reaction force from the side surface of the slit 109, and in a state where the molded body 10 is positioned by the end face of the workpiece stopper 103 The tapered portion is formed by grinding. Since the outer peripheral edge of the end of the molded body 10 abuts on the work stopper 103 side, it is desirable to set the component of force toward the work stopper 103 as small as possible so as to prevent the occurrence of cracking and chipping. It is preferable to set to the following inclination angles.
At the tapered portion formed by grinding, streaks are formed along the axial direction of the molded body, including an angular difference about the above-mentioned inclination angle.

  The grindstone 100 is made of, for example, a bonding material such as a metal bond or the like, using, for example, diamond abrasive grains, CBN (cubic boron nitride) abrasive grains, and the like. As shown in FIG. 5, the outer peripheral surface of the outer peripheral surface is an arc shape in which the center is depressed and protruded toward the outer peripheral side, and while the molded body 10 revolves around the workpiece feed wheel 101 and is ground, The end is ground and chamfered in substantially uniform contact with the grinding wheel 100. By centerless grinding of the tapered portion, it is not necessary to chuck the formed body, and it is not necessary to center the mold at the time of fixing, and productivity can be improved.

  Next, the heat treatment step S3 will be described. In heat treatment process S3, the compact after chamfering processing S2 is heat-treated. The heat treatment forms an oxide derived from the Fe-based alloy, and the stress strain introduced into the compact at the time of compression molding can be alleviated to obtain a dust core with good magnetic properties.

    The heat treatment can be performed in the atmosphere or in an atmosphere in which oxygen is present, such as in a mixed gas of oxygen and an inert gas, but heat treatment in the atmosphere is preferable because it is simple.

  The oxide formed by the heat treatment contains an element constituting an Fe-based alloy. For example, in the case of a FeSiCr alloy, Fe, Si and Cr are contained, and in the case of a FeAlCrSi alloy, Fe, Al, Cr and Si are contained. The oxide formed by the heat treatment is self-generated by the oxidation of the particle surface of the Fe-based alloy, and is formed in a layer form so as to fill the voids between the particles of the Fe-based alloy, and bonds the particles. As a result, the strength of the powder magnetic core after the heat treatment becomes significantly higher than that of the compact. In addition, it is possible to improve the impact resistance of the magnetic core without causing brittle fracture as in the case of a ferrite core. The average thickness of the oxide between the two particles is preferably 100 nm or less, and more preferably 30 to 80 nm.

    The temperature of the heat treatment is preferably set to a temperature at which the formed body becomes 700 ° C. or higher, from the viewpoint of forming the above-described oxide while relaxing the stress strain of the particles of the Fe-based alloy. If the temperature is less than 700 ° C., the removal of stress and strain and the formation of an oxide layer may be insufficient, and a desired strength and specific resistance may not be obtained. When the heat treatment temperature becomes 850 ° C. or more, the particles of the Fe-based alloy are in direct contact with each other, and the part (neck part) where they are partially connected increases, thereby further improving the strength. On the other hand, if the temperature of the heat treatment exceeds 950 ° C., the magnetic properties of the dust core may be affected, and the preferable temperature of the heat treatment is 700 ° C. to 950 ° C. In the heat treatment, the holding time is appropriately set depending on the size of the molded product, the processing amount, the allowable range of the characteristic variation, and the like, and is preferably 0.5 to 3 hours.

  Fig.8 (a) is a perspective view which shows an example of the powder magnetic core obtained by heat processing, (b) is sectional drawing of the axial direction. The dust core is formed in a cylindrical shape having an outer peripheral portion 11 and an inner peripheral portion 12, and the length in the axial direction is about 6 times longer than the outer diameter dimension. A tapered portion 13 formed by grinding processing of a formed body in the chamfering step S2 is provided on the end portion 14a side of the outer peripheral portion 11.

  As shown in the enlarged view of the tapered portion in FIG. 9, by subjecting the compact to grinding processing, processing marks (tool marks, wheel marks) remain on the processing surface of the tapered portion 13 of the dust core. The circumferential surface of the grinding stone 100, which is sufficiently larger than the processing surface, is pressed against the end of the powder magnetic core that rotates, so that substantially linear streak-like processing marks (striations) are cut on the processing surface of the tapered portion 13. . The streaks are marks extending radially from the axis of the dust core. Since the streaks are formed in the tapered portion, they are formed substantially in the direction along the axial direction although the angle is slightly different from the axial direction of the dust core.

  By grinding to a compact, the particles of the Fe-based alloy on the machined surface are in a state in which the alloy phase inside is exposed, but after the heat treatment step, the entire outer periphery 11 and inner periphery 12 of the dust core are oxidized. Since it is covered with an object, there is no exposure of the alloy phase by processing. In the present invention, the state of the surface of such a dust core is referred to as sintered skin. While the insulating property is secured by covering the exposed alloy phase with the oxide, the processing mark formed on the compact is covered with the oxide, so that the processing mark is formed at the end of the thin powder magnetic core. It is possible to suppress the occurrence of chipping and cracking that are derived, improve the resistance to a drop impact, and make up for the reduction in mechanical strength of the tapered portion.

A winding can be applied to the obtained dust core to form an inductance element. The conducting wire used for the winding is not particularly limited, but, for example, even if an enameled wire in which a copper wire is coated with polyamideimide, a stranded wire such as a litz wire, or the like is used to improve the Q factor at high frequencies of the inductance element. good. The number of turns of the conducting wire can be appropriately set based on the required inductance, and the wire diameter can be appropriately selected by the current to be supplied. The powder magnetic core may be directly wound, but if the specific resistance is relatively low, for example, less than 10 ³ Ω · m, polyphenylene sulfide, liquid crystal polymer, polyethylene terephthalate, polybutylene A bobbin made of a resin of terephthalate may be used.

  According to the present invention, the tapered portion formed on the end side of the dust core is formed by centerless grinding, so that it is possible to form with high efficiency without requiring special skill and without the possibility of human error. I assume. The oxide formed by the heat treatment secures the insulation property, improves the impact resistance, and has the excellent practical effect of suppressing the occurrence of cracking and chipping.

DESCRIPTION OF SYMBOLS 10 Molded object 11 Outer peripheral part 12 Inner peripheral part 13a, 13b, 13c Tapered part 14a, 14b End part 80 Dust core 101 Workpiece feed wheel 102 Workpiece presser 103 Work stopper 104 Carrier guide 105 Belt part

Claims (3)

Composed of particles of Fe-based alloy,
A cylindrical or cylindrical body, the axial length of which is larger than the outer diameter,
A dust core having a tapered portion at an end portion, the tapered portion having streaks in a direction along the axial direction, and the entire surface being a sintered skin. A dust core according to claim 1, wherein
A dust core, wherein a surface of the dust core is covered with the oxide derived from the Fe-based alloy, and an oxide derived from the Fe-based alloy is present between the particles. Forming a cylindrical or cylindrical body using iron-based alloy particles as a molded body having a large axial length relative to the outer diameter,
Chamfering a centerless grinding of the formed body to form a tapered portion having a streak-like trace by grinding at a tapered end at the end;
Including a heat treatment step of heat treating the formed body after the chamfering step in an atmosphere containing oxygen,
In the chamfering step, the streaks are formed in a direction along the axial direction of the molded body,
In the heat treatment step, a dust core covering the surface of the dust core and forming an oxide derived from the Fe-based alloy that bonds the particles.

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