Shaped part manufactured from soft magnetic iron-based powder and manufacturing method thereof

Abstract

According to the present invention, provided are a shaped part manufactured by sintering soft magnetic iron-based powder, and a manufacturing method thereof. According to an embodiment of the present invention, provided is a shaped part manufactured by sintering soft magnetic iron-based powder, wherein 90% or more of the soft magnetic iron-based powder has an average particle size of 150 to 400 ㎛, and 10% or less of the soft magnetic iron-based powder has an average particle size of 50 ㎛ or less. The shaped part may be a stator core of a linear motor.

Description

Molded parts manufactured from soft magnetic iron powder and method for manufacturing the same

[0001] The present invention relates to a sintered part manufactured from a soft magnetic iron powder and a method for manufacturing the same.

[0002] Magnetic materials are classified into soft magnetism and hard magnetism. Soft magnetism is magnetized only when a magnetic field is applied and loses its magnetism when the field is removed, whereas hard magnetism, once formed, remains permanent. Soft magnetism is used when energy loss from AC electromagnetic waves must be minimized.

[0003] Soft magnetic materials are used to manufacture various soft magnetic components, including stator and rotor components of motors and inductors, actuators, sensors, and transformer cores. A compressor, a device containing soft magnetic components, receives power from a power-generating device such as a motor or turbine and operates to compress a working fluid such as air or refrigerant. Types of compressors include linear compressors, rotary compressors, and scroll compressors.

[0004] A linear motor used in a linear compressor generally comprises a stator connected to a cylinder and having a coil wound thereon, and a movable member connected to a piston and capable of linear reciprocating motion through electromagnetic interaction with the stator. The stator includes a cylindrical outer stator and a cylindrical inner stator to be inserted into the outer stator. A movable member is installed between the outer stator and the inner stator so as to be able to move in a linear direction.

[0005] Conventionally, as disclosed in Korean Patent Application Publication No. 10-2006-0117522 (Patent Document 1), multiple electrical steel plates are laminated radially to form an outer stator and an inner stator. This structure has the problem that when the frequency increases due to high-speed operation, a large amount of eddy current flows, which generates heat and reduces motor efficiency. Furthermore, the process of laminating multiple electrical steel plates increases the number of components and the manufacturing time, leading to increased manufacturing costs.

[0006] In this way, conventional soft magnetic components were manufactured by laminating electrical steel plates, but recently, a method has been used to manufacture components by compressing and sintering soft magnetic composites (SMCs) made by coating soft magnetic iron powder with an insulating material at high temperatures together with lubricants or binders. Unlike the two-dimensional method of laminating electrical steel plates, SMCs allow for three-dimensional electromagnetic field design, and their increased design freedom allows for a significant increase in complexity.

[0007] SMC typically exhibits lower core loss and superior magnetic properties compared to laminated electrical steel at high frequencies above 10 kHz. However, below 1000 Hz, the primary operating frequency of motors, SMC exhibits higher core loss than laminated electrical steel. Therefore, reducing core loss in the frequency range below 1000 Hz is crucial for SMC applications in motors and other applications.

[0008] A method of applying an insulating coating to iron powder particles to reduce iron loss is known (e.g., U.S. Patent No. 6,348,265 (Patent Document 2)). This method has disadvantages in terms of the powder manufacturing process and manufacturing cost, as it requires coating a separate insulating material or adding a binder, etc. In addition, there is also the problem of lowering the energy density per unit volume and lowering the saturation magnetic flux because the specific gravity of iron in the material decreases by the thickness of the insulating material on the powder.

[0009] In order to solve the above-described problems, the present invention aims to provide a molded part manufactured from a soft magnetic iron powder having low iron loss in a frequency range of 1000 Hz or less and a method for manufacturing the same.

[0010] In order to achieve the above-mentioned purpose, one aspect of the present invention provides a molded part manufactured by sintering a soft magnetic iron powder, wherein 90% or more of the soft magnetic iron powder has an average particle size of 150 to 400 ㎛ and 10% or less has an average particle size of 50 ㎛ or less.

[0011] The above molded part may be a stator core of a linear motor.

[0012] The above molded part may be a stator core of an axial flux motor.

[0013] The above-mentioned soft magnetic iron powder includes an insulating layer having a thickness of 10 to 50 nm containing Si, Al, Mn, and O on the outer surface, and may include, in wt%, Si: more than 2.0% and 6.5% or less, Al: more than 0.02% and 1.0% or less, Mn: more than 0.05% and 0.6% or less, O: more than 0% and less than 0.1%, and the remainder is Fe and unavoidable impurities.

[0014] According to another aspect of the present invention, a stator core of a linear motor is provided, which is manufactured by sintering a soft magnetic iron-based powder, wherein 90% or more of the soft magnetic iron-based powder has an average particle size of 150 to 400 µm and 10% or less has an average particle size of 50 µm or less.

[0015] According to another aspect of the present invention, a method for manufacturing a sintered part is provided, comprising the steps of: a) preparing a soft magnetic iron-based powder containing Si in an amount of more than 2.0% by weight and less than or equal to 6.5% by weight and including an insulating layer on an outer surface, wherein an average particle size of more than 90% of the soft magnetic iron-based powder is 150 to 400 μm and an average particle size of less than 10% is 50 μm or less; b) compressing the soft magnetic iron-based powder; and c) heat-treating the powder compressed in step b).

[0016] In the above step b), the forming pressure may be 600 MPa or more and 2000 MPa or less.

[0017] In the above step c), the insulation layer can be maintained until the heat treatment temperature is 1000°C or lower.

[0018] The above-mentioned soft magnetic iron powder includes an insulating layer having a thickness of 10 to 50 nm containing Si, Al, Mn, and O on the outer surface, and may include, in wt%, Si: more than 2.0% and 6.5% or less, Al: more than 0.02% and 1.0% or less, Mn: more than 0.05% and 0.6% or less, O: more than 0% and less than 0.1%, and the remainder is Fe and unavoidable impurities.

[0019] According to another aspect of the present invention, a molded part manufactured by the above method is provided.

[0020] According to another aspect of the present invention, a stator core of a linear motor manufactured by the above method is provided.

[0021] According to another aspect of the present invention, a stator core of an axial flux motor manufactured by the above method is provided.

[0022] According to the present invention, a molded part manufactured from a soft magnetic iron powder having low iron loss in a frequency range of 1000 Hz or less can be provided.

[0023] A molded part manufactured from the soft magnetic iron powder according to the present invention can have increased magnetic flux density and reduced eddy current loss.

[0024] By applying a stator core manufactured from a soft magnetic iron powder according to the present invention, motor efficiency can be improved.

[0025] Figure 1 is a flow chart showing a method for manufacturing a sintered part according to the present invention.

[0026] Figure 2 illustrates a conceptual diagram of a part of a linear motor.

[0027] Figure 3 conceptually illustrates an outer stator of a linear motor according to the prior art.

[0028] Fig. 4 illustrates an inner stator core of a linear motor according to the prior art.

[0029] Figure 5 is a conceptual diagram explaining the mechanism by which additional iron loss occurs due to eddy current in a motor core according to a prior art.

[0030] Figure 6 illustrates a conceptual shape of a motor core according to the present invention.

[0031] Figure 7 is a conceptual diagram illustrating the magnetic flux formation characteristics of the outer stator core.

[0032] Figure 8 shows an exploded view of the stator assembly of an axial flux motor.

[0033] Hereinafter, the present invention will be described in more detail.

[0034] The present invention provides a molded part manufactured by sintering a soft magnetic iron powder, wherein 90% or more of the soft magnetic iron powder has an average particle size of 150 to 400 ㎛ and 10% or less has an average particle size of 50 ㎛ or less.

[0035] The present invention also provides a stator core of a linear motor manufactured by sintering a soft magnetic iron powder, wherein 90% or more of the soft magnetic iron powder has an average particle size of 150 to 400 ㎛ and 10% or less has an average particle size of 50 ㎛ or less.

[0036] The present invention also provides a method for manufacturing a sintered part, comprising the steps of: a) preparing a soft magnetic iron powder containing Si and including an insulating layer on an outer surface, wherein an average particle size of 90% or more of the soft magnetic iron powder is 150 to 400 µm and an average particle size of 10% or less is 50 µm or less; b) compressing the soft magnetic iron powder; and c) heat-treating the powder compressed in step b).

[0037] The aforementioned purposes, features, and advantages are described in detail below with reference to the accompanying drawings, so that those skilled in the art can readily practice the present invention. In describing the present invention, detailed descriptions of known technologies related to the present invention will be omitted if they are deemed to unnecessarily obscure the gist of the invention.

[0038] Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. The embodiments of the present invention may be modified in various ways, and the technical spirit of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

[0039] In the drawings, the same reference numerals are used to indicate identical or similar components. In the detailed description, terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are based solely on the orientation or positional relationships shown in the drawings and do not suggest or imply that components must be arranged or operated in a specific orientation or positional relationship.

[0040] The terms "about," "approximately," and "substantially" used in this specification are used to mean a numerical value or characteristic or a value close to the numerical value or characteristic mentioned in the context, and it should be understood that the numerical value or characteristic includes a normal tolerance.

[0041] (Method for producing soft magnetic iron powder)

[0042] Hereinafter, a method for manufacturing the soft magnetic iron powder used in the present invention will be described. The soft magnetic iron powder of the present invention can be manufactured by atomizing liquefied steel to powder it.

[0043] More specifically, the manufacturing method may include a step of solidifying molten steel containing, in wt%, Si: more than 2.0% and 6.5% or less, Al: more than 0.02% and 1.0% or less, Mn: more than 0.05% and 0.6% or less, O: more than 0% and less than 0.1%, and the remainder being Fe and unavoidable impurities, by cooling from 1500°C to 1000°C within 10 minutes, a step of cooling from 1000°C to 900°C or less within 100 minutes, a step of liquefying by heating, and a step of pulverizing by atomizing.

[0044] In the above solidification step, the ratio of the surface area (S) to the volume (V) of the solidified molten steel is 4 cm -1 It may be less than 4 cm. The ratio of S / V is 4 cm. -1If it exceeds , the surface area that reacts with atmospheric oxygen at high temperatures to form a thick oxide layer becomes excessively large. The S / V ratio value is more preferably 0.3 cm -1 Below, more preferably 0.11 cm -1 It may be below. However, considering the liquefaction time, the S / V ratio is 0.08 cm because the solidified molten steel is reheated and liquefied. -1 It is desirable that it be ideal.

[0045] (soft magnetic iron powder)

[0046] According to one embodiment of the present invention, a soft magnetic iron powder comprises, in wt%, Si: more than 2.0% and 6.5% or less, Al: more than 0.02% and 1.0% or less, Mn: more than 0.05% and 0.6% or less, O: more than 0% and less than 0.1%, and the remainder is Fe and unavoidable impurities.

[0047] The Si content may exceed 2.0% by weight, and is preferably 6.5% or less. Si increases the resistivity of the iron-based powder. When the Si content exceeds 2% by weight, the iron-based powder may remain in a ferrite phase during a high-temperature forming process such as sintering, so that the particle size of the powder and the particle size of the powder in the molded part after high temperature and / or high pressure may be almost the same. When the Si content is less than 2% by weight, the particle sizes of the powder and the powder in the molded part may be significantly different. On the other hand, when the Si content is high, the attractive and / or repulsive forces between each element are greatly changed by Si, resulting in a large change in the local range of components of the liquefied molten steel. In other words, when the Si content is high, a problem occurs in which the components vary depending on the particle size of the iron-based powder. In addition, in the iron-based powder of the present invention, it was confirmed that the magnetic properties including investment rate and iron loss were the best when the Si content was about 6.5 wt%, and when it exceeded 6.5 wt%, the magnetic properties rather deteriorated, so it is preferable to limit the upper limit of the content to 6.5%.

[0048] The content of Al exceeds 0.02% by weight, and preferably is 1.0% or less. Al also plays a role in increasing the resistivity of the iron-based powder. In addition, it is more preferable that the content of Al exceeds 0.3% by weight in terms of controlling impurities such as O and S so that the magnetism of the iron-based powder can be improved. Meanwhile, since Al easily combines with O at high temperatures, a problem may occur in which the O content becomes excessively high during the process of manufacturing the iron-based powder. The higher the content of Si compared to the Al content, the more easily the increase in the O content due to Al is suppressed. For this reason, the content of Al is preferably 1.0% by weight or less.

[0049] The content of manganese exceeds 0.05% by weight, and preferably is 0.6% or less. Mn, similar to Si, plays a role in increasing the resistivity of iron-based powder. In addition, manganese is an element that controls impurities in the iron-based powder from minimizing the grain size while forming oxides and sulfides, so that the magnetism of the iron-based powder can be improved. For this purpose, it is preferable to add more than 0.05% by weight. In addition, it is preferable that the content of manganese exceeds 0.2% by weight in order to dissolve oxygen or sulfur in the steel as oxides or sulfides. On the other hand, since an excessively high content of manganese may have a negative effect on magnetism, the content is preferably 0.6% by weight or less.

[0050] The content of O exceeds 0% by weight, and preferably is less than 0.1%. O is a component that continuously increases when going through a high-temperature process during the manufacture of iron-based powder. In the final part formed at high temperature and / or high pressure, the lower the O content, the more advantageous the magnetism. For this purpose, the content of O is preferably less than 0.1% by weight. Meanwhile, O combines with Si, Al, or Mn on the surface of the iron-based powder to form an electrically insulating oxide layer. When an insulating layer containing Si, Al, Mn, and O is formed on the surface of the iron-based powder, it is possible to manufacture a soft magnetic part with reduced iron loss. For this purpose, the content of O is preferably more than 0% by weight.

[0051] The remaining components are iron and unavoidable impurities. Impurities can be unintentionally introduced during the normal manufacturing process, and these impurities are predictable by anyone skilled in the art.

[0052] Impurities may include C, N, S, Ti, Mg, etc. The content of C is preferably limited to less than 0.01 wt%, more preferably less than 0.004 wt%. The content of N is less than 0.01 wt%, more preferably less than 0.004 wt%. The content of S can be limited to less than 0.05 wt%, preferably less than 0.05 wt%, more preferably less than 0.01 wt%, more preferably less than 0.003 wt%. The content of Ti is preferably limited to less than 0.01 wt%. The content of Mg is preferably limited to less than 0.05 wt%.

[0053] The soft magnetic iron powder according to the present invention includes an insulating layer containing Si, Al, Mn, and O on the outer surface. Unlike the conventional technology of forming an insulating layer by coating a separate organic / inorganic insulating material on the iron powder, the insulating layer of the soft magnetic iron powder of the present invention is formed when an oxide layer on the upper part of the molten metal is slowly cooled while being mixed with the powder during powder production.

[0054] In one embodiment, the thickness of the insulating layer may be 10 to 50 nm. If the thickness of the insulating layer is less than 10 nm, the insulating properties may be insufficient, which may increase eddy current loss and lead to increased iron loss. If the thickness of the insulating layer exceeds 50 nm, the amount of oxygen in the steel may increase significantly, which may deteriorate the magnetism.

[0055] (Method for manufacturing sintered parts)

[0056] In order to utilize soft magnetic iron powder as a material for soft magnetic components such as motors, it is important to reduce iron loss in the frequency range below 1000 Hz.

[0057] Iron loss is broadly categorized into hysteresis loss and eddy current loss. Hysteresis loss occurs when a magnetic material is magnetized by changes in the electromagnetic field generated by alternating current. Eddy current loss occurs when an induced current is generated by changes in the electromagnetic field generated by alternating current.

[0058] Typically, hysteresis loss is significant at low frequencies, while eddy current loss accounts for the majority of total iron loss at high frequencies. Conventional iron powders exhibit superior eddy current loss characteristics compared to electrical steel, resulting in lower iron loss above 10 kHz. However, their poor hysteresis characteristics have limited their use below 1,000 Hz.

[0059] Hysteresis loss is proportional to 1 / (√Gs), where Gs is the grain size within the metal, and eddy current loss is proportional to (√Gs). Therefore, in order to reduce iron loss, it is necessary to appropriately control the grain size range. The optimal grain size is also affected by the resistivity of the material, and the larger the resistivity, the smaller the iron loss will be in larger grains. This is related to the fact that materials with high resistivity have reduced eddy current loss. In other words, the higher the resistivity, the lower the iron loss.

[0060] In consideration of these points, according to one embodiment of the present invention, a molded part is manufactured by sintering the soft magnetic iron powder, wherein 90% or more of the soft magnetic iron powder may have an average particle size of 150 to 400 μm, and no more than 10% may have an average particle size of 50 μm or less. By adding no more than 10% of the powder having an average particle size of 50 μm or less, the magnetic flux density can be improved.

[0061] When the average particle size of the soft magnetic iron powder is less than 150㎛, there is a concern that the hysteresis loss may not be sufficiently reduced, and thus the core loss may not be sufficiently reduced in the low-frequency range below 1000Hz. On the other hand, when the average particle size exceeds 400㎛, the eddy current loss increases, and there is a problem that the gap between particles cannot be sufficiently narrowed during molding under conditions such as high temperature and high pressure, resulting in a low density of the manufactured parts. The average particle size may more preferably exceed 200㎛, and under these conditions, the hysteresis loss may be sufficiently reduced, while the eddy current loss generated from each particle may not be large.

[0062] Specifically, Fig. 1 is a flowchart showing a method (100) for manufacturing a sintered part according to the present invention. The method (100) for manufacturing a sintered part includes a step (S110) of preparing a soft magnetic iron-based powder containing Si in an amount of more than 2.0% and less than 6.5% by weight and including an insulating layer on an outer surface, wherein an average particle size of 90% or more of the soft magnetic iron-based powder is 150 to 400 µm and an average particle size of less than 10% is 50 µm or less; a step (S120) of compressing the soft magnetic iron-based powder; and a step (S130) of heat-treating the powder compressed in step S120.

[0063] In the above step S120, the forming pressure is preferably 600 MPa or more and 2000 MPa or less. In the above step S130, residual stress can be removed by performing heat treatment at 900°C or less. Here, the insulating layer of the iron-based powder can be maintained until the heat treatment temperature is 1000°C or less.

[0064] A molded part according to the present invention is manufactured by sintering a soft magnetic iron powder, wherein more than 90% of the soft magnetic iron powder has an average particle size of 150 to 400 μm, and less than 10% has an average particle size of 50 μm or less. The soft magnetic iron powder includes an insulating layer having a thickness of 10 to 50 nm containing Si, Al, Mn, and O on an outer surface, and includes, in wt%, Si: more than 2.0% and 6.5% or less, Al: more than 0.02% and 1.0% or less, Mn: more than 0.05% and 0.6% or less, O: more than 0% and less than 0.1%, and the remainder is Fe and unavoidable impurities.

[0065] A sintered component manufactured by the above method comprises a soft magnetic iron powder containing, in wt%, Si: more than 2.0% and 6.5% or less, Al: more than 0.02% and 1.0% or less, Mn: more than 0.05% and 0.6% or less, O: more than 0% and less than 0.1%, the remainder being Fe and unavoidable impurities, and an insulating layer containing Si, Al, Mn, and O on an interface between the soft magnetic iron powders.

[0066] (Method for manufacturing a stator of a linear motor)

[0067] Hereinafter, as an example of a molded part manufactured from a soft magnetic iron powder, a stator of a linear motor will be described in more detail.

[0068] A linear compressor uses a linear motor to form a linear reciprocating motion of a piston to compress a working fluid, and can improve efficiency by reducing the mechanical loss that occurs in converting rotary motion into linear motion in a conventional rotary compressor.

[0069] Figure 2 illustrates a schematic diagram of a part of a linear motor. The linear motor is largely composed of a stator and a moving member. A permanent magnet is attached to the moving member to generate a reciprocating motion of the piston. The stator is composed of an outer stator and an inner stator. The outer stator includes a ring-shaped outer core and a bobbin provided inside the outer core and having a coil wound therein to form a magnetic field. The outer core is a hollow ring that surrounds the bobbin and serves as a path for the magnetic field. The inner stator includes an inner core arranged with a certain gap inside the outer core, and is fixed to the cylinder block of the linear compressor.

[0070] Fig. 3 conceptually illustrates an outer stator of a linear motor according to the prior art. The outer core (21) is composed of two outer core blocks (21a, 21b) that are divided in half in the longitudinal direction. The two outer core blocks (21a, 21b) are integrally joined by welding (W) on the dividing line of the two outer core blocks (21a, 21b) on the outer side of the outer core (21). Each outer core block (21a, 21b) is formed by stacking a plurality of outer core sheets in a ring shape in the circumferential direction and integrally joining the plurality of outer core sheets stacked in the ring shape by a fastening ring (25).

[0071] Compared to the magnetic field formed in the circumferential direction in a typical rotary motor core, the magnetic field direction in the outer stator of the linear motor is formed in the axial direction to create a linear movement of the moving member. Accordingly, when manufacturing a core using electrical steel plates, the electrical steel plates are laminated in the circumferential direction as illustrated in Fig. 3. In the case of this lamination method, since the electrical steel plates have a constant thickness in the radial direction, a difference occurs between the inner and outer diameters of the core (21), and a part where the core does not wrap the coil occurs on the outer diameter side, which causes a problem in that the cross-sectional area through which the magnetic flux can flow is reduced.

[0072] In a conventional linear motor, the inner core is also manufactured by laminating electrical steel plates in the circumferential direction to form an axial magnetic field, similar to the outer core (see Fig. 4). Even in this case, due to the difference between the inner and outer diameters, a gap exists between the laminated steel plates on the outside, which causes fringing flux to occur, as illustrated in Fig. 5, resulting in additional iron loss due to eddy current.

[0073] In the present invention, by sintering soft magnetic iron powder having excellent magnetic properties and being moldable into a desired shape, a donut-shaped inner core and an outer core are manufactured, thereby solving the problems of the prior art and improving motor efficiency. Fig. 6 illustrates a conceptual shape of the motor core of the present invention, and additional shape changes are possible to minimize magnetic flux formation and loss. In particular, in the case of the outer core, as shown in Fig. 2, a space is formed inside for installing a bobbin, and for this purpose, a method of manufacturing the core separately into upper and lower parts and then joining them can be used. In addition, it is also possible to manufacture the outer core or inner core by dividing it in the circumferential direction depending on the design purpose. In this way, the donut-shaped outer core that wraps the entire bobbin increases the area through which the magnetic flux flows compared to the prior art as shown in Fig. 3. As a result, the desired magnetic flux can be generated even at a low magnetic flux density, thereby improving motor efficiency. The relationship between magnetic flux, magnetic flux density, and cross-sectional area is Φ(magnetic flux) = B(magnetic flux density) x A(cross-sectional area).

[0074] In addition, in the case of the outer stator according to the prior art, as shown in Fig. 7, when magnetic flux is generated, the thicknesses a and b must have the same value to achieve maximum efficiency with respect to the saturation magnetic flux density. In contrast, the donut-shaped core of the present invention can maintain the same area through which the magnetic flux can pass even if the thickness b is reduced. As a result, it is possible to reduce the outer diameter of the outer core or increase the radial size of the inner bobbin. Reducing the outer diameter of the outer core has the effect of reducing the overall size of the compressor. In addition, increasing the bobbin size increases the number of turns, which has the effect of reducing the current for generating the same magnetic flux. As a result, the motor efficiency can be improved.

[0075] A method for manufacturing a stator core of a linear motor of the present invention comprises the steps of: a) preparing a soft magnetic iron-based powder containing Si in an amount of more than 2.0% by weight and less than or equal to 6.5% by weight and including an insulating layer on an outer surface, wherein an average particle size of more than 90% of the soft magnetic iron-based powder is 150 to 400 μm, and an average particle size of less than or equal to 10% is 50 μm or less; b) compressing the soft magnetic iron-based powder; and c) heat-treating the powder compressed in step b). In step b), a molding pressure may be 600 MPa or more and 2000 MPa or less. In step c), residual stress is removed through heat treatment at 900°C or less, and the insulating layer may be maintained until the heat treatment temperature is 1000°C or less.

[0076] The above-mentioned soft magnetic iron powder includes an insulating layer having a thickness of 10 to 50 nm containing Si, Al, Mn, and O on the outer surface, and includes, in wt%, Si: more than 2.0% and 6.5% or less, Al: more than 0.02% and 1.0% or less, Mn: more than 0.05% and 0.6% or less, O: more than 0% and less than 0.1%, and the remainder is Fe and unavoidable impurities.

[0077] The iron loss of the soft magnetic core manufactured in this way is 140 W / kg or less at 1 T, 1000 Hz, the magnetic flux density at 50 Hz, 10000 A / m exceeds 1.1 T, and the resistivity exceeds 40 μΩ·cm.

[0078] Using the above method, compared to manufacturing a motor core by laminating electrical steel plates, it is possible to manufacture a core that wraps the entire bobbin. This improves motor efficiency, while the characteristics of the soft magnetic powder reduce eddy current generation, reducing iron loss in the high-frequency range, enabling further efficiency gains.

[0079] In addition, the motor core manufactured by the above method includes a soft magnetic iron powder containing, in wt%, Si: more than 2.0% and 6.5% or less, Al: more than 0.02% and 1.0% or less, Mn: more than 0.05% and 0.6% or less, O: more than 0% and less than 0.1%, the remainder being Fe and inevitable impurities, and an insulating layer containing Si, Al, Mn, and O on an interface between the soft magnetic iron powders.

[0080] (Method for manufacturing stator of axial flux motor)

[0081] An example of a molded component manufactured from soft magnetic iron powder is the stator of an axial flux motor. Axial flux motors can be used in electric vehicles, in-wheel motors, drones, and other applications.

[0082] An axial flux motor operates on the principle that a rotor reacts by generating an axial flux in a direction parallel to, rather than perpendicular to, the shaft of the rotor. The axial flux motor includes a rotor assembly having a disc-shaped rotor core including a magnetic material, a shaft disposed on the central axis of the rotor core and rotating together with the rotor core, and a stator assembly having a stator core and a coil wound around the stator core to generate a magnetic flux in the direction of the rotational axis of the rotor assembly.

[0083] According to one embodiment of the present invention, a method for manufacturing a stator core of an axial flux motor comprises the steps of: a) preparing a soft magnetic iron-based powder containing Si in an amount of more than 2.0% by weight and less than or equal to 6.5% by weight and including an insulating layer on an outer surface, wherein an average particle size of more than 90% of the soft magnetic iron-based powder is 150 to 400 μm, and an average particle size of less than or equal to 10% is 50 μm or less; b) compressing the soft magnetic iron-based powder; and c) heat-treating the powder compressed in step b). In step b), a molding pressure may be 600 MPa or more and 2000 MPa or less. In step c), residual stress is removed through heat treatment at 900°C or less, and the insulating layer may be maintained until the heat treatment temperature is 1000°C or less.

[0084] The above-mentioned soft magnetic iron powder includes an insulating layer having a thickness of 10 to 50 nm containing Si, Al, Mn, and O on the outer surface, and includes, in wt%, Si: more than 2.0% and 6.5% or less, Al: more than 0.02% and 1.0% or less, Mn: more than 0.05% and 0.6% or less, O: more than 0% and less than 0.1%, and the remainder is Fe and unavoidable impurities.

[0085] As an example, an exploded view of a stator assembly of an axial flux motor is illustrated in FIG. 8. As illustrated in FIG. 8, the stator core can be manufactured by manufacturing a plurality of core blocks in a circumferential direction by sintering iron-based powders, and then joining these core blocks. Alternatively, the stator core can be sintered as a single molded part. The stator core of an axial flux motor can have additional shape changes depending on the design purpose. In one embodiment, a method of manufacturing the core separately into upper and lower parts and then joining them can be used.

[0086] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that modifications to other specific forms can be made without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0087] The scope of the present invention is defined by the claims set forth below, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

[0088] According to the present invention, a molded part manufactured from a soft magnetic iron powder having low iron loss in a frequency range of 1000 Hz or less can be provided.

[0089] A molded part manufactured from the soft magnetic iron powder according to the present invention can have increased magnetic flux density and reduced eddy current loss.

[0090] By applying a stator core manufactured from a soft magnetic iron powder according to the present invention, motor efficiency can be improved.

Claims

1. A molded part manufactured by sintering a soft magnetic iron powder, A molded part, wherein more than 90% of the above-mentioned soft magnetic iron powder has an average particle size of 150 to 400 ㎛, and less than 10% has an average particle size of 50 ㎛ or less.

2. In paragraph 1, The above molded part is a stator core of a linear motor.

3. In paragraph 1, The above molded part is a stator core of an axial flux motor.

4. In paragraph 1, The above soft magnetic iron powder is, It comprises an insulating layer having a thickness of 10 to 50 nm containing Si, Al, Mn, and O on the outer surface, A molded part containing, in weight %, Si: more than 2.0% and less than 6.5%, Al: more than 0.02% and less than 1.0%, Mn: more than 0.05% and less than 0.6%, O: more than 0% and less than 0.1%, the remainder being Fe and unavoidable impurities.

5. A stator core of a linear motor manufactured by sintering soft magnetic iron powder, A stator core of a linear motor, wherein more than 90% of the above-mentioned soft magnetic iron powder has an average particle size of 150 to 400 ㎛, and less than 10% has an average particle size of 50 ㎛ or less.

6. A method for manufacturing a sintered part, a) A step of preparing a soft magnetic iron powder including Si and including an insulating layer on an outer surface, wherein an average particle size of 90% or more of the soft magnetic iron powder is 150 to 400 ㎛, and an average particle size of 10% or less is 50 ㎛ or less; b) a step of compressing the above soft magnetic iron powder; and c) a step of heat-treating the compressed powder in step b) above; A method for manufacturing a sintered part comprising:

7. In paragraph 6, A method for manufacturing a sintered part, wherein the forming pressure in step b) is 600 MPa or more and 2000 MPa or less.

8. In paragraph 6, A method for manufacturing a sintered part, wherein the insulating layer is maintained until the heat treatment temperature in step c) is 1000°C or lower.

9. In paragraph 6, The above soft magnetic iron powder is, It comprises an insulating layer having a thickness of 10 to 50 nm containing Si, Al, Mn, and O on the outer surface, A method for manufacturing a sintered part, comprising, in weight %, Si: more than 2.0% and less than 6.5%, Al: more than 0.02% and less than 1.0%, Mn: more than 0.05% and less than 0.6%, O: more than 0% and less than 0.1%, and the remainder being Fe and unavoidable impurities.

10. A molded part manufactured by the method of any one of claims 6 to 9.

11. A stator core of a linear motor manufactured by the method of any one of claims 6 to 9.

12. A stator core of an axial flux motor manufactured by the method of any one of claims 6 to 9.

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