WO2015151244A1

WO2015151244A1 - Squirrel-cage rotor

Info

Publication number: WO2015151244A1
Application number: PCT/JP2014/059741
Authority: WO
Inventors: 佳樹岡田; 由晴 ▲高▼島
Original assignee: 三菱電機株式会社
Priority date: 2014-04-02
Filing date: 2014-04-02
Publication date: 2015-10-08
Also published as: JP5745703B1; JPWO2015151244A1

Abstract

A squirrel-cage rotor (3) used in an induction motor comprises: a core (7) laminated to a cylindrical shape; slots (6) formed within a radial position of the core (7); conductor bars (4) formed in the slots (6); conductor end rings (31a, 31b) disposed on both axial end surfaces of the core (7) and connected to the conductor bars (4); and ring-shaped coated materials (21a, 21b) formed by spraying conductive particles (43) in a solid phase state from an outer peripheral direction or an end surface direction of the conductor end rings (31a, 31b) with a shaft (10) or a sleeve fitted in an inner circumferential portion of the core (7), so that the coated materials are integrated with the conductor end rings (31a, 31b) and the shaft (10) or the sleeve.

Description

Cage rotor

The present invention relates to a cage rotor.

In forming a secondary conductor of a squirrel-cage rotor used for an induction motor, aluminum die casting is often used because of cost and ease of manufacturing, and many are applied to induction motors for machine tools. However, in recent years, the need for high efficiency and high-speed rotation of induction motors for machine tools has become very high, such as demand for energy saving due to resource depletion, reduction of machining tact and handling of difficult-to-cut materials. Yes.

In order to meet these needs, it is necessary to improve both the conductivity of the secondary conductor of the rotor and the strength of the secondary conductor that can withstand the centrifugal force generated by the high-speed rotation of the rotor. As a response to these needs, for example, alloying the secondary conductor with aluminum, applying copper, and adding a reinforcing member to the conductor end ring are available.

However, in the case of alloyed aluminum, the strength for high-speed operation can be ensured, but the efficiency of the induction motor decreases because the conductivity of the alloyed aluminum is low. On the other hand, in the case of application of copper, efficiency can be improved by improving conductivity, but brazing is used in the manufacturing method, so it is difficult to ensure strength reliability. On the other hand, the addition of a reinforcing member to the conductor end ring is problematic because the reinforcing member becomes a separate component and the cost increases when difficult-to-process metals (stainless alloy, titanium, etc.) with high specific strength are used. It is easy to become.

For example, in Patent Documents 1 to 3, solid-state metal material powder is sprayed to improve the strength reliability of the conductor bar, to form a conductor end ring, or to form a conductor coating material for the purpose of reinforcing the conductor end ring. An induction motor using a so-called “cold spray method” is disclosed.

JP 2012-19634 A Japanese Patent No. 5155423 Japanese Patent No. 5326012

In conductor end ring reinforcement by the cold spray method, by forming a high-strength annular coating material on the surface of the conductor end ring, it is possible to obtain a reinforcement effect that suppresses deformation in the rotor outer circumference due to centrifugal force during high-speed rotation. However, when the annular coating material is molded integrally with the core skin surface, the metal powder in the solid state collides with the core at a high speed. The efficiency of the electric motor may deteriorate.

In addition, when connecting the conductor end ring and the conductor bar by the cold spray method and forming the annular coating only on the outer peripheral surface of the conductor end ring, the linear expansion coefficient between the conductor bar material (aluminum, copper, etc.) and the iron core when the motor is driven The expansion in the axial direction due to the difference cannot be suppressed. Therefore, when the temperature rises, the conductor end ring is supported only by the conductor bar. In such a state, during the acceleration / deceleration operation of the motor, since a large repetitive stress is applied to the joint between the conductor bar and the conductor end ring, there is a concern about fatigue failure of the part.

In addition, in the process of forming the conductor bar, conductor end ring and annular coating material by the cold spray method, a core metal or the like which has been processed to prevent the coating material from adhering to the inner periphery of the core Must be inserted into the inner periphery of the core. Therefore, there is a problem that man-hours are required for maintenance such as manufacturing cost of the cored bar, insertion / removal of the cored bar, and removal of the coating material attached to the cored bar.

The present invention has been made in view of the above, and is a squirrel-cage rotation capable of achieving both improvement in conductivity and strength of a secondary conductor while suppressing adhesion of a coating material to a core and an increase in cost. The purpose is to get a child.

In order to solve the above-described problems and achieve the object, the present invention provides a squirrel-cage rotor for use in an induction motor, a core stacked in a cylindrical shape, and a slot formed in a radial position of the core. A conductor bar formed in the slot, a conductor end ring disposed on both axial end surfaces of the core and connected to the conductor bar, and a conductor end with a shaft or sleeve fitted into the inner peripheral portion of the core Solid conductor particles are sprayed from the outer circumferential direction or the end face direction of the ring, and are provided with a conductor end ring and an annular coating material integrated with the shaft or sleeve.

The squirrel-cage rotor according to the present invention has an effect that it is possible to improve both the conductivity and the strength of the secondary conductor while suppressing the adhesion of the coating material to the core and the increase in cost.

FIG. 1 is a cross-sectional view of the squirrel-cage rotor according to the first embodiment of the present invention along the rotation center axis. FIG. 2 is a cross-sectional view of a squirrel-cage rotor taken along line AA shown in FIG. FIG. 3 is a cross-sectional view schematically showing a manufacturing process of the cage rotor. FIG. 4 is a cross-sectional view schematically illustrating a manufacturing process of the cage rotor according to the first modification of the first embodiment. FIG. 5 is a cross-sectional view schematically showing a manufacturing process of the cage rotor according to the second modification of the first embodiment. FIG. 6 is a cross-sectional view schematically illustrating a manufacturing process of the cage rotor according to the third modification of the first embodiment. FIG. 7 is a cross-sectional view schematically showing a manufacturing process of the cage rotor according to the fourth modification of the first embodiment. FIG. 8 is a cross-sectional view schematically showing a manufacturing process of the cage rotor according to the second embodiment of the present invention. FIG. 9 is a cross-sectional view schematically showing a manufacturing process of the cage rotor according to the first modification of the second embodiment. FIG. 10 is a cross-sectional view schematically showing a manufacturing process of the cage rotor according to the second modification of the second embodiment. FIG. 11 is a cross-sectional view schematically showing a manufacturing process of the cage rotor according to the third modification of the second embodiment. FIG. 12 is a cross-sectional view schematically illustrating a manufacturing process of the cage rotor according to the fourth modification of the second embodiment.

Hereinafter, embodiments of a cage rotor according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view of the squirrel-cage rotor 3 according to the first embodiment of the present invention along the rotation center axis 1. FIG. 2 is a cross-sectional view of the cage rotor 3 taken along the line AA shown in FIG. The squirrel-cage rotor 3 is attached to, for example, a cylindrical cored bar 2. The squirrel-cage rotor 3 includes a cylindrical core 7, a pair of annular

conductor end rings

31 a and 31 b that are disposed at both ends and sandwich the core 7, and a conductor bar 4 that fills a slot 6 that penetrates the core 7. Consists of.

The core 7 is formed of a laminate in which a required number of annular thin plates punched from electromagnetic steel plates, which are thin steel plates, are laminated in the direction of the rotation center axis 1. In the center of the core 7, a core through-hole 5 that is penetrated along the rotation center axis 1 is formed. The cored bar 2 is inserted into the core through hole 5. In the vicinity of the outer peripheral surface of the core 7, a plurality of slots 6 are formed at positions that are equally spaced in the circumferential direction around the rotation center axis 1. The slot 6 is positioned parallel to the rotation center axis 1 with a specified angle skewed. The slot 6 penetrates the core 7 in a direction along the rotation center axis 1. A conductor bar 4 is formed in the slot 6.

A pair of

conductor end rings

31 a and 31 b are arranged at the end of the conductor bar 4. The conductor bar 4 and the pair of

conductor end rings

31a and 31b are formed by die casting using a conductor material such as aluminum, aluminum alloy, copper, or copper alloy. At the center of the

conductor end rings

31a and 31b, an end ring through hole 8 is formed with the rotation center axis 1 as the center.

FIG. 3 is a cross-sectional view schematically showing a manufacturing process of the cage rotor 3. The manufacturing process is performed in a state in which the shaft 10 is press-fitted into the core through hole 5 and the end ring through hole 8 with respect to the squirrel-cage rotor 3 and is coupled by shrinking or the like.

The

annular coating materials

21a and 21b are formed on both end faces of the core 7 by a cold spray method. In performing the cold spray method, a Laval nozzle 41 shown in FIG. 3 is used. The Laval nozzle 41 is formed with a flow path that widens toward the outlet at the tip. A supersonic flow gas 42 is introduced into the flow path toward the tip. The flow rate of the gas 42 is set to 500 to 700 m / s, for example.

Conductor particles 43 are introduced into the gas 42 flowing through the flow path. The gas 42 is set to a temperature lower than the melting point or softening temperature of the conductor particles 43. The conductive particles 43 are more rigid than conductive materials such as copper and copper alloys, which have a lower specific resistance than the conductive end rings 31a and 31b, or aluminum (pure aluminum) defined by the JIS (Japan Industrial Standards) A1000 series. High-rigidity materials such as high iron and iron alloys are used. The particle diameter of the conductor particles 43 is set to 5 to 50 μm, for example. The temperature of the gas 42 is set to, for example, room temperature to about 500 ° C.

The Laval nozzle 41 is arranged so as to blow out the conductor particles 43 along the rotation center axis 1. The tip of the Laval nozzle 41 is opposed to the upper end surface of the core 7. The tip of the Laval nozzle 41 changes the posture from a position perpendicular to the core end surface to a horizontal position and blows out the conductor particles 43. Supersonic flow conductor particles 43 are blown out from the tip of the Laval nozzle 41.

The blown conductor particles 43 are sprayed onto the conductor end ring 31a and the shaft 10. Since the temperature of the gas 42 is set to a temperature lower than the melting point of the conductor particles 43, the conductor particles 43 collide with the conductor end rings 31a and 31b in a solid state.

When the Laval nozzle 41 rotates around the rotation center axis 1 or the cage rotor 3 rotates around the rotation center axis 1, the annular coating material 21 a is formed on the surfaces of the conductor end ring 31 a and the shaft 10. Further, the cage-shaped rotor 3 is rotated 180 ° in the direction perpendicular to the rotation center axis 1 and the conductor particles 43 are sprayed on the conductor end ring 31b side, whereby the surface of the conductor end ring 31b and the shaft 10 is coated with the annular coating material 21b. Is formed. Although the thickness of the

annular coating materials

21a and 21b is not particularly specified, it is set within a range of several mm to several tens mm in order to maintain sufficient coating material strength and inter-member bonding.

The

annular coating materials

21 a and 21 b are joined to the conductor end rings 31 a and 31 b and the shaft 10. By the joining, deformation of the conductor end rings 31a and 31b due to centrifugal force during high-speed rotation is suppressed.

As described above, according to the manufacturing method of the present invention, the conductor particles 43 are introduced into the gas 42 having a temperature lower than the melting point thereof, so that the conductor end rings 31a and 31b and the shaft 10 are in a solid state. Is sprayed on. Thereby, the enlargement of the crystal grain of the conductor which forms cyclic |

annular coating material

21a, 21b can be suppressed. Further, it is possible to make the laminated body of the coating dense. Further, the conductor end rings 31a and 31b and the shaft 10 are reliably joined by the

annular coating materials

21a and 21b. Further, since the conductor does not melt in the process of forming the

annular coating materials

21a and 21b, there is no thermal contraction that occurs when the conductor is melted, and the gap formed between the different members can be suppressed. In addition, since the shaft 10 is coupled to the core through hole 5 in advance, it is possible to prevent the conductor particles 43 from adhering to the inner peripheral surface of the core 7. Thereby, the process of removing the conductor particles 43 and the process of attaching / detaching the cored bar provided to suppress the adhesion of the conductor particles 43 to the core through hole 5 can be omitted, and the manufacturing cost can be suppressed. .

As described above, in the formation of the

annular coating materials

21a and 21b by the cold spray method, thermal strain and composition embrittlement caused by welding or brazing can be suppressed. In addition, it is possible to reduce the man-hours by omitting the cooling time generated by brazing or the like.

FIG. 4 is a cross-sectional view schematically showing a manufacturing process of the cage rotor 3 according to the first modification of the first embodiment. In Modification 1, an example is shown in which a sleeve 11 used for connection to a spindle or the like is coupled to a cage rotor 3 by press-fitting or shrinking into a core through hole 5 and an end ring through hole 8. The conductor particles 43 are sprayed in the same process as in the above-described example. Also in the first modification, the

annular coating materials

21a and 21b, the conductor end rings 31a and 31b, and the sleeve 11 can be more reliably joined to improve the reliability.

FIG. 5 is a cross-sectional view schematically showing a manufacturing process of the cage rotor 3 according to the second modification of the first embodiment. In the second modification, the conductor particles 43 are sprayed in a state where the pair of reinforcing

members

12a and 12b are arranged on the inner peripheral side of the conductor end rings 31a and 31b (inside the end ring through hole 8). Reinforcing member through holes 13 having the same diameter as the core through holes 5 are formed in the reinforcing

members

12a and 12b. The reinforcing

members

12a and 12b are arranged so that the reinforcing member through hole 13 and the core through hole 5 communicate with each other.

The reinforcing

members

12a and 12b are preferably non-magnetic materials in order to suppress a decrease in the output of the induction motor due to leakage magnetic flux. Further, the reinforcing

members

12a and 12b are disposed on the inner peripheral side of the conductor end rings 31a and 31b, either in the form of shrinkage with the inner peripheral side of the conductor end rings 31a and 31b, or in the form of being cast during aluminum or copper die casting. It is desirable to do. In addition, the shape of the reinforcing

members

12a and 12b in this modification 2 is an example, and is not limited to the shape.

When the Laval nozzle 41 rotates around the rotation center axis 1 or the cage rotor 3 rotates around the rotation center axis 1, the

annular coating materials

21 a and 31 b are formed on the surfaces of the conductor end rings 31 a and 31 b and the reinforcing

members

12 a and 12 b. 21b is formed.

The

annular coating materials

21a and 21b are joined to the conductor end rings 31a and 31b and the reinforcing

members

12a and 12b. Thereafter, the reinforcing

members

12a and 12b are coupled to the shaft, the sleeve, and the like using the reinforcing member through holes 13, so that the conductor end rings 31a and 31b are prevented from being deformed by the centrifugal force during high-speed rotation. Moreover, the end surface of the conductor end rings 31a and 31b on the direction side along the rotation center axis 1 is exposed from the

annular coating materials

21a and 21b, so that the region where the conductor particles 43 are sprayed is formed on the conductor end rings 31a and 31b. It can be limited to the outer peripheral side. That is, the region where the conductor particles 43 are sprayed can be separated from the core through hole 5 of the core 7. Therefore, it is possible to suppress the conductor particles from adhering to the inner peripheral surface of the core through hole 5. Thereby, the process of removing the conductor particles 43 and the process of attaching / detaching the cored bar provided to suppress the adhesion of the conductor particles 43 to the core through hole 5 can be omitted, and the manufacturing cost can be suppressed. .

FIG. 6 is a cross-sectional view schematically showing a manufacturing process of the cage rotor 3 according to the third modification of the first embodiment. In the third modification, similarly to the second modification, the conductor particles 43 are sprayed in a state where the pair of reinforcing

members

12a and 12b are arranged on the inner peripheral side of the conductor end rings 31a and 31b. Reinforcing member through holes 13 having the same diameter as the core through holes 5 are formed in the reinforcing

members

12a and 12b. The reinforcing

members

12a and 12b are arranged so that the reinforcing member through hole 13 and the core through hole 5 communicate with each other. In the third modification, the conductor particles 43 are sprayed in a state where the shaft 10 is fitted in the core through hole 5 and the reinforcing member through hole 13.

At the time when the

annular coating materials

21a and 21b are formed, the conductor end rings 31a and 31b, the reinforcing

members

12a and 12b, and the shaft 10 are joined to each other, so that the conductor end rings 31a and 31b are subjected to centrifugal force during high-speed rotation. Deformation is suppressed.

Further, since the shaft 10 is fitted in the core through hole 5, the conductor particles 43 do not adhere to the inner peripheral surface of the core through hole 5 even if the conductor particles 43 are sprayed around the core through hole 5. Therefore, the conductor particles 43 are sprayed to the periphery of the core through hole 5 to form the

annular coating materials

21a and 21b so as to cover the end faces on the direction side along the rotation center axis 1 of the reinforcing

members

12a and 12b. it can. As a result, the reinforcing effect of the

annular coating materials

21a and 21b can be more reliably exhibited.

FIG. 7 is a cross-sectional view schematically showing a manufacturing process of the cage rotor 3 according to the fourth modification of the first embodiment. In the fourth modification, instead of the shaft shown in the third modification, the conductor particles 43 are sprayed in a state where the sleeve 11 is fitted in the core through hole 5. Similar to the third modification, when the

annular coating materials

21a and 21b are formed, the conductor end rings 31a and 31b, the reinforcing

members

12a and 12b, and the sleeve 11 are joined to each other, so that the conductor end rings 31a and 31b are joined together. The deformation with respect to the centrifugal force during high-speed rotation is suppressed.

Further, since the sleeve 11 is fitted in the core through hole 5, the conductor particles 43 do not adhere to the inner peripheral surface of the core through hole 5 even if the conductor particles 43 are sprayed around the core through hole 5. Therefore, the conductor particles 43 are sprayed to the periphery of the core through hole 5 to form the

annular coating materials

members

12a and 12b. it can. As a result, the reinforcing effect of the

annular coating materials

21a and 21b can be more reliably exhibited.

Embodiment 2. FIG.
FIG. 8 is a cross-sectional view schematically showing the manufacturing process of the cage rotor 3 according to the second embodiment of the present invention. In addition, about the structure similar to the said embodiment, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted. In the present embodiment, a conductor bar 14 cast and extruded with aluminum, copper, or the like, or a conductor bar 14 manufactured by cutting is disposed in the slot 6 penetrating the core 7. The conductor bar 14 protrudes from the end surface of the core 7. In addition, a pair of annular conductor end rings 32a and 32b are provided in which holes are provided radially so as to expose the end of the conductor bar 14.

In the present embodiment, the conductor bar 14, the conductor end rings 32a and 32b, and the shaft 10 are joined to each other by using the

annular coating materials

22a and 22b, so that the conductor end rings 32a and 32b are subjected to a centrifugal force during high-speed rotation. Deformation is suppressed. In the present embodiment, the conductor bar 14 has a structure that is convex with respect to the conductor end rings 32a and 32b, but the conductor bar 14 only needs to have a structure that can be exposed on either side.

FIG. 9 is a cross-sectional view schematically showing a manufacturing process of the cage rotor 3 according to the first modification of the second embodiment. In the first modification, the conductor particles 43 are sprayed in a state where the sleeve 11 is fitted in place of the shaft 10 to form the

annular coating materials

22a and 22b.

FIG. 10 is a cross-sectional view schematically showing a manufacturing process of the cage rotor 3 according to the second modification of the second embodiment. In the second modification, the conductor particles 43 are sprayed in a state where the reinforcing

members

12a and 12b are fitted inside the conductor end rings 32a and 32b, thereby forming the

annular coating materials

22a and 22b. In the modified example 2, the region to which the conductor particles 43 are sprayed is the outer peripheral side of the conductor end rings 32a and 32b, and the end surfaces along the rotation center axis 1 of the reinforcing

members

12a and 12b are exposed.

FIG. 11 is a cross-sectional view schematically showing a manufacturing process of the cage rotor 3 according to the third modification of the second embodiment. In the modified example 3, in addition to the configuration of the modified example 2, the conductor particles 43 are sprayed in a state where the shaft 10 is fitted in the core through hole 5 of the core 7 to form the

annular coating materials

22a and 22b.

FIG. 12 is a cross-sectional view schematically showing a manufacturing process of the cage rotor 3 according to the fourth modification of the second embodiment. In the modified example 4, instead of the shaft 10 shown in the modified example 3, the conductor particles 43 are sprayed in a state in which the sleeve 11 is fitted in the core through hole 5 of the core 7 to form the

annular coating materials

22a and 22b.

In the first to fourth modifications of the second embodiment, as in the first to fourth modifications of the first embodiment, the adhesion of the conductor particles 43 to the inner peripheral surface of the core through hole 5 is suppressed, thereby reducing the manufacturing cost. Can be achieved. Further, the joining of the conductor end rings 32a and 32b, the conductor bar 14, the shaft 10, the sleeve 11, and the reinforcing

members

12a and 12b can be further strengthened by the

annular coating materials

22a and 22b. Thereby, deformation | transformation of the conductor end rings 32a and 32b can be suppressed.

In the first and second embodiments, a material having a small specific resistance (for example, a material having a specific resistance smaller than that of the conductor end ring) is used for the conductive particles 43 used for forming the

annular coating materials

21a, 21b, 22a, and 22b. By joining, it becomes possible to reduce the electrical resistance of the conductor end rings 31a, 31b, 32a, 32b as a whole, and the efficiency of the induction motor can be improved.

Further, as the material of the conductor particles 43, copper or a copper alloy such as pure copper, chromium copper, Corson alloy, beryllium copper, or alumina dispersion strengthened copper is used, so that the conductor end rings 31a, 31b, 32a, and 32b as a whole are used. The electric resistance can be reduced, and the efficiency of the induction motor can be improved.

Further, the conductive particles 43 used for forming the

annular coating materials

21a, 21b, 22a, and 22b are, for example, highly rigid materials having higher rigidity than aluminum (pure aluminum) defined in the A1000 series of JIS (Japan Industrial Standards). By joining the conductor end rings 31a, 31b, 32a, 32b, deformation due to centrifugal force during high speed rotation can be suppressed, and the induction motor can be rotated at high speed.

Moreover, as a material of the conductor particles 43, an iron alloy such as iron, stainless steel, chrome molybdenum steel, or the like is used, so that deformation caused by the centrifugal force at the time of high-speed rotation of the conductor end rings 31a, 31b, 32a, and 32b. Thus, the induction motor can be rotated at a high speed.

In the case where the conductor particles 43 (

annular coating materials

21a, 21b, 22a, 22b) are directly joined to the shaft 10, the sleeve 11, etc., the conductor particles 43 are preferably a nonmagnetic iron alloy. When a non-magnetic material is used for the reinforcing

members

12a and 12b, the magnetic path to the core 7 is blocked, so it is possible to use magnetic iron or iron alloy.

As described above, the cage rotor according to the present invention is useful for a cage rotor used in a rotating electrical machine.

1 rotation center axis, 2 cored bar, 3 cage rotor, 4,14 conductor bar, 5 core through hole, 6 slot, 7 core, 8 end ring through hole, 10 shaft, 11 sleeve, 12a, 12b reinforcement member, 13 reinforcing member through hole, 21a, 21b, 22a, 22b annular coating material, 31a, 31b, 32a, 32b conductor end ring, 41 Laval nozzle, 42 gas, 43 conductor particles.

Claims

In squirrel-cage rotors used for induction motors,
A core laminated in a cylindrical shape;
A slot formed in a radial position of the core;
A conductor bar formed in the slot;
A conductor end ring disposed on both axial end faces of the core and connected to the conductor bar;
In a state where a shaft or a sleeve is fitted to an inner peripheral portion of the core, solid state conductive particles are sprayed from an outer peripheral direction or an end surface direction of the conductor end ring, and the conductor end ring and the shaft or A squirrel-cage rotor comprising an annular coating material integrated with the sleeve.
In squirrel-cage rotors used for induction motors,
A core laminated in a cylindrical shape;
A slot formed in a radial position of the core;
A conductor bar formed in the slot;
A conductor end ring disposed on both axial end faces of the core and connected to the conductor bar; and an outer peripheral direction or end face of the conductor end ring in a state in which a reinforcing member is fitted in an inner peripheral portion of the conductor end ring. A squirrel-cage rotor comprising: an annular coating material formed by spraying solid-state conductor particles from a direction and integrated with the conductor end ring and the reinforcing member.
3. The annular coating material is formed by spraying the conductive particles in a state in which a shaft or a sleeve is fitted into an inner peripheral portion of the core, and is integrated with the shaft or the sleeve. The cage rotor described in 1.
The cage rotor according to any one of claims 1 to 3, wherein the conductor end ring and the conductor bar are connected by the conductor particles.
The cage rotor according to any one of claims 1 to 4, wherein the conductor particles are made of a material having a specific resistance smaller than that of the conductor end ring.
The cage rotor according to claim 5, wherein the conductor particles are made of copper or a copper alloy.
The squirrel-cage rotor according to any one of claims 1 to 4, wherein the conductor particles are made of iron or an iron alloy.
The squirrel-cage rotor according to any one of claims 1 to 4, wherein the conductor particles are made of a highly rigid material having rigidity higher than that of aluminum.