Electric motor, core assembly, and slot closing member for core, and manufacturing method therefor

Abstract

Provided in the embodiments of the present application are an electric motor, a core assembly, and a slot closing member for a core, and a manufacturing method therefor. The electric motor comprises the core assembly. The core assembly comprises a core, windings, and a slot closing member for the core. The slot closing member for the core comprises slot filling portions and a connecting portion, wherein the slot filling portions are arranged in slot openings of the core, and the connecting portion is connected to the slot filling portions in the slot openings of the core, so as to form an annular whole. In the slot closing member for the core provided in the embodiments of the present application, the slot filling portions in the slot openings of the core are connected by means of the connecting portion, and after a preset period of time, under a preset pressure and at a preset temperature, the compressed slot filling portions and the connecting portion are cured, such that the connecting portion and the slot filling portions are tightly connected together, forming an integrated annular slot closing member structure, thereby improving the sealing performance and strength of the slot closing member. The core, the windings and the slot closing member form the integral core assembly, such that the slot closing member has a better sealing and fixing effect on the windings in the slot openings.

Description

Electric motor, core assembly, slot closure for core, and method of manufacturing the same

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on the Chinese patent application with application number 202311189861.4 and application date September 14, 2023, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into this application as a reference. Technical Field

[0003] The present application relates to the field of power generation, and in particular to a motor, an iron core assembly, a slot closure of the iron core, and a manufacturing method thereof. Background Art

[0004] During motor manufacturing, slot closures are installed in the slots of the stator or rotor core, tightly securing the winding coils or wire rods within the core slots. They also block environmental factors such as dust, foreign matter, and water vapor, reducing the aging of the winding insulation. Therefore, high strength is the primary selection criterion for all slot closures and is a key factor in improving motor reliability.

[0005] In conventional motors, each slot is typically fitted with a separate slot closure, which provides limited fixing strength. Furthermore, during installation, the closure inevitably wears against the core, reducing its strength and even causing it to fall off, potentially damaging the motor rotor.

[0006] Summary of the Invention

[0007] In view of this, embodiments of the present application are intended to provide a motor, a core assembly, a slot closure for the core, and a manufacturing method thereof, so as to improve the strength of the slot closure and the reliability of the motor operation.

[0008] To achieve the above-mentioned purpose, one aspect of an embodiment of the present application provides a slot closure for an iron core, comprising a slot filling portion and a connecting portion, wherein the slot filling portion is arranged in the slot opening of the iron core; the connecting portion is respectively connected to the slot filling portions in each of the slot openings of the iron core to form an annular whole.

[0009] Furthermore, the slot filling portion includes a sealing unit and a filling unit, wherein the sealing unit is arranged in the slot; the filling unit is filled in the slot and connected to the sealing unit;

[0010] The sealing unit is used to separate the filling unit from the winding of the iron core and the tooth portion of the iron core respectively, and the connecting portion is connected to the sealing unit and the filling unit in each of the slots respectively; or, the sealing unit is used to separate the filling unit from the winding of the iron core and part of the tooth portion of the iron core respectively, the connecting portion is connected to the filling unit in each of the slots, and the connecting portion is not connected to the sealing unit in each of the slots.

[0011] Furthermore, the sealing unit includes a plurality of stacked sealing layers, or the sealing unit is a single sealing layer.

[0012] Furthermore, the filling unit includes a plurality of stacked filling layers, or the filling unit is a single filling layer.

[0013] Furthermore, the connecting portion includes a plurality of stacked connecting layers, or the connecting portion is a single connecting layer.

[0014] Furthermore, the sealing unit, the filling unit and the connecting portion respectively include a reinforcing material and a matrix material.

[0015] Furthermore, the reinforcing material is a polymer material.

[0016] Furthermore, the polymer material includes glass fiber, aramid fiber and / or carbon fiber.

[0017] Furthermore, the matrix material includes thermosetting resin and / or magnetic material.

[0018] Another aspect of an embodiment of the present application provides a method for manufacturing a slot closure for an iron core, comprising:

[0019] placing the slot filling portion in the slot opening of the core mold;

[0020] connecting the connecting portion to the slot filling portion in each of the slots of the core mold;

[0021] The groove filling part and the connecting part are pressed together under a preset time, a preset pressure and a preset temperature, and solidified to form a whole.

[0022] Furthermore, the height of the slot filling portion on a side close to the connecting portion is greater than or equal to the top height of the tooth portion of the core mold.

[0023] Furthermore, the slot filling part includes a sealing unit and a filling unit, and the step of arranging the slot filling part in the slot opening of the core mold includes:

[0024] placing the sealing unit in the notch;

[0025] The filling unit is arranged in the notch and connected to the sealing unit.

[0026] Furthermore, the sealing unit, the filling unit and the connecting portion respectively include a reinforcing material and a matrix material, and the manufacturing method further includes:

[0027] The reinforcing material is impregnated into the matrix material.

[0028] Furthermore, the matrix material is a thermosetting resin; the preset time is 2 to 4 hours, the preset pressure is 10±2 MPa, and the preset temperature is 170±5 degrees Celsius.

[0029] Another aspect of an embodiment of the present application provides an iron core assembly, including an iron core, a winding, and the slot closure member described in any embodiment of the present application, wherein the iron core is configured in a ring shape, having teeth and slots formed between the teeth; the winding is wound on the slots; and the slot closure member is embedded in the slots.

[0030] Another aspect of the embodiments of the present application provides a motor, comprising the core assembly described in any embodiment of the present application.

[0031] The slot closure for the iron core provided in the embodiment of the present application forms an integrated slot closure by forming a slot filling portion in each slot opening into a reinforcing rib along the axial direction of the iron core and an annular bushing combination formed by the connecting portion, so that the slot closure is more excellent in overall strength and sealing performance, thereby improving the reliability of winding insulation.

[0032] The manufacturing method of the slot closure for the iron core provided in the embodiment of the present application utilizes an iron core mold to solidify the material in the slot closure through hot pressing at a preset time, preset pressure, and preset temperature to form an integral body, while simultaneously expelling the air, small molecular organic volatiles, and other substances between the iron core mold and the slot closure, thereby making the slot closure have a higher density.

[0033] The core assembly provided in the embodiment of the present application is connected to the core via a slot closure, and the core, winding and slot closure form a whole, so that the slot closure has a better sealing and fixing effect on the winding in the slot.

[0034] The motor provided in the embodiment of the present application separates the stator and the rotor through an integrated slot closure structure, which can effectively reduce the conduction of stator heat to the rotor side, allowing the rotor to operate at a lower temperature and improve the efficiency of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a schematic cross-sectional view of a matching structure of an iron core assembly provided in an embodiment of the present application;

[0036] FIG2 is a partial enlarged view of point A of the structure shown in FIG1 ;

[0037] FIG3 is a schematic structural diagram of a slot closure of an iron core provided in an embodiment of the present application;

[0038] FIG4 is a schematic cross-sectional view of another core assembly provided in an embodiment of the present application;

[0039] FIG5 is a schematic flow chart of a method for manufacturing a slot closure of an iron core provided in an embodiment of the present application. DETAILED DESCRIPTION

[0040] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0041] In the description of the embodiments of the present application, it should be noted that, unless otherwise specified, “multiple” and “multiple” mean two or more, and two or more, respectively.

[0042] In the description of the embodiments of the present application, it should be noted that, unless otherwise specified, the meaning of “annular” includes a closed annular structure and a non-closed annular structure.

[0043] In the description of the embodiments of this application, it should be noted that, unless otherwise specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of this application based on the specific circumstances.

[0044] During typical motor production, slot closures are used to secure windings, such as coils or wire rods, to prevent electromagnetic forces, vibration, and thermal stress from causing them to move and become damaged within the core slots, leading to premature insulation failure. Slot closures also isolate the windings within the slots from the outside world, preventing rapid insulation aging and ensuring reliable winding insulation.

[0045] In the relevant motors, the slot closures of the core are usually processed according to the shape and size of the core slots. After the windings are placed in the slots, independent slot closures are inserted into each core slot to fix the windings. In the process of inserting the slot closures, there is inevitably wear between the slot closures and the core, which causes the strength of the slot closures to decrease, leading to problems such as the slot closures falling off and the rotor sweeping during the operation of the motor. At the same time, the position of the slot closures cannot be slightly adjusted according to the size of the windings located in the slots, resulting in the insulating paint not being fully filled during the subsequent dipping, or causing the insulating paint to be lost. At the same time, the bonding force between the insulating paint and the slot closures is relatively small, affecting the sealing of the windings. In addition, when the slot closures are inserted into the core slots for fixation, the workload and time costs are high, and the individual slot closures are independent and scattered from each other, providing limited fixing strength.

[0046] Based on the above, a first aspect of an embodiment of the present application provides a core slot closure 13. Referring to Figures 1 to 3 , the slot closure 13 is applied to the stator core of an inner-rotor motor. Referring to Figure 4 , the slot closure 13 is applied to the rotor core of an inner-rotor motor. In addition to being applicable to the rotor core of an inner-rotor motor, the slot closure 13 can also be applied to the rotor core and stator core of an outer-rotor motor, as well as the cores of other types of motors.

[0047] The slot closure 13 includes a slot-filling portion 131 and a connecting portion 132. The slot-filling portion 131 is positioned within the slot opening 11a of the core 11. The connecting portion 132 connects to the slot-filling portion 131 within each slot opening 11a of the core 11, forming an annular, integral unit. The slot-filling portion 131 within each slot forms a reinforcing rib along the axial direction of the core 11, while the connecting portion 132 forms an annular sleeve. This integrally formed slot closure 13 offers superior overall strength and sealing performance, reducing the ingress of dust, foreign matter, and moisture into the winding 12 through the slot opening 11a, thereby improving the insulation reliability of the winding 12.

[0048] When the connecting part 132 is connected to the slot filling part 131 of each slot 11a, the connection method can be to first set the slot filling part 131 of all slots, and then set the connecting part 132, so that the connecting part 132 is fixedly connected to each slot filling part 131 to form an annular whole; or the slot filling part 131 can be first set in part of the slots, and after the slot filling part 131 that has been set is connected with the connecting part 132, the remaining slot filling part 131 is set, and then the connecting part 132 is used to continue to connect, and so on, until the connecting part 132 connects all the slot filling parts 131 to form an annular whole.

[0049] It should be noted that the connection between the connecting portion 132 and the slot filling portion 131 of each slot 11 a may be adhesive, resin cured, a combination of multiple connections, or other forms of connection or combination.

[0050] In some embodiments, the slot filling portion 131 may include a sealing unit 1311 and a filling unit 1312. Referring to FIG2 , when setting the slot filling portion 131, the sealing unit 1311 may be first placed into the slot opening 11a from the inner surface of the stator core, followed by the filling unit 1312. Alternatively, the sealing unit 1311 and the filling unit 1312 may be combined and then placed into the slot opening 11a. Compared to the related art, which requires inserting a molded slot closure from one side of the core slot opening, the slot closure 13 of the present embodiment can reduce the design and processing costs of the slot closure 13 and the teeth 111, and can also reduce the risk of wear and scratches on the slot closure 13 by the teeth 111 and the winding 12, thereby improving the sealing and strength of the slot closure 13.

[0051] It should be noted that the sealing unit 1311 can be connected to either the winding 12 or the tooth portion 111 of the core 11, or can be connected to both the winding 12 and the tooth portion 111. The connection between the sealing unit 1311 and the winding 12 or the tooth portion 111 can be adhesive or other forms of connection. This ensures that the sealing unit 1311 remains fixed relative to the winding 12 or the tooth portion 111, separating the filling unit 1312 from the winding 12 and the tooth portion 111, respectively.

[0052] It should be noted that the connection between the sealing unit 1311 and the filling unit 1312 can be adhesive, or the filling unit 1312 can be pressed tightly against the tooth portion 111 by the pressure generated by the filling, or other forms of connection. The connection between the sealing unit 1311 and the filling unit 1312 can better secure the sealing unit 1311 and the filling unit 1312 within each core slot 11a, so that the sealing unit 1311 and the filling unit 1312 are not easily loosened or dropped out during the manufacturing process of the slot closure 13.

[0053] It should be noted that, in order to improve the sealing performance of the slot closure 13, the sealing unit 1311 can contact the inner walls of the tooth portion 111 on both sides near the connecting portion 132. Furthermore, the sealing unit 1311 can extend to the top surface of the tooth portion 111, or terminate somewhere on the inner walls of the tooth portion 111 on both sides near the connecting portion 132.

[0054] It is understood that when the sealing unit 1311 extends to the surface where the top of the tooth portion 111 is located, the sealing unit 1311 can be connected to the surface where the top of the tooth portion 111 is located, thereby separating the surface where the top of the tooth portion 111 is located from the connecting portion 132. Depending on the extent of extension of the sealing unit 1311, the connecting portion 132 and the surface where the top of the tooth portion 111 is located can be completely separated or partially separated.

[0055] Specifically, if the connection portion 132 is completely separated from the surface where the top of the tooth portion 111 is located by the sealing unit 1311, the connection portion 132 is connected to the sealing unit 1311 and is not connected to the surface where the top of the tooth portion 111 is located. If the connection portion 132 is not completely separated from the surface where the top of the tooth portion 111 is located, the connection portion 132 is connected to both the sealing unit 1311 and the surface where the top of the tooth portion 111 is located.

[0056] When sealing unit 1311 terminates somewhere on the inner walls of tooth portion 111 near connecting portion 132, connecting portion 132 is connected to the top surface of tooth portion 111, and connecting portion 132 is connected to filling unit 1312, but not to sealing unit 1311. Filling unit 1312 fills the portion of tooth portion 111 not covered by sealing unit 1311 and is connected to tooth portion 111. The connection between filling unit 1312 and tooth portion 111 can be adhesive bonding, resin curing, a combination of multiple connections, or other forms of connection or combination of connections.

[0057] In some embodiments, referring to FIG. 2 , the sealing unit 1311 may be a stack of multiple or single sealing layers, the filling unit 1312 may be a stack of multiple or single filling layers, and the connecting portion 132 may be a stack of multiple or single connecting layers.

[0058] It should be noted that the sealing layers, the filling layers, and the connecting layers can be connected by bonding, by resin curing, by a combination of multiple connections, or by other forms of connection or combination connections.

[0059] It should be noted that the sealing layer can be an impregnated fiber cloth strip or other forms, the filling layer can be an impregnated fiber rope or other forms, and the connecting layer can be an impregnated fiber cloth or other forms.

[0060] Specifically, the connecting layer can be a single impregnated fiber cloth that completely covers the surface of the inner ring of the core, or multiple impregnated fiber cloths that completely cover the inner ring of the core.

[0061] It should be noted that the thickness of the connecting portion 132 and the connecting layer needs to be determined according to the gap between the stator and rotor of the motor. In some embodiments, to reduce the difficulty of manufacturing the slot closure 13, the connecting layer is usually set to a preset thickness, which can be 0.3 mm or other specifications.

[0062] In some embodiments, the sealing unit 1311 , the filling unit 1312 , and the connecting portion 132 respectively include a reinforcing material (not shown) and a base material (not shown).

[0063] Specifically, the reinforcing material can be a polymer material. For example, the reinforcing material can be glass fiber, carbon fiber, aramid fiber, or a combination of multiple polymer materials. The low thermal conductivity polymer material used in the reinforcing material, through the structure of the slot closure 13 (see Figure 3), can form an orderly heat dissipation channel, blocking the mutual transfer of heat between the stator and rotor of the motor, creating an independent heat exchange space between the stator and rotor, and providing significant design space for improving motor efficiency.

[0064] Specifically, the matrix material may be a high molecular polymer, for example, a thermosetting resin.

[0065] It should be noted that if a magnetic slot closure is required, a magnetic material may be added to the base material, that is, the base material may be a combination of a thermosetting resin and a magnetic material.

[0066] A second aspect of the present application provides a method for manufacturing a slot closure for an iron core, which can be applied to the slot closure of any of the above embodiments. The method is manufactured using an iron core mold. The iron core mold has a structure that can be contoured to the structure of the iron core. The iron core mold is configured in an annular shape and has teeth and slots formed between the teeth. The iron core mold can include a stator iron core mold and a rotor iron core mold to manufacture the slot closure for the stator iron core and the slot closure for the rotor iron core, respectively. Referring to Figure 5, the manufacturing method includes:

[0067] Step S101: placing a slot filling portion in a slot opening of an iron core mold.

[0068] Step S102 : Connecting the connecting portion to the slot filling portion in each of the slots of the core mold.

[0069] Step S103 , pressing the groove filling portion and the connecting portion at a preset time, preset pressure, and preset temperature, and solidifying them to form a whole.

[0070] The slot closure of the iron core is obtained by the manufacturing method. The slot closure is removed from the iron core mold and assembled into the iron core as a whole, which simplifies the assembly procedure of the slot closure and improves the assembly efficiency of the slot closure.

[0071] Specifically, the slot filling portion may include a sealing unit 1311 and a filling unit 1312. The sealing unit 1311, the filling unit 1312, and the connecting portion 132 include a reinforcing material and a base material, respectively.

[0072] In some embodiments, since the core mold imitates the core, the structure of the core mold can be borrowed from the structural diagram of the core, please refer to Figure 2. When the filling unit 1312 fills the slot 11a, the filling degree can be that the filling unit 1312 is flush with the top of the tooth portion 111, or the filling unit 1312 is slightly higher than the top of the tooth portion 111, to ensure that when the connecting portion 132 is subsequently covered on the slot filling portion 131, the filling unit 1312 can be more fully contacted with the connecting portion 132 through the annular tire expansion tooling or the pressure tooling, thereby improving the overall sealing and strength of the slot closure 13.

[0073] In some embodiments, the matrix material of the sealing unit 1311 , the filling unit 1312 and the connecting portion 132 is a thermosetting resin, and the reinforcing material of the sealing unit 1311 , the filling unit 1312 and the connecting portion 132 is glass fiber, aramid fiber or carbon fiber.

[0074] It is understandable that glass fiber, aramid fiber or carbon fiber can have a strong bonding force with the thermosetting resin, so that the cured slot closure 13 has higher strength and better sealing performance.

[0075] In addition, the combination of thermosetting resin and glass fiber, aramid fiber or carbon fiber makes the slot filling part 131 and the connecting part 132 soft and easy to deform, so that the slot 11a can be more fully filled, and the connection between the connecting part 132 and the various parts of the slot filling part 131 is more tightly connected, thereby increasing the strength of the slot closure 13.

[0076] It should be noted that in step S103, the preset time and preset temperature usually need to be determined based on the high molecular polymer in the matrix material, and the preset pressure, in theory, is within the range that the slot closure 13 and the iron core 11 can withstand. The greater the preset pressure, the better the strength of the slot closure 13.

[0077] In some embodiments, when the matrix material is a thermosetting resin, the preset time in step S103 is 2 to 4 hours; the preset temperature is above the curing temperature of the resin, which is 170±5 degrees Celsius; and the preset pressure is generally about 10±2 MPa.

[0078] In some embodiments, step S103 may use a ring-shaped tire expansion tool or a pressure tool to press the connecting portion 132 , or other forms may be used to apply uniform pressure to the connecting portion 132 , which is not limited here.

[0079] It should be noted that in step S103, the matrix material uniformly fills the slot filling part 131 and the connecting part 132 at the slot opening 11a of the core mold, and at the same time discharges the air, small molecular organic volatiles and other substances in the slot closure 13 and between the slot closure 13 and the core mold, so that the slot closure 13 has higher strength and better sealing performance.

[0080] In order to improve the insulation density of the winding 12, after the slot closure 13 is inserted into the slot 11a, the winding 12 can be insulated and dipped in paint as a whole using vacuum pressure or immersion technology. Under this technology, the pre-baking process of the workpiece can effectively solidify the integrated slot closure 13 without generating new energy consumption.

[0081] The third aspect of the embodiments of the present application provides a core assembly 10, comprising a core 11, a winding 12, and a slot closure 13 for the core according to any embodiment of the present application. The core 11 is configured in a ring shape, and the core has a tooth portion 111 and a slot 11a formed between the teeth; the winding 12 is wound on the slot 11a; and the slot closure 13 is embedded in the slot 11a. The slot closure 13 is in contact with and connected to the core 11, and is also used to fix the winding 12. For example, the overall slot closure 13 is sleeved on the core 11 so that the slot filling portion 131 is arranged in the slot 11a of the core. The core 11, the winding 12, and the slot closure 13 form a whole, so that the slot closure 13 has a better sealing and fixing effect on the winding 12 in the slot 11a.

[0082] It should be noted that the iron core 11 can be a stator iron core or a rotor iron core.

[0083] Specifically, the iron core 11 can be an outer stator iron core, an inner rotor iron core, an inner stator iron core, or an outer rotor iron core, and there is no limitation here.

[0084] A fourth aspect of the embodiments of the present application provides a motor, comprising a core assembly according to any embodiment of the present application.

[0085] Motor heat loss primarily comes from winding losses and core losses. For example, the stator is the primary source of heat. The integrated slot closure structure, which separates the stator and rotor, effectively reduces heat transfer from the stator to the rotor, allowing the rotor to operate at a lower temperature and improving motor efficiency.

[0086] The foregoing description is merely a preferred embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A slot closure for an iron core, comprising: A slot filling portion is disposed in the slot of the core; as well as The connecting part is respectively connected to the slot filling parts in each of the slots of the iron core to form an annular whole.

2. The slot closure according to claim 1, wherein the slot filling portion comprises: A sealing unit, disposed in the notch; as well as A filling unit, filled in the notch and connected to the sealing unit; The sealing unit is used to separate the filling unit from the winding of the iron core and the teeth of the iron core respectively, and the connecting portion is connected to the sealing unit and the filling unit in each of the slots respectively; or, The sealing unit is used to separate the filling unit from the winding of the iron core and the tooth portion of the iron core respectively, and the connecting portion is connected to the filling unit in each of the slots.

3. The slot closure according to claim 2, wherein the sealing unit comprises a plurality of sealing layers stacked together, or the sealing unit is a single sealing layer; and / or, The filling unit includes a plurality of stacked filling layers, or the filling unit is a single filling layer; and / or, The connecting portion includes a plurality of stacked connecting layers, or the connecting portion is a single connecting layer. 4 . The slot closure according to claim 2 , wherein the sealing unit, the filling unit, and the connecting portion respectively comprise a reinforcing material and a matrix material. The slot closure according to claim 4 , wherein the reinforcing material is a polymer material. 6 . The slot closure according to claim 5 , wherein the polymer material comprises glass fiber, aramid fiber and / or carbon fiber.

7. The slot closure according to claim 4, wherein the matrix material comprises a thermosetting resin and / or a magnetic material.

8. A method for manufacturing a slot closure for an iron core, comprising: placing the slot filling portion in the slot opening of the core mold; connecting the connecting part to the slot filling part in each of the slots of the core mold; The groove filling part and the connecting part are pressed together at a preset time, preset pressure and preset temperature, and solidified to form a whole. 9 . The manufacturing method according to claim 8 , wherein a height of the slot filling portion on a side close to the connecting portion is greater than or equal to a top height of the tooth portion of the core mold.

10. The manufacturing method according to claim 8, wherein the slot filling part comprises a sealing unit and a filling unit, and the step of arranging the slot filling part in the slot opening of the core mold comprises: Disposing the sealing unit in the notch; The filling unit is arranged in the notch and connected with the sealing unit.

11. The manufacturing method according to claim 10, wherein the sealing unit, the filling unit and the connecting portion respectively comprise a reinforcing material and a matrix material, and the manufacturing method further comprises: The reinforcing material is impregnated into the matrix material.

12. The manufacturing method according to claim 11, wherein the matrix material is a thermosetting resin; The preset time is 2 to 4 hours, the preset pressure is 10±2 MPa, and the preset temperature is 170±5 degrees Celsius.

13. A core assembly comprising: An iron core configured in a ring shape and having teeth and notches formed between the teeth; A winding, wound on the slot; as well as The slot closure according to any one of claims 1 to 8, wherein the slot closure is embedded in the slot.

14. An electric motor comprising the core assembly according to claim 13.

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