MATERIAL LAYER FOR A LAMINATED CORE OF AN ELECTRIC MACHINE

Abstract

A material layer for a laminated core of an electric machine is made of iron-containing ferromagnetic material and includes an electrically insulating coating on at least one side of the material layer. The electrically insulating coating Includes an electrically Insulating material which Is produced through controlled oxidation of the ferromagnetic material of the material layer and contains iron monoxide and/or triiron tetraoxid. The material layer is produced from a green body, which Is sintered under a reducing atmosphere.

Claims

1.-15. (canceled)

16. A material layer for a laminated core of an electric machine, said material layer made of iron-containing ferromagnetic material and comprising: an electrically insulating coating on at least one side of the material layer, said electrically Insulating coating comprising an electrically insulating material which is produced through controlled oxidation of the ferromagnetic material of the material layer and contains iron monoxide and/or triiron tetraoxide, wherein the material layer is produced from a green body, which is sintered under a reducing atmosphere.

17. The material layer of claim 16, wherein the ferromagnetic material has an electrical conductivity of at least 8 MS/m.

18. The material layer of claim 16, wherein the electrically insulating material of the electrically insulating coating Includes a ferrimagnetic material and/or a permeability of at least 3.

19. The material layer of claim 16, wherein the electrically insulating coating has a layer thickness of at most 1 μm.

20. The material layer of claim 16, wherein the material layer has a layer thickness of 10 μm to 150 μm, in particular, 10 μm to 100 μm.

21. The material layer of claim 16, further comprising a further electrically insulating coating arranged on another side of the material layer.

22. A laminated core for an electric machine, said laminated core comprising a plurality of material layers, each said material layer comprising an electrically insulating coating on at least one side of the material layer, said electrically insulating coating comprising an electrically Insulating material which is produced through controlled oxidation of the ferromagnetic material of the material layer and contains iron monoxide and/or triiron tetraoxide, wherein the material layer is produced from a green body, which is sintered under a reducing atmosphere.

23. An electric rotating machine, comprising a laminated core as set forth in claim 22

24. A method for producing a material layer for a laminated core of an electric machine, said method comprising: producing a green body from a ferromagnetic material; sintering the green body under a reducing atmosphere; and applying immediately after sintering an electrically insulating coating on at least one layer side through controlled oxidation of the ferromagnetic material.

25. The method of claim 24, further comprising setting a redox potential for the controlled oxidation of the ferromagnetic material by adding water vapor.

26. The method of claim 24, wherein the at least one layer side is oxidized in a controlled manner by setting an oxygen partial pressure, a temperature range in which the oxygen partial pressure is available, and a period of time.

27. The method of claim 26, wherein the ferromagnetic material contains iron, and wherein the oxygen partial pressure, the temperature range in which the oxygen partial pressure is available, and the period of time are set in such a way that the electrically insulating material contains a predetermined proportion of iron monoxide and/or triiron tetraoxide.

Description

[0026] The invention is described and explained in more detail hereinafter with reference to the exemplary embodiments shown in the figures, in which:

[0027] FIG. 1 shows a schematic cross-sectional representation of an electric rotating machine,

[0028] FIG. 2 shows a schematic representation of a first embodiment of a material layer,

[0029] FIG. 3 shows a schematic representation of a second embodiment of a material layer,

[0030] FIG. 4 shows a schematic representation of a method for producing a material layer,

[0031] FIG. 5 shows a thermodynamic state diagram for various iron oxides and

[0032] FIG. 6 shows isothermal oxidation kinetics curves for iron as a function of time and temperature.

[0033] The exemplary embodiments explained hereinafter are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent Individual features of the invention which are to be considered independently of one another and which each also develop the invention independently of one another and are thus also to be regarded as part of the invention individually or in a combination other than that shown. Furthermore, the described embodiments can also be supplemented by further features of the Invention already described.

[0034] Identical reference characters have the same meaning in the different figures.

[0035] FIG. 1 shows a schematic cross-sectional representation of an electric rotating machine 2. The electric rotating machine 2, which can be used as a motor and/or as a generator, has a rotor 6, which can be rotated about an axis of rotation 4, and a stator 8, the stator 8 being arranged, for example, radially outside the rotor 6. The axis of rotation 4 defines an axial direction, a radial direction and a circumferential direction. A fluid gap 10, which is designed in particular as an air gap, is formed between the rotor 6 and the stator 8.

[0036] The rotor 6 has a shaft 12 and a rotor laminated core 14, the rotor laminated core 14 being connected to the shaft 12 in a rotationally fixed manner. The rotor laminated core 14 comprises a multiplicity of stacked material layers 16 which are electrically insulated from one another and have a first layer thickness d1 in the range of 10 μm to 150 μm, in particular, 10 μm to 100 μm, and are produced from a ferromagnetic material, for example from iron or an iron alloy. In addition, the rotor 6 comprises a plurality of permanent magnets 18 connected to the rotor laminated core 14 for operation as a synchronous machine. The rotor 6 can have, in particular instead of the permanent magnets 18, a short-circuit cage for operation as an asynchronous machine or an excitation winding. The shaft 12 of the rotor 6 is rotatably arranged over bearings 20.

[0037] The stator 8 comprises a laminated stator core 22 in which a stator winding 24 is accommodated. The laminated stator core 22 comprises a multiplicity of stacked material layers 16 which are electrically insulated from one another and have a second layer thickness d2 in the range of 10 μm to 150 μm, in particular, 10 μm to 100 μm, and are produced from a ferromagnetic material, for example from iron or an iron alloy. The rotor 6 and the stator 8 are accommodated in an enclosed housing 26.

[0038] FIG. 2 shows a schematic representation of a first embodiment of a material layer 16 which has a layer thickness d in the range of 10 μm to 150 μm, in particular, 10 μm to 100 μm, and is produced, for example, by means of screen printing, stencil printing or binder jetting and subsequent sintering. The material layer 16 in FIG. 2 can be configured for a rotor laminated core 14 or a laminated stator core 22 and is produced from a ferromagnetic material, for example from iron or an iron-based alloy, with an electrical conductivity of at least 8 MS/m. A layer side 28 of the material layer 16 has an electrically insulating coating 30 which is suitable for electrically insulating stacked material layers 16 from one another, for example when used in a laminated core 14, 22. The electrically insulating coating 30 is produced from an electrically insulating material, the electrically insulating material having a conductivity which is at least 1000 times less than the conductivity of the ferromagnetic material. In addition, the electrically insulating coating 30 has a layer thickness s1 of at most 1 μm.

[0039] The electrically insulating coating 30 is produced by means of controlled oxidation of the ferromagnetic material of the material layer 16. In the case of controlled oxidation, a composition of the electrically Insulating coating 30 and the layer thickness s are set via a defined redox potential. In this case, the surface of the material layer 16 is oxidized over a defined period of time under a defined oxygen partial pressure in a predetermined temperature range in which the oxygen partial pressure is available. The composition and layer thickness s of the oxide layer forming can thus be controlled by the composition of the atmosphere, the temperature and the period of time.

[0040] In the case of a material layer 16 produced from iron, the surface of the material layer 16 is oxidized with the aid of water vapor, it being possible to adjust the type and thickness of the oxide layer via a proportion of the water vapor in the atmosphere. In this case, the electrically insulating material iron monoxide (FeO) and/or triiron tetraoxide (Fe.sub.3O.sub.4) is produced, the proportions of the iron oxides being able to be controlled via the composition of the atmosphere, the temperature and the period of time.

[0041] In particular, the electrically insulating material of the electrically Insulating coating 30 has a permeability of at least 3, the permeability of the electrically insulating material being able to be controlled via its composition. The further embodiment of the material layer 16 in FIG. 2 corresponds to the embodiment in FIG. 1.

[0042] FIG. 3 shows a schematic representation of a second embodiment of a material layer 16 which has an electrically insulating coating 30, 34 on both layer sides 28, 32. A first layer thickness s1 is formed on the first layer side 28, while a second layer thickness s2 is formed on the second layer side 32. For example, the first layer thickness s1 corresponds to the second layer thickness s2. The further embodiment of the material layer 16 in FIG. 3 corresponds to the embodiment in FIG. 2.

[0043] FIG. 4 shows a schematic representation of a method for producing a material layer 16. In a method step, a suspension 36, which comprises at least one, in particular organic, binder and ferromagnetic solid particles, in particular Iron particles, is applied through a stencil 38 to a base area 40 to obtain a green body 42. For example, the suspension 36 is applied by means of a doctor blade via the stencil 38, which can have a screen, to the base area 40. Alternatively, the green body 42 is produced by means of binder Jetting.

[0044] In a subsequent method step, the binder is driven out of the green body 42, In particular, by means of debindering, and the green body 42 is sintered, the sintering process creating a permanent cohesion of the ferromagnetic solid particles. Sintering and debindering takes place in an enclosed area with a controlled atmosphere. The green body 42 is debindered and sintered under a reducing atmosphere. The reducing atmosphere contains, for example, a hydrogen-nitrogen mixture or a hydrogen-noble gas mixture, in particular, a hydrogen-argon mixture. The nitrogen or the noble gas act as purge gas. For example, the green body 42 is sintered under a forming gas containing 95% nitrogen and 5% hydrogen. Oxidation and thus Impurities are prevented by the reducing atmosphere. In particular, organic binders are driven out essentially without residue in a reducing atmosphere by removing the carbon atoms from the green body. Both during debindering and sintering, the dimensions of the green body 42 are reduced as a function of the material used, so that the material layer 16 produced by the sintering process has a layer thickness d of 10 μm to 150 μm, in particular, 10 μm to 100 μm.

[0045] In a subsequent method step, an electrically insulating coating 30 is produced by means of controlled oxidation of the ferromagnetic material of the material layer 16. The production of the electrically insulating coating 30 by means of oxidation takes place in an enclosed area with a controlled atmosphere. In particular, the production of the electrically insulating coating 30 takes place in the same enclosed area as the sintering process. At least part of the surface 44 of the material layer 16, which is in fluid connection with the atmosphere surrounding the material layer 16, is oxidized over a defined period of time under a defined oxygen partial pressure, in a predetermined temperature range in which the oxygen partial pressure Is available. The layer thickness s is essentially set by the period of time at a given composition of the atmosphere and temperature. The composition of the oxide layer which forms can essentially be controlled by the oxygen partial pressure and the temperature range in which the oxygen partial pressure is available. In particular, the material layer 16 is produced from iron, the surface 44 of the material layer 16 being oxidized with the aid of water vapor in the atmosphere. Two-sided oxidation is made possible, for example, by turning the material layer 16. The further embodiment of the material layer 16 in FIG. 4 corresponds to the embodiment in FIG. 2.

[0046] FIG. 5 shows a thermodynamic state diagram for various iron oxides. The thermodynamic state diagram shows the respective oxygen partial pressure pO.sub.2 as a function of the reciprocal temperature T and the proportion of water vapor In an H.sub.2-H.sub.2O atmosphere, the atmosphere containing nitrogen, hydrogen and water vapor. Furthermore, the decomposition pressures of various iron oxides (FeO, Fe.sub.3O.sub.4, Fe.sub.2O.sub.3) are shown as a function of the reciprocal temperature T. The decomposition pressure, which is also referred to as dissociation pressure or formation pressure, Indicates the oxygen partial pressure at precisely which an equilibrium prevails between an oxidation of the metal to the metal oxide and a reduction of the metal oxide to the metal. If the oxygen partial pressure pO.sub.2 In the atmosphere is greater than the decomposition pressure of the respective metal, oxidation takes place. If, for example, the oxygen partial pressure pO.sub.2 is greater than the decomposition pressure of Fe.sub.3O.sub.4, Fe.sub.3O.sub.4 is stable, but if it is smaller, the oxygen-depleted compound FeO is formed. If the oxygen partial pressure pO.sub.2 at a certain temperature is identical to the decomposition pressure, then two solid phases, e.g. FeO and Fe.sub.3O.sub.4, coexist with one another. Therefore, with the method shown in FIG. 4, It is possible to adjust which oxides form in the electrically Insulating coating 30 via the oxygen partial pressure and the temperature range in which the oxygen partial pressure is available.

[0047] FIG. 6 shows isothermal oxidation kinetics curves for iron as a function of time t and temperature T. A weight increase Δm of iron oxides as a function of time t and temperature T is shown in a defined atmosphere. Therefore, with the method shown in FIG. 4, a defined layer thickness s can be formed for a given atmosphere by varying the time t and temperature T.

[0048] In summary, the invention relates to a material layer 16 for a laminated core 14, 22 of an electric machine 2. In order to allow simpler and more economical production and a greater stacking factor in comparison with the prior art, it is proposed that the material layer 16 is produced from a ferromagnetic material and has an electrically insulating coating 30, 34 on at least one layer side 28, 32, the electrically insulating coating 30, 34 comprising an electrically Insulating material, the electrically insulating material of the electrically Insulating coating 30, 34 being produced by means of controlled oxidation of the ferromagnetic material of the material layer 16.