Material layer for a laminated core of an electric machine

0001The invention relates to a material layer for a laminated core of an electrical machine.

0002The invention further relates to a laminated core for an electrical machine with a plurality of such material layers.

0003Furthermore, the invention relates to an electrical rotating machine with at least one laminated core.

0004In addition, the invention relates to a method for producing such a material layer.

0005In electrical machines, laminated cores made of stacked electrical sheets are usually used to suppress the spread of eddy currents. Such electrical machines are, for example, motors, generators and transformers, such as transformers and switching devices. The electrical sheets, which contain, for example, a soft magnetic material, in particular iron, are usually cut or punched from large rolled sheets. The sheets are then packaged into a sheet metal package. Using such a conventional manufacturing process, it is currently not possible to produce sheets on an industrial scale that have a maximum layer thickness of 100 μm. In addition, waste is generated when cutting or punching the sheets from the large sheets.

0006The disclosure document<patcit id="pcit0001" dnum="EP3595148A1"><text>EP 3 595 148 A1</text></patcit> describes a process for producing a material layer with a layer thickness between 0.5 and 500 pm with the steps: Applying a suspension, comprising at least one binder and solid particles, through a template onto a base surface to obtain a green body, expelling the binder from the green body, in particular by means of debinding, creating a permanent cohesion of the solid particles by heating and/or by means of compaction, in particular by means of sintering .

0007<patcit id="pcit0002" dnum="US2004007289A1"><text>US2004/007289A1</text></patcit>, <patcit id="pcit0003" dnum="DE1433774A1"><text>DE 14 33 774 A1</text></patcit>, <patcit id="pcit0004" dnum="US2543710A"><text>US 2,543,710 A</text></patcit>, <patcit id="pcit0005" dnum="EP3595135A1"><text>EP 3 595 135 A1</text></patcit> and<patcit id="pcit0006" dnum="WO2015074911A2"><text>WO 2015/074911 A2</text></patcit> disclose material layers and/or their manufacturing processes from the prior art.

0008In addition, the surfaces must be treated and functionalized in order to electrically insulate the individual sheets from each other when building stacks of sheets. Electrical sheets that are manufactured using a conventional manufacturing process are usually coated with an insulating varnish with a typical layer thickness of 1 to 4 pm, which represents a significant additional time and cost, especially for very thin electrical sheets with a layer thickness of a maximum of 100 pm. In addition, with such thin electrical sheets, the magnetically ineffective paint layer takes up a significant proportion of the overall sheet thickness and thus noticeably reduces the stacking factor and thus the performance of the electrical machine. The invention is based on the object of specifying a material layer for a laminated core of an electrical machine, which, compared to the prior art, is easier and more cost-effective to produce and enables a larger stacking factor.

0009The object is achieved according to the invention by a material layer for a laminated core of an electrical machine, which is made of a ferromagnetic material and has an electrically insulating coating on at least one side of the layer, wherein the electrically insulating coating comprises an electrically insulating material and wherein the electrically insulating material of the electrically insulating coating is produced by controlled oxidation of the ferromagnetic material of the material layer.

0010Furthermore, the object is achieved according to the invention by a laminated core for an electrical machine with a plurality of such material layers.

0011Furthermore, the object is achieved according to the invention by an electrical rotating machine with at least one laminated core.

0012In addition, the object is achieved according to the invention by a method for producing a material layer for a laminated core of an electrical machine, a green body being produced from a ferromagnetic material, the green body being sintered, with an electrically insulating coating on at least one side of the layer immediately after the sintering process is produced by controlled oxidation of the ferromagnetic material of the material layer.

0013The advantages and preferred embodiments listed below with regard to the material layer can be applied analogously to the laminated core, the electrical machine and the method.

0014The invention is based on the idea of ​​increasing a stacking factor in a laminated core for an electrical machine by reducing the layer thickness of insulation between the material layers. Such material layers are made from a ferromagnetic material. Ferromagnetic materials include iron and iron alloys, especially iron-based alloys. Iron-based alloys include iron-cobalt and iron-silicon. Such insulation is designed as an electrically insulating coating and is arranged on at least one side of the layer, the electrically insulating coating comprising an electrically insulating material. Electrically insulating materials are, for example, iron oxides, in particular iron monoxide (FeO, also called iron (II) oxide), triiron tetraoxide (Fe₃O₄, also called iron (II,III) oxide or magnetite) and diiron trioxide (Fe₂O₃, also called iron(III) oxide). The electrically insulating coating is produced by controlled oxidation of the ferromagnetic material of the material layer. Controlled oxidation takes place in an enclosed area with a controlled atmosphere. This means that for the controlled oxidation, a defined oxygen partial pressure is set over a defined period of time at a predetermined temperature range in which the oxygen partial pressure is available. In this way, a desired composition and layer thickness of the electrically insulating coating can be produced easily and cost-effectively using a defined redox potential. Furthermore, very thin layers, for example thinner than 1 pm, can be produced through controlled oxidation, which increases the stacking factor in the laminated core.

0015A further embodiment provides that the ferromagnetic material has an electrical conductivity of at least 8 MS/m. For example, the ferromagnetic material is iron or an iron alloy. Experience has shown that such conductivity has proven to be particularly advantageous.

0016A further embodiment provides that the ferromagnetic material contains iron, the electrically insulating material containing an iron oxide, in particular iron monooxide and/or triiron tetraoxide. Due to its metallurgical properties, iron is well suited for the production of thin sheets. Furthermore, iron can be oxidized easily and cost-effectively in a controlled manner, and thin oxide layers can be produced by the controlled oxidation, which enable a large stacking factor.

0017A further embodiment provides that the electrically insulating material of the electrically insulating coating has a ferrimagnetic material and/or has a permeability of at least 3. A ferrimagnetic material is, for example, triiron tetraoxide. Such insulation increases the magnetic volume of the laminated core.

0018A further embodiment provides that the electrically insulating coating has a layer thickness of a maximum of 1 pm. Thanks to such a small layer thickness, a sufficiently high stacking factor is achieved even with thin sheets.

0019A further embodiment provides that the material layer has a layer thickness of 10 µm to 150 µm, in particular 10 µm to 100 µm. With such a layer thickness, sufficient eddy current suppression is achieved, for example when used in an electrical machine.

0020A further embodiment provides that the material layer is made from a green body. The green body is produced, for example, by screen printing, stencil printing or binder jetting. In particular, the green body has a, in particular organic, binder and ferromagnetic solid particles, the ferromagnetic solid particles being present, for example, as alloy powders or as mixtures of powders made from pure elements. The powder can be customized in terms of strength, magnetic and/or electrical properties, thermal conductivity and type of oxidation products.

0021A further embodiment provides that the material layer has the electrically insulating coating on both sides of the layer. Insulation on both sides increases reliability, especially with thin insulation layers.

0022A further embodiment provides that the green body is sintered under a reducing atmosphere. A reducing atmosphere contains, for example, a hydrogen-nitrogen mixture or a hydrogen-noble gas, in particular a hydrogen-argon mixture. The nitrogen or the noble gas acts as a purge gas. For example, the green body is sintered under a forming gas that contains 95% nitrogen and 5% hydrogen. The reducing atmosphere prevents oxidation and thus contamination. In particular, organic binders are expelled essentially without residue in a reducing atmosphere by removing the carbon atoms from the green body.

0023A further embodiment provides that a redox potential is specifically set for the controlled oxidation of the ferromagnetic material by adding water vapor. The targeted adjustment of the redox potential occurs, for example, by concentrating the water vapor in the atmosphere at a defined temperature. Oxidation by supplying steam is simple and inexpensive, especially immediately after sintering under a reducing atmosphere.

0024A further embodiment provides that at least one side of the layer 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 time period. For example, at a given oxygen partial pressure and a given temperature at which the oxygen partial pressure is available, the layer thickness is essentially set by the time period, while the composition of the oxide layer that forms is essentially determined by the oxygen partial pressure and the temperature range in which the oxygen partial pressure is available. is controlled. By varying the parameters, oxide layers of the desired type and layer thickness can be produced easily and cost-effectively.

0025A further embodiment provides that the ferromagnetic material contains iron, with the oxygen partial pressure, the temperature range in which the oxygen partial pressure is available, and the time period being adjusted such that the electrically insulating material contains a predetermined proportion of iron monoxide and/or triiron tetraoxide . In this way, iron oxide layers of the desired type and layer thickness can be produced easily and inexpensively.

0026The invention is described and explained in more detail below using the exemplary embodiments shown in the figures.

0027Show it:<dl id="dl0001"><dt>FIG 1</dt><dd>a schematic cross-sectional representation of an electrical rotating machine,</dd><dt>FIG 2</dt><dd>a schematic representation of a first embodiment of a material layer,</dd><dt>FIG 3</dt><dd>a schematic representation of a second version of a material layer,</dd><dt>FIG 4</dt><dd>a schematic representation of a method for producing a material layer,</dd><dt>FIG 5</dt><dd>a thermodynamic state diagram for various iron oxides and</dd><dt>FIG 6</dt><dd>Isothermal oxidation kinetics curves for iron as a function of time and temperature.</dd></dl>

0028The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that can be viewed independently of one another, which also develop the invention independently of one another and are therefore to be viewed 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 that have already been described.

0029The same reference numbers have the same meaning in the different figures.

0030<figref idref="f0001">FIG 1</figref> shows a schematic cross-sectional representation of an electrical rotating machine 2. The electrical rotating machine 2, which can be used as a motor and / or as a generator, has a rotor 6 that can be rotated about an axis of rotation 4 and a stator 8, the stator 8 being, for example, radially outside the Rotor 6 is arranged. The rotation axis 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.

0031The 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 plurality of stacked material layers 16 that are electrically insulated from one another and have a first layer thickness d1 in the range from 10 pm to 150 pm, in particular 10 pm to 100 pm, and are made of a ferromagnetic material, for example iron or an iron alloy are. In addition, the rotor 6 includes a plurality of permanent magnets 18 connected to the rotor laminated core 14 for operation as a synchronous machine. The rotor 6 can, in particular instead of the permanent magnets 18, have a squirrel cage for operation as an asynchronous machine or an excitation winding. The shaft 12 of the rotor 6 is arranged to be rotatable via bearings 20.

0032The stator 8 includes a stator laminated core 22 in which a stator winding 24 is accommodated. The stator laminated core 22 comprises a plurality of stacked material layers 16 that are electrically insulated from one another and have a second layer thickness d2 in the range of 10 pm to 150 µm, in particular 10 pm to 100 pm, and are made of a ferromagnetic material, for example iron or an iron alloy are. The rotor 6 and the stator 8 are housed in a closed housing 26.

0033<figref idref="f0002">FIG 2</figref> shows a schematic representation of a first embodiment of a material layer 16, which has a layer thickness d in the range from 10 pm to 150 pm, in particular 10 µm to 100 µm, and is produced, for example, by screen printing, stencil printing or binder jetting and subsequent sintering. The material layer 16 in<figref idref="f0002">FIG 2</figref> can be configured for a rotor laminated core 14 or a stator laminated core 22 and is made of a ferromagnetic material, for example iron or an iron-based alloy, with an electrical conductivity of at least 8 MS/m. One 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 made of an electrically insulating material, the electrically insulating material having a conductivity that is at least 1000 times lower than the conductivity of the ferromagnetic material. In addition, the electrically insulating coating 30 has a layer thickness s1 of a maximum of 1 pm.

0034The electrically insulating coating 30 is produced by controlled oxidation of the ferromagnetic material of the material layer 16. In a controlled oxidation, a composition of the electrically insulating coating 30 and the layer thickness s are adjusted via a defined redox potential. Here, the surface of the material layer 16 is oxidized under a defined oxygen partial pressure, at a predetermined temperature range in which the oxygen partial pressure is available, over a defined period of time. The composition and layer thickness s of the oxide layer that forms can therefore be controlled by the composition of the atmosphere, the temperature and the length of time.

0035In the case of a material layer 16 made of iron, the surface of the material layer 16 is oxidized with the help of water vapor, the type and thickness of the oxide layer being adjustable via a proportion of the water vapor in the atmosphere. This creates the electrically insulating material iron monoxide (FeO) and/or triiron tetraoxide (Fe₃O₄), whereby the proportions of iron oxides can be controlled via the composition of the atmosphere, the temperature and the length of time.

0036In 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 controllable via its composition. The further design of the material layer 16 in<figref idref="f0002">FIG 2</figref> corresponds to the version in<figref idref="f0001">FIG 1</figref>.

0037<figref idref="f0002">FIG 3</figref> 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 design of the material layer 16 in<figref idref="f0002">FIG 3</figref> corresponds to the version in<figref idref="f0002">FIG 2</figref>.

0038<figref idref="f0003">FIG 4</figref> 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 passed through a template 38 onto a base surface 40 to obtain a green body 42 upset. For example, the suspension 36 is applied to the base surface 40 using a squeegee over the template 38, which may have a sieve. Alternatively, the green body 42 is produced using binder jetting.

0039In a subsequent process step, the binder is expelled from the green body 42, in particular by means of debinding, and the green body 42 is sintered, with the sintering process creating a permanent cohesion of the ferromagnetic solid particles. Sintering and debinding takes place in a closed area with a controlled atmosphere. The green body 42 is debinded and sintered under a reducing atmosphere. The reducing atmosphere contains, for example, a hydrogen-nitrogen mixture or a hydrogen-noble gas, in particular a hydrogen-argon mixture. The nitrogen or the noble gas acts as a purge gas. For example, the green body 42 is sintered under a forming gas that contains 95% nitrogen and 5% hydrogen. The reducing atmosphere prevents oxidation and thus contamination. In particular, organic binders are expelled essentially without residue in a reducing atmosphere by removing the carbon atoms from the green body. Both during debinding and during sintering, the dimensions of the green body 42 are reduced depending on the material used, so that the material layer 16 resulting from the sintering process has a layer thickness d of 10 pm to 150 pm, in particular 10 pm to 100 pm.

0040In a subsequent process step, an electrically insulating coating 30 is produced by controlled oxidation of the ferromagnetic material of the material layer 16. The production of the electrically insulating coating 30 by oxidation takes place in a closed area with a controlled atmosphere. In particular, the production of the electrically insulating coating 30 takes place in the same closed area as the sintering process. At least part of the surface 44 of the material layer 16, which is in fluid communication with the atmosphere surrounding the material layer 16, is oxidized over a defined period of time under a defined oxygen partial pressure, at a predetermined temperature range in which the oxygen partial pressure is available. For a given composition of the atmosphere and temperature, the layer thickness s is essentially set by the time period. The composition of the oxide layer that 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 made of iron, with the surface 44 of the material layer 16 being oxidized with the help of water vapor in the atmosphere. Oxidation on both sides is made possible, for example, by turning the material layer 16. The further design of the material layer 16 in<figref idref="f0003">FIG 4</figref> corresponds to the version in<figref idref="f0002">FIG 2</figref>.

0041<figref idref="f0004">FIG 5</figref> shows a thermodynamic state diagram for various iron oxides. The thermodynamic state diagram shows the respective oxygen partial pressure pO₂ as a function of the reciprocal temperature T and the proportion of water vapor in a H₂-H₂O atmosphere, where the atmosphere contains nitrogen, hydrogen and water vapor. Furthermore, the decomposition pressures of various iron oxides (FeO, Fe₃O₄, Fe₂O₃) shown as a function of the reciprocal temperature T. The decomposition pressure, which is also called dissociation pressure or formation pressure, indicates the oxygen partial pressure at which equilibrium exists between oxidation of the metal to metal oxide and reduction of the metal oxide to metal. The oxygen partial pressure in the atmosphere is pO₂ greater than the decomposition pressure of the respective metal, oxidation occurs. For example, the oxygen partial pressure is pO₂ greater than the decomposition pressure of Fe₃O₄, is Fe₃O₄ If it is stable, however, if it is smaller, the compound FeO, which has less oxygen, is formed. Is the oxygen partial pressure pO₂ at a certain temperature identical to the decomposition pressure, then two solid phases coexist, for example FeO and Fe₃O₄, each other. Therefore, with the in<figref idref="f0003">FIG 4</figref> The method shown can be adjusted via the oxygen partial pressure and the temperature range in which the oxygen partial pressure is available, which oxides form in the electrically insulating coating 30.

0042<figref idref="f0005">FIG 6</figref> shows isothermal oxidation kinetics curves for iron as a function of time t and temperature T. A weight increase Δm of iron oxides is shown as a function of time t and temperature T in a defined atmosphere. Therefore, with the in<figref idref="f0003">FIG 4</figref> In the method shown, a defined layer thickness s can be formed at a given atmosphere by varying the time t and temperature T.

0043In summary, the invention relates to a material layer 16 for a laminated core 14, 22 of an electrical machine 2. In order to enable simpler and more cost-effective production as well as a larger stacking factor compared to the prior art, it is proposed that the material layer 16 is made of a ferromagnetic material and has an electrically insulating coating 30, 34 on at least one layer side 28, 32 , wherein the electrically insulating coating 30, 34 comprises an electrically insulating material, wherein the electrically insulating material of the electrically insulating coating 30, 34 is produced by controlled oxidation of the ferromagnetic material of the material layer 16.