Method for manufacturing elements for electrical working machines, which are formed with superimposed layers of iron or an iron alloy with soft magnetic properties

Abstract

Method for manufacturing elements for electrical working machines, which are formed with superimposed layers (1) of iron or an iron alloy with soft magnetic properties and in which an electrically insulating layer (2) is arranged between each of the layers (2) formed with iron or with the iron alloy, wherein the layers (1) of iron or the iron alloy each with a suspension formed with iron or with a powder of the iron alloy and an organic binder are formed by screen printing in a predetermined geometry with a predetermined first layer thickness and the electrically insulating layers (2) formed between the layers (1) of iron or the iron alloy formed by screen printing, which are formed with a powder and an organic binder, are formed by screen printing in the specified geometry with a specified second layer thickness, wherein the powder is a hydroxide or acetate selected from magnesium hydroxide, aluminum hydroxide, zirconium hydroxide, magnesium acetate, aluminum acetate and zirconium acetate or a carbonate selected from magnesium carbonate and zirconium carbonate and Following screen printing, the resulting layer stack undergoes a thermal treatment, during which In a first stage, debinding takes place in the temperature range between 100 °C and 800 °C, whereby the respective hydroxide, acetate and / or carbonate is decomposed in the temperature range between 100 °C and 300 °C, and a chemical reaction is carried out in which the respective hydroxide, acetate and / or carbonate is formed into the respective metal oxide with a fine particle size distribution of < 1 µm, and following the first stage, a second stage of thermal treatment is carried out, in which in a reducing atmosphere at a temperature in the range of 1200°C to 1350°C, sintering of the iron or the respective iron alloy is carried out to form layers (1) with corresponding soft magnetic properties and porous electrically insulating layers (2) are obtained.

Description

[0001] The invention relates to a method for manufacturing components for electrical machinery, which are formed from superimposed layers of iron or an iron alloy with soft magnetic properties. The components manufactured in this way can be used in electric motors, generators, or transformers, in particular as rotors or stators. Typically, electrically insulated electrical steel sheets stacked one on top of the other are used.

[0002] Conventional electrical steel sheets (e.g., made of Fe-3Si) are rolled and then coated with a baking varnish. This improves their punchability and ensures the insulation of the individual layers of sheet metal in a stack from each other, reducing eddy current losses during operation. The required geometry of the individual sheets is achieved by punching the rolled sheet. This process causes wear on the tools. Due to the rolling and punching process, the minimum sheet thickness is limited to approximately 200 µm and the alloy content to a maximum of 3.5 wt% Si.

[0003] Reducing eddy current losses is necessary to increase the efficiency of electrical machinery. This can be achieved primarily by increasing the silicon content of the respective iron alloy to > 3.5 wt% and reducing the sheet thickness to < 200 µm. However, manufacturing such sheet stacks using conventional methods is not yet possible because the corresponding iron alloys exhibit high strength and brittleness. Al, Cr, Co, and / or P can also be components of the iron alloy, either alone or in addition to silicon. The key factor here is how these alloying elements improve magnetic properties that are not solely related to resistivity.

[0004] Up to now, the individual sheets are coated with conventional baking varnish, then packaged in a separate process step and bonded together to form a sheet package at an elevated temperature of about 200°C-250°C.

[0005] The additive manufacturing of electrical steel sheets enables the production of thin sheets with a high alloy content of Si, Al, Cr or P. Since the further processing of very thin individual sheets is very complex, direct manufacturing of the sheet stack would be desirable and resource-efficient.

[0006] Due to the limited operating temperature ( ~ At temperatures of 250°C, conventional baking lacquer is not actually suitable. The additive manufacturing of components for an electric machine is described, for example, in DE 11 2012 002 953 A5.

[0007] Thin sheets with high alloy contents (> 3.5 wt% Si) can be additively manufactured, particularly by 3D screen printing. The final geometry is formed directly during the printing process, thus eliminating many different individual process steps. Printing the entire sheet stack can eliminate many further process steps. A ceramic insulating layer can also be printed (high specific electrical resistance, high heat resistance) and its heat treatment parameters can be matched to those of the iron alloy. The respective temperature differences between ceramic and iron materials pose a challenge in this process.

[0008] For example, DE 10 2011 109 129 A1 describes how electrical energy converters can be manufactured using printing.

[0009] A method for producing a layer arrangement of electrical steel with a layer arrangement of stator or rotor and electric motor is shown in WO 2021 / 185398 A1.

[0010] US 2021 / 0320571 A1 describes methods for producing material layers for dynamoelectric rotary machines.

[0011] DE 39 35 471 A1 concerns ceramic compositions and their uses.

[0012] It is therefore an object of the invention to provide possibilities by which elements for electrical working machines, which are formed with alternatingly arranged layers of a soft magnetic and an electrically insulating material, can be manufactured simply and effectively, and in which these elements achieve reduced electrical eddy current losses.

[0013] According to the invention, this problem is solved by a method having the features of claim 1. Claim 10 relates to an element produced by this method. Advantageous embodiments and further developments of the invention can be realized with features specified in dependent claims.

[0014] In the process for manufacturing elements for electrical working machines, which are formed with superimposed layers of iron or an iron alloy with soft magnetic properties and between which an electrically insulating oxide layer is arranged, the layers of iron or the iron alloy are each formed with a suspension consisting of a powder of iron or the iron alloy and an organic binder by screen printing in a predetermined geometry with a predetermined first layer thickness.

[0015] The electrically insulating layers formed between the layers of iron or iron alloy created by screen printing, which are formed with a powder and an organic binder, are formed by screen printing in the specified geometry with a specified second layer thickness, wherein a hydroxide or acetate selected from magnesium hydroxide (Mg(OH)2), aluminum hydroxide (Al(OH)3), zirconium hydroxide (Zr(OH)4), magnesium acetate (MgAc), aluminum acetate (AlAc) and zirconium acetate (ZrAc) or a carbonate selected from magnesium carbonate and zirconium carbonate is used.

[0016] Each individual layer can be formed by at least one screen printing, but if a desired target layer thickness cannot be achieved in one go, by printing on top of each other several times until the respective first or second layer thickness has been reached.

[0017] Following screen printing, the resulting stack of layers undergoes thermal treatment.

[0018] In a first stage, a chemical reaction is carried out in the temperature range between 100°C and 800°C, in which the respective hydroxide, acetate and / or carbonate is converted into the respective metal oxide and electrically insulating layers of magnesium, aluminum and / or zirconium oxide are obtained.

[0019] In the first stage, organic components are removed from the layer materials (debinding).

[0020] In the invention, the use of a hydroxide, acetate, or carbonate is advantageous compared to the use of an oxide, since the sinterability of the ceramic particles can be improved by the small particle size after the chemical transformation. In this way, a partially sintered porous oxide ceramic can be advantageously obtained as an electrical insulating layer during the sintering of the iron alloy in the second stage.

[0021] Following the first stage, a second stage of thermal treatment is carried out, in which sintering of the iron or the respective iron alloy is performed in a reducing atmosphere at a temperature in the range of 1200°C to 1350°C to form layers with corresponding soft magnetic properties.

[0022] The electrically insulating oxide ceramic layers between the metal layers can thus be obtained at temperatures below the melting point of iron or the respective iron alloy, so that there are no problems, even though usual sintering temperatures of ceramic and especially oxide ceramic materials are significantly above the melting point of iron or the iron alloys used.

[0023] Due to the comparatively low sintering temperature for ceramics, a completely closed oxide ceramic layer is advantageously not formed. The electrically insulating layers obtained in this way advantageously exhibit a certain degree of porosity, which will be discussed in more detail later.

[0024] Advantageously, a powder of an iron alloy containing at least 3.5 wt% Si can be used. However, alloys of iron with nickel and / or cobalt, optionally without silicon, or an FeSiAl alloy, in particular an Fe-9.5-Si-5.5Al alloy, can also be used. An Fe-6.5Si alloy is also preferred. A powder of an iron alloy containing, in addition to iron, Al, Cr, Co and / or P as alloying element(s) can also be used.

[0025] The layers formed with the iron alloy should have a first layer thickness that takes into account the respective shrinkage during sintering, whereby the sintered layers formed from the iron alloy have a maximum layer thickness of 350 µm, preferably a maximum of 180 µm, and particularly preferably a maximum of 150 µm. Sintered layers formed from iron without alloying elements should have a maximum layer thickness of 150 µm, preferably a maximum of 100 µm.

[0026] It can be iron powder or a powder of the respective iron alloy with a medium particle size d 50 in the range of 1 µm to 20 µm. A powder of the respective oxide, hydroxide, acetate and / or carbonate should have a mean particle size d 50 They can be used in the range of 0.2 µm to 5 µm.

[0027] The electrically insulating layers can be formed with a porosity ranging from 20% to 60%. The air present in the pores provides an additional layer of electrical insulation when an electric machine is in operation.

[0028] The suspensions can be prepared with a solvent, in particular water or an organic solvent, and an organic binder selected from Tylosen, methylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, and polyethylene glycol, to be used as a suspension for screen printing. An organic binder can be used at a proportion of 0.5% to 1% by weight of the powder. The solvent content can be neglected, as the solvent evaporates during thermal treatment.

[0029] The suspensions may contain further additives to adjust the rheology. These can include, for example, thickeners, dispersants, wetting agents (surfactants), or plasticizers. Their primary purpose is to achieve a consistency and processability suitable for screen printing. These additives can be thermally decomposed during heat treatment.

[0030] If a suspension or paste containing organic components is used for screen printing, MgO can be used, for example, whereas aqueous-based pastes or suspensions are required when using Mg(HO)2.

[0031] The first thermal treatment can be carried out in two stages. In the first stage, debinding is performed to remove the organic components. The precursor material decomposes in the temperature range of 100°C to 300°C, causing the chemical decomposition of the starting material (hydroxide, acetate, and / or carbonate). This chemical reaction forms the respective oxide(s) with a fine particle size distribution of < 1 µm. A low heating rate of a maximum of 4 K / min ensures that a sufficiently large proportion of the hydroxide, acetate, and / or carbonate can be chemically converted to the corresponding oxide during the first stage.

[0032] The second stage of thermal treatment should be carried out until the iron or the respective iron alloy is completely sintered. This ensures sufficient strength of each layer and of the stack formed by all layers, advantageously resulting in a component with good magnetic properties.

[0033] The electrically insulating layers should be formed with a second layer thickness, maintaining a minimum distance of 0.5 µm between the sintered layers made of iron or the respective iron alloy. This prevents electrical short circuits or the transmission of any eddy currents that may occur from one layer to an adjacent layer, both made of iron or the iron alloy. The electrically insulating layers do not need to form a completely closed layer. Gaps or openings containing air are permissible. The only requirement is that no direct electrically conductive connection is possible between two adjacent layers made of iron or the iron alloy.

[0034] By forming the layers of iron or iron alloy and the electrically insulating layers of the respective metal oxide(s) directly on top of each other by screen printing and subsequently processing them with thermal treatment, elements are produced which consist of alternatingly arranged layers of iron or the respective sintered iron alloy between which electrically insulating layers of magnesium oxide, aluminum oxide and / or zirconium oxide are arranged and which are joined together in a materially and form-fitting manner.

[0035] In total, at least three, but also more, layers can be created on top of each other by screen printing, forming one element.

[0036] The first and second layers can each be formed by a single screen printing, or each layer can be formed by multiple screen printings in order to achieve the desired layer thickness after the process has been carried out.

[0037] The hydroxides, acetates or carbonates used as precursors form nanometer-sized oxide ceramic particles during debinding, so that during sintering of the iron alloy a porous ceramic layer is formed as an electrical insulating layer between the individual layers of the iron alloy.

[0038] The air within the porous oxide ceramic acts as a very good insulator, further contributing to electrical insulation. The porosity of the oxide ceramic electrical insulation layers significantly reduces the tendency for delamination between the two superimposed and metallurgically bonded layers. This compensates for the different coefficients of thermal expansion of the oxide ceramic and the iron or iron alloy.

[0039] The invention eliminates many previously common, complex individual processes, and allows for virtually unlimited choice of iron alloy and layer thickness of the resulting layers. In particular, alloys can be used that are otherwise difficult or impossible to process. Very thin layers formed with iron or the iron alloy can be achieved, resulting in extremely low remagnetization losses.

[0040] The invention will be explained in more detail below by way of example.

[0041] This shows: Fig. 1 a schematic representation of an example of an element (stator) produced according to the invention.

[0042] With Fig.Figure 1 is intended to illustrate how alternating layers 1 formed by screen printing, each consisting of alternating iron or an iron alloy and electrically insulating layers 2 made of an oxide ceramic, are formed and which, after a two-stage thermal treatment, in which first the layers 2 of the respective oxide ceramic are obtained from a corresponding hydroxide, acetate and / or carbonate after screen printing by chemical conversion and organic components are driven off during debinding, and in a second stage the iron or the iron alloy is sintered in the corresponding layers 1. Example 1

[0043] Fe-3.5Si powder with a 55 wt% powder loading was mixed with a water-soluble organic binder (PVA), 3% defoamer, wetting agent, thickener, and dispersant to form a suspension or printable paste. This suspension or printable paste was used to print the first layer (1), with each layer thickness being 180 µm. The powder used had a mean particle size of d 50 of 15 µm.

[0044] A Mg(OH)₂ powder is used as a precursor for the oxide ceramic used to print second layers. The suspension or printable paste used for this purpose contained 50 wt% of the powdered magnesium hydroxide. This suspension or printable paste was also prepared with components commonly used in screen printing, such as a water-soluble organic binder (PVA), 3 wt% defoamer, wetting agent, thickener, and dispersant. Second layers were printed with a very thin layer thickness of approximately 10 µm. The first and second layers (1 and 2) were printed alternately on top of each other to obtain an electromagnetic element with the desired dimensions and geometry. A volume shrinkage of approximately 14% after sintering must be taken into account.

[0045] In the subsequent thermal treatment, the printed element is debound. In a first thermal treatment, debinding is carried out at a temperature range of 100°C to 800°C with a heating rate of 4 K / min and a holding time of 0.5 h, during which the chemical reactions of magnesium hydroxide are converted to magnesium oxide are performed. In a second thermal treatment stage, sintering is carried out at 1300°C and a holding time of 1 h in a forming gas atmosphere. This results in dense Fe-3.5Si sheet layers as the first layer 1 with a thickness of 150 µm and porous MgO interlayers with a thickness of 8 µm as the second layer 2. Exemplary embodiment 2 (not according to the invention)

[0046] Fe-6.5Si powder with a 55 wt% powder loading was mixed with a water-soluble organic binder (PVA), 4 wt% defoamer, wetting agent, thickener, and dispersant to form a suspension or printable paste. This suspension or printable paste was used to print the first layer (1), with each layer thickness being 400 µm. The powder used had a mean particle size of d 50 of 17 µm. A nanoparticulate ZrO2 powder is used to print the second layers 2. The suspension or printable paste used for this purpose contained 45 wt% of the powdered ZrO2 with a mean particle size d 50of 200 nm. The suspension or printable paste was also prepared here with components commonly used in screen printing, such as water-soluble organic binder (PVA), 3 wt% defoamer, wetting agent, thickener, and dispersant. Second layers were printed with a very thin layer thickness of approximately 10 µm. The first and second layers (1 and 2) were printed alternately on top of each other to obtain an electromagnetic element with the desired dimensions and geometry. A volume shrinkage of approximately 15 vol% after sintering must be taken into account.

[0047] In the subsequent thermal treatment, the printed element is debound. A first thermal treatment takes place at a temperature range of 100°C to 800°C with a heating rate of 4 K / min and a holding time of 0.5 h. In a second thermal treatment stage, sintering is carried out at 1250°C and a holding time of 1 h in a forming gas atmosphere. This results in dense Fe-6.5Si sheet layers as the first layer 1 with a thickness of 350 µm and porous ZrO2 interlayers with a thickness of 10 µm as the second layer 2.

Claims

[1] Method for manufacturing elements for electrical working machines, which are formed with superimposed layers (1) of iron or an iron alloy with soft magnetic properties and between the layers (2) formed with iron or with the iron alloy an electrically insulating layer (2) is arranged, wherein the layers (1) of iron or the iron alloy each with a suspension formed with iron or with a powder of the iron alloy and an organic binder are formed by screen printing in a predetermined geometry with a predetermined first layer thickness and the electrically insulating layers (2) formed between the layers (1) of iron or the iron alloy formed by screen printing, which are formed with a powder and an organic binder, are formed by screen printing in the specified geometry with a specified second layer thickness, wherein the powder is a hydroxide or acetate selected from magnesium hydroxide, aluminum hydroxide, zirconium hydroxide, magnesium acetate, aluminum acetate and zirconium acetate or a carbonate selected from magnesium carbonate and zirconium carbonate and Following screen printing, the resulting layer stack undergoes a thermal treatment, during which In a first stage, debinding takes place in the temperature range between 100 °C and 800 °C, whereby the respective hydroxide, acetate and / or carbonate is decomposed in the temperature range between 100 °C and 300 °C, and a chemical reaction is carried out in which the respective hydroxide, acetate and / or carbonate is formed into the respective metal oxide with a fine particle size distribution of < 1 µm, and following the first stage, a second stage of thermal treatment is carried out, in which in a reducing atmosphere at a temperature in the range of 1200°C to 1350°C, sintering of the iron or the respective iron alloy is carried out to form layers (1) with corresponding soft magnetic properties and porous electrically insulating layers (2) are obtained. [2] Method according to claim 1, characterized bythat a powder of an iron alloy is used which contains at least 3.5 wt% Si, preferably at least 6 wt% Si; wherein in particular an Fe-6.5Si or Fe-9.5Si-5.5Al alloy is used. [3] Method according to claim 1 or 2, characterized by , that a powder of an iron alloy is used in which, in addition to iron, Al, Cr, Co and / or P are also contained as alloying element(s). [4] Method according to any one of the preceding claims, characterized by, that the layers (1) formed with the iron alloy are formed with a layer thickness taking into account the respective shrinkage during sintering, whereby the sintered layers formed from the iron alloy have a maximum layer thickness of 400 µm, preferably a maximum of 180 µm, particularly preferably a maximum of 150 µm, or the layers (1) formed from iron are formed with a layer thickness taking into account the respective shrinkage during sintering, whereby the sintered layers have a maximum layer thickness of 150 µm, preferably a maximum of 100 µm. [5] Method according to any one of the preceding claims, characterized by that an iron powder or a powder of the respective iron alloy with a medium particle size d 50 in the range of 1 µm to 20 µm and / or a powder of the respective hydroxide, acetate and / or carbonate with a mean particle size d 50It is used in the range of 0.5 µm to 5 µm. [6] Method according to any one of the preceding claims, characterized by , that the electrically insulating layers (2) are formed with a porosity in the range of 20% to 60%. [7] Method according to any one of the preceding claims, characterized by , that the suspensions are used with a solvent, in particular water, and the organic binder selected from Tylosen, Methylcellulose, Polyvinyl alcohol, Polyvinylpyrrolidone and Polyethylene glycol. [8] Method according to any one of the preceding claims, characterized by that the second stage of thermal treatment is carried out until the iron or the respective iron alloy is completely sintered. [9] Method according to any one of the preceding claims, characterized by, that the electrically insulating layers (2) are formed with a layer thickness in which a minimum distance of 0.5 µm to 20 µm is maintained between the sintered layers (1) formed with iron or the respective iron alloy.

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