Method for producing an electrical insulation layer on an iron sheet for laminated cores of an electrical machine

Abstract

The present invention relates to a method for producing an electrical insulation layer on an iron sheet for laminated cores of an electrical machine, comprising the steps: a) providing at least one uncoated iron sheet, in particular steel sheet, deep-drawn sheet or electrical sheet, which is a sheet lamination for a laminated core or a sheet coil, b) providing an aluminum-containing first reaction component, in particular in the form of a powder, a paste or a foil, c) providing a carbon-containing second reaction component, in particular in the form of a powder, a paste or a foil, d) applying the two reaction components to at least one side of the at least one uncoated iron sheet to form at least one coating layer, e) heating the at least one coating layer to initiate a reaction between the two reaction components to form aluminum carbide in the coating layer,in particular in a hydrogen atmosphere, f) treating the coating layer with moisture, in particular water vapor, to convert the aluminum carbide present in the coating layer into aluminum hydroxide, and g) thermally converting, in particular decomposing, the aluminum hydroxide of the coating layer into aluminum oxide to produce an electrically insulating property of the coating layer, thereby forming the insulating layer.

Description

State of the art

[0001] The present invention relates to a method for producing an electrical insulation layer on an iron sheet for laminated cores of an electrical machine.

[0002] It is known state of the art to use electrical laminations for laminated cores, with the laminations having a polymer-based insulation coating. Furthermore, it is known that the diffusion of aluminum and silicon into the laminations reduces the electrical conductivity within the laminations, but insulation between adjacent laminations cannot be achieved.

[0003] It is known from the literature that steels in which the proportion of aluminum and silicon is more than 4.5 mass% can no longer be cold rolled and, moreover, are prone to cracking even during hot rolling.

[0004] Therefore, EP 3 511 429 A1 proposes coating the electrical sheets with silicon and aluminum and then stacking the coated electrical sheets to form the rotor or stator. During the subsequent heat treatment, silicon and aluminum diffuse into the electrical sheets and increase the electrical resistance of the sheets without impairing their soft magnetic properties. Disclosure of the invention

[0005] The method according to the invention enables the electrical sheets in a laminated core to be electrically insulated from one another. In particular, it is possible to form an insulating layer between adjacent iron sheets of a laminated core during a heat treatment parallel to the diffusion of silicon and aluminum into iron sheets. The temperature resistance of the insulating layer is advantageously at least 600°C.

[0006] The method for producing an electrical insulation layer on an iron sheet for laminated cores of an electrical machine serves, in particular, to form an electrically insulating aluminum oxide layer in situ. The method comprises the steps described below.

[0007] First, a step of providing a) at least one uncoated iron sheet is performed. An uncoated iron sheet refers, in particular, to an iron sheet without an insulation layer. The iron sheet is preferably a steel sheet, a deep-drawn sheet, or an electrical sheet. The steel sheet is a sheet metal lamination for a laminated core or a sheet metal coil. Advantageously, the steel sheet has high electrical conductivity and / or magnetic conductivity.

[0008] Furthermore, b) an aluminum-containing first reaction component and c) a carbon-containing second reaction component are provided. The first reaction component and / or the second reaction component are preferably provided in the form of a powder, a paste, or a film.

[0009] The order of steps a), b), and c) is not relevant. These three steps are followed by an application step (d). In this step, the two reaction components are applied to at least one side of the at least one uncoated iron sheet. The iron sheet has no insulating coating, at least on the side to which the reaction components are applied. In this way, at least one coating layer is formed.

[0010] In a step e) of heating the at least one coating layer, a reaction is initiated in which the first reaction component and the second reaction component react. In particular, the aluminum of the first reaction component reacts with the carbon of the second reaction component to form aluminum carbide in the coating layer. The heating takes place, in particular, in a hydrogen atmosphere.

[0011] A further step (f) involves treating the coating layer with moisture after step (e) has been performed. This treatment with moisture is, in particular, a treatment with steam. The moisture converts the aluminum carbide present in the coating layer to aluminum hydroxide. The carbon contained in the aluminum carbide is preferably removed as methane.

[0012] This is followed by step g) of thermally converting the aluminum hydroxide of the deposited layer into aluminum oxide. This involves, in particular, decomposition of the aluminum hydroxide. This step creates an electrically insulating property in the deposited layer, forming the insulation layer. This creates a full-surface, cost-effective, electrically insulating layer with very high temperature resistance and sufficiently high dielectric strength in the gap between the electrical sheets.

[0013] The subclaims show preferred developments of the invention.

[0014] The aluminum-containing first reaction component preferably comprises elemental aluminum and / or an aluminum alloy. For example, the first reaction component is an aluminum foil.

[0015] The carbon-containing second reaction component preferably comprises organically bound carbon and / or inorganic carbon. The organically bound plastic is, in particular, a plastic film and / or a plastic powder and / or starch and / or xanthan gum. The inorganic carbon is, for example, graphite and / or graphene and / or carbon black.

[0016] In step e), the at least one coating layer is advantageously heated to at least 600°C. Particularly advantageously, the maximum temperature is 1,300°C.

[0017] A method according to any one of the preceding claims, characterized in that, to convert the aluminum carbide into aluminum hydroxide, the laminated core is heated to a temperature above 100°C. This enables a reliable reaction of the two reaction components to form aluminum carbide. Therefore, it is ensured that electrical insulation is formed on the steel sheet, for which the aluminum carbide is the basis.

[0018] In step f), the coating layer is preferably heated to a temperature above 180°C to convert the aluminum hydroxide into aluminum oxide. The water produced during the conversion is thus optimally removed.

[0019] In an advantageous embodiment, the first reaction component and the second reaction component are applied as a powder mixture in step d). Preferably, the two reaction components are mixed between the respective steps b) and c) of providing the first reaction component and the second reaction component and step d).

[0020] The sheet metal coil preferably comprises pre-punched or pre-cut sheet metal laminations that are connected to the remaining sheet metal coil via remaining bridge webs. This allows for a large number of sheet metal laminations to be prepared easily and with minimal effort, making them available for subsequent work steps. The particular advantage is that the individual sheet metal laminations no longer need to be fully punched or cut. This leads to less stress on the insulation layer of the sheet metal laminations, and particularly advantageously, damage to the insulation layer is avoided or at least reduced.

[0021] The laminations insulated with the insulation layer are preferably stacked into a laminated core. This laminated core can be used, for example, as a stator core or rotor core in an electrical machine.

[0022] In step a), a plurality of laminations is preferably provided. In step d), the iron sheets are each coated with at least one coating layer and subsequently stacked to form a laminated core. The described steps f) and g) are then performed on the stacked laminated core. Thus, a finished laminated core can be produced, with the individual laminations of the laminated core being reliably electrically insulated from one another, since the insulation layer is applied to the laminations as described above.

[0023] In steps f) and / or g), the laminated core is preferably compressed using a compressive force. The compressive force corresponds, in particular, to at least the weight of the laminated core. This prevents, in particular, the methane produced in step f) from forcing the laminated core apart. The same applies to step g), in which water vapor is produced, thus also preventing the laminated core from being forced apart. Embodiments of the invention

[0024] Embodiments of the invention are described in detail below.

[0025] First, several steel sheets are prepared. In addition, a first reaction component containing aluminum and a second reaction component as a carbon source are provided. The aluminum can be applied to the steel sheet as a foil or as a powder. The aluminum can also be part of an alloy such as AlSi45, for example. The carbon source used can be, for example, organically bound carbon such as, in particular, a plastic film, a plastic powder, starch (e.g., amylopectin), or xanthan gum. Inorganic carbon can also be used, such as, in particular, graphite, graphene, or carbon black. Carbon black, as quasi-amorphous carbon, is particularly advantageously suited.

[0026] The two reaction components are applied to at least one side of the steel sheets to form a coating layer. The steel sheets are then stacked on top of each other to form a sheet stack. The first reaction component and the second reaction component can each be a foil, for example. Likewise, both reaction components can be powdered. If the reaction components are in powder form, it is advantageous to mix them thoroughly before application.

[0027] This is followed by a heat treatment in which the deposited layer is heated to a minimum of 600°C and a maximum of 1,300°C. During the heat treatment, the stack of sheets is subjected to a compressive force equal to at least its own weight. During this heat treatment, a portion of the aluminum diffuses into the electrical sheet. At the same time, aluminum also reacts with the carbon to form aluminum carbide (Al4C3) according to the following reaction equation. 4 Al + 3 C → Al4C3 at a temperature >600°C

[0028] The aluminum carbide Al4C3 does not diffuse into the steel sheets and therefore remains as a residue between the individual steel sheets. After this heat treatment, the stack of sheets can be cleaned to remove contaminants, molten beads, or similar contaminants.

[0029] In a further process step, the stack of sheets is exposed to steam. This causes the aluminum carbide Al4C3 to convert into aluminum hydroxide Al(OH)3, as shown in the following reaction equation. The carbon is released as methane CH4. Al4C3 + 12 H2O → 4 Al(OH)3 + 3 CH4 at room temperature

[0030] It is particularly advantageous if the sheet stack is subjected to a force at least equal to its weight, to prevent the sheet stack from being forced apart during heat treatment by the gases generated according to the above reaction equation. Furthermore, it is advantageous if the sheet stack is exposed to steam at a temperature above 100°C, as both the required pressure and temperature accelerate the conversion of aluminum carbide to aluminum hydroxide.

[0031] This is particularly advantageous when the stack of sheets is subjected to a further heat treatment, whereby it is subjected to a force at least equal to its own weight. Temperatures of > 180°C are particularly advantageous. The aluminum hydroxide Al(OH)3 is thermally decomposed, forming aluminum oxide Al2O3 and water H2O with the release of water, as shown in the following reaction equation. Al(OH)3 → Al2O3 + 3 H2O at a temperature >180°C and under pressure, e.g. in the form of a weight load. This process creates an electrically insulating layer between the steel sheets that is stable even at temperatures above 180°C.

[0032] The advantage of the described process is that a melt of aluminum or aluminum-silicon creates a full-surface, electrically insulating layer between the steel sheets. This manufacturing method eliminates defects and therefore short circuits. Example:

[0033] An aluminum foil with a thickness of 0.013 mm and a cellophane film (cellulose film) with a thickness of 7 µm are placed in pairs on an electrical sheet. The electrical sheets are stacked so that there is an aluminum foil and a cellophane film between each electrical sheet.

[0034] This is followed by a heat treatment under hydrogen. In a first step, the aluminum foil and the carbon in the cellophane film are partially converted to aluminum carbide at a minimum of 700°C, and particularly advantageously at 1050°C - 1250°C. The portion of the aluminum that does not react to form aluminum carbide diffuses into the electrical steel sheet, so that after the heat treatment, only aluminum carbide remains in each gap between two electrical steel sheets.

[0035] The aluminum carbide is converted into aluminum hydroxide by steam. The steam temperature is 120°C. Further thermal treatment can convert the aluminum hydroxide into aluminum oxide. Here, too, it is advantageous to apply at least its weight to the stack during heat treatment to counteract the pressure from the released water, as shown in reaction equation 3. The thermal stability of the insulation layer increases from a maximum of 180°C to over 600°C through heat treatment. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 3 511 429 A1

[0004]

Claims

[1] Method for producing an electrical insulation layer on an iron sheet for laminated cores of an electrical machine, comprising the steps: a. Providing at least one uncoated iron sheet, in particular steel sheet, deep-drawn sheet or electrical sheet, which is a sheet metal lamination for a laminated core or a sheet metal coil, b. Providing an aluminum-containing first reaction component, in particular in the form of a powder, a paste or a foil, c. Providing a carbon-containing second reaction component, in particular in the form of a powder, a paste or a film, d. Applying the two reaction components to at least one side of the at least one uncoated iron sheet to form at least one coating layer, e. Heating the at least one coating layer to initiate a reaction between the two reaction components to form aluminium carbide in the coating layer, in particular in a hydrogen atmosphere, f. Treating the coating layer with moisture, in particular steam, to convert the aluminium carbide present in the coating layer into aluminium hydroxide, and g. thermally converting, in particular decomposing, the aluminum hydroxide of the coating layer into aluminum oxide to produce an electrically insulating property of the coating layer, thereby forming the insulating layer. [2] Method according to claim 1, characterized by that the aluminum-containing first reaction component comprises elemental aluminum and / or an aluminum alloy. [3] Method according to one of the preceding claims, characterized bythat the carbon-containing second reaction component comprises organically bound carbon, in particular a plastic film and / or a plastic powder and / or starch and / or xanthan, and / or inorganic carbon, in particular graphite and / or graphene and / or carbon black. [4] Method according to one of the preceding claims, characterized by that the at least one applied layer in step e) is heated to at least 600°C, preferably a maximum of 1,300°C. [5] Method according to one of the preceding claims, characterized by that in order to convert the aluminium carbide into aluminium hydroxide the laminated core is heated to a temperature above 100°C. [6] Method according to one of the preceding claims, characterized by that the applied layer is heated to a temperature above 180°C in step f) to convert the aluminium hydroxide into aluminium oxide. [7] Method according to one of the preceding claims, characterized bythat the two reaction components in step d) are applied as a powder mixture. [8] Method according to one of the preceding claims, characterized by that the sheet metal coil comprises pre-punched or pre-cut sheet metal laminations which are connected to the rest of the sheet metal coil via remaining bridge webs. [9] Method according to one of the preceding claims, characterized by that the sheet metal laminations insulated with the insulation layer are stacked to form a sheet package. [10] Method according to one of the preceding claims, characterized by that in step a) a plurality of iron sheets is provided, wherein in step d) the iron sheets are each provided with at least one coating layer and then stacked to form a sheet stack, and wherein steps f) and g) are carried out on the sheet stack. [11] Method according to claim 10, characterized bythat the laminated core is subjected to a compressive force in steps f) and / or g).