Coating process for a wire assembly of an electric machine

Abstract

Method for applying and foaming an electrically insulating foam structure onto a wire arrangement (100) for an active part of an electric machine, wherein the method comprises applying a thermoplastic coating polymer (110) to the wire arrangement (100), inserting the wire arrangement (100) into the active part, saturating the thermoplastic coating polymer (110) with carbon dioxide under defined temperature and pressure conditions, cooling the active part, lowering an ambient pressure of the active part, and increasing the temperature to form a foam structure such that the foam structure (100X) has electrically insulating properties.

Description

[0001] The invention relates to a coating method for applying an electrically insulating layer to an associated wire arrangement of an electric machine, as well as to a wire arrangement produced by means of the method, and to an electric machine with a wire arrangement produced according to the method.

[0002] Wire coils wound around iron cores of stators, rotors, and transformers play a crucial role in electrical machines such as electric motors, generators, and transformers, converting electrical energy into mechanical energy and vice versa, or—in the case of transformers—transforming electrical energy to higher or lower voltages. Effective wire coating is crucial for the insulation of the windings, heat dissipation, and the performance of electrical machines. Previous techniques and processes for electrical wire coating for stators in electrical machines primarily relate to the development of appropriate wire coating formulations.

[0003] DE 202012104118U1, for example, shows a process for producing the wire enamel layer in which the wire is pulled through a bath of liquid enamel and then further process steps such as baking the enamel and repeating the entire process are carried out.

[0004] Likewise, patent DE 69714491T2 describes the preparation of a lacquer solution that is applied to the conductor and then baked.

[0005] Overall, there has been little progress or innovative approaches regarding the application and coating methods, as well as the chemical composition of wire coating formulations. Furthermore, these approaches often have limited applicability, for example, due to insufficient temperature resistance of the proposed solution.

[0006] In the active parts of electric motors, impregnating resin is often used alongside wire enamels to further protect the wire windings. Due to slight mechanical deflections of the wires at high frequencies, they rub against each other, which can damage and even erode the wire enamel. Using a suitable impregnating resin solves this problem and also protects the thin wire enamels from other influences, such as mechanical forces.

[0007] However, both wire enamels and impregnating resins can be subject to further effects that can lead to cracking and ultimately detachment of the wire enamel insulation from the wire or impregnating resin. The rapid heating and expansion of the wires or electrical conductors during operation of the electric motor, as well as their cooling and shrinkage after shutdown, can lead to cracks in the wire enamel insulation.

[0008] If wire enamels and impregnating resins with different thermal expansion behavior but high adhesive adhesion are combined in an electric motor, this can also lead to cracking at the interface between wire enamel and impregnating resin.

[0009] Another reason for cracking or peeling of wire enamel is trapped air bubbles in the impregnation resin, which can occur during conventional application processes. These air bubbles expand significantly under the influence of heat and contract again upon cooling. The expansion and contraction of the air bubble can lead to large-scale peeling of the wire enamel insulation after numerous heating and cooling cycles.

[0010] If particles (dust or similar) get into the wire enamel or the impregnating resin, these particles can also cause cracking as a stress concentrator.

[0011] US2018 / 0262073A1 describes an electrical insulating material for use in electrical devices. It is a flexible material comprising at least one epoxy resin layer. The patent also describes nonwovens, such as nylon nonwovens, as insulating layers that could serve as the impregnating resin.

[0012] The object of the present invention is therefore to provide a method for wire insulation of active parts of electric motors that at least partially overcomes the aforementioned disadvantages and enables effective coating of a wire arrangement. Furthermore, the object is to provide insulation for the wire arrangements in active parts of electric motors.

[0013] These objects are achieved by the method according to claim 1, the wire arrangement according to claim 14 and the electric machine according to claim 15.

[0014] According to one embodiment, the disclosure provides a method for applying and foaming an electrically insulating foam structure onto a wire arrangement for an active part of an electric machine, the method comprising applying a thermoplastic coating polymer to the wire arrangement, inserting the wire arrangement into the active part, saturating it with carbon dioxide under defined temperature and pressure conditions, cooling the active part, lowering an ambient pressure of the active part, and increasing the temperature to form a foam structure, the foam structure having electrically insulating properties.

[0015] An electric machine can be an electrical machine designed to generate mechanical power from electrical current. In particular, an electric machine can be an electric motor, a generator, combinations of the above, or the like. In particular, an electric machine can be designed to drive a motor vehicle. The electric machine can also be a separately excited synchronous machine.

[0016] An active part of an electric motor is a component of the electric motor that plays an active role in the operation of the electric motor, for example, a moving part of the electric motor or an electrical component of the electric motor. An active part of an electric motor is, for example, a rotor, a stator or armature, a transformer, a coil, or another component in which wire arrangements can be installed. By applying a foam structure according to the disclosure, impregnation of the active part can be omitted, while simultaneously achieving improved insulation.

[0017] According to the disclosure, applying a coating to a wire arrangement also includes applying a coating to wires, in particular wires which are part of the wire arrangement.

[0018] A "wire assembly" is a structure or arrangement of wires intended for use in the active parts of an electrical machine. For example, a wire assembly is a wire winding for a rotor, stator, or transformer, or hairpins for a stator, comprising electrically insulated wires that carry electrical currents.

[0019] Various techniques can be used to apply the thermoplastic coating polymer to the wire assembly, such as extrusion, dipping, spraying, or application with rollers or brushes, sheathing, or similar. Typical layer thicknesses range from approximately 80 to 150 µm; although larger layer thicknesses are possible, they are not desirable if the highest possible conductor fill factor is to be achieved, for example, in a slot.

[0020] A conductor within the meaning of the present disclosure is an electrical conductor element, for example, a wire or a material that exhibits electrical conductivity. Unless otherwise stated, an electrical conductor may be made of copper, copper-containing material, aluminum, or aluminum-containing material, although other materials known to exhibit electrical conductivity may also be provided according to the invention.

[0021] By gassing the thermoplastic coating polymer with carbon dioxide (CO2) under pressure and temperature, the CO2 is introduced into the coating. The thermoplastic coating polymer is saturated with the CO2, which is in a supercritical state due to the selected pressure and temperature conditions. To eliminate the supercritical state of the CO2, the temperature is subsequently reduced, which slows the diffusion of the now liquid CO2 and thus allows the CO2 to remain in the thermoplastic coating polymer for a longer period. For gassing with CO2, the active part, which contains the thermoplastically coated wire arrangement, can be placed in a reactor / autoclave.

[0022] A supercritical state of CO2 can occur, for example, when a temperature of at least 30.9°C and a pressure of at least 73.75 bar prevail in the autoclave / reactor. The supercritical state of CO2 can be induced, for example, at a pressure of 74 bar by increasing the temperature in the autoclave / reactor to more than 30.9°C.

[0023] There are embodiments in which the cooling of the active part comprises cooling to a temperature of less than 30.9°C and the ambient pressure of the active part is suddenly reduced to atmospheric pressure.

[0024] Due to an abrupt reduction in pressure to atmospheric pressure, the CO2 begins to change into the gaseous state, which causes phase separation of the CO2.

[0025] Following the temperature and pressure reduction, the temperature is deliberately increased. CO2 initially dissolved in the polymer acts as a plasticizer, softening the thermoplastic coating polymer and enabling the formation of foam pores. As less and less CO2 remains in the polymer during the temperature treatment, the plasticizing effect also decreases progressively until the thermoplastic polymer, in which foam pores have formed, solidifies. The pore structure can be described as "solidified." The temperature treatment can be achieved, for example, using an induction or resistance heating element placed in the immediate vicinity of the active part of the electric motor, or by using current pulses that briefly increase the current flow through the respective active part of the electric motor. To improve the homogeneity of the temperature distribution, the aforementioned methods can be combined.The increased temperature is set to an appropriate value, which can be 165°C, for example, until the foaming process is completed.

[0026] The process causes the thermoplastic coating polymer to foam, creating a porous / foamed structure, which can be referred to as a foam structure or electrically insulating foam structure. The electrically insulating foam structure then surrounds the outer contour of the wire arrangement or the individual conductor elements of the wire arrangement. The foam structure can be arranged, for example, in spaces within the wire arrangement or in spaces between the wire arrangement and an inner or outer wall of the active part. The foam structure can also be arranged in spaces between the wire arrangement and an inner or outer wall of the electric motor. The foam structure can fill the spaces in which it is arranged.

[0027] The resulting electrically insulating foam structure exhibits a higher surface area ratio compared to non-foamed coating polymers and—in conjunction with the electrically insulating electric motor oil—improved insulation properties. Due to the mechanical dampening effect of the foamed, thermoplastic coating polymer against mechanical forces, the wires are also better protected against mechanical influences. Wire breakage is thus less likely. A longer service life of the electric motor can therefore be expected. The foamed thermoplastic coating polymer can act as a mechanical "buffer material" and prevent damage to the wire assembly.

[0028] Since the process according to the invention does not require impregnation resin and thus no impregnation step, the production of electric motors is simpler and more cost-effective. Furthermore, impregnation systems are maintenance-intensive and require long setup and maintenance times, which leads to longer production times.

[0029] By replacing the impregnating resin with foamed material, the overall weight of the electric motor can be reduced. Furthermore, by eliminating the impregnating resin and ensuring the same material for the slot base insulation and the wire insulation, adhesion problems between the slot base insulation and the wire insulation are eliminated. Furthermore, by eliminating the impregnating resin, corresponding interfaces that can occur, for example, between the impregnating resin and the wire enamel are eliminated, thus also eliminating the resulting adverse interface polarization.

[0030] Since the materials used for the foamed slot base insulation and the foamed wire insulation are thermoplastic, they are also recyclable. This is generally not the case with conventional wire enamel and resin impregnation systems, as they are generally made of thermosetting materials.

[0031] Such an electric motor according to the invention can also be designed with a higher power output due to the higher temperature resistance of the insulation and the improved partial discharge resistance and breakdown field strength, or it can be dimensioned smaller with the same power output. In other words, due to the higher temperature resistance of the insulation, a higher power loss can be permitted.

[0032] The wire arrangement of the active part of an electric motor can also be coated with a thermoset polymer, for example, before the first coating process, which does not foam with CO2. The second, thermoplastic layer is then applied to the first thermoset layer, which can be a primary thermoset layer, and then foams.

[0033] There may be embodiments in which a slot insulation is introduced within the slot, which also comprises a thermoplastic coating polymer. The thermoplastically coated wire arrangement of the active part of an electric motor can then be foamed using the process described above. This procedure allows the wire coating of the active part of an electric motor, consisting of thermoplastic polymers, to be foamed. Eliminating the impregnation resin also eliminates interfaces between the wire coating of the active part of the electric motor and the impregnation resin. Therefore, in these cases, no adverse interfacial polarization can occur.

[0034] There are embodiments that involve filling the pores contained in the foam structure with an insulating material. Insulating materials can be insulating fluids, for example, mineral insulating fluids or synthetic insulating fluids. Mineral insulating fluids are based on mineral oils derived from petroleum. Synthetic insulating fluids are based on organic compounds. Synthetic insulating fluids often offer improved properties compared to mineral insulating fluids, such as higher temperature resistance, better environmental compatibility, and a wider range of possible applications.

[0035] There are embodiments in which the insulating material comprises an oil, in particular a gear oil, or an insulating gas. According to the present invention, the pores of the insulating foam structure are filled with an electrically insulating oil, e.g., by a dipping process. The gear oil is absorbed into the porous or foamed slot insulation material through diffusion effects.

[0036] Alternatively, the pores of the insulating foam structure can be filled with an insulating gas, such as 3M ® -Novec ®-Insulating gas can be filled. This can be achieved, for example, by pressure injection, in which the insulating gas is injected under pressure into the pores of the material, or by an immersion process similar to oil filling. However, the introduction of the insulating fluid may depend on the material properties, pore size, and application requirements. It may therefore be necessary to combine different techniques or use special devices to achieve effective pore filling.

[0037] There are embodiments in which the thermoplastic coating polymer comprises at least one foamable high-temperature polymer and / or a mixture of several foamable high-temperature polymers, wherein foamable high-temperature polymers comprise polyether ketone, in particular polyether ketone ketone, polyether ether ketone, polyphenylene ethers, polyetherimides, polyesters, including polyethylene naphthalate, polyether sulfones, polysulfones, polyether sulfones, polyphenylene sulfides and atactic, isotactic or syndiotactic polystyrenes.

[0038] PEKK's properties make it particularly well-suited for wire coating. It is characterized by very high temperature resistance, for example, with a glass transition temperature of 155°C and a melting temperature of 307°C.

[0039] In addition, it has an extremely low permittivity (dielectric constant) of 2.6 (up to 250°C), which is very advantageous in terms of electrical insulation. Furthermore, PEKK can be foamed with little effort. In practical experiments, density reductions of approximately 44% compared to compact, non-foamed PEKK were achieved. The PEKK foams used to insulate the wire arrangements with oil-filled pores can now also serve as an impregnating resin. In addition to PEKK, the use of polyetheretherketone (PEEK), for example, would also be conceivable, although this is significantly less foamable. Polyetherimides, polyesters (e.g., polyethylene naphthalate), polyethersulfones, polysulfones, polyethersulfones, polyphenylene sulfides, and polystyrenes (atactic, isotactic, and syndiotactic) can also be used.

[0040] There are embodiments in which the saturation of the thermoplastic coating polymer with carbon dioxide takes place under a pressure of approximately 75 - 200 bar and a temperature of 40°C - 80°C for 5 to 40 minutes.

[0041] The reactor / autoclave is then cooled to 30.9°C or below, followed by an abrupt reduction in pressure to atmospheric pressure or below, and then foaming of the thermoplastic material by the action of heat at a temperature in the range of 100–250°C until the foaming process is complete. Preferably, the active part with the PEKK-coated groove and wire assembly is introduced into a reactor and treated with carbon dioxide up to a pressure of approximately 75–80 bar and a temperature of 40°C for a period of 6 minutes. Experiments have shown that, at these parameters, a density reduction of approximately 44% (based on thermoplastic polymers, in this case PEKK) occurs. By increasing the pressure, temperature, and duration, even higher density reductions can be achieved (e.g., 62% at 200 bar and a temperature of 80°C for a saturation period of 15 minutes).

[0042] There are embodiments in which the wire arrangement has a first insulating layer comprising thermosets and a second insulating layer of a thermoplastic coating polymer.

[0043] The thermoplastic insulating layer of the wire assembly is characterized by being made of foamable high-temperature polymers, preferably PEKK. However, it may also be advantageous to use a multilayer insulation, for example, a combination of a first insulating layer of a thermosetting material and a second insulating layer of a foamable thermoplastic coating polymer.

[0044] For example, the wire assembly can be provided with a first base layer of non-foamable polyamide-imide (PAI) and a second insulating layer of a coating polymer made of PEKK, which is then foamed using the process described above. The foamed PEKK forms a high-temperature polymer foam with a high operating temperature, which enables the absorption and binding of, for example, oil as an insulator. By combining these different layers and materials, insulation can be achieved that resists high temperatures and also provides electrical insulation and mechanical damping. Combinations of different thermosetting and thermoplastic coating polymers can also be used.

[0045] There are embodiments in which the insulating foam structure has a layer thickness of more than 80 µm.

[0046] The thermoplastic coating polymer initially applied to the wire arrangement and / or groove has a typical layer thickness of approximately 80–150 µm. During the foaming process, the density of the thermoplastic insulation layer decreases, increasing its volume and potentially resulting in layer thicknesses of 200 µm or more. The increased layer thickness of the insulating foam structure, ranging from 80 to 200 µm or more compared to non-foamed wire enamels, allows for optimal insulation efficiency, depending on the active part in which the foam structure is to be incorporated. The wires can also be better protected from mechanical forces. This reduces the likelihood of wire breakage.

[0047] PEKK or another high-temperature polymer can also be used for insulation, which also allows the insulation to be foamed.

[0048] The available space in the gaps can be taken into account. For example, more space may be available in the winding head of a stator as the active component. Therefore, a higher degree of expansion can be achieved through foaming, resulting in greater final layer thicknesses – 200 µm or more. A final layer thickness is the thickness of the layer at the end of the foaming process.

[0049] For example, if the insulation of an electric machine is to be designed, a desired conductor fill factor can be taken into account.

[0050] There are embodiments in which the diameter of the pores contained in the foam structure is not larger than 100 µm.

[0051] In general, pores or cavities in insulating materials have a detrimental effect on resistance to partial discharges and breakdown field strength. Electrical discharges in individual, larger pores with a diameter of approximately 100 µm or more can significantly increase the risk of complete insulation failure of the entire material. Pore diameters of less than 100 µm can be advantageously achieved using the method according to the invention.

[0052] There are embodiments in which applying the thermoplastic coating polymer to the wire assembly comprises contacting the raw wire with thermoplastic particles or fibers.

[0053] The thermoplastic particles can be applied to the wire arrangement using a suitable spraying process, in particular an electrospraying process ("electrospraying"). The spray material used can be thermoplastic particles or thermoplastic fibers, which can be produced in-situ using a known electrospray or electrospinning process.

[0054] After the application of the thermoplastic particles or thermoplastic fibers, the top layer of the wire coating of the wire assembly or wire has a layer consisting of thermoplastic powder particles or fibers.

[0055] In a next step, the particles or fibers can be melted onto the wire arrangement by means of an appropriate heating device, for example one based on infrared radiator technology, which, in combination with the spraying process, creates a uniform layer.

[0056] There are embodiments in which the application of the thermoplastic coating polymer to the wire assembly comprises a fluidized bed process or an electrostatic fluidized bed process.

[0057] To produce a particularly uniform layer, the wire arrangement can be introduced into a chamber designed to generate an electric field between the spray object, here the wire arrangement, and the spray material. In particular, a fluidized bed process, such as that used by TransApp, can be used. ® in the state of the art.

[0058] In a next step, the particles or fibers can be melted onto the wire arrangement by means of an appropriate heating device, for example one based on infrared radiator technology, which, in combination with the fluidized bed process, creates a particularly uniform layer.

[0059] There are embodiments in which applying the thermoplastic coating polymer to the wire assembly comprises applying the thermoplastic coating polymer to a raw wire and fabricating the wire assembly from the raw wire.

[0060] Raw wire, as defined in the present disclosure, is an untreated wire or a wire having a thermosetting coating according to the above description, and which has not been or has not yet been manufactured into a wire assembly. By applying the thermoplastic coating polymer to the raw wire, the wire assembly can be formed on the intended active part, while the foam structure is only formed once the wire assembly is in its intended position, thereby creating a particularly snug fit for the foam structure.

[0061] Furthermore, wire that is not processed into a wire assembly for an active part of an electric motor can be used as an intermediate product in other applications. For example, the coated wires could be used in communications technology for communication lines, for wires in actuators, or as "bell wire" in acoustic applications such as horns and signaling devices.

[0062] There are embodiments in which the application of the thermoplastic coating polymer comprises prior mixing of a thermosetting polymer into the coating polymer.

[0063] Pre-mixing refers to the introduction of a thermosetting polymer into the coating polymer before the coating polymer is applied to the wire arrangement or the raw wire.

[0064] By previously mixing the thermosetting polymer into the coating polymer and a subsequent baking step in which the thermosetting layer is formed, a multilayer structure consisting of a thermosetting polymer and a thermoplastic coating polymer can be formed in one step.

[0065] In another aspect, the present disclosure comprises a wire assembly treated by the method of any preceding claim and further comprising: an insulating foam structure surrounding a surface of the wire assembly, wherein the insulating foam structure is a foamed coating polymer.

[0066] In one embodiment, the pores created by the foaming process are filled with an insulating fluid.

[0067] In another embodiment, the wire assembly comprises an insulating foam structure applied to a first insulating layer, wherein the first insulating layer is a thermosetting material and the insulating foam structure is a foamed thermoplastic coating polymer. This multilayer insulation surrounds the surface of the wire assembly. In another embodiment, the pores created by the foaming process are filled with an insulating fluid.

[0068] According to a further aspect, the present disclosure comprises an active part for an electric motor, further comprising: the wire arrangement treated according to the disclosed method and having an electrically insulating foam structure enclosing the wire arrangement. During the process, the outline of the wire arrangement forms a thermoplastic polymer foam that completely closes the remaining cavities in the active part of the electric motor.

[0069] Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 shows an overall view of a stator equipped with wire arrangements, wherein the wire arrangements are coated with the coating according to the invention; Fig. 2 a partial perspective view of a stator with a coated wire arrangement according to the invention in a slot; Fig. 3 schematically shows two different embodiments 3A and 3B of the coated wire arrangement according to the invention; Fig. 4 a flowchart of a method according to the invention in a first embodiment; Fig. 5 a flowchart of a method according to the invention in a second embodiment; Fig. 6 is an overall view of a prior art stator filled with wire arrangements; Fig. 7 an illustration of a cross section of a coated wire assembly according to the invention in a non-foamed state 7A and in a foamed state 7B.

[0070] Fig. 1 shows an overall view of a stator 10 with a plurality of slots 20 concentrically surrounding a central cavity, and wire arrangements 100 arranged in the slots 20, forming a winding head 30 and coated with an insulating foam structure 110X according to the invention. The insulating foam structure 110X according to the invention has, for example, a layer thickness of 600 µm. After the foaming process, the slots 20 are completely filled with the wire arrangements 100, the foamed wire insulation, and the foamed slot insulation. Due to the expansion of the coating polymer 110 during the foaming process, more spacing can be achieved between critical wires in the winding head 30 than with a simple wire coating, thereby increasing insulation efficiency.The pores of the foamed slot base insulation and the foamed wire assembly are additionally filled with an insulating fluid that has a similar permittivity to the coating polymer 110 of the slot base insulation and the wire insulation. The insulating fluid can be filled during or after the foaming process.

[0071] The perspective partial view according to Fig. 2 shows an example of a section of a stator 10 and schematically a wire arrangement 100 located therein. The wire arrangement 100, which is inserted into a slot 20 of the stator 10, has an insulating foam structure 110X that encloses the wire arrangement 100. Prior to the foaming process, not only the wire arrangement 100 but also the slot 20 of the stator 10 can be provided with a thermoplastic coating polymer 110, so that a uniform insulating foam structure 110X can be formed during the foaming process. Both the outline of the wire arrangement 100 and the thermoplastic coating polymer 110 optionally introduced into the slot 20 form a thermoplastic polymer foam during the process, which completely closes the cavities remaining in the slot 20. The pores created during the foaming process can be filled with an electrically insulating oil, for example, a gear oil.This increases the insulation efficiency of the entire stator.

[0072] Fig. Figure 3 schematically shows two different embodiments of the coated wire arrangements, before and after the foaming process. Fig. 3A shows a wire assembly 100 with a coating polymer 110. After the foaming process, represented by an arrow, the coating polymer 110 increases in volume or decreases in density, creating an insulating foam structure 110X with open-cell pores that encloses the wire assembly 100. The pores created in the insulating foam structure 110X can now be filled with an electrically insulating oil, such as a gear oil, to increase the permittivity.

[0073] In Fig. 3B shows another embodiment of the coated wire arrangement 100, which has a multi-layer insulation layer. In a first coating process, it may be expedient to apply a first insulation layer 110B that is non-foamable and surrounds the surface of the wire arrangement 100. This can be a thermosetting material, for example. In a second step, a second insulation layer of a thermoplastic coating polymer 110A is then applied to the wire arrangement 100 already coated with a first insulation layer 110B. After the foaming process, represented by an arrow, the coating polymer 110 increases in volume or the density decreases, and an insulating foam structure 110X with open-cell pores is created around the surface of the wire arrangement 100, which now additionally has an unchanged first insulation layer 110B.The pores created in the insulating foam structure 110X can now be filled with an electrically insulating oil, such as a gear oil, to increase the permittivity. A non-foamed, first insulation layer 110B made of a thermosetting material, for example, has the advantage that the insulation efficiency can be increased by this additional layer.

[0074] Fig. 4 shows a flow diagram of a coating method according to the invention for applying an electrically insulating layer to a wire arrangement 100 or to a slot 20 of a stator 10. The stator 10 is to be seen here as representative of an active part within the meaning of the present disclosure. In a first step S001A, a thermoplastic coating polymer 110 is applied to a wire arrangement 100. At the same time, in a step S001B, a thermoplastic coating polymer 110 can be introduced into a slot 20 of a stator 10. In a second step, the wire arrangement 100 coated with a thermoplastic polymer is inserted into a slot 20 of the stator. In a next step S003, the entire stator 10, including the wire arrangement 100, is placed in a reactor / autoclave.In the reactor / autoclave, the coating polymer is loaded or saturated with carbon dioxide (CO2) in a next step (S004) through defined pressure and temperature exposure (at least 73.75 bar and 30.9°C). In a fifth step (S005), the stator is cooled to a desired temperature of at least below 30.9°C while maintaining constant pressure. This slows the diffusion rate of the CO2, allowing the CO2 to remain in the coating polymer for longer. In a subsequent step (S006), the pressure in the reactor / autoclave is suddenly reduced to atmospheric pressure. Due to the abrupt reduction in pressure to atmospheric pressure, the CO2 begins to transform into a gaseous state, initiating phase separation of the CO2. In a final step (S007), the temperature is deliberately increased (e.g., 165°C).CO2 initially dissolved in the polymer acts as a plasticizer, softening the thermoplastic coating polymer and thus enabling the formation of foam pores (S008). As CO2 becomes increasingly less present in the polymer during the heat treatment, the plasticizing effect also decreases progressively until the thermoplastic polymer "solidifies" in the pore structure.

[0075] Fig. Figure 5 shows a flow diagram of a coating method according to the invention for applying an electrically insulating layer to a wire arrangement 100 and installing it in an active part, for example, a stator 10. In a first step S0011, a thermoplastic coating polymer 110 is applied to a raw wire intended for producing the wire arrangement 100. The raw wire can, according to the above explanation, be uncoated or have a previously applied and cured duromer layer.

[0076] The thermoplastic particles are applied to the raw wire using a suitable spraying process, in particular an electrospraying process (“electrospraying”). The spray material can be either thermoplastic particles or thermoplastic fibers. For this purpose, the raw wire is introduced into a chamber designed for this purpose. The raw wire is grounded, and a spray device suitable for spraying the selected spray material is electrically charged. This results in the particles or fibers, electrostatically charged by the electrical charge of the spray device, adhering to the raw wire. As an alternative to an electrospraying process, the raw wire can be coated using a fluidized bed process. For this purpose, the raw wire is introduced into a chamber in which the particles or fibers are held in an electrostatically charged state in a fluidized bed. For example, the particles or fibers can be, according to the well-known TransApp® -Technology from the electrostatic fluidized bed to a transfer belt and from there transferred to the passing raw wire by means of an additional high-voltage electrode.

[0077] Advantageously, the particles or fibers can be produced in-situ by an electrospray or electrospinning process known from the prior art.

[0078] After the application of the thermoplastic particles or thermoplastic fibers, the top layer of the wire coating of the raw wire has a layer consisting of thermoplastic powder particles or fibers.

[0079] In a next step S0012, the particles or fibers can be melted onto the raw wire by means of an appropriate heating device, for example one based on infrared radiator technology, whereby, in combination with the spraying process or fluidized bed process, a uniform layer is created.

[0080] In a next step S0021, the raw wire is manufactured into the wire assembly 100. For example, the wire is arranged in the wire assembly in the active part, for example, the stator 10.

[0081] It follows from Fig. 4 known step S003. From step S003 onwards, the method can be carried out in accordance with the method in Fig. 4 with corresponding process steps S003, S004, S005, S006, S007 and S008.

[0082] Fig. Figure 6 shows an overall view of a stator 10 with a plurality of slots 20 concentrically surrounding a central cavity, and wire arrangements 100 arranged in the slots 20, forming a winding head 30 and coated with a coating polymer 200 from the prior art. Layer thicknesses of 80 to 150 µm are known from the prior art.

[0083] Fig. Figure 7 schematically shows a comparison of an embodiment of the present disclosure of the coated wire assemblies 100 in Fig. 7A with a coating polymer 110 in a foam structure 110X and a wire arrangement coated with a coating polymer 110 according to the prior art in Fig. 7B. The different volumes of the coating polymer 110 structures in Fig. 7B and the coating polymer 110, 100X Fig. 7A are for illustrative purposes only. Likewise, the structure may vary in actual embodiments. In particular, the foam structures 110X in Fig. 7A merge into one another or form a coherent structure, which can also be referred to as foam structure 110X. List of reference symbols 10 Stator 20 grooves 30 winding head 100 wire arrangement 110 thermoplastic coating polymer 110A first insulating layer of a coating polymer 110X insulating foam structure 200 state-of-the-art coating S000 Start of the method according to a first embodiment S001A Applying a thermoplastic coating polymer to the wire assembly S001B Introducing a thermoplastic coating polymer into a groove S002 Inserting the coated wire assembly S003 Placing the entire stator in a reactor / autoclave S004 Loading the coating polymer with carbon dioxide and setting defined temperature and pressure conditions S005 Cooling of the active part S006 Sudden drop in pressure S007 Temperature increase and formation of an insulating foam structure S008 Completion of the coating and foaming process S0000 Start of the method according to a second embodiment S0011 Application of a thermoplastic coating polymer to raw wire S0012 Temperature treatment S0021 Installation of the raw wire 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] DE 202012104118U1

[0003] DE 69714491T2

[0004] US 2018 / 0262073A1

[0011]

Claims

[1] Method for applying and foaming an electrically insulating foam structure onto a wire arrangement (100) for an active part of an electric machine, the method comprising: (S001A) applying a thermoplastic coating polymer (110) to the wire assembly (100); (S002) inserting the wire arrangement (100) into the active part; (S004) saturating the thermoplastic coating polymer (110) with carbon dioxide under defined temperature and pressure conditions; (S005) Cooling of the active part; (S006) lowering an ambient pressure of the active part; (S007) Temperature increase to form a foam structure (100X); wherein the foam structure (100X) has electrically insulating properties. [2] The method of claim 1, wherein cooling the active part comprises cooling to a temperature of less than 30.9°C; and when lowering the ambient pressure, the ambient pressure of the active part is abruptly lowered to atmospheric pressure. [3] A method according to any one of the preceding claims, further comprising filling the pores contained in the foam structure (110X) with an insulating material. [4] Method according to claim 3, wherein the insulating material comprises an oil, in particular a gear oil, or an insulating gas. [5] Method according to one of the preceding claims, wherein the thermoplastic coating polymer (110) comprises at least one foamable high-temperature polymer and / or a mixture of several foamable high-temperature polymers, wherein foamable high-temperature polymers comprise polyether ketone, in particular polyether ketone ketone, polyether ether ketone, polyphenylene ethers, polyetherimides, polyesters, including polyethylene naphthalate, polyether sulfones, polysulfones, polyether sulfones, polyphenylene sulfides and atactic, isotactic or syndiotactic polystyrenes. [6] Method according to one of the preceding claims, wherein the saturation of the thermoplastic coating polymer (110) with carbon dioxide takes place under a pressure of approximately 75 - 200 bar and a temperature of 40°C - 80°C for 5 to 40 minutes. [7] A method according to any one of the preceding claims, wherein the wire assembly (100) comprises a first thermosetting insulating layer (110A) and a second insulating layer of a thermoplastic coating polymer (110). [8] Method according to one of the preceding claims, wherein the insulating foam structure (110X) has a layer thickness of more than 80 µm. [9] Method according to one of the preceding claims, wherein a diameter of the pores contained in the foam structure (110X) is not greater than 100 µm. [10] A method according to any one of the preceding claims, wherein applying the thermoplastic coating polymer (110) to the wire assembly (100) comprises bringing the raw wire into contact with thermoplastic particles and / or fibers. [11] A method according to any one of the preceding claims, wherein applying the thermoplastic coating polymer (110) to the wire assembly (100) further comprises a fluidized bed process or an electrostatic fluidized bed process. [12] The method of any preceding claim, wherein applying the thermoplastic coating polymer (110) to the wire assembly (100) comprises applying the thermoplastic coating polymer (110) to a raw wire and fabricating the wire assembly from the raw wire. [13] A method according to any one of the preceding claims, wherein applying the thermoplastic coating polymer (110) comprises pre-mixing a thermosetting polymer into the coating polymer. [14] A wire assembly (100) manufactured by the method of any preceding claim, comprising: a foam structure (110X) surrounding a surface of the wire assembly (100), the foam structure (100X) comprising a foamed thermoplastic coating polymer (110). [15] Electric machine comprising: A wire arrangement (100) according to claim 14, which is arranged in an active part of the electric machine.

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