Filling a groove with a thermoplast compound in an electric machine

Abstract

A groove closure of a winding groove of an electric machine is to be efficiently produced. For this purpose, a viscous groove closure material is provided (S5, S6), the thermoplastic matrix of which is mixed with magnetizable particles. The viscous groove closure material is applied (S7) into the groove of the electric machine, and finally the viscous groove closure material is cooled (S8) in the groove, whereby the groove closure material is cured in the groove.

Description

[0001] Description

[0002] Groove filling using thermoplastic compound of an electrical machine

[0003] The present invention relates to a method for filling a slot of an electrical machine. Furthermore, the present invention relates to a corresponding device for filling such a slot.

[0004] Low-voltage motors are typically manufactured with a round wire winding, which is wound into coils in advance using a flyer / stencil winder and then drawn fully automatically into the laminated core with the respective slots. The critical point here is always the slot gap, which is defined by the two adjacent slot teeth. This is significantly smaller than the slot itself, which ideally closes the magnetic circuits more effectively, but the entire copper winding has to be drawn through this cross-sectional taper. In order to generate ideal magnetic field properties in the laminated core, the slot gap would have to be chosen to be so narrow that the slot gap width is smaller than the diameter of a single wire in the winding. However, this would lead to major problems in production, as typical winding drawing-in processes can no longer be used.Current sheet geometries represent a compromise that accommodates both requirements. The slot gap has approximately the inside width of two to four individual wires (diameter), whereby a suitable lamination guide partially compresses the copper bundle to this width during insertion, while the disadvantage regarding the magnetic circuit dimensioning remains acceptable.

[0005] Particularly in larger machines (medium-voltage or high-voltage motors) with higher requirements, the existing slot gap is subsequently closed using a magnetic slot seal. This consists of magnetic iron particles of various designs, which are usually combined with a plastic compound. This compound (filler particles = iron, matrix = plastic) is often prefabricated and used as slot wedges, which are inserted mechanically. This has the disadvantage that the slot seal can become loose and come off during operation of the machine due to vibrations and forces occurring, thus blocking the rotor and leading to machine failure.

[0006] On the other hand, prefabricated slot gaps are not an economical solution for a product portfolio with a wide variety of variants, as is often the case in the area of ​​low-voltage motors.

[0007] Another application for medium- and high-voltage machines involves the use of an uncrosslinked, highly filled paste consisting of iron filler particles and a chemically reactive resin (mixing ratio of approximately 90% by weight iron filler to 10% by weight polymer matrix). The compound must be kneaded for several hours under active cooling to ensure homogenization of the particles in the matrix. It must then be stored and transported in a cooled environment, as it is a single-component, reactive compound. The matrix component, for example, is an anhydrite-cured epoxy resin, which cures when exposed to elevated temperatures (150°C for several hours) to form a molded material with sufficient mechanical strength and a glass transition temperature of over 140°C, thus meeting the requirements of medium- and high-voltage machines for the insulation system and peripherals.Due to the choice of matrix and iron filler composition, as well as the high mechanical demands placed on the final molding material and during application, additional additives such as talc (as a lubricant) and polymer fibers (for reinforcement of the mass and thixotropy during processing) are required in single-digit weight percentages. The material is applied at room temperature either manually ("spat in") or by a (semi-)automated bead application followed by pressing in using a special squeegee. Thermal curing is subsequently achieved using a hot-air oven or by applying current to the windings.

[0008] The object of the present invention is to propose an economical and low-energy possibility for slot filling, particularly in low-voltage machines.

[0009] According to the invention, this object is achieved by a method and a device according to the independent claims. Advantageous developments of the invention emerge from the subclaims.

[0010] The invention is based on the finding that low-voltage motors with high efficiency have only very low power losses, which manifest themselves in heating of the rotor and stator, whereby a temperature of over 100 ° C is almost impossible, particularly in the area of ​​a possible slot closure. This allows a new perspective on the thermal stability of the insulation system and its periphery. In particular, the periphery (e.g. the cover slide) can be well below the thermal class F / H (155 ° / 180 ° C, 20,000 h) otherwise required for the primary insulation system, without negatively affecting the service life or performance of the machine.

[0011] Based on this development, the invention presents an alternative polymer solution for the slot filling, which is an economical and at the same time CCt-friendly solution (with regard to application and process), especially for low-voltage motors.

[0012] According to the invention, a method is provided for filling a slot of an electrical machine. The slot is, in particular, a winding slot into which a winding or coil can be drawn. The slot typically results in a laminated core of a magnetically active part of the electrical machine. The electrical machine can be, for example, a motor, a generator, a transformer, and the like.

[0013] The process involves providing a (cured or molten) slot closure material with magnetizable particles mixed into its thermoplastic matrix. The slot closure material is therefore available as a separate product before processing. For example, it is provided as granules or in another form. In any case, the slot closure material is in cured, i.e. solid, form. The slot closure material has a thermoplastic matrix with magnetizable particles. The magnetizable particles are preferably distributed as homogeneously as possible in the plastic matrix. Ferromagnetic particles, and in particular iron powder, can be used for the magnetizable particles. This results in a so-called "compound" consisting of a matrix of plastic and filler particles (e.g. iron).Instead of iron, other ferromagnetic metals or alloys can be used for the magnetizable particles.

[0014] When hardened or solid slot sealing material is provided, it is melted. The slot sealing material (compound) is heated to a temperature that allows for suitable processing. For efficiency reasons, the temperature should not be significantly higher than necessary for processing. After melting, the previously solid slot sealing material becomes viscous, i.e., thick-flowing.

[0015] In a further step, the molten or viscous slot sealing material is applied to the slot of the electrical machine. Typically, the respective winding or coil is already in the slot, so that the molten slot sealing material is applied to the respective wire bundle or cover slide. The amount of slot sealing material introduced into the slot should be sufficient to ultimately form a suitable slot seal after curing.

[0016] In a further process step, the molten or viscous slot sealing material is cooled in the groove, causing it to harden. After heating the slot sealing material once, it can cool completely in the groove. Further heat input is therefore not necessary, as a thermoplastic matrix is ​​used.

[0017] In an advantageous manner, a simple method for filling a slot of an electrical machine can be provided which is particularly energy efficient.

[0018] In one embodiment, the plastic matrix is ​​a polyolefin hot melt adhesive. Polyolefins are polymers produced from alkenes such as ethylene, propylene, 1-butene or isobutenes by chain polymerization. In particular, they are semi-crystalline thermoplastics that are easy to process and have good electrical insulating properties. Hot melt adhesives or melt adhesives (also called hot melt adhesives) are solvent-free and are more or less solid products at room temperature, existing as a viscous liquid when hot. On cooling, they solidify reversibly and can create a strong bond between the adjacent components. A polyolefin hot melt adhesive therefore has advantageous properties for electrical machines and is easy to process.

[0019] Alternatively, a polyamide hot melt adhesive, and in particular a polyamide 6 hot melt adhesive, can be used for the plastic matrix. Polyamides are linear polymers with regularly repeating amide bonds. They possess excellent strength and toughness, as well as good chemical resistance to organic solvents. Polyamides are also thermoplastics. Polyamide 6 is also known as polycaprolactam. Polyamide 6 is known for its toughness and wear resistance. Polyamide can also be used as a hot melt adhesive with the properties mentioned above.

[0020] In a further embodiment, 75 to 90 percent by weight of magnetizable particles, particularly ferromagnetic particles (e.g., iron powder), are mixed into the slot closure material or compound. The high weight fraction of the magnetizable particles results in a highly efficient slot closure.

[0021] Furthermore, the molten slot sealing material can be applied to the slot of the electrical machine by extrusion or injection molding. Thus, proven standard methods for applying the slot sealing material can be used.

[0022] Specifically, the slot sealant material can be applied using a single-screw extruder or an application gun. Because the compound material used consists of a plastic matrix and filler, it's not necessary to mix components during application. Instead, a simple single-screw extruder can be used to apply the slot sealant material. The same applies to the application gun. In principle, it's sufficient to use a so-called "hot glue gun," which melts the thermoplastic matrix.

[0023] According to a further embodiment, the slot sealing material is melted from granules. The slot sealing material, or compound, is thus in granular form, and each grain contains the mixture of plastic matrix and (iron) filler. Therefore, no further mixing is required.

[0024] According to a further advantageous embodiment, the slot sealing material is melted immediately before application. For example, the melting takes place in the extruder or the application gun, and the molten slot sealing material is immediately applied into the slot. This has the advantage that the molten slot sealing material does not have to be kept viscous for an extended period of time. This saves energy.

[0025] According to a further embodiment, during the application of the viscous or molten slot sealing material into the slot of the electrical machine, a viscous strand of the slot sealing material is applied to a wire bundle in the slot. The viscous strand represents a pasty "bead" formed from the compound paste. The viscous strand is generally applied indirectly to the wire bundle. In particular, it is applied to a cover slide that covers the wire bundle toward the slot. The slot sealing material can thus advantageously be closed.

[0026] In a particularly advantageous embodiment, the wire bundle is pressed toward the groove base immediately before applying the viscous strand. In particular, the cover slide provided on the wire bundle can be pressed downward toward the groove base, which indirectly also pushes the wire bundle toward the groove base. This downward pressure creates additional space between the wire bundle or cover slide and the groove opening, which can be at least partially filled by the groove closure material.

[0027] In a further development, it can be provided that after the application of the viscous strand, the wire bundle relaxes in the groove, and a portion of the strand is pressed behind a groove projection to form a positive fit. For example, part of the viscous strand is already brought into the undercut of the groove during application. If the wire bundle relaxes after being pressed in, it presses the portion of the viscous strand in the undercut further into the undercut. This allows a positive fit in the groove to be achieved after the slot closure material has hardened.

[0028] In a further embodiment, the viscous strand, after being introduced into the groove, is removed flush with the surface and / or smoothed with a heating device. The viscous strand can be removed, for example, using the application tool or a separate removal tool. A heating device such as an infrared lamp can be used to smooth the surface. This melts the groove closure material at least on the surface, and the surface tension is utilized for smoothing.

[0029] The above object is also achieved according to the invention by a device for filling a slot (winding slot) of an electrical machine, wherein

[0030] - a melting device designed to melt a slot closure material in whose thermoplastic matrix magnetizable particles are mixed,

[0031] - an application device designed to apply the molten or viscous slot closure material into the slot of the electrical machine and to allow the molten slot closure material to cool in the slot, whereby the slot closure material hardens in the slot.

[0032] The melting device can also be integrated into the application device. The application device is capable, for example, of applying the aforementioned pasty bead to the cover slide in the groove. The advantages and variants described above in connection with the method according to the invention also apply analogously to the device according to the invention. The individual method features can be viewed as functional features of the device.

[0033] For use cases or application situations that may arise during the method and which are not explicitly described here, it may be provided that, in accordance with the method, an error message and / or a request to enter user feedback is issued and / or a standard setting and / or a predetermined initial state is set.

[0034] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identity are included.

[0035] The present invention will now be explained in more detail with reference to the accompanying drawings, in which:

[0036] FIG 1 a slot of an electrical machine filled with a wire bundle;

[0037] FIG 2 the groove of FIG 1 with pressed-in wire bundle;

[0038] FIG 3 the groove with applied groove sealing compound;

[0039] FIG 4 the groove with closed groove slot;

[0040] FIG 5 the application of the slot sealing compound in the longitudinal direction of the slot; and

[0041] FIG 6 shows a schematic process flow.

[0042] The exemplary embodiments described below represent preferred embodiments of the present invention.

[0043] The fact that low-voltage motors in particular can be operated very efficiently and the slot seal hardly reaches a temperature above 100 ° C is used to produce the slot seal using a thermoplastic compound that has a thermoplastic matrix with a filler of magnetizable particles.

[0044] In a specific embodiment, the polymer matrix is ​​replaced by a material deviating from the state of the art, regardless of the composition and, if necessary, optimization of the particle size distribution of the iron filler. Due to the significantly smaller groove gap (approx. 2 to 5 mm compared to larger machines with approx. 2 cm), the addition of polymer fibers to the reinforcement is not necessary. Regardless of other features, at least one embodiment should therefore be based on the thermoplastic matrix not containing polymer fibers. Conventional subsystems can thus be used for the application of the thermoplastic melt, since no "high-shear / high-viscosity" component is added to the thermoplastic, which would have made fully automated conveying and introduction very difficult.

[0045] According to the invention, a compound consisting of a thermoplastic matrix and a filler with magnetizable particles (e.g., iron powder) is used to fill a (winding) slot of an electrical machine. A practical approach, for example, is to compound the filler (e.g., iron powder) at 75 to 90 percent by weight, for example, into a polyolefin hotmelt adhesive or polyamide 6 hotmelt adhesive matrix. Polyolefin is preferred due to its lower melting and processing temperature (melting temperature approximately 140 degrees Celsius, processing temperature 200 degrees Celsius), provided the mechanical properties are sufficient during operation of the motor or electrical machine (softening below 100 degrees Celsius).

[0046] The compounding of (iron powder) filler and thermoplastic matrix can occur independently of the groove closure or immediately prior to it. If compounding occurs immediately prior to a groove closure, the compound does not need to be melted twice. Otherwise, if compounding occurs independently of the groove closure, the groove closure material is processed as an intermediate product, for example, into granules (for extrusion) or rods (for application guns). In this case, the groove closure material or intermediate product must be melted again prior to application.

[0047] For example, incorporation and further processing by extrusion or injection molding with a 90 percent by weight iron powder filler in polyamide 6 hot melt adhesive can be achieved. Such a compound softens at 120 to 150 degrees Celsius and is processable at 230 to 250 degrees Celsius.

[0048] A specific thermoplastic-based slot sealant can also be manufactured with a polyolefin matrix. The processing temperature would then be, for example, 200 degrees Celsius, and a weight ratio of 90:10 (filler to matrix) could be achieved.

[0049] After compounding, the material can be introduced into the application device, for example in the form of granules, and heated to processing temperature. Using a single-screw extruder or a suitable thermoplastic application gun (hot glue gun), for example, a bead can now be applied, at or slightly above processing temperature, e.g. into the stator slot. Specifically, the bead can be applied through the slot gap onto a pusher which closes off a wire bundle inserted into the slot. After cooling to below the softening temperature, the slot closure is preferably interlocked and glued to the undercuts of the slot gap geometry.

[0050] The application can be achieved, for example, by depositing a bead (= compound paste), which fits positively into the slot gap or onto the cover slide. The bead should be flush with the inner radius of the laminated core on the inside (in the case of an external stator). Optionally, the copper or wire bundle can be briefly compressed before application so that the bead is mechanically pressed into the undercuts while still at high temperature. This is explained in more detail using the following example.

[0051] FIGS. 1 to 4 show a groove 1 formed in a laminated core 2. The groove 1 has a groove base 3, which, for example, is formed radially outward in an external stator. Opposite the groove base 3 (radially inward in the external stator) is a groove gap 4. The groove gap 4 is located in the circumferential direction between one or two groove projections 5.

[0052] A wire bundle 6 of a winding of the electrical machine is located in the slot 1. The wire bundle 6 was inserted into the slot 1 through the slot gap 4. A cover slide 7, which extends in the longitudinal direction of the slot and forms a positive connection with the slot projections 5, prevents the wire bundle 6 from escaping from the slot 1. In the state shown in FIG. 1, the cover slide 7 rests against the slot projections 5 through the wire bundle 6.

[0053] FIG. 5 shows the groove 1 in longitudinal section. A point in the cross-section of FIG. 1 prior to application of the bead / thermoplastic groove sealing material is designated by I in FIG. 5.

[0054] FIG. 2 shows a cross-section through the groove 1 at point II of FIG. 5. Specifically, at this point, the cover slide 7 and the underlying wire bundle 6 are pressed toward the groove base by a pressure roller 8 or another suitable tool, thereby compressing them. FIG. 5 also shows that at cross-sectional point II, the cover slide 7 is pressed deeper into the groove 1.

[0055] Immediately following the pressing roller 8, the molten slot closure material (including thermoplastic matrix and magnetizable particles) is applied as a strand or bead 10 to the wire bundle 6 or the cover slide 7 using an application device 9 (e.g., extruder or application gun, each heatable), as shown in FIG. 3 at cross-sectional point III. At this cross-sectional point III, the wire bundle 6 or the cover slide 7 is still compressed by the pressing roller 8, which also shows the deep position of the cover slide 7 at cross-sectional point III of FIG. 5.

[0056] The bead 10 can have a circular segment-shaped cross-section. Preferably, it is somewhat wider than the slot gap 4. This has the advantage that undercuts 11 can be formed by parts of the bead 10, i.e., the slot closure compound, that protrude behind the slot projections 5 when the wire bundle 6 relaxes again as shown in FIG. 4 and presses the cover slide 7 toward the slot gap 4. The still-hot, plastic bead 10 fills the slot gap 4, resulting in the slot closure 12 shown in FIG. 4, which has a T-shaped cross-section with the undercuts 11.

[0057] An enlarged section of the slot closure 12 is also shown in FIG 4. It shows how, in particular, the undercut 11 of the slot closure 12 protrudes below the slot projection 5 and thus forms a positive connection when the solidified, solid slot closure material is used.

[0058] If necessary, the bead 10 is removed from the upper side 13 of the groove 1 so that the groove closure 12 is flush with the upper side 12. The application device 9 or a separate tool can be used for removal.

[0059] Due to the high filler content (e.g., 75 to 90 percent by weight iron powder filler) of the hot melt adhesive paste, it remains dimensionally stable in the grooves and cools and solidifies quickly. Time-consuming CO2 curing of the material is eliminated. Compared to thermosetting solutions, it is recyclable through remelting and the use of recycled material.

[0060] The possible process steps of an exemplary embodiment are explained in more detail in conjunction with FIG. 6. Not all process steps are absolutely necessary. Rather, individual process steps can also be performed optionally and, if necessary, can also overlap in time.

[0061] In a first step S1, thermoplastic material can be provided, for example in the form of granules for compounding. In step S2, the thermoplastic material is melted. In step S3, the thermoplastic material is mixed with magnetizable particles (in particular iron powder). The mixing according to step S3 can take place before, during, and after the melting in step S2.

[0062] Optionally, according to step S4, the compound can solidify into a solid slot-sealing material in the form of rods or granules. The thermoplastic rods or the thermoplastic granules are thus present as a solid intermediate product.

[0063] The solid slot sealing material can now be provided, for example, in an application device. For example, an extruder or an application gun is fed with the slot sealing material.

[0064] Then, according to step S 6, the slot closure material is melted in a melting device or the application device.

[0065] According to step S7, the molten slot closure material is applied into a slot of an electrical machine by means of the application device. The application may be preceded by a step (not shown in FIG. 6) of pressing down a wire bundle in the slot. Finally, the slot closure material is cooled according to step S8. If necessary, the thermoplastic slot closure material bonds to the slot and the cover slide and / or forms a positive connection with the slot.

[0066] Advantageously, a high filler content of, for example, 75 to 90 percent by weight can be achieved using a prefabricated compound. A brief temperature increase, e.g., using an IR lamp, to the processing temperature proves particularly advantageous for smoothing the surface of the groove seal. Due to the high filler content, subsequent curing at room temperature occurs very quickly.

[0067] Another advantage is that the compound requires no fiber reinforcement, allowing for fully automated application. The potentially low softening temperature is perfectly acceptable for highly efficient low-voltage motors.

[0068] The recyclability of the thermoplastic slot closure is particularly advantageous compared to 3D cross-linked thermoset.

Claims

Patent claims 1. Method for filling a groove (1) of an electrical machine characterized by - providing (S5, S6) a viscous slot closure material, in whose thermoplastic matrix magnetizable particles are mixed, - applying (S7) the viscous slot sealing material into the slot (1) of the electrical machine, and - Cooling (S8) of the viscous slot sealing material in the groove, whereby the slot sealing material in the groove (1) hardens.

2. The method according to claim 1, wherein the plastic matrix is ​​a polyolefin.

3. The method according to claim 1, wherein the plastic matrix is ​​a polyamide and in particular a polyamide-6.

4. Method according to one of the preceding claims, wherein 75 to 90 percent by weight of magnetizable particles, in particular iron powder, are mixed into the slot closure material (S3).

5. Method according to one of the preceding claims, wherein the application (S7) of the viscous slot sealing material into the slot of the electrical machine is carried out by extrusion or injection molding.

6. Method according to one of the preceding claims, wherein the application of the slot sealing material is carried out by a single-screw extruder or an application gun.

7. Method according to one of the preceding claims, wherein the slot closure material is heated to a maximum of 250°C, in particular to a maximum of 200°C, for application (S7).

8. Method according to one of the preceding claims, wherein the viscous slot closure material is melted (S6) from a granulate.

9. The method according to claim 8, wherein the melting (S6) of the slot closure material takes place immediately before the application (S7).

10. Method according to one of the preceding claims, wherein during the application (S7) of the viscous slot closure material into the slot (1) of the electrical machine, a viscous strand (10) of the slot closure material is applied to a wire bundle (6) in the slot (1).

11. The method according to claim 10, wherein the wire bundle is pressed in the direction of the groove base (3) of the groove (1) immediately before the application (S7) of the viscous strand (10).

12. The method according to claim 11, wherein after the application (S7) of the viscous strand (10), the wire bundle (6) relaxes in the groove and a part of the strand (10) is pressed behind a groove projection (5) of the groove (1) to form a positive connection.

13. Method according to one of the preceding claims, wherein the viscous strand (10) is drawn off flush with the surface after being introduced into the groove and / or is smoothed with a heating device.

14. Device for filling a groove (1) of an electrical machine characterized by - a melting device designed to melt (S2, S6) a slot closure material, in whose thermoplastic matrix magnetizable particles are mixed (S3), - an application device designed to apply (S7) the molten slot sealing material into the slot of the electrical machine and to allow to cool (S8) the molten slot closure material in the groove (1), whereby the slot closure material in the groove (1) hardens.

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