Determining course of hardening of electrically insulating layer

Abstract

The invention relates to a method for determining a hardening change (C1, C2) when applying an electrically insulating layer made of a liquid insulating material (40) to an electrical product, in particular to an electrical winding system (25). In order to improve the hardening of the insulating material, the following steps are proposed:-providing a temperature change process (TC) traversed by the electrical product during the application and hardening of the insulating layer,-providing a reaction model of the insulating material, which outputs a hardening change process of the insulating material as an input variable on the basis of the temperature change process, the measured enthalpy of reaction (h1,..., h6) of the insulating material (40) is modeled at at least two, preferably at least four, different heating rates on the basis of the measured enthalpy of reaction (h1,..., h6) of the insulating material (40), and-the hardening course (C1, C2) is determined from the temperature course (TC) by means of the reaction model. The invention further relates to a method for applying an insulating material (40) to an electrical product, preferably to an electrical winding system (25).

Description

Technical Field

[0001] The invention relates to a method for determining a curing profile, for applying an electrical insulation layer made of a liquid insulating material, and to a method for applying an insulating material to an electrical product, preferably to an electrical winding system. Background Art

[0002] This method is used, for example, when impregnating rotors and stators of electric motors. In particular, the impregnation process, which is often carried out in the form of immersion impregnation and subsequent hot air furnace curing, is a major cost factor in production in terms of investment costs, maintenance, cycle time, production space requirements, etc. Optimization potential can be found here, on the one hand, in terms of material consumption, curing temperature / time (energy costs, CO2) and on the other hand in terms of automation. Summary of the invention

[0003] The invention is based on the object of improving the hardening of insulating materials.

[0004] This object is achieved by a method having the features specified in claim 1. In particular, the method for determining a curing profile when applying an electrical insulation layer made of a liquid insulating material to an electrical product, in particular to an electrical winding system, comprises the following steps:

[0005] - providing the temperature profile that the electrical product traverses when applying and curing the insulating layer,

[0006] - providing a reaction model of the insulating material, which outputs a hardening course of the insulating material based on the temperature course as an input variable and is modeled for at least two, preferably at least four, different heating rates based on a measured reaction enthalpy of the insulating material, and

[0007] - Determining the hardening profile using the temperature profile by means of the reaction model.

[0008] In addition to windings in electric motors, ie stators or rotors, the electrical winding system can also be a coil for other applications, such as a magnetic field coil or an HF coil in magnetic resonance tomography.

[0009] The hardening profile can be normalized to 1 with respect to the complete enthalpy of hardening of the respective insulating material and plotted over time. The heating rate is the temperature increase used in the measurement. As a special case, a heating rate of 0 K / min, i.e. an isotherm, can also be used here.

[0010] The reaction model interpolates the enthalpy or reaction rate for a temperature increase that differs from the heating rate used in the measurement. The reaction model can thus output the progression of hardening for all temperature increases that occur within the range of application and hardening. Thus, the temperature slope can be determined for each time step, from which the reaction model can output the progression of the hardening process.

[0011] In another embodiment, the measured reaction enthalpy is measured by means of dynamic differential calorimetry of the insulating material. Therefore, advantageously, only a few samples of the insulating material must be measured to parameterize the model. The DSC signal measured in this way can be integrated to determine the reaction enthalpy at the corresponding heating rate. Based on the complete reaction enthalpy that occurs when the insulating material is completely crosslinked, the reaction course for the insulating material can then be explained. In other words, complete crosslinking is a crosslinking degree that is as high as possible due to the potential presence of free reaction partners in the case of containing steric hindrance (i.e., monomers that remain free due to too little diffusion possibility and too large a distance from potential reaction partners).

[0012] In another embodiment, the heating rate is in the range of 0.1 K / min to 10 K / min. In particular, a heating rate in the range of 0.25 K / min to 8 K / min has been found to be advantageous, since this ensures that the temperature increase that usually occurs during curing is covered.

[0013] In another embodiment, the reaction model is modeled based on the measured reaction enthalpy under at least four different heating rates. In order to interpolate the reaction enthalpy for a temperature increase different from the measured heating rate, it has proven to be advantageous to perform measurements (e.g. DSC measurements) of the insulating material under at least four different heating rates.

[0014] In another embodiment, in order to model the reaction model, the reaction rate course of the hardening is determined based on the reaction enthalpy of the insulating material. Here, for example, the reaction rate course can be determined by normalizing the DSC signal to the complete enthalpy of the hardening reaction. In addition, the hardening course is determined by integrating the reaction rate course.

[0015] In another embodiment, the reaction model is modeled based on the Arrhenius equation. If a variable value over the hardening process is used instead of a constant for the activation energy E in the Arrhenius equation A , is particularly beneficial.

[0016] In another embodiment, the temperature profile is a measured temperature profile of an electrical product, in particular a temperature profile measured using a thermocouple in an electrical winding system. Thus, the temperature profile can be provided simply and efficiently. After the insulating material has been applied, the thermocouple can usually remain in the winding system. The hardening profile can even be calculated together in real time. When producing many similar products, it is usually sufficient if the hardening profile is determined once for the corresponding insulating material and the electrical product.

[0017] In another embodiment, the temperature profile is a set temperature profile of the electrical product. Here, the set temperature profile may be a temperature profile that is predetermined and contained in the installation. It is thus possible to check whether the temperature profile reliably leads to sufficient hardening of the insulating material.

[0018] In another embodiment, the determination of the hardening process by the reaction model includes determining the gel point. The gel point can be mapped onto the hardening process and determined, for example, by rheological measurements. The gel point or gelling point is characterized by a defined viscosity increase and can be determined at the intersection of the storage and loss modulus during rheological measurements. The advantage of taking the gel point into account is that the insulating material can thus already adhere better to the electrical product and no longer flow away. Accordingly, the subsequent steps (e.g. removal from the bath) can thus be timed more accurately. It is also possible to define a viscosity threshold value different from the gel point, which must be exceeded if the next process step is to be performed.

[0019] In another embodiment, the insulating material is a resin, preferably a liquid reactive resin, in particular an epoxy resin, an unsaturated polyester or a polyester imide. The reaction model can also be used to determine the curing process of a multi-component resin (e.g., an amino-hardening epoxy resin, an isocyanate polyurethane) that is mixed immediately before being applied to the electrical product.

[0020] The object is furthermore achieved by a method for applying an electrical insulation layer made of a liquid insulating material to an electrical product, in particular to an electrical winding system, comprising the steps of:

[0021] - providing said electrical product,

[0022] - Provide liquid insulating material,

[0023] - applying said insulating material to the product,

[0024] - hardening of the insulating material,

[0025] - provide the temperature profile that the electrical product traverses when applying and curing the insulating layer, and

[0026] If the curing profile determined using the method according to any of the preceding claims exceeds a threshold value, curing is terminated.

[0027] Temperature profiles can be measured by thermocouples located in or on the electrical product, but this is generally not necessary for every product.

[0028] In this case, hardening can be carried out with the supply of external heating energy.

[0029] The threshold value of the curing process, i.e. the degree of hardening from which hardening can be terminated, can be, for example, 80%. The termination of hardening here means the termination of active hardening under the supply of external heating energy. The insulating material can then still be completely post-hardened, for example under the influence of residual waste heat in the product; for this purpose it does not have to remain in the plant.

[0030] In another embodiment, the application is to immerse the electronic product in a bath of liquid insulating material. In the bath, the electrical product itself can be heated, for example by energizing the winding system.

[0031] In another embodiment, the application is the dripping of the electronic product with a liquid insulating material. It may be meaningful here to observe the temperature course only from a certain amount of insulating material applied by dripping. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be described and explained in more detail below based on the embodiments shown in the drawings.

[0033] Figure 1 A method for applying insulating material to an electrical winding system is schematically shown.

[0034] Figure 2 The temperature course during application and curing is shown by way of example.

[0035] Figure 3 shows DSC measurements of insulating materials at different heating rates,

[0036] Figure 4 Shown in Figure 3 The reaction rates of the insulating materials measured in the experiment were determined from DSC measurements.

[0037] Figure 5 shows the progress of the reaction integrated from the reaction rate,

[0038] Figure 6 a schematic diagram showing a reaction model for an insulating material, and

[0039] Figure 7 The hardening curves determined for two different insulating materials using a respective reaction model are shown. DETAILED DESCRIPTION

[0040] Figure 1 The method for applying a liquid insulating material 40 to an electrical winding system 25, which is designed here as a stator winding of an electric motor, is schematically shown. The stator or winding system 25 is arranged here on a carrier 30 for transport through a production facility.

[0041] Step S30 schematically shows the preheating of the winding system 25 with a temperature profile TPRE outside the insulating material or the preheating of the winding system 25 to a temperature TPRE.

[0042] Step S40 shows the immersion of the winding system into an immersion bath filled with liquid insulating material 40. During the immersion, the electrical winding system 25 can continue to be energized and heated.

[0043] Step S50 shows the hardening of the insulating material 40 under the effect of a temperature profile TCURE. In addition to or as an alternative to energizing the winding system 25, the temperature profile can be provided by a furnace.

[0044] In step S60 , UV curing is now performed by UV radiation UV. This has the advantage that the insulating material is thus cured well even at the surface and is no longer sticky. UV curing is optional here.

[0045] Figure 2 As shown exemplarily in Figure 1 The temperature course TC during the application and curing of the insulating material, as shown in FIG. , is similar to the temperature course that the insulating material is subjected to at the electrical product, for example at the winding system 25 .

[0046] The first temperature T0 results from the temperature of the product when the liquid insulating material is applied and the temperature of the insulating material when it is applied. When immersed in the liquid insulating material 40, for example, the temperature T0 thus occurs. Heating to the second temperature T1 can be caused on the one hand by the thermal inertia of the electrical winding system and on the other hand by additional heating of the winding system. The temperature course T40 describes the course of change that the resin undergoes directly at the product when it is still applied. Another area shows the temperature course TCURE during hardening, for example in a furnace. The last area TUV shows the temperature course during UV irradiation, which in particular causes a high degree of surface hardening while the product is still heated to the final temperature T2. Then, cooling occurs and the insulating material still hardens afterwards.

[0047] With the invention it is now possible to determine the hardening course for such a temperature profile TC, even if the temperature profile has a different slope which does not correspond to the heating rate.

[0048] Figure 3 DSC measurements (dynamic differential calorimetry) of the insulating material are shown at different heating rates, in this case 0.25 K / min, 0.5 K / min, 1 K / min, 2 K / min, 4 K / min and 8 K / min. The heat flow in mW is plotted against the temperature. The DSC measurement compares the sample container filled with the insulating material used with a similar empty sample container per standardized sample mass, i.e. the difference in heat flow is shown.

[0049] The integration below the baseline B provides the specific enthalpy for the corresponding reaction. This analysis can be performed using commercially available programs for DSC measuring equipment.

[0050] The progressive enthalpy is in this case a measure of the progress of the reaction in each case with respect to one of the heating rates.

[0051] Figure 4 shows the plotted image in the opposite direction after correcting for the offset. Figure 3 The reaction rates r1, ..., r6 of the insulating material measured in the DSC measurement in 1 / s are again plotted over the temperature. The reaction rates r1, ..., r6 are derived from the enthalpy for the complete reaction (also the complete enthalpy) and the enthalpy currently determined for the corresponding time point or here the temperature point. For example, the complete enthalpy can be found in Figure 3 is defined in such a way that no changes occur here relative to the baseline B.

[0052] The reaction rate r1 was determined here at a heating rate of 0.25 K / min, the reaction rate r2 was determined at 0.5 K / min, the reaction rate r3 was determined at 1 K / min, the reaction rate r4 was determined at 2 K / min, the reaction rate r5 was determined at 4 K / min, and the reaction rate r6 was determined at 8 K / min. The heating rates are merely exemplary here and can be selected depending on the insulating material used.

[0053] Figure 5 The progress of the reaction is shown by integrating the reaction rate, which can be obtained by Figure 4 The integral of the curve of is determined. This results in a reaction progress that is absolutely normalized to 1 with respect to the temperature. In this case, the reaction progress is the degree of hardening. Here, similar to Figure 4, the reaction progress is assigned as follows: reaction progress p1 is determined here at a heating rate of 0.25 K / min, reaction progress p2 is determined at 0.5 K / min, reaction progress p3 is determined at 1 K / min, reaction progress p4 is determined at 2 K / min, reaction progress p5 is determined at 4 K / min, and reaction progress p6 is determined at 8 K / min.

[0054] Figure 6 We now show how to use isoconversion analysis (also known as isoconversion kinetic analysis) to convert Figure 4 and Figure 5 The data shown in are converted into a model and the reaction progression or hardening profile is determined also for temperature changes that are inconsistent with the heating rate.

[0055] In the scale of 1000 / temperature with units of 1000 / K, 1n is first shown for the reaction rate (1 / s) as Figure 4 The reaction rates r1, ..., r6 shown in . However, the actual reaction model is represented by the straight lines s1, ..., sn, wherein a solution based on the Arrhenius equation with variable activation energy is preferably used for modeling here. As a model, it is assumed here that the hardening reaction is only influenced by the temperature profile. UV hardening of the surface is not modeled together, but improves the surface quality of the insulation layer.

[0056] Isoconversion analysis can be performed, for example, according to Friedman or Ozawa-Flynn-Wall. Here, the activation energy values ​​are equalized by differential or integral methods. The differential isoconversion method is based on the Arrhenius equation.

[0057] Straight lines s1, ..., sn interpolate the reaction rate for the degree of hardening and thus the reaction parameters such as the activation energy for the region between the curves r1, ..., r6. It has been shown that very high accuracy can be achieved in determining the hardening course for unmeasured heating rates or temperature changes.

[0058] Figure 7The hardening processes determined for two different insulating materials with the aid of a respective reaction model under the same temperature course TC are shown. In the present case, the first original insulating material (resin) is hardened with the first hardening process C1. It can be seen that, despite the long duration and high temperature, complete hardening does not occur. Another second insulating material can go through the second hardening process C2 under the same temperature course TC and has been completely hardened in the region TCURE (for example in a furnace) approximately halfway through the hardening process. Accordingly, the second insulating material can be hardened significantly faster and with lower energy. It is thus advantageously possible to optimize the temperature course, for example by shortening or using a lower maximum temperature.

[0059] In summary, the invention relates to a method for determining a hardening profile (C1, C2) when applying an electrical insulation layer made of a liquid insulating material (40) to an electrical product, in particular to an electrical winding system (25). In order to improve the hardening of the insulating material, the following steps are proposed:

[0060] - Provide the temperature progression (TC) that the electrical product goes through when applying and curing the insulation layer,

[0061] - providing a reaction model of the insulating material, which outputs a hardening course of the insulating material based on the temperature course as an input variable and is modeled based on a measured reaction enthalpy (h1, . . . , h6) of the insulating material (40) under at least two, preferably at least four different heating rates, and

[0062] - Determining the hardening profile (C1, C2) by means of a reaction model using the temperature profile (TC). The invention also relates to a method for applying an insulating material (40) to an electrical product, preferably to an electrical winding system (25).

[0063] Reference numerals

[0064] 25 Electrical winding system

[0065] 30 Carrier

[0066] 40 Liquid insulating material

[0067] S30 Warm-up

[0068] Temperature change during TPRE preheating

[0069] S40 Application of insulation material

[0070] T40 Temperature change process of electrical products when applying insulating materials

[0071] S50 Hardened

[0072] TCURE Temperature change during hardening

[0073] S60 Curing under UV

[0074] UV UV curing device

[0075] Temperature change process of TUV during UV curing

[0076] Temperature progression of TC during application and hardening

[0077] T0 First temperature

[0078] T1

[0079] DSC1, ..., DSCn DSC signal

[0080] H1, ..., hn specific enthalpy in J / g

[0081] R1, ..., r6 reaction rate

[0082] P1, ..., p6 Hardness

[0083] C1 and C2 hardening process.

Claims

1. A method for determining a hardening profile (C1, C2) when applying an electrical insulation layer made of a liquid insulating material (40) to an electrical product, in particular to an electrical winding system (25), comprising the steps of: - providing the temperature progression (TC) that the electrical product traverses when applying and curing the insulating layer, - providing a reaction model of the insulating material, which outputs a hardening course of the insulating material based on a temperature course as an input variable and is modeled based on a measured reaction enthalpy (h1, . . . , h6) of the insulating material (40) under at least two, preferably at least four different heating rates, and - Determining the hardening course (C1, C2) by means of the reaction model using the temperature course (TC). 2 . The method according to claim 1 , wherein the measured reaction enthalpy is measured by means of dynamic differential calorimetry of the insulating material. 3 . The method according to claim 1 , wherein the heating rate is in the range of 0.1 K / min to 10 K / min, in particular in the range of 0.25 K / min to 8 K / min. 4 . The method according to claim 1 , wherein the reaction model is modeled based on the measured reaction enthalpy under at least four different heating rate conditions. 5 . The method according to claim 1 , wherein, for modeling the reaction model, a reaction rate profile of the hardening is determined based on the reaction enthalpy of the insulating material, and the hardening profile is determined by integrating the reaction rate profile.

6. The method according to any of the preceding claims, wherein the reaction model is modeled based on the Arrhenius equation.

7. The method according to claim 1, wherein the temperature profile (TC) is a measured temperature profile of an electrical product, in particular a temperature profile measured using thermocouples in an electrical winding system.

8. The method according to any of the preceding claims, wherein the temperature profile (TC) is a rated temperature profile of an electrical product.

9. The method according to any of the preceding claims, wherein determining the hardening profile by means of the reaction model comprises determining a gel point.

10. The method according to any of the preceding claims, wherein the insulating material is a resin, preferably a liquid reactive resin, in particular an epoxy resin, an unsaturated polyester or a polyesterimide.

11. A method for applying an electrical insulation layer made of a liquid insulating material (40) to an electrical product, in particular to an electrical winding system (25), comprising the steps of: - providing said electrical product, - providing a liquid insulating material (40), - applying said insulating material (40) to the product, - hardening of the insulating material (40), - providing the temperature progression (TC) that the electrical product traverses when applying and curing the insulating layer, and If the curing profile determined using the method according to any of the preceding claims exceeds a threshold value, curing is terminated.

12. The method of claim 11, wherein the applying is by immersing the electronic product in a bath of liquid insulating material (40).

13. The method according to claim 11, wherein the applying is dripping the electronic product with liquid insulating material (40).

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