Determining a curing profile of an electrical insulation layer
Patent Information
- Application Number
- EP2023739136
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-07-06
- Filing Date
- 2023-06-27
- Publication Date
- 2025-03-19
AI Technical Summary
The existing methods for determining the curing process of electrical insulation layers, particularly in electrical cooling systems, are costly due to high investment, energy consumption, and space requirements, with inefficiencies in material usage and curing temperature/time.
A method involving a temperature profile and a reaction model based on measured reaction enthalpies at various heating rates to determine the curing process, allowing for interpolation of curing progress across different temperature gradients, and using dynamic differential calorimetry to parameterize the model for efficient insulation hardening.
This approach optimizes the curing process by reducing energy costs, improving material efficiency, and enabling real-time monitoring, allowing for precise control of the curing process and enhanced adhesion of the insulation layer.
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Determining the curing process of an electrical insulation layer
[0003] The invention relates to a method for determining a curing process, applying an electrical insulation layer made of an insulation material in the liquid state and a method for applying the insulation material to an electrical product, preferably to an electrical curing system.
[0004] Such a process is used, for example, in the impregnation of rotors and stators of electric motors. The impregnation process, which often involves immersion impregnation followed by hot-air oven curing, is a major cost factor in manufacturing in terms of investment costs, maintenance, cycle times, production space requirements, etc. The optimization potential here lies in material consumption, curing temperature / time (energy costs, CO2), and automation.
[0005] The invention is based on the object of improving the curing of the insulation material.
[0006] This object is achieved by a method having the features specified in claim 1. The method for determining a curing process when applying an electrical insulation layer made of an insulation material in the liquid state to an electrical product, in particular to an electrical winding system, comprises the steps:
[0007] - Providing a temperature profile through which the electrical product passes during the application and curing of the insulation layer,
[0008] - Providing a reaction model of the insulation material which outputs the curing process of the insulation material on the basis of a temperature profile as an input variable and is modelled on the basis of measured reaction enthalpies of the insulation material for at least two, preferably at least four different heating rates and
[0009] - Determine the curing process using the reaction model with the temperature curve.
[0010] In addition to windings in electric motors, i.e. stators or rotors, the electrical winding system can also include coils for other applications, e.g. magnetic field coils in magnetic resonance imaging or RF coils.
[0011] The curing curve can be a curve normalized to 1 with respect to the total enthalpy of curing of the respective insulation material and is plotted over time. The heating rates are temperature gradients used in the measurements. As a special case, heating rates of 0 K / min, i.e., isotherms, can also be used.
[0012] The reaction model interpolates the enthalpies or reaction rates for temperature gradients that differ from the heating rates used in the measurements. This allows the reaction model to output a curing progress for all temperature gradients occurring during application and curing. A temperature gradient can therefore be determined for each period, allowing the reaction model to output a curing progress.
[0013] In a further embodiment, the measured reaction enthalpies are determined using dynamic differential calorimetry of the insulation material. This advantageously means that only a few samples of the insulation material need to be measured in order to parameterize the model. The DSC signals measured in this way can be integrated to determine the reaction enthalpy at the respective heating rate. Based on a complete reaction enthalpy, which occurs when the insulation material is completely cross-linked, a reaction profile for the insulation material can then be specified. In other words, complete cross-linking is the highest possible degree of cross-linking due to the potentially available free reaction partners, taking into account steric hindrance (i.e. free monomers due to insufficient diffusion potential and too great a distance to potential reaction partners).
[0014] In a further embodiment, the heating rates are in the range from 0.1 K / min to 10 K / min. In particular, heating rates in the range from 0.25 K / min to 8 K / min have been found to be advantageous, as this ensures coverage of the temperature increases typically occurring during curing.
[0015] In a further embodiment, the reaction model is based on measured reaction enthalpies at at least four different heating rates. To improve the interpolation of reaction enthalpies for temperature gradients that differ from the measured heating rates, it has proven advantageous to perform measurements (e.g., DSC measurements) of the insulation material at at least four different heating rates.
[0016] In a further embodiment, reaction rate curves of the curing process are determined based on the reaction enthalpies of the insulation material to model the reaction model. The reaction rate curves can be determined, for example, by normalizing the DSC signal to the complete enthalpy of the curing reaction. Furthermore, the curing curves are determined by integrating the reaction rate curves.
[0017] In a further embodiment, the reaction model is based on the Arrhenius equation. It is particularly advantageous if the activation energy E Ain the Arrhenius equation, a value that varies throughout the curing process and not a constant is used. In a further embodiment, the temperature profile is a measured temperature profile of an electrical product, in particular a temperature profile measured with a thermocouple in an electrical winding system. In this way, a temperature profile can be provided simply and efficiently. The thermocouple can often remain in the winding system after the insulation material has been applied. The curing process could even be calculated in real time. It is often sufficient if the curing process is determined once for the respective insulation material and the electrical product if many similar products are manufactured.
[0018] In another embodiment, the temperature profile is a target temperature profile of an electrical product. The target temperature profile can be a temperature profile that is specified and maintained within the system. This allows verification of whether the temperature profile reliably leads to sufficient curing of the insulation material.
[0019] In a further embodiment, determining the curing process using the reaction model includes determining a gel point. The gel point can be applied to the curing process and determined, for example, by rheological measurements. The gel point or gelling point is characterized by a defined increase in viscosity and can be determined at the intersection of the storage and loss moduli in the rheological measurements. The advantage of taking the gel point into account is that the insulation material adheres better to the electrical product and no longer flows off. Subsequent steps (e.g. removal from the bath) can therefore be timed more precisely. It is also possible to define a viscosity threshold that is different from the gel point and that must be exceeded if the next process step is to be carried out.In a further embodiment, the insulation material is a resin, preferably a liquid reactive resin, in particular epoxy resin, unsaturated polyester or polyesterimide.
[0020] Curing processes of multi-component resins (e.g. amine-curing epoxy resins, polyurethanes with isocyanate) that are mixed immediately before application to the electrical product can also be determined using the reaction model.
[0021] The object is further achieved by a method for applying an electrical insulation layer made of an insulation material in the liquid state to an electrical product, in particular to an electrical winding system, comprising the steps:
[0022] - Providing the electrical product,
[0023] - Providing the insulation material in liquid state,
[0024] - Applying the insulation material to the product,
[0025] - Curing of the insulation material,
[0026] - Providing a temperature profile through which the electrical product passes during the application and curing of the insulation layer and
[0027] - Terminating the curing if a curing process determined using a method according to one of the preceding claims exceeds a threshold value.
[0028] Measuring the temperature curve using a thermocouple positioned in or on the electrical product can be carried out, but is usually not necessary for every product.
[0029] Curing can be carried out by supplying external heating energy.
[0030] The threshold value of the curing process, i.e., the degree of curing at which curing can be terminated, can be, for example, 80%. Completion of curing is defined as the termination of active curing with the addition of external heating energy. The insulation material can then, for example, fully cure under the influence of the residual heat in the product; it is not necessary to remain in the system for this.
[0031] In a further embodiment, the application involves immersing the electronic product in a bath of the insulating material in the liquid state. In the bath, the electrical product itself can be heated, e.g., by applying current to the winding system.
[0032] In another embodiment, the application involves dripping the insulating material in liquid form onto the electronic product. In this case, it may be useful to consider the temperature profile only after a certain amount of insulating material has been applied by dripping.
[0033] The invention is described and explained in more detail below with reference to the exemplary embodiments shown in the figures. They show:
[0034] FIG 1 schematically shows a method for applying an insulating material to an electrical winding system,
[0035] FIG 2 shows an example of a temperature curve during application and curing,
[0036] FIG 3 DSC measurements of an insulation material at different heating rates,
[0037] FIG 4 reaction rates determined from the DSC measurements of the insulation material measured in FIG 3,
[0038] FIG 5 reaction progress integrated from the reaction rates,
[0039] FIG 6 a schematic representation of the reaction model for the insulation material and
[0040] FIG. 7 shows a curing process determined using a reaction model for two different insulation materials. FIG. 1 schematically shows a method for applying an insulation material 40 in the liquid state to an electrical winding system 25, which is designed here as stator windings of an electric motor. The stator or winding system 25 is arranged on a carrier 30 for transport through a production line.
[0041] A step S30 schematically shows a preheating of the winding system 25 outside the insulation material with a temperature profile TPRE or to a temperature TPRE.
[0042] A step S40 shows immersion of the winding system in a bath filled with liquid insulation material 40. During immersion, the electrical winding system 25 can be further energized and heated.
[0043] A step S50 shows a curing of the insulation material 40 under the influence of a temperature profile TCURE. This can be provided by an oven in addition to or as an alternative to energizing the winding system 25.
[0044] In step S60, UV curing is performed using UV radiation. This has the advantage that the insulation material hardens well on the surface and is no longer sticky. UV curing is optional.
[0045] FIG. 2 shows an example of a temperature profile TC during the application and curing of an insulating material, for example as shown in FIG. 1, which the insulating material experiences approximately on the electrical product, e.g. on the winding system 25.
[0046] A first temperature TO results from the temperature of the product when the liquid insulation material is applied and the temperature of the insulation material during application. When immersed in the liquid insulation material 40, the temperature T0 is established, for example. Heating up to the second temperature TI can be caused by thermal inertia of the electrical winding system, or by additional heating of the winding system. The temperature curve T40 describes the curve that the resin experiences directly on the product during application. Another area shows the temperature curve TCURE during curing, e.g. in an oven. A final area TUV shows a temperature curve during UV irradiation, which primarily ensures high surface curing, while the product is still heated to the final temperature T2. After that, cooling occurs and the insulation material continues to cure.
[0047] With the invention, it is now possible to determine a curing curve for such a temperature profile TC, even if it has different gradients that do not correspond to the heating rates.
[0048] FIG 3 shows DSC (differential scanning calorimetry) measurements of an insulation material at different heating rates, in this case at 0.25 K / min, 0.5 K / min, 1 K / min, 2 K / min, 4 K / min, and 8 K / min. Here, a heat flow in mW is plotted against the temperature. The DSC measurement compares the heat flow per standardized sample mass in a sample vessel filled with the insulation material used with a similar empty sample vessel, i.e., a difference in heat flow is shown.
[0049] Integration below a baseline B provides a specific enthalpy for the respective reactions. Such analyses can be performed using commercially available DSC software.
[0050] The advancing enthalpy is a measure of the progress of the reaction, each related to one of the heating rates.
[0051] FIG. 4 shows the reaction rates rl,...,r6 determined from the DSC measurements in 1 / s after correction for offset and plotted in the opposite direction for the insulation material measured in FIG. 3, again plotted against temperature. The reaction rates rl,...,r6 result from the enthalpy for the complete reaction (also called the complete enthalpy) and the currently determined enthalpy for the respective time or, in this case, temperature point. The complete enthalpy can, for example, be set in FIG. 3 such that no further change occurs with respect to the baseline B.
[0052] Reaction rate rl was determined at a heating rate of 0.25 K / min, reaction rate r2 at 0.5 K / min, reaction rate r3 at 1 K / min, reaction rate r4 at 2 K / min, reaction rate r5 at 4 K / min, and reaction rate r6 at 8 K / min. The heating rates are only examples and can be selected according to the insulation material used.
[0053] FIG. 5 shows reaction progress integrated from the reaction rates, which can be determined by integrating the curves from FIG. 4. This results in an absolute reaction progress over temperature normalized to 1. In this case, the reaction progress is the degree of curing. The reaction progresses are assigned analogously to FIG. 4 as follows: Reaction progress p1 was determined at a heating rate of 0.25 K / min, reaction progress p2 at 0.5 K / min, reaction progress p3 at 1 K / min, reaction progress p4 at 2 K / min, reaction progress p5 at 4 K / min, and reaction progress p6 at 8 K / min.
[0054] FIG 6 now shows how the data shown in FIG 4 and 5 are converted into a model by an isoconversion analysis (also isoconversional kinetic analysis) and how the reaction progress or the curing process is determined even for temperature changes that do not correspond to the heating rates.
[0055] The reaction rates rl,...,r6 are shown on a scale of 1000 / temperature in 1000 / K over the reaction rate (1 / s), as shown in Fig. 4. The actual reaction model, however, is represented by the straight lines sl,...,sn. For modeling, an approach based on the Arrhenius equation with variable activation energy is preferably used. The model assumption here is that the curing reaction is influenced only by the temperature profile. UV curing of the surface is not modeled, but improves the surface quality of the insulation layer.
[0056] Isoconversion analysis can be performed, for example, according to Friedman or Ozawa-Flynn-Wall. The activation energy values are adjusted using differential or integrating methods. The differential isoconversion methods are based on the Arrhenius equation.
[0057] The straight lines sl,...,sn interpolate the reaction rates for each degree of curing, and thus the reaction parameters such as the activation energy, for the ranges between the curves rl,...,r6. It has been shown that this allows for very high accuracy in determining the curing process for heating rates or temperature changes that were not measured.
[0058] FIG 7 shows a curing curve determined using a reaction model for two different insulation materials at the same temperature curve TC. In the present case, a first, original insulation material (a resin) was cured using a first curing curve Gl. It can be seen that, despite a long duration and high temperature, complete curing does not occur. A different, second insulation material can undergo a second curing curve C2 at the same temperature curve TC and is already completely cured approximately halfway through the curing process in the TCURE range (e.g., in an oven). Accordingly, the second insulation material can be cured much faster and more energy-efficiently. An optimization of the temperature curve - e.g., shortening it or using a lower maximum temperature - would thus be advantageously possible.In summary, the invention relates to a method for determining a curing process (C1, C2) during the application of an electrical insulation layer made of an insulating material (40) in the liquid state to an electrical product, in particular to an electrical winding system (25). To improve the curing of the insulating material, the following steps are proposed:
[0059] - Providing a temperature profile (TC) through which the electrical product passes during the application and curing of the insulation layer,
[0060] - providing a reaction model of the insulation material, which outputs the curing process of the insulation material on the basis of a temperature profile as an input variable and is modeled on the basis of measured reaction enthalpies (hl,...,h6) of the insulation material (40) at at least two, preferably at least four, different heating rates, and
[0061] - Determining the curing process (C1, C2) using the reaction model with the temperature profile (TC). Furthermore, the invention relates to a method for applying the insulating material (40) to an electrical product, preferably to an electrical winding system (25).
[0062] Reference symbol
[0063] 25 electrical winding system
[0064] 30 carriers
[0065] 40 Insulation material in liquid state
[0066] S30 Preheat
[0067] TPRE temperature curve of preheating
[0068] S40 Application of the insulation material
[0069] T40 Temperature profile of the electrical product when applying the insulation material
[0070] S50 Curing
[0071] TCURE Curing temperature curve
[0072] S60 UV curing
[0073] UV UV curing device
[0074] TUV temperature curve during UV curing
[0075] TC temperature curve during application and curing
[0076] TO first temperature
[0077] TI
[0078] DSC1, DSCn DSC signal hl,...,hn specific enthalpy in J / g rl,...,r6 reaction rate pl,...,p6 degree of curing
[0079] Cl, C2 curing process
Claims
Patent claims 1. A method for determining a curing process (C1, C2) when applying an electrical insulation layer made of an insulation material (40) in the liquid state to an electrical product, in particular to an electrical winding system (25), comprising the steps: - Providing a temperature profile (TC) through which the electrical product passes during the application and curing of the insulation layer, - providing a reaction model of the insulation material, which outputs the curing process of the insulation material on the basis of a temperature profile as an input variable and is modeled on the basis of measured reaction enthalpies (hl,...,h6) of the insulation material (40) at at least two, preferably at least four, different heating rates, and - Determination of the curing process (C1,C2) using the reaction model with the temperature curve (TC).
2. The method according to claim 1, wherein the measured reaction enthalpies are measured by means of dynamic differential calorimetry of the insulation material.
3. The method according to claim 1 or 2, wherein the heating rates are in the range from 0.1 K / min to 10 K / min, in particular in the range from 0.25 K / min to 8 K / min.
4. Method according to one of the preceding claims, wherein the reaction model is modeled on the basis of measured reaction enthalpies at at least four different heating rates.
5. Method according to one of the preceding claims, wherein, for modelling the reaction model, reaction rate curves of the curing are determined on the basis of reaction enthalpies of the insulation material and curing curves are determined by integrating the reaction rate curves.
6. Method according to one of the preceding claims, wherein the reaction model is based on the Arrhenius equation.
7. Method according to one of the preceding claims, wherein the temperature profile (TC) is a measured temperature profile of an electrical product, in particular a temperature profile measured with a thermocouple in an electrical winding system.
8. Method according to one of the preceding claims, wherein the temperature profile (TC) is a target temperature profile of an electrical product.
9. Method according to one of the preceding claims, wherein determining the curing process by the reaction model comprises determining a gel point.
10. Method according to one of the preceding claims, wherein the insulating material is a resin, preferably a liquid reactive resin, in particular epoxy resin, unsaturated polyester or polyesterimide.
11. A method for applying an electrical insulation layer made of an insulation material (40) in the liquid state to an electrical product, in particular to an electrical winding system (25), comprising the steps: - Providing the electrical product, - Providing the insulation material (40) in the liquid state, - applying the insulation material (40) to the product, - Curing of the insulation material (40) , - Providing a temperature profile (TC) through which the electrical product passes during the application and curing of the insulation layer and - Terminating the curing when a curing time determined by a method according to one of the preceding claims course exceeds a threshold.
12. The method of claim 11, wherein the application comprises immersing the electronic product in a bath of the insulating material (40) in the liquid state.
13. The method according to claim 11, wherein the application is a dripping of the insulating material (40) in the liquid state onto the electronic product.