EP1023588A1 - Impregnation method and device for monitoring the impregnation of a carrier material - Google Patents

Abstract

According to the inventive impregnation method, a carrier material (1) is impregnated with an impregnating medium (2). The impregnation of the carrier material (1) is determined using the dielectric constants ( epsilon r) of the carrier material (1), preferably by determining a capacitance (C). The invention also relates to a device for monitoring the impregnation of the carrier material (1) with the impregnating medium (2).

Description

description

Impregnation method and device for monitoring the impregnation of a carrier material

The invention relates to an impregnation process in which a carrier material is impregnated with an impregnation medium. The invention also relates to a device for monitoring the impregnation of a carrier material with an impregnation medium.

An impregnation process emerges from the article "Analysis of Mold Filling in RTM Process" by Zhong Cai in Journal of Composite Materials, Vol. 26, 9/1992. A resin transfer molding (RTM) process is described in which fibers are impregnated with a resin to form a composite material. A numerical model is presented, which is based on Darcy's law and describes the watering process.

The object of the invention is to provide an impregnation process. Another object of the invention is to provide a device for monitoring the impregnation of a carrier material.

The object relating to specification of a impregnation method this object is achieved by a soaking process in which a carrier material is impregnated with an impregnating medium so that the dielectric constant of the carrier material än ^¬ changed, one is dependent on the permittivity measured value measured and determines a saturation of the carrier material becomes.

The invention is based on the insight that by a ^¬ of the impregnation medium penetrate into the carrier material the dielectric constant of the carrier material is changed. By determining the dielectric constant, it can be inferred, for example, how far the impregnation medium has impregnated the carrier material. This makes it possible to monitor the impregnation process. The electrical capacitance of an arrangement of electrical conductors in which the carrier material serves as a dielectric is preferably used as the measured variable. This configuration in the form of a capacitor enables simple determination of the dielectric constant by measuring an electrical capacitance. The capacitance can be determined, for example, by applying a DC voltage, or also by determining a capacitive resistance.

A time course of the measured variable is preferably measured and a time course of the impregnation is determined therefrom. This makes it possible to display the time course of the quantities characterizing the impregnation process.

A functional relationship between a reference impregnation and the measured variable is further preferably determined and the impregnation is inferred from the functional relationship. The determination of a reference impregnation as a function of the measured quantity represents one possibility of obtaining a value for the impregnation from the measured quantity.

The time course of the impregnation according to the context is preferred

D (t) = D _R (C (t))

calculated, where D is the impregnation, D _R the reference impregnation, C the measured variable, in particular the capacitance, and t is the time. With the functional relationship of the reference impregnation with the measured variable obtained, the temporal course of the impregnation can be obtained directly from the measured time profile of the measured variable with the aid of the above-mentioned relationship.

The functional relationship is preferably determined in that • a degree of impregnation is defined as the ratio of the impregnated to the impregnated volume of the carrier material;

• for a sequence of degrees of impregnation with given process parameters each degree of impregnation by means of a

A reference impregnation with a spatial distribution in the carrier material of at least one impregnated dry area and at least one soaked wet area is assigned to the simulation using a flow model;

A first dielectric constant is assigned to the at least one dry area and a second dielectric constant is assigned to the at least one wet area;

• a measurement variable is assigned to each reference impregnation with the aid of these dielectric constants, and the functional relationship sought is thus obtained.

The impregnation medium penetrates into the carrier material to form a flow front. Dry areas and / or wet areas can be connected so that they each represent a continuous volume. The flow front can also lead to a complex spatial distribution of dry and wet areas. This results in a complex electrical field due to different dielectric constants of these areas. By means of the above-mentioned procedure, it is now possible to establish a functional connection between an impregnation and the capacity, even with more complicated flow fronts of the impregnation medium in the carrier material. This is done by a simulation based on a flow model, which provides a certain distribution of dry and wet areas for a given percentage impregnation. By assigning a certain dielectric constant to each of these different areas, depending on the spatial distribution of these different areas that arises, a potential distribution in the carrier material can be rial can be calculated. The capacity is then obtained from the formula

Here, the integration takes place over the area T of electrodes of the conductor arrangement that are applied for the capacitance measurement. ε ₀ is the dielectric constant of the vacuum, ε _{r is} the average dielectric constant that results from the dielectric constants of the dry and wet areas, φ is the potential and U is the voltage applied to the electrodes.

The spatial distribution of the reference moisture content is more preferably calculated for a porous carrier material using the Darcy law for a flow of a Newtonian impregnation medium or using a suitable modification of this Darcy law for a flow of a non-Newtonian impregnation medium. The calculation of the spreading of flow fronts can be simulated for porous media with the help of the Darcy law, which is recognized as being a sufficiently good representation of the physical conditions.

A penetration depth of the impregnation medium into the carrier material is preferably obtained from the impregnation. More preferably, a ^" " course of the penetration depth is obtained and at least one of the following sizes of the carrier material is determined therefrom:

• Filtration coefficient • Flow resistance

• permeability

• relative porosity.

In the event that the impregnating medium flows with a straight flow front through a shape with a constant diameter, the following relationships apply: d_ qo (t) E (t) (i) dt

The symbols used are explained in the following table:

For simple geometries of the carrier material, for example a cylinder, there is a simple and uniform flow front. In this case, without calculating a reference impregnation, an impregnation and thus a penetration depth of the impregnation medium can be derived over time from the determination of the measured variable. By determining such a time course of the penetration depth, a material property such as the filtration coefficient or the flow resistance can be obtained. A temporal course of the penetration depth and from this a viscosity of the impregnation medium is more preferably obtained.

A resin, in particular an epoxy resin, is preferably used as the impregnation medium. Impregnations with resins and in particular with epoxy resins play e.g. in the manufacture of

Composite materials and in the impregnation of electrical windings of generators play a major role. The fibers of a fiber composite material to be produced are preferably used as the carrier material.

An electrical insulation material is preferably used as the carrier material. The electrical winding of a stator of a generator, in particular a turbogenerator, is further preferably impregnated, in particular in an all-impregnation process (VPI process, VPI = Vacuum Pressure Impregnation). Turbogenerators are often manufactured today by completely impregnating their stator. The stator is flooded with epoxy resin and impregnated with epoxy resin under pressure and at elevated temperature. After the epoxy resin has hardened, this results in a particularly durable and resistant stator cladding.

From the measured impregnation, it is preferably concluded that there is an impregnation error in the carrier material. Impregnation errors are permanently impregnated areas. The measurement of the impregnation with the aid of the measured variable makes it possible, for example, to give impregnation due to material properties. recognizable. An indication of an impregnation error can be, in particular, that the usual end capacity, that is to say the capacity which is usually established at the end of the impregnation process, is not reached.

According to the invention, the object aimed at specifying a device is achieved by a device for monitoring the impregnation of a carrier material with an impregnating medium, a conductor arrangement being arranged such that the carrier material serves as a dielectric influencing the capacitance of the conductor arrangement and a measuring device for measuring the electrical Capacity is connected to the conductor arrangement.

The advantages of such a device result from the above explanations regarding the advantages of the impregnation process.

The carrier material is preferably an insulation of a conductor rod of the stator of a turbogenerator, the conductor arrangement comprising an electrically conductive band which surrounds the insulation and the electrical conductor of the conductor rod. The impregnation during a complete impregnation process of a stator of a turbogenerator can be checked particularly easily by this configuration. It is only necessary to measure the capacitance between the electrically conductive band and the electrical conductor of the conductor bar. The impregnation can be inferred from this capacitance measurement in accordance with the explanations above regarding the impregnation process.

The invention is explained in more detail with reference to the drawing. Show it:

1 shows a schematic representation of a body to be impregnated; 2 shows a representation of the method steps for calculating the impregnation from the capacitance and

3 shows a section of a conductor bar of the stator of a turbogenerator.

The same reference symbols have the same meaning in the different figures.

A longitudinal section through a rectangular body 1A made of a carrier material 1 is shown schematically in FIG. An electrical conductor arrangement 3 is arranged on the narrow sides IB, IC of the body 11. It comprises a first conductor 3B on the narrow side IB and a second conductor 3C on the narrow side IC. The conductors 3B and 3C are connected to a measuring device 9 such that the capacitance of the conductor arrangement 3 can be determined via the measuring device 9. The carrier material 1 is impregnated with an impregnating medium 2 from the narrow side IB. The impregnation medium 2 penetrates the carrier material 1 over time from the narrow side IB to the narrow side IC. A flow front 2A is formed. The flow front 2A divides the carrier material 1 into a wet area 4 and a dry area 5. The wet area 4 has the dielectric constant ε _F. The drying area 5 has the dielectric constant ε _τ . The flow front 2A defines an average penetration depth E (t) of the impregnation medium 2 into the carrier material 1 at a specific time t.

How the impregnation of the carrier material 1 is obtained from a capacitance measurement is explained in the following in FIG. 2. FIG. 2 shows three process steps VI, V2, V3. In method step VI, a functional relationship D (C) between a reference impregnation D _R and the capacitance C is calculated. Process parameters are used for this, for example: The pressure P under which the impregnating medium 2 is pressed into the carrier material 1, the prevailing temperature T, the viscosity V of the impregnating medium 2 and the filtration coefficient FK or the flow resistance FW of the carrier material 1, which leads to a permeability S of the carrier material 1. For a porous carrier material 1, the Darcy equation is used to determine which spatial distribution of soaked wet areas 4 and non-soaked dry areas 5 is to be expected for a given degree of soaking. In a one-dimensional form, the Darcy equation is written as:

S δp q = -

V δx

where q is the flow rate of the impregnation medium 2, S is the permeability of the carrier material 1, V is the viscosity of the impregnation medium 2 and δp / δx the pressure gradient. From the spatial distribution of wet areas 4 and dry areas 5 thus simulated, the capacitance C can be obtained by assigning the wet areas 4 a dielectric constant ε _F and the dry areas 5 a dielectric constant ε _τ . The desired functional relationship D _R (C) between reference impregnation D _R and capacitance C is thus established.

In a second method step V2, the capacitance C - is measured with the aid of the measuring device 9 according to FIG. 1 as a function of the time t. The results of process steps VI and V2 are summarized in a process step V3 in which the moisture content D is determined as a function of the time t from the formula D (t) = D _R (C (t)).

Depending on the desired measurement accuracy, the shape of the flow fronts and thus the precise spatial distribution of wet areas 4 and dry areas 5 can be negligible. In this case, a simulation with a flow model, such as with the Darcy equation, is not necessary. From the capacity tat can then be directly deduced from a percentage of wet areas 4 and dry areas 5, that is, the moisture content D.

FIG. 3 shows a section of a conductor bar 12 of a stator (not shown) of a turbogenerator. The conductor bar 12 consists of an electrical conductor 10, preferably of copper. It is surrounded by insulation 1, which in this case is the carrier material 1. The insulation 1 is surrounded by an externally wound, not shown, glow protection tape. A conductive tape 11 is wound over the glow protection tape. The conductive band 11 and the conductor 10 are connected to a measuring device 9 for measuring the capacitance C. Such a conductor bar 12 is inserted into grooves in a laminated core (not shown) and connected to other, correspondingly arranged conductor bars 12 to form an electrical winding. This entire arrangement forms the stator of a turbogenerator. It is impregnated with an epoxy resin in a full impregnation process. For this purpose, the entire stator is placed in a pressure vessel. The epoxy resin, which forms the impregnation medium 2, is then introduced into the carrier material 1, that is to say the insulation 1, at elevated temperature and high pressure. A perfect and practically complete impregnation is essential for the operational safety and the service life of the generator. The impregnation of the insulation 1 can be monitored by measuring the capacitance C with the aid of the measuring device 9. For example, Impregnation errors, i.e. impregnated areas, can be determined at the end of the impregnation process by not reaching an end capacity normally reached.

In addition to the application for monitoring the impregnation process in full impregnation processes of a stator, the invention can also be used advantageously in other areas. In particular, the production of fiber composite materials often requires impregnation with a resin. Here provides surveillance of the impregnation process in terms of quality assurance great advantages.

Claims

claims 1. Impregnation method, in which a carrier material (1) is impregnated with an impregnating medium (2), so that the dielectric constant (ε _r ) of the carrier material (1) changes, a measurement variable dependent on the dielectric constant (ε _r ) ( C) is measured and an impregnation (D) of the carrier material (1) is determined therefrom. 2. Impregnation method according to claim 1, in which the electrical capacitance (C) of an arrangement of electrical conductors (3) is used as the measured variable (C), in which the carrier material (1) serves as a dielectric. 3. Impregnation method according to claim 1 or 2, in which a time profile (C (t)) of the measured variable (C) is measured and a time profile (D (t)) of the impregnation is determined therefrom. 4. Impregnation process according to one of the preceding claims, in which a functional relationship (D _R (C)) between a Reference impregnation (D _R ) and the measured variable (C) determined and from the functional relationship (D _R (C)) to the Soak is closed. 5. impregnation method according to claim 3 and 4, wherein the temporal profile (D (t)) of the impregnation (D) according to the context D (t) = D _R (C (t)) is calculated, where D the impregnation, D _R the reference impregnation, C is the measured variable, in particular a capacitance, and t is the time. 6. impregnation method according to claim 4 or 5, in which the functional relationship (D _R (C)) is determined in that • a degree of impregnation is defined as the ratio of impregnated to impregnated volume of the carrier material (1); • for a sequence of degrees of impregnation with given method parameters, each degree of impregnation is assigned a reference impregnation (D _R ) with a spatial distribution in the carrier material (1) of at least one impregnated dry area (4) and at least one soaked wet area (5) by means of a simulation using a flow model ; • the at least one dry area (4) is assigned a first dielectric constant (ε _r ) and the at least one wet area (5) is assigned a second dielectric constant (ε _F ); • each reference impregnation (D _R) with the aid of these dielectric constants (ε _r, ε _F) thus the sought functional connection (D _R (0 is obtained), a process variable (C) and assigned. 7. Impregnation method according to claim 6, in which for a porous carrier material (1) the spatial distribution of the reference impregnation (D _R ) using the Darcy law for a flow of a Newtonian impregnation medium or using a suitable modification of this Darcy law for a flow of a non-Newtonian impregnation medium is calculated. 8. Impregnation method according to one of claims 1 to 3, in which a penetration depth (E) of the impregnation medium (2) into the carrier material (1) is obtained from the impregnation (D). 9. Impregnation method according to claim 8, in which a time profile (E (t)) of the penetration depth (E) is obtained and at least one of the following sizes of the carrier material (1) is determined therefrom: • Filtration coefficient (FK); • flow resistance (FW); • permeability; • relative porosity; 10. Impregnation method according to claim 8, in which a time course (E (t)) of the penetration depth (E) and therefrom a viscosity (V) of the impregnation medium (2) is obtained. 11. Impregnation process according to one of the preceding claims, in which a resin, in particular an epoxy resin (2), is used as the impregnation medium (2). 12. Impregnation method according to one of the preceding claims, in which fibers (6) are used as carrier material (1), which are impregnated for a fiber composite material (7) to be produced. 13. Impregnation method according to one of the preceding claims, in which an electrical insulation material (1) is used as the carrier material (1). 14. Impregnation method according to claim 13, in which the electrical winding (7) of a stator (8) of a generator, in particular a turbogenerator, is impregnated, in particular in a full impregnation method. 15. Impregnation method according to one of the preceding claims, in which from the impregnation (D) to the presence of a Impregnation in the carrier material (1) is closed. 16. Device for monitoring the impregnation (D) of a carrier material (1) with an impregnation medium (2), a conductor arrangement (3) being arranged such that the carrier material (1) serves as a dielectric influencing the capacitance of the conductor arrangement (3) and where a measuring device device (9) for measuring the electrical capacitance (C) with the conductor arrangement (3) is connected. 17. The apparatus of claim 16, wherein the carrier material (1) is an insulation of a conductor rod (12) of the stator of a turbogenerator, the conductor arrangement (3) an electrically conductive tape (11) which surrounds the carrier material (1), and the electrical conductor (10) of the conductor bar (12) comprises.