Insulation pull rod vacuum pressure dipping forming device and method

Abstract

The invention discloses a vacuum pressure impregnation forming device and method for an insulating pull rod. The device comprises an outer mold module and an inner mold module which are coaxially arranged in a nested mode. A pull rod dipping forming cavity is formed between the inner wall of the outer mold module and the outer wall of the inner mold module; an upper pressing plate is arranged at the top of the forming cavity and provided with a pressure structure used for adjusting the pressure of the upper pressing plate. A plurality of overflow ports which are communicated with the forming cavity and can be controlled to be opened and closed are uniformly distributed in the upper pressing plate; bottom die modules are arranged at the bottoms of the outer die modules and the bottoms of the inner die modules, and a plurality of feeding ports which are communicated with the forming cavity and can be controlled to be opened and closed are evenly formed in the bottom die modules. A grounding module and a high-voltage module are arranged on the two opposite side faces in the forming cavity correspondingly and used for enabling an electric field to be formed in the forming cavity so as to generate the electric field effect on impregnation liquid in the forming cavity. The tensile strength, the shear strength and the fracture toughness of the processed and formed insulating pull rod are greatly improved, and meanwhile, the curing temperature of the epoxy resin is also remarkably reduced.

Description

Technical Field

[0001] The invention relates to an electrical component molding device and method, in particular to an insulating pull rod vacuum pressure impregnation molding device and method. Background Art

[0002] The insulating pull rod is generally prepared by using a vacuum pressure impregnation process to prepare a composite insulating tube, which is then machined and matched with a metal joint.

[0003] Vacuum pressure impregnation (VPI) refers to placing the product to be processed in a closed container (mold) for vacuum treatment, injecting impregnation liquid, and applying a certain pressure to allow the impregnation liquid to enter the processed product, and then solidify and form. VPI technology is currently the best insulation treatment technology. The VPI molding process of insulating pull rods includes: winding the fiber fabric on the mandrel and placing it in the corresponding metal mold, heating and vacuuming the mold after closing it, and removing moisture and air from the mold cavity; degassing the prepared epoxy resin system, injecting the resin through the valve pipe under appropriate vacuum pressure and temperature to fill the mold cavity, and then solidifying and forming it under a certain pressure and temperature; machining the fully cured composite material tube, and bonding the metal joints to make an insulating pull rod.

[0004] In recent years, during the operation of high-voltage GIS, breakdown and flashover failures of insulating rods have occurred frequently, posing great challenges to the safe and stable operation of the power grid. It is urgent to improve the mechanical and electrical properties of insulating rods. The performance reliability of insulating rods mainly depends on the quality of the composite insulating tube. Composite insulating tubes are made by VPI molding process. The common defect of VPI molding process is incomplete impregnation of epoxy resin and reinforcing materials, which is manifested in the appearance of unimpregnated dry spots and micropores on the product body, which seriously affect the electrical performance of the insulating rods and are prone to breakdown and flashover failures.

[0005] The most common method to reduce the number of dry spots and micropores is to chemically modify the fiber surface. Add oxygen-containing functional groups or perform coupling agent treatment, but these methods are relatively complex and difficult to accurately control, and the effect on the fiber fabric from the outside to the inside is uneven (gradually decreasing). Moreover, this solution has a potential risk of chemical pollution and is not conducive to large-scale production. Improving the fluidity of the resin by improving the curing process is also a common technical means. For example, vacuum-assisted resin transfer molding is used to reduce the porosity content in composite materials. However, the processes involved are complex, costly and difficult to control. On the other hand, it may lead to poor interlaminar fracture toughness. In order to compensate for this, nanoparticles are usually added to the resin matrix to enhance interlaminar toughness, but the nanoparticles are dispersed in the matrix and embedded in the interlayers, which hinders the crosslinking of the matrix, reduces the strength of the matrix, and reduces the overall performance of the composite material.

[0006] The long curing time and high temperature of epoxy resin lead to high processing energy consumption, large carbon emissions and low molding efficiency, making molding a high energy consumption and high carbon emission process. There is a strong practical demand to reduce the energy consumption and carbon emissions in the production process of epoxy products.

[0007] Therefore, there is an urgent need to explore alternative technologies with simple, controllable processes, scalable production, no chemical pollution, and low energy consumption to control the defects of the VPI forming process of insulating pull rods and improve process stability. Summary of the invention

[0008] Purpose of the invention: The purpose of the present invention is to provide a vacuum pressure impregnation molding device for insulating pull rods that can improve the mechanical and electrical properties of insulating pull rods;

[0009] The second object of the present invention is to provide a method for impregnating an insulating pull rod to reduce energy consumption, cost and carbon emission while ensuring mechanical and electrical properties.

[0010] Technical solution: The insulating pull rod vacuum pressure impregnation molding device described in the present invention comprises an outer mold module and an inner mold module which are concentrically nested; a pull rod impregnation molding cavity is formed between the inner wall of the outer mold module and the outer wall of the inner mold module; an upper pressure plate is provided on the top of the molding cavity, and the upper pressure plate is provided with a pressure structure for adjusting the pressure of the upper pressure plate; the upper pressure plate is evenly provided with a number of overflow ports which are controllably opened and closable and communicate with the molding cavity; a bottom mold module is provided at the bottom of the outer mold module and the inner mold module, and the bottom mold module is evenly provided with a number of feed ports which are controllably opened and closable and communicate with the molding cavity; a grounding module and a high-voltage module are respectively provided on two opposite sides of the molding cavity, and the grounding module and the high-voltage module are used to form an electric field in the molding cavity, thereby generating an electric field effect on the impregnation liquid in the molding cavity.

[0011] Wherein, the direction of the electric field formed between the high voltage module and the grounding module is perpendicular to the flow direction of the impregnation liquid flowing into the molding cavity.

[0012] Among them, the high-voltage module is arranged in the outer mold module and is located on the side of the molding cavity away from the inner mold module; the grounding module is arranged in the inner mold module and is located on the side of the molding cavity close to the inner mold module.

[0013] Among them, the molding device of the present invention also includes a first insulating structure and a second insulating structure; the outer mold module is provided with a receiving groove that penetrates the wall of the outer mold module and corresponds to the molding cavity; the high-voltage module is accommodated in the receiving groove, and the first insulating structure is arranged between the high-voltage module and the inner wall of the receiving groove to insulate the high-voltage module from the outer mold module; the second insulating structure is arranged in the inner mold module to insulate the surrounding wall of the molding cavity from the inner mold module.

[0014] The method for impregnating an insulating rod by using the above-mentioned insulating rod vacuum pressure impregnation molding device comprises the following steps:

[0015] (A) fixing an insulating core rod on the inner mold module, wrapping a fiber fabric around the outer side of the core rod, and fixing the outer mold module and the inner mold module on the bottom mold module;

[0016] (B) controlling the feeding system to meet the feeding conditions, and delivering the impregnation liquid from the feeding unit through the feeding port into the molding cavity for impregnation;

[0017] (C) Turn on the high voltage module to form an electric field on both sides of the molding cavity;

[0018] (D) After the impregnation is completed, the curing and molding is carried out.

[0019] Wherein, the impregnation solution contains an electrolyte; the structural formula of the electrolyte is:

[0020]

[0021] Among them, R1 and R2 are alkyl groups having 1 to 3 carbon atoms.

[0022] Preferably, the electrolyte is at least one of N,N-dimethylmorpholine tetrafluoroborate, N,N-diethylmorpholine tetrafluoroborate or N-methyl-N-ethylmorpholine tetrafluoroborate; and the concentration of the electrolyte is 1 to 5 mmol / L.

[0023] The electric field strength applied to the high voltage module (40) is 2-5 kV / cm. The voltage source used by the high voltage module is direct current, alternating current, or pulse voltage, or a superposition source formed by any two of the above three voltage sources.

[0024] Wherein, the impregnation liquid is a bisphenol A epoxy system with a viscosity ranging from 200 to 500 mPa·s.

[0025] Principle of the invention:

[0026] Liquid epoxy resin flows in the inter-fiber gaps, so the dynamic evolution of liquid epoxy resin wetting the fiber bundle can be described by the Navier-Stokes equation. Under a uniform external electric field, the molecular dipoles in the epoxy resin form a net macroscopic dipole moment along the direction of the electric field. Therefore, an electric field force f (Maxwell stress) is generated at the gas-liquid resin interface, which serves as the driving force for the flow of liquid resin and can be expressed as:

[0027]

[0028] ρ is the spatial density of free charges in the dielectric liquid, ▽ε is the dielectric gradient, and E is the electric field. The first and second terms on the right side of the equation represent the Coulomb force and the dielectric force, respectively. Since epoxy contains few or no conductive ions, only the dielectric force appears in the epoxy when only the electric field is applied.

[0029] Maxwell stress is not only related to the electric field strength, but also to the electrical properties of epoxy resin. The application of electric field leads to a rapid wetting state transition of epoxy droplets due to the dielectric arrangement of polar epoxy molecules and the migration of dissociated ions. Epoxy resin with electrolyte exhibits significantly higher wetting rate under the applied electric field. In addition, the wetting rate increases with the increase of ion concentration. This enhancement is attributed to the introduction of conductive ions in epoxy resin, which changes the driving force from dielectric force to the sum of dielectric force and Coulomb force under the action of electric field.

[0030] Specifically, when the fiber filler and epoxy resin are well mixed under the drive of an electric field compared to the conventional impregnation process, some additional heat will be released. On the other hand, because the thermal conductivity of the fiber filler is better than that of the epoxy material, heat is easier to transfer, which is beneficial to the curing reaction. These two reasons allow the well-impregnated epoxy material to be cured at a lower temperature. Because of the aforementioned principle, the additional Maxwell stress caused by the addition of the electrolyte further increases the compatibility of the fiber filler and the epoxy resin, optimizing the curing temperature and curing effect. A small amount of electrolyte is dispersed at the molecular level in the epoxy resin without forming obvious agglomerates or particles. At the same time, due to the promotion of the compatibility of the epoxy resin and the glass fiber, the microstructure of the cured resin is more compact and uniform, so it has less effect on the electrical properties of the finished product.

[0031] However, if the electrolyte content is further increased, the viscosity of the liquid resin will gradually increase as the curing temperature decreases, resulting in an increase in surface tension and viscous resistance, which will increase the resistance of the resin to penetrate the gaps between fibers and also reduce the effectiveness of the electric field in driving the resin flow. On the other hand, the formation of a small amount of conductive pathways after curing will also reduce the comprehensive insulation properties and dielectric constant of the material. When a small amount of ionic electrolyte is added to epoxy, the ionic electrolyte may form ion pairs or ion clusters in the epoxy resin. These ions will move in a directional manner under the action of the electric field to form ionic current. The presence of ionic current will increase the conductivity of the material and reduce its insulation properties and dielectric constant.

[0032] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects: (1) The tensile strength, shear strength and fracture toughness of the epoxy resin prepared by the molding device of the present invention under the action of the electric field are greatly improved, and the curing temperature of the impregnating liquid, i.e., bisphenol A epoxy resin, is reduced by about 10°C; (2) The electrolyte of the present invention can significantly improve the effect of the electric field on the impregnating liquid, and the mechanical properties of the insulating rod can be further improved by adding organic macromolecular electrolytes; (3) The high-voltage insulating rod molding method of the present invention simply and effectively overcomes the lack of resin fluidity between fabric fibers, improves the wettability of the resin, and reduces the pore content in the fiber-reinforced composite material; (4) The present invention can significantly reduce the cost of the production process, reduce the curing temperature by 10°C, and reduce the overall carbon emissions by more than 10%, thereby expanding the scope of use of composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic longitudinal section diagram of a molding device according to Example 1 of the present invention;

[0034] Figure 2 It is a schematic cross-sectional view of the molding device of Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The present invention is described in further detail below.

[0036] Example 1

[0037] like Figure 1 , 2 As shown, a vacuum pressure impregnation molding device 100 provided by the first embodiment of the present invention is shown. The vacuum pressure impregnation molding device 100 is used to receive the impregnation liquid and solidify it with the core rod and the wound fiber fabric 201 into an insulating pull rod 1000. The vacuum pressure impregnation molding device 100 includes an outer mold module 10, an inner mold module 20, a bottom mold module 30, a high voltage module 40 and a grounding module 50.

[0038] The bottom mold module 30 is formed with a feed port 301 and a first transmission channel 302 connected to the feed port 301. The feed port 301 is used to connect the injection device ( Figure 1 301 ), to receive the impregnation liquid injected by the injection device. When the injection device injects the impregnation liquid into the feed port 301 , the impregnation liquid will flow into the first transmission channel 302 .

[0039] The outer mold module 10 comprises an outer mold module set 101 and an upper pressing plate 102. The upper pressing plate 102 is located at the top of the outer mold module set 101 and is used to control the length of the insulating pull rod 1000. The outer mold module is formed with an overflow port 103 and a second transmission channel 104 communicating with the overflow port 103.

[0040] The outer mold module 10 and the inner mold module 20 can be fixed to the bottom mold module 30 by means of buckles, screws, etc. The outer mold module 10 is used to cooperate with the inner mold module 20 to form the injection-insulated pull rod 1000.

[0041] The outer mold module 10 and the inner mold module 20 form a molding cavity 60, which is communicated with the second transmission channel 104 and the first transmission channel 302. The molding cavity 60 includes a first side and a second side that are oppositely disposed.

[0042] The high-voltage module 40 is located inside the outer mold module 10, that is, on the first side of the molding cavity 60; the first side of the molding cavity is the side away from the inner mold module 20 in the direction from the inner mold module 20 to the outer mold module 10, the grounding module 50 is arranged in the inner mold module 20, and the second side of the molding cavity is the side close to the inner mold module 20 in the direction from the inner mold module 20 to the outer mold module 10, so that the direction of the electric field formed between the first side and the second side of the molding cavity is perpendicular to the direction of flow of the impregnation liquid flowing into the molding cavity.

[0043] Alternatively, the high-voltage module is located in the inner mold module, on the side close to the inner mold module 20 in the direction from the inner mold module 20 to the outer mold module 10 in the molding cavity, and the grounding module position 50 is arranged in the outer mold module 10, on the side away from the inner mold module 20 in the direction from the inner mold module 20 to the outer mold module 10 in the molding cavity, so that the direction of the electric field formed between the first side and the second side of the molding cavity is perpendicular to the direction of flow of the impregnating liquid flowing into the molding cavity.

[0044] Example 2

[0045] The present invention provides a high-voltage insulating rod forming method, which uses the insulating rod vacuum pressure impregnation forming device of Example 1 to implement impregnation forming of the insulating rod, comprising the following steps:

[0046] (1) Fix the insulating core rod 201 on the inner mold module 20, wrap the fiber fabric 202 around the outer side of the core rod 201, and fix the outer mold module 10 on the bottom module 30;

[0047] (2) Controlling the feeding system to meet the feeding conditions, delivering the impregnation liquid from the feeding unit through the feeding port 301 and the first transmission channel 302 to the molding cavity to perform the impregnation operation;

[0048] (3) Turn on the high voltage module 40 and the grounding module 50 to form an electric field on both sides of the molding cavity 60;

[0049] (4) After the impregnation operation is completed, the curing and molding operation is carried out.

[0050] The electric field strength is 5kV / cm, and the high voltage module is a DC voltage source. The fiber fabric is a glass fiber woven into a three-dimensional structure of a certain size by a three-dimensional mixing method. The impregnation liquid is a bisphenol A epoxy system with a viscosity range of 300mPa·s. The curing temperature is 85℃. The impregnation time is 30min. N,N-dimethylmorpholine tetrafluoroborate is added to the impregnation liquid at a concentration of 5mmol / L.

[0051] The specific steps of Examples 3-11 and Comparative Examples 1-11 are the same as those of Example 1, and the values ​​of the parameters are shown in Table 1. The same operations as in Example 2 were performed except that the electric field intensity, curing temperature, concentration and type of added electrolyte, and immersion time in the molding method were changed to produce the pull rods shown in Table 1.

[0052] Table 1 Tie rod forming process parameters of each embodiment and comparative example

[0053]

[0054] Each embodiment and comparative example embodies a combination of different parameters and methods, including applying an electric field, adding electrolytes, changing the curing temperature, etc. By comparing and analyzing these embodiments and comparative examples, the effects of the electric field and electrolyte on the mechanical properties and curing temperature of the tie rod can be obtained. The details are as follows.

[0055] Test method:

[0056] Porosity: The porosity of the cured product is estimated by grayscale statistics of the SEM image cross section.

[0057] Interlaminar shear strength, the interlaminar shear strength formula is:

[0058]

[0059] Where P b The maximum load observed during the test is also measured by a universal mechanical testing machine. Each test is performed at least 5 times, and the final result is the average of the results obtained in each test. The relevant test results are shown in Table 2.

[0060] Table 2 Effect of molding process on impregnation quality

[0061]

[0062] Comparing the test results of Example 2, Example 8, Comparative Example 9 and Comparative Example 1, after the electric field is applied during the impregnation process, the porosity of the tie rod is significantly reduced, and decreases with the increase of the electric field strength. At the same time, the interlaminar shear strength of the tie rod is significantly improved, and increases with the increase of the electric field strength.

[0063] Comparing the test results of Example 2, Example 9, Comparative Example 9, Comparative Example 1 and Comparative Example 8, after adding the electrolyte, the porosity further decreases with the increase of the electrolyte content, and the interlaminar shear strength increases accordingly.

[0064] By comparing Example 2 and Comparative Example 10, it can be seen that if the electric field strength is too low, the improvement of the tie rod forming quality is not obvious.

[0065] Tensile strength, modulus and flexural strength, modulus:

[0066] According to national standards, a universal mechanical testing machine is used to measure the tensile strength and flexural strength of composite materials. The tensile modulus of composite materials is measured using an extensometer. Each test is performed at least 5 times, and the final result is the average value of the results obtained in each test.

[0067] By comparing Comparative Example 1 and Comparative Example 8, it can be seen that the mechanical strength of the rod is significantly improved before and after the electric field is applied during the immersion process; by comparing the test results of Examples 2, 3, 9 and Comparative Example 8, it can be seen that when the same electric field is applied, the mechanical strength of the rod is significantly improved by increasing the electrolyte concentration.

[0068] Table 3 Effect of molding process on mechanical strength

[0069]

[0070] The influence of molding method on curing temperature:

[0071] By comparing the test results of Examples 2, 4-7 with Comparative Examples 1-5, it can be seen that compared with Comparative Example 1, under the premise of achieving similar mechanical properties, the required curing temperature of the composite material can be reduced by more than 10°C by applying an electric field and adding electrolyte.

[0072] Table 4 Effect of molding process on temperature

[0073]

[0074] Surface flashover voltage:

[0075] The insulation flashover voltage and axial electrical strength of the finished pull rod are tested by a flashover voltage breakdown tester.

[0076] Compare the test results of Examples 2 and 3 with Comparative Examples 1, 6 and 11. After adding the ionic liquid electrolyte, the flashover voltage and axial electrical strength slightly decrease, but when the electrolyte concentration is too high or replaced with an ionic electrolyte, the electrical characteristics decrease significantly.

[0077] Table 5 Effect of molding process on electrical strength

[0078] name Flashover voltage(kV) Axial electrical strength (kV / mm) Comparative Example 1 185 17 Comparative Example 6 155 13 Comparative Example 11 165 13 Example 2 175 15 Example 3 177 16

[0079] In summary, by using the molding device and molding method of the present invention, after applying an electric field during the impregnation process, the porosity of the rod is significantly reduced, and the impregnation quality is significantly improved; when the same electric field is applied, as the electrolyte concentration increases, the impregnation quality increases accordingly. Under the premise of achieving the same mechanical properties, the curing temperature required for the molding of the composite material can be reduced by applying an electric field and adding electrolytes. When the electrolyte concentration is too high or replaced with an ionic electrolyte, the electrical strength of the rod decreases significantly; if no electrolyte is added and the impregnation time is too short, the mechanical strength of the rod decreases significantly.

Claims

1. A vacuum pressure impregnation molding device for insulating pull rods, characterized in that: The invention comprises an outer mold module (10) and an inner mold module (20) which are coaxially nested; a rod impregnation molding cavity (60) is formed between the inner wall of the outer mold module (10) and the outer wall of the inner mold module (20); an upper pressing plate (102) is provided at the top of the molding cavity (60), and the upper pressing plate (102) is provided with a pressure structure for adjusting the pressure of the upper pressing plate (102); the upper pressing plate (102) is evenly distributed with a plurality of overflow ports (103) which are in communication with the molding cavity (60) and can be controlled to open and close; the outer mold module (10) is provided with a plurality of inner mold modules (20) which are coaxially nested; a rod impregnation molding cavity (60) is formed between the inner wall of the outer mold module (10) and the outer wall of the inner mold module (20); an upper pressing plate (102) is provided at the top of the molding cavity (60), and a pressure structure for adjusting the pressure of the upper pressing plate (102) is provided; a plurality of overflow ports (103) which can be controlled to open and close and are in communication with the molding cavity (60) are evenly distributed on the upper pressing plate (102); A bottom mold module (30) is provided at the bottom of the mold module (10) and the inner mold module (20), and the bottom mold module (30) is evenly distributed with a plurality of feed ports (301) that are in communication with the molding cavity (60) and can be controlled to open and close; two opposite sides of the molding cavity (60) are respectively provided with a grounding module (50) and a high-voltage module (40), and the grounding module (50) and the high-voltage module (40) are used to form an electric field in the molding cavity (60) so as to generate an electric field effect on the impregnation liquid in the molding cavity (60).

2. The insulating rod vacuum pressure impregnation molding device according to claim 1, characterized in that: The direction of the electric field formed between the high-voltage module (40) and the grounding module (50) is perpendicular to the flow direction of the impregnation liquid flowing into the molding cavity (60).

3. The insulating rod vacuum pressure impregnation molding device according to claim 1, characterized in that: The high-voltage module (40) is arranged in the outer mold module (10) and is located on a side of the molding cavity (60) away from the inner mold module (20); the grounding module (50) is arranged in the inner mold module (20) and is located on a side of the molding cavity (60) close to the inner mold module (20).

4. The insulating rod vacuum pressure impregnation molding device according to claim 1, characterized in that: The invention also includes a first insulating structure and a second insulating structure; the outer mold module (10) is provided with a receiving groove which penetrates the wall surface of the outer mold module (10) and corresponds to the molding cavity (60); the high-voltage module (40) is received in the receiving groove, and the first insulating structure is arranged between the high-voltage module (40) and the inner wall of the receiving groove to insulate the high-voltage module (40) from the outer mold module (10); the second insulating structure is arranged in the inner mold module (20) to insulate the peripheral wall of the molding cavity (60) from the inner mold module (20).

5. A method for impregnating an insulating rod by using the insulating rod vacuum pressure impregnation molding device according to claim 1, characterized in that: The following steps are involved: (A) fixing an insulating core rod (201) on the inner mold module (20), wrapping a fiber fabric (202) around the outer side of the core rod, and fixing the outer mold module (10) and the inner mold module (20) on the bottom mold module (30); (B) controlling the feeding system to meet the feeding conditions, and delivering the impregnation liquid from the feeding unit through the feeding port (301) into the molding cavity (60) for impregnation; (C) turning on the high voltage module (40) to form an electric field on both sides of the molding cavity (60); (D) After the impregnation is completed, the curing and molding is carried out.

6. The method for impregnating an insulating pull rod according to claim 5, characterized in that: In step (B), the impregnation solution contains an electrolyte.

7. The method for impregnating an insulating pull rod according to claim 6, characterized in that: The structural formula of the electrolyte is: Among them, R1 and R2 are alkyl groups having 1 to 3 carbon atoms.

8. The method for dipping and molding an insulating pull rod according to claim 7, characterized in that: The electrolyte is at least one of N,N-dimethylmorpholine tetrafluoroborate, N,N-diethylmorpholine tetrafluoroborate or N-methyl-N-ethylmorpholine tetrafluoroborate.

9. The method for impregnating an insulating pull rod according to claim 6, characterized in that: The concentration of the electrolyte is 1-5 mmol / L.

10. The method for dipping and molding an insulating pull rod according to claim 5, characterized in that: In step (C), the electric field strength applied to the high voltage module (40) is 2 to 5 kV / cm.

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