Dielectrophoresis-based controllable gradient material preparation device and method

Abstract

The application discloses a controllable gradient material preparation device and method based on dielectrophoresis. A vacuumizing device is communicated with the inner cavity of an oven, and an experimental platform is arranged in the inner cavity of the oven. The experimental platform comprises a bottom plate mold and a pressurizing layer mold. The pressurizing layer mold has a pouring cavity, and the bottom plate mold is arranged at the bottom of the pressurizing layer mold and blocks the bottom of the pouring cavity. Two pairs of electrodes for simulating the electric field environment of the dielectric functional gradient material under actual working conditions are arranged in the pouring cavity of the pressurizing layer mold in a height direction. The outlet of a solution supply generator is arranged above the pouring cavity of the pressurizing layer mold, the solution supply generator is used for pouring a composite solution into the pouring cavity of the pressurizing layer mold, and a controllable voltage source is connected with all the electrodes. The application can improve the dielectric constant distribution of the material, adapt to complex electric fields in multi-dimensional space, reduce internal defects of the polymer material and improve the dielectric and electrical properties of the insulating material.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of dielectric and electrical insulation research, and particularly relates to a controllable gradient material preparation device and method based on dielectrophoresis. BACKGROUND

[0002] With the rapid development of extra-high voltage and large-capacity power transmission technology, higher requirements are put forward for the insulation of devices and equipment of power systems. In order to effectively regulate the electric field distribution in the actual operation of power equipment, dielectric functional gradient materials, as a new type of insulation material with spatial non-uniform dielectric parameter distribution, can significantly improve the electric strength of insulation devices by adjusting the spatial distribution of dielectric constant or electrical conductivity of the material.

[0003] Dielectrophoresis effect refers to the polarization of medium particles under the action of non-uniform electric field, causing the movement of the particles. It is found that the medium particles can be electrically neutral, and the swimming behavior of the particles is strongly related to the size, geometric shape, dielectric properties of the particles, and factors such as frequency, voltage polarity, and strength gradient of the external electric field. At the same time, it is also affected by the physical and chemical properties of the base solution (dielectric constant, electrical conductivity, density, fluid dynamic viscosity, etc.) and the environmental temperature. Therefore, by adjusting the influencing factors of the dielectrophoretic force experienced by the solution outside and inside, the volume fraction of the material components can be continuously changed in a specified direction by using the dielectrophoresis effect.

[0004] At present, the dielectrophoresis control technology can realize the aggregation and ordered arrangement of particles in the material, but the existing device focuses on realizing the single change of particle distribution in the material along a single electric field direction (such as radial direction).

[0005] For the strong electric field environment of power electronic devices (such as IGBT, MOSFET), the electric field application direction is not unique (such as three-phase pulse rectifier circuit), and the insulation ability of the silicon gel filled outside the high-voltage chip is difficult to adapt to the complex and changeable electric field environment; for DC GIL, in the insulation application of power equipment, the electric field change form is not unique, such as the phenomenon of high surface electric field of high-voltage inserts and low-voltage inserts in the support insulator. The existing device cannot use dielectrophoresis control technology to prepare gradient insulation materials that meet the above application scenarios.

[0006] On the other hand, as the main insulation material of power equipment operation, polymer materials usually have defects such as incomplete vacuum extraction, mixing of dust and impurities during the experiment, and the existence of flaws in the sample. In addition, due to the small size of defects and bubbles, it is difficult to eliminate them. SUMMARY

[0007] In order to solve the problems in the prior art, the present application aims to provide a dielectrophoresis-based controllable gradient material preparation device and method, which can prepare dielectric functional gradient polymer composites and self-adaptive dielectric composites, improve the dielectric constant distribution of the material, adapt to complex electric fields in multi-dimensional space, and reduce internal defects of the polymer material and improve the dielectric and electrical properties of the insulating material.

[0008] The technical scheme adopted by the present application is as follows:

[0009] A dielectrophoresis-based controllable gradient material preparation device, comprising an oven, an experimental platform, a solution supply generator, a vacuumizing device and a controllable voltage source.

[0010] The vacuumizing device is in communication with the inner cavity of the oven, and the experimental platform is arranged in the inner cavity of the oven.

[0011] The experimental platform comprises a bottom plate mold and a pressurized layer mold, the pressurized layer mold has a pouring cavity, and the bottom plate mold is arranged at the bottom of the pressurized layer mold and blocks the bottom of the pouring cavity; two or more pairs of electrodes for simulating the electric field environment in which the dielectric functional gradient material is located under actual working conditions are arranged in the pouring cavity of the pressurized layer mold along the height direction.

[0012] The outlet of the solution supply generator is arranged above the pouring cavity of the pressurized layer mold, the solution supply generator is used for pouring a composite solution into the pouring cavity of the pressurized layer mold, and the controllable voltage source is connected with all the electrodes.

[0013] Preferably, the experimental platform further comprises a top plate mold arranged at the top of the pressurized layer mold, and the top plate mold is provided with a pouring port in communication with the pouring cavity.

[0014] Preferably, the shape of the electrode head comprises a spherical shape and / or a broad bean shape.

[0015] Preferably, the electrode comprises a metal ball head and a ball rod, the metal ball head is mounted at one end of the ball rod, the ball rod is in a cylindrical shape, the metal ball head serves as the head of the electrode, the pressurized layer mold is provided with an electrode insertion hole, the other end of the ball rod abuts against the port of the electrode insertion hole, the diameter of the ball rod is greater than that of the port of the electrode insertion hole, and an electrode connecting plug is connected in the electrode insertion hole.

[0016] The ball rod is made of a conductor, the junction between the metal ball head and the ball rod is smoothly transitioned, a threaded hole is formed at the end of the ball rod abutting against the port of the electrode insertion hole, the electrode connecting plug is threadedly connected with the threaded hole of the ball rod, and the port of the electrode insertion hole is blocked by the end of the ball rod.

[0017] Preferably, a vacuum ceramic electrode is mounted on the oven, the electrode connecting plug and the vacuum ceramic electrode are connected through a wire, and the vacuum ceramic electrode is connected with the controllable voltage source through the wire.

[0018] Preferably, the two electrodes in each pair of electrodes are symmetrically arranged on the pressurized layer mold.

[0019] Preferably, the solution supply generator is arranged outside the oven, and the solution supply generator comprises a liquid storage bottle, an oil bath heating pot and a stirrer, the liquid storage bottle is arranged in the oil bath heating pot, the stirring part of the stirrer is arranged in the liquid storage bottle, a liquid injection pipe is connected to the outlet of the liquid storage bottle, the outlet of the liquid injection pipe serves as the outlet of the entire solution supply generator, and a valve is arranged on the outlet of the liquid storage bottle.

[0020] Preferably, the pressurized layer mold adopts a laminated structure, and comprises at least two pressurized layer mold units stacked together, and at least one pair of electrodes is arranged on each pressurized layer mold unit.

[0021] The application also provides a preparation method of the dielectrophoretic controllable gradient material, which is prepared by using the preparation device of the dielectrophoretic controllable gradient material as described above, and comprises the following steps:

[0022] S1, adjusting the oven to the pouring temperature of the corresponding composite solution of the dielectric functional gradient material;

[0023] S2, pouring the composite solution into the pouring cavity of the pressurized layer mold by using the solution supply generator until the pouring cavity of the pressurized layer mold is filled with the composite solution;

[0024] S3, performing vacuum degassing treatment on the composite solution poured into the pressurized layer mold by using the vacuumizing device to vacuumize the inner cavity of the oven;

[0025] S4, applying a non-uniform electric field under actual working conditions to the electrodes on the pressurized layer mold by using the controllable voltage source to pressurize the composite solution, so that the polarized particles in the composite solution are changed from a disordered state to an ordered state of self-assembly arrangement;

[0026] S5, controlling the temperature of the oven, and solidifying the composite solution under atmospheric pressure.

[0027] Preferably, the voltage amplitude of the voltage applied to the composite solution by the controllable voltage source does not exceed the breakdown voltage that can be borne by the dielectric functional gradient material, or the voltage amplitude of the voltage applied to the composite solution by the controllable voltage source does not exceed the maximum safety value specified when the dielectric functional gradient material is used for the solid insulation system of high-voltage equipment.

[0028] Compared with the prior art, the application has the following beneficial effects:

[0029] The preparation device of the present application is provided with two pairs of electrodes for simulating the electric field environment of the dielectric function gradient material under actual working conditions in the pouring cavity of the pressurizing layer mold along the height direction, and the electrodes on the pressurizing layer mold are applied with non-uniform electric field under actual working conditions by the controllable voltage source, so that the preparation device of the present application can realize the controllable adjustment of the gradient vector dimension, gradient direction and dielectric particle arrangement in the material preparation process, and the non-uniformity of the internal field strength and surface electric field of the composite material is obviously improved. Specifically, the present application can realize the regular dielectric particle doping concentration change of the composite material in multiple directions in three-dimensional space, and the dielectric constant distribution is improved by adaptively adjusting the dielectric constant of the material. The preparation device of the present application can be used to prepare the internal and external insulation materials for power electronic devices (such as IGBT, MOSFET) and power equipment by using dielectrophoresis control technology. At the same time, there is no obvious interface in the gradient material, and the effects of body charge accumulation and insulation deterioration caused by interface effect are eliminated. On the other hand, the present application can make the dielectric particles migrate and gather to the defects by means of the extremely non-uniform electric field existing at the defects, so as to reduce the field distortion degree of the defects and achieve the self-repairing effect in the sample preparation process. Therefore, the preparation device of the present application can effectively reduce the adverse effects of defects on the dielectric function gradient material. As can be seen from the above, the present application can improve the dielectric constant distribution of the material to adapt to the complex electric field in multiple-dimensional space, and can also reduce the internal defects of the polymer material and effectively prevent the adverse effects of the distorted electric field caused by defects, thereby improving the dielectric and electrical properties of the insulation material. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the overall structure schematic diagram of the controllable gradient material preparation device based on dielectrophoresis of the present application;

[0031] Figure 2 is the structure schematic diagram of the experimental platform of the embodiment of the present application;

[0032] Figure 3 is the structure schematic diagram of the first electrode (or the second electrode) of the embodiment of the present application;

[0033] Figure 4 is the structure schematic diagram of the solution supply generator of the embodiment of the present application;

[0034] Figure 5 is the structure schematic diagram of the vacuum ceramic electrode used in the embodiment of the present application;

[0035] Figure 6 is the structure schematic diagram of the electrode connection plug-in of the present application;

[0036] Figure 7is a cross-section electric field two-dimensional distribution diagram of the dielectric functional gradient material prepared by the embodiment of the present application;

[0037] Figure 8 is a volume electric field three-dimensional distribution diagram of the dielectric functional gradient material prepared by the embodiment of the present application;

[0038] In the figure: 1 is an oven, 1-1 is an air outlet, 2 is an experimental platform, 2-1 is a top plate mold, 2-2 is a pressurized layer mold unit, 2-3 is a bottom plate mold, 2-4 is a first electrode, 2-5 is a second electrode, 2-6 is an electrode connecting plug, 2-7 is an electrode socket, 2-8 is a pouring port, 2-9 is a metal ball head, 2-10 is a ball rod, 3 is a solution supply generator, 3-1 is a solution storage bottle, 3-2 is an oil bath heating pot, 3-3 is a stirrer, 3-4 is a support rod, 3-5 is a support table, 3-6 is a valve, 4 is a vacuum pump, 5 is a vacuum ceramic electrode, 6 is a controllable voltage source, 7 is a liquid injection pipe, 8 is a conductive rod, 9 is a high-purity aluminum ceramic insulator string, 10 is a KF flange, and 11 is a clamp. DETAILED DESCRIPTION

[0039] The present application is further described below in conjunction with the accompanying drawings.

[0040] The present application provides a controllable gradient material preparation device and method based on dielectrophoresis for prolonging the service life of polymer materials, ensuring the safe and stable operation of equipment, and preventing failures. In the preparation of dielectric functional gradient composites, the orientation and arrangement of particles and targeted swimming are controlled by electric field induction, the local distortion of the over-high field strength is reduced, and the electric field inside the medium is homogenized. At the same time, the sample itself achieves self-repairing effect, avoiding local structural defects. The method has flexible application mode and has obvious improvement effect on the partial discharge resistance, aging resistance and space charge suppression performance of insulating materials, providing reference for the design means of insulating structure and the optimization and adjustment of preparation process.

[0041] Referring to Figure 1 and Figure 2 , the controllable gradient material preparation device based on dielectrophoresis comprises an oven 1, an experimental platform 2, a solution supply generator 3, a vacuumizing device and a controllable voltage source 6. The vacuumizing device is communicated with the inner cavity of the oven 1, and the experimental platform 2 is arranged in the inner cavity of the oven 1. The experimental platform 2 comprises a bottom plate mold 2-3 and a pressurized layer mold. The pressurized layer mold has a pouring cavity, and the bottom plate mold 2-3 is arranged at the bottom of the pressurized layer mold and blocks the bottom of the pouring cavity. Two pairs of electrodes for simulating the electric field environment of the dielectric functional gradient material under actual working conditions are arranged in the pouring cavity of the pressurized layer mold along the height direction. The outlet of the solution supply generator 3 is arranged above the pouring cavity of the pressurized layer mold, the solution supply generator 3 is used for pouring a composite solution into the pouring cavity of the pressurized layer mold, and the controllable voltage source 6 is connected with all the electrodes.

[0042] The application also provides a preparation method of the controllable gradient material based on dielectrophoresis, which is prepared by using the preparation device of the controllable gradient material based on dielectrophoresis, and comprises the following steps:

[0043] S1, adjusting the oven 1 to the pouring temperature of the corresponding composite solution of the dielectric functional gradient material;

[0044] S2, pouring the composite solution into the pouring cavity of the pressurized layer mold through the solution supply generator 3 until the pouring cavity of the pressurized layer mold is filled with the composite solution;

[0045] S3, vacuumizing the inner cavity of the oven 1 by using the vacuumizing device to perform vacuum defoaming treatment on the composite solution poured into the pressurized layer mold;

[0046] S4, applying an analog non-uniform electric field under actual working conditions to the electrode on the pressurized layer mold by using the controllable voltage source 6 to pressurize the composite solution, so that the polarized particles in the composite solution are changed from a disordered state to an ordered state of self-assembly arrangement; the judgment method of the polarized particles in the composite solution being changed from a disordered state to an ordered state of self-assembly arrangement is as follows: 1, measuring the dielectric constant of the composite solution, and when the dielectric constant of the composite solution is stable, it is considered that the polarized particles in the composite solution are changed from a disordered state to an ordered state of self-assembly arrangement; 2, monitoring the voltage signal and the current signal, and when the phase difference between the applied voltage signal and the current signal is less than 1% with the change of time, it is considered that the polarized particles in the composite solution are changed from a disordered state to an ordered state of self-assembly arrangement;

[0047] S5, controlling the temperature of the oven 1 to solidify the composite solution under atmospheric pressure.

[0048] In the above method of the application, before S1, the following process is further included: preparing an experimental platform 2 capable of simulating a non-uniform electric field under actual working conditions, and installing the experimental platform 2 in the oven 1, and then performing S1.

[0049] In S3, when the inner cavity of the oven 1 is vacuumized by using the vacuumizing device, in order to avoid the loss of small molecular substances in the composite solution, the air pressure in the inner cavity of the oven 1 is controlled to be not less than 100 Pa.

[0050] In S4, when the voltage is applied to the electrode on the pressurized layer mold by using the controllable voltage source 6, the voltage amplitude is not more than the breakdown voltage that can be borne by the inside of the dielectric functional gradient material or the maximum safety value specified when the dielectric functional gradient material is used for the solid insulation system of high-voltage equipment.

[0051] In the above scheme, the surface of the experimental platform 2 in contact with the composite solution can also be provided with a release agent, which is beneficial to demolding after curing; when the release agent is provided, the release agent is sprayed on the surface of the experimental platform 2 in contact with the composite solution, and then heating and drying are performed.

[0052] In S5, when the composite solution is cured, demolding can be performed, and the cured material is taken out of the mold.

[0053] In the above method of the present application, in order to simulate the non-uniform electric field under actual working conditions, the shape, number, position and applied voltage parameters of the electrode need to be designed, and the experimental platform 2 is applied with an electric field by an external power supply for a suitable length of time. The voltage parameters applied by the pressure layer mold include but are not limited to power supply type (DC / AC), voltage amplitude, voltage frequency, voltage polarity. The specific design process can be adjusted according to actual needs, and the present application does not make specific limitations.

[0054] Referring to Figure 2 The experimental platform 2 of the present application also includes a top plate mold 2-1 provided on the top of the pressure layer mold, which is detachably connected between the top plate mold 2-1 and the top of the pressure layer mold. The top plate mold 2-1 is provided with a pouring opening 2-8 in communication with the pouring cavity. The shape of the pouring opening 2-8 is square, and the area of the pouring opening 2-8 is not greater than the sample pouring opening inside the pressure layer mold (i.e. the upper port of the pressure layer mold). The top plate mold 2-1 adopts a sheet structure with a certain thickness, which can control the liquid level of the composite solution within the thickness direction of the top plate mold 2-1 when pouring the composite solution into the pouring cavity of the pressure layer mold. The pouring opening 2-8 in the middle of the top plate mold 2-1 can accommodate a certain amount of composite solution to meet the thermal expansion and contraction requirements of the composite solution during the curing process. At the same time, the bubbles, impurities and the like that float up can be accommodated in the pouring opening 2-8. After curing is completed, the corresponding part of the top plate mold 2-1 can be cut off to ensure the quality of the obtained sample.

[0055] The electrode of the present application is used to generate a non-uniform electric field. In order to avoid edge effect and prevent local high field distortion of the electrode, the shape of the electrode head is spherical and / or mung bean-shaped. The two electrodes in each pair of electrodes are symmetrically arranged on the pressure layer mold; the two electrodes in each pair of electrodes are spherical electrodes.

[0056] Referring to Figure 2 and Figure 3The electrode structure adopted by the present application is as follows: including a metal ball head 2-9 and a ball rod 2-10, the metal ball head 2-9 is installed at one end of the ball rod 2-10 as the head of the electrode, the ball rod 2-10 adopts a cylindrical rod, the pressing layer mold is provided with an electrode insertion hole 2-7, the other end of the ball rod 2-10 abuts against the mouth of the electrode insertion hole 2-7, the diameter of the ball rod 2-10 is larger than that of the mouth of the electrode insertion hole 2-7, and the electrode insertion hole 2-7 is connected with an electrode connecting plug 2-6; the ball rod 2-10 adopts a conductor, the junction of the metal ball head 2-9 and the ball rod 2-10 is smoothly transitioned, a threaded hole is arranged at the end of the ball rod 2-10 abutting against the mouth of the electrode insertion hole 2-7, the electrode connecting plug 2-6 is threadedly connected with the threaded hole of the ball rod 2-10, and the mouth of the electrode insertion hole 2-7 is blocked by the end of the ball rod 2-10. When the electrode is demolded, the electrode connecting plug 2-6 is disassembled from the ball rod 2-10, at this time, the whole electrode structure is embedded in the solidified material, the electrode is taken out from the pressing layer mold together with the solidified material when demolding, and only the solidified material needs to be cut and the part containing the electrode needs to be cut off. In addition, if the ball rod 2-10 is not arranged and the metal ball head 2-9 is directly blocked at the mouth of the electrode insertion hole 2-7, because the dielectric constants of the metal ball head 2-9, the mouth of the electrode insertion hole 2-7 and the composite solution are different, at this time, the electric field distortion is serious at the junction of the metal ball head 2-9, the mouth of the electrode insertion hole 2-7 and the composite solution, which can cause the material of the composite solution to decompose, the substances generated by the decomposition can be dissolved in the composite solution, and then the composition of the finally prepared dielectric functional gradient material is changed; in addition, the electric tree can be generated in the finally prepared dielectric functional gradient material, which can cause the dielectric functional gradient material to be deteriorated. Therefore, the ball rod 2-10 is arranged in the present application, the ball rod 2-10 generally adopts a cylindrical shape, and after the electrode is pressed, the ball rod 2-10 can effectively reduce the electric field distortion degree at the junction of the cylindrical ball rod 2-10, the mouth of the electrode insertion hole 2-7 and the composite solution, and the above problems can be avoided.

[0057] Reference Figure 2, as a preferred embodiment of the present application, the length of the top plate mold 2-1 is a1, the width is b1, the thickness is c1, the length of the pressure layer mold unit 2-2 is a2, the width is b2, the thickness is c2; the length of the bottom plate mold 2-3 is a3, the width is b3, the thickness is c3. Typically, a1, a2, a3 are 20cm, 20cm, 35cm respectively, b1, b2, b3 are 15cm, 15cm, 20cm respectively, c1, c2, c3 are 1cm, 4cm, 6cm respectively. In a specific embodiment, three pressure layer mold units 2-2 are each equipped with a first electrode 2-4 on the left side of the mold and a second electrode 2-5 on the right side, the first electrode 2-4 and the second electrode 2-5 are symmetrical structures, the electrode shape is selected as a ball electrode, the ball electrode includes a metal ball head 2-9 and a ball rod 2-10, the ball rod 2-10 is a conductive rod, and the ball rod 2-10 is embedded with a screw hole. The diameter of the metal ball head of the first electrode 2-4 and the second electrode 2-5 is 1.6cm, and the length of the ball rod is 0.5cm. The top plate mold 2-1 is placed on the uppermost layer of all molds, and the square pouring gate 2-8 of the top plate mold 2-1 is 14cm long and 10cm wide. Four screw holes are provided on the top plate mold 2-1, the pressure layer mold unit 2-2 and the bottom plate mold 2-3, and the top plate mold 2-1, the pressure layer mold unit 2-2 and the bottom plate mold 2-3 are detachably fixed and connected as a whole structure by screw columns and nuts at the screw holes.

[0058] Referring to Figure 1 , the present application is installed with a vacuum ceramic electrode 5 on the oven 1, the electrode connecting plug 2-6 is connected between the vacuum ceramic electrode 5 through the wire, and the vacuum ceramic electrode 5 is connected with the controllable voltage source 6 through the wire, so as to realize the electrical connection between the controllable voltage source 6 located outside the oven 1 and the experimental platform 2 located inside the oven 1.

[0059] Referring to Figure 1 and Figure 4The solution supply generator 3 comprises a solution storage bottle 3-1, an oil bath heating pot 3-2 and a stirrer 3-3, the solution storage bottle 3-1 is used for storing the composite solution, the solution storage bottle 3-1 is arranged in the oil bath heating pot 3-2, the composite solution in the solution storage bottle 3-1 can be heated and maintained at the pouring temperature by using the oil bath heating pot 3-2, the stirring part of the stirrer 3-3 is arranged in the solution storage bottle 3-1, the composite solution in the solution storage bottle 3-1 can be kept in a uniform state by using the stirring action of the stirrer 3-3, so that the curing agent and the accelerator can be uniformly mixed with the solution, the outlet of the solution storage bottle 3-1 is connected with a liquid injection pipe 7, the outlet of the liquid injection pipe 7 serves as the outlet of the whole solution supply generator 3, a valve 3-6 is arranged on the outlet of the solution storage bottle 3-1, and the pouring speed and the pouring amount can be controlled by controlling the valve 3-6 during pouring. The solution supply generator 3 further comprises a support rod 3-4 and a support table 3-5, the oil bath heating pot 3-2 is arranged on the support table 3-5, and the stirrer 3-3 is fixed on the support table 3-5 through the support rod 3-4. When the composite solution is configured in the solution supply generator 3, the raw materials of the composite solution are added into the solution storage bottle 3-1 according to the formula proportion, the temperature of the oil bath heating pot 3-2 is set as a preset constant temperature, and the solution is stirred by using the stirrer 3-3, so that the composite solution is obtained after uniform stirring.

[0060] The vacuumizing device can adopt a vacuum pump 4, the oven 1 is provided with an air outlet 1-1, and the air inlet of the vacuum pump 4 is connected with the air outlet 1-1, so that the structure is relatively simple and the cost is low.

[0061] The pressurizing layer mold can be integrated, the pressurizing layer mold with a corresponding height is adopted according to the height of the sample material, and the pressurizing layer mold can also adopt a laminated structure, at this time, referring to Figure 2 The pressurizing layer mold comprises at least two pressurizing layer mold units 2-2 stacked together, and at least one pair of electrodes is arranged on each pressurizing layer mold unit 2-2, so that the pressurizing layer mold can select a proper number of pressurizing layer mold units 2-2 to assemble the pressurizing layer mold according to the height of the sample material, the adaptability of the pressurizing layer mold is wider, and the number of specifications of the pressurizing layer mold is reduced. The top plate mold 2-1, the pressurizing layer mold unit 2-2 and the bottom plate mold 2-3 can be detachably connected through long bolts, so that the whole test platform can be assembled and demolded with the curing material in the later period. The top plate mold 2-1, the pressurizing layer mold unit 2-2, the bottom plate mold 2-3 and the long bolt can all be made of high-temperature-resistant polytetrafluoroethylene insulating material, and the material has excellent chemical stability and electrical insulation.

[0062] Referring to Figure 5The typical structure of the vacuum ceramic electrode 5 used in the present application is as follows: the vacuum ceramic electrode 5 comprises an electrically conductive rod 8, a high-purity aluminum ceramic insulator string 9, a KF flange 10 and a clamp 11, the upper end of the electrically conductive rod 8 is connected with the output end of the controllable voltage source 6, the lower end is connected with the electrode connecting plug 2-6 corresponding to the pressure layer mold 2-2, and the clamp 11 is used for fixing the KF flange 10.

[0063] With reference to Figure 6 The electrode connecting plug 2-6 used in the present application is fitted with the electrode insertion hole 2-7 on both sides of the pressure layer mold unit 2-2, the electrode connecting plug has threads at the plug end and can be fixed by rotation, and the electrode connecting plug maintains good electrical contact with the electrode.

[0064] In the above scheme of the present application, the particle size of the particles doped in the composite solution is less than 70 μm, and the composite solution has good dispersibility and suspensibility. The viscosity of the base solution of the composite solution is less than or equal to 50 Pa·s at normal temperature (25℃), and preferably, the viscosity of the base solution is in the range of 10-20 Pa·s. The overall assembly of the preparation device is used for the preparation of polymer composite materials, and the electric field, temperature, vacuum degree and pressure can be controlled by connecting with external equipment, so that the pouring and curing of the polymer material with gradient characteristics and repair function are realized, and the overall thickness of the sample can be realized by selecting the pressure layer mold.

[0065] Example 1

[0066] In this embodiment, the preparation of dielectric functional gradient polymer composite material is taken as an example. At normal temperature 25℃, the viscosity of the base solution of the polymer composite solution is 10-14 Pa·s, the filler is spherical particle with an average particle size of 10 μm, and the addition mass ratio is 150%. Three pressure layer mold units 2-2 with the same thickness are selected, and the electrode connecting plugs 2-6 are connected with the electrodes in the pressure layer mold units 2-2 according to the electrode arrangement shown in the figure. Figure 2 The mold is assembled. For the convenience of description, the six electrodes are numbered from top to bottom, the first electrode of the first pressure layer mold unit 2-2 is the A electrode, the second electrode of the first pressure layer mold unit 2-2 is the B electrode, the first electrode of the second pressure layer mold unit 2-2 is the C electrode, and so on. The purpose of the experiment is to form an electric field environment similar to the GIS support insulator with large sides and small middle.

[0067] The main process of preparing the dielectric functional gradient polymer composite material in this embodiment includes mold cleaning, assembly, batching, pouring, degassing and pressure curing, and the specific steps are as follows:

[0068] (1) Clean each part of the controllable gradient material preparation device based on dielectrophoresis, wipe the surface of each part with a dust-free cloth soaked with alcohol, so that the surface is clean, smooth and dust-free;

[0069] (2) Spray the release agent on the inner side of the top plate mold 2-1 and the pressurized layer mold unit 2-2, the upper surface of the bottom plate mold 2-3, and the studs and nuts used for assembling the mold, and then heat all the parts at a constant temperature of 130°C for 2-3 hours to dry and remove moisture;

[0070] (3) Assemble the experimental platform. After the parts sprayed with the release agent are cooled, assemble the top plate mold 2-1, the pressurized layer mold unit 2-2, and the bottom plate mold 2-3, tighten the nuts, and ensure the sealing during the sample preparation. Screw the first electrode 2-4 and the second electrode 2-5 into the corresponding electrode connection plug 2-6 on the left and right sides of each pressurized layer mold unit 2-2, respectively, and fix them;

[0071] (4) Set the temperature of the oven 1 to the pouring temperature of the solution, which is 60°C. Configure the solution according to the ratio of 1:0.85:0.003 of the liquid polymer, the curing agent, and the accelerator. At the same time, add inorganic particles to the solution. Set the temperature of the oil bath heating pot 3-2 to a constant temperature of 60°C. Use the stirrer 3-3 to stir at a speed of 400 r / min for 30 min to ensure uniform mixing of the solution. Then open the valve 3-6 and pour the composite solution into the square pouring port 2-8 of the experimental platform 2.

[0072] (5) Use the vacuum pump 4 for vacuum degassing treatment. This process lasts for 3-4 hours, and the gas pressure in the oven 1 cavity is not less than 100 Pa to avoid the loss of small molecules in the solution.

[0073] (6) Apply power to the electrodes on the three-layer pressurized layer mold unit 2-2. Set the power source type to direct current. The voltage amplitude applied to the first electrode 2-4 and the second electrode 2-5 of each pressurized layer mold unit 2-2 is equal. The positive polarity voltage of the A electrode and the B electrode is 40 kV, the positive polarity voltage of the C electrode and the D electrode is 15 kV, and the negative polarity voltage of the E electrode and the F electrode is 10 kV. Apply an electric field to the solution for 1.5-2 hours.

[0074] (7) Keep the voltage applied and follow the curing process. Set the temperature of the oven 1 at different time periods. Complete the temperature rising, curing, and slow cooling in an atmospheric pressure environment to release internal stress and avoid the formation of obvious curing shrinkage lines on the material surface.

[0075] The relative dielectric constant of the inorganic spherical particles added in the solution is more than 6 times that of the bubbles, so it can effectively homogenize the electric field at the defect and improve the distortion degree of the internal electric field.

[0076] Typically, the dielectric functionally graded polymer composite material is formed by pressurizing and curing an epoxy resin as the matrix and inorganic fillers such as silicon oxide, aluminum oxide, titanium dioxide, or barium titanate (low filler content).

[0077] Figure 7The figure is a simulation result of two-dimensional electric field distribution of the dielectric functional gradient polymer composite section, and the arrow represents the gradient direction of electric field square, that is, the particle trajectory direction. Figure 7 As can be seen from the figure, the filler particles have obvious orientation from the area with weak electric field to the area with high electric field, and the filler particles move and arrange from the middle to the two electrode areas based on dielectrophoresis force, so that the particle concentration on the section is monotonically decreasing first and then increasing (U-shaped distribution) from left to right, the dielectric constant distribution of the material is higher on the left and lower on the right, so as to reduce the field strength on the two sides of the material, and the internal electric field is correspondingly lifted, and the electric field distribution is further homogenized. Figure 8 The figure shows a more intuitive three-dimensional electric field distribution of the geometric body, and the gradient near the electrode in the solution matrix increases significantly, causing the phenomenon that the filler particles gather to the electrode area, so that the particle concentration in the electrode area increases to weaken the high distortion electric field.

[0078] In summary, the present application has the following characteristics:

[0079] Firstly, the present application aims to provide a preparation device and method of controllable dielectric functional gradient polymer composite based on dielectrophoresis, by changing the shape, number and position distribution of the electrode and applying different electric field conditions to the electrode, so as to adjust the direction of the applied electric field to be basically consistent with the actual electric field, obtain a non-uniform electric field environment similar to the actual electric field, improve the dielectric constant distribution in the material and along the surface adjustment area, and control the electric field distribution; secondly, the present application aims to provide a preparation device and method of self-adaptive dielectric composite based on dielectrophoresis, by using the serious electric field distortion at the local defects (bubbles, impurities, etc.) in the solution after pressurization, promoting the directional movement of the dielectric particles to the defect area under the action of the larger dielectrophoresis force, and wrapping the defects to form a protection circle, so as to reduce the electric field distortion degree of the defects and further homogenize the electric field.

[0080] The preparation device of controllable gradient material provided by the present application is suitable for preparing various materials, including but not limited to the casting forming of thermosetting polymer insulating materials, such as multilayer thermosetting resin samples, and the melt injection of thermoplastic materials. The dielectric functional gradient polymer composite is applied to various fields, such as the internal, external and interface insulation of power equipment and power electronic devices, and the multidimensional performance and internal mechanism research of insulating materials.

[0081] The preparation device of the present application has the advantages that the thickness of the sample can be controlled by adjusting the thickness of the pressurized layer mold; the electric field, temperature, vacuum degree and pressure can be controlled by connecting with external equipment, so as to realize the casting and curing of polymer materials with gradient characteristics and repair function; the overall mold has good sealing property, the mold contact surface is sprayed with release agent, sampling is facilitated, and the integrity of the sample is ensured.

[0082] From the above scheme can be seen, the present application process simple and convenient, sample preparation mode flexible, sample thickness controllable, through the polymer composite solution two sides can be realized under a variety of conditions of material preparation, preparation to meet the single and multiple direction different dielectric properties of the dielectric function gradient material, also can realize in the process of sample preparation to the defect timely remedy, effectively prevent solid partial discharge, breakdown, aging and other faults occur, therefore the present application can effectively improve the composite insulating material's insulation and electric performance, prolong the service life of the material, improve the sample preparation efficiency. The present application can further explore the influence mechanism of multidimensional space dielectrophoresis force on particle orientation arrangement and target swimming, study the improvement and promotion effect of dielectrophoresis repair method on material electrical performance.

Claims

1. A dielectrophoretic based controllable gradient material preparation apparatus, characterized in that, The oven (1), the experimental platform (2), the solution supply generator (3), the vacuumizing device and the controllable voltage source (6) are included. The vacuumizing device is communicated with the inner cavity of the oven (1), and the experimental platform (2) is arranged in the inner cavity of the oven (1). The experimental platform (2) includes a bottom plate mold (2-3) and a pressurized layer mold, the pressurized layer mold has a pouring cavity, and the bottom plate mold (2-3) is arranged at the bottom of the pressurized layer mold and seals the bottom of the pouring cavity; two pairs of or more electrodes for simulating the electric field environment of the dielectric function gradient material under actual working conditions are arranged in the pouring cavity of the pressurized layer mold along the height direction. The outlet of the solution supply generator (3) is arranged above the pouring cavity of the pressurized layer mold, the solution supply generator (3) is used for pouring a composite solution into the pouring cavity of the pressurized layer mold, and the controllable voltage source (6) is connected with all the electrodes. The electrode includes a metal ball head (2-9) and a ball rod (2-10), the metal ball head (2-9) is installed at one end of the ball rod (2-10), the ball rod (2-10) is in a cylindrical shape, the metal ball head (2-9) serves as the head of the electrode, the pressurized layer mold is provided with an electrode insertion hole (2-7), the other end of the ball rod (2-10) abuts against the mouth of the electrode insertion hole (2-7), the diameter of the ball rod (2-10) is larger than that of the mouth of the electrode insertion hole (2-7), and the electrode insertion hole (2-7) is connected with an electrode connecting plug (2-6). The ball rod (2-10) is made of a conductor, the junction of the metal ball head (2-9) and the ball rod (2-10) is smoothly connected, a threaded hole is arranged at the end of the ball rod (2-10) abutting against the mouth of the electrode insertion hole (2-7), the electrode connecting plug (2-6) is screwed with the threaded hole of the ball rod (2-10), and the mouth of the electrode insertion hole (2-7) is sealed by the end of the ball rod (2-10).

2. The dielectrophoretic based controllable gradient material preparation device of claim 1, wherein, The experimental platform (2) further includes a top plate mold (2-1), the top plate mold (2-1) is arranged at the top of the pressurized layer mold, and the top plate mold (2-1) is provided with a pouring port (2-8) communicated with the pouring cavity.

3. The dielectrophoretic based controllable gradient material preparation device of claim 1, wherein, The shape of the electrode head includes a spherical shape and / or a broad bean shape.

4. The dielectrophoretic based controllable gradient material preparation device of claim 1, wherein, The vacuum ceramic electrode (5) is arranged on the oven (1), the electrode connecting plug (2-6) and the vacuum ceramic electrode (5) are connected through a wire, and the vacuum ceramic electrode (5) is connected with the controllable voltage source (6) through the wire.

5. The dielectrophoretic based controllable gradient material preparation device of claim 1, wherein, The two electrodes in each pair of electrodes are symmetrically arranged on the pressurized layer mold.

6. The dielectrophoretic based controllable gradient material preparation device of claim 1, wherein, The solution supply generator (3) is arranged outside the oven (1), the solution supply generator (3) includes a liquid storage bottle (3-1), an oil bath heating pot (3-2) and a stirrer (3-3), the liquid storage bottle (3-1) is arranged in the oil bath heating pot (3-2), the stirring part of the stirrer (3-3) is arranged in the liquid storage bottle (3-1), the outlet of the liquid storage bottle (3-1) is connected with a liquid injection pipe (7), the outlet of the liquid injection pipe (7) serves as the outlet of the entire solution supply generator (3), and the outlet of the liquid storage bottle (3-1) is provided with a valve (3-6).

7. The dielectrophoretic based controllable gradient material preparation device of claim 1, wherein, The pressurized layer mold adopts a laminated structure, and comprises at least two pressurized layer mold units (2-2) stacked together.

8. A method for preparing a controllable gradient material based on dielectrophoresis, characterized in that, The preparation method is performed by using the dielectrophoretic controllable gradient material preparation device according to any one of claims 1-7, and comprises the following steps: S1, adjusting the oven (1) to the pouring temperature of the corresponding composite solution of the dielectric functional gradient material; S2, pouring the composite solution into the pouring cavity of the pressurized layer mold through the solution supply generator (3) until the pouring cavity of the pressurized layer mold is filled with the composite solution; S3, vacuumizing the inner cavity of the oven (1) by using the vacuumizing device to perform vacuum defoaming treatment on the composite solution poured into the pressurized layer mold; S4, applying a non-uniform electric field under actual working conditions to the electrodes on the pressurized layer mold by using the controllable voltage source (6) to pressurize the composite solution, so that the polarized particles in the composite solution change from a disordered state to an ordered state of self-assembly arrangement; S5, controlling the temperature of the oven (1) and solidifying the composite solution under atmospheric pressure.

9. The method of claim 8, wherein the method further comprises, The voltage amplitude of the voltage applied to the composite solution by the controllable voltage source (6) does not exceed the breakdown voltage that can be withstood inside the dielectric functional gradient material, or the voltage amplitude of the voltage applied to the composite solution by the controllable voltage source (6) does not exceed the maximum safety value specified when the dielectric functional gradient material is used for a solid insulation system of a high-voltage device. The voltage amplitude of the voltage applied to the composite solution by the controllable voltage source (6) does not exceed the breakdown voltage that can be withstood inside the dielectric functional gradient material, or the voltage amplitude of the voltage applied to the composite solution by the controllable voltage source (6) does not exceed the maximum safety value specified when the dielectric functional gradient material is used for a solid insulation system of a high-voltage device.

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