阅读说明：本技术 聚丙烯基针板电极试样制备模具及制备方法 (Polypropylene-based needle plate electrode sample preparation mold and preparation method ) 是由 牛越 赵洪 胡巍 李春阳 于 2019-11-28 设计创作，主要内容包括：聚丙烯基针板电极试样制备模具及制备方法,属于电气绝缘材料介电性能测试技术领域。解决了现有实验测试技术存在制样困难、步骤繁琐、试样统一性差的问题。技术要点：底板上加工有开口凹槽,模板安装在开口凹槽内,且模板的底端面与开口凹槽的底面之间形成放料凹槽,模板靠近放料凹槽的一侧均匀开设有多个曲率半径一致的下半圆柱体放针凹槽,盖板上设有多个上半圆柱体放针凹槽,上半圆柱体放针凹槽的曲率半径与下半圆柱体放针凹槽保持一致；盖板盖装在模板上并与模板完全重合,上半圆柱体放针凹槽与下半圆柱体放针凹槽两两位置对应构成圆柱放针腔体,利用该模具可以实现用于聚丙烯基绝缘材料电树枝特性测试的针板电极试样的高效制备。(A polypropylene-based needle plate electrode sample preparation mold and a preparation method belong to the technical field of dielectric property testing of electrical insulating materials. The problems of difficulty in sample preparation, complex steps and poor sample uniformity in the existing experimental testing technology are solved. The technical points are as follows: an opening groove is processed on the bottom plate, the template is installed in the opening groove, a discharging groove is formed between the bottom end face of the template and the bottom face of the opening groove, a plurality of lower semi-cylinder needle releasing grooves with consistent curvature radius are uniformly formed in one side, close to the discharging groove, of the template, a plurality of upper semi-cylinder needle releasing grooves are formed in the cover plate, and the curvature radius of the upper semi-cylinder needle releasing grooves is consistent with that of the lower semi-cylinder needle releasing grooves; the cover plate covers the template and completely coincides with the template, the upper semi-cylinder needle placing groove and the lower semi-cylinder needle placing groove correspond to each other in position to form a cylindrical needle placing cavity, and the efficient preparation of the needle plate electrode sample for polypropylene-based insulating material electrical tree characteristic testing can be realized by using the mold.)

1. The polypropylene-based needle plate electrode sample preparation mold is characterized by comprising a cover plate (3), a template (2) and a bottom plate (1), wherein an open groove is processed on the bottom plate (1), the template (2) is installed in the open groove, a discharging groove (4) is formed between the bottom end surface of the template (2) and the bottom surface of the open groove, one side, close to the discharging groove (4), of the template (2) is uniformly provided with a plurality of lower semi-cylinder needle placing grooves (5-1) with consistent curvature radius, the cover plate (3) is uniformly provided with a plurality of upper semi-cylinder needle placing grooves (5-2), and the curvature radius of the upper semi-cylinder needle placing grooves (5-2) is consistent with the curvature radius of the lower semi-cylinder needle placing grooves (5-1); the cover plate (3) is covered on the template (2) and completely coincided with the template (2), the upper semi-cylinder needle placing groove (5-2) and the lower semi-cylinder needle placing groove (5-1) correspond to each other in two positions to form a cylindrical needle placing cavity, and a tungsten needle is placed in the cylindrical needle placing cavity.

2. The polypropylene-based needle plate electrode sample preparation mold according to claim 1, wherein a lower separation groove (6-2) is formed in the middle of one side of the template (2) far away from the discharge groove (4), and an upper separation groove (6-1) is formed in a position, corresponding to the lower separation groove (6-2), on the cover plate (3).

3. The polypropylene-based needle plate electrode sample preparation mold according to claim 1 or 2, wherein two corners of one side of the template (2) far away from the discharge groove (4) are provided with positioning notches (7-1), the cover plate (3) is provided with positioning protrusions (7-2) at positions corresponding to the positioning notches (7-1), and the positioning notches and the positioning protrusions are matched to realize positioning.

4. The die for preparing a polypropylene-based needle plate electrode specimen as claimed in claim 3, wherein the base plate is made of a flat stainless steel plate having a length of 30cm, a width of 20cm and a thickness of 8mm to 12 mm.

5. The die for preparing a polypropylene-based needle plate electrode sample according to claim 4, wherein the radius of curvature of the lower semi-cylindrical needle placing groove (5-1) is 0.3 mm.

6. A preparation method of a polypropylene-based needle plate electrode sample, which adopts an embedded needle method to prepare the needle plate electrode sample in the hot press molding process and is realized by depending on a preparation mold of the polypropylene-based needle plate electrode sample as claimed in any one of claims 1 to 5, and is characterized by comprising the following specific steps:

grinding or cutting a polypropylene-based material to be pressed into particles in advance, taking a steel plate, flatly paving a polyester film with the same size as the steel plate on the steel plate, placing a bottom plate (1) on the polyester film, uniformly paving the polypropylene-based material particles in a material placing groove (4), wherein the tiled height is not more than the lower edge of a lower semi-cylinder needle placing groove (5-1) on a template (2), then sequentially flatly placing a plurality of tungsten needles with the same length in the lower semi-cylinder needle placing groove (5-1), selecting the length of the tungsten needle to be longer than the length of the lower semi-cylinder needle placing groove (5-1), ensuring that the bottom ends of the tungsten needles are tightly attached to the bottom end of the lower semi-cylinder needle placing groove (5-1), then sequentially paving a polypropylene-based insulating material between two adjacent needle points of the tungsten needles, paving the thickness of the tungsten needles to be not more than that of the template (2), and covering a cover plate (3) on the template, and (3) completely coinciding the cover plate with the template, then sequentially paving polyester films and steel plates with the same size on the cover plate, clamping, putting the cover plate into a flat vulcanizing machine, taking out the mold after hot press molding and cooling, separating the mold, taking out a sample containing the tungsten needle, and finally cutting the sample into independent single samples.

7. The method for preparing a polypropylene-based needle plate electrode specimen as claimed in claim 6, wherein the polypropylene-based material to be pressed is ground or cut in advance to 1mm or less³The lengths of the tungsten needles in the needle placing grooves are consistent with the curvature radius of the needle point, and the electrode distance between the electrode sample needle of the needle plate and the plate is adjusted by changing the length of the tungsten needles.

8. The method for preparing a polypropylene-based needle plate electrode specimen as defined in claim 6 or 7, wherein the cover plate (3) is placed on the template (2) with the positioning notches (7-1) and the positioning projections (7-2) as axes so that the cover plate and the template completely coincide with each other.

9. The method for preparing a polypropylene-based needle plate electrode specimen as set forth in claim 8, wherein the mold is divided by the upper separation groove (6-1) and the lower separation groove (6-2) and a specimen containing a tungsten needle is taken out.

Technical Field

The invention relates to a die and a method for preparing an electrode sample, in particular to a die and a method for preparing a polypropylene-based needle plate electrode sample, and belongs to the technical field of dielectric property testing of electrical insulating materials.

Background

Compared with thermosetting cross-linked polyethylene, the polypropylene-based insulating material has the advantages of high breakdown strength, recyclability, rich raw materials, low price, excellent heat resistance and the like, and accords with the development concept and value orientation of environmental protection. Therefore, polypropylene-based insulating materials have great development potential no matter applied to alternating current cables or direct current cables, and are widely concerned by researchers at home and abroad. Whether polypropylene-based insulating materials can be used as main insulating materials of cables or not is required to be researched, and the research on the electrical performance of the polypropylene-based insulating materials is one of essential important links. The research on the initiation and growth mechanisms of polypropylene-based insulating material electric tree branches is of great significance to the reliability evaluation of power cables and the safe operation of power systems.

The electric tree phenomenon is researched in a laboratory, most researchers often adopt a needle-plate electrode, and the selected material is high in transparency and good in toughness. Taking crosslinked polyethylene as an example, in the preparation process of the electrical tree test sample, after a material is pressed into a test sample with a proper thickness by a flat vulcanizing machine, a metal needle can be inserted into the test sample by using some tools, the distance consistency between the needle and the plate of the test sample can be easily ensured, and meanwhile, the metal needle is coaxial with the test sample and the needle point is not damaged.

However, polypropylene-based insulating materials have high hardness and high melting point, are brittle materials at normal temperature, are difficult to insert pins under heating conditions or at normal temperature, the radius of curvature of a metal pin used for electrical tree initiation experiments is about several micrometers, and the metal pin is easy to bend or damage in the process of inserting the pin. Meanwhile, because the sample has poor mechanical impact resistance and high hardness, the distance between the needle point of the needle-plate electrode sample and the flat plate electrode is difficult to unify, and the needle-plate distance and the curvature radius of the needle point have obvious influence on an electric field in the process of initiating the electrical tree of the needle plate electrode sample, so that the dispersibility of a test result is overlarge, the introduced errors and uncertainty factors are too much, and the reliability of the test result is poor. Therefore, the preparation of needle plate electrode samples for the alternating current dendritic characteristic test of polypropylene-based insulating materials is always a difficult problem in the testing technology.

Disclosure of Invention

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. It should be understood that this summary is not an exhaustive overview of the invention. It is not intended to determine the key or critical elements of the present invention, nor is it intended to limit the scope of the present invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

In view of the above, the invention designs a process method and a preparation mold for preparing a polypropylene-based needle plate electrode sample by using a needle embedding method, in order to solve the problems of difficult sample preparation, complicated steps and poor sample uniformity in the existing experimental testing technology.

The first scheme is as follows: the polypropylene-based needle plate electrode sample preparation mold comprises a cover plate, a template and a bottom plate, wherein an opening groove is processed in the bottom plate, the template is installed in the opening groove, a material placing groove is formed between the bottom end surface of the template and the bottom surface of the opening groove, a plurality of lower semi-cylinder needle placing grooves with the same curvature radius are uniformly formed in one side, close to the material placing groove, of the template, a plurality of upper semi-cylinder needle placing grooves are uniformly formed in the cover plate, and the curvature radius of the upper semi-cylinder needle placing grooves is consistent with that of the lower semi-cylinder needle placing grooves; the cover plate covers the template and is completely coincided with the template, the upper semi-cylinder needle placing groove and the lower semi-cylinder needle placing groove correspond to each other in position to form a cylindrical needle placing cavity, and a tungsten needle is placed in the cylindrical needle placing cavity.

Further: the middle part of one side of the template, which is far away from the discharging groove, is provided with a lower separation groove, and the position of the cover plate, which corresponds to the lower separation groove, is provided with an upper separation groove. So set up, carry out the mould separation after the sample shaping of being convenient for, conveniently unload.

Further: and two corners of one side of the template, which is far away from the discharging groove, are provided with positioning notches, the positions of the cover plate, which correspond to the positioning notches, are provided with positioning bulges, and the positioning notches and the positioning bulges are matched to realize positioning. So set up, be convenient for fix a position at system appearance in-process, make things convenient for system appearance.

Further: the bottom plate is made of a stainless steel flat plate with the length of 30cm, the width of 20cm and the thickness of 8mm-12 mm.

Further: the curvature radius of the lower semi-cylinder needle placing groove is 0.3 mm.

Scheme II: the preparation method of the polypropylene-based needle plate electrode sample adopts an embedded needle method to prepare the needle plate electrode sample in the hot press molding process, and is realized by the polypropylene-based needle plate electrode sample preparation mold according to the first scheme, and the preparation method specifically comprises the following steps:

grinding or cutting a polypropylene-based material to be pressed into particles in advance, taking a steel plate, flatly paving a polyester film on the steel plate, placing a bottom plate on the polyester film, uniformly flatly paving the polypropylene-based material particles in a material placing groove, wherein the flatly paved height is not more than the lower edge of a lower semi-cylinder needle placing groove on a template, then sequentially flatly paving a plurality of tungsten needles with the same length in the lower semi-cylinder needle placing groove, wherein the selected tungsten needle length is longer than the length of the lower semi-cylinder needle placing groove, ensuring that the bottom ends of the tungsten needles are tightly attached to the bottom end of the lower semi-cylinder needle placing groove, then sequentially paving a polypropylene-based insulating material between the needle points of two adjacent tungsten needles, paving a template with a thickness not more than the thickness, covering the template with a cover plate, completely coinciding the cover plate with the template, then sequentially paving the polyester film and the steel plate with the same size on the cover plate, clamping and then placing, and taking out the die after the hot press molding is cooled, separating the die, taking out the sample containing the tungsten needle, and finally cutting the sample into independent single samples.

Further: grinding or cutting the polypropylene-based material to be pressed into the size of less than or equal to 1mm in advance³The particles of (1).

Further: the lengths of the tungsten needles in the needle placing grooves are consistent with the curvature radius of the needle point, and the electrode spacing between the electrode sample needle and the plate of the needle plate is adjusted by changing the length of the tungsten needles.

Further: and covering the cover plate on the template by taking the positioning notch and the positioning bulge as axes, so that the cover plate and the template are completely overlapped.

Further: the mold is separated and the sample containing the tungsten needle is taken out by using the upper separation groove and the lower separation groove.

The invention achieves the following effects:

(1) when a sample is prepared, a combined die is designed, a mode of an embedded needle is adopted, the preparation of a needle-plate electrode sample is completed while the sample is subjected to hot press molding, the possibility that a needle point is damaged in the needle inserting process is avoided, the unification of the distance between the needle and the plate electrode of each sample is also ensured, the experimental steps are greatly simplified, the problem of sample preparation difficulty is solved, and the success rate and the convenience of sample preparation and the accuracy of the test process are also improved.

(2) The mould for preparing the samples can prepare a plurality of samples through one-time hot press molding, and the sample preparation efficiency is improved.

(3) According to the sample preparation method and the combined die, the distance between the needle and the plate of the needle plate electrode sample can be changed by changing the uniform length of the tungsten needle, the test conditions of different needle plate electrode distances can be realized, and the flexibility is good.

Drawings

FIG. 1 is a view showing a construction of a mold for preparing a polypropylene-based needle plate electrode sample;

FIG. 2 is an isometric view of a polypropylene-based needle plate electrode specimen preparation die;

FIG. 3 is a schematic drawing showing needle setting of a polypropylene-based needle plate electrode sample preparation mold;

FIG. 4 is a schematic diagram of an experimental apparatus for AC tree initiation;

FIG. 5 is a top view of a plate electrode of the AC tree initiation experiment apparatus;

FIG. 6 is a front view of the high electrode;

fig. 7 is a schematic structural view of a sample obtained by die pressing.

In the figure: the device comprises a base plate 1, a template 2, a cover plate 3, a discharge groove 4, a lower semi-cylinder needle placing groove 5-1, an upper semi-cylinder needle placing groove 5-2, an upper separation groove 6-1, a lower separation groove 6-2, a positioning notch 7-1, a positioning bulge 7-2, a high-voltage alternating current power supply 8, a high-voltage electrode 9, an electrode support 10, a transparent oil groove 11, a ground level 12, an experiment support 13, a Rogowski coil 14, an oscilloscope 15 and a computer 16.

Detailed Description

Exemplary embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. In the interest of clarity and conciseness, not all features of an actual implementation are described in the specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The meaning of "inside and outside" in the present invention means that the direction pointing to the inside of the device is inside and vice versa with respect to the device itself, and is not a specific limitation of the mechanism of the apparatus of the present invention.

The meaning of "left and right" in the present invention means that when the reader is facing the drawings, the left side of the reader is left, and the right side of the reader is right, and is not a specific limitation on the mechanism of the apparatus of the present invention.

The term "connected" as used herein may mean either a direct connection between the components or an indirect connection between the components via other components.

It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the device structures and/or processing steps closely related to the solution according to the present invention are shown in the drawings, and other details not so relevant to the present invention are omitted. Preferred embodiments of the present invention are explained in detail below with reference to the accompanying drawings.