CN115586099A - Model selection method of high-swelling-resistance silicone grease for cable and accessory interface - Google Patents

Model selection method of high-swelling-resistance silicone grease for cable and accessory interface Download PDF

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Publication number
CN115586099A
CN115586099A CN202211228322.2A CN202211228322A CN115586099A CN 115586099 A CN115586099 A CN 115586099A CN 202211228322 A CN202211228322 A CN 202211228322A CN 115586099 A CN115586099 A CN 115586099A
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silicone grease
silicone
rubber sample
grease
sample
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王霞
姜泉旭
吴超
陈宇奇
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Xian Jiaotong University
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Xian Jiaotong University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N5/00—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid
    • G01N5/02—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by absorbing or adsorbing components of a material and determining change of weight of the adsorbent, e.g. determining moisture content
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G01N27/221—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance by investigating the dielectric properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/006—Crack, flaws, fracture or rupture
    • G01N2203/0067—Fracture or rupture
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/026—Specifications of the specimen
    • G01N2203/0262—Shape of the specimen
    • G01N2203/0268—Dumb-bell specimens

Abstract

A type selection method for high swelling resistance silicone grease of a cable and accessory interface comprises the following steps: soaking the silicon rubber sample in different silicon greases, and primarily screening the silicon greases with the mass change rate of the silicon rubber sample within 3%; testing the broadband dielectric spectrum of the screened silicone grease, and screening out the silicone grease with the relative dielectric constant larger than 4 under the power frequency of 50 Hz; testing the broadband dielectric spectrum of the silicone rubber sample coated with the selected silicone grease before and after being wetted, and screening out the silicone grease with the change rate of the relative dielectric constant of the silicone rubber sample exceeding 10%; carrying out a high-temperature accelerated aging test on the silicone rubber sample coated with the model-selecting silicone grease, and screening out the silicone grease with obvious drying, hardening and crack marks on the surface; and measuring the elongation at break and the tensile strength of the silicone rubber sample coated with the selected silicone grease after corona aging, and screening out the silicone grease corresponding to the silicone rubber sample with the elongation at break higher than 400% and the tensile strength higher than 4 MPa. The method is simple and easy to implement, and is convenient for screening various silicone greases at the same time.

Description

Model selection method of high-swelling-resistance silicone grease for cable and accessory interface
Technical Field
The invention belongs to the technical field of cable accessory installation, and particularly relates to a model selection method of silicone grease with high swelling resistance of a cable and accessory interface.
Background
The cable comprises a cable body and accessories thereof, and the cable accessories play an important role in connection and transition. Because the insulation structure at the accessory is complex, the double-layer composite interface between the silicon rubber for the cable joint and the crosslinked polyethylene of the cable body is a weak insulation link of the cable accessory. In the actual operation process of the cable, the accessories are often affected by electricity, heat, humid environment and the like, and the aging of the silicon rubber material can be accelerated under more complicated environmental conditions. In the actual installation of the cable accessories, the interface of the accessories is coated with silicone grease in consideration of improving the tightness of the interface and the lubrication degree of the accessories, and meanwhile, the electrical insulation performance of the interface of the accessories is improved.
The existing research shows that silicone grease can generate a swelling effect on silicone rubber, small molecules of the silicone grease can enter the silicone rubber to destroy the cross-linking structure of the silicone rubber, so that the mechanical property and the dielectric property of the silicone rubber are influenced, but a type selection method of the silicone grease with high swelling resistance on an interface between a cable and an accessory is not provided at present.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a method for selecting silicone grease with high swelling resistance at an interface between a cable and an accessory, wherein the selected silicone grease can ensure the long-term reliable operation of the accessory.
In order to achieve the purpose, the invention has the following technical scheme:
a type selection method of high swelling resistance silicone grease for a cable and accessory interface comprises the following steps:
soaking the silicon rubber sample in different silicone greases, and primarily screening the silicone greases with the mass change rate of the silicon rubber sample within 3% by adopting a soaking-weighing method;
testing the broadband dielectric spectrum of the preliminarily screened silicone grease, and screening out the silicone grease with the relative dielectric constant larger than 4 under the power frequency of 50 Hz;
testing the broadband dielectric spectrum of the silicone rubber sample coated with the selected silicone grease before and after being wetted, and screening out the silicone grease with the relative dielectric constant change rate of the silicone rubber sample exceeding 10%;
carrying out a high-temperature accelerated aging test on the silicone rubber sample coated with the model-selecting silicone grease, and screening out the silicone grease with obvious drying, hardening and crack marks on the surface;
and measuring the elongation at break and the tensile strength of the silicone rubber sample coated with the selected silicone grease after corona aging, and screening out the silicone grease corresponding to the silicone rubber sample with the elongation at break higher than 400% and the tensile strength higher than 4 MPa.
Preferably, the preliminary screening of the silicone grease with the mass change rate of the silicone rubber sample within 3% by adopting the dipping-weighing method comprises the following steps:
taking a plurality of crucibles with equal volumes, and respectively placing different silicone greases in the crucibles in equal amounts; cutting the silicon rubber sample into a plurality of square original sheets, wiping the surface of the silicon rubber sample with deionized water and absolute ethyl alcohol in sequence, drying the silicon rubber sample, placing the silicon rubber sample in a dry environment for cooling after completely volatilizing the moisture on the surface of the silicon rubber sample, measuring and recording the mass of the silicon rubber sample which is not coated with the silicon grease before swelling, and recording the initial mass of the sample as m 0 Completely immersing the sample in different types of silicone grease respectively;
respectively drying the crucibles at a set temperature, taking out samples at set time intervals, cleaning silicone grease on the surfaces of the samples by using a carbon tetrachloride solution, and then drying the samples in a thermostat at 50 ℃ to ensure that no carbon tetrachloride remains on the surfaces of the samples; measuring the mass m of the sample after it has cooled t Then, the sample is immersed in the silicone grease again, the test is repeated until the mass change rate of the silicone rubber sample is lower than 2%, and the mass increase change rate omega of the silicone rubber sample at the immersion time t is calculated according to the following formula:
Figure BDA0003880943620000021
and preliminarily screening out the silicone grease corresponding to the silicone rubber sample with the mass change rate within 3 percent.
As a preferred scheme, the testing of the broadband dielectric spectrum of the preliminarily screened silicone grease comprises the following steps:
coating the selected silicone grease on a silicone rubber sample, uniformly coating the silicone grease from the center to the outside of the silicone rubber sample by a ring-making mode of an absorbent cotton swab, and keeping the thickness of the coated silicone grease consistent in the coating process;
carrying out a humidity aging test on the silicone rubber sample coated with the selected silicone grease, and carrying out standing comparison on the silicone rubber sample at normal temperature;
the silicone grease on the surface of the silicone rubber sample is wiped off, the silicone rubber sample is subjected to metallization treatment, a liquid electrode is adopted for measurement when the dielectric spectrum of the type-selecting silicone grease is measured, and the silicone grease with the relative dielectric constant larger than 4 under the power frequency of 50Hz is not suitable for being used as a direct-current cable coating material.
Preferably, the thickness of the coating silicone grease is kept consistent by the following method: firstly, weighing the mass of the silicon rubber sample by using a precision analytical balance, and recording the mass as m 1 Then, the silicone grease is taken and placed on a silicone rubber sample, and the mass m of the sample at the moment is weighed 2 Control m 2 And m 1 The mass difference of (2) was 0.1g.
As a preferable scheme, the step of performing a moisture aging test on the silicone rubber sample coated with the type-selection silicone grease, and the step of performing a normal-temperature standing control on the silicone rubber sample specifically comprise: placing the silicon rubber sample coated with the selected silicone grease in an environment with the relative humidity of 100% at 25 ℃ for aging for 10 days; and the control of standing at normal temperature is that the silicone rubber sample coated with the selected silicone grease is placed in an environment with the temperature of 25 ℃ and the relative humidity of 30% for 10 days.
As a preferable scheme, when the silicone rubber sample coated with the selective silicone grease is subjected to the high-temperature accelerated aging test, the silicone rubber sample coated with the selective silicone grease is placed in an environment at 120 ℃ for high-temperature accelerated aging for a set number of days; and observing the surface conditions of the silicone rubber sample which is just coated with the selective silicone grease and the surface conditions of the silicone rubber sample after high-temperature accelerated aging under the condition of magnifying by 100 times by using a polarizing microscope, carrying out comparative analysis, and finding out the silicone grease corresponding to the obvious drying, hardening and crack marks on the surface of the silicone rubber sample for screening.
As a preferred embodiment, the measurement of the elongation at break and tensile strength of the silicone rubber sample coated with the silicone grease after corona aging comprises the steps of:
coating the selected silicone grease on a silicone rubber sample, specifically, uniformly coating the silicone grease from the center to the outside of the silicone rubber sample in a mode of looping by using an absorbent cotton swab, wherein the thickness of the coated silicone grease is kept consistent in the coating process; applying corona discharge effect on silicone rubber samples of different types of silicone grease through a corona aging test device, wherein the corona aging time is 30 days;
wiping off silicone grease coated on the surface of the silicone rubber sample after corona aging, cutting the silicone rubber sample into a standard dumbbell shape, performing a mechanical stretching experiment on different silicone rubber samples by adopting a mechanical stretching machine, wherein the stretching speed is 200mm/min, and each group retains a plurality of effective data, and after obtaining an average value, taking the average value as effective data of different aging forms and different silicone grease coatings.
Preferably, the thickness of the coating silicone grease is kept consistent by the following method: firstly, weighing the mass of the silicon rubber sample by using a precision analytical balance, and recording the mass as m 1 Then, the silicone grease is taken and placed on a silicone rubber sample, and the mass m of the sample is weighed 2 Control m 2 And m 1 The mass difference of (2 g).
As a preferred scheme, the corona aging test device comprises an aluminum plate and a glass plate which are arranged in parallel, wherein the aluminum plate and the glass plate are supported by an epoxy support column, and a high-voltage copper electrode is placed on the glass plate; the aluminum plate is grounded, the high-voltage copper electrode is connected with the high-voltage end, and the silicon rubber sample coated with the selective silicone grease is placed on the aluminum plate.
Compared with the prior art, the invention has the following beneficial effects:
common silicone grease and silicone rubber both have a siloxane bond as a main chain and a large amount of Si (CH) on a side chain 3 ) 2 、Si(CH 3 ) 3 The molecular structure of the group, silicone grease and silicone rubber are similar in structure and easy to be subjected to similar intermiscibility, micromolecular silicone grease as solvent molecules enters a silicone rubber polymer chain through the permeation effect to be subjected to swelling, and the swelling effect of the silicone grease is greatly damagedThe cross-linking structure of the silicon rubber is adopted, so the selection of the interface coating material firstly ensures that the anti-swelling effect of the silicon grease is good, and the silicon grease which ensures that the mass change rate of the silicon rubber sample is within 3 percent is preliminarily screened by adopting a dipping-weighing method. Silicone grease having a relative dielectric constant greater than 4 at a power frequency of 50Hz is not suitable for use as a coating material for dc cables because the relative dielectric constant reflects the polarization ability of the dielectric material, and the higher the relative dielectric constant, the stronger the ability to bind charges. Under the direct current working condition, the silicone grease with high dielectric constant is easier to accumulate charges on the interface, and the problems of insulation failure, partial discharge and the like are easily induced for a long time; the relative dielectric constant of water is far higher than that of silicon rubber and silicone grease, and by testing the broadband dielectric spectrum of the silicon rubber coated with the selected silicone grease before and after being wetted, if the change rate of the relative dielectric constant of the silicon rubber exceeds 10%, the corresponding silicone grease has extremely strong water absorption, and the risk of interface breakdown is aggravated by water intrusion, so that the corresponding coated silicone grease is not suitable for a moist operating environment of an accessory. The silicon rubber sample coated with the selected silicone grease is subjected to a high-temperature accelerated aging test, if the surface of the sample is found to have obvious drying, hardening and crack traces, the corresponding coated silicone grease loses due lubricity, so that the interface roughness is greatly increased, the risk of mechanical abrasion of accessories is increased, and the corresponding coated silicone grease is not suitable for the high-temperature operation environment of the accessories. In order to explore the influence of coating different silicone greases on the mechanical properties of the silicone rubber after long-term corona aging, the elongation at break and the tensile strength of a silicone rubber sample coated with the selected silicone grease after corona aging are measured, and the silicone grease corresponding to the silicone rubber sample with the elongation at break higher than 400% and the tensile strength higher than 4MPa is screened out. The experiment related by the invention is simple and easy to implement, is convenient for carrying out screening work of various silicone greases at the same time, can carry out targeted screening according to different actual environments of operation of the cable accessories, ensures that the screened silicone greases are slightly influenced by performance degradation brought by accessory interface environments in engineering use, and provides service for long-term operation of the cable accessories.
Drawings
FIG. 1 is a flow chart of a method for selecting a silicone grease with high swelling resistance for an interface between a cable and an accessory according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a corona aging test device according to an embodiment of the invention;
FIG. 3 is a graph showing the mass change rate of silicone rubber impregnated with different silicone greases according to an embodiment of the present invention;
FIG. 4 is a broad band dielectric spectrum of a silicone grease of an embodiment of the present invention;
FIG. 5 (a) a broadband dielectric spectrum of a silicone rubber sample coated with selected silicone grease by standing at normal temperature in an embodiment of the present invention;
FIG. 5 (b) is a broadband dielectric spectrum of a silicone rubber sample coated with a silicone grease of an embodiment of the present invention after exposure to moisture;
FIG. 6 (a) a graph of the high temperature accelerated aging surface of a silicone rubber sample freshly coated with silicone grease No. 0 according to an example of the present invention;
FIG. 6 (b) is a surface view of a silicone rubber sample coated with silicone grease No. 0 according to an example of the present invention after aging at high temperature for 240 h;
FIG. 7 (a) a graph of the high temperature accelerated aging surface of a silicone rubber sample of an example of the present invention freshly coated with No. 3 silicone grease;
FIG. 7 (b) is a surface view of a silicone rubber sample coated with silicone grease No. 3 according to an example of the present invention after aging at high temperature for 240 h;
FIG. 8 (a) is a graph of the high temperature accelerated aging surface of a silicone rubber sample freshly coated with silicone grease No. 8 according to an example of the present invention;
FIG. 8 (b) is a surface view of a silicone rubber sample coated with silicone grease No. 8 according to an example of the present invention after aging at high temperature for 240 h;
FIG. 9 (a) elongation at break plot of silicone rubber samples coated with select silicone greases;
FIG. 9 (b) tensile Strength Profile of silicone rubber samples coated with select silicones.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Referring to fig. 1, a method for selecting a silicone grease with high swelling resistance for a cable and accessory interface according to an embodiment of the present invention includes the following steps:
the method comprises the following steps: soaking and weighing the silicon rubber sample in different silicone greases, primarily screening the silicone greases with the mass change rate of the silicon rubber sample within 3%, and screening the rest silicone greases.
Step two: when the broadband dielectric spectrum of the selected silicone grease is tested, the silicone grease with the relative dielectric constant larger than 4 under the power frequency of 50Hz is not suitable for being used as a coating material for a direct-current cable.
Step three: and testing the broadband dielectric spectrum of the silicone rubber coated with the selected silicone grease before and after being wetted, wherein if the change rate of the relative dielectric constant of the silicone rubber exceeds 10%, the corresponding coated silicone grease is not suitable for the wet operation environment of the accessory.
Step four: and (3) carrying out a high-temperature 120 ℃ accelerated aging test on the silicone rubber coated with the selected silicone grease, and observing the surface of the silicone rubber by using a polarizing microscope, wherein if the silicone grease is obviously dried, hardened and cracked, the corresponding coated silicone grease is not suitable for the high-temperature operation environment of accessories.
Step five: and measuring the elongation at break and the tensile strength of the silicone rubber sample coated with the selected silicone grease after the corona aging for 30 days, and screening out the silicone grease corresponding to the silicone rubber sample with the elongation at break higher than 400% and the tensile strength higher than 4MPa, wherein the silicone grease can ensure the long-term reliable operation of the accessory.
In a possible embodiment, the dipping-weighing method of the first step is as follows:
in order to obtain the quality change of the silicon rubber samples before and after different silicone greases are coated, a plurality of arc-shaped corundum crucibles with the volume of 10ml are arranged in the experiment, and different silicone greases are respectively placed in the crucibles in equal amount. Cutting a silicon rubber sample into a plurality of square original sheets with the side length of 20mm by using a cutter, wiping the surface of the silicon rubber sample by using deionized water and absolute ethyl alcohol in sequence, placing the silicon rubber sample in an electrothermal blowing dry box at 90 ℃ for drying, taking out the silicon rubber sample after completely volatilizing the moisture on the surface of the silicon rubber sample, placing the silicon rubber sample in a dry environment for cooling for 6 hours, measuring and recording the mass of the silicon rubber which is not coated with the silicone grease before swelling by using an electronic balance, and recording the initial mass m of the sample 0 The samples were immersed in different types of silicone grease, respectively, and were ensured to be completely immersed.
The long-term running temperature of the insulated crosslinked polyethylene of the cable body is generally not more than 90 ℃, and the test temperature is set to be 90 ℃ in the experiment; placing the crucibles in electrothermal blowing dry boxes with set temperature respectively, and taking out samples every 48hAfter the silicone grease on the surface of the sample is cleaned by a carbon tetrachloride solution, the sample is placed in a thermostat at 50 ℃ for drying for 6 hours, so that the surface of the sample is ensured to have no carbon tetrachloride residue; measuring the mass m of the sample after it has cooled t Then, the sample is dipped into the silicone grease again, and the test is repeated until the mass change rate of the silicone rubber is lower than 2 percent, so that the mass growth change rate omega of the silicone rubber sample at the dipping time t is obtained as follows:
Figure BDA0003880943620000071
and preliminarily screening out the silicone grease corresponding to the silicone rubber sample with the mass change rate within 3 percent. Common silicone grease and silicone rubber both have a siloxane bond as a main chain and a large amount of Si (CH) on a side chain 3 ) 2 、Si(CH 3 ) 3 The molecular structure of the group, silicone grease and silicone rubber are similar in structure and easy to be subjected to similar intermiscibility, micromolecule silicone grease as a solvent molecule enters a silicone rubber polymer chain under the permeation action to be subjected to swelling, and the silicone grease swelling action greatly destroys the cross-linking structure of the silicone rubber, so that the selection of the interface coating material firstly ensures that the anti-swelling effect of the silicone grease is good.
In a possible embodiment, the testing method of the broadband dielectric spectrum in the second step includes:
the broadband dielectric spectrum test system can be used for accurately measuring the dielectric constant of the insulating material under different frequencies, and the test system is used for measuring different silicone greases and silicone rubber sample wafers coated with different silicone greases before and after humid aging under the room temperature condition (25 ℃), and the frequency range is set to be 0.1-106 Hz.
Selecting a plurality of square silicon rubber sample sheets with the side length of 100mm and the thickness of 0.2mm, coating the selected silicon rubber with the type silicon grease, and uniformly coating the silicon grease from the center to the outside of the sample by adopting a degreasing cotton swab looping mode. In the coating process, the thickness of the coated silicone grease needs to be ensured to be basically consistent so as to reduce the influence of the thickness of the silicone grease on the experimental result. The density difference of the silicone grease used in the test is not great, and in order to ensure the consistency of the thickness of the silicone grease, the silicone rubber is weighed by using a precision analytical balanceMass of the sample, recorded as m 1 Then, a small amount of silicone grease is selected by a cotton swab and placed on a silicone rubber sample, and the mass m of the silicone rubber sample is weighed 2 Control m 2 And m 1 The mass difference of (A) is about 0.1g.
Setting a humidity aging test, and aging the silicon rubber sample coated with the selected silicone grease in a constant-temperature constant-humidity oven with the relative humidity of 100% at 25 ℃ for 10 days; setting a normal temperature standing control, and placing the silicon rubber sample coated with the selected silicone grease in a room temperature environment (the temperature is 25 ℃, and the relative humidity is 30%) for 10 days.
Before testing, the silicone grease on the surface of the silicone rubber sample needs to be wiped off, the silicone rubber sample is subjected to metallization treatment, and a metal film is formed on the surface of the sample by adopting a metal spraying method so as to ensure that the electrode is reliably contacted with the sample wafer as far as possible and reduce errors. Because the shape of the silicone grease is close to that of liquid, a liquid electrode is adopted for measurement when the dielectric spectrum of the selected silicone grease is measured, the liquid electrode is composed of a metal tray, an upper electrode, a lower electrode, a gasket and a quartz rod, wherein the quartz rod is placed between the two electrodes to play a role of supporting the electrodes, when the liquid electrode is used, a burette is used for adding liquid until the quartz rod is completely covered by the silicone grease, finally, the upper electrode and the lower electrode are well pressed, and the electrodes are placed in test notches corresponding to a broadband dielectric spectrometer for testing.
Silicone grease having a relative dielectric constant greater than 4 at a power frequency of 50Hz is not suitable for use as a coating material for dc cables because the relative dielectric constant reflects the polarization ability of the dielectric material, and is higher, the stronger the ability to bind charges. Under the direct current working condition, the silicone grease with high dielectric constant is easier to accumulate charges on the interface, and the problems of insulation failure, partial discharge and the like are easily induced for a long time; the relative dielectric constant of water is far higher than that of silicon rubber and silicone grease, and by testing the broadband dielectric spectrum of the silicon rubber coated with the type-selection silicone grease before and after being wetted, if the change rate of the relative dielectric constant of the silicon rubber exceeds 10%, the corresponding silicone grease has extremely strong water absorption, and the risk of interface breakdown is aggravated by water invasion, so that the corresponding coated silicone grease is not suitable for the wet operation environment of accessories.
In one possible embodiment, the method for performing the high temperature 120 ℃ accelerated aging test in step four is as follows:
and (3) placing the silicon rubber sample coated with the selected silicone grease in an electrothermal blowing dry box at 120 ℃, and carrying out high-temperature accelerated aging for 10 days. The surface of the silicone rubber sample immediately after coating and aging for 10 days was observed under a magnification of 100 times using a polarization microscope, and comparative analysis was performed. If the surface of the silicon rubber sample is obviously dry, hard and cracked, the corresponding coating silicone grease loses due lubricity, so that the interface roughness is greatly increased, and the risk of mechanical abrasion of accessories is increased, so that the corresponding coating silicone grease is not suitable for the high-temperature operation environment of the accessories.
In one possible embodiment, the method of measuring elongation at break and tensile strength in step five is as follows:
selecting a plurality of square silicon rubber sample sheets with the side length of 100mm and the thickness of 2mm, and uniformly coating the silicon rubber from the center to the outside of the silicon rubber sample sheets by adopting a mode of making circles with absorbent cotton swabs for the silicon rubber sample sheets coated with the type silicon rubber. In order to ensure the consistency of the thickness of the silicone grease, the mass of the silicone rubber sample is weighed by using a precision analytical balance and is recorded as m 1 Then, a small amount of silicone grease is selected by a cotton swab and placed on a silicone rubber sample, and the mass m of the sample at the moment is weighed 2 Control m 2 And m 1 The mass difference of (2) is about 2g.
The built corona aging test device is shown in fig. 2, and comprises an aluminum plate 1 and a glass plate 2 which are arranged in parallel, wherein the aluminum plate 1 and the glass plate 2 are supported by an epoxy support 3, and a high-voltage copper electrode 4 is placed on the glass plate 2; aluminum plate 1 ground connection, high-voltage copper electrode 4 connect the high-pressure end, and the silicon rubber sample that the coating has the lectotype silicone grease is placed on aluminum plate 1. In the experiment, 15kV power frequency alternating current voltage is applied to enable air to generate corona discharge. The silicon rubber samples coated with different types of silicone grease are placed between copper parallel plate electrodes, the silicon rubber samples are subjected to corona discharge, and the corona aging time is 30 days.
In order to research the influence of coating different silicone greases on the mechanical properties of a silicone rubber sample after long-term corona aging, the silicone greases coated on the surface of the silicone rubber sample after corona aging are wiped off according to the national standard GB13022-1991, and the silicone rubber sample is cut into a standard dumbbell shape. And (3) carrying out mechanical stretching experiments on different samples by adopting a mechanical stretching machine, wherein the used stretching speed is 200mm/min, at least seven effective data are reserved in each group, and the average value is obtained and then used as the effective data of different aging forms and different coating silicone grease. The most important mechanical performance indexes of the materials adopted in the experiment are as follows: and the silicone grease corresponding to the silicone rubber sample with the elongation at break higher than 400% and the tensile strength higher than 4MPa is screened out from the tensile strength and the elongation at break, and the silicone grease can ensure the long-term reliable operation of the accessory.
The present invention will be described in further detail below by taking nine kinds of silicone insulators commonly used for mounting accessories collected by a cable accessory factory as an example.
Nine kinds of silicone insulators commonly used for mounting accessories collected by a cable accessory factory are numbered as silicone grease 0 to silicone grease 8.
1. Measuring the mass change of the silicon rubber sample after swelling action of different silicon greases;
and measuring the mass change rate of different silicone grease soaked silicone rubber samples according to a dipping-weighing method. As is clear from FIG. 3, the silicone grease in which the rate of change in mass of the silicone rubber sample is within 3% is 0,3,8. The rest silicone grease is screened out.
2. Measuring the relative dielectric constant of the selected silicone grease;
the relative dielectric constant of the selected silicone grease 0,3,8 was tested according to the test method for liquids in the broad-band dielectric spectrum. As shown in FIG. 4, the silicone grease with the relative dielectric constant greater than 4 at the power frequency of 50Hz is No. 8 silicone grease, and the silicone grease is not suitable for coating the DC cable.
3. Measuring the relative dielectric constant of the silicone rubber coated with the selected silicone grease at normal temperature and after being wetted;
according to the test method of the silicone rubber sample in the broadband dielectric spectrum, as shown in fig. 5 (a) and 5 (b), after being wetted, the change rate of the relative dielectric constant of the silicone rubber sample coated with the No. 3 silicone grease is more than 10%, and the silicone grease is not suitable for the wet environment of accessories.
4. High-temperature accelerated aging observation;
the test was carried out according to the high temperature accelerated ageing method: the surface of the silicone rubber sample just coated with silicone grease No. 0,3,8 and the surface of the silicone rubber sample after aging for 10 days were observed under a magnification of 100 times using a polarization microscope. As shown in fig. 6 (a) and 6 (b), fig. 7 (a) and 7 (b), and fig. 8 (a) and 8 (b), it can be seen that the surface of the sample coated with silicone grease No. 8 has a distinct crack after aging at high temperature, and it is visible to the naked eye that the silicone grease is completely dried and hardened, and part of the silicone rubber is exposed. Therefore, the No. 8 silicone grease is not suitable for the high-temperature operation environment of accessories.
5. Measuring the elongation at break and the tensile strength of the silicon rubber sample coated with the type-selection silicone grease after 30 days of corona aging;
and (3) performing mechanical tensile test after corona aging on the silicone rubber samples coated with the No. 0,3 and 8 silicone greases according to a mechanical performance test method, and setting a normal-temperature group for comparison. As shown in fig. 9 (a) and 9 (b), after corona aging, the elongation at break of the silicone rubber samples coated with the silicone greases No. 3 and No. 8 is higher than 400%, and the tensile strength is higher than 4MPa, which can ensure long-term reliable operation of the accessories.
The above-mentioned embodiments are only used to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present application and are intended to be included within the scope of the present application.

Claims (9)

1. A type selection method for high swelling resistance silicone grease at an interface of a cable and an accessory is characterized by comprising the following steps:
soaking the silicon rubber sample in different silicon greases, and preliminarily screening the silicon greases with the mass change rate of the silicon rubber sample within 3% by adopting a soaking-weighing method;
testing the broadband dielectric spectrum of the preliminarily screened silicone grease, and screening out the silicone grease with the relative dielectric constant larger than 4 under the power frequency of 50 Hz;
testing the broadband dielectric spectrum of the silicone rubber sample coated with the selected silicone grease before and after being wetted, and screening out the silicone grease with the change rate of the relative dielectric constant of the silicone rubber sample exceeding 10%;
carrying out a high-temperature accelerated aging test on the silicone rubber sample coated with the model-selecting silicone grease, and screening out the silicone grease with obvious drying, hardening and crack marks on the surface;
and measuring the elongation at break and the tensile strength of the silicon rubber sample coated with the selected silicone grease after corona aging, and screening out the silicone grease corresponding to the silicon rubber sample with the elongation at break higher than 400% and the tensile strength higher than 4 MPa.
2. The method for selecting the silicone grease with high swelling resistance at the interface between the cable and the accessory according to claim 1, wherein the preliminary screening of the silicone grease with the mass change rate of the silicone rubber sample within 3% by adopting a dipping-weighing method comprises the following steps:
taking a plurality of crucibles with equal volumes, and respectively placing different silicone greases in the crucibles with equal volumes; cutting a silicon rubber sample into a plurality of square original sheets, wiping the surface of the silicon rubber sample by using deionized water and absolute ethyl alcohol in sequence, drying the silicon rubber sample, placing the silicon rubber sample in a dry environment for cooling after completely volatilizing the moisture on the surface of the silicon rubber sample, measuring and recording the quality of the silicon rubber sample which is not coated with the silicon grease before swelling, and recording the initial mass of the sample as m 0 Completely immersing the sample in different types of silicone grease respectively;
respectively drying the crucibles at a set temperature, taking out samples at set time intervals, cleaning silicone grease on the surfaces of the samples by using a carbon tetrachloride solution, and then drying the samples in a thermostat at 50 ℃ to ensure that no carbon tetrachloride remains on the surfaces of the samples; measuring the mass m of the sample after it has cooled t Then, the sample is immersed in the silicone grease again, the test is repeated until the mass change rate of the silicone rubber sample is lower than 2%, and the mass increase change rate omega at the immersion time t of the silicone rubber sample is calculated according to the following formula:
Figure FDA0003880943610000011
and preliminarily screening out the silicone grease corresponding to the silicone rubber sample with the mass change rate within 3%.
3. The method of claim 1, wherein the step of testing the broadband dielectric spectrum of the preliminarily selected silicone grease comprises the steps of:
coating the selected silicone grease on a silicone rubber sample, uniformly coating the silicone grease from the center to the outside of the silicone rubber sample by a ring-making mode of an absorbent cotton swab, and keeping the thickness of the coated silicone grease consistent in the coating process;
carrying out a humidity aging test on the silicon rubber sample coated with the selected silicone grease, and carrying out a normal-temperature standing comparison on the silicon rubber sample;
the silicone grease on the surface of the silicone rubber sample is wiped off, the silicone rubber sample is subjected to metallization treatment, a liquid electrode is adopted for measurement when the dielectric spectrum of the type-selecting silicone grease is measured, and the silicone grease with the relative dielectric constant larger than 4 under the power frequency of 50Hz is not suitable for being used as a direct-current cable coating material.
4. A method for selecting a silicone grease with high swelling resistance at the interface of cable and accessories as claimed in claim 3, wherein the thickness of the coating silicone grease is kept consistent by the following method: firstly, weighing the mass m of the silicon rubber sample by using a precision analytical balance 1 Then, the silicone grease is taken and placed on a silicone rubber sample, and the mass m of the sample at the moment is weighed 2 Control m 2 And m 1 The mass difference of (2) was 0.1g.
5. The method for selecting the silicone grease with high swelling resistance at the interface of the cable and the accessory according to claim 3, wherein the step of performing a humid aging test on the silicone rubber sample coated with the selected silicone grease and the step of performing a normal-temperature standing control on the silicone rubber sample are as follows: placing the silicon rubber sample coated with the type selection silicone grease in an environment with the relative humidity of 100% at 25 ℃ for aging for 10 days; and standing at normal temperature for comparison, namely, placing the silicon rubber sample coated with the selected silicone grease in an environment with the temperature of 25 ℃ and the relative humidity of 30% for 10 days.
6. The method for selecting the silicone grease with high swelling resistance at the interface between the cable and the accessory according to claim 1, wherein when the silicone rubber sample coated with the selected silicone grease is subjected to the high-temperature accelerated aging test, the silicone rubber sample coated with the selected silicone grease is placed in an environment at 120 ℃ for high-temperature accelerated aging for a set number of days; and observing the surface conditions of the silicone rubber sample which is just coated with the selective silicone grease and the surface conditions of the silicone rubber sample after high-temperature accelerated aging under the condition of magnifying by 100 times by using a polarizing microscope, carrying out comparative analysis, and finding out the silicone grease corresponding to the obvious drying, hardening and crack marks on the surface of the silicone rubber sample for screening.
7. The method for selecting the silicone grease with high swelling resistance at the interface of the cable and the accessory according to claim 1, wherein the step of measuring the elongation at break and the tensile strength of the silicone rubber sample coated with the selected silicone grease after corona aging comprises the following steps:
coating the selected silicone grease on a silicone rubber sample, specifically, uniformly coating the silicone grease from the center to the outside of the silicone rubber sample in a manner of looping by using an absorbent cotton swab, wherein the thickness of the coated silicone grease is kept consistent in the coating process; applying corona discharge effect on silicone rubber samples of different types of silicone grease through a corona aging test device, wherein the corona aging time is 30 days;
wiping off silicone grease coated on the surface of the silicone rubber sample after corona aging, cutting the silicone rubber sample into a standard dumbbell shape, performing a mechanical stretching experiment on different silicone rubber samples by adopting a mechanical stretching machine, wherein the stretching speed is 200mm/min, and each group retains a plurality of effective data, and after obtaining an average value, taking the average value as effective data of different aging forms and different silicone grease coatings.
8. A method for selecting a silicone grease with high swelling resistance at the interface of cable and accessories as claimed in claim 7, wherein the thickness of the coating silicone grease is kept consistent by the following method: firstly, the silicon rubber is weighed by a precision analytical balanceMass of sample, denoted m 1 Then, the silicone grease is taken and placed on a silicone rubber sample, and the mass m of the sample is weighed 2 Control m 2 And m 1 The mass difference of (2 g).
9. The type selection method of the silicone grease with high swelling resistance at the interface of the cable and the accessory according to claim 7, characterized in that the corona aging test device comprises an aluminum plate (1) and a glass plate (2) which are arranged in parallel, wherein the aluminum plate (1) and the glass plate (2) are supported by an epoxy support column (3), and a high-voltage copper electrode (4) is placed on the glass plate (2); aluminum plate (1) ground connection, high-voltage copper electrode (4) are connected the high-pressure end, the silicon rubber sample that the coating has the lectotype silicone grease is placed on aluminum plate (1).
CN202211228322.2A 2022-10-09 2022-10-09 Model selection method of high-swelling-resistance silicone grease for cable and accessory interface Pending CN115586099A (en)

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