Method for testing and evaluating the hydrophobicity of a pollution flashover resistant silicone rubber insulating coating

Abstract

The application provides a method for testing and evaluating hydrophobicity and hydrophobicity migration of anti-pollution flashover silicone rubber insulation coating, and a testing method, which comprises the following steps: obtaining pollution of silicone rubber insulation coating; pretreating the pollution, loading the pollution into a sample tube to form a sample column; connecting the sample tube with an upper container and a lower air pressure tube after sealing the sample tube; injecting water into the container, and recording the penetration depth of the water into the sample column l or air pressure difference p , and calculating the slope k ; using a reference solvent to obtain the slope k 0; and obtaining the contact angle. By using the method, the hydrophobicity of actual pollution generated during operation of the silicone rubber insulation coating is verified, and good results are obtained. The method can be applied to testing of hydrophobicity and hydrophobicity migration of the insulation coating, thereby providing a universal and accurate testing method.

Description

Technical Field

[0001] This invention belongs to the technical field of hydrophobic migration testing of insulating coatings in the power industry, and in particular, it is a method for testing and evaluating the hydrophobic migration of anti-pollution flashover silicone rubber insulating coatings. Background Technology

[0002] Insulating coatings play a crucial role in the electrical protection of power transmission and supply systems. Complex natural environments and climates, such as high and low temperatures, rain and snow, fog and haze, and ultraviolet radiation, can severely affect the electrical and service performance of insulating coatings. Room temperature vulcanizing (RTV) silicone rubber coatings with hydrophobic migration properties can improve the flashover voltage of power systems and are therefore widely used in insulator protection and ensuring the safe operation of power grids.

[0003] Excellent hydrophobicity and hydrophobic migration are key indicators for evaluating silicone rubber insulating coatings. Traditional methods for evaluating the hydrophobicity of silicone rubber insulating coatings (GB / T19519-2014) involve applying simulated contaminants (diatomaceous earth, SiO2, NaCl, etc.) to the experimental coating surface or actual contaminants to the insulator coating surface, then measuring the static contact angle of the contaminated coating; or performing apparent hydrophobicity grading by spraying multiple samples with water multiple times (DL / T 627-2018). While these methods are widely used, the experimental results depend on the coating surface, the condition of the contaminant application, and the operator's skill, resulting in low accuracy and repeatability. Invention patent CN105067761 B discloses a method for testing the hydrophobic migration of coatings by immersing contaminants in distilled water, recording the complete settling time of different contaminants, and establishing a correlation with hydrophobicity grading through numerous experiments. While this method is simple, it lacks theoretical basis. In reality, contaminant settling time is related to contaminant particle size, hydrophobicity, and dispersibility, which this method does not consider. Invention patent CN101398365A, based on the capillary penetration phenomenon, designed a method for measuring the contact angle of powders. However, this method is only applicable to hydrophilic particles with a contact angle <90°. For silicone rubber insulating coatings, due to hydrophobic migration, the surface contaminants are generally hydrophobic powders, and the sources and compositions of these powders are very complex. How to accurately measure the contact angle of these complex, hydrophobic powders is a scientific and technological problem that urgently needs to be solved. Summary of the Invention

[0004] This invention, based on the capillary repulsion of hydrophobic particles on liquids, presents a novel method for measuring the contact angle of hydrophobic particles and thus evaluating their hydrophobic migration properties. This method was successfully applied to verify the hydrophobicity of actual contamination generated during the operation of silicone rubber insulating coatings. This method holds promise for testing the hydrophobicity of insulating coating contamination and the hydrophobic migration properties of coatings, thus providing a universal and accurate testing method.

[0005] To achieve the above-mentioned technical objectives, the present invention provides the following technical solution:

[0006] A method for testing the water repellency of a silicone rubber insulating coating, comprising the following steps:

[0007] Step 1: Obtain dirt that accurately represents the condition of the silicone rubber insulating coating, either on-site or in a laboratory.

[0008] Step 2: In the laboratory, the contaminant obtained in Step 1 is pretreated to remove larger particles, and a quantitative amount of contaminant is weighed, loaded into a sample tube and compressed to form a sample column.

[0009] Step 3: After sealing the sample tube from Step 2 with sealing material, connect it to the upper container and the lower pressure tube.

[0010] Step 4: Pour water into the container from Step 3 and stabilize the liquid level; under water pressure, the water in the container seeps into the sample column. Due to the hydrophobic nature of the sample, the water penetrates to a certain depth. l Stop the permeation. Start timing from when water has penetrated 1 mm into the sample column, and record the penetration depth at regular intervals. l Or air pressure difference △ p With △ p 2 For the ordinate, t Plot the measured data on the x-axis, perform linear fitting, and calculate the slope. k .

[0011] Step 5: Repeat steps 2-4, using the reference solvent in step 4. Replace water to obtain the slope. k 0.

[0012] Step 6: Using the Washburn formula (GB / T 36086-2018), determine the contact angle of the powder with water. .in, These are the surface tension and molecular viscosity of water, respectively. These are the parameters for the powder column. ,in, These represent the surface tension and molecular viscosity of the reference solvent, respectively.

[0013] Furthermore, the pretreatment refers to the process whereby the contaminant is first passed through a 200-mesh sieve, then vacuum dried at 60-80°C for 2 hours, and finally placed in a desiccator for cooling and storage.

[0014] Furthermore, the sample tube refers to a glass tube with a diameter of 8-10 mm.

[0015] Furthermore, the sealing material used is hydrophilic filter paper or porous ceramic.

[0016] Furthermore, in step 4, water is poured into the container, and the liquid level is 20cm-30cm.

[0017] Furthermore, the reference solvent is a good solvent for silicone rubber, including petroleum ether, n-heptane, n-hexane, toluene, xylene, or tetrahydrofuran.

[0018] A method for evaluating the hydrophobic migration properties of silicone rubber insulating coatings includes the following steps:

[0019] Step 1: First, sample the coating contaminants whose hydrophobic migration properties are to be investigated. When the contaminant is thin, sample according to the observation time of hydrophobic migration; when the contaminant is thick, sample both the surface and deeper layers. This will obtain contaminant samples of the insulating coating generated at different times or locations.

[0020] Step 2: Using the above-invented test method for the hydrophobicity of coating dirt, determine the contact angle of the dirt sample collected in Step 1.

[0021] Step 3: Evaluate the hydrophobic migration behavior of the coating based on the contact angles of different contaminants measured in Step 2.

[0022] The advantages of this invention are: the test method is scientifically based, the test results have good reliability and repeatability; the test object can be either simulated coating contamination or actual contamination of power system insulation coatings; the contact angle of the test reflects the hydrophobicity and physicochemical properties of the contamination itself, and can shield the interference of the coating itself. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the testing method of the present invention;

[0024] In the diagram, 1 is the container, 2 is the liquid, 3 is the glass tube, 4 is the sealing material, 5 is the air pressure pipe, 6 is the liquid infiltration line, and 7 is the powder column. Detailed implementation method:

[0025] The present invention will be further described below with reference to embodiments.

[0026] The following is in conjunction with the appendix Figure 1 The feasibility of the technical solution of the present invention is illustrated through these embodiments, but the present invention is not limited to these embodiments.

[0027] Example 1:

[0028] A method for testing the hydrophobic migration properties of silicone rubber insulating materials includes the following steps:

[0029] Step 1: In the laboratory, collect 10g of a sample of a mixture of hydrophobic and migratory silicone rubber insulating coating contaminants, such as diatomaceous earth, SiO2, and salt.

[0030] Step 2: Pass the mixture sample from Step 1 through a 200-mesh sieve, then vacuum dry at 60℃ for 2 hours, and store it in a desiccator; take 5g of sample from the desiccator, fill it into a Φ8mm glass tube, and press it tightly.

[0031] Step 3: After sealing the sample tube from Step 2 with filter paper, connect it to the upper container and the lower pressure tube.

[0032] Step 4: Pour water into the container from Step 3 until the liquid level is stable above 20 cm; after the water has penetrated 1 mm into the sample column, record the pressure difference Δ every 10 seconds. p Make a triangle. p 2 - t Data graph, find k = 0.031×10 -4 Pa 2 / s.

[0033] Step 5: Repeat steps 2-4, replacing water with the reference solvent n-hexane, to obtain the slope. k 0 = 0.0605 × 10 -4 Pa 2 / s.

[0034] Step 6: Calculate the contact angle of the powder with water. This indicates that the hydrophobic properties of the insulating coating migrate to the contaminated surface, demonstrating that the coating exhibits good hydrophobic migration properties.

[0035] Example 2:

[0036] A method for testing the hydrophobic migration properties of silicone rubber insulating materials includes the following steps:

[0037] Step 1: At the power system site, collect 50g of dirt from the silicone rubber insulation coating after one year of use.

[0038] Step 2: Pass the mixture sample from Step 1 through a 200-mesh sieve, then vacuum dry it at 80℃ for 1 hour, and store it in a desiccator; take 6g of sample from the desiccator, fill it into a Φ10mm glass tube, and press it tightly.

[0039] Step 3: After sealing the sample tube from Step 2 with filter paper, connect it to the upper container and the lower pressure tube.

[0040] Step 4: Pour water into the container from Step 3 until the liquid level is stable above 20 cm; after the water has penetrated 1 mm into the sample column, record the pressure difference Δ every 5 seconds. p Make a triangle. p 2 - t Data graph, find k = 0.025×10 -4 Pa2 / s.

[0041] Step 5: Repeat steps 2-4, replacing water with xylene as the reference solvent, to obtain the slope. k 0 = 0.0862 × 10 -4 Pa 2 / s.

[0042] Step 6: Calculate the contact angle of the powder with water. =107.62°> 90°. This indicates that the insulating coating still has good hydrophobic migration properties after one year of operation.

[0043] Example 3:

[0044] A method for testing the hydrophobic migration properties of silicone rubber insulating materials includes the following steps:

[0045] Step 1: In the laboratory, collect 8 samples of silicone rubber insulating coating contamination at different migration times and label them as #1, #2, ..., #8.

[0046] Step 2: Using the test method of Example 1, the contact angles of the eight contaminated samples from Step 1 were measured. The results are summarized below:

[0047]

[0048] Step 3: Evaluate the hydrophobic migration behavior of the coating based on the contact angles of different contaminants measured in Step 2. The table above shows that after a migration time of 2 hours, small molecules inside the silicone rubber insulating coating migrate to the sample surface, completing the transformation from hydrophilic to hydrophobic. The coating exhibits good hydrophobicity and hydrophobic migration.

[0049] Example 4:

[0050] A method for evaluating the hydrophobic migration properties of silicone rubber insulating coatings includes the following steps:

[0051] Step 1: At the power system site, collect 10 samples of contamination from the silicone rubber insulation coating after one year of operation, and label them as #A1 / #A2, #B1 / #B2, #C1 / #C2, #D1 / #D2, and #E1 / #E2. A, B, C, D, and E represent 5 sampling points, and 1 / 2 indicates the upper / lower layer of contamination.

[0052] Step 2: Using the test method of Example 2, the contact angles of the 10 contaminated samples from Step 1 were measured. The results are summarized below:

[0053]

[0054] Step 3: Evaluate the hydrophobic migration behavior of the coating based on the contact angles of different contaminants measured in Step 2. The table above shows that after one year of field operation, the silicone rubber insulating coating maintains good hydrophobicity even under thick layers of contaminants. The average contact angle of the upper layer of the contaminant coating is 102.84°, and the average contact angle of the lower layer is 107.34°. This indicates that the hydrophobicity of the lower layer is higher than that of the upper layer, possibly because more small coating molecules migrate to the lower layer than to the upper layer, resulting in better hydrophobicity.

Claims

1. A method for testing the water repellency of a silicone rubber insulating coating, characterized in that, Includes the following steps: Step 1: Obtain dirt that accurately represents the condition of the silicone rubber insulating coating, either on-site or in a laboratory. Step 2: In the laboratory, the contaminant obtained in Step 1 is pretreated to remove larger particles, and a quantitative amount of contaminant is weighed, loaded into a sample tube and compacted to form a sample column. Step 3: After sealing the sample tube from Step 2 with sealing material, connect it to the upper container and the lower pressure tube; Step 4: Pour water into the container from Step 3 and stabilize the liquid level; under water pressure, the water in the container seeps into the sample column; due to the hydrophobic nature of the sample, the water penetrates to a certain depth. l Stop the infiltration; Timing begins when water penetrates 1 mm into the sample column; the penetration depth is recorded at regular intervals. l Or air pressure difference △ p ; with △ p 2 For the ordinate, t Plot the measured data on the x-axis, perform linear fitting, and calculate the slope. k ; Step 5: Repeat steps 2-4, replacing water with the reference solvent in step 4, to obtain the slope. k 0; Step 6: Using the Washburn equation, calculate the contact angle of the powder with water. ,in, , These are the surface tension and molecular viscosity of water, respectively. For powder column parameters; ,in, These represent the surface tension and molecular viscosity of the reference solvent, respectively.

2. The method for testing the water repellency of a silicone rubber insulating coating according to claim 1, characterized in that, The pretreatment refers to the process where the contaminant is first passed through a 200-mesh sieve, then vacuum dried at 60-80°C for 2 hours, and finally placed in a desiccator for cooling and storage.

3. The method for testing the water repellency of a silicone rubber insulating coating according to claim 1, characterized in that, The sample tube is a glass tube with a diameter of 8-10 mm.

4. The method for testing the water repellency of a silicone rubber insulating coating according to claim 1, characterized in that, The sealing material is hydrophilic filter paper or porous ceramic.

5. The method for testing the water repellency of a silicone rubber insulating coating according to claim 1, characterized in that, Fill the container with water until the liquid level is 20-30cm.

6. The method for testing the water repellency of a silicone rubber insulating coating according to claim 1, characterized in that, The reference solvent is selected from petroleum ether, n-heptane, n-hexane, toluene, xylene, or tetrahydrofuran.

7. A method for evaluating the hydrophobic migration properties of a silicone rubber insulating coating, characterized in that, Includes the following steps: Step 1: First, take samples of the coating dirt whose hydrophobic migration properties are to be investigated; Step 2: Using the test method for the hydrophobicity of the coating as described in any one of claims 1-6, determine the contact angle of the soiled sample collected in Step 1; Step 3: Evaluate the hydrophobic migration behavior of the coating based on the contact angles of different contaminants measured in Step 2.

8. The method for evaluating the hydrophobic migration properties of a silicone rubber insulating coating according to claim 7, characterized in that, When the contamination is thin, samples are taken according to the observation time of hydrophobic migration; when the contamination is thick, samples are taken according to the surface and deep layers of the contamination to obtain contamination samples generated by the insulating coating at different times or locations.

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