GB/T 2951.3-1997 General test methods for cable insulation and sheathing materials Part 1: General test methods Section 3: Density determination method - Water absorption test - Shrinkage test
Some standard content:
1 Scope National Standard of the People's Republic of China Common test methods for insulating and sheathing materials of electric cables Part 1: Methods for general application Section three: Methods for determining the density-Water absorption tests-Shrinkage test GB/T 2951.3—1997 IEC 811-1-3:1993 Replacing GB/T 2951.194 GR/T 2951.5—9
GB/T2951.19~2951.20--94
GH/T2951.29~2951.30—94
GB/T 2951.33—94
GB/T2951 standard specifies the test methods for polymer insulation and sheath materials of power distribution cables and communication cables, including marine cables.
GB/T2951.3 specifies the density determination method, water absorption test method and shrinkage test method. Applicable to the most commonly used insulation and sheath materials for wires and cables (elastomers, polyvinyl chloride, polyethylene, polyolefins, etc.) 1.1 References
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest version of the following standards. ISO1183+1987 Plastics - Density and relative density determination method of non-foamed plastics 2 Test principles
This standard does not specify the test conditions (such as temperature, duration, etc.) and all test requirements, which should be specified in the relevant cable product standards.
Any test requirements specified in this standard can be modified in the relevant cable standards to meet the needs of special types of cables. 3 Applicable range
The test conditions and test parameters specified in this standard are applicable to the most commonly used types of cables, wires and cords. 4 Type tests and other tests
The test methods specified in this standard are primarily used for type tests. The conditions for type tests and frequently performed tests (such as routine tests) for certain test items are essentially different. This standard has pointed out these differences. 5 Pretreatment
All tests should be carried out after the insulation and sheath materials have been stored for at least 16 hours after extrusion or vulcanization (or cross-linking). Approved by the State Administration of Technical Supervision on October 28, 1997 and implemented on October 1, 1998
CB/T 2951. 3—1997
If the test is conducted retrograde at quasi-ambient temperature, the specimen shall be stored at (23 ± 5)°C for at least 3h. 6 Test temperature
Unless otherwise specified, the test shall be conducted at ambient temperature. 7 Intermediate value
Arrange the test data obtained in ascending or descending order. If the number of valid data is an odd number, the intermediate value shall be the middle value. If it is an even number, the intermediate value shall be the average of the two middle values. 8 Density determination method
8.1 Suspension method (general method)
8.1.1 Test equipment
1) Analytical grade ethanol (alcohol) or other suitable test solution with a density less than 1g/mL; 2) A density greater than or equal to 1g/mL 1) zinc chloride solution; 2) distilled water:
3) mixing cylinder,
4) thermostat:
5) hydrometer calibrated at 23r;
7) thermometer with 0.1 scale.
8.1.2 Test steps
8.1.2.1 Cut the sample from the insulation or sheath to be tested in a direction perpendicular to the conductor axis and cut it into small pieces with a side length of 1~2nm. Put the sample into the test solution to make it suspended and measure its density. The test solution should not react chemically with the test material. Suitable test solutions are as follows!
- A mixture of ethanol and water with a density less than 1g/mL.; A mixture of zinc chloride and water with a density greater than or equal to 1g/mL. 8.1.2.2 Place three samples in the test solution at a temperature of 23 ± 0.1°C to avoid the formation of bubbles, and then add distilled water to the test solution until the sample is suspended in the test solution. The test mixture should be homogenized and stored at the specified temperature. The density of the mixed test solution is determined by a hydrometer, and the reading is to one decimal place. The measured density is the density of the test sample. Note: The specific gravity method specified in ISO 1183 can also be used. 8.2 Pycnometer method (reference method)
8.2.1 Test equipment
The test equipment used in this method includes:
-Accuracy (. 1 mg Large flat,
—density bottle with a capacity of 50mL,
—liquid bath with constant temperature control.
8.2.2 Samples
Cut the samples from the insulation and sheath, and the sample weight should not be less than 1g and not more than 5g. Then cut the insulation and sheath samples into several small pieces; tubular insulation and sheath samples should be cut into two or several parts longitudinally to avoid bubbles. 8.2.3 Pretreatment
The samples should be kept at (23+2) temperature. 8.2.4 Test steps
First weigh the empty and dry density bottle, and then weigh an appropriate amount of sample in the density bottle. Then inject the test solution (96% alcohol) into the density bottle to submerge the sample, and try to remove the bubbles on the surface of the sample, such as placing the density bottle in a vacuum dryer to evacuate. Destroy the vacuum state CB/T 2951+ 3-- 1997
After the test liquid is injected into the pycnometer, the temperature of the test liquid should reach (23 ± 0.5)°C in the liquid bath, and the pycnometer is filled with the test liquid to the limit volume. Wipe the pycnometer dry and weigh it together with the contents in the bottle. Then fill the empty pycnometer with the test liquid again, remove the air, and weigh the pycnometer and its contents at a temperature of (23 ± 0.5)°C.
8.2.5 Calculation
The density of insulation and sheath is calculated according to the following formula: Density at 23°C =
Where: m——test mass: 81
m——mass of test liquid required to fill the pycnometer, g;Xd
mj - mg
2—The mass of test solution required to fill the specific gravity bottle when loaded with the sample·g1d----The density of the test solution with an alcohol content of 96% at 23C, d=0.7988g/mL at 23C. 8.3 Correction of poly (PE) containing fillers Anti-aging agents and organic colorants are generally used in very small quantities and can be ignored. However, when other additives such as mineral fillers are used in large quantities, corrections should be made. Use standardized chemical methods to determine the properties and quantities of additives and make corrections according to the following formula; mXX
mX-mxo
Where: ——PE Density (corrected value) g/cm; --- density of PE material, g/cm
r: - density of additive or filler (measured value), /cm: period - mass of PE material (difference between m. and m) g; m. mass of PE material (measured value), g
mass of filler (measured value) + B.
Material containing carbon black shall be corrected by the following simplified formula: 8=6--0.045XC
Wherein, Cr is the percentage value of carbon black.
9 Water absorption test
9.1 Electrical test method
9.1.1 Test equipment
1) AC or DC voltage source;
2) Voltmeter:
3) Water tank with heating device.
9.1.2 Sample preparation
Cut the insulated wire core to be tested about 3m long from the cable sample. When removing the insulated core, be careful to avoid damaging the insulation. 9.1. 3 Test steps
a) Pre-test
Immerse the insulated core in a water tank, and heat the water in the water tank to the temperature specified in the relevant cable product standards. The two ends of the insulated core should be long enough to extend out of the water surface to prevent damage due to leakage current on the surface of the insulated core when the specified voltage is applied between the conductor and the water.
After the insulated core is immersed in water for 1 hour, apply an AC voltage of 4kV between the conductor and the water.Keep for 5 minutes. If any insulated core sample is punctured, remove the sample from the water tank and do not use it for the main test specified in item 1 below. The same pre-test shall be carried out on another sample of the same insulated core, and the number of repeated tests shall not exceed two times. The purpose of the pre-test is to ensure that only undamaged insulated cores are used for the main test. b) Main test
GB/T 2951. 3 1997
The cores that have passed the pre-test remain in the water tank. The water temperature is maintained at the temperature specified in the relevant cable product standards. Apply the DC voltage specified in Table 1 between the conductor and the water. The pressure is applied in accordance with the provisions of the relevant cable product standards. The negative electrode is connected to the conductor of each sample.
The average insulation thickness of the gauge is 1.8 and 1.9 mm
1.0 and 1.2
9. 1.4 Evaluation of test results
The sample should not be punctured.
9.2 Gravimetric water absorption test
9.2.1 Preparation of test specimens
Direct current
a) Cables with rated voltage of 0.6/1kV and below and conductor nominal cross-sectional area less than or equal to 25mm2: Each test specimen shall be a section of insulated wire core about 300mm long. b) All other cables:
The insulation is ground or shaved into a sheet of 0.6~0.9mm thick, with a smooth and substantially parallel surface. From the sheet, a specimen of 80~100mm long + 4~5mm wide is punched out. c) Two specimens are prepared from each insulated wire core to be tested. 9.2.2 Test steps
a) The specimens specified in 9.2.1a).
Wipe the surface of the test specimen clean with wet filter paper. Dry the sample at (70 + 2) °C to constant weight. Alternatively, place the sample in a low-pressure oven at a temperature of (70 ± 2) °C and a pressure not exceeding 6.6 rnbar for 24 h, and cool the sample in a dryer. Weigh the sample M, in mg, accurate to 1 mg. Bend the sample into an L shape on a test rod with a diameter of 6 to 8 times the diameter of the sample, and pass both ends through the holes in the lid 1 of the glass container. Only two samples of one insulated wire core should be placed in the glass container. After filling the glass container with water to the edge of the lid, adjust the position of the sample so that a section of about 250 mm long is immersed in the water. Use pre-boiled distilled water. The temperature and time of the sample in the water shall be in accordance with the provisions of the relevant product standards. If the time is not specified, the duration is two weeks for samples with an insulation thickness of 1.0 mm or less; three weeks for samples with an insulation thickness of 1.1 to 1.5 mm; and four weeks for samples with an insulation thickness of more than 1.5 mm. If the temperature is not specified, it shall be the maximum temperature of the conductor minus 5°C but not exceeding 90°C. The horizontal plane shall be maintained on the inner surface of the lid of the glass container. After the water has cooled to ambient temperature, remove the sample and shake off any water drops attached to the sample. Gently dry the sample with filter paper and weigh it within 2 to 3 minutes after the sample is removed from the water. The final mass shall be in ng. The sample shall be dried under the same conditions as before immersion in water, that is, any of the two methods used before the first weighing as described above. The final mass shall be weighed in tng. b) Samples specified in 9.2.1h) The surface of the sample is completely wiped clean and heated at a temperature of (7012)°C under vacuum (residual pressure of approximately 1 mbar) for 72 h. Materials with essentially non-ferrous components shall not be heated in a container or oven at the same time. After the above treatment, the sample shall be cooled in a desiccator for 1 h and then weighed (mass M) to the nearest 0.1 mg. GB/T 2951. 3—1997
Then immerse the sample in deionized water (or distilled water) for a time and temperature as specified in the relevant standards for electrical relay products. If the temperature is not specified, the temperature is the maximum temperature of the conductor minus 5°C, but not more than 90°C. Each sample is immersed in a separated glass tube with a condenser or in a beaker with a glass cover.
If a condenser is used, its upper part should be covered with an aluminum mold to avoid contamination. After immersion in water for the time specified in the relevant cable product standards, or if the product standards do not specify the immersion time, after 14 days of flooding, the sample should be transferred to deionized water (or distilled water) at room temperature and cooled there. Then remove each sample from the water, shake off any attached water drops, absorb with special filter paper without leaving fibers, and weigh the sample (mass M.) to an accuracy of 0.1 mg. Finally, treat the sample under the same conditions as before immersion, and weigh the final mass 4:. In units of n, 9.2.3 Method of expressing test results
a) The water absorption is calculated according to the following formula in units of g/cm 1) If the final weight M, is less than Mi: Www.bzxZ.net
(M,-M)/A
2) If the final weight M is greater than M1:
(M,-M2/A
In the formula, for the sample specified in 9.2.1a), A is the surface area of the 250 mm long flooded part of the sample, in units of cm; for the sample specified in 9.2.1b), 4 is the total surface area of the immersed sample. h) The average value of the test results of the two samples is taken as the maximum water absorption of the insulated core. 10 Insulation shrinkage test
For each insulated core to be tested: Cut a sample of about 1.5Lmm in length at least 0.5m away from the cable end. The length should be the length specified in the relevant cable product standard. 10.2 Preparation of test specimens
Except for the adhered extruded semi-conductive shielding layer (if any), all sheaths shall be removed from the insulated core test specimens in a timely manner. Within 5 minutes after the test specimens are cut, mark the test length L±5 m in the middle of each insulated core test specimen and measure the distance between the marks to an accuracy of 0.5 mm. Then remove the insulation at 2 to 5 mm from the marks at both ends of each test specimen. 10.3 Test procedure
The exposed ends of the test conductors shall be placed horizontally in an air oven or flat on the surface of a talcum powder bath to allow the insulation to shrink. Heat the test specimens at the temperature and time specified in the relevant cable product standards. Then cool the test specimens in air to room temperature and remeasure the distance between the marks of each test specimen to an accuracy of 0.5 mm. 10.4 Method of expressing test results
Shrinkage ratio The difference between the distance between the marks before heating and the distance between the marks after heating and cooling is expressed as a percentage of the distance between the marks before heating.
11 Shrinkage test of PE sheath
11.1 Test equipment
Electrically heated oven with natural ventilation.
Measurement tape with 1 mm graduation.
11.2 Sample
Before the test, the cable to be tested shall be placed at room temperature for at least 24 hours, and a sample of (500 ± 5) mm in length shall be cut at least 2 m away from the cable end. 11.3 Sample preparation
Measure the original length (L) of the sheath immediately after cutting the sample. The original length shall be the average of the two measured values. The two measurements shall be made along the longitudinal direction of the cable parallel to the cable axis, and at the two marks opposite to the cable end. If the sample is curved, the measurement shall be made on the inside and outside of the curved sample respectively.
11.4 Test steps
The sample should be placed horizontally in a preheated oven. The preheating temperature and placement time shall comply with the relevant cable product standards. Remove the sample from the oven and cool it at room temperature. Repeat this cold and hot cycle 5 times. Finally, cool to air temperature and measure the final length () as specified in Article 11.3.
11.5 Test result expression method
The shrinkage rate (L) is calculated as follows:
×100%1a) Specimen specified.
Wipe the surface of the specimen clean with wet filter paper. Dry the specimen at (70+2)°C to constant weight. Alternatively, place the specimen in a low-pressure oven at a temperature of (70±2)°C and a pressure not exceeding 6.6 rnbar for 24 h, and cool the specimen in a desiccator. Weigh the specimen M, in mg, accurate to 1 mg. Bend the specimen into an L shape on a test rod with a diameter of 6 to 8 times the diameter of the specimen, and pass both ends through the holes in the lid 1 of the glass container. Only two specimens of one insulated wire core should be placed in the glass container. After filling the glass container with water to the edge of the lid, adjust the position of the specimen so that a section of about 250 mm long is immersed in the water. Use pre-boiled distilled water.
The temperature and time for which the specimen is placed in the water shall comply with the provisions of the relevant product standards. If the time is not specified, the duration is two weeks for samples with insulation thickness of 1.0 mm or less; three weeks for samples with insulation thickness of 1.1 to 1.5 mm; and four weeks for samples with insulation thickness of more than 1.5 mm. If the temperature is not specified, it shall be the maximum temperature of the conductor minus 5°C but not exceeding 90°C. The horizontal plane shall be maintained on the inner surface of the lid of the glass container. After the water cools to ambient temperature, remove the sample and shake off the water droplets attached to the sample. Gently dry with filter paper and weigh the sample within 2 to 3 minutes after the sample is removed from the water. Finally, dry the sample under the same drying conditions as before immersion, that is, any of the two methods used before the first weighing as mentioned above, and weigh the final mass in tng. b) Samples specified in 9.2.1h) The surface of the completely cleaned sample is heated at a temperature of (7012)°C under vacuum (residual pressure close to 1mbar) for 72h. Materials with essentially non-ferrous components cannot be heated in a container or oven at the same time. After the above treatment, the sample should be placed in a desiccator to cool for 1h and then weighed (mass M) with an accuracy of 0.1mg. GB/T 2951. 3-1997 The sample is then immersed in deionized water (or distilled water) for a time and temperature in accordance with the provisions of the relevant electrical relay product standards. If the temperature is not specified, the temperature is the maximum temperature of the conductor minus 5°C, but not more than 90°C. Each sample is immersed in a separated glass tube with a condenser or in a beaker with a glass cover. If a condenser is used, its upper half should be covered with an aluminum mold to prevent contamination. After immersion in water for the time specified in the relevant cable product standards, or if the product standards do not specify the immersion time, after 14 days of flooding, the samples should be transferred to deionized water (or distilled water) at room temperature and cooled there. Then take each sample out of the water, shake off any attached water droplets, absorb them with special filter paper without leaving any fibers, and weigh the sample (mass M.) with an accuracy of 0.1 mg. Finally, treat the sample under the same conditions as before immersion, and weigh the final mass 4:. In units of n, 9.2.3 Method of expressing test results
a) The water absorption is calculated according to the following formula in units of g/cm 1) If the final weight M, is less than Mi:
(M,-M)/A
2) If the final weight M is greater than M1:
(M,-M2/A
In the formula, for the sample specified in 9.2.1a), A is the surface area of the 250 mm long flooded part of the sample, in units of cm; for the sample specified in 9.2.1b), 4 is the total surface area of the immersed sample. h) The average value of the test results of the two samples is taken as the maximum water absorption of the insulated core. 10 Insulation shrinkage test
For each insulated core to be tested: Cut a sample of about 1.5Lmm in length at least 0.5m away from the cable end. The length should be the length specified in the relevant cable product standard. 10.2 Preparation of test specimens
Except for the adhered extruded semi-conductive shielding layer (if any), all sheaths shall be removed from the insulated core test specimens in a timely manner. Within 5 minutes after the test specimens are cut, mark the test length L±5 m in the middle of each insulated core test specimen and measure the distance between the marks to an accuracy of 0.5 mm. Then remove the insulation at 2 to 5 mm from the marks at both ends of each test specimen. 10.3 Test procedure
The exposed ends of the test conductors shall be placed horizontally in an air oven or flat on the surface of a talcum powder bath to allow the insulation to shrink. Heat the test specimens at the temperature and time specified in the relevant cable product standards. Then cool the test specimens in air to room temperature and remeasure the distance between the marks of each test specimen to an accuracy of 0.5 mm. 10.4 Method of expressing test results
Shrinkage ratio The difference between the distance between the marks before heating and the distance between the marks after heating and cooling is expressed as a percentage of the distance between the marks before heating.
11 Shrinkage test of PE sheath
11.1 Test equipment
Electrically heated oven with natural ventilation.
Measurement tape with 1 mm graduation.
11.2 Sample
Before the test, the cable to be tested shall be placed at room temperature for at least 24 hours, and a sample of (500 ± 5) mm in length shall be cut at least 2 m away from the cable end. 11.3 Sample preparation
Measure the original length (L) of the sheath immediately after cutting the sample. The original length shall be the average of the two measured values. The two measurements shall be made along the longitudinal direction of the cable parallel to the cable axis, and at the two marks opposite to the cable end. If the sample is curved, the measurement shall be made on the inside and outside of the curved sample respectively.
11.4 Test steps
The sample should be placed horizontally in a preheated oven. The preheating temperature and placement time shall comply with the relevant cable product standards. Remove the sample from the oven and cool it at room temperature. Repeat this cold and hot cycle 5 times. Finally, cool to air temperature and measure the final length () as specified in Article 11.3.
11.5 Test result expression method
The shrinkage rate (L) is calculated as follows:
×100%1a) Specimen specified.
Wipe the surface of the specimen clean with wet filter paper. Dry the specimen at (70+2)°C to constant weight. Alternatively, place the specimen in a low-pressure oven at a temperature of (70±2)°C and a pressure not exceeding 6.6 rnbar for 24 h, and cool the specimen in a desiccator. Weigh the specimen M, in mg, accurate to 1 mg. Bend the specimen into an L shape on a test rod with a diameter of 6 to 8 times the diameter of the specimen, and pass both ends through the holes in the lid 1 of the glass container. Only two specimens of one insulated wire core should be placed in the glass container. After filling the glass container with water to the edge of the lid, adjust the position of the specimen so that a section of about 250 mm long is immersed in the water. Use pre-boiled distilled water.
The temperature and time for which the specimen is placed in the water shall comply with the provisions of the relevant product standards. If the time is not specified, the duration is two weeks for samples with insulation thickness of 1.0 mm or less; three weeks for samples with insulation thickness of 1.1 to 1.5 mm; and four weeks for samples with insulation thickness of more than 1.5 mm. If the temperature is not specified, it shall be the maximum temperature of the conductor minus 5°C but not exceeding 90°C. The horizontal plane shall be maintained on the inner surface of the lid of the glass container. After the water cools to ambient temperature, remove the sample and shake off the water droplets attached to the sample. Gently dry with filter paper and weigh the sample within 2 to 3 minutes after the sample is removed from the water. Finally, dry the sample under the same drying conditions as before immersion, that is, any of the two methods used before the first weighing as mentioned above, and weigh the final mass in tng. b) Samples specified in 9.2.1h) The surface of the completely cleaned sample is heated at a temperature of (7012)°C under vacuum (residual pressure close to 1mbar) for 72h. Materials with essentially non-ferrous components cannot be heated in a container or oven at the same time. After the above treatment, the sample should be placed in a desiccator to cool for 1h and then weighed (mass M) with an accuracy of 0.1mg. GB/T 2951. 3-1997 The sample is then immersed in deionized water (or distilled water) for a time and temperature in accordance with the provisions of the relevant electrical relay product standards. If the temperature is not specified, the temperature is the maximum temperature of the conductor minus 5°C, but not more than 90°C. Each sample is immersed in a separated glass tube with a condenser or in a beaker with a glass cover. If a condenser is used, its upper half should be covered with an aluminum mold to prevent contamination. After immersion in water for the time specified in the relevant cable product standards, or if the product standards do not specify the immersion time, after 14 days of flooding, the samples should be transferred to deionized water (or distilled water) at room temperature and cooled there. Then take each sample out of the water, shake off any attached water droplets, absorb them with special filter paper without leaving any fibers, and weigh the sample (mass M.) with an accuracy of 0.1 mg. Finally, treat the sample under the same conditions as before immersion, and weigh the final mass 4:. In units of n, 9.2.3 Method of expressing test results
a) The water absorption is calculated according to the following formula in units of g/cm 1) If the final weight M, is less than Mi:
(M,-M)/A
2) If the final weight M is greater than M1:
(M,-M2/A
In the formula, for the sample specified in 9.2.1a), A is the surface area of the 250 mm long flooded part of the sample, in units of cm; for the sample specified in 9.2.1b), 4 is the total surface area of the immersed sample. h) The average value of the test results of the two samples is taken as the maximum water absorption of the insulated core. 10 Insulation shrinkage test
For each insulated core to be tested: Cut a sample of about 1.5Lmm in length at least 0.5m away from the cable end. The length should be the length specified in the relevant cable product standard. 10.2 Preparation of test specimens
Except for the adhered extruded semi-conductive shielding layer (if any), all sheaths shall be removed from the insulated core test specimens in a timely manner. Within 5 minutes after the test specimens are cut, mark the test length L±5 m in the middle of each insulated core test specimen and measure the distance between the marks to an accuracy of 0.5 mm. Then remove the insulation at 2 to 5 mm from the marks at both ends of each test specimen. 10.3 Test procedure
The exposed ends of the test conductors shall be placed horizontally in an air oven or flat on the surface of a talcum powder bath to allow the insulation to shrink. Heat the test specimens at the temperature and time specified in the relevant cable product standards. Then cool the test specimens in air to room temperature and remeasure the distance between the marks of each test specimen to an accuracy of 0.5 mm. 10.4 Method of expressing test results
Shrinkage ratio The difference between the distance between the marks before heating and the distance between the marks after heating and cooling is expressed as a percentage of the distance between the marks before heating.
11 Shrinkage test of PE sheath
11.1 Test equipment
Electrically heated oven with natural ventilation.
Measurement tape with 1 mm graduation.
11.2 Sample
Before the test, the cable to be tested shall be placed at room temperature for at least 24 hours, and a sample of (500 ± 5) mm in length shall be cut at least 2 m away from the cable end. 11.3 Sample preparation
Measure the original length (L) of the sheath immediately after cutting the sample. The original length shall be the average of the two measured values. The two measurements shall be made along the longitudinal direction of the cable parallel to the cable axis, and at the two marks opposite to the cable end. If the sample is curved, the measurement shall be made on the inside and outside of the curved sample respectively.
11.4 Test steps
The sample should be placed horizontally in a preheated oven. The preheating temperature and placement time shall comply with the relevant cable product standards. Remove the sample from the oven and cool it at room temperature. Repeat this cold and hot cycle 5 times. Finally, cool to air temperature and measure the final length () as specified in Article 11.3.
11.5 Test result expression method
The shrinkage rate (L) is calculated as follows:
×100%3 Method of expressing test results
a) The water absorption is calculated according to the following formula in units of g/cm 1) If the final weight M, is less than Mi:
(M,-M)/A
2) If the final weight M is greater than M1:
(M,-M2/A
In the formula, for the sample specified in 9.2.1a), A is the surface area of the 250 mm long flooded part of the sample, in cm; for the sample specified in 9.2.1b), A is the total surface area of the immersed sample. h) The average value of the test results of the two samples is taken as the maximum water absorption of the insulated core. 10 Insulation shrinkage test
For each insulated core to be tested: Cut a sample of about 1.5Lmm in length at least 0.5m away from the cable end. The length should be the length specified in the relevant cable product standard. 10.2 Preparation of test specimens
Except for the adhered extruded semi-conductive shielding layer (if any), all sheaths shall be removed from the insulated core test specimens in a timely manner. Within 5 minutes after the test specimens are cut, mark the test length L±5 m in the middle of each insulated core test specimen and measure the distance between the marks to an accuracy of 0.5 mm. Then remove the insulation at 2 to 5 mm from the marks at both ends of each test specimen. 10.3 Test procedure
The exposed ends of the test conductors shall be placed horizontally in an air oven or flat on the surface of a talcum powder bath to allow the insulation to shrink. Heat the test specimens at the temperature and time specified in the relevant cable product standards. Then cool the test specimens in air to room temperature and remeasure the distance between the marks of each test specimen to an accuracy of 0.5 mm. 10.4 Method of expressing test results
Shrinkage ratio The difference between the distance between the marks before heating and the distance between the marks after heating and cooling is expressed as a percentage of the distance between the marks before heating.
11 Shrinkage test of PE sheath
11.1 Test equipment
Electrically heated oven with natural ventilation.
Measurement tape with 1 mm graduation.
11.2 Sample
Before the test, the cable to be tested shall be placed at room temperature for at least 24 hours, and a sample of (500 ± 5) mm in length shall be cut at least 2 m away from the cable end. 11.3 Sample preparation
Measure the original length (L) of the sheath immediately after cutting the sample. The original length shall be the average of the two measured values. The two measurements shall be made along the longitudinal direction of the cable parallel to the cable axis, and at the two marks opposite to the cable end. If the sample is curved, the measurement shall be made on the inside and outside of the curved sample respectively.
11.4 Test steps
The sample should be placed horizontally in a preheated oven. The preheating temperature and placement time shall comply with the relevant cable product standards. Remove the sample from the oven and cool it at room temperature. Repeat this cold and hot cycle 5 times. Finally, cool to air temperature and measure the final length () as specified in Article 11.3.
11.5 Test result expression method
The shrinkage rate (L) is calculated as follows:
×100%3 Method of expressing test results
a) The water absorption is calculated according to the following formula in units of g/cm 1) If the final weight M, is less than Mi:
(M,-M)/A
2) If the final weight M is greater than M1:
(M,-M2/A
In the formula, for the sample specified in 9.2.1a), A is the surface area of the 250 mm long flooded part of the sample, in cm; for the sample specified in 9.2.1b), A is the total surface area of the immersed sample. h) The average value of the test results of the two samples is taken as the maximum water absorption of the insulated core. 10 Insulation shrinkage test
For each insulated core to be tested: Cut a sample of about 1.5Lmm in length at least 0.5m away from the cable end. The length should be the length specified in the relevant cable product standard. 10.2 Preparation of test specimens
Except for the adhered extruded semi-conductive shielding layer (if any), all sheaths shall be removed from the insulated core test specimens in a timely manner. Within 5 minutes after the test specimens are cut, mark the test length L±5 m in the middle of each insulated core test specimen and measure the distance between the marks to an accuracy of 0.5 mm. Then remove the insulation at 2 to 5 mm from the marks at both ends of each test specimen. 10.3 Test procedure
The exposed ends of the test conductors shall be placed horizontally in an air oven or flat on the surface of a talcum powder bath to allow the insulation to shrink. Heat the test specimens at the temperature and time specified in the relevant cable product standards. Then cool the test specimens in air to room temperature and remeasure the distance between the marks of each test specimen to an accuracy of 0.5 mm. 10.4 Method of expressing test results
Shrinkage ratio The difference between the distance between the marks before heating and the distance between the marks after heating and cooling is expressed as a percentage of the distance between the marks before heating.
11 Shrinkage test of PE sheath
11.1 Test equipment
Electrically heated oven with natural ventilation.
Measurement tape with 1 mm graduation.
11.2 Sample
Before the test, the cable to be tested shall be placed at room temperature for at least 24 hours, and a sample of (500 ± 5) mm in length shall be cut at least 2 m away from the cable end. 11.3 Sample preparation
Measure the original length (L) of the sheath immediately after cutting the sample. The original length shall be the average of the two measured values. The two measurements shall be made along the longitudinal direction of the cable parallel to the cable axis, and at the two marks opposite to the cable end. If the sample is curved, the measurement shall be made on the inside and outside of the curved sample respectively.
11.4 Test steps
The sample should be placed horizontally in a preheated oven. The preheating temperature and placement time shall comply with the relevant cable product standards. Remove the sample from the oven and cool it at room temperature. Repeat this cold and hot cycle 5 times. Finally, cool to air temperature and measure the final length () as specified in Article 11.3.
11.5 Test result expression method
The shrinkage rate (L) is calculated as follows:
×100%
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