GB/T 2951 standard specifies the test methods for polymer insulation and sheath materials of power distribution cables and communication cables, including marine cables. GB/T 2951.7 specifies the weight loss test method and thermal stability test method. Applicable to polyvinyl chloride mixture insulation and sheath of wires and cables. GB/T 2951.7-1997 General test methods for cable insulation and sheath materials Part 3: Special test methods for polyvinyl chloride mixtures Section 2: Weight loss test--Thermal stability test GB/T2951.7-1997 standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Test methods for insulating and sheathing materials of electric cables Part 3: Methods specific lo PVC eompoundsSection 2: Weight loss test- Thermal stability test1 Scope
GB/T 2951-7—1997
idt IEC 811-3-2:1985
No.1(1993)1st amendment
Replaces GI3/T2951.—94
GB/T2951.102951.11--94
GB/T 2951.40- 91
GB/T2951 standard specifies the test methods for polymer insulation and sheath materials of power distribution cables and communication cables, including marine cables.
GB/T2951.7 specifies the weight loss test method and thermal stability test method. Applicable to polyvinyl chloride compound insulation and sheath of wires and cables.
2 Test principles
This standard does not specify all 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 product standards to meet the needs of special types of relays. 3 Scope of application
The test conditions and test parameters specified in this standard are applicable to the most commonly used types of insulation and sheath materials for cables, wires and cords. 4 Type tests and other tests
The test methods specified in this standard are first used as type tests. For some test items, the conditions for type tests and frequently performed tests (such as routine tests) are essentially different. This standard promotes these differences. 5 Pretreatment
All tests should be carried out after the insulation and sheath materials are stored for at least 16 hours after extrusion. 6 Test temperature
Unless otherwise specified, the test should be carried out at ambient temperature 7 Intermediate value
The test data obtained should be arranged in ascending or descending order. If the number of valid data is odd, the intermediate value is the middle value. If it is an even number, the intermediate value is the average of the two middle values. 8 Weight loss test for insulation and sheath
8.1 Weight loss test for insulation
8.1.1 Test equipment
a) Natural ventilation oven or pressure ventilation oven. The air should enter the oven in such a way that it flows evenly over the surface of the test piece and then is discharged near the top of the oven. At the specified aging temperature, the air in the oven should be replaced no less than 8 times and no more than 20 times per hour. In case of dispute, a natural ventilation oven should be used. Rotating fans shall not be used in the oven.
b) Analytical balance with a sensitivity of 0.1 mg.
c) Punch die for dumbbell specimens (see Chapter 9 of GB/T2951.1-1997). d) Dryer using silica gel or similar materials. 8.1-2 Sampling
If the weight loss test is combined with the mechanical properties test (Chapter 9 of CB/T2951.1-1997), the test pieces shall be 3 of the test pieces subjected to the heat aging test in accordance with Article 8.1.3 of GB/T2951.2-1997, and 1 set of test pieces shall be taken for each insulated wire core. If it is no longer used for other tests and its thickness meets the requirements of 8.1.3c), it may also be another 3 test pieces prepared from each insulated wire core in accordance with the provisions of Chapter 9 of GB/T2951.1-1997. Otherwise, 3 samples shall be cut from each insulated wire core to be tested, each sample is about 100mm long, and then the test piece shall be prepared from each sample in accordance with the method specified in Article 8.1.3.
8.1.3 Preparation of test pieces
a) Remove all the sheaths and extract the conductive core. The semi-conductive layer on the insulation (if any) shall be removed mechanically without solvent. b) Test specimens,
1) Make a dumbbell specimen as shown in Figure 1 as far as possible; 2) If the size of the insulated wire core is too small to make a bell specimen as shown in Figure 1, a dumbbell specimen as shown in Figure 2 can be made; 3) For specimens with an inner diameter not exceeding 12.5 mm, a tubular specimen can be used instead of a dumbbell specimen as long as there is no semi-conductive layer adhered to the insulation.
If there is any residual insulating layer, it should be removed by appropriate methods without solvents: The ends of the tubular specimen should not be closed.
c) Dumbbell test pieces shall be prepared in accordance with the provisions of 9.1.3 a) of GB/T2951.1-1997, but the two surfaces of the test piece shall be parallel, its thickness shall be (1.0 ± 0.2) mm, and no marking line is required: tubular test pieces shall be prepared in accordance with 9.1.3 b) of GB/T2951.1-1997, no marking line is required, and the total surface area of ​​each test piece (see 8.1.4 a)) shall not be less than 5 cm. d) There are grooves on both sides between the cores of the double-core fan flat soft wire, and the insulated cores shall not be separated during the test. Regarding the calculation of the volatile surface area of ​​the double-core flat flexible cable, it can be considered as two separate tubular test pieces. 8.1.4 Calculation of volatile surface area A
The surface area of ​​each test piece (in m) should be calculated according to the following formula before the weight loss test: a) Tubular test piece
Surface area A = surface area + internal surface area + cross-sectional area A = 2(D - 5) × (1 + 8)
Where: 3—average thickness of test piece + mm, if 3≤0.4mm. to two decimal places: if >0.4mm, to one decimal place D—average outer diameter of test piece, mm. If D≤2mm, to two decimal places; if D>2mm, to one decimal place I—length of test piece, mm. to one decimal place. bzxz.net
GB/T 2951. 7—1997
and D are measured on the thin slice cut from the end of each tubular specimen according to the provisions of GB/T 2951.1-1997 8.1 and 8.3. This formula is also applicable to the tubular specimen with the cross-sectional shape shown in Figure 3. b) Dumbbell specimen shown in Figure 2
c) Sleeping bell specimen shown in Figure 1
A-624+1186
A=1256+1808
where is the average thickness of the specimen, measured according to GB/T2951.1-1997 9.1.4a), in mm, to two decimal places. 8.1.5 Test steps
a) The prepared specimens should be stored in a desiccator at ambient temperature for at least 20 hours. Each specimen shall be accurately weighed immediately after being taken out of the desiccator, in mg, to one decimal place. b) Unless otherwise specified, the three specimens shall be stored in an oven at (80 ± 2)°C under atmospheric pressure for 7 × 24 h (see 8.1.1).
-Materials with significantly different compositions shall not be tested simultaneously in the same oven! The specimens shall be hung vertically in the middle of the oven, with a spacing of at least 20 mm between the specimens; the volume occupied by the specimens shall not exceed 0.5% of the oven volume. c) After the heat treatment, the specimens shall be placed back in the desiccator at ambient temperature for 20 h, and then accurately weigh each specimen again, in mg, to one decimal place.
Calculate the difference between the weights of each specimen measured in a) and e) and round it off to mg. 8.1.6 Method of expressing test results
The weight loss of each test piece shall be the difference in its weight, in mg (see 8.1.5e)), divided by the surface area, in cm2 (see 8.1.4).
The median value of the test results of the three test pieces taken from each insulated core shall be taken as the weight loss of the insulation of the core, expressed in mg/cm. 8.2 Sheath weight loss test
8.2.1 Test equipment
See 8.1.1 8.2.2 Sampling
Three sheath samples shall be taken in accordance with 8.1.2. 8.2.3 Preparation of test pieces
All components inside the sheath (and outside, if any) shall be removed, taking care not to damage the sheath, and then prepare the test piece in accordance with 8.1.3.
8.2.4 Calculation of volatile surface area A
According to 8.1.4. The formula for calculating the volatile surface area is modified as follows: The formula for the substituted test piece is only applicable to the case where the cross section is shown in Figures 1 and 5. The inner and outer surface areas of the sheath of flat flexible cords and cables shall be calculated according to their cross-sectional dimensions. These dimensions shall be measured to two decimal places in mm. The wedge-shaped ridges on the inside of the flat sheath can be considered to be flat. 8.2.5 Test steps
According to the provisions of 8.1.5.
8.2.6 Method of expressing test results
According to the provisions of 8.1.6.
9. Thermal stability test of insulation and sheath
9.1 Test equipment
GB/T2951.7—1997
a) A glass tube with a length of 110 mm and an outer diameter of about 5 mm + an inner diameter of (4.0 ± 0.5) mm and one end sealed (such as sealed by melting method).
Tubes made of AR glass shall comply with:
IS0719: Grade $ hydrolysis resistance
-ISO 1776: Grade 1 acid resistance;
-ISO 695: Grade 2 alkali resistance.
b) Universal test paper with a pH value in the range of 1 to 10. () Temperature-controlled heater. The test temperature shall be as specified in the relevant cable product standards. If not specified, it shall be controlled at (200 ± 0.5) °C. Oil bath is preferred. Oil bath should be used for type tests and in disputed cases. d) Barometer with a calibrated graduation value of 0.1r. Mercury column correction may be necessary depending on the type of thermometer used and the calibration and use method. e) Stopwatch or suitable timer.
9.2 Test steps
Note: In order to obtain reliable test results and limit their scatter, it is absolutely necessary to use a sufficiently accurate thermometer and comply with the specified or test temperature limits. a) Cut three samples from the insulation of each insulated wire core or the tested sheath. Each sample consists of two or three strips of 20~30mm long and weighs about (50±5)mg. Place the sample in the glass tube specified in 9.1a). The sample should not be higher than 30mm from the bottom of the glass tube. b) Insert a piece of dry universal test paper (as specified in 9.1b)) about 15mm long and 3mm wide into the open end (top) of the glass tube. The paper strip extends about 5mm out of the tube mouth and is bent and fixed in this position. c) Place the glass tube in a heating device heated to the specified test temperature to a depth of 60mm. d) Determine the time taken for the universal test paper to change color from pH 5 to pH 3; or the test is continued until the color of the test paper does not change within the specified test time. When the red color on the universal test paper corresponding to pH 3 begins to change significantly, it should be considered that the color change point has been reached. When the expected test time is about to end, the universal test paper should be replaced every 5 to 10 minutes (especially for long-term stability tests) to make the change point easier to see. 9.3 Evaluation of test results
The average value of the thermal stability time of the three samples should not be lower than the specified value of the relevant cable product standards. You record line
Dimensions in mm
Figure 1 Bell test piece
1) ISO 50695, 1991 Test and classification methods for glass resistant to corrosion by boiling alkali solutions.
1S0719: 1985, Glass resistant to hydrolysis of glass particles at 98°C - Test and classification methods. IS01776: 1985. Drum side of resistance to hydrogen peroxide corrosion at 100°C - Flame emission or flame atomic absorption spectrometry. Figure 3
CB/T 2951. 7—1997
Marking number
Figure 2 Small saliva bell test piece
Dimensional sheet
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