GB/T 2951.2-1997 General test methods for cable insulation and sheath materials Part 1: General test methods Section 2: Thermal aging test methods
Some standard content:
National Standard of the People's Republic of China
Common test methods for insulating and sheathing materials of electrlc cables Part 1: Common test methods
Section 2: Thermal ageing methods
Common test methods for insulating and sheathing materials of electrlc cables Part 1 : Methods for general application Section two: Thermal ageing methods 1 Scope
GB/T 2951. 2—1997
idt IEC 811-1-2:1985
No.1(1989)1st amendment
Replace GB
GB/T 2951.7~2951. 9-94
GB/T2951 specifies the test methods for polymer insulation and sheathing materials of distribution cables and communication cables, including marine relays.
GB/T2951.2 specifies the thermal aging test methods. Applicable to the most commonly used insulation and sheath materials (elastomers, polyvinyl chloride polyethylene, polypropylene, etc.) for 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 cables. 3 Scope of application
The test conditions and test parameters specified in this standard are applicable to the most common types of insulation and sheath materials for cables, wires and cords. 4 Type tests and other tests
The tests and methods specified in this standard are first used as type tests. There are essential differences between the conditions of type tests and frequently performed tests (such as routine tests) for some test items. This standard has pointed out these differences. 5 Pretreatment
All tests should be carried out after the insulation and sheath materials are extruded or vulcanized (or cross-linked) and stored for at least 16 hours before testing. 6 Test temperature
Unless otherwise specified, the test shall be carried out at ambient temperature. 7 Intermediate value
Arrange the test data obtained in ascending or descending order. When 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 Heat aging method
8.1 Air oven aging
8.1.1 Overview
Air oven aging treatment can be carried out according to the requirements of relevant cable product standards: a) For prepared insulation and sheath material test pieces (see 8.1.3.1): b) For prepared insulated core test pieces (conductor and insulation) (see 8.1.3.2, and if necessary, refer to the following clauses) c) For finished cable samples (see 8.1.4) d) For weight loss test (see Chapter 8 of GB/T2951.7-1997). Aging test a) and weight loss test d) can be combined and carried out on the same test piece I:. 8.1.2 Test equipment
Natural ventilation oven and pressure ventilation oven The air should enter the oven in such a way that the air flows over the surface of the test piece and then is discharged from near the top of the oven. At the specified aging temperature, the total air replacement frequency in the oven should be no less than 8 times per hour and no more than 20 times. There are two methods for measuring the air flow through the oven, see 8.4. Blowers should not be used in the oven.
8.1.3 Preparation of test pieces
8.1.3.1 Aging of test pieces of insulating materials and sheathing materials without conductors Aging should be carried out in an atmosphere of ambient air composition and pressure. Test pieces prepared in accordance with Chapter 9 of GB/T2951.1-1997 should be suspended vertically in the middle of the drying pin, with a spacing of at least 20tmm between each test piece and any other test piece.
If any of the test pieces are to be used for weight loss tests, the volume of the oven occupied by these samples should not exceed 0.5%. The overflow and time of the test pieces in the oven shall be in accordance with the provisions of the relevant cable product standards. Materials with substantially different compositions should not be tested at the same time. After the aging test, the test pieces should be removed from the oven and placed at ambient temperature for at least 16 hours, avoiding direct sunlight. Then, the insulation and sheath are subjected to tensile tests in accordance with 9.1.6 and 9.1.7 of GB/T2951.1-1997. 8.1.3.2 Aging of insulated wire core test pieces with conductors a) If the conductor and the separation layer (if any) can be removed from the insulation without damaging the insulation after aging, the test procedure is as follows: Cut the insulated wire core sample into sample sections. The length should be sufficient and the sample should be taken as close as possible to the sample used for the tensile test before aging (see GB/T2951.1). These sample sections are aged in accordance with 8.1.3.1. After aging, 5 test pieces are prepared in accordance with 9.1.3 of GB/T2951.1-1997. The cross-sectional area is measured in accordance with 9.1.4 of GB/T2951.1-1997. Then, the tensile test is carried out in accordance with 9.1.6 and 9.1.7 of GB/T2951.1-1997.
b) If the conductor and the insulating layer (if any) cannot be stripped from the insulation without damaging the insulation after aging, the appropriate test piece preparation method and test method specified in Table 1 shall be used. Note: At present, these test methods are only applicable to low-voltage cables (i.e. cables without conductor shielding> 90CEPR or 9>CXLPE insulated cores. 8.1.3.3 Aging of tubular test pieces with solid non-bonded layer conductors of reduced diameter according to GB/T2951.1-1997 Section 9.1.3b) After preparing 5 test pieces, a non-bonded solid conductor with a diameter 10% smaller than the original conductor is reinserted into the tubular test piece. This conductor can be obtained by pulling the original conductor or directly using a small diameter conductor. These test pieces are aged according to the provisions of Article 8.1.3.1, and the conductor is pulled out of the tubular test piece after aging. The cross-sectional area of the tubular test piece shall be determined in accordance with Article 9.1.4 of GB/T2951.1-1997, and then the tensile test shall be carried out in accordance with Articles 9.1.6 and 9.1.7 of GB/T2951.1-1997.
8.1.3.4 Aging and winding test of insulated wire core specimens a) Sampling and specimen preparation
GB/T 2951.2-1997
Two specimens of appropriate length shall be taken from each insulated wire core to be tested, and the specimens shall be cut as close as possible to the specimens used for the tensile test before aging (see GB/T2951.1).
h) Aging procedure
The specimens shall be hung roughly in the middle of the oven, with a spacing of at least 20 mm between each specimen and the adjacent specimen, and the specimens shall be supported at both ends, and their insulation shall not come into contact with other objects. The volume of the oven occupied by the sample should not exceed 2%, and the aging should be carried out in the oven according to the temperature and time specified in the relevant relay product standards. Table 1
Categories of copper conductors and conductor forms
Category 1: Uncoated copper conductors
Category 1, metal-fed conductors
Category 1: Conductors with an insulating layer outside
Category 2: 16mm and below patterned conductors made of uncoated single wires or metal-inlaid single wires, including zigzag conductors with an insulating layer outside
Category 2: 16mm* and above shaped or formed conductors made of uncoated single wires or metal-inlaid single wires. The insulation or insulating layer of the conductor after aging is bonded, which makes the preparation of the test group difficult. For the aging test method of 90% ethylene rubber or 90℃ cross-linked polyvinyl insulated wire cores of low-temperature cables, please refer to 8.1.3.3. If this method also produces bonding problems, please refer to 8.1.3.4. In case of dispute, the winding test should be carried out after aging. See 8.1.3.4
See 8.1.3.4
See 8.1.3.4
See 8.1.3.5
Note: During the winding test (see 8.1.3, 4), the aging conditions may be different from the aging conditions for determining the tensile performance requirements (see 8.1.3.2, 8.1.3.3.8.1.3.5); refer to the relevant cable product standards. c) Winding test
After the aging test, take out the sample from the oven and place it at ambient temperature for at least 16 hours to avoid direct exposure to light. Then, each sample is evenly wound around the test rod at a speed of about 1 turn/5 at ambient temperature to form a tight spiral winding test. The winding test can be extended to 8.1 of GB/T2951.4-1997.3. The diameter of the test rod shall be times the diameter of the insulated wire core. The value of T and the number of windings are shown in Table 2. Table 2
Conductor area, mn
2.5 and below
10 and 16
d) Requirements
Factor
After the winding test is completed, the test specimens still on the test rod shall be inspected. When inspected with normal vision or corrected vision without a microscope, both insulation specimens shall be free of any cracks. Any cracks on the first and last winding specimens of the test rod shall not be evaluated. 8.1.3.5 Aging of insulated wire core samples prepared by special methods a) Sampling and sample preparation
Take 3 samples of about 200mm in length from each insulated wire core to be tested. The samples are cut as close as possible to the samples used for the tensile test before aging (see GB/T2951.1).
When testing the insulated wire core samples of fan-shaped conductors, a narrow strip with a width of not less than 10mm1 should be cut on the insulation of the fan-shaped back along the conductor axis, and it should be separated from the conductor. Then the narrow strip insulation is re-placed in the original position and tied with a suitable metal wire in the middle of the sample and about 20mm from the end, so that the narrow strip is in good contact with the conductor again, as shown in Figure 1. A similar method should be used when testing the insulated wire core samples of round conductors. For insulated wire cores of smaller sizes (such as 1 conductor cross-sectional area 25Ⅱm\), the insulation can be cut in half along the conductor axis. h) Aging step
GB/T 2951. 2- 1997
Binding wire (aluminum wire or zinc wire)
The samples prepared by special methods should be hung in the middle of the oven so that the distance between each sample and any other sample is at least 20mm, and it cannot contact with any other objects, except for the metal binding wire. The volume of the oven occupied by the test sample should not exceed 2%. The aging temperature and time shall be in accordance with the provisions of the relevant cable product standards. After the aging test, the sample is taken out of the oven and placed at ambient temperature for at least 16 hours to avoid direct sunlight, and then the sample is peeled off. Two sleeping bell specimens are prepared on each sample according to Article 9.1.3 of GB/T2951.1-1997. As shown in the figure below, the cross-sectional area of the specimen is measured according to Article 9.1.4 of GB/T2951.1·1997. As shown in Figure 2. Then, perform the tensile test according to Articles 9.1.6 and 9.1.7 of GB/T2951.1-1997. Figure 2
8.1.4 Preparation of finished cable samples
Take two sample sections of about 200 mm long from the finished cable and cut them as close as possible to the sample used for the tensile test (see GB/T2951.1) before aging.
The sample section should be hung vertically in the middle of the oven, with a spacing of at least 20 mm between it and other sample sections, and the area of the oven occupied by the section should not exceed 2%. The aging temperature and time shall be in accordance with the provisions of the relevant cable product standards. After aging, take out the sample from the oven and place it at an ambient temperature of at least 161°C, avoiding direct sunlight. Then peel off three sample sections and cut two test pieces from the insulation of each insulated core (up to three cores) and the sheath of each cable section according to the provisions of Chapter 9 of GB/T 2951.1-1997. In this way, 6 test pieces can be made from each core and sheath. If the test piece needs to be flattened or ground to a thickness of no more than 2mm, it should be ground or flattened as little as possible on the side where different types of materials contact in the middle of the finished cable. If it is necessary to cut off the ridge or grind it on the side facing the different materials, the material removed on this side should be as little as possible, limited to moderate flatness.
After the cross-sectional area measurement and pretreatment: all test pieces are subjected to tensile test according to Chapter 9 of GB/T2951.1-1997 8.2 Air bomb aging
Place the test pieces specified in Chapter 9 of GB/T2951.1-1997 in an air bomb at low temperature, and the test pieces are not in contact with each other. The effective volume of the air bomb occupied by the test piece should not be more than one-tenth. Materials with substantially different components should not be subjected to aging tests at the same time. The air bomb should be filled with oil-free and moisture-free air, with a pressure of (0.55±0.02)MPa. The aging temperature and time shall be in accordance with the relevant cable product standards. After the aging is completed, the pressure shall be gradually reduced to atmospheric pressure within a period of not less than 5 minutes. The formation of pores in the test piece shall be avoided. Then remove the sample from the air bomb and place it at ambient temperature for at least 16 hours, avoiding direct sunlight. Perform tensile test according to Articles 9.1.6 and 9.1.7 of GB/T 2951.1-1997. 8.3 Ammonia bomb aging
Place the test pieces specified in Chapter 9 of GB/T 2951.1-1997 in an oxygen bomb at room temperature, without contact between the test pieces. The effective volume of the oxygen bomb occupied by the test piece should not exceed one tenth. Materials with substantially different components should not be tested at the same time. The oxygen bomb should be filled with industrial oxygen with a purity of not less than 97% and a pressure of (2.1 + 0.07) MPa. The aging temperature and time shall be in accordance with the provisions of the relevant cable product standards. Immediately after the aging is completed, the pressure shall be gradually reduced to the atmospheric pressure within a period of not less than 5 minutes. The formation of pores in the test piece shall be avoided. Then remove the sample from the oxygen bomb and place it at ambient temperature for at least 16 hours, avoiding direct sunlight. Perform the tensile test according to Articles 9.1.6 and 9.1.7 of GB/T 2951.1-1997. 8.4 Methods for Measuring Air Flow through the Oven
8.4.1 Method 1—Indirect or Power Loss Method a) In this method, the difference between the power required to maintain the oven at the specified test temperature with the damper open and the power required to maintain the oven at the same temperature with the damper closed is used to determine the air flow through the oven. The average power (1 watt) required to maintain the oven at the specified aging temperature with the damper open shall be determined for 30 min or longer. Then close the vent (and the thermometer socket if necessary), and measure the average power (households, watts) required to operate the oven at the same temperature in the same fashion. It is very important that the difference between the oven temperature and the ambient temperature should be the same for the two groups of tests. The difference should be less than 0.2℃. The ambient leakage should be measured at a distance of about 2㎡ from the oven, approximately horizontal to the bottom of the oven, and at least 0.6 m away from any object. b) The total amount of air flowing through the oven when the valve is open is calculated by the following formula: P— F2
m = C(tf= t)bZxz.net
Vu.3.600m
Where: C.--The heat of air at normal pressure (1.003J/g)fRoom temperature,
t—Oven temperature, ℃:
P,—P,—Power consumption difference, as specified above! m----air quality.&/s:
V——air volume, L/h
·Density of air in the laboratory during the test g/. GB/T 2951. 2—1997
Note: The air density is 1.205 g/L at 20 and 760 mmHg. 3 600(P,-P.).
3 590(P,-P,)
Therefore: V=
1.003d(izt) No.
This formula assumes that when the valve is closed, no air passes through the oven. Therefore, the oven should be leak-free. The seams of the oven door should be sealed with adhesive tape, and all holes (including air inlets) should be effectively sealed. c) If a wattmeter is used to measure the power loss, the total time (s) when the oven heater is in the "on" state is measured with a stopwatch, and a special meter reading is recorded during each "on" state. The average of the wattmeter readings multiplied by the total time indicated by the stopwatch and divided by the test duration (s) is the power required to maintain a constant temperature ().
d) If a watt-hour or kilowatt-hour meter is used, the total energy loss reading recorded by the meter should be divided by the test duration, expressed in fractions of an hour. If a household dry watt-hour meter is used, the scale unit is too large to read sufficiently accurate data in a short time, so the dial inside the meter should be used as a power loss indicator. The meter should be run until the indicator mark on the disk turns to the other side of the center of the window IT. Then the power is cut off until the test begins. In order to reduce possible errors, the test cycle should be longer, using a disk of about 100 revolutions. The test should preferably be terminated when the disk mark is visible. If the mark is still not visible at the end of the test, a fraction of the estimated number of revolutions should be added. The start and end of the test should be at corresponding points in the heating cycle "on-off" (for example, the moment the heater is turned on by the thermostat). 8.4.2 Method 2 - Direct and continuous weighing method Installation and instructions
Start from a high-pressure air source, that is, from an air bottle in the air pipe system. a) Air pressure regulator
A device that reduces the air pressure from the high pressure of the air supply source to the very low pressure required for the oven. It has a regulation that ensures constant pressure output. b) Flow meter
An instrument used to measure the air flow rate, as shown in Figure 3.It works on the principle of a pressure gauge and has: 1) a capillary with a calibration inner diameter of about 2 mm and a calibration length of about 70 mm. Figure 4 shows a typical calibration curve, which can control air flow rates of 500 L/h or 60 L/h and below.
2) a dual-scale differential pressure gauge. The pressure difference range is between 0 and ±300 mm of water column. The liquid in the differential pressure gauge is distilled water. c) air oven
An air oven operating under complete sealing, including the air inlet pipe around the oven. The air inlet pipe is preferably fed into the oven from the bottom. The air outlet should be in the front of the oven, and only this hole is open. Note: The following two points can improve the reliability of this method and equipment: a) the upper flow meter can be considered to be completely reliable, easy to produce and calibrate, and also suitable for the air flow rate range mentioned above. ) Experiments have shown that taking a slight "strong pursuit" ventilation will not actually change the uniformity of the temperature at each point in the oven. GB/T 2951. 2—1997
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Figure 3 Flowmeter for controlling oven air flow in method 2
GB/T 2951.2 1997
Gas flow rate, L/h
[Figure 4 Calibration curve of the capillary of the flowmeter for controlling air flow in method 2 (capillary d=2mm, =70mm)
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