GB/T 2951.9-1997 General test methods for cable insulation and sheathing materials Part 4: Specific test methods for polyethylene and polypropylene mixtures Section 2: Elongation at break test after pretreatment - Winding test after pretreatment - Winding test after air heat aging - Determination of quality
Some standard content:
National Standard of the People's Republic of China
General test methods for insulating and sheathing materials of electric cables Part 4: Test methods specific to polyethylene and polypropylene compounds Section 2: Elongation at break test after pre-conditioning-- Wrapping test after pre-conditioning-- Wrapping test after thermal aging in air Determination of mass increase
Appendix A: Long-term thermal stability test
Appendix B: Copper catalytic oxidative degradation test method Camumon test methods for insulating and sheathing materials of electric cables GB/T 2951.9—1997
idt IEC 811-4-2: 1990
Recommended GB/T 2951.42—94
Part 4 :Methods specific to polyethylene and polypropylene compounds Srctian twa; Elangatian at break after pre-conditionlng-- Wrappingtest after pre-conditioning Wrapping test nfter thermal agcing in airmeasurement of mass Increase-Long-term stability tes1 (Appendix A) Test method for copper catalysed oxidative degradation (Appendix B) 1 Scope
GB/T2951 standard specifies the test methods for polymer insulation and sheath materials of distribution cables and general cables, including marine cables.
GB/T2951.9 specifies the test method for elongation at break after pre-embedding, the test method for winding after quality treatment, the test method for winding after heat aging in air, the method for determining mass increase, the test method for long-term thermal stability and the test method for copper catalyzed oxidative degradation. Applicable to polyolefin insulation 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 cables. 3 Applicable scope
The test conditions and test parameters specified in this standard apply to the most commonly used types of insulation and sheath materials for cables, wires and cords. 4 Definition
For the purpose of the test, a distinction should be made between low-density, medium-density and high-density polyethylene (23): Approved by the State Administration of Technical Supervision on October 28, 1997 and implemented on October 1, 1998
Low-density polyethylene
Medium-density polyethylene
High-density polyethylene
GB/T 2951. 9—1997
d≤0. 925 g/cm
0.9250.940 g/em
Note: These densities refer to unfilled resins, and the determination method is in accordance with the provisions of Chapter 8 of CB/T2951.3-1997. 5 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, and this standard has pointed out these differences. 6 Pretreatment
All tests should be carried out after the insulation and sheath materials have been extruded or vulcanized (or cross-linked) and stored for at least 16 hours. 7 Intermediate value
Arrange the test data that should be obtained in increasing or decreasing order. If the number of valid data is odd, the intermediate value is the middle value. If it is even, the intermediate value is the average of the two middle values. 8 Elongation at break after pretreatment
8.1 General provisions
This test is applicable to the olefin insulation of filled cables with an insulation thickness of less than 0.8mm. 8.2 Pretreatment steps
A section of finished cable specimen of appropriate length should be pretreated in air (i.e. hung in an oven), and the air temperature in the oven should be kept constant. The test temperature and test time are specified as follows: 60±1℃.7×24h* for filling pastes with a nominal dropping point of 50~70℃ (including 70℃); 70±1℃,7×24h - for filling pastes with a nominal dropping point above 70℃. After pretreatment, the relay specimens should be stored at ambient temperature for at least 16h, and should be protected from direct sunlight. Then the sheath should be removed and the insulated core should be cleaned by appropriate methods.
8.3 Test equipment
Tensile testing machine. For tubular specimens, the fixture can be either white-tightening or non-self-tightening. 8.4 Sampling and specimen preparation
Cut at least two Tubular test pieces, each of which is not less than 100 mm in length, are to be used with care not to damage the insulation. If it is difficult to remove the conductor, the conductor shall be pulled out by any appropriate method. Before the tensile test, two parallel marking lines are marked in the middle of each test piece, with a distance of 20 mm between the marking lines. Note: It should be emphasized that in some cases, stranded conductors with relatively thick insulation may not be able to be pulled out without damaging the insulation. 8.5 Tensile test after pretreatment
The test pieces pretreated in accordance with Clause 8.2 and prepared in Clause 8.4 shall be subjected to tensile tests at ambient temperature. When in doubt, the test shall be carried out at (23 ± 2) ℃ and redo the test.
The total length between the clamps is approximately:
50mm---when using a self-tightening clamp for testing; mm when using a non-self-tightening clamp for testing.
The separation speed of the clamp is (25±5) mm/min. For routine tests, the separation speed of the clamp is allowed to be (25050) mm/min. 8.6 Evaluation of test results
The test result shall take the middle value of the elongation at break. 9 Winding test after pretreatment
9.1 General provisions
CB/T 2951. 9 -- 1997
This test is applicable to polyolefin insulated filled cable specimens with insulation thickness less than 0.8 Ⅱ. 9.2 Test procedures
The test shall be carried out in accordance with the method specified in Article 9.5 of GB/T2951.8-1997. However, the aging test shall be carried out in accordance with Article 10.4 of this standard.
For foamed insulation with insulation thickness less than or equal to 0.2 mm, the tensile force applied to the exposed conductor shall be reduced to about 7.5 N/mm relative to the cross-section of the conductor. 9.3 Evaluation of test results
After cooling to ambient temperature, the test specimen shall be inspected with normal vision or corrected vision without a magnifying glass. The test specimen shall not be cracked. If a test specimen is cracked, the test may be repeated once more. 10 Winding test after air heat aging
The method specified in this standard should be considered as an aging method for polyolefin insulation and is therefore included in this standard. Note: It is advisable to refer to GH/T for comparison of this content. 2951.81997 Chapter 9 will be deleted and will not be included in this standard. 10.1 General provisions
This test method is applicable to the polyolefin insulation of non-filled cables with an insulation thickness of less than 0.8 mm and the polyolefin insulation of the insulated core of filled cables.
10.2 Test equipment
10.2.1 Metal test rods and load-bearing components. 10.2.2 Winding device, preferably with the function of mechanically driving the test rod. 10.2.3 Naturally ventilated electric heating test box. 10.3 Sample
Take 4 test pieces for each cable or insulated core to be tested, take a 2-length sample, cut it into four test pieces of equal length, and carefully remove the outer expansion sheath, braiding layer (if any) and fillers that may adhere to the insulated core of the test piece. Keep the conductor in the insulation and then straighten the test piece. 10.4 Aging procedure
Hang the test piece prepared in accordance with 10.3 vertically in the middle of the electric heating test chamber. The test temperature and time are (100±2)℃, 14×24h, the distance between the test pieces is at least 20mm, and the volume occupied by the test pieces should not exceed 2% of the volume of the test chamber. After the aging cycle, take out the test piece immediately and place it at ambient temperature for at least 16h, and avoid direct sunlight. Note: The aging time and temperature can be increased as specified in the relevant cable product standards. 10.5 Test procedure
The test piece aged in accordance with 10.4 is wound under ambient temperature. For this purpose, the conductor should be exposed at one end of the test piece. A load is applied to the exposed conductor end to produce a tensile force of 15V/mm±20% relative to the conductor cross section. Then, the other end of the test piece is wound on the metal test rod with the device specified in 10.2.2. The winding speed is about 1r/5s. The diameter of the test rod is 1 to 1.5 times the outer diameter of the test piece. Then remove the wound test piece from the test rod and keep its spiral shape. Then place it in the vertical state, basically in the middle of the electric heating test box, and place it at (70±2)C for 24 hours. 10.6 Evaluation of test results
After the test piece cools to the ambient temperature, it should be checked with normal force or corrected vision without a magnifying glass. There should be no cracks. If one test piece cracks, the test is allowed to be repeated for 10 times.
11 Determination of insulation quality increase
11.1 General provisions
GB/T 2951.9-1997
This test is used to check the possible mutual influence between the insulating material and the filling paste of the filled cable. The purpose of this test is only for selecting materials.
11.2 Sampling
Take three samples from each color of the insulated core wire of the cable before the filling process. Each section of the test strip of about 2m is cut into three test pieces of 600mm, 800mm and 600mm in length.
11.3 Test steps
Put about 200g of filling paste in a glass container, and immerse the 800mm long sample in the filling paste preheated to the following overflow: (601)℃ - for filling paste with a dropping point of 50 to 70℃ (including 70), (70±1) - for filling paste with a dropping point of more than 70℃. The middle part of this test piece should be at least 500mm long immersed in the filling sound and should not contact the wall of the glass container and other test pieces. The filling hole should be exposed at both ends of the test piece. The glass container should be placed in an oven for 10×24h and kept constant at the temperature specified for the corresponding filling paste.
After the test time is over, remove the test piece from the filling paste and clean it carefully with absorbent paper. Then cut off the two ends of the test piece, leaving at least 500mm of the immersed part in the middle. Two 600mm long test pieces of F are cut to the same length as the immersed test piece. Remove the conductors in the three test pieces and then weigh them at ambient temperature to an accuracy of 0.5mg. 11. 4 Calculation
The increased mass is calculated by the following formula;
1×100%
Where: M,——the average mass of the two dry test pieces, M,——the mass of the test piece immersed in the filling. GB/T 2951.9-1997
Appendix A
(Standard Appendix)
Long-term thermal stability test
Note+This test method is only applicable to communication cables. Similar test methods for distribution cables are under consideration. A1 General
It is generally accepted that the quality of cable components must be satisfactory during the expected life of the cable. In particular, polyethylene insulation must have adequate aging performance in service. For polyethylene-filled cables, the compatibility between insulation and filler should be assessed. The test time, temperature, environment and failure criteria should be carefully determined. A method suitable for material selection is given in this appendix. Due to the long test time, this test is not suitable for routine quality control inspection. This method is only used as a test for material selection to ensure that the selected material is satisfactory for the expected life of the cable. For routine quality control, a short-term test method needs to be developed. A2 Test equipment
A2.1 Air oven in accordance with ISO 188, in particular the following requirements: - Test humidity: (105 ± 1) °C.
Go to 1: This test temperature should be further investigated. - Clean and dry air is replaced at least 6 times per hour. In case of dispute, the air is replaced up to 10 times per hour. Note 2: As an alternative to the loading, a test device consisting of one or more unit containers can be used as long as the above requirements are met, provided that its dimensions meet the following provisions: bzxz.net
Unit container height: at least 250 mml +
Unit container diameter: at least 75 mm
Height to diameter ratio: between 3:1 and 4:1. A2.2 Air flow meter, the measuring range is determined by the size of the air oven specified in A2.1. A2.3 Thermocouple or thermometer, the reading resolution is 0.2℃. A2.4 Balance, accurate to ±0.0005g + sensitivity 0.1mg. A43 Sampling
Take samples from the insulated cores of non-filled cables or filled cables. Take three samples of each color of insulated core. The sample length is 2 m. Each sample forms a test piece.
A4 Test Procedure
A4.1 Unfilled Cable
A4.1.1 The test piece is wound into a loose spiral coil with a point diameter of about 60 mm. The test piece should not be twisted or tangled. If necessary, two loose knots can be tied with lead wire to fix the coil. A4.1.2 Weigh the test piece to an accuracy of 0.1 mg. Then the test piece can be hung in the air oven with the help of a lead wire hook under the top lamp. Use a thermocouple or a suitable thermometer to check whether the temperature of the air in the middle of the coil is maintained at (105 ± 1) ° C. Take three test pieces of each color. If a test device consisting of an aging unit container is used, it is best to place each test piece in a separate container for aging test. If necessary, up to three test pieces can be placed in a unit container for aging together, as long as the distance between the test pieces is 3~5 mm. There should be no contact between the test pieces and the container wall. A4.1.342 After the extinguishing test time is over, the test piece shall be taken out of the air oven and allowed to cool to ambient temperature; GB/T2951.9—1997
1) Visually inspect the insulation for cracks or cracks and the polymer for other signs of damage. The color shall be easily identifiable. 2) Weigh the sample again to an accuracy of 0.1 mg + the mass increase shall not exceed 1 mg A4.1.4 The test piece inspected in A4.1.3 shall be tested as follows: Cut the test piece into five 200 mm long sections at equal intervals. The first section shall be 0.2 m away from the end of the test piece. One end of each 200 mm long section shall be manually wrapped around the other end for at least 10 consecutive turns. Then visually inspect for cracks and cracks. The five sections thus made shall be hung in a ventilated oven at a center of (60 ± 1) for 7 days. After the aging is completed, inspect the test piece for cracks and cracks. A4.2 Fully filled cable
A4.2.1 The test piece shall be pretreated in the corresponding filling paste for 7 days. The pretreatment temperature shall be as follows: (60±1)℃—when the dropping point of the filling paste is greater than 50℃ and less than or equal to 70℃: (70±1)℃—when the dropping point of the filling paste is greater than 70℃. Note: The definition of dropping point can be found in Chapter 4 of GB/T2951.101997. Pretreatment can be performed on a single test piece or on a section of cable. For a single test piece, the test piece should be immersed in about 200g of filling paste in a glass container (except for the two ends). If it is a section of relay, the test piece should be carefully removed after treatment. A4.2.2 After pretreatment, use a lint-free absorbent paper to remove the remaining filling paste on the test piece, then cut off the two ends that have not overflowed, and then cut the test piece into the length specified in A3.
A4.2.3 Then, test according to the steps specified in A4.1.1~A4.1.4. Appendix B
(Appendix of Standard Male)
Sawing Oxidation Degradation Test Method for Olefin Insulated Wire (OIT Test)
B1 Overview
Manufacturers need to monitor their cable production to ensure that they have sufficient antioxidant properties. Once the appropriate materials are selected, the OIT test has proven to be suitable for monitoring raw materials and relays to determine whether they meet the requirements. The OIT test is not suitable for the selection of raw materials. For the above-mentioned purpose, it is best to use a long-term thermal aging test. With the help of a long-term thermal stability test, the material applicability and compatibility of the material can be determined. The OIT test is then used to determine the performance of the material. In order to ensure that the material meets the long-term stability performance, the relationship between the OIT test and the long-term stability test must be determined. This correspondence can be used to control materials and production, but it may not be the same between test laboratories. Manufacturers need to use this method to evaluate all insulation and insulation and filler combinations used in the production of cables. The OIT test method given in this annex is applicable to copper catalytic oxidative degradation tests. B2 Test equipment
B2.1 Differential thermal analyzer or differential scanning calorimeter. The heating rate is at least (20 ± 1) K/min, and it can automatically record the temperature difference (or heat transfer difference) between the sample and the reference material, and the sensitivity and accuracy meet the requirements. B2.2 X-Y recorder. The Y axis displays heat flow or temperature difference, and the X axis displays time. The time baseline should be accurate to ± 1% and can be read to 1 minute. B2.3 High-purity nitrogen and oxygen gas switch and regulator. B2.4 Analytical balance, capable of weighing 30g, with a sensitivity and repeatability of ± 0.1mg. B2.5 Sample cup, aluminum scale, with a diameter and height of about 6 to 7mm or a cup of similar size provided by the instrument manufacturer. B3 Sampling
Cut an appropriate number of conductor samples from the insulated wire. The sample length is about 4mm. In this way, 3~5mg of insulating material can be obtained. B4 Instrument calibration
GB/T2951.9—1997
B4.1 Before using the instrument, it should be calibrated according to the manufacturer's instructions. Use analytical pure steel as the temperature reference material B4.2 Put (2±0.5) mg of analytical pure smoke into an aluminum cup and cover it with an aluminum lid. Put the prepared sample in the instrument and refer to the aluminum cup and cover.
If the sample, aluminum cup and cover must be cleaned, petroleum ether or other suitable solvents can be used to remove contaminants. B4.3 Raise the temperature from 145℃ to 165℃ at a rate of 1K/min, and record the temperature rise process. B4.4 Calibrate the instrument according to the manufacturer's instructions to obtain the first-stage transformation temperature of indium of 156.6℃. For calibration, the melting point of indium, 156.6°C, is determined as the intersection of the extrapolated line of the baseline and the extrapolated line of the peak starting line (see Figure B1): B5 Instrument preparation
B5.1 Open the valves of the nitrogen and oxygen cylinders. Set the gas selector switch to the nitrogen position. Use a flow meter to adjust the flow rate to (50±5) ml/min.
B5.2 Place the wire sample taken according to B3 into the pot cup (see B4.2). B5.3 Place the prepared wire sample into the sample cup of the instrument. Place the empty aluminum cup in the reference position. Note that aluminum or stainless steel wire mesh can be used to restrain the sample so that they are in better contact with the sample cup. B5.4 Purge with nitrogen for 5 minutes + check the flow rate as required and repeat until it reaches (50±5) ml./min. B 5.5 Set the instrument to zero, amplify the signal and adjust the sensitivity of the recorder to the maximum offset of the recorder pen corresponding to the exothermic reaction. B5.6 Adjust the heating rate to 20K/min
B6 Test steps
B6.1 Start program heating and record the heating process. B6.2 Continue heating to the specified test overflow, control it within the range of ±1°C, stop program heating, and allow the sample temperature to reach a constant temperature. It has been determined that the temperature range of 190 to 200°C is appropriate for polyethylene. Ⅱ After reaching temperature equilibrium (stable recorder signal), switch the purge gas to oxygen and adjust the flow rate to (50 ± 5) mL/min. Mark this point on the record and use this turning point of oxygen purge as the starting time (T) of the test time. B6.3 Continue this isothermal operation until the maximum pen offset after the exothermic reaction appears on the recorder curve (see Figure B2). At each stage of exothermic reaction, continue the isothermal operation until the maximum pen offset appears. B6.4 After the test, turn off the recorder and switch the gas selector valve to nitrogen. B6.5 Allow the instrument to cool to the starting temperature.
B6.6 Repeat the entire process test 4 more times on the new sample. In this way, a total of 5 temperature curves are obtained. Each sample can be tested with a new reference lead cup.
The steps described in B6.2 and B6.3 can omit the preheating step in fluorine gas to simplify the operation. When performing this operation, the unit container of the instrument should be heated to the required temperature in oxygen. First, place the reference cup in the unit container, and then once the heating unit reaches the specified test temperature, put the pot cup with the sample in place. The corresponding point is taken as the starting time (T,) B7 Calculation
B7.1 Extend the baseline outward along the starting point of time to the oxidation exotherm, and then extrapolate the steepest part of the curve formed by the exotherm to the phase change with the extension line of the baseline (see Figure B2)
B7.2 Determine the oxidation induction period from the starting point of time. The practical minimum time interval shall not exceed 1min. 88 Test report
B8.1 Sample identification
B8.2 Test temperature
GB/T2951.9—1997
B8.3 Calculate the average and standard deviation of the OIT measured 5 times, in min. 156.6℃
The intersection point of the extrapolated line of the peak starting line and the extrapolated line of the baseline is defined as 156.6℃Figure B1
Sample sequential heating (atmosphere)
Melting endotherm of indium
Isothermal mode (oxygen)
Convert to isothermal operation:
Switch to oxygen
2 Obtain OIT from the recorded time-temperature curveFigure B2
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.