Test method for flame retardant performance of cable materials

Most polymer materials are flammable and combustible materials. They have a large heat release rate during combustion, high calorific value, fast flame propagation speed, difficult to extinguish, and sometimes produce dense smoke and toxic gases, which cause huge damage to people’s lives and the environment. harm. Today we will introduce in detail the three common flame retardancy tests of polymer materials: horizontal combustion test method, vertical combustion test method, and oxygen index method.

1. Horizontal combustion test method
The horizontal burning test method is to test the burning performance of a sample under horizontal support under laboratory conditions. There are many standards for horizontal burning test methods, mainly in the testing of wires and cables, plastics, leather, and blankets.
Horizontal combustion test chamber of National High Material Analysis and Testing Center
Horizontal burning test test standard
GB/T 12666.2-2008 Single wire and cable burning test method Part 2: Horizontal burning test
GB/T 8332-2008 Test method for the combustion performance of foam plastics Horizontal combustion method
MH/T 6047-2008 Four-layer horizontal burning test method for aviation blanket
QB/T 2729-2005 Leather Physical and mechanical test Determination of horizontal burning performance
Specific test method of horizontal combustion test
1) Test device
The test was carried out in a combustion box, and a Bunsen burner with an inner diameter of 9.5 mm was installed on the left inner side of the box. There is a test piece clamp for fixing the test piece on the right side of the inside. The Bunsen burner tilts up 45 degrees and is equipped with a forward and backward device. The test gas is natural gas, liquefied petroleum gas or coal gas, and it is equipped with a stopwatch and a caliper.
2) Test method
A. Specimen preparation
Each material needs 5 specimens, each specimen shall be flat and smooth, without bubbles, 125±5mm in length, 13.0±0.3mm in width, and 3.0±0.2mm in thickness. The test can also be carried out on samples with a thickness of 2-13mm. , But the results can only be compared between the same thickness.
B. experiment procedure
First, draw a marking line on the wide surface of the sample at 25 mm and 100 mm from the ignition source, and then place the test piece horizontally on the long axis, and fix it on the test piece clamp at a 45-degree angle to the horizontal axis of the cross section. Place a drip tray 300mm below it. Ignite the Bunsen burner, adjust the flame length to 25mm and create a blue flame, and apply the tip of the flame core to the lower edge of the sample about 6mm in length. And start timing, applying flame time is 30 seconds. During this period, the Bunsen burner shall not be moved, but during the test, if the specimen has burned to the first marking line in less than 30 seconds, the application of flame shall be stopped immediately. The following observation records should be made after stopping the flame.

a. Whether there is a visible flame within 2S;
b. If the sample continues to burn, record the time t that the flame front takes from the first marking to the second marking, and find the burning speed V: V=75/t (mm/min)
c. If the flame reaches the second mark and extinguished before, record the burning length S:S=(100-L)mm where: L——the shortest distance from the second mark to the unburned part, accurate to 1mm. Observe other phenomena, such as melting, curling, carbon formation, dripping and whether the dripping material burns.
C. Evaluation of results
Each trial is classified as follows
a. GB2408-80/Ⅰ: The sample is extinguished within 2s after the fire source is evacuated
b. GB2408-80/Ⅱ: The flame front is extinguished before reaching the second standard. At this time, the burning length S of the sample should be reported (if the burning length is 50mm, report it as GB2408-80/Ⅱ-50mm)
c. GB2408-80/Ⅲ: When the flame front reaches or exceeds the second marking line, the burning speed V should be reported at this time (if the burning speed is 20mm/min, report as GB2408-80/Ⅲ-20mm/min). The test results are based on 5 tests. The category with the largest number in the piece is used as the evaluation result of the material, and the maximum burning length or burning speed is reported.
2. Vertical burning test method
The vertical combustion method is a method to classify the combustion of a sample with a certain specification placed vertically after applying flame action under specified conditions.
Vertical burning test test standard
GB 32086-2015 Technical requirements and test methods for vertical combustion characteristics of specific types of automotive interior materials
GB/T 12666.1-2008 Single wire and cable burning test method Part 1: Vertical burning test
GB/T 8333-2008 Rigid foamed plastic burning performance test method vertical burning method
JB/T 4278.18-2011 Rubber plastic wire and cable testing equipment verification method Part 18: Single copper core insulated thin wire and cable vertical burning test device
JB/T 4278.5-2011 Rubber plastic wire and cable testing equipment verification method Part 5: Single insulated wire and cable vertical burning test device
JJF (Textile) 068-2016 Calibration Specification for Vertical Burning Tester
JJF (Textile) 068-2018 Vertical Burning Tester Calibration Specification
FZ/T 98017-2018 Textile Vertical Burning Performance Tester
Specific test method of vertical combustion test
1) Test device
The test is carried out in a combustion box with an internal size of 329mm×329mm×780mm. The top of the combustion box has an exhaust hole with a diameter of 150mm. In order to prevent the influence of external airflow on the test, a top plate is added 25mm from the top of the box. The right side of the combustion box is equipped with a test piece holder support, and the test piece can be fixed. Located in the center of the combustion box. A Bunsen burner inclined 45 degrees upwards is installed on the left side of the box. Fixed on the horizontal slide of the control box. A bracket for putting absorbent cotton is placed in the lower part of the box. Other spares are a stopwatch and calipers.

2) Test method
A. Specimen
Each group of samples requires 5 test pieces, which are required to be smooth and free of bubbles. Length 130±3mm, width 13.0±0.3mm, thickness 3.0±0.2mm. The prepared test piece should be adjusted for 48 hours under standard climatic conditions.
B. experiment procedure
The test piece is vertically fixed on the test piece clamp, and the clamped part of the upper end of the test piece is 6mm. Put the absorbent cotton. Ignite the Bunsen burner at a distance of 150mm from the test piece, adjust the flame height to 20±2mm, and show a blue flame. Place the center of the Bunsen burner 10mm at the lower end of the test piece, and aim the flame at the center of the lower end of the test piece. start the timer. After applying flame to the test piece for 10 seconds, remove the fire source, record the flame burning time of the test piece. After the flame burning of the test piece is extinguished, apply the flame for another 10 seconds according to the above method, and record the flame burning and non-flame burning of the specimen after the flame is removed. Flame burning time.
C. Result evaluation
The combustion performance of the test piece is specified as FV-0, FV-1, FV-2 three levels as follows.
FV-0: The vertical sample stops burning within 10 seconds; no droplets are allowed;
FV-1: The vertical sample stops burning within 30 seconds; no droplets are allowed;
FV-2: The vertical sample stops burning within 30 seconds; burning substances are allowed to drip.
If one group of 5 samples does not meet the requirements in the table, another group of samples should be taken for testing, and the second group of 5 samples should all meet the requirements. If there is still one sample in the second group that does not meet the corresponding requirements in the table, the level with the largest value in the two groups shall be used as the level of the material. If the test result exceeds the requirements of FV-2, the material cannot be evaluated by the vertical combustion method for oxygen index.
3. Oxygen index method
There are still many products suitable for flame retardant performance testing-oxygen index method, such as viscose, polyester fiber, synthetic fiber, plastic, textile, asphalt and so on.
Flame Retardant Performance Test-Oxygen Index Test Standard
FZ/T 50016-2011 Viscose staple fiber flame retardant performance test method Oxygen index method
FZ/T 50017-2011 Flame Retardant Test Method of Polyester Fiber Oxygen Index Method
FZ/T 50029-2015 Synthetic fiber raw material chip flame retardant test method-oxygen index method
GB/T 16581-1996 Test method for burning performance of insulating liquid-Oxygen index method
GB/T 2406.1-2008 Plastics Determination of combustion behavior by oxygen index method Part 1: Guidelines
GB/T 2406.2-2009 Plastics Determination of combustion behavior by oxygen index method Part 2: Room temperature test
GB/T 5454-1997 Textiles Burning performance test Oxygen index method
GB/T 8924-2005 Test method for burning performance of fiber reinforced plastics Oxygen index method
GSB 08-3562-2019 Plastic (PMMA) oxygen index standard sample
NB/SH/T 0815-2010 Determination of Asphalt Combustion Performance Oxygen Index Method
TB/T 2919-1998 Fabric combustion oxygen index test method
Specific test method of oxygen index
1) Refer to GB2406 “Plastic Flammability Test Method-Oxygen Index Method”, which stipulates that the lower end of the clamp can be used to measure the plastic that can stand upright. The burning time of the sample is 3 minutes. A marking line is drawn from the wide surface of the sample 50mm from the ignition end. When the burning time of the sample exceeds 3 minutes or the flame front exceeds the marking line, the oxygen concentration is reduced. When the burning time of the sample is less than 3 minutes or the flame front is less than the marking line, the oxygen concentration is increased. Repeat this process until the oxygen concentration obtained by both The difference is less than 0.5%.
2) Test method
A. Specimen preparation
Each group of samples should have 5-10 test pieces, each of which is 70-150mm long, 6.5±0.5mm wide, and 3.0±0.5mm thick, and the surface of the test piece is required to be smooth and free of bubbles.
B. experiment procedure
Before the test is carried out, the test piece shall be marked with a graduation line at a distance of 50mm from the ignition source, and then installed vertically on the test piece holder. The distance between the upper end and the combustion cylinder shall be greater than 10mm. The initial oxygen concentration shall be estimated and adjusted, and it shall be kept burning at all times. The air flow velocity in the barrel is 40±10mm/s. Let the adjusted air flow for 30 seconds to clean the combustion tube. Then use an igniter to ignite the top of the test piece. When it is confirmed that the top of the test piece is fully ignited, remove the igniter and start timing. Do not change the flow rate and oxygen concentration arbitrarily at this time. During the test, if the burning time of the sample exceeds 3 minutes, or the flame front exceeds the marking line, the oxygen concentration should be reduced before the test. , On the contrary, the oxygen concentration should be increased. When adjusted to the oxygen concentration value increase or decrease the difference is less than 0. At 5%, the oxygen index of the material should be calculated based on the reduced oxygen concentration value. Three tests were performed within this range.
C. Result calculation
The calculation formula of oxygen index (OI): OI=[O2] / [O2]+[N2]×100% where [O2]——Oxygen flow rate L/min: [N2]——Nitrogen flow rate L/min. Three times The average of the test results is the oxygen index of the material.
The oxygen index of various organic polymers has been measured. Generally, substances with OI≥27 are flame-retardant substances.
D. discuss
Factors affecting oxygen index
a. Flow rate
At 30 and 120mm/s, OI is almost independent of air flow. The flow rate must be fast enough to remove burned gas from the nearest atmosphere, but not too fast to avoid increasing the mixing speed at the front of the fire.
b. The thickness of the sample
The material becomes more combustible as the sample becomes thinner, and the oxygen index value decreases.
c. pressure
Some polymers have OI that is sensitive to reduced pressure, which may accelerate the degradation of the polymer due to the continuous removal of products.
d. Inert gas
When Ar, Ne, CO2 gas is used, the oxygen fraction (OF) required to maintain combustion is expressed as: OF = [O2] / [inert gas]
The OF value increases linearly with the heat capacity of the gas. When Hr is used, the OI value is 50% larger than expected. This is due to the high thermal conductivity of Hr gas that takes heat away from the flame.
e. temperature
Temperature has a great influence on OI, and temperature has little influence on OI at room temperature. The relationship between OI and temperature of various polymers is different at high temperature.
f. Relationship between value and ignition position
Bottom ignition and top ignition can get different oxygen index values. Bottom ignition is closer to the actual combustion situation than top ignition, and its oxygen index value is much lower.