Discussion on Needle Flame Test in Needle Flame Test Equipment

The needle flame test is the main test item to verify whether electronic products and materials are flame retardant. It simulates the small flame that may result from overheating in the fault or overload conditions of electronic products and components, and reproduces the actual situation, so as to evaluate the fire risk of the product through simulation technology. Combining the requirements of IEC 60695-11-5:2004 and GB/T 5169.5-2008 on the method, equipment, and technical indicators calibration for the needle flame test, this paper analyzes precautions for the needle flame test equipment testing process.

According to IEC60695-2-2, IEC60695-11-5 and GB/T-5169.5, LISUN ZY-3/ZY-3S needle flame test equipment is applied in the production and quality control department of lighting products, hyperpiesia electrical apparatus, domestic appliance, machine electric appliance, electrical machine, power tool, electronic instrument, electrician instrument and technical equipment. Also, the apparatus is fit for the industry of insulation material, engineering plastics and solid combustible material.

I. Differences between old and new standards
1.1 Expansion of the scope of application
GB/T 5169.5-2008 expanded the scope of application. The needle flame test not only considers the risk of fire ignition caused by fault inside the product or component, but also considers the risk of external fire ignition caused by other equipment. Simulation technology is used to evaluate the internal and external ignition, so as to detect the reaction characteristics of the whole equipment or materials to heat and flame more comprehensively.

1.2 Requirements for needle flame test equipment
1) For needle flame test equipment body: GB/T 5169.5-1997 does not have specific requirements for the volume of the needle flame test equipment, while the new version standard clearly stipulates that the volume of the laboratory air cabinet/test box should be at least 0.5m3, the surface color of the box should be dark, and the test should be performed without air ventilation. The standard stipulates the volume of the test box in order to avoid the loss of oxygen caused by air convection, which affects the test results.
2) For burner and flame: the new version standard has clear stipulations on the gas used by the burner. Pure methane gas and large alkane gas can be used with purity not less than 95%. Butane is a flammable, odorless gas that can be easily liquefied and stored. Most needle flame tests usually choose butane gas for use. At the same time, for the flame height requirements of the needle flame test, the equipment and procedures should be confirmed according to Annex A of the standard.

1.3 New requirements for timers
GB/T 5169.5-2008 new version standard adds requirements for timers. The hysteresis of the timer should not exceed 0.5s, while the old version standard does not have such requirements.

1.4 New requirements for test samples
GB/T 5169.5-2008 new version standard adds test sample description, which requires that the test sample should be a complete device, component or part. In case of necessity, appropriate part and parts should be cut off and removed, and it should be ensured that the test conditions have no significant differences from the normal use conditions of the product. The addition of this clause is to more realistically simulate the flame effect when the product is ignited.

1.5 Modification of the evaluation of needle flame test results
How to judge whether the test sample can withstand the needle flame test, GB/T5169.5-2008 the new version standard is more stringent than the old version standard. The new standard stipulates that after the needle flame is removed, the flame or heat of the test sample and the surrounding parts should be extinguished within 30s, and the burning at the bottom layer or packing tissue paper caused by the burning of the test sample is not allowed, it can be judged that the test sample is not qualified. Such provisions are to prevent secondary combustion ignition hazards caused by the flaming of the product drips.

1.6 Addition of test report GB/T 5169.5-2008
The new version standard adds the content of the test report, mainly including: type and description of the test sample, preparation method, all pre-treatment of the test sample, number of the test sample, strict grade, the surface to be tested and the point of needle flame application, the bottom layer or packing tissue paper affected by the burning or heat particles droplets from the test sample, whether more than one point is tested on the same sample, and the test results.

II.Procedure and procedure of needle flame test equipment for needle flame test:
The needle flame test is usually carried out on 3 samples (with exceptions). The test samples should be placed in the most easily flammable position when in normal use, and fixed without affecting the application of the test flame or the flame spread. The test flame should be applied to the surface that is most likely to be affected by the flame. The flame tip is in contact with the sample surface, the flame height is adjusted to 12mm + 1mm, and the time for the flame temperature to rise from 100℃+2°℃ to 700°℃+3℃ is 23.5s+1.0s.

During the test, the test sample will melt and often drip into the combustion tube, which will eventually block the cold air supply channel and affect the test result. In order to avoid this situation, the new standard stipulates that the combustion nozzle can be tilted at 45° and the distance between the center of the top of the combustion nozzle and the bottom of the remaining part of the sample is 8mm + 1mm or 5mm + 1mm on the side. A about 10mm thick smooth wooden board is tightly wrapped with chamois paper and placed 200mm+5mm below the test sample subjected to needle flame. After the flame temperature is reached, start the test switch for observation of the test sample, surrounding components and bottom layer, and record the duration of combustion (tb) from the moment when the test flame is removed to the moment when the flame is completely extinguished and the test sample, the stipulated bottom layer or nearby components can no longer be seen burning.

III.Method for confirming the calibration results of Equipment:
The main performance parameters of needle flame test equipment include box size, burner size and inclination angle, timer, flame height, and temperature calibration.
1) Box size. Clear regulations have been made for the volume of the test box, the volume of the test box should not be less than 0.5m3, the test box should be dark enough, in case of dispute, 20Lux illuminance should be used to facilitate experimental personnel to more accurately adjust the flame height and observe the burning of the sample.
2) Burner size and inclination angle. Use calipers to measure the aperture of the burner, requiring the pipe aperture to be 0.5mm±0.1mm and use the dial caliper to measure the length and outer diameter of the burner pipe, with the length ≥35mm and the outer diameter ≤0.9mm meeting the requirements. Use universal angle ruler to measure the inclination angle of the burner. The standard stipulates that “the burner can be inclined 45° to the vertical line to prevent the material from falling into the combustion pipe”. Therefore, the inclination angle of the burner should reach 45° to meet the requirements.
3) Timer. Use electronic second timer to calibrate the time points of flame application, continuous flame time point and temperature rise time point, and the error of the timer should be ±0.5s to meet the standard requirements.
4) Flame height. During the needle flame test, the flame height can be measured with a dial caliper, which is 12mm±1mm and meets the standard requirements.
5) Temperature calibration. The new standard stipulates the material of the temperature sensing copper block used for flame confirmation test as CU-ETP UNS C11000, the diameter of the copper block as 4mm±0.01mm and the mass as 0.58g±0.01g. This standard clearly stipulates the requirements for the copper block, which not only facilitates the repeatability and comparability of the test, but also helps to improve the accuracy of the test results. After inserting the thermocouple into the hole for the full depth, the copper block is extruded to fix the thermocouple, but not damaged, it is put into the heating pan, and the temperatures of 100℃ and 700℃ are set separately to read the temperature value displayed three times on the thermometer, and the average value is taken as the actual temperature display value, and when the temperature test result is within 100℃+5℃ and 700℃+3℃, it is considered valid.

IV.Precautions for Burner Flame Test Process:
1) The test equipment should comply with the volume size requirements of GB/T 5169.5-2008 standards, and the experiment box door should be locked during the test to avoid air loss of oxygen which may affect the test results.
2) The gas supplied to the burner has specific requirements. When the gas source changes, the flame temperature will inevitably be affected. Therefore, the flame test must be re-confirmed when the gas source is changed.
3) The test sample and the underlayment (wooden board and filter paper) should be pre-treated according to the temperature and humidity specified in the standard before the test, usually requiring at least 24 hours at room temperature.
4) It is necessary to ensure that the deterioration caused by the previous test will not affect the results of the test to be performed on the same sample.
5) Pay attention to keep the inside of the equipment clean, and clean up after the test; check the burner needle hole before each test to avoid blockage of molten droplets, which may affect the full combustion of the flame.

V. Conclusion:
Needle flame test is an important test item to test the fire risk of electrical and electronic products and materials. Test personnel should have a deep understanding of the standards, understand the differences between new and old standards, and familiarly grasp the operation methods, so as to minimize and reduce the factors affecting the test results, thus improving the accuracy of the needle flame test flame test conclusions. This not only helps to improve the product quality of enterprises, but also helps to effectively control the cost of enterprises, thus more effectively improving the overall quality of electrical and electronic products.