More than 40% of the weight of modern electronic and electrical equipment consists of flammable plastic insulation materials. Electrical and electrical equipment can ignite these materials due to overheating, leakage, short circuit, sparks and aging, causing fires to people and Property security poses a huge threat. To this end, countries around the world have issued regulations that impose stringent regulations on the flame retardant properties, heat resistance and electrical properties of plastic insulating materials used in electronic and electrical equipment.
Electrical and electronic products generally have two requirements for the flame retardant heat resistance and electrical properties of plastic insulating materials - high glow wire, high CTI. According to the requirements of the European Union International Electrotechnical Commission (IEC), the IEC60695 glow wire flame retardant test evaluation standard The IEC organization proposed in the IEC60335 household and similar electrical safety standards that the flame retardant properties of plastic parts used in long-term unattended electrical appliances must meet UL94V-0 and 750 °C glow wire contact materials within 30s of no fire or burning time less than 5s, ie Glow wire ignition temperature (GWIT) is greater than 750 ° C. For components such as connectors, contact switches, motors and circuit breaker housings, GWIT temperatures of 850 ° C and glow ash flammability index (GWFI) of 950 ° C are also required.
Colombo PA66 CTI/GWIT test
For friends who are doing electrical appliances, CTI, Glow Wire is a very common word. But for laymen, they are more difficult to understand. So high CTI, what is the high glow wire specifically? Let's look together Look.
First, about CTI
CTI is called Comprehensive Tracking lndex, Chinese is the relative tracking index. CTI is the highest voltage value of the surface of the insulating material that can withstand 50 drops of electrolyte (0.1% ammonium chloride aqueous solution) without forming traces of leakage, in V.
That is to say, CTI is the highest voltage value of the insulating plastic in the case of electrification, the surface of which drops 50 drops of conductive liquid without causing a carbonization short circuit. Generally, the higher the CTI value of the insulating plastic, the better the leakage resistance. .
1. Why do you have a CTI test?
Plastic insulation materials have a special electrical damage phenomenon: When the surface of the material is relatively moist, there is debris and the electric field is large enough, the surface will form a carbonization circuit, which will eventually form a short circuit, which will most likely cause a fire!
Insulation plastic leakage motor
The mechanism is as follows: When the surface of the material is relatively moist, there is debris and the electric field is large enough, the impurities on the surface may be energized, the heat generated by the electricity will evaporate the water, and then form a drying belt (conducting tape without water); The evaporation can take away a lot of heat, the drying belt does not contain water, and accumulates a large amount of heat; enough heat makes the surface of the insulating plastic carbonized, forming a carbonization guiding circuit, and finally forming a short circuit!
CTI is to simulate the process to measure the minimum voltage of the insulating plastic to produce tracking marks, so that it can be judged whether the material is suitable for some specific environments.
2. What is the CTI test?
Figure: Electrode device (left) and experimental equipment (right)
As shown in the figure above: The left picture shows the electrode device, and the right picture shows the experimental equipment. The size of the sample should be greater than 15mm × 15mm, the thickness should be no less than 3mm; the distance between the two electrodes should be 4.0 mm ± 0.1mm, clip The angle is 60°; the height of the droplet mouth and the sample should be 30 -40mm.
Internal structure of leakage tracking device
After the experimental setup is installed, it is tested:
Given a voltage (generally starting from 300V), the droplet size is preferably controlled at 20-23mm3, and the droplets are dropped on the surface of the sample at intervals of 30s ± 5s; until the formation of electrical traces causes damage or until dripping 50 Before dropping the electrolyte, repeat the test by increasing or decreasing the voltage value (in multiples of 25V or 25V) until two adjacent voltage values are obtained (small voltage after 50 drops, no leakage, large voltage leakage), and smaller The voltage value is the CTI value of the material.
Second, about the glow wire
The glow wire test is to test the stability of electronic and electrical products during work, and the glow wire itself is actually a fixed-size resistance wire ring.
Glow wire
During the test, it should be electrically heated to the specified temperature, so that the top of the glow wire contacts the sample to the standard required time, and then observe and measure its state. The test range depends on the specific test procedure.
Glow wire test icon
The glow wire test mainly involves two terms:
1, flammability index GWFI
GWFI - glow-wire flammability index
The highest test temperature of a test sample of a specified thickness in three consecutive tests shall meet one of the following conditions:
a) the flame or heat of the test sample is extinguished within 30 seconds after removal of the glow wire, and the packaged crepe paper placed under the test sample does not ignite;
b) The test sample does not light up.
GWFI way record:
For example, for a 3 mm thick test specimen with a test temperature of 850 ° C, record as: GWFI: 850/3.0
If one of the above two conditions or one of the two conditions is not met, a lower test temperature is required and the test is repeated with a new test sample.
2, light-off temperature GWIT
GWIT——glow-wire ignition temperature
The maximum temperature above the top of the glow wire that is not ignited by the test sample of the specified thickness is 25K (30K higher between 900 °C and 960 °C) than in the three consecutive tests. In short, it is: as long as it is at the test temperature Non-flammable (3 consecutive samples) is tested by GWIT (25 °C for temperature and 75 °C for 900-960 °C)
GWIT recording method:
For example, for a 3.0 mm thick test sample, the highest test temperature that does not cause light-off is 825 ° C, which is recorded as:
GWIT: 850/3.0 (Note: 850 °C = 825 °C + 25 °C)
Note: The so-called light-off, IEC for GWIT regulations, means that the burning time is more than 5 seconds before the light-off, that is, as long as the flame does not burn for more than 5s, please pay special attention to this!
The glow wire experiment is more of an industry standard for unattended electrical appliances. The glow wire of IEC60335 is the unattended electrical standard. The selection criterion is to first require GWFI of 850 degrees; the second step of material passes 775 degrees of GWIT, ie Passable; or the second step is the final product passing 750 degrees of GWT.