Glow Wire Test and Needle Flame Test to evaluate the flame resistance of plastic materials Mar 26, 2019

In the plastic material test, the Glow Wire Test and the Needle Flame Test are two common flame resistance tests, and the test points of the two tests are different. The glow wire test is a fire source that uses a heat source such as a hot component or an overload resistor in an environment to evaluate the thermal stress caused by a short-term heat source. The ignition source used to simulate the heat source is a glow wire that is heated by electricity. The needle flame test uses simulation technology to assess the fire risk of a small flame caused by fault conditions inside the equipment. It is used to simulate the ignition of a small flame is the flame produced by the burner.

1.Glow Wire Test

The glow wire is a ring made of nickel/chromium wire having a diameter of 4 mm. During the test, the sample is clamped with a jig and the jig can be moved on the track. The glow wire is energized and heated to the temperature specified by the standard. For example, GB2099.1-1996 stipulates:”For the insulating material parts that are necessary to contact the current-carrying parts and the grounding circuit, but not to keep them in the normal position, the test shall be Perform at a temperature of 650 ℃." The jig was moved so that the glow wire was applied to the sample with a force of 0.8 N to 1.2 N for an application time of 30 seconds. A layer of crepe paper was wrapped tightly on a smooth white pine board approximately 10 mm thick, placed under the glow wire application point (200±5) mm. If the sample does not ignite, or although it ignites, but automatically extinguishes within 30 seconds after the glow wire is removed, and does not ignite the underlayer, the glow wire test passes.

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2.Needle Flame Test

The needle flame test uses a needle tube with butane to produce a flame with a height of 12 mm ±1 mm from the tip of the needle to the highest point of the flame, according to the time specified by the selected standard (eg 60 seconds, 30 seconds or 10 seconds). The longer and the more severe the time is applied to the surface of the sample, the distance from the tip side of the needle to the side surface of the needle is 5 mm, or the lower surface and the distance is 8 mm. The bottom layer is the same as the glow wire test. If the sample does not produce a flame or the flame is automatically extinguished within thirty seconds after the application is completed, and the drip does not ignite the underlayer, the needle flame test passes. The needle flame test equipment simulate flames due to fault conditions such as fault current flowing through the leakage path, overheating of components or parts, bad contact, etc., which may hit the nearby parts again. This test is to simulate a small flame generated inside the product under fault conditions, and use the simulation technology to assess the fire hazard. For small parts (or components) where the glow wire test or the horizontal and vertical flammability test method is not suitable, the needle flame test method can be cited. If the sample ignites during the glow wire test, the resulting flame hazard condition requires a needle flame test. Applicable to electronic and electrical products, parts and components of household appliances, such as: wiring board, centrifugal switch, rice cooker socket.

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In addition, the material's flame resistance is inseparable from the addition of flame retardant. A suitable flame retardant can make the test material not reach the ignition point in the test, or reach the ignition point and will automatically extinguish after the ignition. It can be seen in the glow wire test and the needle flame test that some plastic materials without flame retardant may ignite at a certain temperature or time severity and the afterburning time is more than 30 seconds, but a suitable flame retardant is added. After that, it may turn to no igniting at this temperature or time severity level or, although it ignites, it will automatically extinguish within 30 seconds after the glow wire or the needle flame is removed, thus meeting the requirements of the standard.

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