Investigation of ignition of thermoplastics through the Hot Wire Ignition Test

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De Araujo, Luiz Claudio Bonilla
Texas A&M University
safety engineering.; Major safety engineering.
thesis / dissertation description
The purpose of this research was to investigate the ignition phenomena of selected polymeric materials using the Hot Wire Ignition Test. This test is prescribed by Underwriters Laboratories as one of various requirements for polymeric materials used in enclosures or insulation systems of electrical equipment. The main objective of this project was to identify the effect of specimen thickness on the ignition time. In addition, temperature changes at the surface of some materials during the ignition process were also investigated. The apparatus used for this test was specified by ASTM D 3874-90a-Standard Test Method for Ignition of Materials by Hot Wire Sources. It consisted of a supply circuit capable of maintaining a continuous 60 Hz power density of 0.26 W/mm over 12 inches (304.8 mm) of No. 24 AWG, Nichrome V wire and a variable transformer for adjustment of the voltage to achieve the desired current. A representative piece of the wire was calibrated according to procedure given by ASTM D 3874. Temperature measurements were made using a 12-channel scanning thermometer and 30 AWG chromel-alumel (type K) thermocouples. A direct relationship between time to ignition and thickness was verified. Although this was an expected result, since extensive research has already detected this relation no similar study using this procedure was found in the literature. Furthermore, from the results of temperature measurements, it is clear that this procedure may be used to obtain important information regarding the thermo-physical characteristics of polymeric materials.