Oxygen Index Tester
It can not only serve as a means to identify the flammability of polymers, but also as a research tool, providing a powerful testing method for laboratory research on flame retardant formulations and the development of new flame retardant materials. It is suitable for combustion testing of solid materials, laminated materials, foam plastics, fabrics, soft sheets, and films.
Oxygen index is a method for evaluating the combustion performance of materials under laboratory conditions. For example, some university textbooks define oxygen index as: the so-called oxygen index refers to the minimum oxygen concentration required for a specimen to maintain stable combustion, i.e., flaming combustion, in an oxygen-nitrogen mixed gas flow under specified test conditions, expressed as the volume percentage of oxygen. Some literature also includes smoldering in the category of "stable combustion." There is currently no unified and clear definition. However, because the definition of "oxygen index" is not clear enough, it may cause confusion when measuring the oxygen index, and also lead to deviations in measurement.
However, the oxygen index method is not the only criterion and testing method; the oxygen index is also affected by factors such as temperature, humidity, and the dimensions of the material. For the same material, the higher the temperature it is exposed to, the lower the limiting oxygen index.
Main Uses of Oxygen Index Tester:
Oxygen Index Tester is used to determine the volume percentage of oxygen required during the combustion of polymers. The oxygen index value of a polymer is the minimum oxygen concentration (also called oxygen index) in an oxygen-nitrogen mixed gas flow that just maintains the combustion of the specimen after it is ignited, keeping the combustion length of 50mm or the combustion time of 180s. It is used to evaluate the combustion performance of related products. It is suitable for combustion testing of solid materials, laminated materials, foam plastics, fabrics, paper, soft sheets, and films.
Test Principle of Oxygen Index Tester
Under specified test conditions, a mixed gas of oxygen and nitrogen at 23℃±2℃ is introduced, and the test method determines the minimum oxygen concentration required to maintain combustion. A specimen is vertically fixed in a transparent combustion cylinder with an upward flow of oxygen-nitrogen mixed gas. The top of the specimen is ignited, and the combustion characteristics of the specimen are observed. The continuous combustion time or combustion length of the specimen is compared with the given standard. Through a series of tests at different oxygen concentrations, the minimum oxygen concentration is estimated. To compare with the specified minimum oxygen index value, three specimens are tested, and according to the standard, at least two specimens must extinguish.
Ignition Methods of Oxygen Index Tester
Top Surface Ignition Method:
For self-supporting materials (such as molded materials, foam materials, thick sheets, molded and sheet materials for electrical appliances), the top surface ignition method is adopted, and a marking line is drawn at 50mm from the ignition end. During the test, the igniter is removed every 5 seconds, and the removal time is just enough to determine whether the entire top surface of the specimen is ignited. After confirming that the top surface of the specimen is ignited, immediately remove the igniter, and start timing and observing the combustion length. The maximum time for the flame to contact the top surface is 30 seconds. If ignition cannot be achieved within 30 seconds, increase the oxygen concentration and continue ignition until ignition is achieved within 30 seconds.
Diffusion Ignition Method:
For non-self-supporting materials (such as soft sheets or films), the diffusion ignition method is adopted (also applicable to self-supporting materials). The flame is applied to the top surface of the specimen and simultaneously to the vertical surface. During ignition, the igniter is removed every 5 seconds or so to observe the specimen. The maximum flame application time is 30 seconds, until the vertical side surface burns steadily or the front edge of the visible combustion part reaches the upper marking line, then remove the flame. For film products, when using a frame fixture, due to phenomena such as shrinkage during combustion, it is recommended by standard ISO/TC61/SC4 to use the roll method for testing to obtain better stability and reproducibility.
Structure Introduction of Oxygen Index Tester
Oxygen Index Tester mainly consists of a specimen holder, combustion cylinder, flow meters, gas source, and control system.
Combustion Cylinder: This part consists of a heat-resistant glass cylinder vertically fixed on a base, which can uniformly introduce the oxygen-nitrogen mixed gas. The standard specifies that the height of the combustion cylinder is (500±50) mm, and the inner diameter is (75～100) mm.
