The flame retardant test chamber is a specialized equipment that evaluates the flame retardant performance of materials (such as combustion rate, afterburning time, oxygen index, etc.) by simulating specific combustion environments, applying standardized combustion conditions, and monitoring the combustion behavior of materials. Its working principle revolves around the four core links of "environmental control → combustion triggering → process monitoring → result judgment", and strictly follows international/domestic standards (such as GB, ISO, UL series standards) to ensure the objectivity and comparability of test results. The specific analysis is as follows:

1、 Core principle: Construction of standardized combustion environment and monitoring of combustion behavior

The core of flame retardant testing is to allow materials to burn under unified and controllable conditions, avoiding environmental factors such as temperature, oxygen concentration, and airflow from interfering with test results. At the same time, by accurately monitoring key parameters during the combustion process, the flame retardant ability of materials can be quantified. The principles of different types of flame retardant test chambers (such as horizontal/vertical combustion chambers, oxygen index testers, and heating wire test chambers) may differ slightly, but the core logic is consistent: by controlling the "three elements of combustion (combustible material, combustion aid oxygen, ignition source flame/high temperature)", the response of materials to combustion can be observed.

2、 The specific working principle of typical types of flame retardant test chambers

According to different testing standards and evaluation indicators, flame retardant test chambers are mainly divided into three categories: "horizontal/vertical combustion test chamber", "oxygen index tester", and "heating wire test chamber", each with its own working principle and emphasis:

1. Horizontal/vertical combustion test chamber (commonly used to evaluate the combustion spread characteristics of materials)

Suitable for materials such as plastics, rubber, textiles, etc., the flame retardant level (such as UL94V0/V1/V2, GB/T2408) can be determined by monitoring the "ignition time, smoldering time, and combustion length" of the material through "fixed combustion angle (horizontal/vertical) and standard ignition source". Workflow and principle: ① Sample preparation and fixation: Cut the material into standard sizes (such as 125mm × 13mm × thickness, depending on the standard), fix it on the sample rack at a "horizontal" or "vertical" angle (when burning vertically, the lower end of the sample is suspended, and when burning horizontally, the sample is laid flat on the insulation support); ② Combustion environment control: Close the door of the test chamber and ensure that the chamber is in a "normal temperature and pressure air environment" (some equipment can control the airflow velocity to be ≤ 0.5m/s to avoid scattering flames or accelerating combustion). There is a "fire extinguishing groove" at the bottom of the chamber (filled with water or fire extinguishing cotton to prevent burning droplets from igniting other objects); ③ Ignition and combustion monitoring:

The ignition source is a "propane flame" (the flame height is adjusted according to the standard, such as a flame height of 20mm ± 2mm when burning vertically), and it contacts the sample ignition point for a specified time (such as 10 seconds) (it contacts the lower end of the sample when burning vertically and the free end of the sample when burning horizontally);

After ignition, start timing immediately: record the "continuation time" (the time the material continues to burn with flames after the ignition source is removed) and the "smoldering time" (the time the material burns without flames after the continuation is completed); If it is horizontal combustion, it is also necessary to measure the "combustion length" (the distance of flame spread);

④ Result judgment: Determine the flame retardant level of the material based on whether the ignition/smoldering time and combustion length meet the standard threshold (such as UL94V0 level requirements: the ignition time after two ignitions should be ≤ 10s, and there should be no combustion droplets igniting the degreased cotton below).

2. Oxygen index tester (to evaluate the minimum oxygen concentration required for material combustion)

By "adjusting the concentration of oxygen and nitrogen mixture", find the "minimum oxygen concentration (oxygen index OI)" that can just maintain the combustion of the material. The higher the OI value, the stronger the flame retardancy of the material (applicable to plastics, rubber, foam, etc.). Follow the standards such as GB/T2406, ISO4589-2. Workflow and principle: ① Oxygen nitrogen mixed gas control: The equipment is equipped with "oxygen steel cylinders" and "nitrogen steel cylinders", which mix the two gases in proportion through a "precision flow controller" (oxygen concentration can be adjusted from 10% to 60%). After the mixed gas is stabilized by a "stabilizing valve", it is uniformly introduced into the combustion cylinder (vertically placed, with an inner diameter of about 75mm) to ensure stable airflow inside the cylinder (flow rate of 50mm/s ± 10mm/s); ② Sample fixation and ignition: Make the material into a standard sample (such as 80mm × 10mm × 4mm), vertically fix it on the sample clamp inside the combustion cylinder, and use an "igniter" (such as an electric spark or small flame) to ignite from the top of the sample to ensure that the top of the sample is fully burned; ③ Oxygen concentration gradient test:

First, set a higher oxygen concentration (such as 30%). If the sample continues to burn for more than 3 minutes or the burning length exceeds 50mm, it indicates that the oxygen concentration is too high and needs to be reduced (such as by 2% each time);

If the sample extinguishes immediately after ignition, it indicates that the oxygen concentration is too low and needs to be increased (e.g. by 2% each time);

Repeat the test and find the minimum oxygen concentration that can maintain the sample burning for 3 minutes or 50mm, which is the oxygen index (OI) of the material;

④ Result significance: OI<21% is a flammable material, 21% ≤ OI<27% is a flammable material, and OI ≥ 27% is a non flammable material (such as OI=32% material, which requires an oxygen concentration of ≥ 32% in the air to burn and is not flammable in daily environments).

3. Hot wire test chamber (simulating the scenario of "hot element ignition" to evaluate the material's resistance to ignition)

Simulate the ignition risk of "overheating components (such as resistance wires and solder joints)" in electrical equipment on surrounding materials. Monitor whether ignition and flame spread occur by contacting the material with a "standard hot wire (high-temperature metal wire)", suitable for electrical enclosures, cable insulation layers, etc., following standards such as GB/T5169.10 and IEC60695-2-11. Workflow and principle: ① Heating and temperature control of heating wire: The heating wire is a "nickel chromium alloy wire" (diameter 4mm), which is heated by "current" and monitored in real time by a "thermocouple" to accurately control the temperature between 500 ℃ and 1000 ℃ (set according to testing requirements, such as simulating different overheating element temperatures); ② Sample fixation and contact conditions: Fix the material sample (thickness ≥ 3mm, surface flat) on the sample table, the height of the sample table can be adjusted, so that the hot wire contacts the sample surface vertically with a pressure of "1N ± 0.2N" for 30s ± 1s; ③ Ignition monitoring and result judgment:

During the contact process, observe whether the sample is "ignited" (with flames or continuous smoldering); If ignited, record the "continuation time" and "smoldering time", and observe whether the burning droplets ignite the "degreased cotton" 100mm below;

If the sample is not ignited, or the subsequent ignition/smoldering time is ≤ 2s, and there are no droplets igniting the degreased cotton, the material is judged to have "passed the hot wire test at that temperature"; Otherwise, it will not pass.