Testing device and method for measuring flash-burning spontaneous combustion temperature of material through hot air furnace method

Abstract

The invention discloses a testing device and method for measuring the flash-burning spontaneous combustion temperature of a material through a hot air furnace method, the testing device comprises a heating furnace system, an air supply system, a testing system and an intelligent control system, the heating furnace system is used for heating a sample and decomposing the sample to generate combustible gas; the air supply system is used for providing stable, clean and flow-controllable air flow for the heating furnace system; the test system is used for periodically generating a pilot ignition source at a furnace mouth and detecting whether combustion occurs or not; and the intelligent control system is integrated with a touch screen man-machine interaction interface and is used for controlling the operation, parameter setting and data acquisition and processing of the whole device. By adopting the results, the problems that a traditional simple device is low in temperature control precision, low in automation stability degree, large in manual operation error, low in safety, insufficient in standard adaptability, capable of meeting the requirements of transnational standard compatibility detection differentiation and the like, tedious in data recording and the like are solved. The detection device has the advantages that the size is small, the automation degree is high, the weight is light, the operation steps are simple and convenient, the operation of the microcomputer PC upper computer and the operation of the touch screen are controlled, and the like, and the detection device can be used for detecting the flash burning temperature (FIT, flash-ignition temperature) and the self-ignition temperature (SIT, self-ignition temperature) of the material in a laboratory or in a monitoring field. The method is high in safety, high in treatment speed, simple in process and suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of material combustion thermal safety performance testing technology, specifically an automated experimental device based on the hot air furnace method for accurately determining the flashover temperature and auto-ignition temperature of materials. The device complies with the relevant requirements of national standards GB / T4610-2008 and GB / T 9343-2008, as well as ISO 871:2006 and other standards. It has accurate temperature control and automatic identification functions for flashover and auto-ignition temperatures, and can simultaneously measure the flashover temperature and auto-ignition temperature of materials. Background Technology

[0002] In the field of materials safety testing, flashover temperature (the lowest temperature at which a material ignites instantly upon contact with an ignition source) and auto-ignition temperature (the lowest temperature at which a material spontaneously combusts without external ignition) are key indicators and core safety parameters for assessing the fire risk of materials. They provide important reference data, especially in the production, storage, selection, and application of polymer materials such as plastics and rubber. The determination of flashover and auto-ignition temperatures requires accurate measurement using standard methods while simultaneously meeting the requirements of collaborative testing across multiple international standards. Currently available traditional testing devices have the following shortcomings:

[0003] Traditional hot air furnace testing devices often suffer from problems such as low temperature control accuracy, low automation, poor stability, large human error, low safety, and insufficient standard compatibility. They barely meet national standards and do not satisfy the requirements of ISO 871:2006 regarding the gas atmosphere and heating procedure for auto-ignition temperature determination, making it impossible to meet the requirements of cross-border standard compatibility and differentiated testing. Data recording is also cumbersome. For example, air flow relies on manual adjustment of the rotor flowmeter, temperature control accuracy is low, ignition operation requires manual operation and visual observation, and the air compressor (pump) is noisy, making it impossible to detect slight popping or cracking sounds during flashover. All of these directly affect the accuracy and repeatability of test results.

[0004] Therefore, there is an urgent need for a "device + method" solution that can achieve automated control, accurate temperature control and measurement, fixed ignition position, uniform sample heating, multi-standard compatibility, safety and reliability, and meet the requirements of multiple standards. This solution aims to improve the accuracy and safety of flashover and auto-ignition temperature measurement of materials, and to provide an experimental device that can achieve stable air supply, automatic temperature point identification, and simultaneous measurement of flashover and auto-ignition temperatures, thus filling the gap in standard adaptation and functional integration of existing technologies and equipment. Summary of the Invention

[0005] Purpose of the invention: To address the aforementioned technical defects and deficiencies, this invention provides a testing device and method for determining the flashover and auto-ignition temperatures of materials using a hot air furnace method. This device features high integration, strong automation, accurate test results, simple process, and safe operation.

[0006] To achieve the above objectives, the technical solution of the present invention is: a testing device and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method, comprising: a heating furnace system, an air supply system, a testing system, and an intelligent control system.

[0007] The heating furnace system is used to heat the sample and decompose it to produce combustible gas. The furnace includes an outer furnace tube, an inner furnace tube, a furnace shell, heating wires, a refractory layer, a heat insulation layer, a heat source layer, a central positioning ring, a circular refractory partition (furnace cover), a sample tray, a clamp, thermocouples, and a fixing bracket. The heating furnace system is based on a closed-loop design of a PID algorithm intelligent temperature control system to achieve precise temperature control. The heating device is connected and controlled via a switching power supply, drive wire circuit, and SSR solid-state relay to control the furnace temperature, making the deviation approach zero and achieving constant temperature control output between the target temperature and the heating rate setpoint. Three K-type thermocouples are used to monitor the furnace cavity temperature in real time (placed near the furnace heating coil, thermocouple T3), the air temperature flowing through the sample (thermocouple T2, located 10±2mm below the sample tray), and the temperature at the sample center (thermocouple T1). A handle is provided on the circular refractory partition (furnace cover) for easy lifting and sample replacement.

[0008] The gas supply system provides a stable, clean, and controllable airflow to the heating furnace system. The air supply system includes an air compressor, a gas drying, purification, and filtration device, a solenoid valve, a pressure transmitter, an electronic mass flow controller, and a U-shaped copper tube. The pressure transmitter automatically reads the pressure to adjust the air ratio, and the solenoid valve automatically opens and closes to supply air, precisely controlling the airflow within the range of 1-10 L / min. The U-shaped tube supplies air to the heating furnace system by being positioned at the bottom of the furnace body.

[0009] The aforementioned testing system is used to periodically attempt to ignite the gas escaping from the sample at the furnace opening to detect whether combustion occurs. It includes a flame generator (comprising a miniature propane flame Bunsen burner, ignition needle, and flame height adjustable to 20mm±2mm), a flame height adjustment knob, a 2mm inner diameter copper tube, an optical flame sensor, a fixed bracket, and a solenoid valve controlling the gas switch. The optical flame sensor features a lifting and rotating sleeve design on its column (to avoid affecting the lifting of the circular refractory baffle (furnace cover) for sample replacement), a knurled nut for height adjustment, and automatically detects flashover and spontaneous combustion sparks, sending signals to the PLC. The data register automatically locks the temperature point and receives ignition status commands.

[0010] The intelligent control system primarily collects and records experimental data automatically. It analyzes temperature changes and flame detection signals to automatically identify flashover and spontaneous combustion temperatures, and outputs test results. The intelligent control system uses a PLC as its core controller, integrating a touchscreen human-machine interface for controlling the entire device's operation, parameter settings, data storage, miniature thermal printing, USB interface, thermocouple interface, and data management. The communication module includes an Ethernet port, network cable, and enclosure network cable interface, allowing communication with an external PC via the network cable interface. The intelligent control system is connected to the touchscreen. The touchscreen can set the temperature, view temperature curves, retrieve historical data, monitor real-time temperature, and save data. The USB interface can be used to export experimental results and reports. The intelligent control system includes an over-temperature and test completion alarm module. The intelligent control system includes supporting software (PC-based host computer software) and a control box. The supporting software is flashover and spontaneous combustion temperature testing software, supporting data storage, temperature curve display, saving, and printing. It also supports database management of test data, subsequent report querying, analysis, and report generation, meeting the requirements of industrial production and daily life.

[0011] As a preferred embodiment, the intelligent control system receives temperature signals from the heating furnace system and flame detector signals from the testing system, and outputs control commands to the SSR solid-state relay, electronic mass flow controller, gas solenoid valve, miniature propane flame Bunsen burner, and ignition needle.

[0012] Preferably, the intelligent control system has built-in test programs that conform to GB / T4610-2008, GB / T 9343-2008 and ISO871 standards, and the control and interaction system PLC is linked with the industrial touch screen, which meets the requirements of automated testing.

[0013] Preferably, the central positioning ring matches the inner wall of the inner furnace tube to ensure that the sample is in the center of the heating chamber. The central positioning design of the component ensures that the distance between the edge of the sample and the heating furnace wall is consistent, and the sample is heated to a uniform temperature and the signal is captured stably.

[0014] Preferably, the stainless steel rod with a diameter of 2mm connected to the circular refractory partition (furnace cover) has two small holes on both sides for passing through and fixing thermocouples T1 and T2; a handle is provided to facilitate picking up and replacing samples and avoid high-temperature burns.

[0015] Preferably, the testing system includes an optical flame sensor that automatically identifies temperature points, eliminating the need for manual observation of the sample flame state and reducing missed or incorrect judgments due to visual errors caused by manual observation.

[0016] Preferably, the device has a fixed bracket that effectively stabilizes the relative position of the miniature propane flame Bunsen burner and the furnace opening, thus providing a fixing function. This prevents the Bunsen burner nozzle from shaking or shifting left, right, up, or down, resulting in a high success rate for igniting the escaping gas and good repeatability of the measurement results.

[0017] Preferably, the safety protection module is used for over-temperature protection. When the temperature of the heating furnace exceeds 750°C, the PLC automatically cuts off the power supply to the heating furnace and triggers an alarm when there is abnormal airflow or combustion.

[0018] A testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method, specifically including the following steps:

[0019] Step 1: Sample Preparation

[0020] Prepare samples according to the relevant requirements of GB / T4610-2008, GB / T 9343-2008, and ISO 871 standards. If the samples are composite materials, this should be stated in the report. For samples with a density greater than or less than 100 kg / m³... 3 The samples should be cut into different states required for the test. The samples should be conditioned at a temperature of 23℃±2℃ and a relative humidity of 50%±5% for no less than 40 hours before the test, in accordance with the provisions of GB / T1918-1998.

[0021] Step 2: Parameter Settings

[0022] Test parameters, test number, operator, test date, temperature, air flow, etc. can be set via touch screen;

[0023] By controlling the temperature of thermocouple T3, the temperature of thermocouple T2 is controlled at the predicted initial flashover temperature (estimated initial flashover temperature is 400℃); the air flow rate is set according to GB / T4610-2008, GB / T 9343-2008 and ISO 871 standards; as described in GB / T4610-2008 standard 8.1.1, the inner tube air flow rate Qv is adjusted to regulate the air velocity to 25mm / s, and the Qv value is calculated using the formula: Qv=6.62*293 / T;

[0024] Qv – The unit is liters per minute (L / min);

[0025] T—T2 temperature value, in Kelvin (K);

[0026] Step 3: Sample Testing

[0027] The system preheats to stabilize the furnace temperature at a preset value. The sample is then placed in the furnace, and the system automatically heats and controls the air flow.

[0028] The start-up device and PLC control system use PID algorithm to control the heating element to keep the furnace temperature stable at 400℃ (estimated).

[0029] After the temperature of thermocouple T2 stabilizes, pick up the circular refractory partition (furnace cover), place the sample tray container containing the prepared sample into the holder with the center fixing ring, place thermocouple T1 on the center surface of the sample, and then put it into the furnace; adjust the sleeve on the rotating column of the optical flame sensor to the appropriate position and fix it with the knurled nut.

[0030] Ignite the miniature propane flame Bunsen burner by clicking the ignition button on the touchscreen, press the timer button, and observe whether there is obvious flashover or slight popping of flammable gas after the sample is ignited. Wait 10 minutes, and depending on whether combustion occurs, lower or raise the temperature of T2 by 50°C accordingly, and repeat the test with a new sample. Once the flashover temperature range is determined, start testing within this range at a temperature 10°C lower than the highest temperature, and continue testing at a 10°C lower temperature each time until there is no combustion within 10 minutes. Record the lowest air temperature thermocouple T2 temperature value. The lowest temperature at which flashover can be observed within 10 minutes is the flashover temperature.

[0031] In the flashover test, a miniature propane flame Bunsen burner was used to attempt to ignite the escaping gas; in the auto-ignition temperature test, as described in standard GB / T4610-2008 8.2 and GB / T9343-2008 7.2, no flame was applied, and the sample was made to spontaneously combust only by heating.

[0032] Step 4: Data Recording and Output of Test Results: The system automatically records experimental data and identifies flashover and spontaneous combustion phenomena.

[0033] Conduct the test according to the procedure without an ignition flame; spontaneous combustion is defined as the sample exhibiting flame combustion or incandescent combustion. For some materials, when combustion is primarily incandescent, it is difficult to visually observe spontaneous combustion. In such cases, the rate of increase of T1 is faster than that of T2, making this judgment more reliable than visual inspection. Record the lowest air temperature T2 at this point; this temperature, which is the lowest temperature at which flame combustion or incandescent combustion can be observed within 10 minutes, is the spontaneous combustion temperature.

[0034] Criteria for judgment:

[0035] Flashover: When a flame is applied, the gas escaping from the sample is ignited and produces a sustained flame;

[0036] Spontaneous combustion: When no flame is applied, the sample spontaneously produces a flame or exhibits continuous glowing; the system outputs the measurement results of flash temperature (FIT) and auto-ignition temperature (SIT);

[0037] The beneficial effects of this invention are as follows:

[0038] 1. Precise temperature control: Through the combination of PID temperature control algorithm and high-precision thermocouples and high-precision electronic mass flow controller, the temperature fluctuation inside the heating furnace is small and the heating rate deviation is small, which ensures the high stability of furnace temperature and airflow. Automatic gas filling ensures stable experimental conditions.

[0039] 2. High degree of automation and intelligence: Parameters are set via touch screen, and the PLC controls the entire testing process (automation of heating, gas supply, ignition, judgment, data storage and recording), eliminating errors caused by manual operation and human eye recognition, and significantly improving the repeatability and accuracy of test results.

[0040] 3. Uniform heating of the sample: The sample tray with a central positioning ring ensures uniform heating around the sample, avoiding misjudgment of flashover signals caused by local temperature deviations.

[0041] 4. Safe, compliant and reliable: It integrates overheat protection, explosion-proof exhaust protection, and waste gas treatment structure to meet the requirements of experimental safety and environmental protection, and improve experimental safety.

[0042] 5. Comprehensive functions: Simultaneously measures the temperature of flashover (ignition trigger) and auto-ignition (no ignition) without the need to replace the device, improving detection efficiency;

[0043] 6. Multi-standard compatibility: The core structure and workflow strictly comply with the requirements of GB4610-2008, GB9343-2008 and ISO 871 for the determination of flashover and auto-ignition temperatures, and can be adapted to the testing specifications of different countries and regions;

[0044] 7. Easy to operate: Simultaneous dual control via touchscreen and PC, providing visual operation and supporting temperature curve storage and export for easy data traceability. Automatically records and stores all experimental data and curves for subsequent querying, analysis, and report generation. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced. Obviously, the drawings described below are from some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0046] Figure 1 This is a flowchart illustrating the operation process of a testing device and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method, according to the present invention.

[0047] Figure 2 This is a schematic cross-sectional view of the heating furnace system;

[0048] Figure 3 for Figure 2 Enlarged view of point A in the middle;

[0049] Figure 4 A schematic diagram of a circular refractory baffle (furnace cover) with a centrally positioned positioning ring;

[0050] Figure 5 Schematic diagram of the control box;

[0051] Figure 6 This is a side view of the control box.

[0052] Explanation of reference numerals in the attached figures

[0053] 2. Heating Furnace System: 2-1 Inner Furnace Tubes; 2-2 Refractory Pads; 2-3 Outer Furnace Tubes; 2-4 Heating Wires; 2-5 Refractory Layer; 2-6 Thermal Insulation Layer; 2-7 Furnace Shell; 2-8 Thermocouple T1; 2-9 Thermocouple T2; 2-10 Thermocouple T3; 2-11 Insulation Source Layer; 2-12 U-shaped Copper Tubes; 2-13 Columns;

[0054] 3. Circular refractory baffle (furnace cover): 3-1, Centering positioning ring; 3-2, Sample tray; 3-3, Clamp; 3-4, Fixing bracket; 3-5, Ignition needle; 3-6, Miniature propane flame Bunsen burner; 3-7, Flame height adjustment knob; 3-8, Stainless steel rod; 3-9, Handle;

[0055] 4. Intelligent Control System: 4-1. Control Box; 4-2. Touch Screen; 4-3. Mini Printer; 4-4. Emergency Stop Switch; 4-5. USB Interface; 4-6. Thermocouple Interface; 4-7. PC Network Communication Interface; 4-8. Power Socket; 4-9. Power Switch; 4-10. Optical Flame Sensor Interface; 4-11. Drive Wire Circuit Outlet; 4-12. Gas Outlet; 4-13. Reset Button; 5. Optical Flame Sensor. Detailed Implementation

[0056] To better explain and facilitate understanding of the present invention, the technical solution and effects of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0057] like Figure 1-4 As shown, a test apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method includes a heating furnace system, an air supply system, a test system, and an intelligent control system.

[0058] The innermost layer of the hot air furnace is a high-temperature resistant ceramic inner furnace tube 2-1 (inner diameter 75mm±2mm, length 240mm±20mm, wall thickness 3mm), supported by three refractory blocks 2-2. A U-shaped copper tube, placed at the bottom of the furnace body, provides air to the inner furnace tube 2-1. The inner furnace tube 2-1 is vertically placed within the outer furnace tube 2-3 (outer furnace tube 2-3 has an inner diameter of 100mm±5mm and a length of 240mm±20mm) on the furnace bottom plug. The outer furnace tube 2-3 is wrapped with heating wire 2-4, which is then covered by a refractory layer 2-5. The refractory layer 2-5 is further filled with a heat-insulating layer 2-6 to improve insulation performance, and is placed within the furnace shell 2-7. The heating wire 2-4 is a metal alloy heating wire with a power of 2.6kW, capable of heating the furnace to a temperature not lower than 750℃. The refractory layer 2-5 is composed of 60mm thick mineral fiber wool. The sample tray 3-2 with a centrally positioned ring 3-1 is also included. The clamp 3-3 is connected to the circular refractory partition (furnace cover) 3-2 with a central opening of 25±2mm in diameter by a stainless steel rod 3-8 with a diameter of 2mm. The stainless steel rod 3-8 passes through the circular refractory partition (furnace cover) 3-2 on top and is welded to the central positioning ring 3-1 on the bottom. The clamp 3-3, made of stainless steel with a diameter of 2mm, is embedded in the center of the central positioning ring 3-1 and welded into a whole. The sample tray 3-2 is made of stainless steel plate with a diameter of 40±2mm, a depth of 15±2mm, and a thickness of 0.7mm±0.2mm. Its bottom is located 185mm±2mm below the circular refractory partition (furnace cover) 3-2 with a handle 3-9. The circular refractory partition (furnace cover) 3-2 has a fixing bracket 3-4 for fixing the ignition needle 3-5 and the miniature propane flame Bunsen burner 3-6. The miniature propane flame Bunsen burner 3-6 has a flame height adjustment knob 3-7 installed on its pipeline.

[0059] The optical flame sensor 5 is connected to a sleeve, which is fitted onto the column 2-13 located on the furnace shell 2-7. A knurled nut is provided in the middle of the sleeve to fix and adjust the height.

[0060] Three K-type thermocouples were used to monitor the furnace cavity temperature in real time (placed near the furnace heating coil, thermocouple T3 / 2-10), the air temperature flowing through the sample (thermocouple T2 / 2-9, located 10±2mm below sample tray 3-2), and the temperature of the sample center (thermocouple T1 / 2-8).

[0061] The intelligent control system includes a control box 4-1, a touch screen 4-2, a micro printer 4-3, an emergency stop switch 4-4, a USB interface 4-5, a thermocouple interface 4-6, a PC network cable communication interface 4-7, a power socket 4-8, a power switch 4-9; an optical flame sensor interface 4-10, a drive wire circuit outlet 4-11, a gas outlet 4-12, and a reset button 4-13.

[0062] A testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method, specifically including the following steps:

[0063] Step 1: Sample Preparation: Prepare the material to be tested into a sample of the specified size.

[0064] (1) Prepare test specimens in accordance with the relevant requirements of GB / T4610, GB / T 9343 and ISO 871 standards;

[0065] Step Two: Parameter Setting: Set test parameters, test number, operator, test date, temperature, air flow rate, etc. via the touchscreen.

[0066] By controlling the temperature of thermocouple T3, the temperature of thermocouple T2 is controlled at the predicted initial flashover temperature (initial temperature set at 400℃); the air flow rate is set according to the standard.

[0067] Step 3: Sample Testing: The system is preheated to stabilize the furnace temperature at the preset value. The sample is then placed in the furnace, and the system automatically heats and controls the airflow.

[0068] The start-up device and PLC control system use PID algorithm to control the heating element to keep the furnace temperature stable at 400℃ (estimated).

[0069] Place the sample in the sample tray container, ready for testing. The system begins heating the furnace body at the set rate. After the temperature of thermocouple T2 stabilizes, place the sample tray with the sample on the holder with the centering positioning ring, and place thermocouple T1 on the center surface of the sample before placing it into the furnace; adjust and fix the optical flame sensor to the appropriate position.

[0070] Ignite the miniature propane flame Bunsen burner by clicking the ignition button on the touchscreen, press the timer button, and observe whether there is obvious flashover or slight popping of flammable gas after the sample is ignited. Wait 10 minutes, and depending on whether combustion occurs, lower or raise the temperature of thermocouple T2 by 50°C accordingly, and repeat the test with a new sample. Once the flashover temperature range is determined, start testing within this range at a temperature 10°C lower than the highest temperature, and continue testing at a 10°C decrease each time until there is no combustion within 10 minutes. Record the lowest air temperature thermocouple T2; the lowest temperature at which flashover can be observed within 10 minutes is the flashover temperature.

[0071] In the flash fire test, an attempt is made to ignite the escaping gas; in the spontaneous combustion test, no flame is applied, and the sample is spontaneously combusted only by heating.

[0072] Step 4: Data Recording and Test Results:

[0073] The system automatically records experimental data and identifies and outputs flash temperature (FIT) and auto-ignition temperature (SIT) to recognize combustion phenomena.

[0074] Conduct the test according to the procedure without an ignition flame; spontaneous combustion is defined as the sample exhibiting flame combustion or incandescent combustion. For some materials, when combustion is primarily incandescent, it is difficult to visually observe spontaneous combustion. In such cases, the rate of increase of T1 is faster than that of T2, making this judgment more reliable than visual inspection. Record the lowest air temperature T2 at this point; this temperature, which is the lowest temperature at which flame combustion or incandescent combustion can be observed within 10 minutes, is the spontaneous combustion temperature.

[0075] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the implementation of the present invention is not limited thereto.

[0076] Example 1:

[0077] Determination of flashover and auto-ignition temperatures of polystyrene materials

[0078] Step 1: Sample Preparation

[0079] Polystyrene was molded into 20*20mm stacks and conditioned in a standard environment (23℃±2℃, 50%±5%RH) for 40 hours before the experiment. The mass was measured to be 3.01g (the standard requirement is 3.0g±0.2g).

[0080] Step 2: Parameter Settings

[0081] Test parameters, test number, operator, test date, temperature, air flow, etc. can be set via touch screen;

[0082] Main test parameters:

[0083] Target temperature: 400℃ (expected flashover temperature approximately 350℃)

[0084] Heating rate: 10℃ / min

[0085] Airflow rate: 2.88L / min

[0086] [Based on the formula Qv=6.62*293 / T, with a preset temperature of 400℃, Qv=6.62×293÷(400+273), we get Qv≈2.88L / min].

[0087] Step 3: Sample Testing

[0088] The start-up device and PLC control system use a PID algorithm to control the heating element, stabilizing the furnace temperature at 400℃. The PID parameters are set based on experience.

[0089] When the temperature stabilizes at 400℃±2℃, the temperature of thermocouple T2 stabilizes at 371.6℃. Take out the circular refractory partition (furnace cover) to the furnace opening, place the sample tray with the sample on the holder with the center positioning ring, and place thermocouple T1 on the center surface of the sample and then put it into the furnace; adjust the optical flame sensor to the appropriate position and tighten the knurled nut to fix it.

[0090] (1) Flashover test

[0091] Press the ignition button on the touchscreen to ignite the miniature propane flame Bunsen burner. Rotate the flame height adjustment knob to adjust the flame height to 20±2mm. Press the timer button and wait for 10 minutes. After placing the sample, as it leaves the hot air furnace, the temperature of thermocouple T2 first drops and then gradually rises and stabilizes. After about 3 minutes, a slight pungent odor can be smelled from the material. At 5 minutes and 26 seconds, a small amount of smoke emerges from the furnace opening. The temperature of thermocouple T2 is quite stable, fluctuating within the range of 367℃±2℃. There are no other changes in the sample. The optical flame sensor does not detect any flame. After thermocouples T1 and T2 stabilize and tend to be linear for 10 minutes, there is no reaction, and the test is stopped. Replace with a new sample and place it in the sample tray for later use.

[0092] Set the temperature (thermocouple T3) to 450℃ and increase the temperature at a set rate of 10℃ / min. Thermocouple T2 stabilizes at 421.6℃. Remove the circular refractory partition (furnace cover) to the furnace opening. Place the sample tray with the new sample on the holder with the centering positioning ring, and place thermocouple T1 on the center surface of the sample before placing it into the furnace. Adjust and fix the position of the optical flame sensor. Click the ignition button on the touch screen to ignite the miniature propane flame Bunsen burner. Rotate the flame height adjustment knob to adjust the flame height to 20±2mm. Press the timer button. After 4 minutes and 16 seconds, a pungent odor gradually appears, and black smoke emerges from the furnace opening. After 6 minutes and 29 seconds, the temperature of thermocouple T1 is 435.4℃, with a weak flame continuously flashing. The flame sensor alarm sounds.

[0093] The heating temperature (thermocouple T3) was reset to 440℃, 430℃, and 420℃, and the temperatures of thermocouple T2 were 412.6℃, 400.5℃, and 390.2℃, respectively. There was no significant temperature rise or alarm.

[0094] The temperature was set to stabilize at 410℃ again. The temperature of thermocouple T2 was 381.6℃ and the temperature of thermocouple T1 was 408.4℃. At 8 minutes and 33 seconds, an alarm was triggered for flashover.

[0095] By setting thermocouple T3 to 400℃, it was found that when thermocouple T2 reached 370.9℃, no flame or alarm was generated after 10 minutes of timing. Therefore, the lowest recorded air temperature for thermocouple T2 was determined to be the flashover temperature of 381.6℃.

[0096] (2) Spontaneous combustion test

[0097] In another set of tests, the temperature of thermocouple T3 was set to 450℃ and the temperature of thermocouple T2 was set to 426.8℃. Without starting the igniter, the timer button on the touch screen was clicked to make the sample spontaneously combust. After 8 minutes and 30 seconds, there was a smell and a little smoke. The edges of the material were deformed. After 10 minutes, there was no fire and no alarm was sounded.

[0098] When a new sample was replaced, the temperature of thermocouple T3 was set to 500℃. The temperature of thermocouple T2 in the hot air furnace was between 478.4℃ and 492.6℃. A slight popping sound was heard inside the furnace, and a faint yellow spark appeared at the furnace opening. The buzzer sounded an alarm, and the system monitored the temperature changes and visible light phenomena.

[0099] The sample was reinstalled, and the temperature was set to 490℃. Thermocouple T2 temperature stabilized at 467.7℃. At 7 minutes and 46 seconds, sporadic sparks and faint popping sounds of burning occurred, and thermocouple T1 temperature reached 482.5℃, triggering an alarm. When thermocouple T3 temperature was set to 480℃, thermocouple T2 temperature in the hot air furnace was 457.6℃, with sparks appearing at the furnace opening. Thermocouple T1 temperature reached 485.5℃, triggering a burning alarm at 4 minutes and 55 seconds. When thermocouple T3 temperature was set to 470℃, thermocouple T2 temperature was 446.8℃. After waiting 10 minutes, there was no significant temperature rise or alarm. Therefore, the lowest recorded air temperature thermocouple T2 temperature was determined to be the auto-ignition temperature of 457.6℃.

[0100] Step 4: Data Recording and Test Results

[0101] The system automatically records experimental data and outputs flash temperature (FIT) and auto-ignition temperature (SIT) to identify combustion phenomena;

[0102] Experimental results:

[0103] Flash point (FIT): 381.6℃;

[0104] Autoignition temperature (SIT): 457.6℃.

[0105] Example 2:

[0106] Determination of flashover and auto-ignition temperatures of lightweight polyurethane foam materials

[0107] Step 1: Sample Preparation

[0108] Cut the polyurethane foam into 20*20*50mm blocks and weigh them to a weight of 2.91g (the standard requirement is 3.0g±0.2g).

[0109] Step 2: Parameter Settings

[0110] Test parameters, test number, operator, test date, temperature, air flow, etc. can be set via touch screen;

[0111] Main test parameters:

[0112] Target temperature: 380℃ (expected flashover temperature approximately 350℃)

[0113] Heating rate: 10℃ / min

[0114] Airflow rate: 2.97 L / min

[0115] [Based on the formula Qv=6.62*293 / T, with a preset temperature of 380℃, 6.62×293÷(380+273) yields Qv≈2.97L / min].

[0116] Step 3: Sample Testing

[0117] The start-up device and PLC control system use a PID algorithm to control the heating element, stabilizing the furnace temperature at 380℃. The PID parameters are set based on experience.

[0118] When the temperature stabilizes at 380℃, the temperature of thermocouple T2 is 358.6℃. Take out the circular refractory partition (furnace cover) to the furnace opening, place the sample tray with the sample loaded on the holder with the center positioning ring, and place thermocouple T1 on the center surface of the sample and then put it into the furnace; adjust the optical flame sensor to the appropriate position and fix it.

[0119] (1) Flashover test

[0120] Press the ignition button on the touchscreen to ignite the miniature propane flame Bunsen burner. Rotate the flame height adjustment knob to adjust the flame height to 20±2mm. Press the timer button and wait for 10 minutes. After placing the sample, the temperature of thermocouple T2 first drops and then gradually rises. After about 2 minutes and 30 seconds, a pungent plastic burning smell can be smelled from the material, and black smoke is emitted. The temperature of thermocouple T2 stabilizes between 357.3℃ and 358.6℃. After 4 minutes and 15 seconds, the material ignites. The optical flame sensor detects the flame and sounds an alarm. The highest temperature of thermocouple T1 is 399.2℃, and the temperature of thermocouple T2 is 375.5℃. Stop the test.

[0121] Replace the sample with a new one and place it in the sample tray for later use;

[0122] Set the temperature (thermocouple T3) to 330℃ and increase the temperature at a set rate of 10℃ / min. The temperature of thermocouple T2 is 306.4℃. Take out the circular refractory partition (furnace cover) to the furnace opening. Place the sample tray with the new sample on the holder with the center positioning ring, and place thermocouple T1 on the center surface of the sample before putting it into the furnace. Adjust and fix the position of the optical flame sensor. Click the ignition button on the touch screen to ignite the miniature propane flame Bunsen burner. Rotate the flame height adjustment knob to adjust the flame height to 20±2mm. Press the timer button. At 4 minutes and 36 seconds, an irritating odor is produced, and a small amount of black smoke comes out of the furnace opening. At 8 minutes and 45 seconds, the temperature of thermocouple T1 is 308.2℃. In the no-flame mode, the flame sensor does not respond and there is no buzzer alarm.

[0123] The heating temperature (thermocouple T3 temperature) was reset to 340℃, 350℃, and 360℃, and the corresponding thermocouple T2 temperatures were 312.8℃, 321.6℃, and 331.4℃, respectively. Slight smoke was emitted from the sample, and an irritating odor was detected. There was no significant temperature rise or alarm on thermocouple T1.

[0124] The temperature of thermocouple T3 was set to 370℃ again. The temperature of thermocouple T2 in the air furnace stabilized at 345.7℃, while the temperature of thermocouple T1 reached 376.2℃. A slight popping sound was heard at 8 minutes and 49 seconds, and a few sparks flashed at 9 minutes and 11 seconds, triggering an alarm. Therefore, the lowest recorded air temperature and thermocouple T2 temperature were determined to be the flashover temperature of 345.7℃.

[0125] (2) Spontaneous combustion test

[0126] A new set of samples was weighed and tested. The temperature of thermocouple T3 was set to 450℃ and the temperature of thermocouple T2 to 422.5℃ by heating. The igniter was not activated, and the samples were allowed to spontaneously combust. After 5 minutes and 22 seconds, the material had an odor and produced thick smoke. The temperature of thermocouple T1 reached 433.6℃. After 6 minutes and 24 seconds, the material caught fire and the alarm sounded.

[0127] Replace with a new sample, set thermocouple T3 temperature to 400℃, thermocouple T2 temperature in hot air furnace fluctuates around 384.3℃, thermocouple T1 temperature reaches 402.3℃, a few popping sounds are heard in the furnace at 8 minutes and 12 seconds, a few faint red sparks are seen at the bottom of the furnace opening, and the buzzer alarm sounds.

[0128] When a new sample was used, the temperature of thermocouple T3 was set to 390℃, and the temperature of thermocouple T2 was stable at 375.4℃. At 9 minutes and 41 seconds, sporadic sparks and faint popping sounds of burning occurred, and the detector alarm sounded.

[0129] The sample was reinstalled and the temperature was set to 380℃. The temperature of thermocouple T2 stabilized at 366.2℃ and there was no alarm for 10 minutes. The temperature of thermocouple T1 was 381.2℃ with a slight temperature rise, shrinkage and deformation at the edges and corners, a pungent odor, and a small amount of smoke and dust.

[0130] When thermocouple T3 is set to 370℃, thermocouple T2 in the hot air furnace is 356.6℃. There is a small amount of smoke at the furnace opening, and an irritating odor can be smelled. There is no alarm output. Therefore, the lowest recorded air temperature thermocouple T2 temperature is the auto-ignition temperature of 375.4℃.

[0131] Step 4: Data Recording and Test Results

[0132] The system automatically records experimental data and outputs flash temperature (FIT) and auto-ignition temperature (SIT) to identify combustion phenomena;

[0133] Experimental results:

[0134] Flash point (FIT): 345.7℃;

[0135] Autoignition temperature (SIT): 375.4℃.

[0136] Example Effects

[0137] This embodiment successfully determined the flashover and auto-ignition temperatures of polystyrene and lightweight polyurethane foam. The entire process is highly automated, reducing misjudgments and omissions caused by human intervention and visual observation. The test results are accurate and repeatable, the device operates stably, the PID temperature control is effective, the temperature fluctuation is small, and the combustion status is accurately and quickly determined.

[0138] in conclusion

[0139] This invention provides a testing device and method for determining the flash ignition and auto-ignition temperatures of materials using a hot air furnace method. The experiment involves heating a sample at different temperatures within the heating chamber of a hot air furnace, and then directly igniting the escaping gas with a small flame at the furnace's opening to determine the flash ignition and auto-ignition temperatures. In short, the furnace creates a heating chamber controlled by a thermocouple T3 within the furnace cavity, through which hot air flows. The ambient temperature of the heating chamber is measured by thermocouple T2. The desired flash ignition and auto-ignition temperatures are the ambient temperature within the furnace, i.e., the temperature value of thermocouple T2. Although the ignition point needs to be repeatedly located during the test, the equipment integrates automated control, precise temperature regulation, automatic ignition, and identification functions, significantly improving the accuracy, efficiency, and reliability of the test. The device complies with multiple standards, including GB4610-2008, GB / T9343-2008, and ISO871-2006, and is suitable for testing the combustion performance of various materials such as plastics, rubber, and textiles, possessing broad application value.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate and demonstrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to preferred embodiments and accompanying drawings, those skilled in the art should understand that it can still be within the scope of the experimental working principle and technical concept of the present invention. Various changes, modifications, equivalent substitutions or variations can be made to these embodiments without causing the modified technical solutions to deviate from the spirit and scope of the timing scheme of the present invention.

Claims

1. A testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method, characterized in that, include: Heating furnace system, air supply system, testing system, and intelligent control system: The heating furnace system is used to heat the sample and decompose it to produce combustible gas. The heating furnace includes an outer furnace tube, an inner furnace tube, a furnace shell, heating wires, a refractory layer, a heat insulation layer, a heat source layer, a central positioning ring, a circular refractory partition (furnace cover), a sample tray (i.e., a stainless steel crucible used to hold the sample), a clamp (i.e., a crucible placement ring), thermocouples, and a fixing bracket. The heating furnace system is based on a closed-loop design of a PID algorithm intelligent temperature control system to achieve precise temperature control. The heating furnace temperature is controlled by connecting the heating device through a switching power supply, a drive wire circuit, and an SSR solid-state relay, so that the deviation approaches zero, achieving constant temperature control output between the target temperature and the heating rate temperature setpoint. The thermocouples are three K-type thermocouples used to monitor the furnace cavity temperature in real time (placed near the furnace heating coil, thermocouple T3), the air temperature flowing through the sample (thermocouple T2, located 10±2mm below the sample tray), and the temperature of the sample center (thermocouple T1). The circular refractory baffle (furnace cover) is equipped with a handle for easy picking up and replacing of the sample. The gas supply system provides a stable, clean, and controllable airflow to the heating furnace system. The air supply system includes an air compressor, a gas drying, purification, and filtration device, a solenoid valve, a pressure transmitter, an electronic mass flow controller, and a U-shaped copper tube. The pressure transmitter automatically reads the pressure to adjust the air ratio, and the solenoid valve automatically opens and closes to supply air, precisely controlling the airflow within the range of 1-10 L / min. The U-shaped copper tube, placed at the bottom of the furnace body, provides air to the heating furnace system, creating a hot air environment. The aforementioned testing system is used to periodically attempt to ignite the gas escaping from the sample at the furnace opening to detect whether combustion occurs. It includes a flame generator (comprising a miniature propane flame Bunsen burner, ignition needle, and flame height adjustable to 20mm±2mm), a flame height adjustment knob, a 2mm inner diameter copper tube, an optical flame sensor, a mounting bracket, and a solenoid valve (linked to a PID controller, allowing for automatic or manual ignition at set temperature points). The optical flame sensor is connected to a sleeve, which is fitted onto a column. The sleeve has a knurled nut for height adjustment. It automatically detects flashover and spontaneous combustion sparks, sending signals to the PLC. The data register automatically locks the temperature point and receives ignition status commands. The intelligent control system primarily collects and records experimental data automatically. It analyzes temperature changes and flame detection signals to automatically identify flashover and spontaneous combustion temperatures, and outputs test results. The intelligent control system uses a PLC as its core controller, integrating a touchscreen human-machine interface for controlling the entire device's operation, parameter settings, data storage, miniature thermal printing, USB interface, thermocouple interface, and data management. The communication module includes an Ethernet port, network cable, and enclosure network cable interface, connecting to an external PC via a network cable communication interface. The intelligent control system is connected to the touchscreen. The touchscreen can set the temperature, view temperature curves, retrieve historical data, monitor real-time temperature, and save data. The USB interface can be used to export experimental results and reports. The safety protection module of the intelligent control system is mainly for overheat protection, equipped with over-temperature and test completion alarm modules. The intelligent control system includes supporting software (PC-based host computer software) and a control box. The supporting software is flashover and spontaneous combustion temperature testing software, supporting data storage, temperature curve display, saving, and printing, as well as database management of test data, subsequent report querying, analysis, and report generation.

2. The testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method according to claim 1, characterized in that: The intelligent control system includes a programmable logic controller (PLC), which receives temperature signals from the heating furnace system and flame detector signals from the testing system, and outputs control commands to the SSR solid-state relay, electronic mass flow controller, and buzzer alarm.

3. The testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method according to claim 1, characterized in that: The intelligent control system has built-in test programs that comply with GB / T4610-2008, GB / T9343-2008 and ISO 871:2006 standards. The control and interaction system PLC is linked with the industrial touch screen for parameter setting, data storage and monitoring, which meets the requirements of automated testing.

4. The testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method according to claim 1, characterized in that: The centering positioning ring is fixed together with the clamp of the sample tray and is connected to the circular refractory baffle (furnace cover) by a 2mm diameter stainless steel rod, extending to the top of the furnace cover. The centering positioning ring matches the inner wall of the inner furnace tube to ensure that the sample is in the center of the heating chamber. The central positioning design of the component ensures uniform heating of the sample and stable signal capture. There is a small hole on the centering positioning ring for thermocouple T2 to pass through. The 2mm diameter stainless steel rod connected to the circular refractory baffle (furnace cover) has two small holes on both sides for passing through and fixing thermocouples T1 and T2.

5. The testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method according to claim 1, characterized in that: The automatic ignition and detection system includes an optical flame sensor that eliminates the need for manual intervention. It automatically identifies flashover and spontaneous combustion without requiring visual observation of the sample's flame heat state, reducing missed or incorrect judgments due to visual errors caused by manual observation. In particular, it is difficult to capture the spontaneous combustion phenomenon in the initial weak combustion of the sample during the determination of spontaneous combustion temperature.

6. The testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method according to claim 1, characterized in that: The safety protection module is used to trigger alarms and safety interlock actions in case of overheating, abnormal airflow, or combustion.

7. The testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method according to claim 1, characterized in that: The device's fixing bracket is made of heat-resistant material and is fixed to a circular refractory partition (furnace cover), aligning the miniature propane flame Bunsen burner nozzle with the center of the vent opening of the circular refractory partition (furnace cover), thus providing a fixing function. The miniature propane flame Bunsen burner nozzle has no deviation or shaking, resulting in a high success rate of ignition of the venting gas and good repeatability of the measurement results.

8. The testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method according to claim 1, characterized in that: The aforementioned safety protection module is mainly used for overheat protection: when the furnace temperature exceeds 750℃, the PLC automatically cuts off the power supply to the furnace and triggers an audible and visual alarm to prevent danger.

9. The testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method according to claim 1, characterized in that: The gas supply system is equipped with gas protection, and the air pipeline is equipped with a pressure safety valve (automatic pressure relief in case of overpressure; the exhaust port is connected to an explosion-proof exhaust fan, which automatically runs 5 minutes after the experiment to discharge waste gas).

10. The testing apparatus and method for determining the flashover and auto-ignition temperature of materials using a hot air furnace method according to claim 1, characterized in that: Specifically, the following steps are included: Step 1: Sample preparation: In accordance with the relevant requirements of GB / T4610-2008, GB / T 9343-2008 and ISO 871 standards, the material to be tested is prepared into a sample of the specified size; (1) The material can be any material, including composite materials, but should be specified in the report (the same material may produce different test results for different shapes); (2) For densities greater than 100 kg / m³ 3 The sample should weigh 3.0g ± 0.2g. If the material is spherical or powdery, it usually needs to be molded. For sheets, they should be cut into squares of 20×20mm ± 2mm and stacked to meet the sample's quality requirements. For film materials, roll up a strip 20±2mm wide to meet the sample's quality requirements. (3) Density less than 100 kg / m³ 3 The foam material is cut off, the outer skin is removed, and it is cut into 20×20×50mm blocks; (4) The sample shall be prepared in accordance with the provisions of GB / T1918-1998, and the condition shall be conditioned at a temperature of 23℃±2℃ and a relative humidity of 50%±5% for no less than 40 hours before the test; Step 2: Parameter Setting: Set test parameters, test number, operator, test date, temperature, air flow, etc. via the touch screen; By controlling the temperature of thermocouple T3, the temperature of thermocouple T2 is controlled at the predicted initial flashover temperature (the initial flashover temperature can be estimated to be 400℃); according to the description in GB / T4610-2008 standard 8.1.1, the air flow rate Qv in the inner tube is adjusted to regulate the air velocity to 25mm / s. The value of Qv is calculated using the formula: Qv=6.62*293 / T; Qv – The unit is liters per minute (L / min); T—T2 temperature value, in Kelvin (K); Step 3: Sample testing: The system is preheated to stabilize the furnace temperature at the preset value. The sample is then placed in the furnace, and the system automatically heats and controls the air flow. The start-up device and PLC control system use a PID algorithm to control the heating element, stabilizing the furnace temperature at 400℃ (estimated). PID parameters are set based on experience: proportional band (P) = 60%, integral time (I) = 120s, derivative time (D) = 20s; Sample testing: After the temperature of thermocouple T2 stabilizes, pick up the circular refractory partition (furnace cover), place the sample tray container containing the prepared sample into the holder with the center fixing ring, place thermocouple T1 on the center surface of the sample, and then put it into the furnace; adjust the sleeve on the rotating column of the optical flame sensor to the appropriate position and fix it with the knurled nut. Ignite the miniature propane flame Bunsen burner by clicking the ignition button on the touchscreen, press the timer button, and observe whether there is obvious flashover or slight popping of flammable gas after the sample is ignited. Wait 10 minutes, and depending on whether combustion occurs, lower or raise the temperature of T2 by 50°C accordingly, and repeat the test with a new sample. Once the flashover temperature range is determined, start testing within this range at a temperature 10°C lower than the highest temperature, and continue testing at a 10°C lower temperature each time until there is no combustion within 10 minutes. Record the lowest air temperature thermocouple T2 temperature value. The lowest temperature at which flashover can be observed within 10 minutes is the flashover temperature. In the flashover test, a miniature propane flame Bunsen burner was used to attempt to ignite the escaping gas; in the auto-ignition temperature test, as described in standard GB / T4610-2008 8.2 and GB / T9343-2008 7.2, no flame was applied, and the sample was made to spontaneously combust only by heating. Step 4: Data Recording and Output of Test Results: The system automatically records experimental data and identifies flashover and spontaneous combustion phenomena; Conduct the test according to the procedure without an ignition flame; spontaneous combustion is indicated by flame combustion or incandescent combustion of the sample. For some materials, when combustion is mainly incandescent, it is difficult to observe spontaneous combustion visually. In this case, the rate of increase of thermocouple T1 is faster than that of thermocouple T2. This method is more reliable than visual inspection. Record the lowest temperature of air thermocouple T2 at this point. This temperature is the lowest temperature at which flame combustion or incandescent combustion can be observed within 10 minutes, and it is the spontaneous combustion temperature. Criteria for judgment: Flashover: When a flame is applied, the gas escaping from the sample is ignited and produces a sustained flame; Spontaneous combustion: When no flame is applied, the sample spontaneously produces a flame or exhibits continuous glowing; the system outputs the measurement results of flash temperature (FIT) and auto-ignition temperature (SIT).

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