Ozone aging test chamber, also known as ozone corrosion test chamber, is a special environmental test equipment that simulates and strengthens the effect of ozone conditions in the atmosphere on materials. Its core function is to expose the specimen to a closed and lightless test chamber containing constant ozone concentration and a constant temperature, so that the specimen can be tested at a predetermined time under static or dynamic tensile deformation, and evaluate the ozone aging resistance of the material from the degree of cracking or other changes in properties on the surface of the specimen. This equipment is mainly used for rubber products such as vulcanized rubber, thermoplastic rubber, cable insulation sheath and other products, and is also suitable for the aging resistance test of polymer materials such as plastics and coatings. By manually simulating the ozone environment, the equipment can obtain the effect of long-term exposure of materials under actual use conditions in a short period of time, providing a basis for material formulation improvement, product life evaluation and quality control.
Principle
The working principle of the ozone aging test chamber is based on the strong oxidation effect of ozone on polymer materials, especially rubber materials containing unsaturated double bonds. Under the action of stress and strain, the ozone molecules on the surface of the material react with the polymer chain, resulting in the breakage of the molecular chain, and then the surface cracking.
The equipment usually consists of three core parts: the ozone generator, the aging test chamber, and the ozone concentration control or detection device. There are two main types of ozone generators: UV lamps and silent discharge tubes. The ultraviolet lamp method generates ozone by irradiating the air with a specific wavelength of ultraviolet rays, which is more suitable for low-concentration ozone testing, because the required voltage and current are small, and the concentration control is relatively easy. The silent discharge tube method uses a high-voltage electric field to ionize oxygen to generate ozone, which is more suitable for high-concentration ozone testing, but in order to avoid the generation of nitrogen oxides, the use of oxygen as an air source is more effective.
When working, the ozone generated by the ozone generator is mixed with the treated air and enters the working room through the control system regulation. A circulating air system is used in the chamber to ensure uniform ozone concentration and temperature distribution. The equipment monitors the ozone concentration in the box in real time through a closed-loop control system, and feeds back the signal to the ozone generator, dynamically adjusting the amount generated to maintain the set concentration value. At the same time, the heating and humidification system works together to meet the temperature and humidity conditions required for the test.
Measurement methods and parameters
The measurement method of ozone aging test is divided into two main methods: static tensile test and dynamic tensile test according to GB/T 7762, GB/T 13642, ISO 1431 and other standards.
1. Static Tensile Test:The specimen is fixed on the specimen fixture with a specified elongation (such as 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 80%), and then placed in an ozone-free dark room for 24 to 48 hours, then placed in an aging chamber that has reached the set temperature for 15 minutes, and then the test is started by passing through the specified concentration of ozone. After the test cycle, use at least 7 times magnifying glass to check the surface cracking of the specimen. If only one elongation is used, 20% is usually recommended, as this value is close to the actual state of use of most rubber products.
2. Dynamic Tensile Test:Specimens are stretched cyclically between zero and specified maximum elongation, continuously or intermittently exposed to ozone. The maximum elongation of dynamic stretching is usually stipulated as 5%, 10%, 15%, 20%, 25%, 30%, and 10% is recommended if only one is used. The dynamic stretching frequency is generally specified as 0.5±0.025Hz, that is, 30 times per minute.
3. Ozone Concentration Measurement:The main measurement methods of ozone concentration include chemical analysis, electrochemical method, ultraviolet absorption method, etc. Modern equipment mostly uses ultraviolet absorption sensors to monitor the ozone concentration in the box in real time and control it within ±10% deviation of the set value. The unit of ozone concentration is commonly expressed as pphm (parts per billion) or μmol/mol, and the common test range is between 10~1000pphm.
4. Evaluation method:The test results can be evaluated in the following ways: report the test results with no cracks or cracks, and determine the degree of cracking if there are cracks; determine the critical strain range for the maximum strain without cracking and the minimum strain with cracking after the specified exposure time; The degree of aging can also be assessed by measuring the rate of change in tensile properties.
Main influencing factors
The accuracy and reproducibility of ozone aging test results are restricted by many factors, and the following aspects should be focused on when operating and interpreting the results:
1. Ozone concentration:The ozone aging rate of rubber generally accelerates with the increase of ozone concentration. The concentration selection should be determined according to the aging resistance and use conditions of the material: a low concentration of 50pphm or less should be used for general-purpose unsaturated rubber (such as natural rubber, styrene-butadiene rubber); For medium aging resistant rubber (such as neoprene), a medium concentration of 100~200pphm should be used; For aging resistant saturated structural rubber (such as ethylene propylene rubber), a high concentration of more than 500~1000pphm can be used. Concentration fluctuations should be controlled within ±10%.
2. Test temperature:Temperature affects the reaction rate of ozone with the material, and also affects the decomposition rate of ozone itself. The test temperature should not exceed 60°C, otherwise the aging of thermal oxygen will gradually play a leading role, and will accelerate the decomposition of ozone, affecting the objectivity of the test results. National standards usually stipulate that the optimal test temperature is 40±2°C.
3. Tensile Deformation Rate:Ozone aging of rubber must occur under stress strain. The selection of elongation should be close to the actual use state, if the elongation is too large, mechanical fatigue cracking may replace ozone cracking, resulting in wrong test results. If the elongation is less than the permanent deformation value of the specimen during dynamic stretching, it is difficult for the specimen to produce ozone cracking.
4. Gas Flow Rate and Flow Rate:The uniform and stable flow rate or flow rate of ozone-containing air is an important factor in obtaining good test results. The standard stipulates that the average flow rate of ozone-containing air is not less than 8mm/s, and the most suitable is 12~16mm/s. The gas flow rate should be adjusted according to the volume of the aging chamber, and the hourly flow rate should be controlled at about 2 to 5 times the volume to ensure that there is enough fresh ozone replenishment in the tank.
5. Specimen shape and surface condition:Long rectangular specimens should be used to evaluate the ozone cracking test, because the stress distribution is uniform when stressed, and the cracks will not cause stress relaxation in adjacent parts. The cracks produced by dumbbell-shaped specimens tend to be concentrated at the bends at both ends. The thickness and width of the specimen mainly affect the size and number of cracks, but have little effect on the time of crack appearance.
6. Humidity Conditions:ISO 1431 stipulates that the relative humidity of the test is generally not more than 65%, and the relative humidity of products used in humid environments is required to be tested in the range of 80~90%. When the temperature of the test chamber is 40°C, the relative humidity of the moisture brought in from the atmosphere after heat exchange usually does not exceed 65%, so the humidity in the general environment has little effect on the test results.
Typical application areas
Ozone aging chambers have penetrated into several industrial areas where the ozone resistance of materials needs to be evaluated:
Rubber industry:It is used to test the ozone cracking resistance of vulcanized rubber and thermoplastic rubber, including tires, seals, hoses, tapes and other products. The effect of anti-aging agents in rubber formulations is evaluated through experiments, and material modification and quality control are guided.
Wire and cable industry:Cable insulation jackets and cable jackets are exposed to ozone attack for a long time in outdoor or industrial environments. Ozone aging tests are carried out according to GB/T 2951.21 and other standards to evaluate its aging resistance and service life.
Automotive Industry:Rubber components such as automobile door and window seals, wiper rubber strips, hoses, and shock absorbers need to maintain good performance in the ozone environment. The test is used to verify its reliability under actual use conditions.
Textile industry:Outdoor textiles need to be tested for ozone color fastness in accordance with AATCC 109, AATCC 129, ISO 105-G03 and other standards to evaluate the color change and performance degradation of materials in ozone environment.
Coatings and Plastics:Evaluate the aging resistance of organic coatings and plastic products in ozone environment, and provide data support for material applications.
Quality supervision and scientific research institutions:third-party testing institutions use ozone aging test chambers to conduct compliance inspections of various products; The research unit is used for the research and development of new materials and the research of aging resistance mechanism.
Selection points to consider
When selecting suitable ozone aging test equipment for laboratories or quality inspection departments, it is necessary to make a comprehensive judgment based on technical requirements, standards and specifications, and practical application scenarios:
1. Tested standards met:Clarifying the test standards that the product needs to meet is the primary basis for selection. Common standards include GB/T 7762, GB/T 13642, ISO 1431-1, ISO 1431-3, ASTM D1149, ASTM D1171, DIN 53509, etc. The design of the equipment needs to cover all the requirements of the target standard, in particular the degree to which static and dynamic stretching functions are supported.
2. Ozone concentration range and control accuracy:The desired ozone concentration range is selected according to the material type, and common equipment provides a regulation range of 20~1000pphm or 10~1000pphm. Focus on concentration deviation indicators, usually requiring no more than ±5% or ±10% of the set value. The concentration detection method should use ultraviolet absorption sensors with online real-time monitoring to ensure the accuracy and stability of control.
3. Temperature and Humidity Control Capabilities:Confirm whether the temperature range of the equipment covers the common test temperature (e.g. 40°C) and whether the temperature uniformity and fluctuation meet the requirements. If humidity testing is involved, confirm whether the equipment is equipped with accessories such as humidification systems and wet ball yarn belts, as well as the range and accuracy of humidity control.
4. Stretching device and specimen rack form:Equipment with static stretching function or dynamic stretching function is selected according to the test requirements. Static tensile fixtures should be able to securely grip a wide range of specimen sizes and achieve precise elongation adjustment. Dynamic stretching devices need to pay attention to the stretching frequency adjustment range (e.g., 0~30 times/min), maximum stretching length, and cycle mode (continuous/intermittent). Whether the specimen rack has a 360-degree rotation function can help improve the uniformity of specimen exposure.
5. Safety protection and emission system:Ozone is harmful to the human body, and the equipment must be equipped with an effective exhaust gas emission system, which usually discharges ozone into a water tank to dissolve it. The equipment should have safety functions such as door opening linkage protection, over-temperature protection, and water shortage alarm. The observation window should be made of multi-layer hollow tempered glass, with anti-fog function on the inside, which is convenient for observing the state of the specimen.
6. Ease of operation and data management:The control system should adopt a touch screen man-machine interface, with two modes: program control and fixed value control. Data logging and export functions (e.g., USB interface, curve display) facilitate experiment traceability and analysis. The equipment should reserve communication interfaces to facilitate connection to the laboratory information management system.