| Positive temperature coefficient(PTC)thermistor ceramic resistors have unique temperature resistance characteristics and are widely used as electric heating elements in air conditioners,plumbing heaters,new energy vehicles and other fields.In order to improve the reliability and life of PTC thermistor,the higher requirements for its aging performance have been put forward within the industry.The influencing factors and testing conditions of PTC aging performance were mainly studied in this thesis.And a more reasonable aging test scheme was designed,which systematically improved the problems in the existing aging tester such as concentrated voltage,large current impact and single test content.In addition,the effects of element contents in the formulation on the performance and aging properties of PTC were studied.The following main parts are included:When the existing equipment is used for aging measurement,the start interval of each station is fixed at 1 second,and the aging rate is calculated by measuring the room temperature resistance of the sample before and after the aging test.In this thesis,the existing aging test equipment was improved,and a plan for sequentially applying voltage was proposed according to on voltage time,off voltage time and the number of samples to calculate and allocate the voltage interval time reasonably.After software programming and debugging,the purpose on good consistency of experimental conditions for each sample was achieved regardless of the sequence,and the problem of concentrated appling volatge and excessive current impact in existing aging equipment was solved also.At the same time,the real-time power,current,voltage,and resistance of each sample can be calculated,which makes the aging evaluation parameters more abundant and comprehensive.The probe fixture with spring was used to replace the old fixture which is easily deformed after applying pressure,and the new fixture had a larger and more uniform holding force,which reduces the fragmentation rate caused by the unsuitable fixture;the experimental results also indicated that its aging performance were improved by the PTC in series.The effect of Li,Al and Mn content on the aging of PTC was studied,and the content range with better aging performance was obtained,which provided a reference for further obtaining the best formulation of PTC.The experimental results also show the aging performance of the samples can be improved by pre-treating the PTC thermal ceramic resistors once,which can make the resistance aging rate less than 23.5% during the process of 1000 onoff aging tests. |
