Motor Starting With The Development Of Positive Temperature Coefficient Thermistor

Positive Temperature Coefficient（PTC） is a kind of new semiconductor materialwhich resistance present positive temperature coefficient characteristic with thetemperature changes.PTC material is widely used in many domains, such as householdappliances, power electronic device, automobile industry etc because of its uniqueproperty. PTC thermistor for motor starter has many advantages, such as non contact,low noise, high reliability and long service life. It is widely used in compressors ofhousehold appliances such as refrigerators, air conditioners, etc. As the compressorstarts frequently, how to improve the reliability of PTC thermistor for motorstarter——the motor protection component is the main study purpose of this paper.This thesis is aimed to the characteristics that PTC ceramics bear high current, highvoltage pulse repeatedly in the starting circuit caused by the compressor’s frequent start,carried out a study on the matrix doping and manufacturing process of product in orderto improve the ability of withstanding voltage and high current and the durability ofthe PTC ceramics chip. The optimizing formula and processing technique of ceramicspowder were carried out by performance evaluation of test instruments, such as SEM,Metallurgical microscope, laser particle size analyzer, V-I characteristics tester,oscillograph, R-T characteristics tester, X-ray coating thickness gauge, etc.This article’sprimary research is as follows:First of all, in order to improve the impact resistance of PTC ceramics, in our work,we reformed its microstructure, refined grains, increased grain boundary thickness ofbarrier layers and so on. The author undertook double-donor doping withsemiconducting element, Sr-Pb doping, Mn（NO₃）2doping, doped with grain refinerCaCO₃, glass doping research. Through comparing the experimental results, we obtainedthe best component formation eventually, and produced the PTC ceramics power withlow resistivity（90¹50·cm） and high proof voltage（≥750V）.Secondly, the thesis studied the effect of fabrication process on properties of PTCceramic.The author studied the Process parameters in raw material particle size and morphology, mix pre-firing temperature of grinding time and equipment, and the slurrydensity, granulation process in aspect of ceramics production and in the forming dentisy,sintering temperature and the thickness of electrode in chip production. The experimenteventually determined the best process parameters, which laid the technologicalfoundation for volume production of high quality PTC ceramics.Finally, the issues succeed in producing the MZ35-2-15RM thermistor for motorstarter by means of matrix doping and optimization of production process. This resistorhas the features of uniform grain structure, withstanding voltage over750v，the switchlifetime is more than500thousand. All the performance indexes meet the designrequirements and achieved a continuous mass production，the product quality close tothe level of similar products abroad.