【作者】 傅江华；

【导师】 熊惟皓；

【作者基本信息】 华中科技大学 ， 纳米科学与技术， 2007， 硕士

【摘要】 电触头是继电器的关键部件之一,其性能直接关系到继电器的可靠性。随着欧盟环保指令的实施,以及汽车供电系统由14V升高到42V的趋势,汽车继电器的服役条件对电触头材料提出了更加苛刻的要求。在触头的各种失效形式中,最为严重的是电弧放电导致的触头熔焊。对熔焊现象进行理论上的分析,能够为触头材料的开发提供指导。本文对触头电弧熔焊中的传热与流动过程进行了数值分析,讨论了相关因素对AgMeO触头材料抗熔焊能力的影响。通过建立圆柱形触头受电弧作用的轴对称模型,采用有限体积方法求解了触头熔池的温度场、速度场和浓度场。计算分析表明,电弧作用在触头的局部,熔池体积小,但温度梯度大,约107K/m的数量级,温度变化剧烈,约107K/s的数量级。改变MeO的热导率、比热、分解温度和分解热,对触头的抗熔焊能力影响很小。触头熔池中的流体流动主要由表面张力驱动,电磁力和浮力的影响不大。负温度系数的表面张力使熔池中的流体从中心流向边缘,熔池变宽变浅;正温度系数的表面张力使熔池中的流体从边缘流向中心,熔池变窄变深。流动使触头表面的MeO颗粒含量升高,MeO的颗粒越大,在触头表面的富集效应越显著。触头表面的MeO富集使熔化面积增加,而熔焊强度下降。为了改善材料的抗熔焊能力,应该添加适当的元素改变电弧特性,使燃弧时间缩短,电弧半径扩大;还可添加活性元素改变触头材料的表面张力温度系数,使熔池的形状发生改变。本文中还设计了一套触头动作模拟装置,可用于测试触头材料的抗熔焊能力。采用电磁铁和弹簧控制触头的往复运动,接触压力可调,熔焊力可测,触头装拆方便。更多还原

【Abstract】 Electrical contact is the key component of relays. Its performance affects the reliability of electrical power system greatly. With the implement of environment restriction from the European Union and the improving from 14V to 42V of the power supply in automobile, the requirement to the electrical contact materials for automobile relays will be more rigorous. Contact welding because of arc is the most serious failure phenomenon. Theoretic analyses for welding phenomena can give the guidance to the research and development of contact materials.The heat and flow process during contact welding by arc is investigated by numerical method, and correlative factors which can affect the welding resistant ability of the AgMeO contact material are discussed. The axial symmetry model of cylindrical contact under arc is set up. The temperature distribution, velocity distribution and content distribution are calculated by the Finite Volume Method.The results show that the weld molten pool is on the local area of the contact and its size is small. The gradient of temperature distribution is on the order of 107K/m, and the rate of temperature change is on the order of 107K/s. Changes the thermal conductivity、heat capacity、decomposition temperature or decomposition enthalpy of the MeO phases give little benefit to improve the welding resistant ability of the AgMeO contact material. The fluid flow in weld pool is mainly driven by surface tension. The effect of the flow driven by electromagnetic force and buoyancy force is weak. The negative value of surface tension temperature coefficient causes near surface fluid moving from the centre to the periphery, the shape of the pool become shallow and wide. The positive value of surface tension temperature coefficient for causing near surface fluid moving from the periphery to the centre results in a very deep pool. The content of the MeO on the surface of the contact increases because of the fluid flow. The bigger size of the MeO particle is, the more obvious the segregation is. The segregation of MeO on the contact surface increases the welding area and decreases the welding strength of the contact material.Adding some appropriate element in contact material may be an efficient means to improve the welding resistant ability. By the additive, the arc duration can be shorter and the arc can be more dispersed on the electrical contact. The additive which changes the surface tension temperature coefficient can make the weld pool shallow.An apparatus which simulates the contact action is designed to test the weld performance of the real electrical contact material. The movement of the contacts is controlled by electromagnet and springs. The contact force can be adjusted and the welding force can be measured. It is easy to assemble and disassemble the contacts.更多还原