Dissertation > Excellent graduate degree dissertation topics show

Study on the Behavior of Arc Welding Resistance for AgMeO Electrical Contact Materials in Automobile Relays

Author: XuJian
Tutor: XiongWeiZuo
School: Huazhong University of Science and Technology
Course: Materials Science
Keywords: Composites AgMeO electrical contacts Welding behavior Bath Flow Surface tension Numerical Analysis
CLC: TM58
Type: PhD thesis
Year: 2008
Downloads: 139
Quote: 1
Read: Download Dissertation

Abstract

The electrical contact is one of the key components of the relay, and its performance is directly related to the working life and reliability of the relay. With the implementation of EU environmental directives, as well as automotive power supply system increased by 14V to 42V trends, automotive relay service conditions more demanding requirements for electrical contact material. Contact the various failure modes of the most serious of which is the result of contact welding arc discharge. Theoretical analysis of the welding phenomenon, it is possible to provide guidance for the design and production of the contact material. In order to facilitate subsequent electrical properties of the contact material, design simulation test device of an electrical contact can be used to the analog relay contacts working condition, test the ability to anti-welding of the contact material. Solenoid and spring complexation to the reciprocating movement of the control contact, the contact material clamping, current and voltage signal acquisition. In cylindrical coordinates established AgMeO composite contact material in the arc under flow mathematical model of the process of heat transfer with molten pool, and the finite volume method to calculate the temperature field of the contact material, flow rate and concentration fields. The detailed analysis of the characteristics of the the contact material molten pool morphology and its evolution, and discuss the impact of anti-welding capacity of the matrix material and the second-phase metal oxide the nature of AgMeO contact material. Temperature field calculation results show that the role of arc energy after the contact material, the contact material has experienced from the room temperature to the melting point, the melting point to the boiling point, the boiling point to the highest temperature point, and then start cooling to the boiling point, melting point, and start to solidify until it has cooled to room temperature for five different status stage. Arcing contact material reprocessing the physical chemistry of metallurgical processes, thus greatly changed the original composition, microstructure and properties of the contact material. Contact material solidification process has the easy nucleation bath temperature gradient is large (107K · m-1), the fast cooling rate (107 K · s-1), is easy to form holes loose structure, or even chemical reaction occurs five prominent feature. Pairs the MEO volume fraction of certain AgMeO contact material, changing the MeO thermal conductivity, specific heat capacity, the density, the decomposition temperature and the decomposition enthalpy, and has little effect on the anti-welding capability of the contact material. MeO the volume fraction is increased to help to improve the anti-welding capability of the contact material, but this will increase the contact resistivity of the material should be controlled to within 20%, to ensure the electrical properties of the contact material of MeO volume fraction. Arc input power on the welding force of the contact material is great, the input power is doubled, and its corresponding the bath contact area also doubled, the welding force is doubled, so the performance of the generated for different materials and dispersing arc is the contact resistance of the material welding performance focus of the study. Under conditions of a small current, the flow of the fluid in the contact material for the bath is mainly driven by surface tension, followed by the electromagnetic force, the buoyancy effects. Arc under the action of the bath fluid flow direction by the surface tension temperature coefficient determined by: having a negative surface tension temperature coefficient of the fluid from the molten pool center flow to the pool edge, while having a positive surface tension temperature coefficient of the fluid from the pool edge flow to the bath center. Add can increase the temperature coefficient of surface tension of the liquid silver alloying elements to about zero, not only can reduce the probability of contact material splashes and can reduce the volume of the molten pool of the contact material, thus contributing to the uniformity of the silver-based contact material, stable. Finally, the article discusses the the segregation phenomenon caused by Bath Flow MeO ingredients. The calculations show that, to the bath fluid flow causes the contact surface of the MeO elevated average content. MeO the enrichment of the contact surface so that the melted area is increased, the welding strength is lowered, thus facilitating contact materials, the welding force reduction resistance welding. MeO the density of the impact of the component distribution is smaller, but in the mass fraction of the MeO is certain, select low density oxide, allowing it to increase in volume fraction, the welding force reduction. In short, to improve AgMeO anti-welding capability of the contact material should priority adding alloying elements to improve AgMeO contact material is dispersed, and the ability to extinguish the arc; Secondly, in the case of a certain mass fraction, select low density MeO While the puddle the increase in size, but it the contacts welding force can be reduced, thereby improving the anti-welding capability of the contact material.

Study on the Behavior of Arc Welding Resistance for AgMeO Electrical Contact Materials in Automobile Relays

Abstract

Related Dissertations