Research On Contact Behavior And Heat Transfer Characteristics Of Graphite Bath In Deep Penetration Brazing Of Cu/Ni Metal Wires

The low-temperature radiant heating technology of heating cables has the characteristics of high efficiency,energy saving,environmental protection,comfort and safety.It has become an internationally recognized advanced heating method.The key technology of the heating cable is the manufacture of heating cable cores.The core of the heating cable is formed by pairing Cu wires(cold wire,?0.4-1.13 mm)with different diameters and Ni-based alloy wires(hot wire,?0.3-0.85 mm)after deep penetration brazing.Deep-welding of heat-generating cable cores is a special welding method between the thermal conduction welding and the brazing.It mainly uses the contact resistance between the copper electrode and the perforated graphite welding pool to generate heat to melt the Ag-based solder,and then achieve Cu/Ni-based brazing in perforated graphite welding pool.Therefore,the study of contact interface contact behavior is the key to the formation of stable welding heat source.This subject is a sub-project of the Guizhou Provincial Key Equipment and Manufacturing Technology Key Laboratory undertaking the National Natural Science Foundation project “The Effect and Mechanism of Ablation of Graphite Melts on the Flow of Brazing Materials”.Focus on the contact characteristics of the interface between the graphite pool and the electrode during the deep-melting brazing process,and analyze the mechanism of the static contact resistance and the dynamic contact resistance under ablation on the temperature of the graphite pool.The specific research work is as follows:1.The surface profile measuring instrument and scanning electron microscope are used to obtain the surface roughness and morphological characteristics of the graphite molten pool.Combined with the Greenwood-Williamson(GW)model of Elastic-plastic Contact,the mechanical model of the graphite molten pool interface contact is established to analyze the contact force The interaction between the contact area and other factors,and to clarify the contact behavior of the graphite pool and the electrode interface.2.Based on the fractal geometry theory,combined with the contact characteristics of the graphite molten pool and the copper electrode interface,a static fractal contact resistance model between the graphite molten pool and the electrode is established,and the MATLAB software is used for numerical calculation to analyze the contact pressure,contact surface,fractal parameters and different effect of factors such as graphite molten pool on the contact resistance.The comparative analysis of numerical calculation values and experimental measurement results are basically consistent,verifying the accuracy of the model establishment.3.Through the integration of temperature acquisition,pressure testing,contact resistance measurement and other integrated Cu / Ni-based alloy wire deep penetration brazing experimental test platform to obtain the high temperature contact ablation characteristic change of cylindrical graphite molten pool.Then,the characteristic of ablation of graphite molten pool with equal diameter is proposed,and the model of dynamic contact resistance under the ablation of graphite molten pool is established.The experimental measurement results verify the rationality of the model.4.A simulation model for the heat generation process of the weld pool under the conditions in line with the actual working conditions is established,and The COMSOL software was used to simulate the thermoelectric coupling of the heat generation process of Cu / Ni-based alloy wire welding.Then,a comprehensive analysis of the effects of static contact resistance and dynamic contact resistance under ablation on welding heat provides a theoretical basis for predicting the research of graphite molten pool contact and heat transfer performance.