Analysis of open-flame electric arc in transverse magnetic field

The distribution of temperature and pressure, electromagnetic fields, and the structure of flow under the effect of an external transverse magnetic field are determined using a three-dimensional magnetogasdynamic model of a steady-state curved arc. The calculation results are consistent with the experimentally observed properties of the arc, such as stabilizing effect of current strength and the magnetogasdynamic mechanism of arc extinction.     

Effect of Ti-Zr addition on the microstructure and the arc chopping current of melt-spun CuCr ribbon

The microstructure and the arc chopping current of melt-spun Cu₇₁Cr₂₉ ribbon added by Ti-Zr are studied in the article. The results reveal that the melt spinning could partly restrain the liquid phase separation of CuCr alloys because it has a high cooling rate (about 10⁶ K/s), the size of the Cr rich phase from liquid phase separation in the Cu₇₁Cr₂₉ microstructure can be decreased from the micron-scale to about 250 nm by using melt spinning. On the melt-spun base, alloying by Ti-Zr could further decrease the size of the Cr rich phase from 250 nm to about 100 nm. For nano-grained CuCr alloys, its lower arc chopping current is advantageous to the use of contact and the circuitry protect, its long arc trace route and high velocity of spot direction motion could mitigate the partial ablate of cathode surface and the lifetime of contact could be prolonged.     

外加直流磁场下微束等离子电弧行为与焊缝成形研究

为实现薄壁件金属在增材制造中成形及成性的精确控制,基于带电粒子在直流磁场作用下的运动规律,研究了外加直流磁场作用下电弧行为,得到电弧偏转程度、偏转方向与外加磁场之间的关系.在电弧偏转的基础上分析了焊缝形貌、焊缝晶粒变化原因.结果表明:外加直流磁场作用下电弧发生偏转,在试验参数范围内随磁场强度增加,电弧偏转程度增大,且电弧偏转方向与外加磁场方向相关;外加正向直流磁场时熔池向焊接方向后方偏移,焊缝余高相对增加,焊缝晶粒较无外加磁场细化;外加反向直流磁场时熔池位于电弧下方,焊缝余高相对降低,焊缝晶粒较外加正向磁场更加细化.外加正向直流磁场控制焊缝形貌,具有"控形"效果;外加反向直流磁场有明显的细化晶粒作用,可以达到"控性"目的.     

A theoretical study of the impact of magnetic field of Hall current on the parameters of a high-current vacuum-arc discharge

It is demonstrated that the magnetic field of Hall current in a short high-current vacuum-arc discharge significantly distorts the external axial magnetic field and affects the distribution of current density in the discharge gap. This effect decreases with increasing external magnetic field, with decreasing arc current, and with decreasing ratio of the length of discharge gap to its transverse dimension. A 2D magnetohydrodynamic mathematical model is used to calculate the discharge parameters for different values of induction of external magnetic field. The calculation results are compared with similar results obtained using a 1.5D model in which the impact made by magnetic field of Hall current is ignored. It is inferred that the simpler 1.5D model may be employed in calculations of parameters of vacuum arc in a wide range of variation of arc current and of induction of external magnetic field.     

Effects of applied magnetic field on twin-wire indirect arc shapes

Research on regularity of indirect arc shapes change with variation of applied magnetic field is studied. Results show that indirect arc would be elongated or compressed in XOZ plane with variation of applied transverse magnetic field’s direction and intensity, while the indirect arc would be deflected with the application of longitude magnetic field in YOZ plane, and the deflection degree and direction will be also changed by the variation of longitude magnetic field’s intensity and direction. It is considered that change of arc shapes is caused by variation of arc forces. The influence of Ampere force on indirect arc deformation and deflection is analyzed in this paper.     

Effects of applied magnetic field on twin-wire indirect arc shapes

Research on regularity of indirect arc shapes change with variation of applied magnetic field is studied. Results show that indirect arc would be elongated or compressed in XOZ plane with variation of applied transverse magnetic field’s direction and intensity, while the indirect arc would be deflected with the application of longitude magnetic field in YOZ plane, and the deflection degree and direction will be also changed by the variation of longitude magnetic field’s intensity and direction. It is considered that change of arc shapes is caused by variation of arc forces. The influence of Ampere force on indirect arc deformation and deflection is analyzed in this paper.     

A scanning electron microscope study of the role of copper oxide layers on arc cathode erosion rates

The results are described of scanning electron microscopy of copper surfaces covered initially with oxide films of thickness from 2.5 to 340 nm, which have been the cathodes of electric arcs. The objective of the work has been to learn more about the mechanisms of electrical conduction through oxide films on non-refractory arc cathodes, electron emission into the arc and the erosion of the cathode. It is the latter aspect upon which this paper concentrates. Cathode erosion is a major problem when arcs rotate over electrode surfaces for very long times in certain industrial processes. Erosion rates are calculated here using SEMs, both for stationary 4.5 A arcs of duration 1ec, and for higher current arcs which were magnetically driven once over the cathode surface. Making allowance for the effect of current, these erosion rates are shown to be similar in magnitude and in their variation with oxide thickness, and reasons for this are given. Comparison is then made with erosion rates measured by weight loss for long-duration rotating arcs. In the light of the new data given here, it is now possible to understand better the remarkable changes which have occurred for long-duration arcs when varying arc velocity, water-cooling flow rate and arcing duration.     

水或液氮中电弧放电制备炭纳米材料

利用特制的电弧放电装置，研究了水或液氮中碳电弧放电形成炭纳米材料的机理。借助高分辨率透射电子显微镜对电弧放电生成的产物进行了观察和分析。结果表明：在水或液氮中碳电弧放电可以生成多壁碳纳米管和碳纳米洋葱结构，液氮中碳电弧放电可以生成单壁碳纳米角，水中钴催化碳电弧放电可以生成碳包裹的纳米钴颗粒。横向低频交变磁场会影响碳纳米材料的形核过程，并且可以推测磁场交变的频率5Hz与纳米管、纳米洋葱等结构的生长周期存在某种拟合。根据实验现象，提出了一种解释液体中碳电弧放电过程纳米材料生成的理论模型。     

横向稳态磁场作用下微束等离子电弧数值分析

为分析外加横向稳态磁场作用下电弧特性与电弧对工件热、力输入的变化规律,本文建立了微束等离子电弧三维模型,将外加磁场简化为背景场添加至模型,使用有限元分析软件COMSOL进行求解计算。结果表明:外加横向稳态磁场作用下,喷嘴内部各项特性均未发生较大变化,喷嘴下方电弧等离子体在洛伦兹力的作用下向x负方向移动,电弧温度、等离子体速度与电流密度等均发生相应的偏转,因此造成电弧对工件的热输入减小、压力降低。最后在薄壁件上进行了焊接试验,试验过程中拍摄的电弧轮廓与仿真电弧形态基本一致,加磁区域堆焊层余高增加、熔宽减小,焊缝向两侧"下塌"现象消失。外加横向稳态磁场可减小电弧对熔池的热、力输入,进而改变焊缝形貌,抑制薄壁件堆焊过程中由于热、力输入过大而产生的"下塌"现象,有利于薄壁件的堆焊成形。     

Aerosol synthesis of titanium nitride nanoparticles by direct current arc discharge method

Arc discharge synthesis has industrial relevance due to its low cost and scale-up potential. The production of titanium nitride nanoparticles was achieved by direct current arc discharge in an atmospheric-pressured ambient composed of N₂ and Ar. We systematically investigated the effect of the synthesis parameters, including quench gas velocity, quench gas composition, and applied arc current, on the particle quality, yield, and size. It is found that increasing quench gas velocity enables to produce particles with a primary size of 10–15 nm, while titanium nitride particles of 20–50 nm are produced at low quench gas velocity based on scanning electron microscope (SEM) analysis. X-ray diffraction (XRD) results indicated that titanium nitride particles produced at various nitrogen compositions are almost stoichiometric, while the crystallite size increases almost 20 nm when increasing nitrogen contents in the quench gas. Quench gas composition also has a significant impact on the arc voltage as well as particle production rate. When increasing the nitrogen concentration from 20% to 100%, the production rate can be enhanced by a factor of three. Besides, raising the applied arc current from 12 A to 50 A leads to a yield enhancement of factor 10. According to the Brunauer-Emmett-Teller (BET) measurement, the increase of applied arc current has a limited impact on primary particle size. The enhancement in particle production rate is mainly reflected by the larger agglomerate sizes and agglomerate number concentration. Additionally, based on experimental observations and previous studies, a mechanism is presented to explain the growth of deposits on the cathode tip.