Control of vacuum arc source cathode spots contraction motion by changing electromagnetic field

This paper investigates the magnetic field component impact on cathode spots motion trajectory and the mechanism of periodic contraction.Electromagnetic coils and permanent magnets were installed at the different sides of cathode surface,the photographs of cathode spots motion trajectory were captured by a camera.Increasing the number of magnets and decreasing the distance between magnets and cathode both lead to enhancing cathode spots motion velocity.Radii of cathode spots trajectory decrease gradually with the increasing of electromagnetic coil＇s current,from 40 mm at 0 A to 10 mm at 2.7 A.Parallel magnetic field component intensity influence the speed of cathode spots rotate motion,and perpendicular magnetic field component drives spots drift in the radial direction.Cathode spot＇s radial drift is controlled by changing the location of the ‘zero line＇ where perpendicular magnetic component shifts direction and the radius of cathode spots trajectory almost equal to ‘zero line＇.

Distribution of Cathode Spots in Vacuum Arc Under Nonuniform Axial Magnetic Fields

Recent results on the distribution of vacuum arc cathode spots （CSs） in nonuniform axial magnetic field （AMF） are presented. Based on previous studies, we deem that two contrary influences of AMF, inward effect and outward effect, are attributed to CSs distribution. With this notion, we have analyzed the controlling effectiveness of nonuniform AMF on CSs distribution. Experiments were conducted in a detachable vacuum chamber with iron-style AMF electrodes. Images of vacuum arc column and the distribution of CSs were photographed with a high-speed charge coupled device （CCD） camera. Experimental results agreed well with the theoretical analysis.

A magnetic sensor array for spot welding quality monitor

Spot welding is affected by many factors and is difficult to monitor the nugget information with single sensor. In this paper, a new monitor system based on sensors array technique was developed for spot welding quality detection. The key part in the system is cross magnetic sensor array. It is composed of six magnetic sensors. An improved algorithm was proposed to extract the signal eigenvalue, which was based on principle component analysis. The results show that in the case of the 60 mm experiment, cross magnetic sensor array works well. And when the eigenvalues range of the cross magnetic sensor array is 0. 090 1 - 0. 098 2, the spots quality is good. The analysis of the eigenvalues of the cross magnetic sensor array allows us to determine whether the spot qualty is good or bad.

Reconstruction of Current Density Distribution in Weld Area During Resistance Spot Welding of Aluminum Alloy Based on Magnetic Field

Magnetic flux density around the weld area was used to reconstruct the current density distribution during resistance spot welding(RSW) of aluminum alloy according to inverse problem theory. A current-magnetic field model was established and the conjugate gradient method was used to solve this model. The results showed that the current density was low at the center of nugget while high on the edge of nugget. Moreover, the welding time of 30ms—60 ms is a key period for nucleation. The current density distribution can reflect whether the weld nugget is formed or splashed, therefore it has the potential to monitor the weld quality of RSW.

Investigation of cathode spot characteristics in vacuum under transverse magnetic field (TMF) contacts

With the continuous improvement of current levels in power systems, the demands on the breaking capacity requirements of vacuum circuit breakers are getting higher and higher. The breaking capacity of vacuum breakers is determined by cathode spots, which provide electrons and metal vapor to maintain the arc. In this paper, experiments were carried out on two kinds of transverse magnetic field（TMF） contacts in a demountable vacuum chamber, the behavior of the cathode spots was recorded by a high-speed charge-coupled device（CCD） video camera, and the characteristics of the cathode spots were analyzed through the image processing method. The phenomenon of cathode spot groups and the star-shaped pattern of the spots were both discovered in the experiment. The experimental results show that with the condition of TMF contacts the initial expansion speed of cathode spots is influenced by some parameters, such as the tested current, contact gap, the structure of the contact, the contact diameter, the number of slots, etc. In addition, the influence of the magnetic field on the formation of the cathode spot groups, the distribution, and the dynamic characteristics of the cathode spots were analyzed. It is concluded that the characteristics of the cathode spots are due to the effect of the magnetic field on the near-cathode plasma. The study of the characteristics of cathode spots in this paper would be helpful in the exploration of the physical process of vacuum arcs, and would be of guiding significance in optimizing the design of vacuum circuit breakers.

The Sunspots

In the present paper, the theoretical frame work of magneto hydrodynamics (MHD) is used to give a solution of the problem about the origin, persistence and disappearance of the Sunspots;as well as their tendency to appear as bipolar magnetic couples. According to the results obtained, a possible explanation about the change of polarity in both solar hemispheres is given. Heuristic but logical arguments about the periodicity of the phenomenon of the observed magnetic polarity and the tendency of couples of Sunspots to appear solely in certain latitudes that can be called tropical regions of the Sun are presented. Finally, an indirect experimental test is proposed to show the possible process that produces the polarity of the Sunspots in a given cycle, as well as the invertion of that polarity in the next solar cycle.

Effect of retained austenite and nonmetallic inclusions on the thermal/electrical properties and resistance spot welding nuggets of Si-containing TRIP steels

Five advanced high-strength transformation-induced plasticity(TRIP) steels with different chemical compositions were studied to correlate the retained austenite and nonmetallic inclusion content with their physical properties and the characteristics of the resistance spot welding nuggets. Electrical and thermal properties and equilibrium phases of TRIP steels were predicted using the JMatPro? software. Retained austenite and nonmetallic inclusions were quantified by X-ray diffraction and saturation magnetization techniques. The nonmetallic inclusions were characterized by scanning electron microscopy. The results show that the contents of Si, C, Al, and Mn in TRIP steels increase both the retained austenite and the nonmetallic inclusion contents. We found that nonmetallic inclusions affect the thermal and electrical properties of the TRIP steels and that the differences between these properties tend to result in different cooling rates during the welding process. The results are discussed in terms of the electrical and thermal properties determined from the chemical composition and their impact on the resistance spot welding nuggets.

基于双磁场的管道非体积损伤检测研究

管道应力集中区的应力量化对管道寿命评估及安全预防具有重要作用。弱磁检测技术是一种有效的应力集中检测方法,但是管道的硬点也会产生类似的缺陷信号对应力量化分析产生干扰。本文建立了管道非体积损伤的磁信号检测解析模型,分析了硬点及应力对管材磁特性参数的影响,对硬点及应力集中区在不同励磁强度下的信号特征进行了研究,提出利用强弱励磁的双磁场应力检测方法用以排除硬点对应力弱磁信号的干扰,对理论研究进行了试验验证。研究结果表明:弱励磁下,磁化强度随应力及硬度增大而减弱。磁化强度的衰减梯度随应力增大而增大,随硬度增大而减小;强磁激励下,磁化强度随硬度增大呈近线性减小趋势且不受应力变化影响。引入信号特征磁敏系数表征不同励磁强度下非体积缺陷的检测能力,10 kA/m励磁下,随着应力增大,磁信号的切向磁敏系数从1.54增强到25.87,随着硬度的增大,磁信号的切向磁敏系数从7.46增强到33.87,应力及硬点均有较好的识别能力;30 kA/m励磁下,随着应力增大,磁信号的切向磁敏系数从0.07增强到0.54,随着硬度的增大,磁信号的切向磁敏系数从0.49增大到4,硬点仍有较好的识别能力,应力识别能力低,因此利用强弱磁双场检测方法可以排除硬点对应力检测的干扰。

磁脉冲点焊焊枪的设计及仿真分析

目的根据现有平板线圈的不足,设计了一种用于自动化作业的磁脉冲点焊焊枪。方法采用有限元模拟方法对比分析了磁脉冲点焊焊枪线圈和现有平板线圈的性能差异,并对磁脉冲点焊焊枪线圈的结构进行了优化。结果当线圈工作部分高10 mm、宽4 mm时,焊枪线圈和平板线圈的最大电流密度、最大磁感应强度、最大洛伦兹力分别为3.142×10^(10)A/m^(2)和3.639×10^(10)A/m^(2)、19.40 T和21.69 T、5.149×10^(11)N和1.626×10^(12)N。当线圈工作部分宽4 mm时,随着高度由10 mm降低至4 mm,焊枪线圈的最大电流密度和最大洛伦兹力分别提升了27.56%和57.64%。当驱动能力接近时,焊枪线圈所产生的位移仅为平板线圈的13.09%。当焊枪线圈工作部分截面为10 mm×10 mm的方形时,飞板凸台在20μs时的速度仅为200 m/s;而当截面为ϕ5.6 mm的圆形时,飞板凸台在19.2μs时便产生237 m/s的速度。结论在工作部分的高度和宽度相同的情况下,焊枪线圈的性能要弱于现有平板线圈的性能。在宽度不变的条件下降低焊枪线圈工作部分的高度可以增大飞板的电流密度、洛伦兹力和速度,并且在性能相近的情况下,焊枪线圈工作部分所受应力要小于现有平板线圈所受应力。另外,将磁脉冲点焊焊枪线圈工作部分的截面由方形替换为相同面积的圆形,可以获得更优的焊接条件。

外加磁场对高强不锈钢电阻点焊熔核组织与性能调控技术研究

针对轨道车辆高强不锈钢材料电阻点焊存在的压痕明显、熔核直径波动较大、熔核中心缩孔等问题,探索了磁控电阻点焊技术对提升焊接质量和接头性能的潜力。通过在现有电阻点焊设备上增加环形永磁体,利用外加磁场对熔融金属进行电磁搅拌,发现磁控电阻点焊能够显著改善焊点质量和接头性能。与传统电阻点焊相比,磁控点焊可降低凸痕高度80.6%,增大熔核直径12.0%,并将熔核等轴晶区的枝晶间比例从29%改善至6%。此外,磁控点焊接头的拉剪断裂载荷提高11.8%,疲劳强度也得到了提升。通过微观组织观测发现,磁控点焊能够有效细化熔核晶粒,使枝晶间比例大幅下降,从而提高接头表面强度,降低压痕深度。疲劳试验结果表明,磁控点焊接头的疲劳寿命显著提高,且断裂模式由传统点焊的界面断裂转变为高韧性的纽扣断裂模式。研究为磁控电阻点焊技术在不锈钢轨道车辆制造中的应用提供了实验数据支持,并为无涂装车辆高可靠无痕点焊提供了借鉴。

风电机组永磁发电机温度场疲劳仿真研究

针对MW风电机组永磁发电机温度场疲劳计算问题进行研究,通过预埋在发电机绕组附近的温度传感器采集温度获得温度场疲劳载荷;分析确认发电机定子结构的材料力学性能、几何结构、应力与温度载荷满足线性关系;提出一种发电机母材及焊缝温度场疲劳计算的新方法;运用子模型技术及热点应力法对新方法的计算结果进行对比验证。研究结果表明,这种新方法满足发电机温度场疲劳计算的工程需求。

基于磁透镜结构参数的电子枪磁聚焦特性分析

磁透镜是电子枪的重要组成部分,其结构会影响磁聚焦性能,从而影响束斑直径与电子束焊接质量。文章以国产ZD-VEBW系列高压电子束焊接设备电子枪为研究对象,构建电子枪束源与电磁聚焦结构的物理模型,并借助CST平台,仿真分析了球差影响下的束斑形貌和不同聚焦电流下磁透镜铁壳内径、铁壳开口对束斑直径的影响。设计环形挡板实现了磁透镜铁壳内径、铁壳开口参数的调整,并进行聚焦电流变化下的焊接实验研究。实验结果表明:磁透镜结构参数的合理设计可以达到更优的磁聚焦特性、更小束斑直径与更大的焊缝深宽比,实验验证了仿真结果的正确性,文章的研究对国产ZD-VEBW系列高压电子枪磁透镜结构的设计和该系列电子枪焊接质量的提升提供了理论和实验指导。

磁流变抛光数学模型的建立

介绍了近年来的一种新兴的光学加工技术———磁流变抛光 (MRF)。以Preston方程为依据建立了这种抛光方法的数学模型。利用该数学模型详细分析了被加工工件表面材料去除率与压力参数P成正比的关系 ,指出了工件表面所受的压力P主要是由流体动压力Pd 和磁化压力Pm 两部分组成的。以用磁流变抛光方法加工凸球面工件为例 ,具体推导出流体动压力Pd 和磁化压力Pm 的数学表达式 ,并通过实验对压力P的数学表达式及抛光模型的合理性进行了验证。

高阶统计量在地震弱信号及"磁亮点"识别中的应用

烃渗漏蚀变带"磁亮点"是近年来发展起来的一种直接找油的新技术,随之出现了不少用于提取"磁亮点"的方法,本文主要探讨了提取"磁亮点"的高阶统计量方法。文中主要对高阶统计量的有关性质进行了研究,并且从理论上证明了高阶统计量不仅可以完全抑制信号中的高斯有色噪声影响,而且还能提供功率谱所没有的相位信息,表明高阶统计量比功率谱方法更具优越性。文中还分析了由烃渗漏蚀变带产生的"磁亮点"的统计特征,表明了高阶统计量用于提取"磁亮点"的可行性。最后,将此法用于巴彦浩特盆地航磁资料提取"磁亮点"。结果表明,高阶统计量方法与宽度幅值特征滤波方法相似,而且效果更好,高阶统计量方法在地球物理信号分析中一定会得到更加广泛的应用。

烃渗漏引起的磁异常的提取与识别

本文对近年来国内外在烃渗漏与磁异常关系以及磁异常提取与识别技术领域取得的进展进行了论述与总结.利用磁异常寻找油气资源,特别是在圈划异常远景区方面具有经济、快速、有效的优势.但也存在多解性问题.为了有效判别异常源性质,本文提出利用人工神经网络作为以上方法补充的思路,可以作为磁法预测油气远景区技术流程中的一环,有助于减少多解性.

巴彦浩特盆地烃渗漏蚀变带“磁亮点”的识别

采用多层组合棱柱体建立了磁性蚀变带磁场正演模型 ,并分析了由它产生的“磁亮点”的特征 ,运用“磁亮点”的宽度和异常幅值特征构制的滤波器 ,提取了 7个可能与烃运移有关的“磁亮点”。结合地质与伽马能谱测量资料的分析得出 ,其中的 2个“磁亮点”位于含油地层石炭系较厚的凹中隆和山前断阶带 ,且该区也有放射性低值异常显示 ,是值得进一步工作的油气远景区。

多脉冲点焊与磁控制点缝焊技术及其现状

论述了多脉冲点焊及磁控交流点、缝焊的原理、工艺特点及其发展现状,特别对可淬硬钢的二次、三次及多脉冲点焊作了较详细的介绍。并指出多脉冲点焊与磁控点缝焊能有效消除焊点应力、改善组织性能、消除焊接缺陷、细化组织等优点。

插接式真空灭弧室电弧形态的试验研究

为了解决传统对接式真空负荷开关在大容量发电机出口负荷开关开发过程中存在无法满足大负荷电流的瓶颈问题,基于插接式触头结构的真空灭弧室具有承载大负荷电流的优势,使其成为发电机出口端真空负荷开关设计的一种优选方案。同时,通过引入横向磁场对插接式触头结构进行了改进,改进后的真空灭弧室经过试验验证也具有了开断大负荷电流的能力。在小电流情况下(I<2 kA),插接式电极结构真空电弧特性的试验研究发现:阴极斑点或者仅在单一触指上分布,或者在各个触指之间跨越同时并联存在。当阴极斑点在单一触指上分布时,一部分阴极斑点在触指开槽处成群聚集静止不动,另一部分阴极斑点沿着S型轨迹在该触指表面边缘运动;当阴极斑点从一个触指向相邻触指跨越过程中,原来触指上的阴极斑点并不熄灭而是同时并联存在。

基于磁流变抛光技术的实验装置研究

在介绍了磁流变抛光的基本原理的基础上,对磁流变抛光的实验装置进行了分类设计,从工件与抛光盘的相对位置和磁流变液的注入形式考虑,分别通过平置式、倒置式和正置式,使抛光装置与不同机床进行整合,实现了模块化设计理念。同时对不同的整合方案进行了比较,得出合理的设计方案。

磁纳米肿瘤热疗中的一维靶点磁控方法研究

"肿瘤热疗"是一种新型的治疗癌症的手段,在临床方面已取得良好的效果。然而目前还没有一种对肿瘤位置实时精准把控的治疗方法,这成为以磁纳米为载体的靶向药物定点释放和肿瘤热疗的瓶颈。利用零磁场在磁场中的唯一性实现磁场空间定位,推导单一线圈空间任意一点的磁感应强度,利用磁场的矢量合成原理,推导出亥姆赫兹线圈中零磁场点与线圈施加电流的关系,构建基于亥姆赫兹线圈的一维零磁场点位置模型。利用COMSOL实现了零磁场点位置的运动仿真,仿真结果表明,基于COMSOL的仿真结果与理论推导相吻合,零磁场点在一维上能够通过对亥姆赫兹线圈施加不同电流进行精确控制,为磁靶向治疗提供物理可行性。