Characteristics of Eddy Current Attenuation and Thickness Measurement of Metallic Plate

In eddy current testing, the law of attenuation of eddy current(EC) is of great concern. In conductive half space under the excitation of uniform magnetic field, the EC density decreases exponentially in the depth direction. However, in conductor with finite thickness tested by coil, the distribution of EC in the depth direction is more complicated. This paper studies the characteristics of EC attenuation in metallic plate of finite thickness. Simulation results show that there is an EC reflection at the bottom of plate, which changes the law of EC attenuation. A new concept, namely the equivalent attenuation coefficient, is proposed to quantify the speed of EC attenuation. The characteristics of EC attenuation are utilized to explain the nonmonotonic relation between coil voltage and plate thickness. Procedure of selecting frequency is discussed. Thereafter, measurement of plate thickness is carried out and accurate result is obtained.

Magneto-elastic combination resonances analysis of current-conducting thin plate

Based on the Maxwell equations, the nonlinear magneto-elastic vibration equations of a thin plate and the electrodynamic equations and expressions of electromagnetic forces are derived. In addition, the magneto-elastic combination resonances and stabilities of the thin beam-plate subjected to mechanical loadings in a constant transverse magnetic filed are studied. Using the Galerkin method, the corresponding nonlinear vibration differential equations are derived. The amplitude frequency response equation of the system in steady motion is obtained with the multiple scales method. The excitation condition of combination resonances is analyzed. Based on the Lyapunov stability theory, stabilities of steady solutions are analyzed, and critical conditions of stability are also obtained. By numerical calculation, curves of resonance-amplitudes changes with detuning parameters, excitation amplitudes and magnetic intensity in the first and the second order modality are obtained. Time history response plots, phase charts, the Poincare mapping charts and spectrum plots of vibrations are obtained. The effect of electro-magnetic and mechanical parameters for the stabilities of solutions and the bifurcation are further analyzed, Some complex dynamic performances such as perioddoubling motion and quasi-period motion are discussed.

General series expression of eddy-current impedance for coil placed above multi-layer plate conductor

This paper presents a closed expression of the layered-plate factor used to calculate the coil eddy-current impedance over the multi-layer plate conductor. By using this expression, the general series of eddy-current impedance can be written directly without solving the undetermined constant equations. The series expression is easy to use for theoretical analysis and programming. Experimental results show that calculated values and measured values are in agreement. As an application, when the bottom layer of the layered plate is a non-ferromagnetic thin layer conductor and the product of the thickness and conductivity of the layer remains unchanged, using the layered-plate factor expression proposed in this paper, it can be theoretically predicted that the eddy-current impedance curves corresponding to different thin layer thickness values will coincide.

Effect of Hall current on MHD natural convection flow from vertical permeable flat plate with uniform surface heat flux

The effect of the Hall current on the magnetohydrodynamic （MHD） natural convection flow from a vertical permeable flat plate with a uniform heat flux is analyzed in the presence of a transverse magnetic field.It is assumed that the induced magnetic field is negligible compared with the imposed magnetic field.The boundary layer equations are reduced to a suitable form by employing the free variable formulation （FVF） and the stream function formulation （SFF）.The parabolic equations obtained from FVF are numerically integrated with the help of a straightforward finite difference method.Moreover,the nonsimilar system of equations obtained from SFF is solved by using a local nonsimilarity method,for the whole range of the local transpiration parameter ζ.Consideration is also given to the regions where the local transpiration parameter ζ is small or large enough.However,in these particular regions,solutions are acquired with the aid of a regular perturbation method.The effects of the magnetic field M and the Hall parameter m on the local skin friction coefficient and the local Nusselt number coefficient are graphically shown for smaller values of the Prandtl number P r （= 0.005,0.01,0.05）.Furthermore,the velocity and temperature profiles are also drawn from various values of the local transpiration parameter ζ.

Inverse problem of pulsed eddy current field of ferromagnetic plates

To determine the wall thickness, conductivity and permeability of a ferromagnetic plate, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy current testing on the plate. From time-domain analytical expressions of the partial derivatives of induced voltage with respect to parameters,it is deduced that the partial derivatives are approximately linearly dependent. Then the constraints of these parameters are obtained by solving a partial linear differential equation. It is indicated that only the product of conductivity and wall thickness, and the product of relative permeability and wall thickness can be determined accurately through the inverse problem with time-domain induced voltage. In the practical testing, supposing the conductivity of the ferromagnetic plate under test is a fixed value, and then the relative variation of wall thickness between two testing points can be calculated via the ratio of the corresponding inversion results of the product of conductivity and wall thickness. Finally, this method for wall thickness measurement is verified by the experiment results of a carbon steel plate.

Numerical Solution of MHD Convection and Mass Transfer Flow of Viscous Incompressible Fluid about an Inclined Plate with Hall Current and Constant Heat Flux

The present numerically study investigates the influence of the Hall current and constant heat flux on the Magneto hydrodynamic (MHD) natural convection boundary layer viscous incompressible fluid flow in the manifestation of transverse magnetic field near an inclined vertical permeable flat plate. It is assumed that the induced magnetic field is negligible compared with the imposed magnetic field. The governing boundary layer equations have been transferred into non-similar model by implementing similarity approaches. The physical dimensionless parameter has been set up into the model as Prandtl number, Eckert number, Magnetic parameter, Schmidt number, local Grashof number and local modified Grashof number. The numerical method of Nactsheim-Swigert shooting iteration technique together with Runge-Kutta six order iteration scheme has been used to solve the system of governing non-similar equations. The physical effects of the various parameters on dimensionless primary velocity profile, secondary velocity profile, and temperature and concentration profile are discussed graphically. Moreover, the local skin friction coefficient, the local Nusselt number and Sherwood number are shown in tabular form for various values of the parameters.

金刚石微粉电镀镍品质影响因素研究

金刚石微粉在镀液中易漂浮导致电镀镍困难,为获得金刚石微粉电镀镍工艺,本文研究了镀瓶转速和电镀电流对金刚石微粉电镀镍品质的影响。通过对金刚石微粉颗粒在不同镀瓶转速时运动状态进行理论分析,得到了镀瓶转速调节方法,并通过实验确定了不同电镀电流时镀瓶转速的调节范围。采用单因素实验,研究了电镀电流对镀层增重率、形貌和密度的影响。结果表明:镀瓶转速在1~7 r/min范围内,从小到大逐步提高,同时电镀电流不超过3.0 A条件下,能够实现金刚石微粉电镀镍。电镀电流在0.5 A时镀层失重,出现明显退镀现象,在1.0 A时镀层有少部分漏镀现象,在1.5~2.5 A时镀层包裹完整,基本无漏镀;电镀电流在1.0~2.5 A范围时,随着电镀电流增大,镀层增重率逐渐增大,镀层密度逐渐减小。采用低转速低电流、逐步提高镀瓶转速的方法对金刚石微粉进行电镀镍,镀瓶转速在1~7 r/min,电镀电流在1.5~2.5 A时金刚石微粉电镀镍品质较好。

基于SegFormer的钛板缺陷涡流C扫描检测图像分割

为了获得涡流检测图像中缺陷的形状与长度信息,对检测图像进行图像分割是其中一种重要的方法。由于边缘效应的影响,TA2钛板涡流C扫描图像中缺陷区域边缘模糊、对比度低,导致通过图像分割后估计的缺陷长度与实际值差别过大,难以通过图像分割方法对缺陷长度进行准确估计。针对此问题,提出一种基于SegFormer的钛板缺陷涡流检测图像分割方法。首先,利用涡流C扫描成像获得TA2钛板表面裂纹缺陷检测图像数据集;根据SegFormer网络的结构组成,设计基于SegFormer钛板缺陷涡流检测图像的分割框架和分割流程,并进行网络参数的设置。随后,利用钛板表面裂纹缺陷检测图像数据集对4个分割模型分别进行训练和测试,并利用平均交并比、平均精度和训练时间对其分割效果进行评价。实验表明:相比于Deeplabv3+、Swim Transformer和OCRNet,SegFormer具有更好的分割效果,更快的训练速度。可视化和定量化结果表明:与非深度学习方法相比,该方法具有更小的缺陷长度估计误差。

航空锂电池焊缝的多通道多频涡流检测

为了实现航空锂电池极耳极板激光焊缝的高效准确检测,设计制作了带有层析成像功能的多通道多频涡流检测系统.采用该系统及5通道防干扰差分结构涡流传感器对极耳极板焊缝中的局部断焊、整体漏焊、焊缝变形内凹、微小缺陷等典型缺陷进行检测,并基于趋肤效应原理,采用层析成像技术对焊瘤缺陷进行扫查成像.结果表明,研发的带有层析成像功能的多通道多频涡流检测系统可有效检测出锂电池极耳极板焊缝中的多种典型缺陷,最小可检测1 mm的缺陷,层析成像技术可实现不同深度下缺陷的形貌观测.通过对大量检测结果的对比分析,总结了缺陷种类、位置及长度的判别方法,提出了一套缺陷判别流程与评定准则,为实现锂电池极耳极板焊缝检测的工程化奠定了良好的基础.

高锰钢表面耐磨蚀镀层研究

研究了不同化学镀工艺对高锰钢镀层组织和性能的影响。得出化学镀Ni-P的最佳参数为:NiSO_(4)·6H_(2)O质量浓度30 g/L;NaH_(2)PO_(2)·H_(2)O质量浓度35 g/L;pH值4.7。非晶态Ni-P镀层致密,厚度约25μm。镀层硬度由330 HV提高到600 HV以上,磨损体积减少。镀层的腐蚀电流密度从基体的8.51 mA/cm^(2)降低到1.82 mA/cm^(2)。镀层明显提高了高锰钢基体的表面硬度、耐磨性能和耐腐蚀性能。

基于电流场的阵列极板水下通信系统仿真分析

电流场通信是一种无线通信技术,通过传导电流在水体中传播。传统的水下电磁波通信存在信号衰减大、天线复杂、架设困难等问题。因此,结合电流场水下传播理论,提出了一种基于阵列极板的水下通信系统。使用有限元软件Comsol建立了阵列极板电场模型,并通过频域分析模拟了1×4阵列切面的电场和电势分布。同时,在1×4阵列和1×2阵列之间进行了信号接收效果的对比。在此基础上,分析了6组正负极接线方式对信号接收强度的影响。瞬态时域分析则用于模拟输入输出波形的变化。实验证明,在不增加发射功率的条件下,通过增加阵列排布数量,可以有效提高通信效果。同时,传输过程中信号波形基本保持不变,无相位偏移,从而证明了阵列极板水下通信的可行性。研究结果为新型电流场水下通信系统的建立提供了理论基础。

不锈钢双极板等离子喷涂TiC涂层耐腐蚀性研究

为了提高质子交换膜燃料电池(PEMFC)双极板的耐腐蚀性,采用大气等离子喷涂技术(APS)制备TiC涂层,利用扫描电镜、X射线衍射仪表征涂层的形貌与组织,采用动电位极化、恒电位极化、电化学阻抗谱等方法研究了3种不同电流制备的TiC涂层在PEMFC环境中的耐腐蚀性能。结果表明:TiC涂层的腐蚀电流密度比不锈钢基体低了1个数量级,表明该涂层可以有效提高316L不锈钢的耐腐蚀性。随着喷涂电流的增大,500 A的涂层显示出了最佳的耐蚀性和导电性,这主要是由于随着电流的增大,粒子得到充分的熔化,使涂层致密度得到了提高,孔隙等缺陷减少。

基于恒压控制模式镀锡工艺研究

目前,航空产品镀锡通常采用恒流控制模式生产,此模式下,产品出入槽需立即更改电流,在连续生产方面存在一定局限性。为降低产品镀锡加工控制难度,提升生产效率,通过探究电流密度、电压、加工面积之间关联关系,进行相关性能验证,形成基于恒压控制模式镀锡工艺,该工艺适用于27dm^(2)及以下加工面积零件的恒压镀锡生产。

多重雷击下线路避雷器氧化锌阀片的劣化特性试验

多重雷击会加速劣化氧化锌阀片,造成阀片的电、热性能急剧下降,不同多重雷击参数下氧化锌阀片的破坏具有显著差异性。为此,开展了不同多重雷击参数对氧化锌阀片劣化特性的研究:首先,搭建了多重雷击试验研究平台,对阀片进行了单重1.0倍额定电流、单重1.5倍额定电流、4重1.0倍额定电流、单重1.5倍额定电流和12重1.0倍额定电流的5种工况冲击试验,测试了阀片的直流参数和温升;其次,分析了多重雷击参数对试验结果的影响,最后对阀片的非线性系数、热应力和破坏形式进行了讨论。结果表明:不同工况下直流参考电压变化均呈“下降—平稳—下降”趋势,4重出现直流参考电压陡降现象,12重出现泄漏电流陡升现象;1.5倍额定电流工况下阀片泄漏电流在前期与标称电流工况的变化幅度相近,后期急剧劣化;非线性系数也存在“下降—平稳—下降”规律,增大冲击重数和幅值会使非线性系数下降趋势增大;冲击重数和幅值增大使阀片外圈处最大热应力增加,阀片外圈出现不同长度的缺块。

电控离子交换复合膜电极的界面结合行为与提锂性能

【目的】电控离子交换(ESIX)作为一种新型的离子选择性分离和回收的技术,可以用于从盐湖中提取锂资源。其中,集流体与电活性复合膜之间的界面结合行为对复合膜的电控提锂性能具有重要的影响。【方法】以LiMn2O_(4)为电活性锂离子交换材料,并分别以钛板和石墨板为集流体制备了钛基和碳基复合膜电极。通过附着力测试探讨了集流体与复合膜的界面结合行为,并采用循环伏安、交流阻抗、恒流充放电测试分析了不同复合膜电极的电化学性能。【结果】结果表明:石墨板与复合膜之间的粘附强度(1.33N/cm)约为钛板(0.71N/cm)的2倍,且碳基复合膜电极表现出更优异的电化学性能。在10次连续的ESIX过程中,碳基复合膜电极具有更好的提锂性能。这是由于石墨板与复合膜之间具有更充分的粘结性,使两者之间显现出更杰出的界面导电性,从而增强了复合膜电极的电活性和循环稳定性。此外,钛板在多次氧化还原后表面生成的氧化膜会产生较大界面电阻,从而降低了钛板的导电性。

电镀温度对钢板镀铬效果的影响研究

传统二步法电镀铬工艺要求镀液温度一般较高,需要控制在50℃-60℃,高温电镀带来许多不利影响。针对这一问题,本文研究了不同温度对二步法电镀铬效果的影响,开发了精准控温六价铬电镀技术,将温度控制在45℃~48℃,研究结果表明温度越低电流效率越高,即在镀铬层同样厚度的情况下,所需消耗的电镀电流减少,实现节能降耗,降低电镀成本,同时提高生产效率,减少镀铬污水排放。

大电流空气电弧栅片烧蚀数值模拟与分析

电网输配电容量不断增加对低压断路器的开断性能提出了更高的要求。低压断路器开断大电流时,电弧烧蚀灭弧栅片产生的金属蒸汽会极大的影响断路器开断性能,阻碍断路器发展并且不利于电网安全运行。因此,建立了开断电流为10 kA的栅片烧蚀模型,研究了栅片烧蚀特性。模型考虑了栅片阴极端和阳极端不同的电弧能量注入,栅片材料的熔化、蒸发以及栅片表面形貌变化,并将弧根运动引入模型中。利用此模型计算了铁栅片烧蚀质量以及温度和熔化材料分布。仿真结果表明:栅片阴极端温升大小和范围均小于栅片阳极端的值。栅片表面熔化区域尺寸和位置随着弧根的移动而改变。栅片阳极端熔沸点来临时刻分别是2.19 ms和2.89 ms,烧蚀质量为1.84 mg。而栅片阴极端熔点来临时刻为4.12 ms,温度始终低于栅片材料沸点,烧蚀质量近乎为0。该文得到了单次开断下栅片两端烧蚀形貌,为研究多次开断下栅片烧蚀引起的栅片间短弧长度和移动路径变化对断路器开断性能的影响献力。

碱溶液中电积回收镓的工艺研究

针对碱性条件下,镓电积过程中不锈钢阴极易发生析氢反应,致使电流效率低这一难题,重点研究了电积镓过程电流密度、初始NaOH浓度、Ga^(3+)浓度、电积温度对电流效率的影响,优化了电积镓工艺条件。实验结果表明,采用镀镓不锈钢作为阴极,较优的电积工艺参数为温度45℃、电流密度500 A/m^(2)、初始NaOH浓度140 g/L、初始Ga^(3+)浓度150 g/L;在优化工艺参数下,可以有效地减少镓电积过程中氢气的析出,电流效率稳定在75%以上,产品纯度达99.995%。

镀银铜材料在大电流条件下的载流微动磨损特性

利用化学电镀方法在T2紫铜管表面镀银制备镀银铜试样,采用自主研制的切向微动磨损试验设备在圆柱/圆柱的正交点接触模式下进行室温载流切向微动磨损试验,探究了镀银铜试样在5 A电流以及不同法向载荷(5,10,15 N)和位移幅值(30,50,70,100μm)下的载流微动磨损行为及其磨损机制。结果表明:随着位移幅值的增加,镀银铜试样的载流微动磨损程度加剧,随着循环次数的增加,不同位移幅值下的摩擦因数整体呈先减小后增大最后趋于稳定的趋势,而接触电阻呈相反趋势,不同位移幅值下稳定阶段的摩擦因数相差不大;随着载荷的增加,载流微动磨损程度先变大后变小,当载荷为10 N时,磨损程度最大,此时有效接触面积较大,接触电阻较低;随着载荷的增加,稳定阶段的摩擦因数增大。镀银铜试样在磨损初期的磨损机制主要黏着磨损和氧化磨损,在磨损后期主要为磨粒磨损、氧化磨损和剥层,且随着循环次数的增加,氧化磨损程度加剧。

电絮凝法处理垃圾中转站渗滤液的效能及条件优化

采用电絮凝法处理垃圾中转站的渗滤液,分别考察了阳极材料、电流密度、极板间距、反应时间、初始pH及电解质过硫酸钾对渗滤液COD去除率的影响。结果表明:在最佳反应条件下,即采用铁板为阳极材料、电流密度为0.042 A/cm^(2)、极板间距为1 cm、初始pH为7,电絮凝反应3 h后,可将渗滤液COD浓度从23525 mg/L降低至10619 mg/L,其去除率可达54.86%。投加电解质过硫酸钾与电絮凝协同作用对渗滤液进行预处理,可有效强化电絮凝反应对渗滤液COD的去除效果,反应初期COD去除率相对提高了6.68%;但当电解时间大于3 h后,过硫酸钾的强化作用逐渐减弱。