漏磁法检测薄带钢内部缺陷的研究进展

漏磁法检测带钢内部缺陷是利用铁磁性材料在磁场中的导磁现象,若材料中有缺陷存在,就会在材料表面缺陷处形成漏磁场,通过漏磁场大小即可检测出缺陷大小。文章中给出了基于漏磁技术的薄带钢内部缺陷检测试验结果。在试验中,采用厚度为0.13mm的薄带钢为检测对象,并在其上打出直径为0.13mm的通孔和盲孔作为人工缺陷,将钢板磁化至深度饱和,能够较好地得到该缺陷的漏磁信号。目前,日本太平工业和Nireco两家公司开发出的漏磁检测设备已经进入工业化大生产阶段,二者的缺陷检测精度分别为0.0014mm3和0.000373mm3。分析认为可以根据现场检测条件和检测精度需求选择合适的磁敏传感器,并采用直流磁化方法,将带钢磁化至深度饱和来保证微小缺陷信号的检出。采集到漏磁信号后,用小波分析法进行信号预处理,然后以统计法或者神经元网络法来实现缺陷尺寸量化,往往能够得到较为精准的检测结果。对漏磁技术应用中的难点和技术发展趋势进行了展望。     

油气输送管道腐蚀缺陷检测与识别研究

应用漏磁检测仪进行埋地油气管道腐蚀检测和识别,叙述了检测仪的硬件采集和信号处理过程.在直径273 mm的管道表面上加工人工缺陷,采集缺陷漏磁场信号,进行处理和转化为漏磁场云图,从信号和云图两者来分析漏磁场,提出了缺陷漏磁场的干扰消除方法、影响因素补偿技术和缺陷漏磁场图像的截取,并分别获得较好的效果,分析了缺陷定性和定量识别的方法,研究了缺陷外形参数量化的方法,得出了缺陷外形量化的数学模型,试验验证缺陷识别的效果,证明整个过程和方法有效可行,大大提高了管道缺陷检测和量化的精度.     

基于特征量和神经网络的钢管缺陷预测模型

分析了钢管缺陷几何大小与缺陷漏磁信号(MFL)特征量之间关系，建立了一组全方位的钢管缺陷信号特征量，并将人工神经网络理论和算法应用于钢管缺陷预测。通过实验取得样本，在对网络进行训练的基础上，建立了基于钢管缺陷漏磁信号特征量和神经网络的缺陷预测模型，继而根据漏磁信号对缺陷进行定量预测。给出了实验结果，结果表明采用这种方法能够较好地实现管道缺陷的定量识别。     

基于小波神经网络的管道腐蚀缺陷定量识别研究

漏磁检测是目前广泛采用的油气管道检测方法,通过漏磁检测仪获得腐蚀缺陷漏磁场切向分量的漏磁场信号,提取与腐蚀缺陷外形长、宽、深有关的漏磁场信号波形特征量,结合小波分析和神经网络的优势形成小波神经网络,分析设计了小波神经网络的结卡句,给出了网络训练算法,利用网络的非线性逼近性能,对腐蚀缺陷外形进行定量评价,给出预测评价曲线,试验验证方法有效可行。     

漏磁检测与超声波检测技术应用比较

叙述了采用漏磁法和超声波法进行钢管检测的基本原理和国内外的应用情况。这两种方法钢管检测的特定环境条件下具有不同的特性、优缺点及适用范围。在对钢管检测技术研究应用和设备的开发过程中,应充分考虑到不同方法的适用性。     

用磁介质环电流模型对裂纹状缺陷磁粉和漏磁探伤能力的研究

采用磁介质环电流模型计算各种槽形缺陷产生的漏磁场,包括标准规定的漏磁探伤对比试件上的人工伤、磁粉探伤标准试块上的人工伤、用数学方法模拟的疲劳裂纹和被检工件表面粗糙度等产生的漏磁场.将上述各种缺陷产生的漏磁场加以比较可以看出,由于疲劳裂纹开裂的缝隙十分狭窄,它所产生的漏磁场远小于人工标准伤所产生的漏磁场,也小于表面粗糙度所产生的漏磁场.因此结论认为用磁粉法和漏磁法探测疲劳裂纹时,需要特别谨慎.换言之,磁粉和漏磁两种方法不适合探测开裂缝隙很窄的疲劳裂纹.     

钢管漏磁探伤的新方法

介绍了一种新开发的“探头固定”／钢管螺旋前进“的钢管漏磁探伤技术,分析了它与传统漏磁探伤方式的差异和优劣,探伤实验的结果表明,这种钢管漏磁探伤方法是可行并适合国情的。     

微分处理方法在漏磁检测信号分析中的应用研究

提出用微分方法处理含有趋势项和幅值相等的内外伤漏磁检测信号,对微分算法及其选取进行了深入探讨。试验结果表明,经过微分处理后,内外伤缺陷区别明显,内外伤信号的幅值与直接提取原始信号内外伤缺陷的幅值相比差别明显,分辨率大大提高。     

磁性液体密封结构中漏磁的研究

为了研究磁性液体密封结构几何参数的变化对漏磁场的影响规律,选取不同的密封间隙、极齿宽度、齿槽宽度、齿槽深度及密封级数建立物理模型,用有限元方法计算各模型的漏磁场.结果表明在密封结构的轴向和径向距离上存在某一临界值,在临界值的两侧,漏磁场磁感应强度随密封结构几种几何参数的变化趋势不同:在轴向距离大于临界值时,轴向漏磁场磁感应强度随间隙的增大而增大,随级数的增加而减小,随齿宽的增大而减小,随槽宽和槽深的增大而增大;在径向距离小于临界值时,径向漏磁场磁感应强度随间隙的增大而减小,随级数的增加而增大,随齿宽的增大而增大,随槽宽的增大而增大,随槽深的增大而减小;径向距离大于临界值时的情况与小于临界值时的情况刚好相反.     

连铸机漏钢预报系统优化改造

连铸机漏钢预报系统由检测和控制两部分组成,检测部分负责采集现场结晶器内的温度变化,通过控制部分在上位机显示发出漏钢预报信号,并通过PLC自动降低拉速。为提高漏钢预报准确率,对检测系统及应用软件进行二次开发和优化,增设了热电偶连接缓冲器、大容量中继补偿导线,优化了检测部位的密封性,重点对信号进行防水、防振动、防高温处理,并增加了离线仿真功能,使得漏钢预报系统长期稳定运行,综合漏钢次数从10次/a降到低于4次/a。     

MAGNETIC FLOCCULATION OF MINERAL FINES IN AN EXTERNAL MAGNETIC FIELD

This article highlights the magnetic flocculation of mineral fines in aqueous suspensions, including ferromagnetic and weakly magnetic minerals. The magnetic attraction between magnetic mineral particles in an external magnetic field, the stability of magnetic mineral fines in aqueous suspensions, kinetics of magnetic flocculation, and the main parameters of magnetic flocculation are discussed and summarized. Some of the experimental results are presented and the applications of magnetic flocculation to fine mineral beneficiation are briefly described.     

2D Measurements of Magnetic Field near an Oscillating Interface between Two Fluids Carrying an Electrical Current

An experimental technique is presented to measure two‐dimensional magnetic fields outside a cylindrical cell containing two electrically conducting fluids as the primary step of magnetic field tomography (MFT). The magnetic field is induced by a direct current through the fluids. Under a periodic, vertical vibration driven by a pneumatic shaker, Faraday instabilities are generated, which lead to a series of non‐axisymmetrical wave modes, and the non‐axisymmetrical interface shape introduces a perturbation to the magnetic field which can be measured by eight two‐dimensional fluxgate sensors fixed concentrically and uniformly around the cell. The original signals from the sensors are collected by a Keithley data acquisition board and processed by fast Fourier transform (FFT). The amplitude and frequency of the magnetic flux density are extracted successfully. Based on the measured magnetic field distribution, the maximum of the interface displacement is reconstructed by an evolutionary strategy, which is in good agreement with the optical measurement. This MFT system can be applied to study the interface movements in aluminium reduction cells, in iron/steel making, in glass melts, and in other electromagnetic processing of materials.     

Numerical Simulation of Level Magnetic Field

TheLMF (LevelMagneticField)technologybasedonstaticmagneticfieldcanbeusedtoimprovecontinuouscasting ,suchasforreducingimpactonnarrowsidesofshell ,eliminatinglargenonmetallicinclusions ,preventingmoldfluxentrappingandim provingslabcleanliness ,etc[1,2 ] .Theeffectofstaticmagneticfieldonsolutebehaviorandcrystallizationduringsolidificationwasinvestigated[3 ] .Theknowl edgeanddesignofmagneticfieldisveryimportantbaseofLMFtechnology .However ,themagneticfieldwasgenerallytakenasaone dimensionalfie…     

Oscillation Characteristics of Molten Metal Free Surface Under Compound Magnetic Field

  The free surface waves of a molten low melting point Sn 32%Pb 52%Bi alloy under the imposition of an AC and a static magnetic field were visualized and recorded by use of a laser displacement sensor and a high speed video camera. The Fourier analysis method was used to analyze the oscillation characteristics. The results show that at the center of the free surface, the azimuthal and radial oscillation mode can be found simultaneously owing to AC magnetic field. With increasing coil current intensity, the amplitude and the main frequencies of the oscillations increase, and the azimuthal fluctuation at the center of the free surface is also enhanced. The fluctuation characteristics are closely related to the turbulent flow induced by the alternating electromagnetic force. A series of regular traveling waves can be observed on free surface, and the main frequencies of oscillations at three phase points decrease owing to superposing AC and static magnetic field. The static magnetic field can remarkably control the unstable swinging behavior of free surface. With increasing static magnetic flux density, the amplitude of oscillations at the center of free surface decreases firstly, and then increases, but the fluctuation amplitude at the triple phase point always reduces and keeps within 1 mm, and the azimuthal waves at the center of free surface are weakened. Especially at 144 T, the radial waves are dominant. The static magnetic flux density should be controlled in an appropriate range to obtain more stable free surface. With compound magnetic field, even if the static magnetic flux density is above 10 T, the free surface still vibrates with lower amplitude and dominant frequency.     

1Cr25Ti管件开关漏气原因分析

本文通过对1Cr25Ti管件开关焊接部位的低倍观察,以及对其硬度和金相组织的检验,分析了管件开关的漏气原因.从而得知该管件开关漏气是由于焊接处的热应力裂纹引起的,而热应力裂纹的形成与焊接缺陷、旋锤加工内应力和老化试验所产生的脆性等多种因素有关.     

横向拉应力对晶粒取向Si－Fe的磁畴结构及磁声发射强度的影响

观察了晶粒取向３％Ｓｉ－Ｆｅ在横向磁化场及横向拉应力作用下，磁畴结构和磁声发射强度的变化。在横向拉应力下，横向条状畴形成并增长。应力增大，横向条状畴碎化形成点状畴结构。磁畴与磁声发射强度变化相对应，揭示了磁场发射强度受横向拉应力影响的实质。