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磁粉探伤是利用铁磁性材料磁化后,缺陷处有磁通泄漏到空气中,形成漏磁场。漏磁场能够吸附磁粉积聚到缺陷上,显示出缺陷的形状。漏磁场的大小及分布状态与钢材磁化状态、缺陷埋藏深度、缺陷宽度、缺陷自身高度、漏磁场的测定位置、漏磁场与缺陷倾角的关系以及试件表面覆盖层的影响等因素有关。磁粉探伤主要用于表面和近表面缺陷的检测,其优点是操作简单、灵敏度高.检测速度快、直观性强;缺点是不能用来检测非铁磁性材料及工件内部缺陷。磁粉探伤常用的磁化方法有:直接通电法、触头法、中心导体法、线圈法、磁轭法、感应电流法、复合磁化法和旋转磁场法。磁化电流可采用交流、半波整流、全波整流和直流。由于交流电有趋肤效应,它产生的磁场集中于零件表面,因此对表面缺陷的检测具有较高的灵敏度。而半波整流、全波整流和直流电产生的磁场有利于检测近表面缺陷。1 压力容器制造中的磁粉探伤压力容器制造中的磁粉探伤可用于锻件、棒材、管材、螺栓(双头螺栓、螺母)、坡口、焊缝、焊接夹具除去后的疤痕、补焊部位以及堆焊层的检测。在此只介绍焊
Magnetic particle inspection is the use of ferromagnetic material magnetization, the defect at the magnetic flux leakage into the air, the formation of leakage magnetic field. The leakage magnetic field can absorb the magnetic powder to accumulate on the defect, showing the shape of the defect. The size and distribution of the leakage magnetic field are related to the magnetization state of the steel, the depth of the buried defect, the width of the defect, the height of the defect itself, the location of the leakage magnetic field, the relationship between the leakage magnetic field and the defect dip, and the influence of the surface coating on the specimen. Magnetic particle inspection is mainly used for the detection of surface and near surface defects, which has the advantages of simple operation, high sensitivity, fast detection speed and strong visualization. The disadvantage is that it can not be used to detect internal defects of non-ferromagnetic materials and workpieces. Magnetizing methods commonly used in magnetic particle inspection include: direct current method, contact method, center conductor method, coil method, yoke method, induced current method, composite magnetization and rotating magnetic field method. Magnetizing current can be used AC, half-wave rectifier, full-wave rectifier and DC. Due to the skin effect of alternating current, the magnetic field generated by it is concentrated on the surface of the part, so it has high sensitivity to the detection of surface defects. The half-wave rectification, full-wave rectification and DC magnetic field generated is conducive to the detection of near-surface defects. 1 Magnetic particle inspection in the manufacture of pressure vessels Magnetic particle inspection in the manufacture of pressure vessels can be used for forgings, rods, tubes, bolts (studs, nuts), bevels, welds, scar removal after welding jig removal, Surfacing layer testing. Here only describes the welding