钢结构表面缺陷的检测磁粉探伤的基本原理发布时间：2015-12-17 10:23:18 浏览次数:523
The magnetic field of the workpiece (only ferromagnetic materials) magnetization, workpiece is magnetized if there is no defect, then its magnetic characteristics of each part of the basic agreement, and the existence of cracks, pores or non metal slag and other defects, because they will cause the workpiece gap in air gap magnetic or not the reluctance, defect position increases greatly, normal transmission lines within the workpiece by magnetic barrier, according to the principle of continuity, then the magnetic field lines are forced to change the path and escape from the workpiece, and the formation of leakage magnetic field on the surface of the workpiece.
The intensity of the magnetic field is mainly determined by the intensity of the magnetic field and the influence of the defect on the vertical cross section of the magnetic field. The magnetic particle can be used to display and measure the leakage magnetic field, so as to analyze the existence of the defect and its position and size.
The powder of the ferromagnetic material is not scattered on the workpiece in the magnetic field of the magnetic leakage magnetic field is adsorbed, which forms the magnetic mark of the shape of the defect. This method is one of the earliest and most widely used nondestructive testing methods.
General use of industrial pure iron powder or iron oxide production, usually with magnetite (Fe3O4) made of fine particles as magnetic powder. Magnetic powder can be divided into two kinds of fluorescent magnetic particle and non fluorescent magnetic particle, the fluorescent magnetic particle is a layer of fluorescent material coated on the surface of the particles, so that it can emit fluorescence under the irradiation of ultraviolet light, the main role is to improve the contrast, easy to observe. Magnetic particle inspection and two kinds of dry and wet method:
1 dry process
- the magnetic particle is directly cast on the surface of the workpiece. In order to facilitate the magnetic particle to roll to the magnetic field, the magnetic particle particle used in dry method is usually used to detect the magnetic particle, so the detection sensitivity is lower. But when the workpiece is not allowed to use wet with water or oil contact, such as the higher temperature of the specimen, the only use of wet and dry method.
Wet - magnetic suspension is formed in the surface of the workpiece surface, which can be easily moved by the weak magnetic field, and the magnetic particle is more easily to be adsorbed on the magnetic field due to the fine magnetic particles.