Frequently Asked Questions of Magnetic Particle Detector
1. The principle of magnetic particle inspection
Its basic principle is: when the workpiece is magnetized, if there is a defect on the surface of the workpiece, magnetic flux leakage occurs due to the increase of the magnetic resistance at the defect, and a local magnetic field is formed. The magnetic powder will show the shape and location of the defect here to determine the defect The presence.
2. Basic knowledge of magnetic particle flaw detector
1. According to the different magnetization directions of the workpiece, it can be divided into circumferential magnetization method, longitudinal magnetization method, composite magnetization method and rotating magnetization method.
2. According to the different magnetizing currents, it can be divided into: DC magnetization method, half-wave DC magnetization method, and AC magnetization method.
3. According to the different preparation of magnetic powder used in flaw detection, it can be divided into dry powder method and wet powder method.
3. Defects of magnetic particle inspection
Magnetic particle inspection equipment is simple, easy to operate, quick to inspect, and has high inspection sensitivity. It can be used to find the surface or near surface defects of ferromagnetic materials nickel, cobalt and its alloys, carbon steel and certain alloy steels; it is suitable for The inspection of thin-walled parts or weld surface cracks can also reveal incomplete penetration defects of a certain depth and size; but it is difficult to find pores, ballasts and defects hidden in the depth of the weld.
Four, the type of defect mark
1. Magnetic traces of various technological defects;
2. Hairline magnetic marks caused by material inclusions;
3. Point-like magnetic marks caused by slag inclusions and pores.
Fifth, the cause of magnetic flux leakage
Since the magnetic permeability of ferromagnetic materials is much greater than that of non-ferromagnetic materials, it is analyzed according to the magnetic flux density B=μH after the workpiece is magnetized, and B magnetic wires pass through the unit area of the workpiece, and the unit in the defect area The area cannot allow B magnetic lines of force to pass through, which forces a part of the magnetic lines of force to squeeze into the material below the defect, and other magnetic lines of force have to be forced to escape from the surface of the workpiece to form magnetic flux leakage, and the magnetic powder will be attracted by the magnetic flux leakage caused by this.
six. Factors influencing magnetic flux leakage
1. The permeability of the defect: the smaller the permeability of the defect, the stronger the magnetic leakage.
2. The intensity of magnetizing magnetic field (magnetizing force): the greater the magnetizing force, the stronger the magnetic flux leakage.
3. The shape and size of the workpiece to be inspected, the shape and size of the defect, the depth of burial, etc.: When other conditions are the same, the magnetic leakage generated by the pores buried in the same depth under the surface is smaller than the magnetic leakage generated by the transverse crack.
Seven, why some parts need to be demagnetized
The residual magnetism of some rotating parts will attract iron filings and cause frictional damage to the parts during rotation, such as shaft bearings. The residual magnetism of some parts will cause the indication of nearby instruments to malfunction. So why some parts need to be demagnetized after magnetic particle inspection.
8. What is electromagnetic induction?
The magnetic flux passing through the closed loop changes, and the phenomenon of generating electromotive force in the loop is called electromagnetic induction; the electromotive force generated in this way is called induced electromotive force, if the conductor is a closed loop, there will be current flowing, and the current is called induced current; transformer , Generators and various inductance coils all work according to the principle of electromagnetic induction.
Nine, the safe operation requirements of the magnetic particle probe?
1. When the workpiece is directly electromagnetized, pay attention to the poor contact between the chucks, or use too much magnetizing current to cause arc flashing, and protective glasses should be worn, and it should not be used in places where there is a possibility of flammable gas;
2. When the wet magnetic suspension is used continuously, protective cream can be applied to the skin;
3. If used in water magnetic suspension, the equipment must be well grounded to prevent electric shock; 4. When using cocoon fire magnetic powder, the ultraviolet light used must pass through a filter to protect eyes and skin.