Views: 7 Author: Site Editor Publish Time: 2018-04-04 Origin: Site
The common nondestructive testing methods include: ray detection, magnetic powder (or magnetic flux leakage) detection, penetration testing, ultrasonic testing, eddy current testing.
1. Ray detection (RT)
One of the earliest methods of nondestructive testing has been widely used to test the internal defects of metal and non-metallic materials and products, for at least 50 years. It has an unparalleled unique advantage, that is, the correctness, reliability and intuition of inspection defects. The obtained radiographic film can be used for defect analysis and archiving as quality certificate. But this method also has the disadvantages of complex equipment and high cost, and the protection of radiation should be paid attention to.
2 . Magnetic Particle Detection (MT) or Magnetic Flux Leakage (EMI)
The detection principle is based on that a ferromagnetic material is magnetized in a magnetic field, a leakage magnetic field is generated at the discontinuity (defect) of the material or product, and the magnetic powder is adsorbed (or detected by a detection element) and is displayed (or displayed on the instrument). ). Therefore, this method can only be used for surface or near surface defect inspection of ferromagnetic materials or products.
3 Penetration Testing (PT)
Including fluorescence, coloring two. Because of its simple equipment and convenient operation, it is an effective method to make up for the defect of the surface of the magnetic powder. It is mainly used for surface defect inspection of non-magnetic materials.
The principle of the fluorescence test is to immerse the article to be inspected into the fluorescent liquid. Due to the capillary phenomenon, the fluorescent liquid is absorbed in the defect, and the surface liquid is removed. Due to the photo-induced effect, the fluorescent liquid emits visible light under the irradiation of ultraviolet rays to show defects. The principle of the staining test is similar to that of the fluorescence test. No special equipment is required. Only the toner used to suck the stain liquid absorbed in the defect is sucked out of the surface of the part to show defects.
4 Ultrasonic Testing (UT)
This method is the use of ultrasonic vibration to find the internal (or surface) defects of materials or parts. According to different modulation methods of ultrasonic vibration, it can be divided into continuous wave and pulsed wave; according to different vibration and propagation modes, it can be divided into four kinds of longitudinal wave, transverse wave, surface wave and Lamb wave propagation in the workpiece; according to the sound wave emission Different from acceptance conditions, they can be divided into single probe and multi-probe methods.
5 Eddy Current Testing (ET)
The principle of eddy current testing is that an alternating magnetic field generates eddy currents of the same frequency in a metal material, and the defect is detected by using the relationship between the magnitude of such eddy current and the specific resistance of the metal material. When the surface of the metal material has a defect (such as a crack), the specific resistance of the metal material increases due to the presence of a defect, and the associated eddy current decreases accordingly. The eddy current with a slight change is indicated by the instrument after amplification. , you can show the existence and size of defects.