NDT refers to the defect that does not damage the surface or interior of the casting, or called NDT. There are many NDT test methods, and the following four methods are widely used in production: magnetic particle flaw detection, ultrasonic flaw detection, radiographic flaw detection, and liquid penetrant flaw detection.
1. Magnetic particle flaw detection: ferromagnetic materials such as iron and steel will be subject to this if they pass through a large current or are placed in a magnetic field. For defects on the surface, such as cracks and inclusions, the magnetic line of force is not easy to pass through, so it can only bypass the defects, leak on nearby surfaces, and form local magnetic poles.
2. Ultrasonic flaw detection
In a broad sense, ultrasonic flaw detection refers to the method of using ultrasonic vibration to find defects in materials or workpieces. According to the different modulation methods, the ultrasonic vibration may be continuous vibration – generating continuous waves or pulse vibration – generating pulse waves. Its working principle is roughly the same, but the inspection methods are different. Ultrasonic flaw detection can be divided into three methods: penetration method, resonance method and reflection method.
3. Radiographic inspection
The method of X-ray and Y-ray transillumination or fluoroscopy is used to inspect the macro defects of finished products or semi-finished products, which is called radiographic inspection. X/Y rays can penetrate materials that cannot be penetrated by ordinary light; As well as the photochemistry, ionization and fluorescence of some substances in your formation. And all these effects increase with the increase of ray intensity.
4. Liquid penetrant flaw detection
This is a method of checking surface defects. It is to apply penetrant on the cleaned workpiece surface to make it penetrate into the defects at the opening, then remove the excess penetrant on the surface, and apply a layer of developer, which will suck out the residual penetrant in the defects due to the capillary action, so as to show the defects.