Roll flaw detection is essential for almost all high-standard rolling mill. Common methods for roll flaw detection include magnetic particle flaw detection, penetrant color flaw detection, eddy current flaw detection, and ultrasonic flaw detection.
- Magnetic Particle Flaw Detection: This technology is primarily used to identify surface cracks on the roll body and fatigue cracks in the roll neck area. When a magnetizing current passes through the ferromagnetic workpiece surface, it creates an electromagnetic field. Any defects present will disrupt the magnetic lines of force, forming a leakage field that attracts magnetic powder. This buildup of magnetic powder creates a visible magnetic trace, which magnifies the defects and makes them observable. Magnetic particle flaw detection can identify surface and subsurface linear discontinuities in ferromagnetic materials and is relatively simple to operate.
- Penetrant Color Flaw Detection: This method is widely used for inspecting surface cracks on rolls. It does not require power and can reveal the shape and size of defects in both ferrous and non-ferrous metals. However, the test piece surface must be clean, oil-free, and dry for accurate results.
- Eddy Current Flaw Detection: This technique detects defect locations and the severity of cracks on the roll surface and is suitable for electrically conductive materials. Key features include non-contact coil operation, rapid detection speed, and high sensitivity to surface or near-surface defects, providing good linear indication within a certain range. Eddy current flaw detection can also measure the thickness of metal coatings or non-metallic layers and generates electrical signals for data analysis. However, it can only be used on conductive materials, has a shallow penetration depth, and a certain blind zone (typically at the beginning and end of the detection region).
- Ultrasonic Flaw Detection: This method uses the propagation, reflection, and attenuation of ultrasonic waves in the material to identify defects. It offers high sensitivity, fast detection speed, low cost, ease of operation, and is harmless to humans and the environment. Ultrasonic flaw detection can penetrate deep into many materials, detect subsurface flaws, and identify internal small cracks. However, it requires a good coupling agent and an experienced operator.
