High-speed steel rolls have good wear resistance and resistance to thermal cracking, but they are sensitive to cracks caused by improper cooling, use, or mechanical damage. Surface cracks are the main cause of high-speed steel roll failure. Typically, high-speed steel rolls are prone to mechanical cracks, reticulated "heat" cracks, stress cracks, and fatigue cracks. Manufacturers generally adopt good non-destructive testing methods and procedures to regularly inspect the rolls, and to repair and replace high-speed steel rolls with problems in advance to avoid rolling accidents. So, let's learn about the common testing methods for high-speed steel rolls.

　　Common high-speed steel roll testing methods include:

　　1. Eddy Current Automatic Flaw Detection

　　Advantages: It is automatic flaw detection, with an automatic recording system, which can accurately determine the axial position of defects on the roll. The detection sensitivity is high, and it can find some small surface or near-surface defects, which is unmatched by other flaw detection methods such as ultrasonic waves.

　　Disadvantages: It cannot determine the type, shape, and depth of the crack, nor can it determine the true equivalent of the defect. Sometimes it will be affected by various factors, such as: the distance between the probe coil and the tested roller, the material, size, shape, conductivity, permeability, and defect type of the roller. Regular calibration of eddy current sensitivity and auxiliary other flaw detection methods are important means to ensure the effectiveness of the detection.

　　2. Rolling Eddy Current Detection

　　In recent years, automatic ultrasonic flaw detection systems for rolled materials have become popular and are used in conjunction with eddy current flaw detection.

　　Advantages: It has good penetration and directivity, and it is easy to find defects inside and outside the roll. Defects can be located, quantified, and defined. For defects such as cracks and internal delamination, the sound beam is perpendicular to the defect to obtain a high reflection echo. Various defects can be easily found and the nature of the defects can be judged by using waveform conversion and frequency conversion.

　　Disadvantages: Requires a good couplant; requires trained and experienced operators; operators have a broad understanding of defects

　　Ultrasonic flaw detection methods can be manual or automatic. Although manual ultrasonic testing methods can be used to detect surface and subsurface defects as well as internal defects and voids in the roll body, the advent of automated roll body testing systems means that manual ultrasonic testing is now mainly used to detect internal defects, and also used to detect the crack depth at the fillet of the roll neck. Most roll shops use a pulse-echo ultrasonic flaw detector with a fluorescent screen display for manual flaw detection.

　　Ultrasonic testing is commonly used to determine the integrity of the roll. Most roll manufacturers include this testing as part of the production process, but based on experience, it is very necessary for users to perform ultrasonic flaw detection on internal defects in the rolls.

　　3. Magnetic Particle Inspection

　　Magnetic particle inspection technology is mainly used to detect surface cracks on the roll body and fatigue cracks in the roll neck area, excessive cyclic loading, or subsequent normal corrosion.

　　Advantages: Convenient and fast, it can detect open defects and subsurface defects on the metal surface, and can clearly show the shape of the defects. Disadvantages: Defects cannot be quantified. In addition, the cleanliness and smoothness of the roll surface will also affect the results of magnetic particle inspection.

　　4. Liquid Penetrant Inspection

　　Due to its simple use, liquid penetrant inspection is widely used in the detection of surface cracks in rolls.

　　Advantages: No power supply required; can detect complex shapes, indicating the shape and size of defects; can show small and dense defects; can detect ferrous and non-ferrous metals.

　　Disadvantages: Cannot detect subsurface defects; surface must be clean, oil-free, and dry.

　　Precautions when testing defects in high-speed steel rolls:

　　1. Mass detection of the surface quality of high-speed steel rolls is mainly based on automatic eddy current detection of grinding machines, with other detection methods as supplementary.

　　2. In eddy current detection, when the signal is abnormal, the authenticity of the defect and the location of the defect are the main tasks of the grinding machine operator and the flaw detection personnel.

　　3. If the amplitude far exceeds the set sensitivity value, visual inspection is required. In this case, the defect is visible to the naked eye. If there is no visible defect, the area is subjected to secondary flaw detection after demagnetization according to the positions displayed on the X-axis and Y-axis.

　　4. If there is an abnormal signal, magnetic powder or immersion and ultrasonic auxiliary detection are performed in this area to identify the authenticity of the defect, and the defect is quantified by ultrasound.

　　5. Compared with several auxiliary methods, magnetic particle inspection combined with ultrasonic inspection is more practical, reliable, and fast.

　　The above is an introduction to the common detection methods for high-speed steel rolls. For more information, please contact us!