High-speed steel rolls have good wear resistance and thermal crack resistance, but they are sensitive to cracks caused by cooling, improper use or mechanical damage. Surface crack is the main reason of high speed steel roll failure. Generally, the surface of high-speed steel rolls is prone to mechanical cracks, network "hot" cracks, stress cracks and fatigue cracks. All manufacturers generally adopt good non-destructive testing methods and procedures to regularly inspect the rolls, and repair and replace the high-speed steel rolls with problems in advance to avoid rolling accidents. So, let's take a look at the common detection methods of high speed steel rolls.

Commonly used high speed steel roll detection methods are:

1. eddy current automatic flaw detection

Advantages: It belongs to automatic flaw detection and has an automatic recording system, which can accurately determine the axial position of defects on the roll. The detection sensitivity is high, and some small surface or near surface defects can be found, which is unmatched by other detection methods such as ultrasonic.

Disadvantages: The type, shape and depth of the crack cannot be determined, and the true equivalent of the defect cannot be determined. Sometimes it is affected by many factors, such as the distance between the probe coil and the measured reel, the material, size, shape, conductivity, magnetic permeability, defect type, etc. of the reel. Regular calibration of eddy current sensitivity and the assistance of other flaw detection methods are important means to ensure the effectiveness of detection.

2. rolling eddy current testing

In recent years, coil ultrasonic automatic flaw detection system has been popularized and used in combination with eddy current flaw detection.

Advantages: It has good penetration and directionality, and it is easy to find internal and external defects of the roller. Defects can be located, quantified and defined. For defects such as cracks and internal delamination, the sound beam perpendicular to the defect obtains high reflection echo. The use of waveform conversion and frequency conversion is easy to find a variety of defects and determine the nature of the defect.

Disadvantages: Need a good couplant; Need a well-trained and experienced operator; Operator has extensive knowledge of defects

The ultrasonic inspection method can be manual or automatic. Although manual ultrasonic inspection methods can be used to detect surface and sub-surface defects of the roll body, as well as internal defects and voids, the emergence of automated roll body inspection systems means that manual ultrasonic inspection is now mainly used to detect internal defects and also to detect the fillet of the roll neck. Crack depth at the place. Most roll shops use a pulse echo ultrasonic flaw detector with a fluorescent screen display for manual flaw detection.

Ultrasound is typically used to determine the integrity of the roll. Most roll manufacturers carry out this inspection as part of the production process, but according to experience, it is very necessary for users to carry out ultrasonic inspection of internal defects of rolls.

3. Magnetic Particle Flaw Detection

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

Advantages: convenient and fast, can detect metal surface opening defects and subcutaneous defects, and can clearly display the shape of 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. penetrant stain inspection

Due to the simple use, penetration dyeing flaw detection is widely used in the detection of surface cracks in rolls.

Advantages: no power supply is required; complex shapes can be detected, indicating the shape and size of defects; few and dense defects can be displayed; ferrous and non-ferrous metals can be detected.

Disadvantages: unable to detect defects under the surface; the surface is clean, oil-free and dry.

Precautions for testing defects of high speed steel roll:

1, high-speed steel roll surface quality batch testing to grinder automatic eddy current testing, supplemented by other detection means.

2. In eddy current testing, when the signal is abnormal, the authenticity of the defect and the location of the defect are the main tasks for the grinder operator and the flaw detector to judge.

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 shall be re-inspected after degaussing according to the parts shown on the X-axis and Y-axis.

4. If there is abnormal signal, magnetic particle or infiltration and ultrasonic auxiliary detection shall be carried out in this area to distinguish the authenticity of defects, and the defects shall be 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 the common detection method of high speed steel roll. Want to know more, welcome to contact us!