Action analysis of various probes in SuCI portable magnetic particle flaw detection machine

Nowadays, the mainstream probe of the portable magnetic particle flaw detection machine is mainly divided into four categories: straight probe, inclined probe, small tube probe and surface wave probe, the effect of using different types of probes on the workpiece flaw detection will be different, the following is by Su magnetic particle flaw detection machine manufacturers technicians to explain to you:

1 straight probe

If the flaw detection machine is a straight probe installed, it is generally used for longitudinal wave detection, because this probe uses a single crystal wafer for vertical detection.

The main components of the straight probe are piezoelectric crystal, sound absorption material, shell, protective film, socket, etc. The head contact surface is a replaceable soft film for detecting the workpiece with rough surface.

2 inclined probe

Compared with the vertical detection of the straight probe, the oblique probe is mainly used for oblique detection, and the main work is used for shear wave detection.

The main components of the straight probe are piezoelectric wafer, sound absorption material, inclined block, socket, shell, etc. The sound beam of the inclined probe is inclined to the probe surface, so it can be used to detect the part that the straight sound beam cannot reach, or the area where the direction of the defect is at an Angle between the detection surface.

3 small tube probe

Single crystal micro shear wave inclined probe used for inspection of welded joints of small diameter thin-walled pipes.

Testing standards refer to the power industry standard DL/T8202002 "Pipe welding joint ultrasonic Inspection Technical Regulations", suitable for testing pipe diameter ≥32mm, less than or equal to 159mm, wall thickness ≥4mm, less than 14mm small diameter thin-walled pipe; It can also be applied to the detection of similar pipelines in other industries.

The probe size is small, the front distance is less than 5mm, the initial pulse width is less than 1.5mm(equivalent to the steel depth), and the resolution is greater than or equal to 20dB.

According to the outer diameter of the pipe being tested, the detection surface is machined into a radian corresponding to the pipe diameter.

4 surface wave probe

The magnetic particle flaw detection machine equipped with surface wave probe is different from other flaw detection machines in the main application field, which is mainly used for transmitting and receiving surface waves.

Surface wave is a wave propagating along the surface of the workpiece, the amplitude decreases rapidly with the depth under the surface, the propagation speed is 0.9 times that of shear wave, the particle vibration trajectory is elliptical.

Common cracks in workpieces:

① Forging crack

Metal flow occurs in forging process, because of the different forces of each part, the deformation degree is different, forging cracks have a great relationship with the internal defects of the forging. If there are bubbles under the skin of forging blank, forging cracks are easy to form, which often appear on the surface of forging; If there are shrinkage holes or inclusions on the forging blank, it is also easy to cause forging cracks, the cracks formed by shrinkage holes are generally longer, appear in the heart of the forging, belong to the internal crack, and the cracks formed by the inclusion or interlayer are slender and distributed irregularly.

② Grinding crack

When the contact surface of the grinding wheel and the workpiece is large, the grinding wheel is too dull, the feed amount is too large, the surface heat dissipation performance of the workpiece is poor, and the cycle cooling is not good, the grinding stress on the surface of the workpiece will change greatly, and the compressive stress state of the workpiece carburizing layer will be seriously damaged, and the surface of the workpiece will be transformed from the compressive stress state to the tensile stress state, and when the stress exceeds the strength limit of the workpiece itself, the surface of the part will be made Cracks occur. It is characterized by narrow cracks, dense, short and shallow, and quenching cracks are wider and thicker and deeper.

③ welding crack

Welding is local heating, from the cold state to the heating melting, the temperature of the molten pool can reach more than 2000 ° C, and it is around the cold metal, the temperature difference between the two is very large, so that the workpiece produces large internal stress and deformation, and the severe crack, that is, welding crack. The way to reduce welding cracks is to preheat before welding.

④ Hairline

Hair marks are metallurgical defects (pores, non-metallic inclusions) that are slowly cooled after deformation welding or annealed after welding. In the process of development formed. The occurrence of hair lines is related to the shape of the parts, and the straight and cylindrical parts are the most easy to produce hair lines. The shape of the hair line is generally straight, distributed along the metal flow line. In most cases, hair lines can be seen with the naked eye. Hair lines caused by sulfides are bright gray, while those caused by oxides are colorless.

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