Probe of ultrasonic flaw detector
The transmission and reception of ultrasonic waves are realized by the probe. The following describes the working principle, main performance and structure of the ultrasonic flaw detector probe.
1. Piezoelectric effect
Under the action of alternating tension and compression, some crystal materials produce an alternating electric field, which is called the positive piezoelectric effect. Conversely, when the crystal material is under the action of an alternating electric field, the effect of stretching and deformation is called the inverse piezoelectric effect. The forward and inverse piezoelectric effects are collectively referred to as the piezoelectric effect.
The piezoelectric wafer in the ultrasonic probe has a piezoelectric effect. When a high-frequency electric pulse excites the piezoelectric wafer, an inverse piezoelectric effect occurs, which converts electrical energy into sound energy (mechanical energy), and the probe emits ultrasonic waves. When the probe receives ultrasonic waves, a positive piezoelectric effect occurs, which converts sound energy into electrical energy. It is not difficult to see that the ultrasonic probe realizes the mutual conversion of electric energy and sound energy when it is working, so the ultrasonic flaw detector probe is often called a transducer.
2. The type and structure of the probe of the ultrasonic flaw detector
Straight probes are used to transmit and receive longitudinal waves, and are mainly used to detect defects parallel to the detection surface, such as flaw detection of plates and forgings.
Oblique probes can be divided into longitudinal wave oblique probes, shear wave oblique probes and surface wave oblique probes, and transverse wave oblique probes are commonly used. The transverse wave oblique probe is mainly used to detect defects perpendicular to the detection surface or at a certain angle, such as welds, steam turbine impellers, etc.
When the incident angle of the oblique probe is greater than or equal to the second critical angle, surface waves are generated in the workpiece, and the surface wave probe is used to detect surface or near-surface defects.
The dual crystal probe has two piezoelectric wafers, one is used to transmit ultrasonic waves, and the other is used to receive ultrasonic waves. According to the angle of incidence, it is divided into dual crystal longitudinal wave probe and dual crystal transverse wave probe.
The dual element probe has the following advantages:
(1) High sensitivity
(2) Less clutter, small blind area
(3) The length of the near field in the workpiece is small
(4) Adjustable detection range
The dual element probe is mainly used to detect near-surface defects.
There are many types of focusing probes.
3. Ultrasonic flaw detector probe model
The composition items and arrangement order of the probe model are as follows:
Fundamental frequency-wafer material-wafer size-probe type-characteristics