The composition of ultrasonic equipment - ultrasonic transducer

Ultrasonic flaw detection equipment generally consists of an ultrasonic flaw detector, a transducer, and a test block.

The ultrasonic transducer, also known as a piezoelectric ultrasonic transducer, is an energy converter that converts electrical and acoustic energy.

1.Types of Transducers

Due to differences in workpiece shape and material, inspection purposes, and inspection conditions, various types of transducers will be used.

The following types of transducers are used in weld inspection:

1)Straight Transducer

A transducer whose acoustic beam is incident perpendicular to the surface of the workpiece being inspected is called a straight transducer. It can transmit and receive longitudinal waves.

Composition: piezoelectric element, absorbing block, protective film, and housing, etc.

a. Piezoelectric Element

Made from piezoelectric wafers after polarization and electrode coating.

The purpose of coating electrodes on the piezoelectric wafer is to ensure that the voltage supplied to the wafer is evenly distributed.

b. Absorbing Block

Made of epoxy resin and tungsten powder, cast on the back of the wafer.

Function: Absorbs noise and allows the wafer to quickly dissipate acoustic energy and stop vibrating after the excitation pulse ends, so that the reflected echo can be received.

c. Protective Film

Protects the piezoelectric element from direct contact with the workpiece to prevent wear and damage.

Classification: Soft film, hard film

d. Housing

Made of metal or plastic

Function: Receiving electrode of the piezoelectric element

2)Angle Beam Transducer

A transducer that uses a sound-transmitting wedge to make the sound beam enter the workpiece at an angle to the surface of the workpiece is called an angle beam transducer.

It can transmit and receive shear waves.

Composition: Transducer core, angled wedge, and housing, etc.

The angled wedge is made of organic glass and forms a fixed inclined heterogeneous interface with the workpiece, so that the longitudinal wave emitted by the piezoelectric element in the transducer core is converted into a refracted wave and propagates in the workpiece.

K=tg γ=1.0、1.5、2.0、2.5、3.0

3)Immersion Focusing Transducer

It is a transducer composed of an ultrasonic transducer and an acoustic lens.

4)Dual Crystal Transducer

Dual crystal transducers, also known as split TR transducers, are mainly used for detecting near-surface defects and measuring the thickness of thin workpieces.

II. Main Parameters of the Transducer

Angle beam transducers are commonly used in ultrasonic testing of welds. The main performance characteristics of angle beam transducers are as follows:

1)Refraction angle γ (or transducer K value)

The size of γ or K value determines the direction of the sound beam entering the work and the propagation path of the sound wave, which provides useful data for defect location calculation.

2) Leading edge length

The distance from the sound beam incidence point to the front surface of the transducer is the leading edge length, also known as the approach length. It reflects the degree to which the transducer can approach a weld with excess height.

3) Acoustic axis deviation angle

The angle between the main acoustic axis of the transducer and the normal to the center of the wafer is called the acoustic axis deviation angle. It reflects the degree of coincidence between the main acoustic beam centerline and the normal to the center of the wafer.

The acoustic axis deviation angle affects the accuracy of defect location and indication length measurement, and the misjudgment of defect directionality, thus affecting the inspection results.

The transducer model consists of five parts, represented by a set of numbers and letters, in the following order:

1)Basic frequency, unit: MHz.

2)Wafer material. Commonly used wafer materials (piezoelectric materials) and their codes are shown in Table 4-3.

3)Wafer Size

For circular wafers, it is the wafer diameter; for square wafers, it is the wafer length × width; for split transducers, it is the size before splitting.

4)Transducer Type

Represented by the abbreviation in Pinyin. Straight transducers may not be marked.

5) Transducer characteristics. For angle beam transducers, it is the K value or γ, unit: °.

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