Ultrasonic surface wave converter and method for manufacture thereof. RU patent 2520950.

FIELD: physics.

SUBSTANCE: ultrasonic surface wave converter comprises piezoelectric elements which can be connected to an ultrasonic flaw detector, an acoustic insulator, a housing, wherein the piezoelectric elements of the converter, which are polarised on the thickness, are mounted on one face perpendicular to the working surface, lie apart from each other by a distance greater than the spatial duration of a probing pulse (L>τc), are acoustically insulated from each other and are electrically connected together or separately with clock or synchronous connection.

EFFECT: designing a surface wave converter which enables to inspect metallic and non-metallic articles, having high efficiency and accuracy of determining coordinates and location of defects, as well as high resolution, having high inspection sensitivity, enabling adaptation when inspecting articles with a complex profile and limited access, which enables to detect differently oriented defects.

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The group invention relates to the field of non-destructive testing and may be used for ultrasonic testing of metals and nonmetals in mechanical engineering, aerospace industry, shipbuilding and others

Known ultrasonic transducer surface waves containing case, the connection cable, the prism of Plexiglas, with glued on her piezoplate [Alyoshin N.P., White V.E., Vopilkin AH and other Methods of acoustic control of metals". M., engineering, 1989, str]. Surface wave Converter of this type is formed by the transformation of an elastic (longitudinal waves propagating through the prism of Plexiglas on the interface plexiglass/metal. The condition of transformation of a longitudinal wave in surface: β>cu (2 , where? - angle prism, 2 CR - 2nd critical angle.

The disadvantages of such a Converter is the significant dimensions, the inability to adapt to control products with restricted access and complex configuration, inaccuracies and difficulties of definition of coordinates and location of defects, not also control non-metals, which reduces the scope of its use.

Closest to the claimed a group of inventions is a Converter with matching element of metal, comb structure of the working surface of the transducer [Viktorov I.A. "Physical bases of application of ultrasonic Rayleigh and lamb waves in engineering". M, publishing house "Nauka", 1965, p.14]. Plate of quartz X-cut top matching element, is made of metal and parallel to the surface. Step, or the period comb structures of matching item selected is equal λ R /2, where : l R - spatial period of the aggregate normal disturbances on the surface of a solid body.

The disadvantages of such a Converter are:

low intensity surface waves at the expense of losses upon occurrence of counter-extinguishing, mixed surface waves under the surface of dies;

- the presence in a controlled environment, concurrently with the surface wave, intensive longitudinal waves, which is the "parasite"that hinder the detection of defects and determination of their coordinates, especially when control thin-walled products on the background of multiple reflections of a longitudinal wave in the testing item;

- the long duration of the echo signal, worsening the condition of the resolution of the Converter;

- the lack of adaptability of such a Converter for control of parts of a complex profile and restricted access;

- considerable complexity and uncertainty when determining coordinates of surface defects on the product, same as in prismatic converters.

The technical result of a group of inventions is the creation of the transducer surface waves, providing control of products from metals and nonmetals with improved productivity and accuracy of definition of coordinates and location of defects, and high-resolution, high sensitivity control, adaptability in the control of products of complex profile and limited access for identifying differently oriented defects.

This technical result provided by the fact that ultrasonic transducer surface waves, containing a piezoelectric elements, with the possibility of connection with ultrasonic flaw detector, acoustic detention centre, case, new is that the piezo transducer polarized in thickness, is established by a line perpendicular to the working surface, located at a distance from each other, larger spatial probing pulse duration (L>t·c s ), acoustically insulated from each other and are electrically connected together or separately with a clock or simultaneous inclusion. In the method of manufacturing of ultrasonic transducer surface waves news is that the piezoelectric transducer is installed in pairs, working surface is damaged, vzaimoponimanie relative to each other, electrically connected in pairs by a separate scheme, with clock or simultaneous inclusion, acoustically insulated, and radiation of elastic waves in a controlled environment is carried out directly or through matching layer (protector).

Below, with links to graphics, the paper presents the design and description of some possible types of transducers, as described in the claims.

Ultrasonic transducer surface waves (Fig 1-5) contains: the connection cable 1, damper or sound insulator 2 and 3, building 4, piezo 5. The Converter can also contain protector 6. Piezoelectric transducer, polarized thickness, have connectivity via wires 1 flaw detector (the position is not indicated). Piezoelements 5 set during installation on a face perpendicular to the working surface of the transducer A. Piezoelements 5 can be in the form of plates (Fig.1-3), mounted in the housing in parallel to each other (figure 1) or at an angle to each other (figure 2). Piezoelements 5 can be rounded, such as radius, form and are perpendicular to each other (figure 4), or cylindrical form (figure 5) and are located centrally in relation to each other.

The Converter can contain (figure 3) four piezoelastic that form two pairs, each of which plates are parallel to each other, and plates of different pairs are perpendicular to each other. Such arrangement of piezoelastic forms a closed rectangle where the parties are themselves piezoelastic, and the area inside of the plates is a zone of control.

In all cases, the piezoelectric elements are located in the building at a distance relative to each other, larger spatial probing pulse duration - L>t·c's .

Assembly (manufacture) of the inverter is as follows.

The piezoelectric elements 5, polarized in thickness, with poddannymi contact wires, set on the edge of the piezoelectric element, perpendicular to the working surface of the transducer and hard (for example, by means of glue or resin) connect with acoustic insulator 2 and 3. Piezoelements 5 can be installed on insulator parallel to each other at an angle to each other, perpendicular to each other, coaxial each other or in pairs, mutually perpendicular to each other, that is, as shown in figure 1-5.

As speaker of the insulator can be used porous or cold pressing polymers such as polystyrene, opaque for ultrasonic oscillations, it is possible to use epoxy resin with absorbent powder fillers, etc. the thickness of the insulator must be such as to ensure, firstly, the resolution of the two echo pulses (probing and held surface waves), and secondly, the direct absorption of longitudinal waves through the insulator. To fulfill the first condition you need to know the duration t of the probe pulse and the speed of propagation of surface waves in a controlled material c's . Thus, the condition of the permission of the two echo pulses: L>t·c s , where L is the thickness of the speaker of the detention facility. Usually these parameters are always known, or can be directly measured with instrumentation. For the second condition is enough to choose a material with a large attenuation of ultrasonic fluctuations; this condition corresponds to the foam and extruded polystyrene.

Next isolator, with a rigidly fixed piezo 5 and conductors are inserted into the building 4, so that the piezo were at some distance from the sides of the chassis, With the piezoelectric elements with an insulator should directly contact with the surface through a thin layer of glue (for example, epoxy resin). After glue hardens, the case is filled with epoxy powder filling (such as iron or lead minium) and the hardener to a level at which the acoustic insulator with piezo completely covered with tar, but podpalnyi conductors are derived for the level of tar and fixed.

After the completion of the process of curing epoxy resin (to speed up the process, it is done heated resin to a temperature of about 40 C) contact wires podpevat to the connectors. As a result of the operations of the obtained design of ultrasonic transducer that with proper connection to the flaw detector can operate in different modes of control: dual, combined, separately or jointly. This piezoelements 5 Converter contact in the process of working with the surface of the controlled material directly or through a thin layer of matching environment (tread) 6.

Made ultrasonic Converter works as follows.

When connected to the flaw detector for dual mode (figure 1, 2) one of the piezoelectric elements, connected to the generator, makes elastic oscillations in pulse mode, at the resonant frequency, the other, connected to the receiver operates in standby mode. On the flaw detector screen there is only one probe pulse. When installing a drive on moistened with water (oil) surface controlled material (metal/nonmetal), piezo, connected to the generator of pulses, his face radiates into the environment of surface elastic wave which is accepted facet of other receiving piezoelectric element, operating in standby mode. If the installation location of the transducer there is no defect, on the flaw detector screen at some distance from the probing signal appears echo-pulse held surface waves. If under the surface of the transducer to the material has a defect (surface/sub-surface), the echo-pulse of past surface waves will weaken to some extent depending on the flaw size and depth. On the flaw detector screen echo-pulse will decline or disappear entirely, and will be registered as a defect (implementation shadow control methods). The location of the defect is localized in the zone of the contact surface of the transducer, between the two piezoelectric elements, and, in fact, is determined only by the duration of a probe pulse and selected by the distance between the piezoelectric elements, with the minimum possible distance is selected permissions two pulses, one of which is probing. Surface wave in a controlled environment is formed by alternating shear deformation, aimed in different directions from the oscillating frequency and amplitude of the piezoelectric element, polarized thickness oriented parallel to the surface of introduction. The particles of the medium perceive pulse shear strain transmissible directly or through protector from the piezoelectric elements, and form the running surface elastic wave with a velocity equal to c's . This surface wave is formed without the transformation of one type waves in the other, as happens, for example, in the prism of Plexiglas or matching "comb"and, consequently, in this case there are no losses on the conversion. Radiation of elastic surface waves from piezo installed on the testing surface, occurs in both directions, in justified cases, improves the performance of control. In converters, working on separate scheme, the second wave becomes a "parasite" and get rid of through the use of acoustic insulation.

It should also be noted that in the offered design of the Converter at excitation of surface waves is missing "parasitic" longitudinal wave, as in the prototype, which makes it difficult to decrypt waveforms/defectograms, especially when control of thin-walled products. Inherent in the design principle of formation of surface waves allows to control, for example, thin foil with a width of a few microns, and delamination of thin coatings. Note, however, that a surface wave will take place only in solid materials, where possible shear deformation of the environment. It can be metals and their alloys and non-metal materials - composite materials, polymers: polycarbonate, organic glass, polyamide, etc. Thus the Converter, as opposed to analogues, at the same time allows the control and nonmetals.

When connected to the flaw detector only one of the piezoelectric element, in combined mode (second piezo disconnected) transducer emits elastic oscillations in both parties, thereby increasing the performance of control. However, it is difficult for the decryption process and identification of defects. In each case the developers control procedures assess and choose the control mode (connect piezoelastic), which ensures the required reliability and performance control.

When connecting two piezoelectric elements in combined mode control, performance is increased two times, however it is possible undesirable effects of fluctuations in one of the piezoelectric element to another. To avoid this, the piezoelectric elements include different cycles: the first cycle of repetition frequency of works first, in the second - the second, in the third bar - again the first in the fourth - a second Or each sensor is connected to different independent channels. This is possible with a dual-channel flaw detector. The work of such a Converter is similar to that described above, the only indication of defects in each of the independent channels.

For inverter operation with two pairs of piezoelastic (figure 3) connecting pairs, for example, separate scheme with a clock, synchronous or channel, independent inclusion. The clock on the first beat of the repetition rate is the excitation and reception of the first couple of piezoelements, in the second, respectively, the second pair in the third bar - again, the first pair, the fourth - the second, and so on throughout the cycle of control. Simultaneous inclusion is simultaneously both pairs of piezoelements. Channel, independent on the work of each pair of elements in the transducer is on two independent channels of the flaw detector with independent display information on defects in the separate or combined mode. It can also include two adjacent piezoelastic to the generator of pulses for work in the mode of radiation, and two other related - in receive mode. Other variants include piezoelastic not covered in this description. When enabled, the Converter in one of the above modes (for example, separate regime with a clock switching) see only one pulse at the beginning of scanning - probe (if the unloaded on the acoustic environment of the Converter). When installing a drive on the moistened contact with the medium surface of the test object on the scan will be two echo-pulse at a distance determined by the delay. When scanning transducer to the product surface with the set step and trajectory control in the time of exposure in the scope of control under the Converter defect (discontinuities environment) the amplitude of the two echo pulses will decrease to some value that will be fixed the flaw detector indicator. And regardless of the orientation of the material defect he will be detected on the particular pair of piezoelastic Converter, against which it is oriented optimal, from the point of view of detection. So, at this location piezo implemented shadow control method with detection in a controlled product defects that are located in any place and any orientation, regardless of the material (metal/nonmetal).

Converter, shown in figure 4, provided with a piezoelectric elements form part of the cylinder 5 (a special case of the piezoelectric element - can).

The characteristic of the Converter with piezo curved shape that if piezo flat shapes emits into the environment in both the opposite side flat front surface waves, using piezo this form at the expense of their curvature with one hand formed converging front elastic waves (with a focusing effect) and focal area at a distance proportional to the radius of curvature, in reverse applies divergent front of elastic surface waves, array (spherical wave). Both these phenomena advantageous to use during the inspection in the following cases: a focusing effect is important from the point of view of increasing the sensitivity and resolution, and the effect of forming non-directional (spherical) waves improves the performance of the control and detection of differently oriented controlled defects of the material.

The use of piezo transducer cylindrical form (figure 5) most appropriate to identify differently oriented defects that get in the ring area sounding, between two coaxially positioned elements. When connecting the Converter to ultrasonic flaw detector, the Converter also works as a Converter in figure 1, the difference is in the shape of the piezoelectric elements, therefore, to describe his work is impractical. Its advantage is that it is due to the form of the cylinder generates in a controlled environment omnidirectional surface wave that identify differently oriented material defects.

Sources of information

1. Alyoshin N.P., White V.E., Vopilkin AH and other Methods of acoustic control metals. M., engineering, 1989, str.

2. Viktorov I.A. Physical basis of application of ultrasonic Rayleigh and lamb waves in the technique. M, publishing house "Nauka", 1965, page 14.

1. Ultrasonic transducer surface waves containing a piezoelectric elements, with the possibility of connection with ultrasonic flaw detector, acoustic isolator, a body, wherein the piezo transducer, polarized thickness, installed on one of the faces perpendicular to the working surface, located at a distance from each other, larger spatial probing pulse duration (L>τc), acoustically insulated from each other and are electrically connected together or separately with a clock or simultaneous inclusion.