RU2649636C1 - Electromagnetic-acoustic transducer for ultrasonic testing - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: application: to detect defects in products made of electrically conductive material in a non-contact way. Summary of the Invention thing is the electromagnetic-acoustic transducer comprises a magnetization assembly of the controlled article in the form of a biaxial trolley, solenoids of the electromagnet are located on the axes of the wheel pairs, and the poles of the electromagnet are the wheels of wheel pairs of the trolley and the inductor assembly with the coils for creating an alternating electromagnetic field of the ultrasonic frequency, located in the region of the magnetic field with the ability to move relative to the magnetizing unit, the coil inductor reinforced in a hermetic flexible shell of wear-resistant electrically insulating material and placed at the minimum possible distance from the contact spot of the wheel of the trolley with the controlled product.

EFFECT: technical result: expansion of functional capabilities of the electromagnetic-acoustic transducer by providing ultrasonic non-contact control of long products at significant scanning speeds.

1 cl, 2 dwg

Description

The invention relates to the field of non-destructive testing and can be used to detect defects and determine the geometric dimensions of products and samples of electrically conductive material in a non-contact manner by means of electromagnetic-acoustic excitation / reception of ultrasonic vibrations at significant scanning speeds.

The most striking and large-scale example of product control at significant (up to 80 km / h and more) speeds is non-destructive testing of railway rails laid on the way. Therefore, an explanation of the principle of operation and an example of the implementation of the proposed technical solution is given by the example of rail monitoring in order to detect factory and operational defects in them. As will be shown below, the scope of the invention is not limited to the control of rails and can be used to control other lengthy industrial products (pipes, beams, sheet strips, etc.).

For non-destructive testing of rails, not only hand-held devices and inspection trolleys are used, but also automated wagons and defectoscopes (mobile means of defectoscopy) that allow high-speed inspection of rails over the entire section (excluding feathers of the sole of the rails). Mostly, magnetic (magnetodynamic (MD)) and contact ultrasonic (ultrasound) control methods are used to control the rail head, and the ultrasonic method is also used for contact detection of acoustic vibrations to detect defects in the neck and sole of the rail [1, 2, 3].

The main disadvantage of the contact method of introducing ultrasonic vibrations is the need to use a large volume of contacting liquid (pure water or water with additives) - up to 5 tons per 200-250 km of the controlled path, the difficulty of monitoring in winter conditions (freezing of the liquid, snow sticking to wet acoustic blocks and their icing) and, as a result, violation of acoustic contact and low reliability of control. In addition, the need for periodic refueling of a mobile device with a contact fluid increases the cost of control and reduces the performance of rail diagnostics.

In this regard, the implementation of the contactless input of ultrasonic vibrations, the reliability and speed of control is not inferior to the contact method of input / reception of ultrasonic vibrations, is relevant.

Of all the known methods for implementing non-contact monitoring of rails (laser excitation and reception of ultrasonic vibrations, monitoring using normal waves over significant distances, etc.), the most promising and feasible is the use of non-contact electromagnetic-acoustic (EMA) converters, which have a number of significant advantages over traditional contact piezoelectric transducer (PEP) method. These include [4]:

- no need for the use of contacting liquids;

- the ability to control rails without special surface preparation;

- the possibility of excitation and reception of any types of waves, including transverse with horizontal polarization, as well as introduced along the normal to the surface of the rail;

- lack of wear of converters;

- the ability to control in a wide range of temperatures, including at abnormally low (up to minus 50 ° С) temperatures;

- the ability to control at high speeds the movement of the EMA transducers and products.

Despite the fact that both normal and inclined input of ultrasonic vibrations is theoretically possible, when using an EMA transducer that inputs and receives ultrasound in a direction perpendicular to the surface, the EMA transducer has certain advantages over traditional methods with contact input of ultrasonic vibrations using traditional piezoplastin (PEP) due to the following. PEP allows you to excite and accept along the normal to the metal surface only longitudinal vibrations, and EMAT (depending on the design) - both longitudinal and transverse. In the latter case, the excitation and reception of transverse waves propagating along the normal to the surface, can be especially effective when controlling ferromagnetic materials. The following advantages have been established due to the use of transverse waves excited normally to the surface of the product [5]:

- the sensitivity of the control increases, the size of the "dead" zone and the resolution decrease, the accuracy of measuring the coordinates of defects and the thickness of the product increases. This is due to the fact that the propagation velocity of transverse waves in materials is almost 2 times lower than the velocity of longitudinal waves;

- the transverse wave is better reflected from plane defects filled with gas, liquid or granular material, since such discontinuities transmit shear stresses poorly;

- the transverse wave with the right choice of the direction of polarization does not experience significant transformations in reflections from the defect and the surface of the controlled product. This makes it possible to reduce the influence on the results of monitoring coherent acoustic noise;

- the amplitude of the shear vibration pulses excited by the direct EMA transducer is attenuated in the product with flat cracks oriented perpendicular to the surface of the controlled product, to a greater extent than the amplitude of the longitudinal vibrations excited by the direct probe. This creates the prerequisites for the successful detection of unfavorably oriented plane defects;

- in comparison with the longitudinal, the transverse wave experiences less attenuation in the material.

Measurements using an EMA transducer are characterized by a small error and signal stability at speed due to the fact that there is no signal passing through a large number of intermediate media (in the case of a contact piezoelectric transducer, the ultrasonic wave is excited in the piezoelectric plate, then passes through a prism with a certain angle, then through the tread, then through the contact medium and only then enters the control object).

Two main structural elements of the EMA converter can be distinguished:

- a magnetic system consisting of a magnet (a set of magnets or an electromagnet) and a magnetic circuit forming a magnetization field;

- an inductor, as a rule, representing an elliptical (or any other configuration) flat inductor (or several coils).

The efficiency of the EMA conversion directly depends on the magnitude of the magnetizing field created by the magnetizing system of the EMA converter. It is known from [6] that the efficiency of EMA converters in the combined mode (radiation – reception) is proportional to the square of the magnetization field B. In this case, it is sufficient to magnetize only the skin layer of a ferromagnet due to the high-frequency electromagnetic field created by the primary EMA converters — inductor coils. It is in the skin layer of a ferromagnet that the mutual conversion of high-frequency electromagnetic and acoustic vibrations occurs. In other words, the efficiency of the EMA conversion depends on the magnetizing system and the magnetic field created by it in the skin layer of the controlled material.

To create large fields using magnetizing systems, which are massive assemblies of permanent magnets. It was found that the magnetizing field strongly depends on the gap between the magnetizing system and the surface of the controlled ferromagnet [6].

Known [5] an EMA converter for exciting shear (transverse) ultrasonic body waves using permanent magnets, containing a magnet in the form of a cylinder with a magnetization direction along the axis, at the end of which there is an inductor coil of the EMA converter. The specified EMA converter does not provide the necessary sensitivity and has a low signal to noise ratio.

Known [7] is an EMA converter in which the magnetic system is made in the form of a concentrator made of a material with high saturation magnetization, on each non-working surface of which a high-energy magnet is installed (based on the NdFeB or SmCo alloy), and the inductor coil is located on the working surface of the concentrator. The specified EMA converter does not provide the necessary sensitivity and has a low signal-to-noise ratio when monitoring products.

Known [8] an EMA converter, which differs from the foregoing in that a hub of soft magnetic material, an additional magnet, a pole piece, a magnetic circuit and an insert of non-magnetic metal are introduced into it, the hub is mounted on the end part of the magnet, the additional magnet is made with a magnetization direction in normal to the lateral faces of the concentrator and ensuring equal polarity of all poles adjacent to the concentrator. Such a magnetic system of the EMA converter allows you to expand the functionality (along with the excitation of shear waves with radial polarization, the excitation of shear waves with linear polarization and longitudinal waves, as well as their simultaneous excitation). The specified magnetic system of the EMA transducer requires an air gap between the surface of the controlled product and the concentrator, does not allow for contactless monitoring of rails at significant scanning speeds and has limited functionality.

All considered EMA converters [4-8] require maintaining a constant gap between the working plane of the magnetizing system and the surface of the controlled product. The possibility of foreign metal objects falling into the specified gap and damaging the system makes it possible to conduct flaw detection work. In the area of bolted joints and turnouts, fragile permanent magnets can quickly fail and become a certain obstacle to the safe movement of trains. Despite the use of high-energy magnets, the magnetic field created by them is insufficient for effective contactless excitation / reception of ultrasonic vibrations, especially with high-speed rail monitoring.

Closest to the claimed device is an electromagnetic acoustic transducer of products and samples of electrically conductive material according to the patent [9] No. 2489713 of the German company “Institute Dr. Ferster GMBKh KO”, containing a magnetization unit of the controlled product and a probe (inductor) assembly with inductors located in area of the magnetic field with the possibility of movement relative to the magnetizing node. An advantage of the known device is the implementation of the magnetization unit and the inductor unit (probe unit) with a certain degree of freedom among themselves. The inductor assembly, having an insignificant mass and is constantly located in the magnetic field of the magnetization assembly, due to the absence of a rigid connection with the magnetizing assembly, can pass along the surface relief when passing surface irregularities, without causing excessive inertial forces that could lead to wear or even destruction transducer. In this case, the strong magnetic attraction between the magnetizing assembly and the controlled ferromagnetic product does not affect (or affects very little) the force that presses the inductor assembly to the surface of the product. Due to this, as claimed by the authors of a well-known patent, the control of the ferromagnetic material can be carried out with high sensitivity and low wear load while maintaining a sliding contact between the inductor assembly and the surface of the controlled product.

A disadvantage of the known device adopted as a prototype is the use as a magnetization unit of a system consisting of permanent magnets (or an electromagnet) located above the inductor assembly at a certain (several - up to 8 mm) distance. The need to comply with this distance leads to the use of a complex design of mutual fastening of nodes and special protective measures to maintain this gap. In case of violation of the conditions for maintaining the gap between the magnetization unit and the inductors unit, all the disadvantages of the analogues are fully manifested - there is rapid wear and the possibility of damage to the inductor coils of the EMA converter. All this limits the functionality of the known device and makes it impossible to use the known device at significant scanning speeds.

The problem solved by the claimed technical solution is to expand the functionality of the electromagnetic-acoustic transducer for monitoring products and samples at significant scanning speeds.

To solve the problem, an electromagnetic-acoustic transducer for ultrasonic testing of products from an electrically conductive material, comprising a magnetization unit of a controlled product and an inductor assembly with inductors to create an alternating electromagnetic field of ultrasonic frequency, located in the magnetic field with the possibility of movement relative to the magnetizing assembly, according to the claimed invention magnetization unit is made in the form of a biaxial trolley, electromagnet solenoids placed on the axles of the wheelsets, and the wheels of the wheels of the bogies are the poles of the electromagnet, the inductor coils of the inductor are reinforced in a sealed flexible shell of wear-resistant electrical insulation material and placed at the minimum possible distance from the contact spot of the wheels of the bogie with the controlled product.

Significant differences of the claimed device in comparison with the prototype are the following features:

1. The implementation of the magnetization unit in the form of a biaxial trolley with solenoids (magnetizing coils) on the axles of the wheelsets and the use of wheels as poles of electromagnets ensures the creation of a stable magnetic flux in the controlled product. In the prototype, despite the use of bounding plates, this value is variable, which affects the quality of control.

2. Zero clearance between the poles of the magnet (wheels) and the surface of the monitored product also helps to increase not only the stability of the flow, but, ceteris paribus, to increase the flow in the product (in the skin layer of the metal of the product), and therefore to increase efficiency excitation / reception of ultrasonic vibrations.

3. For poles of the electromagnet, which are the wheels of the trolley, irregularities on the surface of the monitored product even of significant size (in practice, “steps” on the bolted joints of the rails to 10 mm) are not an obstacle, leading to limited control or damage to the elements of the EMA converter. In the prototype, the collision of the surface roughness of the controlled product with protective elements (spacer element, runners) of the EMA converter can lead to disruption of the device.

4. The implementation of the magnetization unit in the form of a biaxial trolley with coaxial placement on the axles of the wheelsets with solenoids (magnetizing coils) or permanent magnets allows you to create a significant magnetic flux in the controlled product, which also improves the efficiency of EMA conversion.

5. The magnetization system is also the carrier of the EMA converter, which, unlike the prototype, significantly simplifies the design of the device.

6. Reinforcing the inductor coils of the inductor into a sealed enclosure made of wear-resistant material simplifies the design of the inductor, protects the coil from contamination and damage in real operating conditions, and maximizes the inductance coils to the surface of the controlled product, which increases the efficiency of EMA conversion. In the prototype, a mud-proof shell (bellows) basically protects the intermediate space between the magnet pole and the inductor coils and poorly protects the coils themselves, which are the main elements of the EMA converter.

The inventive device is illustrated by the following graphic materials:

FIG. 1 - Scheme of magnetic flux excitation, where:

1 - trolley with two wheelsets;

2a and 2b - rail track with rails 2a and 2b;

3 and 4 - wheelsets with wheels 3a and 3b for wheelset 3 and wheels 4a and 4b for pairs 4, respectively;

5 - coils (solenoids) of electromagnets on the axles of wheel sets 3 and 4;

6 - magnetic flux generated by electromagnets on the axles of the wheelsets, closing through the wheels of the trolley and sections of the rails between the wheels of the trolley 1;

7 - the frame of the trolley 1, made of non-magnetic material.

FIG. 2 - EMA converter with the placement of the inductor assembly under the wheel (for example, 3a of the wheel pair 3) of the truck 1, where:

8 - EMAT inductor coils;

9 - fins - an elastic element for the tight placement of the inductor coils of the EMA converter;

10 - mount;

11 - bracket attached to the axle box 12;

12 - axle box wheel assembly 1;

13 - ultrasonic vibrations excited in the rail.

Consider the possibility and implementation features of the claimed device.

Trolley 1 with two wheelsets 3 and 4 (Fig. 1) is mounted on a rail track with rails 2a and 2b. On the axles 3 and 4 of the wheelsets are located solenoids (magnetization coils) 5. Axes 3 and 4 together with coils 5 form a kind of electromagnets. When an electrical voltage is connected to the coils 5, a closed magnetic flux 6 is formed, without air gaps and corresponding losses. The windings of the coils 5 are connected to a voltage source in a coordinated manner so that the magnetic flux 6 passes along the path: axis 3 of the first pair of wheels — wheel 3a — spot of contact between the wheel and rail 2a, rail 2a (one thread of the rail track) — spot of contact of the wheel 4a of the second wheel pairs 4 - axis 4 of another wheelset - another wheel 4b of this pair - rail 2b of another thread of the rail track and wheel 3b of the first pair.

The connecting structural elements 7 of the trolley 1, in order to eliminate magnetic flux losses, are made of non-magnetic material (for example, stainless steel). Such a magnetization system makes it possible to obtain magnetic induction in the rail of at least 1 T at a consumed electric power of only about 2 kW. The system is safe at significant scanning speeds (tested when monitoring rails up to 80 km / h) on operated railways when passing any sections of the track with bolted and welded joints, turnouts, sections of the track with level crossings and bridges [10, 11].

Such a magnetization system is successfully operated during the implementation of the magnetodynamic (MD) control method, is known from patents and publications [12-17] and confirms the feasibility of the proposed technical solution.

However, the MD method allows you to detect only defects in the rail head, occurring at a depth not exceeding 15-20 mm from the rail rolling surface. Known technical solutions create a magnetic field on the sections of the rails between the wheels for the implementation of magnetic (magneto-dynamic) control and are intended mainly for detecting defects in the rail head and transverse kinks in the rails. Some technical solutions allow additionally, using the MD method signals to determine the control speed using correlation processing of signals from two closely located magnetic field sensors [16], or to analyze the condition of welded rail joints [17]. In the known technical solution [15], the generated magnetic field, in addition to detecting transverse cracks in the rails, is also used to create braking forces of the rolling stock.

But all the known considered and similar magnetization methods have a narrow scope and do not allow to realize non-contact (dry, without the use of a contacting liquid) excitation and reception of elastic (acoustic) vibrations of ultrasonic frequencies and have limited functionality. There are examples of the simultaneous use of MD and ultrasound methods, when, simultaneously with the implementation of the MD method, the ultrasound control method is also implemented [3, 13, 18]. However, contact ultrasound transducers with all their shortcomings are used (the requirement of the contacting fluid to create an acoustic contact, the instability of the contact during scanning, etc.). The placement of contact ultrasonic transducers in known solutions is associated only with the use of a special trolley with electromagnets on the axles of the wheelsets as a carrier or device for placing contact acoustic blocks when scanning a controlled product.

In order to expand the functionality of the claimed invention, it is proposed to use the magnetic flux generated by the considered magnetization system for non-contact (dry, without contacting liquid) rail monitoring by EMA excitation / reception of ultrasonic vibrations. For this, in the zone of maximum magnetic flux, near the contact spot of a wheel with a rail, a flat inductor 8 of an inductor with an alternating electric current of ultrasonic frequency is installed. The coil or several coils 8 of the inductor are hermetically mounted (reinforced) in an elastic fins 9, which, in turn, is attached to the bracket 11 using the mount 10, and the bracket 11 is attached to the axle box 12 of the wheelset 3.

When the solenoids 5 are turned on, a magnetic flux 6 is created in the axles of the wheel pairs 3 and 4, which penetrates through the poles of the electromagnet (cart wheels 3a, 4a, 4b and 3b) into the rails 2a and 2b under study. Magnetic flux 6 passes into the rail through the wheel-rail contact spots and through the air gap between the wheel rim and the rail. By mathematical modeling and experimentally established that:

- the size of the contact spot is about 60 × 40 mm, here the maximum magnetic induction is about 2.0 T;

- at a distance of about 80 mm (77.5 mm) from the edges of the contact spot in the air gap Z between the wheel and the rail (Fig. 2), the level of magnetic induction B is still at a level sufficient for the effective excitation and reception of ultrasonic vibrations by the EMA method.

In the specified gap Z (Fig. 2) in the inventive device, an inductor 8 of an inductor of an EMA converter is placed, which is a flat coil in the form of a meander, a "butterfly" or another shape (the configuration of the coil is not included in the subject of the claimed technical solution). The lines of force created by the electromagnet in the zone under consideration are almost perpendicular to the inductor coil and the rail rolling surface. The pulse current of ultrasonic frequency, flowing in the flat coil 8 of the inductor, causes oscillations of these conductors and the surface layer of the controlled product (rail 2A or 2B) with the same maximum amplitude, i.e. in this converter, magnetic field energy is used almost completely. This ensures the uniformity of the front of ultrasonic vibrations in the skin layer, which together leads to an increase in the conversion coefficient of the transducer and to the creation of volume shear waves 13 in the controlled rail 2a (or 2b). Ultrasonic vibrations, propagating along the path 13 along the height of the rail, fix the desired defects in the rail by echo and / or mirror-shadow methods of ultrasonic testing.

Depending on the sounding schemes of the monitored product (rail 2a, 2b), one, two or several coils 8 of the inductor can be in the gap between the wheel rim and the rolling surface of the rail (two coils are shown in Fig. 2). With a single inductor coil, it simultaneously (more precisely, sequentially: first emits a probe pulse, then receives echo signals) acts as a transmitter and receiver of ultrasonic vibrations.

What kind of ultrasonic waves (in frequency and orientation) will be created in the material of the controlled product depends on the direction of the magnetic field cart created by the magnetic system, as well as on the layout of the inductor coils, their distance from the contact spot and the electronic system (not shown in Fig. )

It should be noted that the formation of shear ultrasonic vibrations propagating normally to the scanning surface is less critical to the technological gap between the flat coil of the inductor 8 and the surface of the controlled object (rail 2a or 2b). A technological gap is inevitable, because inductor coils 8 must be protected from damage, short circuits, etc. Therefore, in the claimed technical solution, it is proposed to place them in an elastic tight sealed elastic plate (fins) 9, which can be made, for example, of wear-resistant polyurethane or other highly non-abrasive non-magnetic materials. With an optimal selection of fins material, the technological gap can be no more than 1.5 mm, which is quite enough to receive up to 10 bottom signals (from the surface of the rail sole) in the static position of the trolley and up to 3-bottom signals in dynamics at maximum scanning speeds. This allows for reliable non-contact (with dry contact) ultrasonic monitoring of rails at significant scanning speeds.

The specific implementation of the bracket 11 and the attachment assembly 10 may differ from the embodiment shown in FIG. 2. It is important that a constant position of the coils 8 of the inductor is ensured relative to the surface of the monitored rail and the contact spot of the wheel with the rail. When moving the fins 9 with the coils of the inductor 8 can follow the surface topography of the controlled product 2A and 2B. In this case, the inductor zone, as a rule, is slightly pressed by the elastic forces of the flexible fins and, under certain conditions, by the inertia forces on the surface of the controlled product (on the rolling surface of the rail), however, the force of this clip is so small that even with the sliding contact of the working surface of the fins 9 and the rolling surface of the rail has only a slight wear. It is also possible to work non-contact in individual phases of the process.

To protect the inductor coils 8 in front of the inductor from the side facing the controlled product, as well as from the wheel side, additionally not shown in FIG. protective plates made of non-magnetic material (for example, ceramic composite). The mount 10 must be made in such a way as to ensure, if necessary, the quick replacement of a worn or damaged fins 9 with coils 8 of the inductor with a workable one.

For the formation of ultrasonic waves oriented normally to the scanning surface, it is necessary to ensure the closest possible location of the inductor to the contact spot. It is upon fulfillment of this requirement that the most effective excitation of shear ultrasonic waves in the one indicated in FIG. 2 direction 13.

In the General case, the placement of the coils 8 of the inductor on each thread of the rail track is possible both in front and behind the wheel (3A in Fig. 2). It was experimentally established that the most effective excitation of ultrasonic vibrations occurs when the inductors are placed near the first wheels along the direction of the trolley 1 (wheels 3a and 3b in Fig. 1, with the direction of the trolley indicated in Fig. 2).

The implementation of the inventive device is possible not only with the control of railway rails, but also with any other products having a parallel arrangement of controlled nodes. For example, it is possible to simultaneously control two adjacent pipes, T-beams, narrow sheet paintings, etc. Naturally, the profile of the wheels forming the cart must be adapted to the profile of the monitored product, the width of the cart is determined by the distance between the products, and the monitored products should not have cross-links made of soft magnetic material.

It is also possible to implement a device in which control of a single long product is provided, and the second, placed parallel to the first, serves as a guide for the trolley. The control performance will be two times lower than with the simultaneous control of two identical products.

At the same time, in any case considered, it becomes possible to significantly simplify the design and significantly expand the functionality of the EMA transducer by increasing the scanning speeds without losing the efficiency of excitation / reception of ultrasonic vibrations in a non-contact way.

Thus, the inventive device can be implemented, allows for non-contact ultrasonic testing of products at significant scanning speeds, significantly expanding the functionality of the EMA transducer.

INFORMATION SOURCES

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Claims (1)

An electromagnetic-acoustic transducer for ultrasonic testing of products from an electrically conductive material, comprising a magnetization unit of a controlled product and an inductor assembly with inductors to create an alternating electromagnetic field of ultrasonic frequency, located in the magnetic field with the possibility of movement relative to the magnetizing unit, characterized in that the magnetization unit is made in the form of a biaxial trolley, the solenoids of the electromagnet are placed on the axles of the wheelsets, and the poles are The electromagnets are the wheels of the wheelsets of the trolley, the inductor coils of the inductor are reinforced in a sealed flexible shell made of wear-resistant electrically insulating material and placed at the minimum possible distance from the contact spot of the trolley wheel with the controlled product.

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