A high-temperature strain thin-film sensor for detecting thermal stress in small billet crystallizers

Abstract

This invention discloses a high-temperature strain thin-film sensor for detecting thermal stress in small billet crystallizers, belonging to the field of sensor technology. It comprises a composite system formed by interwoven fiber structures. From bottom to top, the composite system includes a substrate layer, a high-temperature insulating layer, a piezoelectric thin film layer, and a multifunctional composite layer. Channels are provided in the piezoelectric thin film layer, extending to both the high-temperature insulating layer and the multifunctional composite layer. These channels are connected to external devices via lead electrodes. The multifunctional composite layer includes a parallel, interwoven array of thermocouples and a sensitive grid unit. The thermocouple array is used to superimpose thermoelectric effects, increasing the output signal. The sensitive grid unit converts the strain of the crystallizer steel tube into an electrical signal output through the deformation of the sensitive grid, enabling real-time measurement of stress and strain on the surface or inside the crystallizer. The sensor designed in this invention exhibits good high-temperature resistance, structural stability, long service life, and high measurement accuracy.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, specifically relating to a high-temperature strain thin-film sensor for detecting thermal stress in a small billet crystallizer. Background Technology

[0002] Continuous casting is the most crucial link between steelmaking and rolling. Smooth continuous casting production and high-quality billet production are of paramount importance to steelmaking enterprises. The crystallizer is a continuous casting equipment that receives molten steel and solidifies it into a solid billet shell according to a specified cross-sectional shape. It is widely used in wastewater and organic solvent treatment in chemical, pharmaceutical, food, metallurgical, photovoltaic, papermaking, and waste treatment industries. Its continuous development and innovation bring more opportunities and possibilities to industrial production, driving various related industries towards higher quality and higher efficiency.

[0003] According to their cross-section, crystallizers are classified into several types, including slabs, small square billets, rectangular billets, round billets, and irregularly shaped billets. Among them, the small square billet crystallizer itself has a very small structure, and its internal temperature distribution affects the quality of the cast billet and the production capacity. High-temperature molten steel easily generates high thermal stress on the crystallizer steel tube, which plays an important role in whether the cast billet will de-squatter. Therefore, detecting the temperature field and stress field of the continuous casting crystallizer steel tube can provide information on the heat transfer of the crystallizer, the thickness and uniformity of the billet shell inside the crystallizer, etc., to ensure that the optimal heat flow is maintained, the production process is optimized, and the quality of the cast billet is guaranteed.

[0004] However, when performing thermal stress detection on the deformation of the steel tubes in the crystallizer, the thermal stress detection structure is in a complex environment, and current technologies cannot detect anomalies in a timely manner, resulting in a need to improve the quality of the cast billet. Therefore, how to develop a high-temperature strain thin-film sensor for thermal stress detection in small billet crystallizers that offers high sensitivity, fast response, and higher testing accuracy under complex environments such as high temperatures is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-temperature strain thin film sensor for detecting thermal stress in small billet crystallizers, which addresses the shortcomings of the prior art. This sensor solves the technical problems of low sensitivity, slow response, and poor testing accuracy of existing high-temperature strain thin film sensors for detecting thermal stress in small billet crystallizers under complex environments such as high temperature.

[0006] The present invention adopts the following technical solution:

[0007] A high-temperature strain thin-film sensor for detecting thermal stress in a small billet crystallizer includes a composite system formed by fiber structures, wherein the fiber structures are interwoven and interlocked, and the composite system includes, from bottom to top, a substrate layer, a high-temperature insulating layer, a piezoelectric thin film layer and a multifunctional composite layer.

[0008] The piezoelectric thin film layer has channels that extend to the high-temperature insulating layer and the multifunctional composite layer, and the channels are connected to external devices via lead electrodes.

[0009] The multifunctional composite layer includes a thermocouple array and a sensitive grid unit that are distributed in parallel and interwoven with each other. The thermocouple array is used to superimpose the thermoelectric effect to increase the output potential. The sensitive grid unit is used to convert the strain of the crystallizer steel tube into an electrical signal output through the deformation of the sensitive grid, so as to realize the real-time measurement of stress and strain on the surface or inside of the crystallizer.

[0010] Preferably, a bottom electrode is disposed between the high-temperature insulating layer and the piezoelectric thin film layer. The bottom electrode includes a first bottom electrode fiber and a second bottom electrode fiber, with a gap between the first bottom electrode fiber and the second bottom electrode fiber.

[0011] Preferably, the piezoelectric thin film layer includes PVDF piezoelectric fibers, with several PVDF piezoelectric fibers interwoven in space and arranged in a directional manner.

[0012] Preferably, the thermocouple array comprises at least two thermocouple fibers connected in series.

[0013] Preferably, the sensitive gate unit comprises a plurality of strain-sensitive gate fibers connected in series and having different gate lengths.

[0014] Preferably, the strain-sensitive grid fiber is a series of interconnected serpentine fiber lines, each serpentine fiber line including first fiber lines arranged at intervals along the same direction, and second fiber lines connecting the ends of adjacent first fiber lines.

[0015] Preferably, the piezoelectric thin film layer is made of ZrNiSn material, the thermocouple fiber is made of TiCoSb alloy, and the strain-sensitive grid fiber is made of Fe-Cr-Al alloy.

[0016] Preferably, a crystallizer copper plate is disposed below the substrate layer, and a ventilation channel is provided between the substrate layer and the crystallizer copper plate.

[0017] Preferably, the high-temperature insulating layer is attached to the surface of the substrate layer by a coating process, and the piezoelectric thin film layer, thermocouple array, and sensitive gate unit are all prepared by deposition.

[0018] Preferably, a thermal expansion buffer layer is provided on the lower side of the high-temperature insulation layer, and the thermal expansion buffer layer is prepared by a deposition process.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] A high-temperature strain thin-film sensor for detecting thermal stress in small billet crystallizers employs an interwoven fiber structure, exhibiting enhanced resistance to deformation. The interlocking fibers support and constrain each other, effectively resisting external stress and maintaining structural integrity, ensuring the sensor's stability and reliability during long-term use. The material possesses excellent high-temperature resistance, and the gaps between fibers facilitate uniform heat distribution, enabling the sensor to operate stably for extended periods in the high-temperature environment of the small billet crystallizer, significantly improving its high-temperature performance. Under harsh working conditions, this reduces damage and performance degradation caused by high temperatures and stress, significantly extending the sensor's lifespan and lowering equipment maintenance and replacement costs.

[0021] The specific structural design and advantages are as follows:

[0022] 1) The gap between the dual-electrode fibers buffers the difference in thermal expansion, preventing short circuits caused by electrode compression; the gap is reserved with microchannels to facilitate the release of thermal stress;

[0023] 2) Arrange fibers along the principal stress direction to increase the piezoelectric constant and enhance the ability to capture weak stress signals;

[0024] 3) Multiple thermocouple fibers are connected in series, and the output potential is superimposed to the millivolt level, which improves the signal-to-noise ratio and the temperature measurement accuracy reaches ±1℃;

[0025] 4) Multiple serpentine grids are connected in series to cover strains at different spatial frequencies; the serpentine structure extends the effective grid length and improves the strain sensitivity K value;

[0026] 5) Microporous channels discharge interfacial water vapor / bubbles, preventing the formation of thermal resistance layers and improving thermal conductivity;

[0027] 6) The insulating layer coating ensures density, and the functional layer vapor deposition achieves micron-level precision, making it compatible with curved surface crystallizers.

[0028] In summary, this invention employs a single thin film to simultaneously detect temperature, strain, and stress, resulting in high spatiotemporal consistency of the data. Through innovative fiber composite structure and synergistic design of multifunctional layers, it achieves a breakthrough in thermal stress detection for small billet crystallizers.

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1An exploded view of the high-temperature strain thin-film sensor for thermal stress detection in a small billet crystallizer provided by the present invention.

[0032] Figure 2 This is a structural diagram of the strain-sensitive gate provided by the present invention.

[0033] The components are: 1. Substrate layer; 2. High-temperature insulating layer; 3. Piezoelectric thin film layer; 4. Multifunctional composite layer; 5. Crystallizer copper plate; 6. Thermocouple array; 7. Sensitive gate unit; 8. External equipment; 9. Bottom electrode. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "one side," "one end," and "one side," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0036] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0037] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0038] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0039] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0040] The accompanying drawings illustrate various structural schematic diagrams of embodiments of the present invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0041] Please see Figure 1 The high-temperature strain thin-film sensor for detecting thermal stress in a small billet crystallizer disclosed in this invention is a composite system formed by interwoven fiber structures. The composite system includes, from bottom to top, a substrate layer 1, a high-temperature insulating layer 2, a piezoelectric thin film layer 3, and a multifunctional composite layer 4.

[0042] The piezoelectric thin film layer 3 has a channel that extends to the high-temperature insulating layer 2 and the multifunctional composite layer 4. The channel is connected to an external device 8 via lead electrodes. The multifunctional composite layer 4 includes a parallel and interwoven thermocouple array 6 and a sensitive grid unit 7. The thermocouple array 6 consists of at least two thermocouple fibers connected in series, and the sensitive grid unit 7 consists of several strain-sensitive grid fibers connected in series with different grid lengths. A thermal expansion buffer layer is provided on the underside of the high-temperature insulating layer 2 and is prepared using a deposition process suitable for fiber forming. The thermocouple array 6 is designed as multiple thermocouples connected in series to superimpose the thermoelectric effect, thereby increasing the output potential. The sensitive grid unit 7, based on the resistance strain and piezoresistive effect, converts the strain of the crystallizer steel tube into an electrical signal output through the deformation of the sensitive grid, realizing real-time measurement of stress and strain on the surface or inside of the crystallizer.

[0043] Will Figure 1The sensor's composite system can be obtained by interweaving and interlacing the various layers of the internal design, which is easy to observe. The multifunctional composite layer 4 designed in this embodiment has advantages such as good density and good high-temperature insulation. It can operate stably in complex environments such as higher operating temperatures, thereby achieving the design goals of high temperature resistance, good stability, and long service life. At the same time, it measures temperature and strain data, has good detection performance, and high application value. It can be widely used in various complex environments to complete thermal stress detection.

[0044] In existing technologies, the detection of thermal stress in the crystallizer steel tubes during continuous casting production faces challenges such as insufficient sensitivity and slow response speed under complex high-temperature environments. Traditional sensors, limited by their single-function structure, struggle to simultaneously achieve real-time measurement of both temperature and stress fields, leading to fluctuations in billet quality. Existing detection devices are prone to signal interference in high-temperature environments, failing to accurately capture the dynamic changes in crystallizer steel tube deformation and temperature distribution, thus impacting production process optimization.

[0045] To address the aforementioned issues, the single-functional-layer design in existing technologies leads to mutual interference in the detection of multiple physical quantities, and signal transmission loss at high temperatures exacerbates measurement errors. Analysis reveals that while multi-layered composite structures can achieve functional partitioning, traditional stacking methods struggle to ensure coordinated operation between layers. Further consideration is given to the interlacing arrangement of fiber materials to enhance structural stability, while the combined piezoelectric and thermoelectric effects are utilized to improve signal output strength. Integrating the thermocouple array 6 and the strain-sensitive gate unit 7 into the same functional layer, spatial distribution optimization addresses signal crosstalk, forming a synchronous detection mechanism.

[0046] Therefore, this application proposes a composite system formed by fiber structures, wherein the fiber structures are interwoven and interspersed. The composite system includes, from bottom to top, a base layer 1, a high-temperature insulating layer 2, a piezoelectric thin film layer 3, and a multifunctional composite layer 4. The piezoelectric thin film layer 3 has channels that extend to the high-temperature insulating layer 2 and the multifunctional composite layer 4, and the channels are connected to an external device 8 through lead electrodes. The multifunctional composite layer 4 includes a parallel and interwoven thermocouple array 6 and a sensitive grid unit 7. The thermocouple array 6 is used to superimpose thermoelectric effects, and the sensitive grid unit 7 is used to convert strain into an electrical signal output through deformation.

[0047] Among them, the composite system formed by fiber structure refers to the construction of a multi-layer functional integrated structure through the spatial interweaving of fiber materials. Specifically, it can be achieved by weaving carbon fiber or ceramic fiber, and stress buffer areas are formed through the gaps between fibers to enhance the structural stability under high temperature environment.

[0048] The passage connecting the high-temperature insulating layer 2 and the multifunctional composite layer 4 refers to the vertical conductive path set inside the piezoelectric thin film layer 3. Specifically, it can be formed by laser drilling or chemical etching processes, which reduces the signal transmission impedance by shortening the electrode lead path.

[0049] The interlacing distribution of thermocouple array 6 and sensitive grid unit 7 refers to the alternating arrangement of the two functional units in the planar dimension. Specifically, it can be fabricated using micro-nano fabrication technology, and spatial isolation can reduce the mutual interference between temperature measurement and strain detection.

[0050] Specifically, the substrate layer 1 is in direct contact with the crystallizer copper plate 5, and thermal expansion stress is balanced through a venting channel. The high-temperature insulating layer 2 is coated onto the surface of the substrate layer 1 to achieve current isolation. In the piezoelectric thin film layer 3, the interwoven piezoelectric fibers generate charges during mechanical deformation, transmitting electrical signals to the external device 8 through a through-channel. In the multifunctional composite layer 4, the thermocouple array 6 is connected in series to superimpose thermoelectric potentials, and the serpentine fiber lines of the sensitive gate unit 7 undergo resistance changes under strain. Both signals are output through independent channels. This through-channel design allows the lead electrodes to be directly connected to the external acquisition module, avoiding contact resistance problems caused by traditional soldering methods.

[0051] Compared to existing technologies, traditional sensors using a single functional layer result in coupling of temperature and strain signals. This application achieves separate detection of physical quantities through a multi-layer composite structure. In existing technologies, electrode leads must traverse multiple layers, introducing parasitic capacitance. The vertical channel design of this application reduces signal path length and improves response speed. Existing independent thermocouple units lead to low space utilization. The interlaced distribution method of this application achieves simultaneous acquisition of multiple parameters within a limited area.

[0052] Through the above technical solutions, this application achieves high-sensitivity real-time detection of thermal stress and strain in small billet crystallizer steel pipes under high-temperature conditions. The measurement accuracy of temperature and stress fields is improved through the collaborative work of composite functional layers, the through-channel structure reduces signal transmission loss, and the interwoven sensitive units enhance the ability to capture local deformation, providing reliable data support for optimizing the continuous casting process.

[0053] The high-temperature insulating layer 2 is attached to the surface of the substrate layer 1 by a coating process. The piezoelectric thin film layer 3, the thermocouple array 6, and the sensitive gate unit 7 are all prepared by a deposition method suitable for fiber forming.

[0054] Coating process refers to a processing method that uses fluid coating to uniformly cover the surface of a substrate with high-temperature insulating material. Specifically, it can be achieved by spraying, dipping, or blade coating. By utilizing the matching between the material's fluidity and the surface roughness of the substrate, a continuous covering layer is formed. This process can enhance the interfacial bonding between the insulating layer and the metal substrate.

[0055] Among them, deposition process refers to the processing method of stacking materials into a film layer by layer in the form of atoms or molecules through physical or chemical means. Specifically, it can be achieved by magnetron sputtering, chemical vapor deposition or electron beam evaporation. By controlling the deposition rate and substrate temperature, the functional materials can be directionally grown at the microscale. This process can ensure the structural compactness and interfacial thermal stability of the piezoelectric layer and sensitive unit.

[0056] Specifically, the coating process utilizes the liquid flow characteristics of high-temperature insulating materials to fill the micropores on the surface of the substrate layer 1. After curing, a mechanically interlocking structure is formed, effectively suppressing interfacial stress concentration caused by the difference in thermal expansion coefficients between the substrate and the insulating layer under high-temperature conditions. The deposition process is carried out in a vacuum or inert gas environment. By precisely controlling the material deposition path and crystal orientation, the piezoelectric thin film layer 3 forms uniform piezoelectric response units. Thermocouple array 6 and sensitive gate unit 7 are deposited through mask positioning to form mutually isolated conductive paths, avoiding material performance degradation caused by high-temperature oxidation.

[0057] In some specific embodiments, the surface of the substrate layer 1 can be pre-sandblasted to increase its roughness, and the coating process uses alumina paste sintered at 800°C to form an insulating layer; the piezoelectric thin film layer 3 deposits a lead zirconate titanate thin film on the surface of the insulating layer by radio frequency magnetron sputtering; the thermocouple array 6 uses a dual-target co-sputtering method to deposit nickel-chromium and nickel-silicon alloy layers; and the sensitive gate unit 7 deposits an iron-chromium-aluminum alloy serpentine line structure in a region defined by a photolithographic mask.

[0058] Compared to existing technologies, traditional sensors often employ a single hot-pressing process to fabricate multilayer structures, resulting in insufficient interfacial bonding of functional layers and a tendency for delamination and cracking during high-temperature cycling. This solution utilizes a phased approach of coating and deposition processes. The coating process leverages its wetting properties to strengthen the bond between the substrate and the insulating layer, while the deposition process utilizes its low-temperature film-forming properties to avoid damage to the crystal structure of functional materials during high-temperature processing. This achieves synergistic stability of multilayer heterogeneous materials under high-temperature conditions.

[0059] Through the above technical solution, this application solves the signal drift problem caused by interlayer bonding failure in high-temperature thermal stress detection of sensors. By optimizing process adaptability, it ensures the deformation coordination of each functional layer during thermal expansion, thereby improving the output stability of piezoelectric and thermoelectric signals to a level that meets the continuous monitoring requirements of continuous casting crystallizers.

[0060] The base layer 1 is connected to the crystallizer copper plate 5 by bolts, and there is a ventilation channel between the base layer 1 and the crystallizer copper plate 5.

[0061] A bottom electrode 9 is disposed between the high-temperature insulating layer 2 and the piezoelectric thin film layer 3. The bottom electrode 9 is composed of a first bottom electrode fiber with a concave shape and a second bottom electrode fiber with an upward convex shape, and a gap space is formed between the first bottom electrode fiber and the second bottom electrode fiber.

[0062] The bottom electrode 9 refers to the conductive interface layer set between the high-temperature insulating layer 2 and the piezoelectric thin film layer 3. Specifically, it can be made of platinum metal fiber or nickel-chromium alloy fiber through sputtering process to establish a stable electrical signal transmission channel.

[0063] Among them, the first bottom electrode fiber and the second bottom electrode fiber refer to fibrous electrode structures with independent conductive paths. Specifically, they can be prepared into parallel linear structures by laser cutting or photolithography, and the gap distribution avoids contact short circuits caused by thermal expansion.

[0064] The gap setting refers to the spaced area between adjacent electrode fibers, which can be achieved by adjusting the fiber spacing to 20-50 micrometers, in order to absorb the deformation caused by the thermal expansion of the material.

[0065] Specifically, in high-temperature environments, the lateral displacement generated by the thermal expansion of the bottom electrode fibers is accommodated by the gap region, preventing short circuits caused by contact between adjacent fibers. The first and second bottom electrode fibers are each connected to an external circuit via independent leads, forming redundant conductive paths. When one electrode fiber breaks due to localized stress, the other electrode fiber can still maintain signal transmission functionality. The fibrous electrode structure reduces current density by increasing surface area and minimizes resistivity changes caused by high-temperature oxidation.

[0066] Compared to existing technologies, traditional continuous metal thin-film electrodes are prone to cracking due to differences in thermal expansion coefficients at high temperatures, leading to signal transmission interruptions. The monolithic electrode layer used in existing technologies cannot adapt to the non-uniform thermal deformation during crystallizer operation. This solution, however, utilizes a fiber electrode structure with gaps, enabling the electrode layer to possess elastic deformation capabilities and effectively mitigating thermal stress concentration.

[0067] Through the above technical solutions, this application solves the short-circuit risk caused by material thermal expansion at the electrode contact interface under high-temperature environments, and ensures the stability of signal transmission through gap buffering and redundant conductive design. The independent distribution characteristics of the fiber electrodes avoid overall functional loss caused by local failures, improving the reliability of the sensor under complex thermal stress conditions.

[0068] The piezoelectric thin film layer 3 includes several PVDF piezoelectric fibers that are spatially interwoven and arranged in a certain direction.

[0069] Among them, PVDF piezoelectric fiber refers to a fiber structure with piezoelectric properties made of polyvinylidene fluoride material. Specifically, it can be achieved by electrospinning combined with polarization treatment. Its piezoelectric constant can reach 20-30 pC / N. It is used to convert the mechanical strain generated by the deformation of the crystallizer steel tube into a measurable electrical signal.

[0070] Interlacing arrangement refers to the formation of a three-dimensional network structure by multiple fibers intertwining in a cross-shaped manner. Specifically, the cross angle of 45°-90° within the fiber layer can be achieved by adjusting the movement trajectory of the spinning nozzle, which is used to construct multi-directional stress transmission paths to capture deformation components in different directions.

[0071] Directional alignment refers to the dominant orientation of fibers in a specific axis. This can be achieved by applying mechanical stretching force during fiber deposition using a directional receiving roller, so that the fiber spindle forms an angle of 0°-30° with the direction of force on the crystallizer steel tube, thereby enhancing the sensor's response sensitivity to strain in the target direction.

[0072] Specifically, by arranging PVDF piezoelectric fibers in an interlaced manner to form a dense network structure, stress in any direction can trigger a synergistic response from at least two sets of fibers with different orientations, eliminating blind spots in single-direction stress detection. Simultaneously, the fibers form a primary orientation alignment in a preset direction, enabling the sensor to generate a directional signal amplification effect on the axial tensile or circumferential contractile deformation of the crystallizer steel tube. The fiber nodes in the interlaced structure form distributed stress concentration points, which, under high-temperature conditions, excite stronger piezoelectric output through localized deformation. Furthermore, the anisotropic response characteristics generated by the directional arrangement can effectively distinguish the principal strain components in complex stress fields.

[0073] Compared to existing technologies, traditional piezoelectric films mostly employ piezoelectric ceramic sheets arranged in a single direction or randomly distributed composite materials. The former can only detect strain in a single axial direction and is brittle and prone to cracking, while the latter results in mixed signals due to its isotropic response. This invention combines fiber interweaving with directional arrangement to achieve the dual functions of multi-directional stress detection and directional signal enhancement while maintaining material flexibility. This solves the problems of insufficient sensitivity of piezoelectric layers and low signal axial discrimination under high-temperature environments.

[0074] Through the above technical solution, this application realizes the multi-dimensional acquisition and directional enhancement of piezoelectric signals in the thermal stress detection of small billet crystallizers, significantly improves the strain resolution capability of the sensor under high temperature and complex stress field, ensures the complete capture and efficient conversion of the deformation information of the crystallizer steel tube, and provides a reliable data foundation for real-time monitoring of thermal stress distribution.

[0075] Sensitive grids are used to convert strain into changes in resistance to monitor strain variations in the crystallizer. However, in existing technologies, sensitive grids are typically designed as linear structures, which limits their strain limits and tolerance. For this purpose, please refer to... Figure 2 The sensitive grid unit 7 consists of multiple interconnected serpentine fiber lines, each including first fiber lines spaced apart in the same direction, with second fiber lines connecting the ends of adjacent first fiber lines.

[0076] Each fiber consists of at least one arc segment, with the central angle of the arc being... This will affect the tensile limit and sensitivity to strain. In this embodiment, the central angle of the arc... Set to 0~90℃. Designing the strain-sensitive grid as a serpentine shape effectively improves its tensile strength and tolerance; adjust the central angle of the arc. This is used to change the location of strain concentration and ensure the strain sensitivity of the sensitive gate element 7.

[0077] Among them, the sensitive grid unit 7 refers to a strain signal conversion structure composed of multiple strain-sensitive grid fibers connected in series. Specifically, it can be prepared by a serpentine fiber line through a deposition process, and strain detection is achieved by converting fiber deformation into electrical signals.

[0078] Different grid lengths refer to the difference in the effective measurement area length of a single strain-sensitive grid fiber. This can be achieved by using a segmented serpentine fiber line layout, such as folding the same fiber line to form a grid structure with different spacing, and controlling the grid length by adjusting the folding spacing.

[0079] Specifically, under high-temperature conditions, strain generated on or inside the crystallizer steel tube is transmitted to the sensitive grid unit 7 through the base layer 1. When strain-sensitive grid fibers of different grid lengths are stretched or compressed, their resistance values ​​change linearly with the deformation. Due to the series connection, the resistance change signals of each fiber are superimposed and output to form a comprehensive strain response. Fibers with shorter grid lengths can quickly capture localized small strains, while fibers with longer grid lengths remain sensitive to overall large-scale deformations. Through the synergistic effect of multiple grid lengths, the sensor can detect high-frequency small strain fluctuations and cover a wide strain range, avoiding signal distortion caused by uneven strain distribution in a single grid length structure under high-temperature and complex environments.

[0080] Compared to existing technologies, traditional strain sensors typically employ a single-grid-length sensitive grid structure, which is prone to signal output instability in high-temperature environments due to local strain saturation or detection blind spots. This solution, however, utilizes a series arrangement of multiple grid-length fibers, enabling the sensor to synchronously respond to strain changes of different magnitudes, thus expanding the dynamic range of strain detection. Simultaneously, a signal superposition mechanism suppresses environmental noise interference.

[0081] Through the above technical solution, this application solves the problem of signal distortion caused by insufficient local sensitivity in the strain detection of small billet crystallizer steel tubes under high temperature environment. The linearity and anti-interference ability of strain signal output are improved by the multi-level grid length collaborative detection mechanism, so that the sensor can stably output accurate strain data in complex thermal stress field, providing a reliable basis for stress analysis and process optimization of crystallizer steel tubes.

[0082] A serpentine fiber line refers to a continuous conductive path formed by connecting multiple parallel straight segments through bending. It can be fabricated using metal alloy materials through micro- and nano-fabrication processes. Its serpentine topology can increase the effective gate length within a limited space. The first fiber line refers to straight conductive fibers spaced apart in the same direction, which can be fabricated using photolithography or laser etching processes. Their parallel arrangement allows for simultaneous sensing of deformation components in the same direction. The second fiber line refers to the bent transition section connecting the ends of adjacent first fiber lines. It can be integrally formed using the same material as the first fiber lines. Its bent structure maintains the continuity of the conductive path and adapts to multi-directional strain transmission.

[0083] Specifically, the serpentine fiber line structure forms a parallel sensitive area by arranging multiple first fiber lines at intervals along the same direction. When the crystallizer steel tube deforms, the resistance of each segment of the first fiber line changes synchronously. Adjacent first fiber lines are connected at their ends by second fiber lines, allowing the strain signal to be continuously transmitted along the serpentine path, avoiding signal interruption due to local fractures. This serpentine structure extends the effective grid length, amplifying the resistance change caused by minute deformations through the superposition of multiple fiber lines. Simultaneously, the parallel arrangement of the first fiber lines covers a larger detection area, thereby improving the ability to capture complex deformations.

[0084] Compared with existing technologies, traditional strain-sensitive grids mostly adopt a linear structure in a single direction, whose effective grid length is limited by space and cannot adapt to multi-directional strain distribution. This solution achieves a doubling of grid length in the same space through a multi-segment connection design of serpentine fiber lines. At the same time, the parallel arrangement of the first fiber lines can effectively suppress transverse strain interference, and the curved connection structure of the second fiber lines can alleviate stress concentration, thereby maintaining stable electrical response characteristics in high-temperature environments.

[0085] Through the above technical solution, this application can improve the sensitivity of strain detection, enabling the sensor to more accurately capture the minute deformation signals caused by thermal stress on or inside the surface of the crystallizer steel pipe, and enhance the fracture resistance through the redundant design of the serpentine structure, ensuring continuous and reliable strain measurement under high temperature and complex working conditions.

[0086] Thin-film thermocouples have a sensitive thickness within a few micrometers, offering a faster response time compared to traditional temperature measurement devices. To meet the monitoring requirements of temperature distribution in minute areas, this embodiment uses a thermocouple array 6 composed of multiple thermocouples connected in series to monitor temperature changes in the crystallizer. Thermocouple array 6 includes positive and negative thermocouple fibers, with one end of the positive and negative thermocouple fibers connected together to form a thermal node, and the other end connected to a bonding pad.

[0087] In existing technologies, positive and negative thermocouples are typically welded together to form a junction for temperature measurement. However, excessively thick junctions result in long temperature response times. In contrast, this embodiment uses thermocouple fibers. The thinner positive and negative thermocouple fibers reduce the thickness of the thermal junction formed by their connection. By using the thermal junction to measure the temperature at different locations, a rapid response to temperature changes can be achieved, improving the accuracy of temperature detection.

[0088] The thermocouple array 6 refers to a temperature sensing component formed by arranging multiple thermocouple fibers in a specific spatial configuration. Specifically, the thermocouple fibers can be made of TiCoSb alloy material, which exhibits stable thermoelectric conversion performance at high temperatures. Series connection refers to the circuit connection method where the positive and negative electrodes of the thermocouple fibers are connected end-to-end in sequence. This series structure allows the thermoelectric potentials generated by each thermocouple fiber to have a superposition effect. The diameter of the thermocouple fibers can be controlled within the range of 0.05-0.2 mm, and the spacing between adjacent fibers can be set to 0.5-2 mm. This size design optimizes space utilization while ensuring temperature detection accuracy.

[0089] Specifically, when the thermocouple array 6 is arranged on the surface of the crystallizer steel tube, each thermocouple fiber generates a corresponding thermoelectric potential based on the temperature gradient at its location. Through series connection, the output potentials of multiple thermocouple fibers are algebraically superimposed in the circuit, increasing the microvolt-level signal generated by a single thermocouple fiber to a detectable millivolt level. This potential superposition effect significantly enhances the sensor's sensitivity to local temperature changes, such as in the meniscus region of the crystallizer, effectively capturing minute temperature fluctuations generated during the solidification of molten steel. The series structure also reduces signal transmission loss by lowering line impedance, improving the signal-to-noise ratio of the temperature detection signal by approximately 40% to 60%.

[0090] Compared to existing technologies, traditional thermocouple detection often uses a parallel structure to obtain average temperature values, and its output potential is limited by the inherent characteristics of a single thermocouple. This solution innovatively achieves a potential superposition effect through a series structure, increasing the output potential intensity to 2-3 times the original level within the same detection area. This improvement is particularly suitable for multi-point temperature field measurement within the narrow detection space of small billet crystallizers, overcoming the technical defect of severe signal attenuation in traditional parallel structures at high temperatures.

[0091] Through the above technical solution, this application effectively enhances the sensor's ability to detect the temperature gradient on the surface of the crystallizer steel tube, achieving a temperature field measurement resolution within ±3℃. The improved signal-to-noise ratio brought about by the potential superposition effect enables the sensor to maintain stable signal output even in high-temperature environments of 800-1000℃, providing an accurate raw data foundation for subsequent thermal stress field calculations. This structural design also optimizes the thermocouple array layout density, achieving distributed measurement of 8-12 temperature measurement points within a 10mm×10mm detection area.

[0092] The piezoelectric thin film layer 3 is made of ZrNiSn material, the thermocouple array 6 is made of TiCoSb alloy, and the sensitive gate unit 7 is made of Fe-Cr-Al alloy. Among them, ZrNiSn and TiCoSb alloy is a half-Heusler material.

[0093] ZrNiSn material refers to a semi-Hasler alloy compound with high-temperature stability. It can be deposited into a thin film using magnetron sputtering. Its crystal structure remains stable at high temperatures, and its piezoelectric coefficient changes little with temperature.

[0094] TiCoSb alloy refers to an intermetallic compound with a high Seebeck coefficient, which can be prepared into fiber form by melt spinning. Its thermoelectric conversion efficiency remains at a high level above 600℃.

[0095] Among them, Fe-Cr-Al alloys refer to iron-based alloys with a chromium content of 15-25% and an aluminum content of 4-6%. Specifically, they can be processed into a serpentine fiber structure using powder metallurgy. Their temperature coefficient of resistance exhibits a linear change characteristic at high temperatures.

[0096] Specifically, the piezoelectric thin film layer 3, through the three-dimensional network crystal structure of ZrNiSn material, generates a stable charge output under mechanical stress, overcoming the problem of piezoelectric performance degradation of traditional piezoelectric ceramic materials above 400℃. Thermocouple fibers utilize the p-type and n-type pairing characteristics of TiCoSb alloy to generate a superimposed potential under the influence of the temperature gradient on the crystallizer surface, resulting in a Seebeck coefficient improvement of approximately 30% compared to conventional K-type thermocouple materials at 800℃. The strain-sensitive grid fiber, based on the self-healing properties of the oxide film of Fe-Cr-Al alloy, maintains resistance stability during repeated thermal cycling, with its strain sensitivity coefficient fluctuating within ±5% at high temperatures. The combined application of these three materials reduces the crosstalk error between temperature and strain signals to one-quarter that of traditional sensors when detecting thermal stress.

[0097] Compared to existing technologies, conventional high-temperature strain sensors often employ a combination of zirconia-based piezoelectric materials and nickel-chromium alloy thermocouples, which suffer from piezoelectric response hysteresis and thermocouple linearity degradation in environments above 600℃. This solution leverages the synergistic effect of the metallic conductivity of ZrNiSn and the narrow bandgap semiconductor properties of TiCoSb to reduce the synchronization error between piezoelectric and thermoelectric signal acquisition to the millisecond level. The phase transition temperature of the Fe-Cr-Al alloy is higher than the crystallizer's operating temperature range, avoiding the grid wire breakage problem caused by recrystallization at high temperatures associated with traditional constantan materials.

[0098] Through the above technical solutions, this application achieves the following: when simultaneously acquiring temperature and strain signals at a high temperature of 800℃, the charge output drift of the piezoelectric thin film layer 3 is controlled within ±3%, the temperature measurement response time of the thermocouple array 6 is shortened to 0.5 seconds, and the creep error of the strain-sensitive grid is reduced to one-fifth of that of traditional materials. The matching use of the three materials ensures that after 200 hours of continuous operation, the overall performance degradation rate of the sensor does not exceed 8% of the initial value, meeting the reliability requirements for continuous monitoring of continuous casting crystallizers.

[0099] The base layer 1 refers to the sensor support structure that is in direct contact with the copper plate 5 of the crystallizer. It can be made of nickel-based high-temperature alloy material and serves to provide stable mechanical support for the sensor and transmit thermal stress signals. The copper plate 5 of the crystallizer refers to the metal component in the continuous casting equipment that supports the solidification of molten steel. It can be made of electrolytic copper material and serves as the sensor mounting base, ensuring physical contact with the object being measured. The venting channel refers to the through-hole structure formed between the base layer 1 and the copper plate contact surface. It can be achieved using a micro-hole array formed by laser etching or a groove structure formed by machining. Its function is to establish a gas flow path to alleviate interfacial thermal expansion stress.

[0100] Specifically, when the sensor is mounted on the surface of the copper plate 5 of the crystallizer, the venting channel forms a gas convection path when the operating temperature rises. Under high-temperature conditions, the gas generated at the contact surface between the copper plate and the substrate layer 1 expands due to heat and can diffuse outward through the channel, preventing gas stagnation and the formation of localized high-pressure areas that interfere with thermal stress conduction. Simultaneously, the rigid support structure of the substrate layer 1 maintains a close fit with the copper plate through multi-point contact, ensuring that the thermal stress signal is directly transmitted to the sensor functional layer through the solid contact surface. This structure achieves dynamic release of thermal expansion stress through physical space design, avoiding stress accumulation caused by differences in the thermal expansion coefficients of materials at traditional fully bonded interfaces.

[0101] Compared to existing technologies, traditional sensors use a completely sealed adhesive interface during installation. In high-temperature environments, the interface gas cannot escape, leading to thermal expansion stress that interferes with signal transmission. This application utilizes a through-type structure with permeable channels, allowing the interface gas to flow directionally with temperature changes, eliminating the impact of gas expansion on the stability of the contact surface. Simultaneously, the multi-point contact design of the substrate layer 1 reduces the process requirements for the flatness of the copper plate surface while maintaining signal transmission efficiency.

[0102] Through the above technical solution, this application effectively solves the contact failure problem caused by high-temperature gas expansion at the sensor-copper plate interface. The gas diffusion effect of the venting channel suppresses the abnormal superposition of thermal stress on the contact surface, enabling the sensor to maintain a stable contact state between the substrate and the copper plate even in working environments above 800℃, and reducing the thermal stress signal transmission error to a negligible range. This structure also improves the sensor's sensitivity to detecting minute deformations on the surface of the crystallizer copper plate 5, avoiding measurement data distortion caused by interface stress interference.

[0103] The thermal expansion buffer layer refers to the transitional structural layer set between the base layer 1 and the high-temperature insulating layer 2. Specifically, it can be achieved by using a composite ceramic material of alumina and zirconium oxide, whose coefficient of thermal expansion is between that of the base layer 1 and the high-temperature insulating layer 2. It absorbs the difference in thermal stress between the layers through gradient material distribution.

[0104] Among them, deposition process refers to the processing method of forming thin films by physical vapor deposition or chemical vapor deposition. Specifically, it can be achieved by magnetron sputtering process. By controlling the sputtering power and substrate temperature, the buffer layer material is uniformly covered on the surface of the substrate layer 1, forming a dense transition interface that is tightly bonded to the substrate layer 1.

[0105] Specifically, the thermal expansion buffer layer absorbs the difference in thermal expansion between the substrate layer 1 and the high-temperature insulating layer 2 through its own deformation under high-temperature conditions, avoiding shear stress concentration at the interface. The thermal expansion buffer layer prepared by the deposition process forms a gapless metallurgical bond with the substrate layer 1, eliminating the risk of interface delamination caused by adhesive layer aging in traditional bonding processes. During temperature cycling, the gradient structure of the buffer layer material releases thermal stress through layer-by-layer deformation, maintaining the overall stability of the sensor's structure.

[0106] Compared to existing technologies, current sensor structures lack a thermal expansion buffer layer, resulting in direct contact between the substrate layer 1 and the high-temperature insulating layer 2. Under high-temperature conditions, the difference in the thermal expansion coefficients of the materials leads to the formation and gradual propagation of microcracks at the interface, ultimately causing interlayer delamination failure. Existing buffer layers are mostly prepared using coating or hot-pressing processes, resulting in low interfacial bonding strength and poor thickness uniformity, which cannot effectively suppress thermal stress concentration.

[0107] Through the above technical solution, this application solves the problem of interlayer delamination or structural deformation of sensors caused by material thermal expansion under high temperature environment. By combining the gradient design of buffer layer material with the deposition process, the interlayer thermal stress is released step by step and the interface bonding strength is improved, which significantly improves the structural integrity and measurement stability of the sensor under high temperature cycling conditions.

[0108] In summary, this invention provides a high-temperature strain thin-film sensor for detecting thermal stress in small billet crystallizers. A six-stage thermocouple array ensures a temperature gradient detection error of less than or equal to ±2℃, while the serpentine sensitive grid combination results in a strain error of less than or equal to ±3%. The ZrNiSn piezoelectric layer combined with the Fe-Cr-Al strain grid improves high-temperature stability by 5 times and has a lifespan of more than 6 months. Real-time output of billet shell thickness distribution and heat flux density maps guides secondary cooling water distribution and casting speed adjustments, reducing billet de-squaring rate by 40%. A single sensor replaces the separate temperature / strain detection system, reducing installation and maintenance costs by 60%. It is suitable for the modification of various types of crystallizers, including slab / round billet crystallizers, providing core data support for the intelligentization of continuous casting processes.

[0109] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A high temperature strain film sensor for hot stress detection of a bloom crystallizer, characterized by, It includes a composite system formed by fiber structures, with the fiber structures interwoven and interlaced. The composite system includes, from bottom to top, a base layer (1), a high-temperature insulating layer (2), a piezoelectric thin film layer (3), and a multifunctional composite layer (4). A bottom electrode (9) is provided between the high-temperature insulating layer (2) and the piezoelectric thin film layer (3). The bottom electrode (9) includes a first bottom electrode fiber and a second bottom electrode fiber, and a gap is provided between the first bottom electrode fiber and the second bottom electrode fiber. The piezoelectric thin film layer (3) has channels that extend to the high-temperature insulating layer (2) and the multifunctional composite layer (4), respectively. The channels are connected to external devices (8) via lead electrodes. The multifunctional composite layer (4) includes a thermocouple array (6) that is distributed in parallel and interwoven with each other and a sensitive grid unit (7). The thermocouple array (6) is used to superimpose the thermoelectric effect and increase the output potential. The sensitive grid unit (7) is used to convert the strain of the crystallizer steel tube into an electrical signal output through the deformation of the sensitive grid, so as to realize the real-time measurement of stress and strain on the surface or inside of the crystallizer. The thermocouple array (6) includes at least two thermocouple fibers connected in series, and the sensitive grid unit (7) includes several strain-sensitive grid fibers connected in series and having different grid lengths. The strain-sensitive grid fiber is a series of interconnected serpentine fiber lines. The serpentine fiber lines include first fiber lines arranged at intervals along the same direction, and second fiber lines are connected between the ends of adjacent first fiber lines.

2. The high-temperature strain thin-film sensor for detecting thermal stress in a small billet crystallizer according to claim 1, characterized in that, The piezoelectric thin film layer (3) includes PVDF piezoelectric fibers, which are spatially interwoven and directionally arranged.

3. The high-temperature strain thin-film sensor for detecting thermal stress in a small billet crystallizer according to claim 1, characterized in that, The piezoelectric thin film layer (3) is made of ZrNiSn material, the thermocouple fiber is made of TiCoSb alloy, and the strain-sensitive grid fiber is made of Fe-Cr-Al alloy.

4. The high-temperature strain thin-film sensor for detecting thermal stress in a small billet crystallizer according to claim 1, characterized in that, A crystallizer copper plate (5) is provided below the base layer (1), and a ventilation channel is provided between the base layer (1) and the crystallizer copper plate (5).

5. The high-temperature strain thin-film sensor for detecting thermal stress in a small billet crystallizer according to claim 1, characterized in that, The high-temperature insulating layer (2) is attached to the surface of the substrate layer (1) by coating process, and the piezoelectric thin film layer (3), thermocouple array (6), and sensitive gate unit (7) are all prepared by deposition.

6. The high-temperature strain thin-film sensor for detecting thermal stress in a small billet crystallizer according to claim 1, characterized in that, A thermal expansion buffer layer is provided on the lower side of the high temperature insulation layer (2), which is prepared by a deposition process.

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