Preparation method of bolt type piezoelectric high-temperature transducer

Abstract

The application discloses a preparation method of a bolt type piezoelectric high-temperature transducer, and belongs to the field of nondestructive testing. The silver coupling layer is prepared through the steel screen printing technology based on the pressure-free nanosilver low-temperature sintering technology. The high-temperature piezoelectric wafer is coupled / adhered to the mounting end face of the bolt through the silver coupling layer. The point gluing method is adopted to adhere the sheet electrode to the upper end face and the mounting end face of the piezoelectric wafer. The two end faces of the piezoelectric wafer, the mounting end face of the bolt and the sheet electrode are integrally plated with silver to guarantee the solderability. The excellent coupling performance of the silver coupling layer and the excellent bonding strength of the silver solder joint guarantee the reliability of the transducer working at 350 DEG C, and realize the long-term stable continuous real-time monitoring in the high-temperature environment.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing and relates to a real-time monitoring bolt-type piezoelectric high-temperature transducer and its preparation method. Background Technology

[0002] Pressure vessels, pipelines, and other pressure-bearing special equipment are widely used in pillar industries of the national economy such as petrochemicals, power, and metallurgy, and mostly operate in harsh environments with high temperatures and pressures. Safety accidents caused by bolt failures and loosening of pressure-bearing special equipment are numerous; therefore, long-term, stable, real-time monitoring of bolt preload under high-temperature environments is extremely urgent. Contact ultrasonic testing is a commonly used technique in industrial non-destructive testing. With the development of technology, the requirements for ultrasonic testing in industry are becoming increasingly stringent. To monitor the integrity of critical components and process parameters in power plants and petrochemical plants, ultrasonic transducers are typically installed in high-temperature environments for extended periods to allow for continuous online monitoring.

[0003] On July 20, 2021, Chinese Patent No. CN213749751U disclosed a high-temperature transducer probe, including a first structural component, a second structural component below the first structural component, and a piezoelectric ceramic sheet assembly movably connected between the first and second structural components. An amplitude transformer body is mounted at the bottom of the second structural component. Copper sheets are mounted on both sides of the piezoelectric ceramic sheet assembly. A fixing plate is welded to the outer ring of the first structural component, and two through holes are formed on the fixing plate. Limiting grooves are formed on both the front and back shell walls of the second structural component, and sleeves are movably connected in the limiting grooves. This patent, through the combination of various structures, protects the connection points of the wires, replacing the traditional single adhesive. This not only avoids exposure of the connection points, enhancing the safety of the equipment, but also prevents damage to the connection points due to external forces, extending the service life of the equipment.

[0004] On November 1, 2022, Chinese Patent Application Publication No. CN115266950A disclosed an electromagnetic ultrasonic transducer with high transduction efficiency and stable low water flow impact signal at high temperature. The transducer includes a hollow cylinder, a glass plate, a coil, a permanent magnet, a ring-shaped body, an inner bottom plate with an L-shaped longitudinal section, and an outer bottom plate fitted over the inner bottom plate. The inner bottom plate is installed at the bottom of the hollow cylinder. The glass plate is embedded between the hollow cylinder and the inner bottom plate, sealing the bottom end of the hollow cylinder. The coil is fixed below the glass plate and extends into the inner bottom plate. The annular body is located on the glass plate and is closely attached to the hollow cylinder. The bottom of the permanent magnet is tightly inserted into the annular body. The bottom of the annular body extends inward to form a support platform for the permanent magnet. The annular body has an inlet groove and an outlet groove. The inlet groove is a notch groove that extends upward from the bottom of the annular body to a height higher than the support platform. The outlet groove is a notch groove that extends downward from the top of the annular body to a height lower than the support platform. The inlet groove is connected to a cooling medium inlet on the hollow cylinder. The hollow cylinder also has a cooling medium outlet.

[0005] On May 16, 2023, Chinese Patent CN219024904U disclosed a high-temperature ultrasonic transducer, including a ruggedized module, a liquid waveguide module, and a piezoelectric module. The ruggedized module is disposed at one end of the liquid waveguide module and is in contact with a high-temperature fluid. The end of the liquid waveguide module facing away from the ruggedized module is fixedly connected to the piezoelectric module. This patent overcomes the weakness of the liquid waveguide module's front wall structure, which is prone to deformation and breakage under continuous high-temperature environments, by using the ruggedized module as the detection front end in contact with the high-temperature fluid. The patent has a simple structure, stable performance, and can well meet the performance requirements of high-temperature ultrasonic transducers for practical high-temperature fluid velocity measurement.

[0006] The transducers mentioned above, and even those in current patents, can operate in high-temperature environments; however, they suffer from the following problems:

[0007] 1) Low operating temperature. Most currently disclosed patents use organic materials (such as epoxy resin, machine oil, etc.) for coupling and solder joints. The melting point of solder joints is only 200℃, not to mention organic coupling agents. However, most pressure-bearing equipment operates at a temperature of 350℃, which traditional transducers simply cannot meet.

[0008] 2) Short operating time in high-temperature environments. Due to the long working cycle and service life of pressure-bearing equipment, some pressure-bearing equipment even has a service life measured in years. Traditional transducer instruments are precision instruments with fragile structures, making it impossible to achieve long-term stable monitoring. They can only be used for instantaneous measurement.

[0009] 3) Poor specificity and adaptability. Bolts number in the thousands in equipment and are known as the "mother of industry". However, current transducer structures vary, and even short-term, room-temperature measurements of bolts face problems such as size mismatch and unstable installation, let alone long-term, stable, real-time monitoring at high temperatures. Summary of the Invention

[0010] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for preparing a real-time monitoring bolt-type piezoelectric high-temperature transducer, which addresses the shortcomings of the prior art.

[0011] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0012] A real-time monitoring bolt-type piezoelectric high-temperature transducer includes an upper electrode, a lower electrode, a piezoelectric wafer, a silver coupling layer, and a bolt. The upper electrode is fixed above the piezoelectric wafer by a first solder joint, the piezoelectric wafer is fixed to the mounting end face of the bolt by the silver coupling layer, and the lower electrode is fixed to the mounting end face of the bolt by a second solder joint.

[0013] Furthermore, both the upper and lower electrodes are made of high-temperature resistant sheet material, plated entirely with silver or gold, preferably entirely with silver. The high-temperature resistant sheet material is preferably Kovar alloy.

[0014] Furthermore, both the first and second solder joints are pressureless sintered nano-silver solder joints.

[0015] Furthermore, the piezoelectric wafer is a high-temperature resistant piezoelectric wafer, preferably a LiNbO3 piezoelectric wafer cut at a 36° rotation along the y-direction.

[0016] Furthermore, both sides of the piezoelectric wafer are plated with either silver or gold, preferably silver.

[0017] Furthermore, the thickness of the silver coupling layer is less than 50 micrometers, preferably 30 micrometers.

[0018] Furthermore, the mounting end face of the bolt is plated with either silver or gold, preferably silver.

[0019] Furthermore, the silver coupling layer is prepared by SMT (Surface Mount Technology) stencil printing.

[0020] Furthermore, the silver coupling layer is prepared by sintering pressureless nano-silver paste.

[0021] This invention discloses a method for preparing a real-time monitoring bolt-type piezoelectric high-temperature transducer, comprising the following steps:

[0022] Step 1: Place an SMT stencil of a certain thickness above the mounting end face of the bolt.

[0023] Step 2: Squeeze an appropriate amount of pressureless nano silver paste into the steel mesh and smooth it with a scraper.

[0024] Step 3: Gently lift the stencil to obtain a paste-like nano-silver layer silver coupling layer of the same thickness as the SMT stencil.

[0025] Step 4: Surface mount the piezoelectric wafer on top of the silver coupling layer.

[0026] Step 5: Apply pressure-free nano-silver paste to the first solder joint on the upper surface of the piezoelectric wafer; apply pressure-free nano-silver paste to the second solder joint on the mounting surface of the bolt.

[0027] Step 6: Attach the upper electrode and the lower electrode to the first solder joint position and the second solder joint position respectively in Step 5.

[0028] Step 7: Place the entire transducer into an oven for sintering at a temperature of 350℃ for 50 minutes.

[0029] Beneficial effects:

[0030] 1. This invention uses a high-temperature resistant piezoelectric crystal as the excitation end, realizing ultrasonic excitation in a high-temperature environment. It employs a high-temperature resistant sheet material with overall silver plating as the electrode, achieving stable data transmission in high-temperature environments and improving the reliability of the transducer in such conditions.

[0031] 2. This invention combines high-temperature resistant materials with pressureless nano-silver sintering technology. The nano-silver coupling layer and nano-silver solder joints ensure the overall bonding of the transducer and its reliability under long-term high-temperature conditions. This achieves long-term stable, continuous, real-time monitoring under high-temperature environments.

[0032] 3. This invention is based on pressureless nano silver paste. By combining SMT stencil printing with dispensing process, it achieves one-time sintering molding of transducers without relying on equipment such as hot presses. This greatly shortens the manufacturing cycle of transducers, reduces manufacturing time and labor costs, and significantly improves manufacturing efficiency. Attached Figure Description

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0034] Figure 1 This is a schematic diagram of the system structure of the piezoelectric high-temperature transducer of the present invention.

[0035] The labels in the diagram are as follows: 1. Upper electrode, 2. First solder joint, 3. Lower electrode, 4. Second solder joint, 5. Piezoelectric wafer, 6. Silver coupling layer, 7. Bolt.

[0036] Figure 2 This diagram illustrates the fabrication steps of the piezoelectric high-temperature transducer of the present invention.

[0037] Figure 3This is an experimental diagram of a bolt-type piezoelectric transducer testing system.

[0038] Figure 4 This is a schematic diagram of the connection of a bolt-type piezoelectric transducer testing system.

[0039] Figure 5 This is the output signal of a bolt-type piezoelectric transducer at room temperature.

[0040] Figure 6 This is the output signal of a bolt-type piezoelectric transducer after being kept at 350℃ for 50 hours.

[0041] Figure 7 This is the signal from a conventional ultrasonic transducer damaged by high temperature. Detailed Implementation

[0042] Example 1:

[0043] Figure 1 This is a schematic diagram of the system structure of the piezoelectric high-temperature transducer of the present invention. It includes an upper electrode 1, a first solder joint 2, a lower electrode 3, a second solder joint 4, a piezoelectric wafer 5, a silver coupling layer 6, and a bolt 7. The upper electrode 1 is fixed above the piezoelectric wafer 5 via the first solder joint 2. The piezoelectric wafer 5 is fixed to the mounting end face of the bolt 7 via the silver coupling layer 6. The lower electrode 3 is fixed to the mounting end face of the bolt 7 via the second solder joint 4.

[0044] Figure 2 This diagram illustrates the fabrication steps of the piezoelectric high-temperature transducer of the present invention. In the following embodiments, the piezoelectric wafer is a LiNbO3 piezoelectric wafer cut with a 36° rotation along the y-axis; the upper and lower electrodes are Kovar alloy electrodes; the bolts are 316L bolts; the mounting end face of the bolts (316L), the upper and lower end faces of the LiNbO3 piezoelectric wafer, and the entire Kovar alloy electrode all require silver / gold plating to ensure solderability. The detailed steps are described below:

[0045] Step 1: Place the 30-micron thick SMT stencil above the mounting end face of bolt (316L) 7.

[0046] Step 2: Squeeze an appropriate amount of pressureless nano silver paste into the steel mesh and smooth it with a scraper.

[0047] Step 3: Gently lift the steel mesh to obtain a 30-micron-thick paste-like nano-silver layer silver coupling layer 6.

[0048] Step 4: Surface mount the LiNbO3 piezoelectric wafer 5 onto the silver coupling layer 6.

[0049] Step 5: Apply pressure-free nano-silver paste to the first solder joint 2 on the upper end face of the LiNbO3 piezoelectric wafer 5; apply pressure-free nano-silver paste to the second solder joint 4 on the mounting end face of the bolt 7.

[0050] Step 6: Surface mount the upper electrode 1 (Kovar alloy) and the lower electrode 3 (Kovar alloy) to the first solder joint 2 and the second solder joint 4 positions respectively in Step 5.

[0051] Step 7: Place the entire transducer into an oven for sintering at a temperature of 350℃ for 50 minutes. The transducer is now ready.

[0052] This invention presents a method for preparing a real-time monitoring bolt-type piezoelectric high-temperature transducer. Compared with traditional transducers, its biggest advantages and features are as follows: (1) High service temperature and long service time. This paper uses pressureless sintered nano-silver as the coupling layer / adhesive layer and solder joint of the transducer; LiNbO3 piezoelectric wafers cut in the y-direction at 36° rotation are used as excitation elements; and sheet-like Kovar alloys are used as wires. The melting point of silver is about 962℃, the Curie temperature of LiNbO3 is 1210℃, and the melting point of Kovar alloys is 1450℃. The overall sintering temperature of the transducer reaches 350℃, and theoretically it can withstand a high temperature of 600℃. (2) Long-term stable continuous real-time monitoring under high temperature environment is achieved. The piezoelectric wafer is directly sintered on top of the bolt, ensuring the shear strength and acoustic performance between the piezoelectric wafer and the bolt during long-term monitoring. (3) The preparation method proposed in this invention is relatively simple to operate and does not rely on equipment such as hot presses. It can achieve one-time sintering molding, which further improves the practicality and applicability of the device. Based on acoustic impedance calculations and analysis, this method is applicable to coupling between most piezoelectric wafers and steel-based media. It provides technical support for the stable and safe operation of pressure vessels, pipelines, and other pressure-bearing special equipment.

[0053] Example 2:

[0054] The prepared bolt-type transducer was connected to the testing system for experiments to test its stable detection capability under high-temperature conditions. Figure 3 and Figure 4 As shown, Figure 3 The transducer, as described in this invention, is placed vertically in the middle. The upper and lower electrodes of the transducer are connected to the two pins of the duplexer. No preload is applied to the bolts here. The duplexer is connected to a digital oscilloscope and a power amplifier. The power amplifier and the digital oscilloscope are also connected to a function generator. A five-cycle Hanning window pulse is excited by the function generator. With the power amplifier's amplification factor set to 0.8%, the signal can be obtained on the oscilloscope as shown below. Figure 5 The sound wave signal shown. Figure 5 This is a waveform diagram of the transducer of the present invention at room temperature.

[0055] The transducer was placed in a high-temperature furnace and heated at 350°C for 50 hours; the acoustic signal was as follows. Figure 6 As shown. To highlight the advantages of the present invention, Figure 7This is a signal from a conventional ultrasonic transducer damaged by high temperature. The clarity of the acoustic signal received by the transducer directly determines its measurement accuracy and performance. The transducer's output is calculated based on the time interval between echo packets (i.e., transit time of flight). Therefore, during measurements (even in harsh environments such as high temperatures), the clearer the echo signal, the more regular the echo waveform, and the more pronounced the intervals between echoes, the more accurate the transducer's calculation results and the higher its precision. (Comparison) Figure 5 , 6 From 7, we can know that Figure 5 , 6 The signal shown is clear, the waveform is undistorted, and there is no overlap or interference between the wave packets, demonstrating that the fabricated transducer possesses the ability to provide stable monitoring over long periods at high temperatures. (A counterexample is provided.) Figure 7 As shown, Figure 7 In a conventional transducer operating at high temperatures, the waveform becomes severely distorted, with overlapping and warped waveform packets. At this point, it becomes impossible to distinguish between the primary and secondary echoes, let alone calculate the Time-of-Flight (TOF) between the echoes, rendering the transducer inoperable.

[0056] according to Figure 5 and Figure 6 The transit time (TOF) can be calculated from the signal, where the transit time is the time difference between two adjacent wave packets. Figure 5 As shown. The preload of a bolt can be quantitatively characterized by its TOF. Assuming the transit time of the preloaded bolt is TOF1 and the transit time of the bolt under test is TOF2, when TOF1 < TOF2, the bolt is in a loose state.

[0057] This invention provides a method and approach for fabricating a real-time monitoring bolt-type piezoelectric high-temperature transducer. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A real-time monitoring bolt-type piezoelectric high-temperature transducer, characterized in that, It includes an upper electrode (1), a lower electrode (3), a piezoelectric wafer (5), a silver coupling layer (6), and a bolt (7); the upper electrode (1) is fixed above the piezoelectric wafer (5) by a first solder joint (2), the piezoelectric wafer (5) is fixed to the mounting end face of the bolt (7) by the silver coupling layer (6), and the lower electrode (3) is fixed to the mounting end face of the bolt (7) by a second solder joint (4); The upper electrode (1) and the lower electrode (3) are both high-temperature resistant sheet materials, and are plated with either silver or gold. The high-temperature resistant sheet material is Kovar alloy; The first solder joint (2) and the second solder joint (4) are both pressureless sintered nano-silver solder joints; The silver coupling layer is prepared by pressureless sintering of nano-silver paste; The piezoelectric wafer (5) is plated with either silver or gold on both sides; The mounting end face of the bolt (7) is plated with either silver or gold.

2. The real-time monitoring bolt-type piezoelectric high-temperature transducer according to claim 1, characterized in that, The piezoelectric wafer (5) is a high-temperature resistant piezoelectric wafer.

3. A real-time monitoring bolt-type piezoelectric high-temperature transducer according to claim 1 or 2, characterized in that, The piezoelectric wafer (5) is a LiNbO3 piezoelectric wafer cut by rotating 36° in the y direction.

4. A real-time monitoring bolt-type piezoelectric high-temperature transducer according to claim 1, characterized in that, The silver coupling layer (6) has a thickness of less than 50 micrometers.

5. The method for preparing the real-time monitoring bolt-type piezoelectric high-temperature transducer according to claim 1, characterized in that, It has the following steps: Step 1: Place an SMT stencil of a certain thickness above the mounting end face of the bolt (7); Step 2: Press the pressureless nano silver paste into the SMT stencil holes and smooth it with a scraper; Step 3: Gently lift the stencil to obtain a paste-like nano-silver layer silver coupling layer (6) of the same thickness as the SMT stencil. Step 4: Surface mount the piezoelectric wafer (5) on top of the silver coupling layer (6); Step 5: Apply pressure-free nano silver paste to the first solder joint (2) on the upper end face of the piezoelectric wafer (5); apply pressure-free nano silver paste to the second solder joint (4) on the mounting end face of the bolt (7); Step 6: Attach the upper electrode (1) and the lower electrode (3) to the positions of the first solder joint (2) and the second solder joint (4) in Step 5, respectively; Step 7: Place the entire transducer into an oven for sintering at a temperature of 350℃ for 50 minutes.

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