An ultrasonic-based internal thread outer nut and its preload measurement method

Abstract

The present invention provides an ultrasonic-based internally threaded outer nut and a method for measuring its preload, which is implemented by an ultrasonic-based internally threaded outer nut. The ultrasonic-based internally threaded outer nut includes an outer nut base, a hexagonal end face above the outer nut base, and a sensor prepared by magnetron sputtering above the hexagonal end face. The sensor has the same life cycle as the fastener. The sensor includes an electrode layer, an insulating layer, and a piezoelectric layer. The insulating layer is installed at the bottom of the electrode layer, and the piezoelectric layer is installed at the bottom of the insulating layer. A threaded end is provided inside the outer nut base, and a probe is detachably installed above the sensor. The beneficial effects of the present invention are as follows: the present invention can realize in-situ direct monitoring of the preload during the service of the outer nut. Currently, the present invention has been delivered and applied, with a measurement accuracy within ±5%. Taking this invention as an example, the design and preparation of internally threaded fastener sensors can be promoted to realize preload status monitoring of fastening connection systems and improve system connection reliability.

Description

Technical Field

[0001] The invention belongs to the field of fasteners, and in particular relates to an ultrasonic-based internally threaded outer sleeve nut and a pre-tightening force measurement method thereof. Background Art

[0002] Fastening is a common connection technology used in large-scale equipment. It features simple construction, easy installation and disassembly, high connection strength, and excellent reliability. In hydraulic systems, outer nuts are components that connect pipelines or mount pipelines to hydraulic components, allowing for easy assembly and disassembly within the fluid path. The junction between the outer nut and the pipe fitting is one of the most vulnerable links affecting system structural reliability. This is particularly true given the complex and variable operating conditions faced by large-scale equipment. This can easily reduce system structural stiffness, compromise structural integrity, increase vibration, and increase energy dissipation, thereby impacting the outer nut's performance and safety. Traditional methods for measuring the preload force of fastening connections include torque wrenches, strain gauges, and piezoelectric plates. However, most methods suffer from poor control accuracy and low measurement efficiency, and are limited to externally threaded fasteners. No suitable method exists for monitoring the preload force of internally threaded fasteners. Therefore, a design for an internally threaded outer nut structure for fasteners that enables preload force measurement of outer nuts is crucial for monitoring the preload condition of nut-type fasteners and overall structural health. Summary of the Invention

[0003] In view of this, the present invention aims to propose an ultrasonic-based internally threaded outer sleeve nut and a pre-tightening force measurement method thereof to solve at least one problem existing in the above-mentioned prior art.

[0004] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0005] In the first aspect, the present invention provides an ultrasonic-based internally threaded outer sleeve nut, comprising an outer sleeve nut base, the outer sleeve nut base being an annular structure, the upper portion of the outer sleeve nut base being a hexagonal end face, the upper portion of the hexagonal end face being prepared by a magnetron sputtering method to produce a sensor, the sensor having the same life cycle as the fastener, the sensor comprising an electrode layer, an insulating layer and a piezoelectric layer, the insulating layer being installed at the bottom of the electrode layer, the piezoelectric layer being installed at the bottom of the insulating layer, a threaded end being provided inside the outer sleeve nut base, the wall thickness of the outer sleeve nut base being defined as the outer sleeve nut wall thickness, a probe being detachably installed above the sensor, and an insulating ring being installed above the outer sleeve insulating layer.

[0006] Furthermore, the threaded end is a thin-walled structure, and the thickness of a single side wall is not greater than 4 mm.

[0007] Furthermore, the width of the hexagonal end face is greater than 6 mm.

[0008] Furthermore, the size of the electrode layer should not be larger than the wall thickness of the outer nut.

[0009] Furthermore, the total thickness of the sensor is less than 50 μm.

[0010] In a second aspect, based on the same concept, the present invention further provides a method for measuring the preload force of an internally threaded outer sleeve nut based on ultrasound, comprising the following steps:

[0011] The probe generates an electrical signal;

[0012] Exciting the piezoelectric layer converts the electrical signal into an ultrasonic signal;

[0013] The ultrasonic signal propagates from the sensor end face to the other end face along the outer nut base, and is received by the probe by the reflected ultrasonic signal, forming a closed loop;

[0014] The internal stress of the outer nut is calculated according to the calibrated temperature factor-load factor-ultrasonic time-force value function relationship, and the pre-tightening force value of the outer nut after loading is measured.

[0015] Furthermore, the measuring method further includes a sensor preparation method when measuring the internal thread outer shell nut, and the sensor preparation method includes the following steps:

[0016] The first step is to process the hexagonal end face into a mirror state with a roughness of less than 0.8μm. The non-pre-processed area of ​​the outer nut is wrapped with a high-temperature resistant material, placed in a furnace chamber evacuated to a vacuum state, and then etched.

[0017] The second step is to sputter the piezoelectric layer to produce the piezoelectric effect;

[0018] The third step is to sputter an insulating layer on the basis of the piezoelectric layer to insulate and protect the piezoelectric layer;

[0019] The fourth step is to design the size of the insulating ring according to the wall thickness of the outer nut and the size of the hexagonal end face, fit the insulating ring to the insulating layer, and sputter the electrode layer to protect the insulating layer and the piezoelectric layer.

[0020] Furthermore, the sensor is equally divided into 6 arcs, each arc has an angle of 60°, and each arc corresponds to a hexagonal end face.

[0021] Furthermore, the size of the insulating ring is the same as the size of the hexagonal end face, and six annular structures are cut out from the inside of the insulating ring according to the corresponding six sides, and the size of the six annular structures is the same as the size of the electrode layer.

[0022] Compared with the prior art, the ultrasonic-based internally threaded outer nut and preload measurement method thereof described in the present invention have the following advantages:

[0023] The present invention describes an ultrasonic-based internally threaded outer sleeve nut and a pre-tightening force measurement method thereof. The present invention can realize in-situ direct monitoring of the pre-tightening force of the outer sleeve nut during service. Currently, the present invention has been delivered and applied, with a measurement accuracy within ±5%. Taking this invention as an example, the design and preparation of internally threaded fastener sensors can be promoted to realize pre-tightening force status monitoring of the fastening connection system and improve the system connection reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0025] Figure 1 Schematic diagram of an internally threaded outer nut based on ultrasound according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the hierarchical structure of an internally threaded outer nut based on ultrasound according to an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the insulating ring structure according to an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of the operation of an internally threaded outer sleeve nut based on ultrasound according to an embodiment of the present invention;

[0029] Figure 5 This is a schematic top view of a hexagonal nut according to an embodiment of the present invention;

[0030] Figure 6 This is a schematic diagram of a hexagonal nut according to an embodiment of the present invention;

[0031] Figure 7 This is a schematic top view of the internal thread structure of the special-shaped part according to an embodiment of the present invention;

[0032] Figure 8 This is a schematic diagram of the internal thread structure of a special-shaped part according to an embodiment of the present invention.

[0033] Description of reference numerals:

[0034] 1. Hexagonal end face; 2. Sensor; 3. Electrode layer; 4. Insulation layer; 5. Piezoelectric layer; 6. Jacket nut wall thickness; 7. Threaded end; 8. Insulation ring; 9. Probe; 10. Ultrasonic signal; 11. Reflected ultrasonic signal. DETAILED DESCRIPTION

[0035] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0037] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0038] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0039] like Figures 1 to 4 As shown, an ultrasonic-based internally threaded outer sleeve nut includes an outer sleeve nut base, a hexagonal end face 1 above the outer sleeve nut base, a sensor 2 installed above the hexagonal end face 1, the sensor 2 includes an electrode layer 3, an insulating layer 4 and a piezoelectric layer 5, the insulating layer 4 is installed at the bottom of the electrode layer 3, and the piezoelectric layer 5 is installed at the bottom of the insulating layer. A threaded end 7 is provided inside the outer sleeve nut base, the wall thickness of the outer sleeve nut base is defined as the outer sleeve nut wall thickness 6, a probe 9 is detachably installed above the sensor 2, and an insulating ring 8 is installed above the insulating layer 4.

[0040] The vacuum ion plating and magnetron sputtering technology is used to in-situ grow a sensor on the hexagonal end face of the outer nut. The piezoelectric effect of the sensor is used to generate ultrasonic waves in the outer nut matrix. Through calibration technology, the flight time difference of the ultrasonic waves in the matrix before and after the internal threaded outer nut is loaded is collected to realize the measurement of the internal preload force of the outer nut.

[0041] The load-bearing part of the outer nut is at the threaded end 7, which requires that the ultrasonic wave be transmitted along the total height of the substrate. The threaded end 7 of the outer nut is a thin-walled structure (the single-side wall thickness is not more than 4mm), and the space is not enough to prepare the sensor. The hexagonal end face 1 has enough space (the hexagonal end face width is greater than 6mm). The hexagonal end face 1 of the outer nut is selected to prepare the sensor 2. In order to achieve effective transmission of the ultrasonic signal, the size of the electrode layer 3 should not be larger than the wall thickness 6 of the outer nut (the wall thickness 6 should be at least 1mm larger than the width of the electrode layer 3).

[0042] Because the outer nut is annular and, during installation, is wrenched, it experiences uneven force in different directions after loading. Consequently, the bearing capacity varies on each facet of the hexagonal end face 1 (perpendicularity errors in the hexagonal nut end face result in uneven contact surfaces, and during installation, the nut axis and the bolt axis do not completely coincide, resulting in uneven force on the end faces. Furthermore, external vibrations, impacts, and other conditions can cause the outer nut to loosen, affecting the uniformity of force on each end face). Therefore, a number of equally divided force measurement areas can be designed based on the outer nut structure. Taking the hexagonal structure of the outer nut as an example, sensor 2 is designed to be divided into six arcs at 60°, each corresponding to a hexagonal end face 1. This allows for measurement of preload values ​​in all directions (sensor 2 is divided into six sections on the outer nut end face, and probe 9 can measure preload at each of the six points), improving measurement accuracy.

[0043] According to the wall thickness 6 of the outer nut, the structural dimensions of sensor 2 are designed (the electrode layer 3 of sensor 2 should be at least 1 mm smaller than the wall thickness 6 of the outer nut), so that the ultrasonic wave excited by sensor 2 can propagate along the entire outer nut substrate (according to the formula S=v×t, S is the total height of the outer nut, mm; v is the propagation speed of ultrasonic waves in metal, m / s; t is the measured ultrasonic wave propagation time, ns. The propagation speed of ultrasonic waves in metal needs to be defined according to the material properties. For example, the propagation speed of ultrasonic waves in aluminum alloy materials is about 6200 m / s. The height of the outer nut is a fixed value, so it can be calculated whether the ultrasonic sound collected by probe 9 is propagated collectively along the entire outer nut).

[0044] This outer nut features an internally threaded clamping structure and an array of sensors on one end. Different sensor positions can detect preload forces at different locations within the structure. Trial testing based on the design drawings has proven the product's convenient, efficient measurement and stable signal quality, demonstrating its high practical application value.

[0045] A pre-tightening force outer nut structure for an internally threaded fastener includes three different hierarchical structures: a piezoelectric layer, an insulating layer, and an electrode layer. The piezoelectric layer plays a role in piezoelectric effect and inverse piezoelectric effect. The insulating layer protects the piezoelectric layer and insulates. The electrode layer is prepared using corresponding shielding tooling according to the structure of the internally threaded fastener to achieve pre-tightening force measurement.

[0046] A method for measuring the preload force of an internally threaded outer nut based on ultrasound comprises the following steps:

[0047] In the process of preparing the sensor, the first step is to process the hexagonal end face 1 into a mirror state with a roughness of less than 0.8μm (the sensor 2 is coated by magnetron sputtering ion plating method, and the roughness of the hexagonal end face 1 of the outer nut is required to be higher, generally controlled at the μm level, which can enhance the adhesion and uniformity between the sensor 2 and the substrate). The non-pre-processed area of ​​the outer nut (the part outside the outer nut sensor preparation area, keeping the original appearance of the outer nut, all are non-pre-processed areas) is tightly wrapped with high-temperature resistant materials such as tin foil, placed in the furnace chamber and evacuated to a vacuum state for etching (the vacuum degree of the furnace chamber is less than 10 -3 Pa. The etching function is to remove excess material (contaminants) on the surface of the material, making the hexagonal end face 1 of the outer nut cleaner and enhancing the bonding strength of the sensor 2);

[0048] The second step is to sputter the piezoelectric layer 5 (ZnO) to produce a piezoelectric effect (the piezoelectric layer 5 (ZnO) is the sensor and core. When it receives an electrical signal from the probe 9, it will produce an inverse piezoelectric effect, converting the electrical signal from the probe 9 into an ultrasonic signal. When it receives mechanical stress, it will produce a piezoelectric effect, converting the ultrasonic signal into an electrical signal, that is, sound, which is collected by the probe 9);

[0049] The third step is to sputter an insulating layer 4 (SiO) on the basis of the piezoelectric layer 5 to insulate and protect the piezoelectric layer 5 (the insulating layer 4 (SiO) has a high refractive index and transparency, which increases the refractive index of the ultrasonic wave, facilitating the excitation and collection of the ultrasonic wave; it is insoluble in water, which effectively protects the piezoelectric layer 5, has a certain chemical activity, and further insulates the electrode layer 3 from the piezoelectric layer 5);

[0050] The fourth step is to design the size of the insulating ring 8 based on the wall thickness 6 of the outer nut and the size of the hexagonal end face 1 (the overall size of the insulating ring 8 is consistent with the hexagonal end face 1 of the outer nut. Six ring structures are cut out inside the insulating ring 8 according to the corresponding six sides. The size of the six ring structures is consistent with the size of the electrode layer 3). The insulating ring 8 is tightly fitted to the insulating layer 4, and the electrode layer 3 (Ti) is sputtered to protect the insulating layer 4 and the piezoelectric layer 5. At the same time, the excitation and acquisition of ultrasonic signals (piezoelectric and inverse piezoelectric effects) are realized to complete the precise measurement of the preload force of the outer nut after loading. The total thickness of the sensor 2 is less than 50μm (advantage: the total thickness of the sensor 2 is determined according to the material properties of the outer nut. According to conventional metal materials, the total thickness of the sensor is generally less than 50μm, which shows outstanding performance in terms of bonding strength, frequency response, resolution, and sensitivity. If it is greater than 50μm, the bonding strength will be reduced and it will be easy to fall off, affecting the stability of the sensor performance).

[0051] During the measurement process, the probe 9 generates an electrical signal, which excites the piezoelectric layer 5 to convert the electrical signal into an ultrasonic signal 10. The ultrasonic signal 10 propagates from the sensor end face to the other end face along the outer sleeve nut base, and is received by the reflected ultrasonic signal 11 to the probe 9. The ultrasonic signal 10 forms a closed loop, and the internal stress of the outer sleeve nut is calculated according to the calibrated "temperature factor-load factor-ultrasonic time-force value" function relationship, thereby realizing the measurement of the pre-tightening force value of the outer sleeve nut after loading.

[0052] Example 1

[0053] like Figures 5 and 6 As shown in the figure, ordinary hexagonal nuts with the same principle can also be used to prepare sensors on the end faces, which are evenly distributed at 60° on the six end faces. The piezoelectric and inverse piezoelectric effects of the sensors are used to collect the ultrasonic time difference of the hexagonal nut under different loads to obtain the bearing capacity value of the hexagonal nut.

[0054] The patent of this invention is also applicable to special-shaped internal thread structural parts. The shape and quantity of the sensors are made according to the designer, such as Figures 7 and 8 It adopts a rectangular structure and is evenly distributed at 90° positions. It uses the piezoelectric and inverse piezoelectric effects of the sensor to collect the ultrasonic sound time difference under different loads on the structural parts to obtain the bearing capacity value of the hexagonal nut.

[0055] Calculation of the functional relationship of “temperature factor-load factor-ultrasonic time-force value”:

[0056] Temperature Factor:

[0057] Under no-load conditions, temperature changes in the outer nut cause the outer nut material to expand and contract, resulting in changes in the nut's axial length. This in turn changes the propagation time of the ultrasonic wave excited by the sensor within the outer nut. Experiments have established a functional relationship between the outer nut's temperature and the ultrasonic wave's flight time. The temperature-related proportional factor in this function is the temperature factor.

[0058] Calculation formula: (Formula 1)

[0059] Where: It is the ultrasonic flight time at 0℃ without load, i.e. the calibration reference sound time; is the ultrasonic flight time at the corresponding temperature value of the jacket nut; TEMP The temperature of the tooling used to assemble the outer nut; is the temperature factor.

[0060] Load factor - ultrasonic time - force value:

[0061] The outer nut is subjected to a tensile test using an electronic universal testing machine. The flight time of the ultrasonic wave in the outer nut is measured at the same time, and a functional relationship between the load on the outer nut and the difference in ultrasonic flight time under the test temperature conditions is established. The proportional factor related to the load in the function is the load factor.

[0062] Calculation formula: (Formula 2)

[0063] (Formula 3)

[0064] Where:

[0065] F It is the tensile load of the electronic universal testing machine; is the load factor; is the difference in ultrasonic flight time after temperature correction; is the acoustic time measurement value of the bolt under no-load condition; It is the acoustic time measurement value of the bolt under load conditions.

[0066] This invention, which employs a permanent thin-film sensor designed and fabricated on the end face of an internally threaded fastener, utilizes ultrasonic propagation time differences to measure the axial load of the outer nut, a technique widely used. Based on this theory, internally threaded intelligent fasteners have entered mass production within the fastener industry. This not only improves system reliability and eases maintenance, but also ensures a tight and secure connection.

[0067] The present invention can realize in-situ direct monitoring of the preload force of the outer sleeve nut during service. Currently, the present invention has been delivered and applied, with a measurement accuracy within ±5%. Taking this invention as an example, the design and preparation of internal threaded fastener sensors can be promoted to realize preload state monitoring of the fastening connection system and improve the system connection reliability.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for measuring the preload force of an internally threaded outer nut based on ultrasound, implemented by an internally threaded outer nut based on ultrasound, characterized in that: An ultrasonic-based internal threaded outer nut comprises an outer nut base, the outer nut base being an annular structure, a hexagonal end face (1) being located above the outer nut base, a sensor (2) being prepared above the hexagonal end face (1) by a magnetron sputtering method, the sensor (2) having the same life cycle as the fastener, the sensor (2) comprising an electrode layer (3), an insulating layer (4) and a piezoelectric layer (5), the insulating layer (4) being installed at the bottom of the electrode layer (3), the piezoelectric layer (5) being installed at the bottom of the insulating layer (4), a threaded end (7) being provided inside the outer nut base, the wall thickness of the outer nut base being defined as the outer nut wall thickness (6), a probe (9) being detachably installed above the sensor (2), and an insulating ring (8) being installed above the outer insulating layer (4); The threaded end (7) is a thin-walled structure, with a single-side wall thickness of no more than 4 mm; The width of the hexagonal end surface (1) is greater than 6 mm; The size of the electrode layer (3) should not be larger than the wall thickness (6) of the outer nut; The total thickness of the sensor (2) is less than 50 μm; The method comprises the following steps: The probe (9) generates an electrical signal; Exciting the piezoelectric layer (5) to convert the electrical signal into an ultrasonic signal (10); The ultrasonic signal (10) propagates from the end face of the sensor (2) to the other end face along the outer nut base, and is received by the probe (9) by the reflected ultrasonic signal (11), and the ultrasonic signal (10) forms a closed loop; The internal stress of the outer nut is calculated based on the calibrated temperature factor-load factor-ultrasonic time-force value function relationship, and the pre-tightening force value of the outer nut after loading is measured; Calculation of the functional relationship between temperature factor, load factor, ultrasonic time and force value: Under no-load conditions, temperature changes in the outer nut cause the outer nut material to expand and contract, resulting in changes in the axial length of the outer nut. This changes the propagation time of the ultrasonic wave excited by the sensor within the outer nut. Through experiments, a functional relationship between the outer nut temperature and the ultrasonic wave flight time was established. The temperature-related proportional factor in the function is the temperature factor. Calculation formula: (Formula 1) Where: It is the ultrasonic flight time at 0℃ without load, i.e. the calibration reference sound time; is the ultrasonic flight time at the corresponding temperature value of the outer nut; TEMP is the tooling temperature of the outer nut; is the temperature factor; The outer nut is subjected to a tensile test using an electronic universal testing machine. The flight time of the ultrasonic wave in the outer nut is measured at the same time. The functional relationship between the load on the outer nut and the difference in the ultrasonic wave flight time under the test temperature conditions is established. The proportional factor related to the load in the function is the load factor. Calculation formula: (Formula 2) (Formula 3) Where: F is the tensile load of the electronic universal testing machine; is the load factor; is the difference in ultrasonic flight time after temperature correction; is the acoustic time measurement value of the bolt under no-load condition; It is the acoustic time measurement value of the bolt under load conditions.

2. The ultrasonic-based preload force measurement method for an internally threaded outer nut according to claim 1, characterized in that: The measuring method also includes a sensor preparation method when measuring the internal thread outer shell nut, and the sensor preparation method includes the following steps: The first step is to process the hexagonal end face (1) into a mirror state with a roughness of less than 0.8 μm, wrap the non-pre-processed area of ​​the outer nut with a high-temperature resistant material, place it in a furnace chamber and evacuate it to a vacuum state, and then perform etching; The second step is to sputter the piezoelectric layer (5) to produce the piezoelectric effect; The third step is to sputter an insulating layer (4) on the basis of the piezoelectric layer (5) to play the role of insulating and protecting the piezoelectric layer (5); The fourth step is to design the size of the insulating ring (8) according to the wall thickness (6) of the outer nut and the size of the hexagonal end face (1), fit the insulating ring (8) to the insulating layer (4), and sputter the electrode layer (3) to protect the insulating layer (4) and the piezoelectric layer (5).

3. The ultrasonic preload measurement method for an internally threaded outer nut according to claim 2, characterized in that: The sensor (2) is equally divided into 6 arcs, each arc has an angle of 60°, and each arc corresponds to a hexagonal end face (1).

4. The ultrasonic-based preload force measurement method for an internally threaded outer nut according to claim 3, characterized in that: The size of the insulating ring (8) is the same as that of the hexagonal end face (1), and six annular structures are cut out from the inside of the insulating ring (8) according to the corresponding six sides, and the size of the six annular structures is the same as that of the electrode layer (3).

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