Internal thread jacket nut based on ultrasonic waves and pre-tightening force measuring method thereof

Abstract

The invention provides an internal thread jacket nut based on ultrasonic waves and a pre-tightening force measuring method thereof.The internal thread jacket nut based on the ultrasonic waves comprises a jacket nut base body, the upper portion of the jacket nut base body is a hexagonal end face, and the lower portion of the jacket nut base body is a hexagonal end face; a sensor is prepared above the hexagonal end face by adopting a magnetron sputtering method, the sensor and the fastener have the same life cycle, the sensor comprises an electrode layer, an insulating layer and a piezoelectric layer, the insulating layer is mounted at the bottom of the electrode layer, the piezoelectric layer is mounted at the bottom of the insulating layer, a threaded end is arranged in the outer sleeve nut base body, and a probe is detachably mounted above the sensor. The method has the advantages that in-situ direct monitoring of the pre-tightening force in the service process of the outer sleeve nut can be achieved, delivery and application of the method are completed at present, the measurement precision is within + / -5%, design and preparation of an internal thread fastener sensor can be popularized by taking the method as an example, pre-tightening force state monitoring of a fastening connection system is achieved, and the application range is wide. And the system connection reliability is improved.

Description

Technical Field

[0001] The present invention belongs to the field of fasteners, and in particular relates to an internal thread outer sleeve nut based on ultrasonic waves and a method for measuring its pre-tightening force. Background Art

[0002] Tightening connection is a commonly used connection technology in major model equipment, which has the characteristics of simple structure, convenient installation, easy disassembly, high connection strength and good reliability. In a hydraulic system, an outer sleeve nut is a part that connects pipelines or installs pipelines on hydraulic components, and can be conveniently disassembled and assembled in a liquid passage. The connection and combination part between the outer sleeve nut and the pipe joint is one of the weakest links affecting the structural reliability of the system. Especially for the complex and changeable working conditions faced by model equipment, it is extremely easy to reduce the stiffness of the system structure, damage the structural integrity, increase vibration and energy dissipation, and thus affect the working performance and safety reliability of the outer sleeve nut. Traditional methods for measuring the pre-tightening force of tightening connections include the torque wrench method, the strain gauge method, the piezoelectric sheet method, etc. However, most of these methods have problems such as poor control accuracy and low measurement efficiency, and are limited to external thread fasteners. There is no suitable method for monitoring the pre-tightening force of internal thread fasteners. Therefore, designing a structure for the internal thread outer sleeve nut of a fastener to realize the measurement of the pre-tightening force of the outer sleeve nut type is crucial for monitoring the pre-tightening force state of nut-type fasteners and the overall structural health. Summary of the Invention

[0003] In view of this, the present invention aims to propose an internal thread outer sleeve nut based on ultrasonic waves and a method for measuring its pre-tightening force to solve at least one of the problems existing in the above-mentioned prior art.

[0004] To achieve the above object, the technical solution of the present invention is realized as follows: In the first aspect, the present invention provides an internal thread outer sleeve nut based on ultrasonic waves, including an outer sleeve nut base body. The outer sleeve nut base body is a ring structure. The upper part of the outer sleeve nut base body is a hexagonal end face. A sensor is prepared by magnetron sputtering method above the hexagonal end face. The sensor has the same service 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 sleeve nut base body. The wall thickness of the outer sleeve nut base body is defined as the outer sleeve nut wall thickness. A probe is detachably installed above the sensor, and an insulating ring is installed above the outer insulating layer.

[0005] Further, the threaded end is a thin-wall structure, and the single-side wall thickness is not greater than 4 mm.

[0006] Further, the width of the hexagonal end face is greater than 6 mm.

[0007] Further, the size of the electrode layer should not be greater than the size of the outer sleeve nut wall thickness.

[0008] Further, the total thickness of the sensor < 50 μm.

[0009] In a second aspect, based on the same inventive concept, the present invention further provides a method for measuring the pre-tightening force of an internally threaded outer sleeve nut based on ultrasonic waves, including the following steps: The probe generates an electrical signal; The excitation piezoelectric layer converts the electrical signal into an ultrasonic signal; The ultrasonic signal propagates from the end face of the sensor to the other end face along the matrix of the outer sleeve nut, and the reflected ultrasonic signal is received by the probe, forming a closed-loop circuit for the ultrasonic signal; Calculate the internal stress of the outer sleeve nut according to the calibrated temperature factor - load factor - ultrasonic time - force value function relationship, and realize the measurement of the pre-tightening force value of the outer sleeve nut after loading.

[0010] Further, when measuring the internally threaded outer sleeve nut, the measurement method further includes a method for preparing the sensor, and the method for preparing the sensor includes the following steps: In the first step, the hexagonal end face is processed into a mirror state with a roughness < 0.8 μm. The non-pretreated area of the outer sleeve nut is wrapped with a high-temperature resistant material, placed in a furnace chamber and evacuated to a vacuum state, and etched; The second step is to sputter the piezoelectric layer to generate the piezoelectric effect; The third step is to sputter an insulating layer on the basis of the piezoelectric layer to play the role of insulating and protecting the piezoelectric layer; In the fourth step, according to the wall thickness of the outer sleeve nut and the size of the hexagonal end face, design the size of the insulating ring, fit the insulating ring with the insulating layer, and sputter the electrode layer to protect the insulating layer and the piezoelectric layer.

[0011] Further, the sensor is equally divided into 6 arc-shaped parts, each arc-shaped part has an angle of 60°, and each arc-shaped part corresponds to a hexagonal end face.

[0012] Further, the size of the insulating ring is the same as the size of the hexagonal end face, and 6 annular structures are cut out inside the insulating ring according to the corresponding six sides. The sizes of the 6 annular structures are the same as the size of the electrode layer.

[0013] Compared with the prior art, the method for measuring the pre-tightening force of an internally threaded outer sleeve nut based on ultrasonic waves according to the present invention has the following advantages: For the method for measuring the pre-tightening force of an internally threaded outer sleeve nut based on ultrasonic waves according to the present invention, the present invention can realize the in-situ direct monitoring of the pre-tightening force during the service process of the outer sleeve nut. At present, the present invention has been completed for delivery and application, and the measurement accuracy is within ±5%. Taking this invention as an example, the design and preparation of sensors for internally threaded fasteners can be promoted to realize the monitoring of the pre-tightening force state of the fastening connection system and improve the connection reliability of the system. Description of the Drawings

[0014] The accompanying drawings, which form a part of the present invention, are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not unduly limit the present invention. In the drawings: Figure 1 Schematic diagram of the ultrasonic-based externally threaded nut with internal threads according to an embodiment of the present invention; Figure 2 Schematic diagram of the hierarchical structure of the ultrasonic-based externally threaded nut with internal threads according to an embodiment of the present invention; Figure 3 Schematic diagram of the insulating ring structure according to an embodiment of the present invention; Figure 4 Schematic diagram of the operation of the ultrasonic-based externally threaded nut with internal threads according to an embodiment of the present invention; Figure 5 Top view schematic diagram of the hexagonal nut according to an embodiment of the present invention; Figure 6 Schematic diagram of the hexagonal nut according to an embodiment of the present invention; Figure 7 Top view schematic diagram of the internal thread structure of the special-shaped part according to an embodiment of the present invention; Figure 8 Schematic diagram of the internal thread structure of the special-shaped part according to an embodiment of the present invention.

[0015] Explanation of reference numerals: 1, hexagonal end face; 2, sensor; 3, electrode layer; 4, insulating layer; 5, piezoelectric layer; 6, wall thickness of the externally threaded nut; 7, threaded end; 8, insulating ring; 9, probe; 10, ultrasonic signal; 11, reflected ultrasonic signal. Detailed implementation manners

[0016] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0017] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is 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 thus should not be construed as a limitation to 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 specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0018] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "mounted", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific circumstances.

[0019] The present invention will be described in detail below with reference to the drawings and in conjunction with embodiments.

[0020] As Figures 1 to 4 shown, an internal-threaded outer sleeve nut based on ultrasonic waves includes an outer sleeve nut base body. Above the outer sleeve nut base body is a hexagonal end face 1. Above the hexagonal end face 1, a sensor 2 is installed. 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. Inside the outer sleeve nut base body is a threaded end 7. The wall thickness of the outer sleeve nut base body is defined as the outer sleeve nut wall thickness 6. Above the sensor 2, a probe 9 is detachably installed, and an insulating ring 8 is installed above the insulating layer 4.

[0021] The sensor is in-situ grown on the hexagonal end face of the outer sleeve nut by using vacuum ion plating magnetron sputtering technology. Ultrasonic waves are generated inside the outer sleeve nut base body by using the piezoelectric effect of the sensor. Through calibration technology, the time difference of the ultrasonic wave flight time inside the base body before and after the internal-threaded outer sleeve nut is loaded is collected to realize the measurement of the pre-tightening force inside the outer sleeve nut.

[0022] The load-bearing part of the outer sleeve 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 sleeve nut is a thin-walled structure (single-side wall thickness is not more than 4 mm), and there is not enough space to prepare the sensor. The hexagonal end face 1 has enough space (the width of the hexagonal end face is more than 6 mm). The hexagonal end face 1 of the outer sleeve nut is selected to prepare the sensor 2. In order to achieve effective transmission of ultrasonic signals, the size of the electrode layer 3 should not be larger than the wall thickness 6 of the outer sleeve nut (the wall thickness 6 should be at least 1 mm larger than the width of the electrode layer 3).

[0023] Since the outer nut is annular and is wrenched during installation, there is uneven force in different directions after loading. The bearing capacity is different on each different face of the hexagonal end face 1 (the verticality error of the hexagonal nut end face makes the contact surface uneven, and the axis of the nut and the axis of the bolt do not completely coincide during installation, resulting in uneven force on the end face; in addition, the outer nut may become loose when subjected to external vibration, impact and other conditions, affecting the uniformity of force on each end face). Therefore, several equal force measurement areas can be designed according to the structure of the outer nut. Taking the hexagonal structure of the outer nut as an example, the sensor 2 is designed to be divided into 6 arcs at 60°, and each arc corresponds to a hexagonal end face 1, which can realize the measurement of preload values ​​in all directions (the sensor 2 is divided into 6 parts on the end face of the outer nut, and the probe 9 can be used to measure the preload at 6 points respectively), improving the measurement accuracy.

[0024] 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 wave in metal, m / s; t is the measured ultrasonic wave propagation time, ns. The propagation speed of ultrasonic wave in metal needs to be defined according to the material properties. For example, the propagation speed of ultrasonic wave in aluminum alloy material is about 6200m / s. The height of the outer nut is a fixed value, so it can be calculated whether the ultrasonic wave collected by probe 9 is propagated collectively along the entire outer nut).

[0025] The outer nut is clamped by the internal thread and has an array layout sensor on one end. The preload force values ​​at different structural positions can be detected according to the different positions of the sensor. The product trial-produced according to the design drawings has been tested and verified to be convenient, efficient, and stable in signal, and has high practical application value.

[0026] A preload sheath 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 is for protecting the piezoelectric layer and insulation. The electrode layer is prepared by using corresponding shielding tooling according to the structure of the internally threaded fastener to realize the measurement of preload.

[0027] A pre-tightening force measurement method for an internally threaded outer sleeve nut based on ultrasonic waves, comprising the following steps: During the preparation of the sensor, in the first step, the hexagonal end face 1 is processed into a mirror state with a roughness <0.8 μm (the sensor 2 is coated by magnetron sputtering ion plating method, and the roughness of the hexagonal end face 1 of the outer sleeve nut is required to be relatively high, generally controlled at the μm level, which can enhance the adhesion and uniformity between the sensor 2 and the substrate). The non-pretreated area of the outer sleeve nut (the part outside the area where the sensor of the outer sleeve nut is prepared, maintaining the original appearance of the outer sleeve nut, all of which are non-pretreated areas) is tightly wrapped with a high-temperature resistant material such as tin foil, placed in the furnace cavity and evacuated to a vacuum state, and etched (the vacuum degree of the furnace cavity <10 -3 Pa. The etching effect is to remove the excess substances (contaminants) on the material surface, make the hexagonal end face 1 of the outer sleeve nut cleaner, and enhance the bonding force of the sensor 2); In the second step, the piezoelectric layer 5 (ZnO) is sputtered to generate the piezoelectric effect (the piezoelectric layer 5 (ZnO) is the core of the sensor. When receiving the electrical signal of the probe 9, it will generate the inverse piezoelectric effect, converting the electrical signal of the probe 9 into an ultrasonic signal. When receiving mechanical stress, it will generate the piezoelectric effect, converting the ultrasonic signal into an electrical signal, that is, the acoustic time, which is collected by the probe 9)); In the third step, the insulating layer 4 (SiO) is sputtered on the basis of the piezoelectric layer 5 to play the role of insulating and protecting the piezoelectric layer 5 (the insulating layer 4 (SiO) has a high refractive index and transparency, which can improve the refractive index of ultrasonic waves, facilitate the excitation and collection of ultrasonic waves; it is insoluble in water, can better protect the piezoelectric layer 5, has a certain chemical activity, and further insulates and isolates the electrode layer 3 from the piezoelectric layer 5)); In the fourth step, according to the wall thickness 6 of the outer sleeve nut and the size of the hexagonal end face 1, the size of the insulating ring 8 is designed (the overall size of the insulating ring 8 is the same as that of the hexagonal end face 1 of the outer sleeve nut. Six annular structures are cut out inside the insulating ring 8 according to the corresponding six sides, and the sizes of the six annular structures are the same as those of the electrode layer 3). The insulating ring 8 is closely attached to the insulating layer 4, and the electrode layer 3 (Ti) is sputtered to protect the insulating layer 4 and the piezoelectric layer 5, and at the same time realize the excitation and collection of ultrasonic signals (piezoelectric and inverse piezoelectric effects), and complete the accurate measurement of the pre-tightening force after the outer sleeve nut is loaded. The total thickness of the sensor 2 <50 μm (Advantages: The total thickness of the sensor 2 is determined according to the material properties of the outer sleeve nut. According to conventional metal materials, the total thickness of the sensor is generally <50 μm, showing outstanding performance in terms of bonding force, frequency response, resolution, and sensitivity; if >50 μm, the bonding force will be reduced, it is easy to fall off, and it will affect the performance stability of the sensor).

[0028] In the measurement process, the probe 9 generates an electrical signal, which stimulates 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 matrix, and the reflected ultrasonic signal 11 is received by the probe 9. The ultrasonic signal 10 forms a closed-loop circuit. According to the calibrated "temperature factor - load factor - ultrasonic time - force value" functional relationship, the internal stress of the outer sleeve nut is calculated, and the pre-tightening force value of the outer sleeve nut after loading is measured.

[0029] Embodiment 1 As Figures 5 to 6 shown, for an ordinary hexagonal nut with the same principle, sensors can also be prepared on the end faces, evenly distributed at 60° on 6 end faces. By using the piezoelectric and inverse piezoelectric effects of the sensors, the ultrasonic time difference is collected under different loads on the hexagonal nut, and the bearing capacity value of the hexagonal nut is obtained.

[0030] This invention patent also applies to special-shaped internal thread structural parts. The shape and quantity of the sensors are made according to the designer. For example Figures 7 to 8 , a rectangular structure is adopted and evenly distributed at 90° positions. By using the piezoelectric and inverse piezoelectric effects of the sensors, the ultrasonic time difference is collected under different loads on the structural part, and the bearing capacity value of the hexagonal nut is obtained.

[0031] Calculation of the "temperature factor - load factor - ultrasonic time - force value" functional relationship: Temperature factor: Under the condition of no load on the outer sleeve nut, the change in temperature will cause the thermal expansion and contraction of the outer sleeve nut material, resulting in a change in the axial length of the outer sleeve nut, and the propagation time of the ultrasonic wave excited by the sensor in the outer sleeve nut will change accordingly. The functional relationship between the temperature of the outer sleeve nut and the ultrasonic flight time is established through experiments, and the proportional factor related to temperature in the function is the temperature factor.

[0032] Calculation formula: (Formula 1) In the formula: is the ultrasonic flight time at 0 °C under no load, that is, the calibrated reference acoustic time; is the ultrasonic flight time under the corresponding temperature value of the outer sleeve nut; TEMP is the temperature of the tooling assembled with the outer sleeve nut; is the temperature factor.

[0033] Load factor - ultrasonic time - force value: The outer sleeve nut is subjected to a tensile test using an electronic universal testing machine, and at the same time, the ultrasonic flight time in the outer sleeve nut is measured. The functional relationship between the load applied to the outer sleeve nut and the ultrasonic flight time difference under the test temperature condition is established, and the proportional factor related to the load in the function is the load factor.

[0034] Calculation formula: (Formula 2) (Formula 3) In the formula: 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 measured acoustic time value of the bolt under no-load condition; is the measured acoustic time value of the bolt under load condition.

[0035] In the present invention, by designing and fabricating a permanent thin-film sensor on the end face of the internal-thread fastener, the technology of measuring the axial load of the outer sleeve nut using the ultrasonic propagation time difference has been widely applied. Based on this theory, intelligent internal-thread fasteners have been mass-produced in the field of fasteners. It not only improves the reliability of the system and the convenience of maintenance, but also ensures the tightness and safety of the connection.

[0036] The present invention can realize the in-situ direct monitoring of the pre-tightening force during the service process of the outer sleeve nut. At present, the present invention has been completed for delivery and application, with a measurement accuracy within ±5%. Taking this invention as an example, the design and fabrication of sensors for internal-thread fasteners can be promoted to realize the monitoring of the pre-tightening force state of the fastening connection system and improve the connection reliability of the system.

[0037] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An ultrasonic-based internally threaded outer sleeve nut, characterized in that: It includes an outer sleeve nut base body, the outer sleeve nut base body is of a ring structure, above the outer sleeve nut base body is a hexagonal end face (1), a sensor (2) is prepared above the hexagonal end face (1) by means of magnetron sputtering, the sensor (2) has the same service life cycle as the fastener, 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 (4). A threaded end (7) is provided inside the outer sleeve nut base body, and the wall thickness of the outer sleeve nut base body 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 outer insulating layer (4).

2. The ultrasonic-based internally threaded outer sleeve nut according to claim 1, characterized in that: The threaded end (7) is of a thin-wall structure, and the single-side wall thickness is not greater than 4 mm.

3. The ultrasonic-based internally threaded outer sleeve nut according to claim 1, characterized in that: The width of the hexagonal end face (1) is greater than 6 mm.

4. The ultrasonic-based internally threaded outer sleeve nut according to claim 1, characterized in that: The size of the electrode layer (3) should not be greater than the size of the outer sleeve nut wall thickness (6).

5. The ultrasonic-based internally threaded outer sleeve nut according to claim 1, characterized in that: The total thickness of the sensor (2) < 50 μm.

6. A method for measuring the pre-tightening force of an ultrasonic-based internally threaded outer sleeve nut, applying the ultrasonic-based internally threaded outer sleeve nut according to any one of claims 1 to 5, characterized in that: It includes the following steps: The probe (9) generates an electrical signal; The piezoelectric layer (5) is excited 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 sleeve nut base body, and the reflected ultrasonic signal (11) is received by the probe (9), and the ultrasonic signal (10) forms a closed-loop circuit; According to the calibrated temperature factor - load factor - ultrasonic time - force value function relationship, the internal stress of the outer sleeve nut is calculated to realize the measurement of the pre-tightening force value of the outer sleeve nut after loading.

7. The method for measuring the pre-tightening force of an ultrasonic-based internally threaded outer sleeve nut according to claim 6, characterized in that: When measuring the internal thread outer sleeve nut, the measurement method also includes a method for preparing the sensor. The method for preparing the sensor includes the following steps: In the first step, the hexagonal end face (1) is processed into a mirror state with a roughness < 0.8 μm. The non-pretreated area of the outer sleeve nut is wrapped with a high-temperature-resistant material, placed in a furnace chamber and evacuated to a vacuum state for etching treatment; The second step is to sputter the piezoelectric layer (5) to generate a piezoelectric effect; The third step is to sputter the insulating layer (4) on the basis of the piezoelectric layer (5) to play the role of insulating and protecting the piezoelectric layer (5); In the fourth step, according to the size of the outer sleeve nut wall thickness (6) and the hexagonal end face (1), the size of the insulating ring (8) is designed, the insulating ring (8) is fitted with the insulating layer (4), and the electrode layer (3) is sputtered to protect the insulating layer (4) and the piezoelectric layer (5).

8. The method for measuring the pre-tightening force of an ultrasonic-based internally threaded outer sleeve nut according to claim 7, characterized in that: The sensor (2) is equally divided into 6 arc-shaped parts, and the angle of each arc-shaped part is 60°, and each arc-shaped part corresponds to a hexagonal end face (1).

9. The method for measuring the pre-tightening force of an ultrasonic-based internally threaded outer sleeve nut according to claim 8, characterized in that: The size of the insulating ring (8) is the same as that of the hexagonal end face (1). Six circular structures are cut out in the insulating ring (8) according to the corresponding six sides, and the sizes of the six circular structures are the same as those of the electrode layer (3).

Images