Device and method for measuring tightening torque and friction coefficient of high-strength bolt

Abstract

The present invention discloses a device and a method for measuring the tightening torque and friction coefficient of high-strength bolts, which relate to the technical field of measuring equipment. The device includes an upper end plate and a lower end plate. An elastic element is provided between the upper end plate and the lower end plate. A through hole matching the bolt is provided on the upper end plate, and a threaded hole matching the bolt is provided on the lower end plate. The threaded hole and the through hole are coaxially arranged. The bolt sequentially passes through the upper end plate, the elastic element and the lower end surface, and is threadedly connected to the lower end plate. The height after the superposition of the upper end plate, the disc spring and the lower end plate is the same as the length of the bolt. The distance a between the upper end plate and the lower end plate is measured. Subsequently, a torque wrench is used to tighten the bolt until a1 is equal to a. At this time, the value of the torque wrench is the tightening torque of the bolt. The present invention has the advantages of simplicity, reliability, strong feasibility, and can accurately obtain the pre-tightening force, tightening torque, torque coefficient (equivalent thread friction coefficient), and monitor the influence of temperature on the strength of high-strength bolts, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of measuring devices, and particularly to a device and a method for measuring the tightening torque and friction coefficient of high-strength bolts, which are particularly applicable to high-strength bolts that bear large centrifugal forces in high-speed rotating components. Background Art

[0002] Threaded connection is a detachable connection that connects multiple connected parts together through threaded fasteners to resist external loading, so that when the external load acts on the connected parts, the connected parts do not slip or separate. The force that resists the external load and clamps the connected parts is called the pre-tightening force, which affects the total working load of the thread, connection, bearing capacity of the connected parts, and sealing performance, etc. Inconsistent pre-tightening forces will cause uneven stress on the joint surface between the connected parts and the connected components, reducing the sealing performance, and at the same time there is a possibility of damaging the connected parts and the connected components. If the pre-tightening force is too large, the thread will undergo fatigue fracture and the thread teeth will be damaged, resulting in the inability to achieve connection or excessive pressure on the joint surface between the connected parts and the connected components, leading to gluing, crushing, etc.; if the pre-tightening force is too small, the connected parts will slip, separate or the fastener will become loose, which may also cause vibration and nut loosening, failing to achieve the fastening purpose. Therefore, it is crucial to find the pre-tightening range of the bolt pre-tightening force to ensure the connection quality. However, the pre-tightening force is affected by various factors such as the tightening tool, bolt material, bolt performance grade, gasket grade, pre-tightening speed, lubrication conditions, working temperature, etc., which brings many difficulties to ensuring the accuracy of the pre-tightening force and tightening torque.

[0003] At present, there are torque control method, torque-angle control method, yield point control method, elongation control method and other methods for controlling preload. The torque control method requires a tension sensor and a torque sensor. Through a dual-channel strain gauge, the corresponding tightening torque when the bolt reaches the target value of the preload is tested. The advantages of the torque control method are: low cost, and a simple tightening tool torque wrench can be used to check the tightening quality. Its disadvantages are: insufficient tightening accuracy, inability to fully utilize the material potential, and large environmental impact (temperature, bolt thread, impurities, bumps, etc.). The torque-angle control method requires a torque sensor and an angle sensor to obtain the tightening torque and rotation angle through the torque-angle control algorithm. The advantages of the torque-angle control method are: high tightening accuracy, stable tightening quality, and little influence of the friction coefficient of the threaded part on the tightening quality; it can fully utilize the bearing capacity of the bolt; the bolt can be tightened to the plastic deformation zone without breaking, and the designed preload can be 80% of the yield strength of the bolt. A larger axial clamping force can be obtained. Disadvantages: its control system is relatively complex, and it is not easy to find an appropriate method to check and follow up the tightening results. The yield point control method uses the yield point of the thread material to control the assembly of the thread pair. This method is currently only used by a few automobile engine manufacturers that produce high-end brands, because the required equipment cost is too high and it is sensitive to interference factors. At the same time, it has extremely high requirements for the performance and structural design of the bolts, and it is difficult to control. The elongation control method requires an ultrasonic bolt stress meter to measure the elongation of the bolt in real time and calculate the bolt axial force in real time. The requirements for threaded connections are very high, the corresponding equipment is complex, and there are few engineering applications. It is suitable for high-strength bolts that are subjected to large centrifugal forces in high-speed rotating parts. There is a lack of methods to accurately determine the bolt preload and tightening torque, and the overall performance of high-speed rotating parts cannot be guaranteed. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a device for measuring the tightening torque and friction coefficient of high-strength bolts and a method for using the device. The height of the upper end plate, disc spring and lower end plate after superposition is the same as the actual length of the bolt. The distance a between the upper end plate and the lower end plate is measured, and then the bolt is tightened with a torque wrench until a1 is equal to a. At this time, the value of the torque wrench is the tightening torque of the bolt. The present invention is simple, reliable, and highly feasible. It can accurately obtain preload, tightening torque, torque coefficient, thread equivalent friction coefficient, and monitor the influence of temperature on the strength of high-strength bolts.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A device for measuring the tightening torque and friction coefficient of high-strength bolts, characterized in that it includes an upper end plate and a lower end plate, an elastic element is arranged between the upper end plate and the lower end plate, a through hole matching the bolt is arranged on the upper end plate, the lower end plate is provided with a threaded hole matching the bolt, the through hole and the threaded hole are coaxially arranged, and the bolt passes through the upper end plate, the elastic element and the lower end plate in sequence and is threadedly connected to the lower end plate.

[0007] Preferably, a plurality of through holes are arranged on the upper end plate, and a plurality of threaded holes are arranged on the lower end plate.

[0008] Preferably, the elastic element is composed of a plurality of disc springs stacked together.

[0009] Preferably, both the through hole and the threaded hole are through holes.

[0010] Preferably, placing grooves for placing disc springs are arranged on the lower surface of the upper end plate and the upper surface of the lower end plate, and the disc springs in contact with the lower surface of the upper end plate and the upper surface of the lower end plate are processed with planes.

[0011] A method for measuring the tightening torque and friction coefficient of high-strength bolts, characterized by including the following steps:

[0012] Step 1: A pin shaft passes through the upper end plate, the disc spring and reaches the lower end plate. A specific amount of pressure is applied to the upper surface of the upper end plate through a hydraulic press, and the dimension a between the upper end plate and the lower end plate is measured at this time.

[0013] Step 2: The bolt passes through the upper end plate and the disc spring and is connected to the lower end plate. The bolt is tightened by a torque wrench until the dimension a1 is equal to a. Check the value of the torque wrench and record the value N at this time.

[0014] Preferably, in Step 1, the specific amount of pressure is the theoretical pressure generated after the bolt is pre-tightened.

[0015] Preferably, in Step 1, the height after the upper end plate, the disc spring and the lower end plate are stacked is the same as the length of the bolt.

[0016] Preferably, in Step 1, the pin shaft passes through the upper end plate, the disc spring and reaches the lower end plate. A specific amount of pressure is applied to the surface of the upper end plate through a hydraulic press, and the dimension a between the upper end plate and the lower end plate is measured at this time. The average value is taken after multiple tests.

[0017] Preferably, in Step 2, a quantitative lubricant is applied to the bolt. Then the bolt passes through the upper end plate and the disc spring and is connected to the lower end plate. The bolt is tightened by a torque wrench until the dimension a1 is equal to a. Check the value of the torque wrench and record the value N at this time. The average value is taken after multiple tests.

[0018] Preferably, in the second step, change the test environment temperature, then pass the bolt through the upper end plate and the disc spring and connect it to the lower end plate. Use a torque wrench to tighten the bolt until the dimension a1 is equal to a. Check the value on the torque wrench and record the value N at this time. Conduct multiple tests and take the average value.

[0019] The beneficial effects of this technical solution are as follows:

[0020] First, the present invention provides a device and a method for measuring the tightening torque and friction coefficient of high-strength bolts. The height after the superposition of the upper end plate, the disc spring, and the lower end plate is the same as the actual tightening length of the bolt. Measure the distance a between the upper end plate and the lower end plate, and then use a torque wrench to tighten the bolt until a1 is equal to a. At this time, the value on the torque wrench is the tightening torque of the bolt. The present invention is simple, reliable, and highly feasible, and can accurately obtain the pre-tightening force, tightening torque, torque coefficient (equivalent thread friction coefficient), and monitor the influence of temperature on the strength of high-strength bolts.

[0021] Second, the present invention provides a device and a method for measuring the tightening torque and friction coefficient of high-strength bolts. The distance and dimensions between the bolt holes are the same as those in the actual application working conditions, and the distance and dimensions between the through holes are the same as those in the actual application working conditions, making the measurement of the tightening torque of the bolt more accurate.

[0022] Third, the present invention provides a device and a method for measuring the tightening torque and friction coefficient of high-strength bolts. The upper and lower end plates and the disc spring are provided with planes, effectively preventing the upper and lower end faces from being damaged. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described in detail below in conjunction with the specification drawings and specific embodiments, where:

[0024] Figure 1 is a schematic structural diagram of the measuring device in the present invention;

[0025] Figure 2 is a schematic structural diagram of the first step during the test in the present invention;

[0026] Figure 3 is a schematic structural diagram of the second step during the test in the present invention;

[0027] Reference numerals in the figure: 1, upper end plate; 2, lower end plate; 3, disc spring; 4, bolt; 5, pin shaft; 6, hydraulic press. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0029] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying 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 therefore should not be construed as a limitation to the present invention.

[0030] As Figure 1 shown, a device for measuring the tightening torque and friction coefficient of high-strength bolts includes an upper end plate 1 and a lower end plate 2. An elastic element is arranged between the upper end plate 1 and the lower end plate 2. A through hole matching the bolt 4 is arranged on the upper end plate 1. The lower end plate 2 is provided with a threaded hole matching the bolt 4. The threaded hole and the through hole are coaxially arranged. The bolt 4 passes through the upper end plate 1, the elastic element and the lower end plate 2 in sequence and is threadedly connected to the lower end plate 2.

[0031] Among them, a plurality of through holes are arranged on the upper end plate 1, and a plurality of threaded holes are arranged on the lower end plate 2. The distance and size between the bolt 4 holes are the same as the actual application working conditions, and the distance and size between the through holes are the same as the actual application working conditions, making the measurement of the tightening torque of the bolt 4 more accurate.

[0032] Among them, the elastic element is composed of a plurality of disc springs 3 stacked together.

[0033] Among them, both the through hole and the threaded hole are through holes.

[0034] Among them, placing grooves for placing the disc springs 3 are arranged on the lower surface of the upper end plate 1 and the upper surface of the lower end plate 2. And the disc springs 3 in contact with the lower surface of the upper end plate 1 and the upper surface of the lower end plate 2 are processed with planes. The arrangement of the placing grooves and the planes of the disc springs 3 effectively prevents the upper end plate 1 and the lower end plate 2 from being scratched.

[0035] As Figure 2 and Figure 3 shown, a method for measuring the tightening torque and friction coefficient of high-strength bolts includes the following steps:

[0036] Step 1: The pin shaft 5 passes through the upper end plate 1 and the disc spring 3 to reach the lower end plate 2. A specific amount of pressure is applied to the upper surface of the upper end plate 1 by a hydraulic press 6, and the dimension a between the upper end plate 1 and the lower end plate 2 is measured at this time.

[0037] Step 2: The bolt 4 passes through the upper end plate 1 and the disc spring 3 and is connected to the lower end plate 2. The bolt 4 is tightened by a torque wrench until the dimension a1 is equal to a. Check the value of the torque wrench and record the value N at this time. The height after the superposition of the upper end plate 1, the disc spring 3 and the lower end plate 2 is the same as the actual tightening length of the bolt 4. The distance a between the upper end plate 1 and the lower end plate 2 is measured, and then the bolt 4 is tightened by a torque wrench until a1 is equal to a. At this time, the value of the torque wrench is the tightening torque of the bolt 4. The present invention is simple, reliable and highly feasible, and can accurately obtain the pre-tightening force, tightening torque, torque coefficient, equivalent thread friction coefficient, and monitor the influence of temperature on the strength of the high-strength bolt 4, etc.

[0038] Among them, in the step 1, the specific amount of pressure is the theoretical pressure value generated after the pre-tightening of the bolt 4.

[0039] Among them, in the step 1, the height after the superposition of the upper end plate 1, the disc spring 3 and the lower end plate 2 is the same as the length of the bolt 4.

[0040] Among them, in the step 1, the pin shaft 5 passes through the upper end plate 1 and the disc spring 3 to reach the lower end plate 2. A specific amount of pressure is applied to the upper surface of the upper end plate 1 by a hydraulic press 6, and the dimension a between the upper end plate 1 and the lower end plate 2 is measured at this time. The average value is taken after multiple tests.

[0041] Among them, in the step 2, a quantitative lubricant (the same lubricant as that used during the actual tightening of the bolt 4) is applied to the bolt 4. Then the bolt 4 passes through the upper end plate 1 and the disc spring 3 and is connected to the lower end plate 2. The bolt 4 is tightened by a torque wrench until the dimension a1 is equal to a. Check the value of the torque wrench and record the value N at this time. The average value is taken after multiple tests. At this time, the value N is equal to M 扭紧力矩 。

[0042] Among them, in the step 2, the test environment temperature is changed. Then the bolt 4 passes through the upper end plate 1 and the disc spring 3 and is connected to the lower end plate 2. The bolt 4 is tightened by a torque wrench until the dimension a1 is equal to a. Check the value of the torque wrench and record the value N at this time. The average value is taken after multiple tests.

[0043] F 离心力 =m 连接件 ω 2 r;

[0044]

[0045] F 预紧力 =k 安全系数 ×F离心力 ;

[0046] M 扭紧力矩 = k 摩擦系数 × F 预紧力 × d1;

[0047] Where: F 离心力 is the centrifugal force borne by the connector, m 连接件 is the mass of the connector, ω is the angular velocity of the connector, r is the equivalent radius of the connector, F pre-tightening force is the bolt pre-tightening force, L is the bolt length, ΔL is the bolt elongation, E is the elastic modulus of the bolt material, A is the nominal stress cross-sectional area of the thread, k 安全系数 is the calculated safety factor, M 扭紧力矩 is the bolt tightening torque, k 摩擦系数 is the thread torque coefficient, and d1 is the bolt pitch diameter. After calculation, the pre-tightening force (i.e., F 预紧力 ), the tightening torque (i.e., M 扭紧力矩 ), the torque coefficient (thread equivalent friction coefficient, i.e., k 摩擦系数 ), and the influence of monitoring temperature on the strength of high-strength bolts, etc. can be accurately obtained.

[0048] In summary, after reading the documents of the present invention, all other corresponding transformation schemes made by those of ordinary skill in the art without creative mental labor according to the technical solutions and technical concepts of the present invention shall fall within the scope protected by the present invention.

Claims

1. A device for measuring the tightening torque and friction coefficient of high-strength bolts, characterized in that: It includes an upper end plate (1) and a lower end plate (2). An elastic element is arranged between the upper end plate (1) and the lower end plate (2). A through hole matching the bolt (4) is arranged on the upper end plate (1). The lower end plate (2) is provided with a threaded hole matching the bolt (4). The threaded hole and the through hole are coaxially arranged. The bolt (4) sequentially passes through the upper end plate (1), the elastic element and the lower end plate (2), and is threadedly connected to the lower end plate (2). It also includes a hydraulic press (6), a torque wrench and a pin shaft (5). When the pin shaft (5) passes through the upper end plate (1) and the elastic element and reaches the lower end plate (2), the hydraulic press (6) is used to apply a specific amount of pressure on the upper surface of the upper end plate (1). The specific amount of pressure is the theoretical pressure value generated after the bolt (4) is pre-tightened. The torque wrench is used to tighten the bolt (4).

2. The measuring device for the tightening torque and friction coefficient of a high-strength bolt according to claim 1, characterized in that: A plurality of through holes are arranged on the upper end plate (1), and a plurality of threaded holes are arranged on the lower end plate (2).

3. The measuring device for the tightening torque and friction coefficient of a high-strength bolt according to claim 2, characterized in that: The elastic element is formed by stacking a plurality of disc springs (3).

4. The measuring device for the tightening torque and friction coefficient of a high-strength bolt according to claim 3, wherein: Both the through hole and the threaded hole are through holes.

5. The measuring device for the tightening torque and friction coefficient of a high-strength bolt according to claim 1, characterized in that: Placing grooves for placing the disc springs (3) are arranged on the lower surface of the upper end plate (1) and the upper surface of the lower end plate (2), and the disc springs (3) in contact with the lower surface of the upper end plate (1) and the upper surface of the lower end plate (2) are processed with planes.

6. A method for measuring the tightening torque and friction coefficient of high-strength bolts, characterized in that, It includes the following steps: Step 1: The pin shaft (5) passes through the upper end plate (1), the disc springs (3) and reaches the lower end plate (2). A specific amount of pressure is applied on the upper surface of the upper end plate (1) by the hydraulic press (6). The specific amount of pressure is the theoretical pressure value generated after the bolt (4) is pre-tightened. Measure the dimension a between the upper end plate (1) and the lower end plate (2) at this time. Step 2: The bolt (4) passes through the upper end plate (1) and the disc springs (3) and is connected to the lower end plate (2). The bolt (4) is tightened by the torque wrench until the dimension a1 is equal to a. Check the value of the torque wrench and record the value N at this time. Step 3: Change the temperature of the experimental environment. Then, the bolt (4) passes through the upper end plate (1) and the disc spring (3) and is connected to the lower end plate (2). Use a torque wrench to tighten the bolt (4) until the dimension a1 is equal to a. Check the value on the torque wrench and record the value N at this time. Conduct multiple tests and take the average value. Calculate the friction coefficient through the following formula, that is ; ； ； Wherein: is the bolt pre-tightening force, is the bolt length, is the bolt elongation, is the elastic modulus of the bolt material, is the nominal stress cross-sectional area of the thread, is the bolt tightening torque, is the thread torque coefficient, is the pitch diameter of the bolt.

7. The method for measuring the tightening torque and friction coefficient of a high-strength bolt according to claim 6, characterized in that: In Step 1, the pin shaft (5) passes through the upper end plate (1), the disc springs (3) and reaches the lower end plate (2). A specific amount of pressure is applied on the surface of the upper end plate (1) by the hydraulic press (6). Measure the dimension a between the upper end plate (1) and the lower end plate (2) at this time. Take the average value after multiple tests.

8. A method for measuring the tightening torque and friction coefficient of a high-strength bolt according to claim 7, characterized in that: In Step 2, a quantitative lubricant is applied to the bolt (4). Then the bolt (4) passes through the upper end plate (1) and the disc springs (3) and is connected to the lower end plate (2). The bolt (4) is tightened by the torque wrench until the dimension a1 is equal to a. Check the value of the torque wrench and record the value N at this time. Take the average value after multiple tests.

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