Threaded fastener assembling method for improving connection performance

Abstract

The invention provides a threaded fastener assembly method for improving connection performance, which comprises the following steps: S1, rotating a threaded fastener in a fastening direction with an over-tightening torque, the over-tightening torque being greater than a traditional torque and the over-tightening torque being less than a maximum allowable torque; and S2, the threaded fastener is rotated at a specified angle in the loosening direction, and the torsional stress of the threaded fastener is reduced. The tightening device has the beneficial effects that after the tightening torque is used for rotating in the fastening direction, the tightening device is grabbed at the specified angle along the loosening angle, the bearing face of the fastener slides relatively, the other end face of the fastener is static, residual torque accumulated on a screw rod is reduced, stress distribution of a bolt is improved, and the service life of the fastener is prolonged; under the condition that the equivalent stress of a bolt interface is not improved, the pre-tightening force design quantity of the bolt can be remarkably improved, and the connection performance of the structure is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of threaded fastener assembly, and in particular relates to a threaded fastener assembly method for improving connection performance. Background Art

[0002] The main assembly method of bolts is tightening assembly. Tightening assembly applies torque or angle to the bolt head or nut to make the bolt and the nut screw together to achieve connection. Common methods include: first, torque control method, which ensures the preload of the bolt by controlling the torque applied to the bolt. Due to the dispersion of the friction coefficient of each interface of the connection structure, the actual preload will have a certain error; second, the angle control method is to further control the rotation angle after the inner and outer threads of the bolt and nut are in close contact to achieve the predetermined preload; third, the yield point control method is to detect the torque-angle curve while applying torque, judge the yield of the material, and tighten the bolt to a point close to the yield point, thereby ensuring the stability and accuracy of the preload. This method is suitable for high-demand connections, but requires precise control and measurement equipment; fourth, the preload control method, the preload control method directly measures and controls the preload of the bolt through a force sensor or smart fastener, usually using a dedicated force measuring device. This method can provide the most accurate preload control, but the equipment cost is high, and smart bolts need to be used, or the structure needs to be adjusted to add sensors, so the scope of application is narrow.

[0003] The current assembly method has the following problems: First, the equivalent stress of the dangerous section of the bolt is usually designed to be no more than 90% of the material yield strength. Since torsional stress is generated during the application of torque, the existence of torsional stress will cause the equivalent stress of the dangerous section of the bolt to increase. Therefore, the preload generation rate of the bolt is low, which means that under the same bolt specification, the greater the friction coefficient, the lower the design value of the bolt preload, which affects the connection performance; second, compared with the increase in normal stress, the increase in torsional stress has a greater effect on the equivalent stress. When the friction coefficient of the bolt is high, the stress concentration factor at the bottom of the thread is often high. Due to the existence of residual torque in the screw, when the bolt is subjected to fatigue load, the equivalent stress of the dangerous section increases, the stress concentration factor is larger, and the fatigue life of the structure is affected. Summary of the invention

[0004] In view of this, the present invention aims to provide a threaded fastener assembly method with improved connection performance, in order to solve at least one of the above-mentioned technical problems.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A first aspect of the present invention provides a threaded fastener assembly method for improving connection performance, comprising the following steps:

[0007] S1. Rotate the threaded fastener in the tightening direction with an over-tightening torque, the over-tightening torque is greater than the conventional torque, and the over-tightening torque is less than the maximum allowable torque;

[0008] S2. Rotate the threaded fastener at a specified angle in the loosening direction to reduce the torsional stress of the threaded fastener.

[0009] Furthermore, the calculation formula of the over-tightening torque is as follows:

[0010]

[0011] Among them, T nom is the traditional torque, d is the nominal diameter of the threaded fastener, T tl Over tightening torque, (dμ) min It is the minimum value of the friction torque of the bolt head bearing surface, the friction torque of the nut bearing surface and the friction torque of the thread surface.

[0012] Furthermore, the friction coefficient of the bolt head bearing surface and the friction coefficient of the nut bearing surface are not zero.

[0013] Furthermore, the calculation formula of the specified angle is as follows:

[0014]

[0015] T rod,rem is the residual torque value of the threaded fastener, l k is the clamping length, G is the shear modulus of the threaded fastener material, θ is the specified angle, and J is the polar moment of inertia of the threaded fastener.

[0016] Furthermore, the calculation formula of the residual torque value of the threaded fastener is:

[0017]

[0018] Among them, F tl It is the preload force under over-tightening torque.

[0019] Furthermore, the calculation formula of the preload force under the over-tightening torque is:

[0020]

[0021] Where d2 is the median diameter of the threaded fastener, μ s is the friction coefficient of the thread surface, α is the tooth profile half angle, d w is the equivalent diameter of the bearing surface of the threaded fastener, μ w is the friction coefficient of the bearing surface, and P is the pitch.

[0022] Furthermore, the calculation formula of the traditional torque is as follows:

[0023]

[0024] Among them, T max is the maximum allowable torque, and v is the ratio of the equivalent stress of the dangerous section of the bolt to the ultimate yield strength of the material.

[0025] A second aspect of the present invention provides an electronic device, comprising a processor and a memory communicatively connected to the processor and used to store instructions executable by the processor, wherein the processor is used to execute the method described in the first aspect above.

[0026] The third aspect of the present invention provides a server, comprising at least one processor, and a memory communicatively connected to the processor, the memory storing instructions executable by the at least one processor, the instructions being executed by the processor so that the at least one processor executes the method described in the first aspect.

[0027] A fourth aspect of the present invention provides a computer-readable storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the method described in the first aspect.

[0028] Compared with the prior art, the threaded fastener assembly method for improving connection performance described in the present invention has the following beneficial effects:

[0029] The present invention discloses a method for assembling threaded fasteners for improving connection performance. After the rotation in the tightening direction is completed by using an over-tightening torque, the fastener is grasped at a specified angle along a loosening angle, so that the supporting surface of the fastener slides relatively while the other end surface is stationary, thereby reducing the residual torque accumulated in the screw rod, improving the stress distribution of the bolt and extending the service life of the fastener. The pre-tightening force design amount of the bolt can be significantly increased while ensuring that the equivalent stress of the bolt interface does not increase, thereby increasing the connection performance of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0031] Figure 1 It is a schematic diagram of the process of the fastener assembly method according to an embodiment of the present invention;

[0032] Figure 2 Schematic diagram of torque decomposition of the bolt connection structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] 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.

[0034] 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 positions or positional relationships based on the positions 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", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like 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.

[0035] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0036] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0037] Embodiment 1:

[0038] The threaded fastener can be a combination of a bolt and a nut, and the pre-tightening force is formed by turning the bolt or the nut. The threaded fastener can also be a combination of a bolt and a threaded connection of a plate, and the pre-tightening force is formed by turning the bolt. The threaded fastener can also be a combination of an internally threaded tube and an externally threaded tube, and the pre-tightening force is formed by turning one of the threaded tubes.

[0039] The principle of converting tightening torque into preload is as follows:

[0040] Tightening assembly generates preload by applying torque to the bolt head or nut to screw the internal and external threads together. The calculation method of bolt tightening torque T is (without gasket or other additional structure):

[0041]

[0042] Among them, T s is the thread torque, Tw is the bearing surface torque, F is the preload, d2 is the bolt diameter, α is the thread profile half angle, P is the thread pitch, d w is the equivalent friction diameter of the bearing surface, μ w Friction coefficient of the bearing surface. Schematic diagram of torque decomposition of the bolted connection structure (see Figure 2 ), the physical meaning of the bolt tightening torque T is:

[0043] Item 1: is the friction torque between the meshing thread surfaces without considering the thread lead angle, that is Figure 2 A in

[0044] Item 2: is the additional friction torque caused by the lift angle, that is Figure 2 B in;

[0045] Item 3: is the friction torque of the bolt head / nut bearing surface, that is Figure 2 C+D in;

[0046] Among them, the first and third items are used to overcome the interface friction, and the second item is converted into the effective preload.

[0047] The torque T applied to tighten the bolt needs to overcome the friction torque of the thread surface and the friction torque of the bolt head / nut bearing surface. Therefore, during the process of generating the preload force, the screw segment in the hole of the connected part will accumulate torsional deformation synchronously, generating residual torque at the screw. When the assembly is completed, the residual torque value of the screw is T. rod,rem for:

[0048]

[0049] Among them, d w,head is the equivalent friction diameter of the bolt head bearing surface, μ w,head is the friction coefficient of the bolt head bearing surface, d w,nut is the equivalent friction diameter of the nut bearing surface, μ w,nut The above formula shows that the residual torque of the screw is equal to the minimum value of the friction torque of the bolt head bearing surface and the friction torque of the nut bearing surface when the assembly is completed.

[0050] According to the fourth strength theory of material mechanics, the equivalent stress σ eq With normal stress σ, torsional stress τ as The relationship between them is:

[0051]

[0052] To ensure the same equivalent stress σ eq Under the torsional stress τ asThe larger it is, the smaller the normal stress (bolt preload / cross-sectional area) is, the lower the design value of the bolt preload is, and the worse the connection performance of the structure is.

[0053] like Figure 1 to Figure 2 As shown, a threaded fastener assembly method for improving connection performance includes the following steps:

[0054] S1. Rotate the threaded fastener in the tightening direction with an over-tightening torque, the over-tightening torque is greater than the conventional torque, and the over-tightening torque is less than the maximum allowable torque;

[0055] S2. Rotate the threaded fastener at a specified angle in the loosening direction to reduce the torsional stress of the threaded fastener.

[0056] The over-tightening amount is one of the key parameters of the present invention and needs to be accurately calculated. When the over-tightening amount is large, the equivalent stress of the dangerous section of the bolt will be too large, causing the bolt to break under static load or quickly fatigue fracture; when the over-tightening amount is small, it will not have the effect of increasing the preload and improving the fastening connection performance.

[0057] The residual torque value of the screw when the assembly is completed is T rod,rem The formula simplifies to:

[0058]

[0059] (dμ) min is a whole, indicating min(d w,head μ w,head ,d w,nut μ w,nut ,d2μ s / cosα), which is the minimum value among the friction torque of the bolt head bearing surface, the friction torque of the nut bearing surface and the friction torque of the thread surface. It should be noted that (dμ) min ≠d min μ min .

[0060] The over-tightening amount needs to ensure that the equivalent stress σ of the dangerous interface of the bolt after assembly is completed eq,tl Equivalent stress σ compared with traditional torque method tightening eq,nom The same (the table below tl represents the over-tightening back-off method proposed by the present invention, and the table below nom represents the traditional torque tightening method), that is:

[0061] σ eq,tl =σ eq,nom ;

[0062] Among them, since the present invention proposes to eliminate the residual torque of the screw by backing off, the equivalent stress of the bolt is equal to the normal stress in the theoretical state, that is:

[0063] σ eq,tl =σtl ;

[0064] Equivalent stress σ of traditional torque tightening method eq,nom The calculation method is:

[0065]

[0066] Therefore, the normal stress σ of the bolt assembled by the present invention is tl The calculation method is:

[0067]

[0068] Therefore, the preload force F of the bolt assembled by the present invention is tl Compared with the preload force F of the traditional torque method nom The increase ratio is:

[0069]

[0070] It can be seen from formula (1) that the preload force is proportional to the tightening torque. Therefore, when the present invention is used for assembly, the torque T applied to the bolt is tl for:

[0071]

[0072] The torsional stress τ of the screw in the hole of the connected part (which may have partial threads, back-cut grooves, etc. and can be approximately regarded as a cylinder) assembled by the traditional torque tightening method as,nom for:

[0073]

[0074] Where d is the nominal diameter of the bolt, r is the nominal radius of the bolt, and J is the polar moment of inertia of the screw (approximately a cylinder).

[0075] Bolt normal stress σ assembled by traditional torque tightening method nom for:

[0076]

[0077] You can get:

[0078]

[0079] Finally, the simplified formula is:

[0080]

[0081] Therefore, the overtightening amount ΔT of the overtightening back-off method is tl In fact, it is T tlCompared with the tightening torque T of the traditional torque tightening method nom The difference between

[0082]

[0083] The over-tightening amount of the bolt is only equal to the tightening torque T of the traditional torque tightening method. nom , bolt nominal diameter d, bolt head / nut bearing surface equivalent diameter d w , bolt diameter d2, tooth profile half angle α and bearing surface friction coefficient μ w , thread surface friction coefficient μ s When other parameters remain unchanged, the larger the friction coefficient μ, the larger the overtightening amount ΔT tl The larger the friction coefficient μ is, the over-tightening amount ΔT is. tl =0, that is, when there is no friction on the supporting surface, the torsional deformation in the screw will return to zero after the tightening tool is removed, and no residual torque will accumulate in the screw, so there is no room for improvement of the preload force and installation torque.

[0084] When calculating over-tightening torque, the screw torsional stress is considered to be zero (the same as the final state after over-tightening and backing off), but the screw torsional stress exists during the tightening process. After ensuring that the bolt limit stress meets the requirements after assembly is completed (after over-tightening and backing off), it cannot be guaranteed that the requirements are met during the assembly process (when only the over-tightening process is completed), so there is another restriction on over-tightening torque:

[0085] In the current design manual, the torque design of bolts requires the use factor v (the ratio of the equivalent stress of the dangerous section of the bolt to the ultimate yield strength of the material). For example, in the VDI2230 guide, the calculation of T nom The default utilization coefficient v = 0.9. Therefore, under the premise that the bolt will not be damaged during the tightening process, the calculation formula of the traditional torque is as follows:

[0086]

[0087] Among them, T max is the maximum allowable torque, and v is the ratio of the equivalent stress of the dangerous section of the bolt to the ultimate yield strength of the material.

[0088] Therefore, the over tightening torque T tl The final calculation method is:

[0089]

[0090] and

[0091] Among them, T nom is the traditional torque, d is the nominal diameter of the threaded fastener, T tlOver tightening torque, (dμ) min It is the minimum value of the friction torque of the bolt head bearing surface, the friction torque of the nut bearing surface and the friction torque of the thread surface.

[0092] The friction coefficient of the bolt head bearing surface and the friction coefficient of the nut bearing surface are not zero.

[0093] According to the analysis of the tightening and loosening process, the specified angle is calculated by the residual torque value of the screw: the calculation formula of the specified angle is as follows:

[0094]

[0095] T rod,rem is the residual torque value of the threaded fastener, l k is the clamping length, G is the shear modulus of the threaded fastener material, θ is the specified angle, and J is the polar moment of inertia of the threaded fastener.

[0096] The calculation formula of the residual torque value of the threaded fastener is:

[0097]

[0098] Among them, F tl It is the preload force under over-tightening torque.

[0099] The calculation formula of the preload force under the over-tightening torque is:

[0100]

[0101] Where d2 is the median diameter of the threaded fastener, μ s is the friction coefficient of the thread surface, α is the tooth profile half angle, d w is the equivalent diameter of the bearing surface of the threaded fastener, μ w is the friction coefficient of the bearing surface, and P is the pitch.

[0102] The specified angle formula simplifies to:

[0103]

[0104] The torque data of the traditional torque tightening method comes from Appendix A1 of "VDI 2230 System Calculation of High-Strength Bolt Connections".

[0105] Table 1 shows the torque data applied to the bolt when the traditional torque tightening method and the over-tightening back-off method of the present invention are used, under the condition that the cross-sectional equivalent stress is the same, wherein the bolt model is M12×1.75 metric bolt, and the equivalent diameter of the bolt head bearing surface is the national standard value of 16.5 mm.

[0106] Table 1 Comparison of tightening torques of M12 metric bolts in different tightening methods

[0107]

[0108]

[0109] It can be seen from the data in Table 1 that the larger the friction coefficient, the higher the installation torque of the over-tightening back-off method compared with the traditional torque tightening method, the more obvious the improvement of the bolt preload, and therefore the more obvious the performance improvement of the connection structure; but there is an upper limit value. Since the bolt utilization factor v=0.9 of the VDI 2230 guideline, the upper limit of the preload improvement of the over-tightening method according to this guideline is 1 / v=11.11%.

[0110] In addition, the reduction of equivalent stress by the back-off method is also verified. Through the change of bolt equivalent stress in the back-off angle in the precise finite element analysis given by the present invention, when the bolt is over-tightened, the equivalent stress of the first circle of meshing thread teeth is 575MPa. The bolt head is backed off at a certain angle to eliminate the torsional shear stress while ensuring that the bolt preload remains unchanged. At this time, the equivalent stress of the first circle of meshing thread teeth is reduced to 389MPa, a reduction of up to 32%, with significant effect.

[0111] Beneficial effects of the present invention:

[0112] 1. Eliminate / reduce residual torque of the screw:

[0113] When the bolt is assembled by tightening, residual torque will accumulate inside the screw rod, which will increase the stress inside the bolt and have a negative impact on the structural load-bearing and fatigue life. After the tightening process is completed, the present invention uses an angle-controlled retraction operation to make one end support surface of the bolt head / nut slide relatively while the other end surface is stationary, thereby reducing or even eliminating the residual torque accumulated in the screw rod and improving the stress distribution of the bolt.

[0114] 2. Increase the design value of the bolt preload:

[0115] Through the data analysis in Table 1, the over-tightening and back-off method can significantly increase the design amount of the bolt preload and improve the connection performance of the structure while ensuring that the equivalent stress of the bolt interface does not increase.

[0116] 3. Reduce the influence of friction coefficient on bolt assembly preload:

[0117] Since the higher the friction coefficient, the greater the residual torque of the screw, the smaller the design value of the bolt preload. The present invention eliminates the residual torque of the screw by the back-off method, so that the design preload of the connection structure with a high friction coefficient is almost consistent with that of the structure with a low friction coefficient, thereby reducing the influence of the friction coefficient on the bolt assembly preload and assembly quality.

[0118] In the existing bolt design guidelines, the bolt preload design value is related to the friction coefficient. The essential reason is the influence of torsional stress. The larger the friction coefficient, the greater the torsional stress, and the smaller the normal stress and preload. In fact, due to production process problems, the dispersion of the friction coefficient of fasteners is relatively large, which leads to large dispersion of data of each bolt and uneven assembly quality when tightening with the same preload or torque design value. Under the condition that the dispersion of the friction coefficient remains unchanged, the present invention reduces the torsional stress generated by the assembly, which is equivalent to reducing the influence of the friction coefficient on the torsional stress, thereby reducing the influence of the friction coefficient on the assembly quality.

[0119] Embodiment 2:

[0120] An electronic device comprises a processor and a memory which is communicatively connected to the processor and is used to store instructions executable by the processor, wherein the processor is used to execute the method described in the first embodiment above.

[0121] Embodiment three:

[0122] A server includes at least one processor and a memory communicatively connected to the processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor so that the at least one processor executes the method described in Example 1.

[0123] Embodiment 4:

[0124] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method described in embodiment 1 is implemented.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

[0126] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A threaded fastener assembly method for improving connection performance, characterized in that: The following steps are involved: S1. Rotate the threaded fastener in the tightening direction with an over-tightening torque, the over-tightening torque is greater than the conventional torque, and the over-tightening torque is less than the maximum allowable torque; S2. Rotate the threaded fastener at a specified angle in the loosening direction to reduce the torsional stress of the threaded fastener.

2. A threaded fastener assembly method for improving connection performance according to claim 1, characterized in that: The calculation formula for overtightening torque is as follows: Among them, T nom is the traditional torque, d is the nominal diameter of the threaded fastener, T tl is the over tightening torque, (dμ) min It is the minimum value of the friction torque of the bolt head bearing surface, the friction torque of the nut bearing surface and the friction torque of the thread surface.

3. A threaded fastener assembly method for improving connection performance according to claim 2, characterized in that: The friction coefficient of the bolt head bearing surface and the friction coefficient of the nut bearing surface are not zero.

4. A threaded fastener assembly method for improving connection performance according to claim 1, characterized in that: The calculation formula for the specified angle is as follows: T rod,rem is the residual torque value of the threaded fastener, l k is the clamping length, G is the shear modulus of the threaded fastener material, θ is the specified angle, and J is the polar moment of inertia of the threaded fastener.

5. A threaded fastener assembly method for improving connection performance according to claim 4, characterized in that: The calculation formula for the residual torque value of threaded fasteners is: Among them, F tl It is the preload force under over-tightening torque.

6. A threaded fastener assembly method for improving connection performance according to claim 5, characterized in that: The calculation formula for the preload force under over-tightening torque is: Where d2 is the median diameter of the threaded fastener, μ s is the friction coefficient of the thread surface, α is the tooth profile half angle, d w is the equivalent diameter of the bearing surface of the threaded fastener, μ w is the friction coefficient of the bearing surface, and P is the pitch.

7. A threaded fastener assembly method for improving connection performance according to claim 1, characterized in that: The traditional torque calculation formula is as follows: Among them, T max is the maximum allowable torque, and v is the ratio of the equivalent stress of the dangerous section of the bolt to the ultimate yield strength of the material.

8. An electronic device, comprising a processor and a memory connected to the processor for storing instructions executable by the processor, characterized in that: The processor is used to execute the method described in any one of claims 1 to 7.

9. A server, characterized in that: It includes at least one processor and a memory communicatively connected to the processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor so that the at least one processor executes the method according to any one of claims 1-7.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

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